3 @setfilename coreutils.info
4 @settitle GNU Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change access permissions.
44 * chown: (coreutils)chown invocation. Change file owners and groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * realpath: (coreutils)readpath invocation. Print resolved file names.
98 * rm: (coreutils)rm invocation. Remove files.
99 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
100 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
101 * seq: (coreutils)seq invocation. Print numeric sequences
102 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
103 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
104 * shred: (coreutils)shred invocation. Remove files more securely.
105 * shuf: (coreutils)shuf invocation. Shuffling text files.
106 * sleep: (coreutils)sleep invocation. Delay for a specified time.
107 * sort: (coreutils)sort invocation. Sort text files.
108 * split: (coreutils)split invocation. Split into pieces.
109 * stat: (coreutils)stat invocation. Report file(system) status.
110 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
111 * stty: (coreutils)stty invocation. Print/change terminal settings.
112 * sum: (coreutils)sum invocation. Print traditional checksum.
113 * sync: (coreutils)sync invocation. Synchronize memory and disk.
114 * tac: (coreutils)tac invocation. Reverse files.
115 * tail: (coreutils)tail invocation. Output the last part of files.
116 * tee: (coreutils)tee invocation. Redirect to multiple files.
117 * test: (coreutils)test invocation. File/string tests.
118 * timeout: (coreutils)timeout invocation. Run with time limit.
119 * touch: (coreutils)touch invocation. Change file timestamps.
120 * tr: (coreutils)tr invocation. Translate characters.
121 * true: (coreutils)true invocation. Do nothing, successfully.
122 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
123 * tsort: (coreutils)tsort invocation. Topological sort.
124 * tty: (coreutils)tty invocation. Print terminal name.
125 * uname: (coreutils)uname invocation. Print system information.
126 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
127 * uniq: (coreutils)uniq invocation. Uniquify files.
128 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
129 * uptime: (coreutils)uptime invocation. Print uptime and load.
130 * users: (coreutils)users invocation. Print current user names.
131 * vdir: (coreutils)vdir invocation. List directories verbosely.
132 * wc: (coreutils)wc invocation. Line, word, and byte counts.
133 * who: (coreutils)who invocation. Print who is logged in.
134 * whoami: (coreutils)whoami invocation. Print effective user ID.
135 * yes: (coreutils)yes invocation. Print a string indefinitely.
139 This manual documents version @value{VERSION} of the GNU core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-2013 Free Software Foundation, Inc.
145 Permission is granted to copy, distribute and/or modify this document
146 under the terms of the GNU Free Documentation License, Version 1.3 or
147 any later version published by the Free Software Foundation; with no
148 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
149 Texts. A copy of the license is included in the section entitled ``GNU
150 Free Documentation License''.
155 @title GNU @code{Coreutils}
156 @subtitle Core GNU utilities
157 @subtitle for version @value{VERSION}, @value{UPDATED}
158 @author David MacKenzie et al.
161 @vskip 0pt plus 1filll
174 @cindex core utilities
175 @cindex text utilities
176 @cindex shell utilities
177 @cindex file utilities
180 * Introduction:: Caveats, overview, and authors
181 * Common options:: Common options
182 * Output of entire files:: cat tac nl od base64
183 * Formatting file contents:: fmt pr fold
184 * Output of parts of files:: head tail split csplit
185 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
186 * Operating on sorted files:: sort shuf uniq comm ptx tsort
187 * Operating on fields:: cut paste join
188 * Operating on characters:: tr expand unexpand
189 * Directory listing:: ls dir vdir dircolors
190 * Basic operations:: cp dd install mv rm shred
191 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
192 * Changing file attributes:: chgrp chmod chown touch
193 * Disk usage:: df du stat sync truncate
194 * Printing text:: echo printf yes
195 * Conditions:: false true test expr
197 * File name manipulation:: dirname basename pathchk mktemp realpath
198 * Working context:: pwd stty printenv tty
199 * User information:: id logname whoami groups users who
200 * System context:: date arch nproc uname hostname hostid uptime
201 * SELinux context:: chcon runcon
202 * Modified command invocation:: chroot env nice nohup stdbuf timeout
203 * Process control:: kill
205 * Numeric operations:: factor seq
206 * File permissions:: Access modes
207 * Date input formats:: Specifying date strings
208 * Opening the software toolbox:: The software tools philosophy
209 * GNU Free Documentation License:: Copying and sharing this manual
210 * Concept index:: General index
213 --- The Detailed Node Listing ---
217 * Exit status:: Indicating program success or failure
218 * Backup options:: Backup options
219 * Block size:: Block size
220 * Floating point:: Floating point number representation
221 * Signal specifications:: Specifying signals
222 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
223 * Random sources:: Sources of random data
224 * Target directory:: Target directory
225 * Trailing slashes:: Trailing slashes
226 * Traversing symlinks:: Traversing symlinks to directories
227 * Treating / specially:: Treating / specially
228 * Standards conformance:: Standards conformance
230 Output of entire files
232 * cat invocation:: Concatenate and write files
233 * tac invocation:: Concatenate and write files in reverse
234 * nl invocation:: Number lines and write files
235 * od invocation:: Write files in octal or other formats
236 * base64 invocation:: Transform data into printable data
238 Formatting file contents
240 * fmt invocation:: Reformat paragraph text
241 * pr invocation:: Paginate or columnate files for printing
242 * fold invocation:: Wrap input lines to fit in specified width
244 Output of parts of files
246 * head invocation:: Output the first part of files
247 * tail invocation:: Output the last part of files
248 * split invocation:: Split a file into fixed-size pieces
249 * csplit invocation:: Split a file into context-determined pieces
253 * wc invocation:: Print newline, word, and byte counts
254 * sum invocation:: Print checksum and block counts
255 * cksum invocation:: Print CRC checksum and byte counts
256 * md5sum invocation:: Print or check MD5 digests
257 * sha1sum invocation:: Print or check SHA-1 digests
258 * sha2 utilities:: Print or check SHA-2 digests
260 Operating on sorted files
262 * sort invocation:: Sort text files
263 * shuf invocation:: Shuffle text files
264 * uniq invocation:: Uniquify files
265 * comm invocation:: Compare two sorted files line by line
266 * ptx invocation:: Produce a permuted index of file contents
267 * tsort invocation:: Topological sort
269 @command{ptx}: Produce permuted indexes
271 * General options in ptx:: Options which affect general program behavior
272 * Charset selection in ptx:: Underlying character set considerations
273 * Input processing in ptx:: Input fields, contexts, and keyword selection
274 * Output formatting in ptx:: Types of output format, and sizing the fields
275 * Compatibility in ptx:: The GNU extensions to @command{ptx}
279 * cut invocation:: Print selected parts of lines
280 * paste invocation:: Merge lines of files
281 * join invocation:: Join lines on a common field
283 Operating on characters
285 * tr invocation:: Translate, squeeze, and/or delete characters
286 * expand invocation:: Convert tabs to spaces
287 * unexpand invocation:: Convert spaces to tabs
289 @command{tr}: Translate, squeeze, and/or delete characters
291 * Character sets:: Specifying sets of characters
292 * Translating:: Changing one set of characters to another
293 * Squeezing:: Squeezing repeats and deleting
297 * ls invocation:: List directory contents
298 * dir invocation:: Briefly list directory contents
299 * vdir invocation:: Verbosely list directory contents
300 * dircolors invocation:: Color setup for @command{ls}
302 @command{ls}: List directory contents
304 * Which files are listed:: Which files are listed
305 * What information is listed:: What information is listed
306 * Sorting the output:: Sorting the output
307 * Details about version sort:: More details about version sort
308 * General output formatting:: General output formatting
309 * Formatting the file names:: Formatting the file names
313 * cp invocation:: Copy files and directories
314 * dd invocation:: Convert and copy a file
315 * install invocation:: Copy files and set attributes
316 * mv invocation:: Move (rename) files
317 * rm invocation:: Remove files or directories
318 * shred invocation:: Remove files more securely
322 * link invocation:: Make a hard link via the link syscall
323 * ln invocation:: Make links between files
324 * mkdir invocation:: Make directories
325 * mkfifo invocation:: Make FIFOs (named pipes)
326 * mknod invocation:: Make block or character special files
327 * readlink invocation:: Print value of a symlink or canonical file name
328 * rmdir invocation:: Remove empty directories
329 * unlink invocation:: Remove files via unlink syscall
331 Changing file attributes
333 * chown invocation:: Change file owner and group
334 * chgrp invocation:: Change group ownership
335 * chmod invocation:: Change access permissions
336 * touch invocation:: Change file timestamps
340 * df invocation:: Report file system disk space usage
341 * du invocation:: Estimate file space usage
342 * stat invocation:: Report file or file system status
343 * sync invocation:: Synchronize data on disk with memory
344 * truncate invocation:: Shrink or extend the size of a file
348 * echo invocation:: Print a line of text
349 * printf invocation:: Format and print data
350 * yes invocation:: Print a string until interrupted
354 * false invocation:: Do nothing, unsuccessfully
355 * true invocation:: Do nothing, successfully
356 * test invocation:: Check file types and compare values
357 * expr invocation:: Evaluate expressions
359 @command{test}: Check file types and compare values
361 * File type tests:: File type tests
362 * Access permission tests:: Access permission tests
363 * File characteristic tests:: File characteristic tests
364 * String tests:: String tests
365 * Numeric tests:: Numeric tests
367 @command{expr}: Evaluate expression
369 * String expressions:: + : match substr index length
370 * Numeric expressions:: + - * / %
371 * Relations for expr:: | & < <= = == != >= >
372 * Examples of expr:: Examples of using @command{expr}
376 * tee invocation:: Redirect output to multiple files or processes
378 File name manipulation
380 * basename invocation:: Strip directory and suffix from a file name
381 * dirname invocation:: Strip last file name component
382 * pathchk invocation:: Check file name validity and portability
383 * mktemp invocation:: Create temporary file or directory
384 * realpath invocation:: Print resolved file names
388 * pwd invocation:: Print working directory
389 * stty invocation:: Print or change terminal characteristics
390 * printenv invocation:: Print all or some environment variables
391 * tty invocation:: Print file name of terminal on standard input
393 @command{stty}: Print or change terminal characteristics
395 * Control:: Control settings
396 * Input:: Input settings
397 * Output:: Output settings
398 * Local:: Local settings
399 * Combination:: Combination settings
400 * Characters:: Special characters
401 * Special:: Special settings
405 * id invocation:: Print user identity
406 * logname invocation:: Print current login name
407 * whoami invocation:: Print effective user ID
408 * groups invocation:: Print group names a user is in
409 * users invocation:: Print login names of users currently logged in
410 * who invocation:: Print who is currently logged in
414 * arch invocation:: Print machine hardware name
415 * date invocation:: Print or set system date and time
416 * nproc invocation:: Print the number of processors
417 * uname invocation:: Print system information
418 * hostname invocation:: Print or set system name
419 * hostid invocation:: Print numeric host identifier
420 * uptime invocation:: Print system uptime and load
422 @command{date}: Print or set system date and time
424 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
425 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
426 * Literal conversion specifiers:: %[%nt]
427 * Padding and other flags:: Pad with zeros, spaces, etc.
428 * Setting the time:: Changing the system clock
429 * Options for date:: Instead of the current time
430 * Date input formats:: Specifying date strings
431 * Examples of date:: Examples
435 * chcon invocation:: Change SELinux context of file
436 * runcon invocation:: Run a command in specified SELinux context
438 Modified command invocation
440 * chroot invocation:: Run a command with a different root directory
441 * env invocation:: Run a command in a modified environment
442 * nice invocation:: Run a command with modified niceness
443 * nohup invocation:: Run a command immune to hangups
444 * stdbuf invocation:: Run a command with modified I/O buffering
445 * timeout invocation:: Run a command with a time limit
449 * kill invocation:: Sending a signal to processes.
453 * sleep invocation:: Delay for a specified time
457 * factor invocation:: Print prime factors
458 * seq invocation:: Print numeric sequences
462 * Mode Structure:: Structure of file mode bits
463 * Symbolic Modes:: Mnemonic representation of file mode bits
464 * Numeric Modes:: File mode bits as octal numbers
465 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
469 * General date syntax:: Common rules
470 * Calendar date items:: 19 Dec 1994
471 * Time of day items:: 9:20pm
472 * Time zone items:: EST, PDT, UTC, @dots{}
473 * Combined date and time of day items:: 1972-09-24T20:02:00,000000-0500
474 * Day of week items:: Monday and others
475 * Relative items in date strings:: next tuesday, 2 years ago
476 * Pure numbers in date strings:: 19931219, 1440
477 * Seconds since the Epoch:: @@1078100502
478 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
479 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al.
481 Opening the software toolbox
483 * Toolbox introduction:: Toolbox introduction
484 * I/O redirection:: I/O redirection
485 * The who command:: The @command{who} command
486 * The cut command:: The @command{cut} command
487 * The sort command:: The @command{sort} command
488 * The uniq command:: The @command{uniq} command
489 * Putting the tools together:: Putting the tools together
493 * GNU Free Documentation License:: Copying and sharing this manual
500 @chapter Introduction
502 This manual is a work in progress: many sections make no attempt to explain
503 basic concepts in a way suitable for novices. Thus, if you are interested,
504 please get involved in improving this manual. The entire GNU community
508 The GNU utilities documented here are mostly compatible with the
510 @cindex bugs, reporting
511 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
512 to include the version number, machine architecture, input files, and
513 any other information needed to reproduce the bug: your input, what you
514 expected, what you got, and why it is wrong. Diffs are welcome, but
515 please include a description of the problem as well, since this is
516 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
522 @cindex MacKenzie, D.
525 This manual was originally derived from the Unix man pages in the
526 distributions, which were written by David MacKenzie and updated by Jim
527 Meyering. What you are reading now is the authoritative documentation
528 for these utilities; the man pages are no longer being maintained. The
529 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
530 Pinard did the initial conversion to Texinfo format. Karl Berry did the
531 indexing, some reorganization, and editing of the results. Brian
532 Youmans of the Free Software Foundation office staff combined the
533 manuals for textutils, fileutils, and sh-utils to produce the present
534 omnibus manual. Richard Stallman contributed his usual invaluable
535 insights to the overall process.
538 @chapter Common options
542 @itemx @w{@kbd{--backup}[=@var{method}]}
545 @vindex VERSION_CONTROL
546 @cindex backups, making
547 @xref{Backup options}.
548 Make a backup of each file that would otherwise be overwritten or removed.
551 @macro optBackupSuffix
552 @item -S @var{suffix}
553 @itemx --suffix=@var{suffix}
556 Append @var{suffix} to each backup file made with @option{-b}.
557 @xref{Backup options}.
560 @macro optTargetDirectory
561 @item -t @var{directory}
562 @itemx @w{@kbd{--target-directory}=@var{directory}}
564 @opindex --target-directory
565 @cindex target directory
566 @cindex destination directory
567 Specify the destination @var{directory}.
568 @xref{Target directory}.
571 @macro optNoTargetDirectory
573 @itemx --no-target-directory
575 @opindex --no-target-directory
576 @cindex target directory
577 @cindex destination directory
578 Do not treat the last operand specially when it is a directory or a
579 symbolic link to a directory. @xref{Target directory}.
587 @cindex output NUL-byte-terminated lines
588 Output a zero byte (ASCII NUL) at the end of each line,
589 rather than a newline. This option enables other programs to parse the
590 output of @command{\cmd\} even when that output would contain data
591 with embedded newlines.
598 Append an SI-style abbreviation to each size, such as @samp{M} for
599 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
600 1,000,000 bytes. This option is equivalent to
601 @option{--block-size=si}. Use the @option{-h} or
602 @option{--human-readable} option if
603 you prefer powers of 1024.
606 @macro optHumanReadable
608 @itemx --human-readable
610 @opindex --human-readable
611 @cindex human-readable output
612 Append a size letter to each size, such as @samp{M} for mebibytes.
613 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
614 This option is equivalent to @option{--block-size=human-readable}.
615 Use the @option{--si} option if you prefer powers of 1000.
618 @macro optStripTrailingSlashes
619 @item @w{@kbd{--strip-trailing-slashes}}
620 @opindex --strip-trailing-slashes
621 @cindex stripping trailing slashes
622 Remove any trailing slashes from each @var{source} argument.
623 @xref{Trailing slashes}.
626 @macro mayConflictWithShellBuiltIn{cmd}
627 @cindex conflicts with shell built-ins
628 @cindex built-in shell commands, conflicts with
629 Due to shell aliases and built-in @command{\cmd\} functions, using an
630 unadorned @command{\cmd\} interactively or in a script may get you
631 different functionality than that described here. Invoke it via
632 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
637 @macro multiplierSuffixes{varName}
638 @var{\varName\} may be, or may be an integer optionally followed by,
639 one of the following multiplicative suffixes:
641 @samp{b} => 512 ("blocks")
642 @samp{KB} => 1000 (KiloBytes)
643 @samp{K} => 1024 (KibiBytes)
644 @samp{MB} => 1000*1000 (MegaBytes)
645 @samp{M} => 1024*1024 (MebiBytes)
646 @samp{GB} => 1000*1000*1000 (GigaBytes)
647 @samp{G} => 1024*1024*1024 (GibiBytes)
649 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
652 @c FIXME: same as above, but no ``blocks'' line.
653 @macro multiplierSuffixesNoBlocks{varName}
654 @var{\varName\} may be, or may be an integer optionally followed by,
655 one of the following multiplicative suffixes:
657 @samp{KB} => 1000 (KiloBytes)
658 @samp{K} => 1024 (KibiBytes)
659 @samp{MB} => 1000*1000 (MegaBytes)
660 @samp{M} => 1024*1024 (MebiBytes)
661 @samp{GB} => 1000*1000*1000 (GigaBytes)
662 @samp{G} => 1024*1024*1024 (GibiBytes)
664 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
667 @cindex common options
669 Certain options are available in all of these programs. Rather than
670 writing identical descriptions for each of the programs, they are
671 described here. (In fact, every GNU program accepts (or should accept)
674 @vindex POSIXLY_CORRECT
675 Normally options and operands can appear in any order, and programs act
676 as if all the options appear before any operands. For example,
677 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
678 @samp{:} is an option-argument of @option{-t}. However, if the
679 @env{POSIXLY_CORRECT} environment variable is set, options must appear
680 before operands, unless otherwise specified for a particular command.
682 A few programs can usefully have trailing operands with leading
683 @samp{-}. With such a program, options must precede operands even if
684 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
685 program description. For example, the @command{env} command's options
686 must appear before its operands, since in some cases the operands
687 specify a command that itself contains options.
689 Most programs that accept long options recognize unambiguous
690 abbreviations of those options. For example, @samp{rmdir
691 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
692 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
693 @samp{ls --h}, are identified as such.
695 Some of these programs recognize the @option{--help} and @option{--version}
696 options only when one of them is the sole command line argument. For
697 these programs, abbreviations of the long options are not always recognized.
704 Print a usage message listing all available options, then exit successfully.
708 @cindex version number, finding
709 Print the version number, then exit successfully.
713 @cindex option delimiter
714 Delimit the option list. Later arguments, if any, are treated as
715 operands even if they begin with @samp{-}. For example, @samp{sort --
716 -r} reads from the file named @file{-r}.
720 @cindex standard input
721 @cindex standard output
722 A single @samp{-} operand is not really an option, though it looks like one. It
723 stands for standard input, or for standard output if that is clear from
724 the context. For example, @samp{sort -} reads from standard input,
725 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
726 extra copy of its input to standard output. Unless otherwise
727 specified, @samp{-} can appear as any operand that requires a file
731 * Exit status:: Indicating program success or failure.
732 * Backup options:: -b -S, in some programs.
733 * Block size:: BLOCK_SIZE and --block-size, in some programs.
734 * Floating point:: Floating point number representation.
735 * Signal specifications:: Specifying signals using the --signal option.
736 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
737 * Random sources:: --random-source, in some programs.
738 * Target directory:: Specifying a target directory, in some programs.
739 * Trailing slashes:: --strip-trailing-slashes, in some programs.
740 * Traversing symlinks:: -H, -L, or -P, in some programs.
741 * Treating / specially:: --preserve-root and --no-preserve-root.
742 * Special built-in utilities:: @command{break}, @command{:}, @dots{}
743 * Standards conformance:: Conformance to the POSIX standard.
751 An exit status of zero indicates success,
752 and a nonzero value indicates failure.
755 Nearly every command invocation yields an integral @dfn{exit status}
756 that can be used to change how other commands work.
757 For the vast majority of commands, an exit status of zero indicates
758 success. Failure is indicated by a nonzero value---typically
759 @samp{1}, though it may differ on unusual platforms as POSIX
760 requires only that it be nonzero.
762 However, some of the programs documented here do produce
763 other exit status values and a few associate different
764 meanings with the values @samp{0} and @samp{1}.
765 Here are some of the exceptions:
766 @command{chroot}, @command{env}, @command{expr}, @command{nice},
767 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
768 @command{test}, @command{timeout}, @command{tty}.
772 @section Backup options
774 @cindex backup options
776 Some GNU programs (at least @command{cp}, @command{install},
777 @command{ln}, and @command{mv}) optionally make backups of files
778 before writing new versions.
779 These options control the details of these backups. The options are also
780 briefly mentioned in the descriptions of the particular programs.
785 @itemx @w{@kbd{--backup}[=@var{method}]}
788 @vindex VERSION_CONTROL
789 @cindex backups, making
790 Make a backup of each file that would otherwise be overwritten or removed.
791 Without this option, the original versions are destroyed.
792 Use @var{method} to determine the type of backups to make.
793 When this option is used but @var{method} is not specified,
794 then the value of the @env{VERSION_CONTROL}
795 environment variable is used. And if @env{VERSION_CONTROL} is not set,
796 the default backup type is @samp{existing}.
798 Note that the short form of this option, @option{-b} does not accept any
799 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
801 @vindex version-control @r{Emacs variable}
802 This option corresponds to the Emacs variable @samp{version-control};
803 the values for @var{method} are the same as those used in Emacs.
804 This option also accepts more descriptive names.
805 The valid @var{method}s are (unique abbreviations are accepted):
810 @opindex none @r{backup method}
815 @opindex numbered @r{backup method}
816 Always make numbered backups.
820 @opindex existing @r{backup method}
821 Make numbered backups of files that already have them, simple backups
826 @opindex simple @r{backup method}
827 Always make simple backups. Please note @samp{never} is not to be
828 confused with @samp{none}.
832 @item -S @var{suffix}
833 @itemx --suffix=@var{suffix}
836 @cindex backup suffix
837 @vindex SIMPLE_BACKUP_SUFFIX
838 Append @var{suffix} to each backup file made with @option{-b}. If this
839 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
840 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
841 set, the default is @samp{~}, just as in Emacs.
850 Some GNU programs (at least @command{df}, @command{du}, and
851 @command{ls}) display sizes in ``blocks''. You can adjust the block size
852 and method of display to make sizes easier to read. The block size
853 used for display is independent of any file system block size.
854 Fractional block counts are rounded up to the nearest integer.
856 @opindex --block-size=@var{size}
859 @vindex DF_BLOCK_SIZE
860 @vindex DU_BLOCK_SIZE
861 @vindex LS_BLOCK_SIZE
862 @vindex POSIXLY_CORRECT@r{, and block size}
864 The default block size is chosen by examining the following environment
865 variables in turn; the first one that is set determines the block size.
870 This specifies the default block size for the @command{df} command.
871 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
872 @env{LS_BLOCK_SIZE} for @command{ls}.
875 This specifies the default block size for all three commands, if the
876 above command-specific environment variables are not set.
879 This specifies the default block size for all values that are normally
880 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
881 command-specific environment variables are set. Unlike the other
882 environment variables, @env{BLOCKSIZE} does not affect values that are
883 normally printed as byte counts, e.g., the file sizes contained in
886 @item POSIXLY_CORRECT
887 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
888 @env{BLOCKSIZE} is set, but this variable is set, the block size
893 If none of the above environment variables are set, the block size
894 currently defaults to 1024 bytes in most contexts, but this number may
895 change in the future. For @command{ls} file sizes, the block size
898 @cindex human-readable output
901 A block size specification can be a positive integer specifying the number
902 of bytes per block, or it can be @code{human-readable} or @code{si} to
903 select a human-readable format. Integers may be followed by suffixes
904 that are upward compatible with the
905 @uref{http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html, SI prefixes}
906 for decimal multiples and with the
907 @uref{http://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13
908 (formerly IEC 60027-2) prefixes} for binary multiples.
910 With human-readable formats, output sizes are followed by a size letter
911 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
912 powers of 1024; @samp{M} stands for 1,048,576 bytes.
913 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
914 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
917 A block size specification preceded by @samp{'} causes output sizes to
918 be displayed with thousands separators. The @env{LC_NUMERIC} locale
919 specifies the thousands separator and grouping. For example, in an
920 American English locale, @samp{--block-size="'1kB"} would cause a size
921 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
922 locale, there is no thousands separator so a leading @samp{'} has no
925 An integer block size can be followed by a suffix to specify a
926 multiple of that size. A bare size letter,
927 or one followed by @samp{iB}, specifies
928 a multiple using powers of 1024. A size letter followed by @samp{B}
929 specifies powers of 1000 instead. For example, @samp{1M} and
930 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
931 equivalent to @samp{1000000}.
933 A plain suffix without a preceding integer acts as if @samp{1} were
934 prepended, except that it causes a size indication to be appended to
935 the output. For example, @samp{--block-size="kB"} displays 3000 as
938 The following suffixes are defined. Large sizes like @code{1Y}
939 may be rejected by your computer due to limitations of its arithmetic.
943 @cindex kilobyte, definition of
944 kilobyte: @math{10^3 = 1000}.
948 @cindex kibibyte, definition of
949 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
950 @samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and
951 POSIX use @samp{k} to mean @samp{KiB}.
953 @cindex megabyte, definition of
954 megabyte: @math{10^6 = 1,000,000}.
957 @cindex mebibyte, definition of
958 mebibyte: @math{2^{20} = 1,048,576}.
960 @cindex gigabyte, definition of
961 gigabyte: @math{10^9 = 1,000,000,000}.
964 @cindex gibibyte, definition of
965 gibibyte: @math{2^{30} = 1,073,741,824}.
967 @cindex terabyte, definition of
968 terabyte: @math{10^{12} = 1,000,000,000,000}.
971 @cindex tebibyte, definition of
972 tebibyte: @math{2^{40} = 1,099,511,627,776}.
974 @cindex petabyte, definition of
975 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
978 @cindex pebibyte, definition of
979 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
981 @cindex exabyte, definition of
982 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
985 @cindex exbibyte, definition of
986 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
988 @cindex zettabyte, definition of
989 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
992 @math{2^{70} = 1,180,591,620,717,411,303,424}.
994 @cindex yottabyte, definition of
995 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
998 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
1003 @opindex --block-size
1004 @opindex --human-readable
1007 Block size defaults can be overridden by an explicit
1008 @option{--block-size=@var{size}} option. The @option{-k}
1009 option is equivalent to @option{--block-size=1K}, which
1010 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1011 set. The @option{-h} or @option{--human-readable} option is equivalent to
1012 @option{--block-size=human-readable}. The @option{--si} option is
1013 equivalent to @option{--block-size=si}.
1015 @node Floating point
1016 @section Floating point numbers
1017 @cindex floating point
1018 @cindex IEEE floating point
1020 Commands that accept or produce floating point numbers employ the
1021 floating point representation of the underlying system, and suffer
1022 from rounding error, overflow, and similar floating-point issues.
1023 Almost all modern systems use IEEE-754 floating point, and it is
1024 typically portable to assume IEEE-754 behavior these days. IEEE-754
1025 has positive and negative infinity, distinguishes positive from
1026 negative zero, and uses special values called NaNs to represent
1027 invalid computations such as dividing zero by itself. For more
1028 information, please see David Goldberg's paper
1029 @uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
1030 Computer Scientist Should Know About Floating-Point Arithmetic}.
1033 Commands that accept floating point numbers as options, operands or
1034 input use the standard C functions @code{strtod} and @code{strtold} to
1035 convert from text to floating point numbers. These floating point
1036 numbers therefore can use scientific notation like @code{1.0e-34} and
1037 @code{-10e100}. Modern C implementations also accept hexadecimal
1038 floating point numbers such as @code{-0x.ep-3}, which stands for
1039 @minus{}14/16 times @math{2^-3}, which equals @minus{}0.109375. The
1040 @env{LC_NUMERIC} locale determines the decimal-point character.
1041 @xref{Parsing of Floats,,, libc, The GNU C Library Reference Manual}.
1043 @node Signal specifications
1044 @section Signal specifications
1045 @cindex signals, specifying
1047 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1048 number like @samp{1}, or an exit status of a process terminated by the
1049 signal. A signal name can be given in canonical form or prefixed by
1050 @samp{SIG}@. The case of the letters is ignored. The following signal names
1051 and numbers are supported on all POSIX compliant systems:
1057 2. Terminal interrupt.
1063 9. Kill (cannot be caught or ignored).
1071 Other supported signal names have system-dependent corresponding
1072 numbers. All systems conforming to POSIX 1003.1-2001 also
1073 support the following signals:
1077 Access to an undefined portion of a memory object.
1079 Child process terminated, stopped, or continued.
1081 Continue executing, if stopped.
1083 Erroneous arithmetic operation.
1085 Illegal Instruction.
1087 Write on a pipe with no one to read it.
1089 Invalid memory reference.
1091 Stop executing (cannot be caught or ignored).
1095 Background process attempting read.
1097 Background process attempting write.
1099 High bandwidth data is available at a socket.
1101 User-defined signal 1.
1103 User-defined signal 2.
1107 POSIX 1003.1-2001 systems that support the XSI extension
1108 also support the following signals:
1114 Profiling timer expired.
1118 Trace/breakpoint trap.
1120 Virtual timer expired.
1122 CPU time limit exceeded.
1124 File size limit exceeded.
1128 POSIX 1003.1-2001 systems that support the XRT extension
1129 also support at least eight real-time signals called @samp{RTMIN},
1130 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1132 @node Disambiguating names and IDs
1133 @section chown and chgrp: Disambiguating user names and IDs
1134 @cindex user names, disambiguating
1135 @cindex user IDs, disambiguating
1136 @cindex group names, disambiguating
1137 @cindex group IDs, disambiguating
1138 @cindex disambiguating group names and IDs
1140 Since the @var{owner} and @var{group} arguments to @command{chown} and
1141 @command{chgrp} may be specified as names or numeric IDs, there is an
1143 What if a user or group @emph{name} is a string of digits?
1144 @footnote{Using a number as a user name is common in some environments.}
1145 Should the command interpret it as a user name or as an ID@?
1146 POSIX requires that @command{chown} and @command{chgrp}
1147 first attempt to resolve the specified string as a name, and
1148 only once that fails, then try to interpret it as an ID@.
1149 This is troublesome when you want to specify a numeric ID, say 42,
1150 and it must work even in a pathological situation where
1151 @samp{42} is a user name that maps to some other user ID, say 1000.
1152 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1153 1000---not what you intended.
1155 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1156 that at the same time may result in a significant performance improvement
1157 by eliminating a database look-up.
1158 Simply precede each numeric user ID and/or group ID with a @samp{+},
1159 in order to force its interpretation as an integer:
1163 chgrp +$numeric_group_id another-file
1167 GNU @command{chown} and @command{chgrp}
1168 skip the name look-up process for each @samp{+}-prefixed string,
1169 because a string containing @samp{+} is never a valid user or group name.
1170 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1172 @node Random sources
1173 @section Sources of random data
1175 @cindex random sources
1177 The @command{shuf}, @command{shred}, and @command{sort} commands
1178 sometimes need random data to do their work. For example, @samp{sort
1179 -R} must choose a hash function at random, and it needs random data to
1180 make this selection.
1182 By default these commands use an internal pseudorandom generator
1183 initialized by a small amount of entropy, but can be directed to use
1184 an external source with the @option{--random-source=@var{file}} option.
1185 An error is reported if @var{file} does not contain enough bytes.
1187 For example, the device file @file{/dev/urandom} could be used as the
1188 source of random data. Typically, this device gathers environmental
1189 noise from device drivers and other sources into an entropy pool, and
1190 uses the pool to generate random bits. If the pool is short of data,
1191 the device reuses the internal pool to produce more bits, using a
1192 cryptographically secure pseudorandom number generator. But be aware
1193 that this device is not designed for bulk random data generation
1194 and is relatively slow.
1196 @file{/dev/urandom} suffices for most practical uses, but applications
1197 requiring high-value or long-term protection of private data may
1198 require an alternate data source like @file{/dev/random} or
1199 @file{/dev/arandom}. The set of available sources depends on your
1202 To reproduce the results of an earlier invocation of a command, you
1203 can save some random data into a file and then use that file as the
1204 random source in earlier and later invocations of the command.
1206 @node Target directory
1207 @section Target directory
1209 @cindex target directory
1211 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1212 commands normally treat the last operand specially when it is a
1213 directory or a symbolic link to a directory. For example, @samp{cp
1214 source dest} is equivalent to @samp{cp source dest/source} if
1215 @file{dest} is a directory. Sometimes this behavior is not exactly
1216 what is wanted, so these commands support the following options to
1217 allow more fine-grained control:
1222 @itemx --no-target-directory
1223 @opindex --no-target-directory
1224 @cindex target directory
1225 @cindex destination directory
1226 Do not treat the last operand specially when it is a directory or a
1227 symbolic link to a directory. This can help avoid race conditions in
1228 programs that operate in a shared area. For example, when the command
1229 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1230 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1231 renamed to @file{/tmp/dest/source} instead, if some other process
1232 created @file{/tmp/dest} as a directory. However, if @file{mv
1233 -T /tmp/source /tmp/dest} succeeds, there is no
1234 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1236 In the opposite situation, where you want the last operand to be
1237 treated as a directory and want a diagnostic otherwise, you can use
1238 the @option{--target-directory} (@option{-t}) option.
1240 @item -t @var{directory}
1241 @itemx @w{@kbd{--target-directory}=@var{directory}}
1242 @opindex --target-directory
1243 @cindex target directory
1244 @cindex destination directory
1245 Use @var{directory} as the directory component of each destination
1248 The interface for most programs is that after processing options and a
1249 finite (possibly zero) number of fixed-position arguments, the remaining
1250 argument list is either expected to be empty, or is a list of items
1251 (usually files) that will all be handled identically. The @command{xargs}
1252 program is designed to work well with this convention.
1254 The commands in the @command{mv}-family are unusual in that they take
1255 a variable number of arguments with a special case at the @emph{end}
1256 (namely, the target directory). This makes it nontrivial to perform some
1257 operations, e.g., ``move all files from here to ../d/'', because
1258 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1259 doesn't have a clean way to specify an extra final argument for each
1260 invocation of the subject command. (It can be done by going through a
1261 shell command, but that requires more human labor and brain power than
1264 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1265 @command{install}, @command{ln}, and @command{mv} programs to be used
1266 conveniently with @command{xargs}. For example, you can move the files
1267 from the current directory to a sibling directory, @code{d} like this:
1270 ls | xargs mv -t ../d --
1273 However, this doesn't move files whose names begin with @samp{.}.
1274 If you use the GNU @command{find} program, you can move those
1275 files too, with this command:
1278 find . -mindepth 1 -maxdepth 1 \
1282 But both of the above approaches fail if there are no files in the
1283 current directory, or if any file has a name containing a blank or
1284 some other special characters.
1285 The following example removes those limitations and requires both
1286 GNU @command{find} and GNU @command{xargs}:
1289 find . -mindepth 1 -maxdepth 1 -print0 \
1290 | xargs --null --no-run-if-empty \
1297 The @option{--target-directory} (@option{-t}) and
1298 @option{--no-target-directory} (@option{-T})
1299 options cannot be combined.
1301 @node Trailing slashes
1302 @section Trailing slashes
1304 @cindex trailing slashes
1306 Some GNU programs (at least @command{cp} and @command{mv}) allow you to
1307 remove any trailing slashes from each @var{source} argument before
1308 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1311 This is useful when a @var{source} argument may have a trailing slash and
1312 @c FIXME: mv's behavior in this case is system-dependent
1313 specify a symbolic link to a directory. This scenario is in fact rather
1314 common because some shells can automatically append a trailing slash when
1315 performing file name completion on such symbolic links. Without this
1316 option, @command{mv}, for example, (via the system's rename function) must
1317 interpret a trailing slash as a request to dereference the symbolic link
1318 and so must rename the indirectly referenced @emph{directory} and not
1319 the symbolic link. Although it may seem surprising that such behavior
1320 be the default, it is required by POSIX and is consistent with
1321 other parts of that standard.
1323 @node Traversing symlinks
1324 @section Traversing symlinks
1326 @cindex symbolic link to directory, controlling traversal of
1328 The following options modify how @command{chown} and @command{chgrp}
1329 @c FIXME: note that 'du' has these options, too, but they have slightly
1330 @c different meaning.
1331 traverse a hierarchy when the @option{--recursive} (@option{-R})
1332 option is also specified.
1333 If more than one of the following options is specified, only the final
1335 These options specify whether processing a symbolic link to a directory
1336 entails operating on just the symbolic link or on all files in the
1337 hierarchy rooted at that directory.
1339 These options are independent of @option{--dereference} and
1340 @option{--no-dereference} (@option{-h}), which control whether to modify
1341 a symlink or its referent.
1348 @cindex symbolic link to directory, traverse if on the command line
1349 If @option{--recursive} (@option{-R}) is specified and
1350 a command line argument is a symbolic link to a directory, traverse it.
1357 @cindex symbolic link to directory, traverse each that is encountered
1358 In a recursive traversal, traverse every symbolic link to a directory
1359 that is encountered.
1366 @cindex symbolic link to directory, never traverse
1367 Do not traverse any symbolic links.
1368 This is the default if none of @option{-H}, @option{-L},
1369 or @option{-P} is specified.
1376 @node Treating / specially
1377 @section Treating @file{/} specially
1379 Certain commands can operate destructively on entire hierarchies.
1380 For example, if a user with appropriate privileges mistakenly runs
1381 @samp{rm -rf / tmp/junk}, that may remove
1382 all files on the entire system. Since there are so few
1383 legitimate uses for such a command,
1384 GNU @command{rm} normally declines to operate on any directory
1385 that resolves to @file{/}. If you really want to try to remove all
1386 the files on your system, you can use the @option{--no-preserve-root}
1387 option, but the default behavior, specified by the
1388 @option{--preserve-root} option, is safer for most purposes.
1390 The commands @command{chgrp}, @command{chmod} and @command{chown}
1391 can also operate destructively on entire hierarchies, so they too
1392 support these options. Although, unlike @command{rm}, they don't
1393 actually unlink files, these commands are arguably more dangerous
1394 when operating recursively on @file{/}, since they often work much
1395 more quickly, and hence damage more files before an alert user can
1396 interrupt them. Tradition and POSIX require these commands
1397 to operate recursively on @file{/}, so they default to
1398 @option{--no-preserve-root}, but using the @option{--preserve-root}
1399 option makes them safer for most purposes. For convenience you can
1400 specify @option{--preserve-root} in an alias or in a shell function.
1402 Note that the @option{--preserve-root} option also ensures
1403 that @command{chgrp} and @command{chown} do not modify @file{/}
1404 even when dereferencing a symlink pointing to @file{/}.
1406 @node Special built-in utilities
1407 @section Special built-in utilities
1409 Some programs like @command{nice} can invoke other programs; for
1410 example, the command @samp{nice cat file} invokes the program
1411 @command{cat} by executing the command @samp{cat file}. However,
1412 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1413 this way. For example, the command @samp{nice exit} does not have a
1414 well-defined behavior: it may generate an error message instead of
1417 Here is a list of the special built-in utilities that are standardized
1418 by POSIX 1003.1-2004.
1421 @t{.@: : break continue eval exec exit export readonly
1422 return set shift times trap unset}
1425 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1426 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1427 pwd} do not work as you might expect.
1429 Many shells extend this list. For example, Bash has several extra
1430 special built-in utilities like @command{history}, and
1431 @command{suspend}, and with Bash the command @samp{nice suspend}
1432 generates an error message instead of suspending.
1434 @node Standards conformance
1435 @section Standards conformance
1437 @vindex POSIXLY_CORRECT
1438 In a few cases, the GNU utilities' default behavior is
1439 incompatible with the POSIX standard. To suppress these
1440 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1441 variable. Unless you are checking for POSIX conformance, you
1442 probably do not need to define @env{POSIXLY_CORRECT}.
1444 Newer versions of POSIX are occasionally incompatible with older
1445 versions. For example, older versions of POSIX required the
1446 command @samp{sort +1} to sort based on the second and succeeding
1447 fields in each input line, but starting with POSIX 1003.1-2001
1448 the same command is required to sort the file named @file{+1}, and you
1449 must instead use the command @samp{sort -k 2} to get the field-based
1452 @vindex _POSIX2_VERSION
1453 The GNU utilities normally conform to the version of POSIX
1454 that is standard for your system. To cause them to conform to a
1455 different version of POSIX, define the @env{_POSIX2_VERSION}
1456 environment variable to a value of the form @var{yyyymm} specifying
1457 the year and month the standard was adopted. Three values are currently
1458 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1459 POSIX 1003.2-1992, @samp{200112} stands for POSIX
1460 1003.1-2001, and @samp{200809} stands for POSIX 1003.1-2008.
1461 For example, if you have a newer system but are running software
1462 that assumes an older version of POSIX and uses @samp{sort +1}
1463 or @samp{tail +10}, you can work around any compatibility problems by setting
1464 @samp{_POSIX2_VERSION=199209} in your environment.
1466 @node Output of entire files
1467 @chapter Output of entire files
1469 @cindex output of entire files
1470 @cindex entire files, output of
1472 These commands read and write entire files, possibly transforming them
1476 * cat invocation:: Concatenate and write files.
1477 * tac invocation:: Concatenate and write files in reverse.
1478 * nl invocation:: Number lines and write files.
1479 * od invocation:: Write files in octal or other formats.
1480 * base64 invocation:: Transform data into printable data.
1483 @node cat invocation
1484 @section @command{cat}: Concatenate and write files
1487 @cindex concatenate and write files
1488 @cindex copying files
1490 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1491 standard input if none are given, to standard output. Synopsis:
1494 cat [@var{option}] [@var{file}]@dots{}
1497 The program accepts the following options. Also see @ref{Common options}.
1505 Equivalent to @option{-vET}.
1508 @itemx --number-nonblank
1510 @opindex --number-nonblank
1511 Number all nonempty output lines, starting with 1.
1515 Equivalent to @option{-vE}.
1520 @opindex --show-ends
1521 Display a @samp{$} after the end of each line.
1527 Number all output lines, starting with 1. This option is ignored
1528 if @option{-b} is in effect.
1531 @itemx --squeeze-blank
1533 @opindex --squeeze-blank
1534 @cindex squeezing empty lines
1535 Suppress repeated adjacent empty lines; output just one empty line
1540 Equivalent to @option{-vT}.
1545 @opindex --show-tabs
1546 Display TAB characters as @samp{^I}.
1550 Ignored; for POSIX compatibility.
1553 @itemx --show-nonprinting
1555 @opindex --show-nonprinting
1556 Display control characters except for LFD and TAB using
1557 @samp{^} notation and precede characters that have the high bit set with
1562 On systems like MS-DOS that distinguish between text and binary files,
1563 @command{cat} normally reads and writes in binary mode. However,
1564 @command{cat} reads in text mode if one of the options
1565 @option{-bensAE} is used or if @command{cat} is reading from standard
1566 input and standard input is a terminal. Similarly, @command{cat}
1567 writes in text mode if one of the options @option{-bensAE} is used or
1568 if standard output is a terminal.
1575 # Output f's contents, then standard input, then g's contents.
1578 # Copy standard input to standard output.
1583 @node tac invocation
1584 @section @command{tac}: Concatenate and write files in reverse
1587 @cindex reversing files
1589 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1590 standard input if none are given, to standard output, reversing the
1591 records (lines by default) in each separately. Synopsis:
1594 tac [@var{option}]@dots{} [@var{file}]@dots{}
1597 @dfn{Records} are separated by instances of a string (newline by
1598 default). By default, this separator string is attached to the end of
1599 the record that it follows in the file.
1601 The program accepts the following options. Also see @ref{Common options}.
1609 The separator is attached to the beginning of the record that it
1610 precedes in the file.
1616 Treat the separator string as a regular expression.
1618 @item -s @var{separator}
1619 @itemx --separator=@var{separator}
1621 @opindex --separator
1622 Use @var{separator} as the record separator, instead of newline.
1626 On systems like MS-DOS that distinguish between text and binary files,
1627 @command{tac} reads and writes in binary mode.
1634 # Reverse a file character by character.
1640 @section @command{nl}: Number lines and write files
1643 @cindex numbering lines
1644 @cindex line numbering
1646 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1647 standard input if none are given, to standard output, with line numbers
1648 added to some or all of the lines. Synopsis:
1651 nl [@var{option}]@dots{} [@var{file}]@dots{}
1654 @cindex logical pages, numbering on
1655 @command{nl} decomposes its input into (logical) pages; by default, the
1656 line number is reset to 1 at the top of each logical page. @command{nl}
1657 treats all of the input files as a single document; it does not reset
1658 line numbers or logical pages between files.
1660 @cindex headers, numbering
1661 @cindex body, numbering
1662 @cindex footers, numbering
1663 A logical page consists of three sections: header, body, and footer.
1664 Any of the sections can be empty. Each can be numbered in a different
1665 style from the others.
1667 The beginnings of the sections of logical pages are indicated in the
1668 input file by a line containing exactly one of these delimiter strings:
1679 The two characters from which these strings are made can be changed from
1680 @samp{\} and @samp{:} via options (see below), but the pattern and
1681 length of each string cannot be changed.
1683 A section delimiter is replaced by an empty line on output. Any text
1684 that comes before the first section delimiter string in the input file
1685 is considered to be part of a body section, so @command{nl} treats a
1686 file that contains no section delimiters as a single body section.
1688 The program accepts the following options. Also see @ref{Common options}.
1692 @item -b @var{style}
1693 @itemx --body-numbering=@var{style}
1695 @opindex --body-numbering
1696 Select the numbering style for lines in the body section of each
1697 logical page. When a line is not numbered, the current line number
1698 is not incremented, but the line number separator character is still
1699 prepended to the line. The styles are:
1705 number only nonempty lines (default for body),
1707 do not number lines (default for header and footer),
1709 number only lines that contain a match for the basic regular
1710 expression @var{bre}.
1711 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1715 @itemx --section-delimiter=@var{cd}
1717 @opindex --section-delimiter
1718 @cindex section delimiters of pages
1719 Set the section delimiter characters to @var{cd}; default is
1720 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1721 (Remember to protect @samp{\} or other metacharacters from shell
1722 expansion with quotes or extra backslashes.)
1724 @item -f @var{style}
1725 @itemx --footer-numbering=@var{style}
1727 @opindex --footer-numbering
1728 Analogous to @option{--body-numbering}.
1730 @item -h @var{style}
1731 @itemx --header-numbering=@var{style}
1733 @opindex --header-numbering
1734 Analogous to @option{--body-numbering}.
1736 @item -i @var{number}
1737 @itemx --line-increment=@var{number}
1739 @opindex --line-increment
1740 Increment line numbers by @var{number} (default 1).
1742 @item -l @var{number}
1743 @itemx --join-blank-lines=@var{number}
1745 @opindex --join-blank-lines
1746 @cindex empty lines, numbering
1747 @cindex blank lines, numbering
1748 Consider @var{number} (default 1) consecutive empty lines to be one
1749 logical line for numbering, and only number the last one. Where fewer
1750 than @var{number} consecutive empty lines occur, do not number them.
1751 An empty line is one that contains no characters, not even spaces
1754 @item -n @var{format}
1755 @itemx --number-format=@var{format}
1757 @opindex --number-format
1758 Select the line numbering format (default is @code{rn}):
1762 @opindex ln @r{format for @command{nl}}
1763 left justified, no leading zeros;
1765 @opindex rn @r{format for @command{nl}}
1766 right justified, no leading zeros;
1768 @opindex rz @r{format for @command{nl}}
1769 right justified, leading zeros.
1773 @itemx --no-renumber
1775 @opindex --no-renumber
1776 Do not reset the line number at the start of a logical page.
1778 @item -s @var{string}
1779 @itemx --number-separator=@var{string}
1781 @opindex --number-separator
1782 Separate the line number from the text line in the output with
1783 @var{string} (default is the TAB character).
1785 @item -v @var{number}
1786 @itemx --starting-line-number=@var{number}
1788 @opindex --starting-line-number
1789 Set the initial line number on each logical page to @var{number} (default 1).
1791 @item -w @var{number}
1792 @itemx --number-width=@var{number}
1794 @opindex --number-width
1795 Use @var{number} characters for line numbers (default 6).
1803 @section @command{od}: Write files in octal or other formats
1806 @cindex octal dump of files
1807 @cindex hex dump of files
1808 @cindex ASCII dump of files
1809 @cindex file contents, dumping unambiguously
1811 @command{od} writes an unambiguous representation of each @var{file}
1812 (@samp{-} means standard input), or standard input if none are given.
1816 od [@var{option}]@dots{} [@var{file}]@dots{}
1817 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1818 od [@var{option}]@dots{} --traditional [@var{file}]@c
1819 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1822 Each line of output consists of the offset in the input, followed by
1823 groups of data from the file. By default, @command{od} prints the offset in
1824 octal, and each group of file data is a C @code{short int}'s worth of input
1825 printed as a single octal number.
1827 If @var{offset} is given, it specifies how many input bytes to skip
1828 before formatting and writing. By default, it is interpreted as an
1829 octal number, but the optional trailing decimal point causes it to be
1830 interpreted as decimal. If no decimal is specified and the offset
1831 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1832 number. If there is a trailing @samp{b}, the number of bytes skipped
1833 will be @var{offset} multiplied by 512.
1835 If a command is of both the first and second forms, the second form is
1836 assumed if the last operand begins with @samp{+} or (if there are two
1837 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1838 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1841 The program accepts the following options. Also see @ref{Common options}.
1845 @item -A @var{radix}
1846 @itemx --address-radix=@var{radix}
1848 @opindex --address-radix
1849 @cindex radix for file offsets
1850 @cindex file offset radix
1851 Select the base in which file offsets are printed. @var{radix} can
1852 be one of the following:
1862 none (do not print offsets).
1865 The default is octal.
1867 @item -j @var{bytes}
1868 @itemx --skip-bytes=@var{bytes}
1870 @opindex --skip-bytes
1871 Skip @var{bytes} input bytes before formatting and writing. If
1872 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1873 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1875 @multiplierSuffixes{bytes}
1877 @item -N @var{bytes}
1878 @itemx --read-bytes=@var{bytes}
1880 @opindex --read-bytes
1881 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1882 @code{bytes} are interpreted as for the @option{-j} option.
1884 @item -S @var{bytes}
1885 @itemx --strings[=@var{bytes}]
1888 @cindex string constants, outputting
1889 Instead of the normal output, output only @dfn{string constants}: at
1890 least @var{bytes} consecutive ASCII graphic characters,
1891 followed by a zero byte (ASCII NUL).
1892 Prefixes and suffixes on @var{bytes} are interpreted as for the
1895 If @var{bytes} is omitted with @option{--strings}, the default is 3.
1898 @itemx --format=@var{type}
1901 Select the format in which to output the file data. @var{type} is a
1902 string of one or more of the below type indicator characters. If you
1903 include more than one type indicator character in a single @var{type}
1904 string, or use this option more than once, @command{od} writes one copy
1905 of each output line using each of the data types that you specified,
1906 in the order that you specified.
1908 Adding a trailing ``z'' to any type specification appends a display
1909 of the ASCII character representation of the printable characters
1910 to the output line generated by the type specification.
1914 named character, ignoring high-order bit
1916 ASCII character or backslash escape,
1920 floating point (@pxref{Floating point})
1929 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1930 newline, and @samp{nul} for a zero byte. Only the least significant
1931 seven bits of each byte is used; the high-order bit is ignored.
1932 Type @code{c} outputs
1933 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1936 Except for types @samp{a} and @samp{c}, you can specify the number
1937 of bytes to use in interpreting each number in the given data type
1938 by following the type indicator character with a decimal integer.
1939 Alternately, you can specify the size of one of the C compiler's
1940 built-in data types by following the type indicator character with
1941 one of the following characters. For integers (@samp{d}, @samp{o},
1942 @samp{u}, @samp{x}):
1955 For floating point (@code{f}):
1967 @itemx --output-duplicates
1969 @opindex --output-duplicates
1970 Output consecutive lines that are identical. By default, when two or
1971 more consecutive output lines would be identical, @command{od} outputs only
1972 the first line, and puts just an asterisk on the following line to
1973 indicate the elision.
1976 @itemx --width[=@var{n}]
1979 Dump @code{n} input bytes per output line. This must be a multiple of
1980 the least common multiple of the sizes associated with the specified
1983 If this option is not given at all, the default is 16. If @var{n} is
1984 omitted, the default is 32.
1988 The next several options are shorthands for format specifications.
1989 GNU @command{od} accepts any combination of shorthands and format
1990 specification options. These options accumulate.
1996 Output as named characters. Equivalent to @samp{-t a}.
2000 Output as octal bytes. Equivalent to @samp{-t o1}.
2004 Output as ASCII characters or backslash escapes. Equivalent to
2009 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
2013 Output as floats. Equivalent to @samp{-t fF}.
2017 Output as decimal ints. Equivalent to @samp{-t dI}.
2021 Output as decimal long ints. Equivalent to @samp{-t dL}.
2025 Output as octal two-byte units. Equivalent to @option{-t o2}.
2029 Output as decimal two-byte units. Equivalent to @option{-t d2}.
2033 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
2036 @opindex --traditional
2037 Recognize the non-option label argument that traditional @command{od}
2038 accepted. The following syntax:
2041 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2045 can be used to specify at most one file and optional arguments
2046 specifying an offset and a pseudo-start address, @var{label}.
2047 The @var{label} argument is interpreted
2048 just like @var{offset}, but it specifies an initial pseudo-address. The
2049 pseudo-addresses are displayed in parentheses following any normal
2056 @node base64 invocation
2057 @section @command{base64}: Transform data into printable data
2060 @cindex base64 encoding
2062 @command{base64} transforms data read from a file, or standard input,
2063 into (or from) base64 encoded form. The base64 encoded form uses
2064 printable ASCII characters to represent binary data.
2068 base64 [@var{option}]@dots{} [@var{file}]
2069 base64 --decode [@var{option}]@dots{} [@var{file}]
2072 The base64 encoding expands data to roughly 133% of the original.
2073 The format conforms to
2074 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2076 The program accepts the following options. Also see @ref{Common options}.
2081 @itemx --wrap=@var{cols}
2085 @cindex column to wrap data after
2086 During encoding, wrap lines after @var{cols} characters. This must be
2089 The default is to wrap after 76 characters. Use the value 0 to
2090 disable line wrapping altogether.
2096 @cindex Decode base64 data
2097 @cindex Base64 decoding
2098 Change the mode of operation, from the default of encoding data, to
2099 decoding data. Input is expected to be base64 encoded data, and the
2100 output will be the original data.
2103 @itemx --ignore-garbage
2105 @opindex --ignore-garbage
2106 @cindex Ignore garbage in base64 stream
2107 When decoding, newlines are always accepted.
2108 During decoding, ignore unrecognized bytes,
2109 to permit distorted data to be decoded.
2116 @node Formatting file contents
2117 @chapter Formatting file contents
2119 @cindex formatting file contents
2121 These commands reformat the contents of files.
2124 * fmt invocation:: Reformat paragraph text.
2125 * pr invocation:: Paginate or columnate files for printing.
2126 * fold invocation:: Wrap input lines to fit in specified width.
2130 @node fmt invocation
2131 @section @command{fmt}: Reformat paragraph text
2134 @cindex reformatting paragraph text
2135 @cindex paragraphs, reformatting
2136 @cindex text, reformatting
2138 @command{fmt} fills and joins lines to produce output lines of (at most)
2139 a given number of characters (75 by default). Synopsis:
2142 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2145 @command{fmt} reads from the specified @var{file} arguments (or standard
2146 input if none are given), and writes to standard output.
2148 By default, blank lines, spaces between words, and indentation are
2149 preserved in the output; successive input lines with different
2150 indentation are not joined; tabs are expanded on input and introduced on
2153 @cindex line-breaking
2154 @cindex sentences and line-breaking
2155 @cindex Knuth, Donald E.
2156 @cindex Plass, Michael F.
2157 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2158 avoid line breaks after the first word of a sentence or before the last
2159 word of a sentence. A @dfn{sentence break} is defined as either the end
2160 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2161 spaces or end of line, ignoring any intervening parentheses or quotes.
2162 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2163 breaks; the algorithm is a variant of that given by Donald E. Knuth
2164 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2165 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2168 The program accepts the following options. Also see @ref{Common options}.
2173 @itemx --crown-margin
2175 @opindex --crown-margin
2176 @cindex crown margin
2177 @dfn{Crown margin} mode: preserve the indentation of the first two
2178 lines within a paragraph, and align the left margin of each subsequent
2179 line with that of the second line.
2182 @itemx --tagged-paragraph
2184 @opindex --tagged-paragraph
2185 @cindex tagged paragraphs
2186 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2187 indentation of the first line of a paragraph is the same as the
2188 indentation of the second, the first line is treated as a one-line
2194 @opindex --split-only
2195 Split lines only. Do not join short lines to form longer ones. This
2196 prevents sample lines of code, and other such ``formatted'' text from
2197 being unduly combined.
2200 @itemx --uniform-spacing
2202 @opindex --uniform-spacing
2203 Uniform spacing. Reduce spacing between words to one space, and spacing
2204 between sentences to two spaces.
2207 @itemx -w @var{width}
2208 @itemx --width=@var{width}
2209 @opindex -@var{width}
2212 Fill output lines up to @var{width} characters (default 75 or @var{goal}
2213 plus 10, if @var{goal} is provided).
2216 @itemx --goal=@var{goal}
2219 @command{fmt} initially tries to make lines @var{goal} characters wide.
2220 By default, this is 7% shorter than @var{width}.
2222 @item -p @var{prefix}
2223 @itemx --prefix=@var{prefix}
2224 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2225 are subject to formatting. The prefix and any preceding whitespace are
2226 stripped for the formatting and then re-attached to each formatted output
2227 line. One use is to format certain kinds of program comments, while
2228 leaving the code unchanged.
2236 @section @command{pr}: Paginate or columnate files for printing
2239 @cindex printing, preparing files for
2240 @cindex multicolumn output, generating
2241 @cindex merging files in parallel
2243 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2244 standard input if none are given, to standard output, paginating and
2245 optionally outputting in multicolumn format; optionally merges all
2246 @var{file}s, printing all in parallel, one per column. Synopsis:
2249 pr [@var{option}]@dots{} [@var{file}]@dots{}
2253 By default, a 5-line header is printed at each page: two blank lines;
2254 a line with the date, the file name, and the page count; and two more
2255 blank lines. A footer of five blank lines is also printed.
2256 The default @var{page_length} is 66
2257 lines. The default number of text lines is therefore 56.
2258 The text line of the header takes the form
2259 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2260 @var{string} so that the line takes up the full @var{page_width}. Here,
2261 @var{date} is the date (see the @option{-D} or @option{--date-format}
2262 option for details), @var{string} is the centered header string, and
2263 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2264 category affects the spelling of @var{page}; in the default C locale, it
2265 is @samp{Page @var{number}} where @var{number} is the decimal page
2268 Form feeds in the input cause page breaks in the output. Multiple form
2269 feeds produce empty pages.
2271 Columns are of equal width, separated by an optional string (default
2272 is @samp{space}). For multicolumn output, lines will always be truncated to
2273 @var{page_width} (default 72), unless you use the @option{-J} option.
2275 column output no line truncation occurs by default. Use @option{-W} option to
2276 truncate lines in that case.
2278 The program accepts the following options. Also see @ref{Common options}.
2282 @item +@var{first_page}[:@var{last_page}]
2283 @itemx --pages=@var{first_page}[:@var{last_page}]
2284 @c The two following @opindex lines evoke warnings because they contain ':'
2285 @c The 'info' spec does not permit that. If we use those lines, we end
2286 @c up with truncated index entries that don't work.
2287 @c @opindex +@var{first_page}[:@var{last_page}]
2288 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2289 @opindex +@var{page_range}
2290 @opindex --pages=@var{page_range}
2291 Begin printing with page @var{first_page} and stop with @var{last_page}.
2292 Missing @samp{:@var{last_page}} implies end of file. While estimating
2293 the number of skipped pages each form feed in the input file results
2294 in a new page. Page counting with and without @samp{+@var{first_page}}
2295 is identical. By default, counting starts with the first page of input
2296 file (not first page printed). Line numbering may be altered by @option{-N}
2300 @itemx --columns=@var{column}
2301 @opindex -@var{column}
2303 @cindex down columns
2304 With each single @var{file}, produce @var{column} columns of output
2305 (default is 1) and print columns down, unless @option{-a} is used. The
2306 column width is automatically decreased as @var{column} increases; unless
2307 you use the @option{-W/-w} option to increase @var{page_width} as well.
2308 This option might well cause some lines to be truncated. The number of
2309 lines in the columns on each page are balanced. The options @option{-e}
2310 and @option{-i} are on for multiple text-column output. Together with
2311 @option{-J} option column alignment and line truncation is turned off.
2312 Lines of full length are joined in a free field format and @option{-S}
2313 option may set field separators. @option{-@var{column}} may not be used
2314 with @option{-m} option.
2320 @cindex across columns
2321 With each single @var{file}, print columns across rather than down. The
2322 @option{-@var{column}} option must be given with @var{column} greater than one.
2323 If a line is too long to fit in a column, it is truncated.
2326 @itemx --show-control-chars
2328 @opindex --show-control-chars
2329 Print control characters using hat notation (e.g., @samp{^G}); print
2330 other nonprinting characters in octal backslash notation. By default,
2331 nonprinting characters are not changed.
2334 @itemx --double-space
2336 @opindex --double-space
2337 @cindex double spacing
2338 Double space the output.
2340 @item -D @var{format}
2341 @itemx --date-format=@var{format}
2342 @cindex time formats
2343 @cindex formatting times
2344 Format header dates using @var{format}, using the same conventions as
2345 for the command @samp{date +@var{format}}. @xref{date invocation}.
2346 Except for directives, which start with
2347 @samp{%}, characters in @var{format} are printed unchanged. You can use
2348 this option to specify an arbitrary string in place of the header date,
2349 e.g., @option{--date-format="Monday morning"}.
2351 @vindex POSIXLY_CORRECT
2353 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2354 @samp{2001-12-04 23:59});
2355 but if the @env{POSIXLY_CORRECT} environment variable is set
2356 and the @env{LC_TIME} locale category specifies the POSIX
2357 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2358 @samp{Dec@ @ 4 23:59 2001}.
2361 Time stamps are listed according to the time zone rules specified by
2362 the @env{TZ} environment variable, or by the system default rules if
2363 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2364 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2366 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2367 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2369 @opindex --expand-tabs
2371 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2372 the input tab character (default is the TAB character). Second optional
2373 argument @var{in-tabwidth} is the input tab character's width (default
2381 @opindex --form-feed
2382 Use a form feed instead of newlines to separate output pages. This does
2383 not alter the default page length of 66 lines.
2385 @item -h @var{header}
2386 @itemx --header=@var{header}
2389 Replace the file name in the header with the centered string @var{header}.
2390 When using the shell, @var{header} should be quoted and should be
2391 separated from @option{-h} by a space.
2393 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2394 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2396 @opindex --output-tabs
2398 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2399 is the output tab character (default is the TAB character). Second optional
2400 argument @var{out-tabwidth} is the output tab character's width (default
2406 @opindex --join-lines
2407 Merge lines of full length. Used together with the column options
2408 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2409 @option{-W/-w} line truncation;
2410 no column alignment used; may be used with
2411 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2412 (together with @option{-W} and @option{--sep-string})
2413 to disentangle the old (POSIX-compliant) options @option{-w} and
2414 @option{-s} along with the three column options.
2417 @item -l @var{page_length}
2418 @itemx --length=@var{page_length}
2421 Set the page length to @var{page_length} (default 66) lines, including
2422 the lines of the header [and the footer]. If @var{page_length} is less
2423 than or equal to 10, the header and footer are omitted, as if the
2424 @option{-t} option had been given.
2430 Merge and print all @var{file}s in parallel, one in each column. If a
2431 line is too long to fit in a column, it is truncated, unless the @option{-J}
2432 option is used. @option{--sep-string[=@var{string}]} may be used.
2434 some @var{file}s (form feeds set) produce empty columns, still marked
2435 by @var{string}. The result is a continuous line numbering and column
2436 marking throughout the whole merged file. Completely empty merged pages
2437 show no separators or line numbers. The default header becomes
2438 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2439 may be used with the @option{-h} or @option{--header} option to fill up
2440 the middle blank part.
2442 @item -n[@var{number-separator}[@var{digits}]]
2443 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2445 @opindex --number-lines
2446 Provide @var{digits} digit line numbering (default for @var{digits} is
2447 5). With multicolumn output the number occupies the first @var{digits}
2448 column positions of each text column or only each line of @option{-m}
2449 output. With single column output the number precedes each line just as
2450 @option{-m} does. Default counting of the line numbers starts with the
2451 first line of the input file (not the first line printed, compare the
2452 @option{--page} option and @option{-N} option).
2453 Optional argument @var{number-separator} is the character appended to
2454 the line number to separate it from the text followed. The default
2455 separator is the TAB character. In a strict sense a TAB is always
2456 printed with single column output only. The TAB width varies
2457 with the TAB position, e.g., with the left @var{margin} specified
2458 by @option{-o} option. With multicolumn output priority is given to
2459 @samp{equal width of output columns} (a POSIX specification).
2460 The TAB width is fixed to the value of the first column and does
2461 not change with different values of left @var{margin}. That means a
2462 fixed number of spaces is always printed in the place of the
2463 @var{number-separator} TAB@. The tabification depends upon the output
2466 @item -N @var{line_number}
2467 @itemx --first-line-number=@var{line_number}
2469 @opindex --first-line-number
2470 Start line counting with the number @var{line_number} at first line of
2471 first page printed (in most cases not the first line of the input file).
2473 @item -o @var{margin}
2474 @itemx --indent=@var{margin}
2477 @cindex indenting lines
2479 Indent each line with a margin @var{margin} spaces wide (default is zero).
2480 The total page width is the size of the margin plus the @var{page_width}
2481 set with the @option{-W/-w} option. A limited overflow may occur with
2482 numbered single column output (compare @option{-n} option).
2485 @itemx --no-file-warnings
2487 @opindex --no-file-warnings
2488 Do not print a warning message when an argument @var{file} cannot be
2489 opened. (The exit status will still be nonzero, however.)
2491 @item -s[@var{char}]
2492 @itemx --separator[=@var{char}]
2494 @opindex --separator
2495 Separate columns by a single character @var{char}. The default for
2496 @var{char} is the TAB character without @option{-w} and @samp{no
2497 character} with @option{-w}. Without @option{-s} the default separator
2498 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2499 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2500 @option{-w} is set. This is a POSIX-compliant formulation.
2503 @item -S[@var{string}]
2504 @itemx --sep-string[=@var{string}]
2506 @opindex --sep-string
2507 Use @var{string} to separate output columns. The @option{-S} option doesn't
2508 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2509 does not affect line truncation or column alignment.
2510 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2512 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2513 (same as @option{-S"@w{ }"}).
2514 If no @samp{@var{string}} argument is specified, @samp{""} is assumed.
2517 @itemx --omit-header
2519 @opindex --omit-header
2520 Do not print the usual header [and footer] on each page, and do not fill
2521 out the bottom of pages (with blank lines or a form feed). No page
2522 structure is produced, but form feeds set in the input files are retained.
2523 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2524 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2525 in the input file to 4 spaces but don't make any other changes. Use of
2526 @option{-t} overrides @option{-h}.
2529 @itemx --omit-pagination
2531 @opindex --omit-pagination
2532 Do not print header [and footer]. In addition eliminate all form feeds
2533 set in the input files.
2536 @itemx --show-nonprinting
2538 @opindex --show-nonprinting
2539 Print nonprinting characters in octal backslash notation.
2541 @item -w @var{page_width}
2542 @itemx --width=@var{page_width}
2545 Set page width to @var{page_width} characters for multiple text-column
2546 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2547 off the default page width and any line truncation and column alignment.
2548 Lines of full length are merged, regardless of the column options
2549 set. No @var{page_width} setting is possible with single column output.
2550 A POSIX-compliant formulation.
2552 @item -W @var{page_width}
2553 @itemx --page_width=@var{page_width}
2555 @opindex --page_width
2556 Set the page width to @var{page_width} characters. That's valid with and
2557 without a column option. Text lines are truncated, unless @option{-J}
2558 is used. Together with one of the three column options
2559 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2560 alignment is always used. The separator options @option{-S} or @option{-s}
2561 don't affect the @option{-W} option. Default is 72 characters. Without
2562 @option{-W @var{page_width}} and without any of the column options NO line
2563 truncation is used (defined to keep downward compatibility and to meet
2564 most frequent tasks). That's equivalent to @option{-W 72 -J}@. The header
2565 line is never truncated.
2572 @node fold invocation
2573 @section @command{fold}: Wrap input lines to fit in specified width
2576 @cindex wrapping long input lines
2577 @cindex folding long input lines
2579 @command{fold} writes each @var{file} (@option{-} means standard input), or
2580 standard input if none are given, to standard output, breaking long
2584 fold [@var{option}]@dots{} [@var{file}]@dots{}
2587 By default, @command{fold} breaks lines wider than 80 columns. The output
2588 is split into as many lines as necessary.
2590 @cindex screen columns
2591 @command{fold} counts screen columns by default; thus, a tab may count more
2592 than one column, backspace decreases the column count, and carriage
2593 return sets the column to zero.
2595 The program accepts the following options. Also see @ref{Common options}.
2603 Count bytes rather than columns, so that tabs, backspaces, and carriage
2604 returns are each counted as taking up one column, just like other
2611 Break at word boundaries: the line is broken after the last blank before
2612 the maximum line length. If the line contains no such blanks, the line
2613 is broken at the maximum line length as usual.
2615 @item -w @var{width}
2616 @itemx --width=@var{width}
2619 Use a maximum line length of @var{width} columns instead of 80.
2621 For compatibility @command{fold} supports an obsolete option syntax
2622 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2630 @node Output of parts of files
2631 @chapter Output of parts of files
2633 @cindex output of parts of files
2634 @cindex parts of files, output of
2636 These commands output pieces of the input.
2639 * head invocation:: Output the first part of files.
2640 * tail invocation:: Output the last part of files.
2641 * split invocation:: Split a file into pieces.
2642 * csplit invocation:: Split a file into context-determined pieces.
2645 @node head invocation
2646 @section @command{head}: Output the first part of files
2649 @cindex initial part of files, outputting
2650 @cindex first part of files, outputting
2652 @command{head} prints the first part (10 lines by default) of each
2653 @var{file}; it reads from standard input if no files are given or
2654 when given a @var{file} of @option{-}. Synopsis:
2657 head [@var{option}]@dots{} [@var{file}]@dots{}
2660 If more than one @var{file} is specified, @command{head} prints a
2661 one-line header consisting of:
2664 ==> @var{file name} <==
2668 before the output for each @var{file}.
2670 The program accepts the following options. Also see @ref{Common options}.
2675 @itemx --bytes=@var{k}
2678 Print the first @var{k} bytes, instead of initial lines.
2679 However, if @var{k} starts with a @samp{-},
2680 print all but the last @var{k} bytes of each file.
2681 @multiplierSuffixes{k}
2684 @itemx --lines=@var{k}
2687 Output the first @var{k} lines.
2688 However, if @var{k} starts with a @samp{-},
2689 print all but the last @var{k} lines of each file.
2690 Size multiplier suffixes are the same as with the @option{-c} option.
2698 Never print file name headers.
2704 Always print file name headers.
2708 For compatibility @command{head} also supports an obsolete option syntax
2709 @option{-@var{count}@var{options}}, which is recognized only if it is
2710 specified first. @var{count} is a decimal number optionally followed
2711 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2712 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2713 Scripts intended for standard hosts should use @option{-c @var{count}}
2714 or @option{-n @var{count}} instead. If your script must also run on
2715 hosts that support only the obsolete syntax, it is usually simpler to
2716 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2722 @node tail invocation
2723 @section @command{tail}: Output the last part of files
2726 @cindex last part of files, outputting
2728 @command{tail} prints the last part (10 lines by default) of each
2729 @var{file}; it reads from standard input if no files are given or
2730 when given a @var{file} of @samp{-}. Synopsis:
2733 tail [@var{option}]@dots{} [@var{file}]@dots{}
2736 If more than one @var{file} is specified, @command{tail} prints a
2737 one-line header consisting of:
2740 ==> @var{file name} <==
2744 before the output for each @var{file}.
2746 @cindex BSD @command{tail}
2747 GNU @command{tail} can output any amount of data (some other versions of
2748 @command{tail} cannot). It also has no @option{-r} option (print in
2749 reverse), since reversing a file is really a different job from printing
2750 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2751 only reverse files that are at most as large as its buffer, which is
2752 typically 32 KiB@. A more reliable and versatile way to reverse files is
2753 the GNU @command{tac} command.
2755 The program accepts the following options. Also see @ref{Common options}.
2760 @itemx --bytes=@var{k}
2763 Output the last @var{k} bytes, instead of final lines.
2764 However, if @var{k} starts with a @samp{+}, start printing with the
2765 @var{k}th byte from the start of each file, instead of from the end.
2766 @multiplierSuffixes{k}
2769 @itemx --follow[=@var{how}]
2772 @cindex growing files
2773 @vindex name @r{follow option}
2774 @vindex descriptor @r{follow option}
2775 Loop forever trying to read more characters at the end of the file,
2776 presumably because the file is growing.
2777 If more than one file is given, @command{tail} prints a header whenever it
2778 gets output from a different file, to indicate which file that output is
2781 There are two ways to specify how you'd like to track files with this option,
2782 but that difference is noticeable only when a followed file is removed or
2784 If you'd like to continue to track the end of a growing file even after
2785 it has been unlinked, use @option{--follow=descriptor}. This is the default
2786 behavior, but it is not useful if you're tracking a log file that may be
2787 rotated (removed or renamed, then reopened). In that case, use
2788 @option{--follow=name} to track the named file, perhaps by reopening it
2789 periodically to see if it has been removed and recreated by some other program.
2790 Note that the inotify-based implementation handles this case without
2791 the need for any periodic reopening.
2793 No matter which method you use, if the tracked file is determined to have
2794 shrunk, @command{tail} prints a message saying the file has been truncated
2795 and resumes tracking the end of the file from the newly-determined endpoint.
2797 When a file is removed, @command{tail}'s behavior depends on whether it is
2798 following the name or the descriptor. When following by name, tail can
2799 detect that a file has been removed and gives a message to that effect,
2800 and if @option{--retry} has been specified it will continue checking
2801 periodically to see if the file reappears.
2802 When following a descriptor, tail does not detect that the file has
2803 been unlinked or renamed and issues no message; even though the file
2804 may no longer be accessible via its original name, it may still be
2807 The option values @samp{descriptor} and @samp{name} may be specified only
2808 with the long form of the option, not with @option{-f}.
2810 The @option{-f} option is ignored if
2811 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2812 Likewise, the @option{-f} option has no effect for any
2813 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2815 With kernel inotify support, output is triggered by file changes
2816 and is generally very prompt.
2817 Otherwise, @command{tail} sleeps for one second between checks---
2818 use @option{--sleep-interval=@var{n}} to change that default---which can
2819 make the output appear slightly less responsive or bursty.
2820 When using tail without inotify support, you can make it more responsive
2821 by using a sub-second sleep interval, e.g., via an alias like this:
2824 alias tail='tail -s.1'
2829 This option is the same as @option{--follow=name --retry}. That is, tail
2830 will attempt to reopen a file when it is removed. Should this fail, tail
2831 will keep trying until it becomes accessible again.
2835 This option is useful mainly when following by name (i.e., with
2836 @option{--follow=name}).
2837 Without this option, when tail encounters a file that doesn't
2838 exist or is otherwise inaccessible, it reports that fact and
2839 never checks it again.
2841 @item --sleep-interval=@var{number}
2842 @opindex --sleep-interval
2843 Change the number of seconds to wait between iterations (the default is 1.0).
2844 During one iteration, every specified file is checked to see if it has
2846 Historical implementations of @command{tail} have required that
2847 @var{number} be an integer. However, GNU @command{tail} accepts
2848 an arbitrary floating point number. @xref{Floating point}.
2849 When @command{tail} uses inotify, this polling-related option
2850 is usually ignored. However, if you also specify @option{--pid=@var{p}},
2851 @command{tail} checks whether process @var{p} is alive at least
2852 every @var{number} seconds.
2854 @item --pid=@var{pid}
2856 When following by name or by descriptor, you may specify the process ID,
2857 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2858 after that process terminates, tail will also terminate. This will
2859 work properly only if the writer and the tailing process are running on
2860 the same machine. For example, to save the output of a build in a file
2861 and to watch the file grow, if you invoke @command{make} and @command{tail}
2862 like this then the tail process will stop when your build completes.
2863 Without this option, you would have had to kill the @code{tail -f}
2867 $ make >& makerr & tail --pid=$! -f makerr
2870 If you specify a @var{pid} that is not in use or that does not correspond
2871 to the process that is writing to the tailed files, then @command{tail}
2872 may terminate long before any @var{file}s stop growing or it may not
2873 terminate until long after the real writer has terminated.
2874 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2875 will print a warning if this is the case.
2877 @item --max-unchanged-stats=@var{n}
2878 @opindex --max-unchanged-stats
2879 When tailing a file by name, if there have been @var{n} (default
2880 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2881 iterations for which the file has not changed, then
2882 @code{open}/@code{fstat} the file to determine if that file name is
2883 still associated with the same device/inode-number pair as before.
2884 When following a log file that is rotated, this is approximately the
2885 number of seconds between when tail prints the last pre-rotation lines
2886 and when it prints the lines that have accumulated in the new log file.
2887 This option is meaningful only when polling (i.e., without inotify)
2888 and when following by name.
2891 @itemx --lines=@var{k}
2894 Output the last @var{k} lines.
2895 However, if @var{k} starts with a @samp{+}, start printing with the
2896 @var{k}th line from the start of each file, instead of from the end.
2897 Size multiplier suffixes are the same as with the @option{-c} option.
2905 Never print file name headers.
2911 Always print file name headers.
2915 For compatibility @command{tail} also supports an obsolete usage
2916 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2917 only if it does not conflict with the usage described
2918 above. This obsolete form uses exactly one option and at most one
2919 file. In the option, @var{count} is an optional decimal number optionally
2920 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2921 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2922 which has the same meaning as @option{-f}.
2924 @vindex _POSIX2_VERSION
2925 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2926 the obsolete option syntax with the same meaning as in counts, and
2927 obsolete usage overrides normal usage when the two conflict.
2928 This obsolete behavior can be enabled or disabled with the
2929 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2932 Scripts intended for use on standard hosts should avoid obsolete
2933 syntax and should use @option{-c @var{count}[b]}, @option{-n
2934 @var{count}}, and/or @option{-f} instead. If your script must also
2935 run on hosts that support only the obsolete syntax, you can often
2936 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2937 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2938 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2939 then @dots{}} to decide which syntax to use.
2941 Even if your script assumes the standard behavior, you should still
2942 beware usages whose behaviors differ depending on the POSIX
2943 version. For example, avoid @samp{tail - main.c}, since it might be
2944 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2945 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2946 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2947 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2952 @node split invocation
2953 @section @command{split}: Split a file into pieces.
2956 @cindex splitting a file into pieces
2957 @cindex pieces, splitting a file into
2959 @command{split} creates output files containing consecutive or interleaved
2960 sections of @var{input} (standard input if none is given or @var{input}
2961 is @samp{-}). Synopsis:
2964 split [@var{option}] [@var{input} [@var{prefix}]]
2967 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2968 left over for the last section), into each output file.
2970 @cindex output file name prefix
2971 The output files' names consist of @var{prefix} (@samp{x} by default)
2972 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2973 default), such that concatenating the output files in traditional
2974 sorted order by file name produces the original input file (except
2975 @option{-nr/@var{n}}). By default split will initially create files
2976 with two generated suffix characters, and will increase this width by two
2977 when the next most significant position reaches the last character.
2978 (@samp{yz}, @samp{zaaa}, @samp{zaab}, @dots{}). In this way an arbitrary
2979 number of output files are supported, which sort as described above,
2980 even in the presence of an @option{--additional-suffix} option.
2981 If the @option{-a} option is specified and the output file names are
2982 exhausted, @command{split} reports an error without deleting the
2983 output files that it did create.
2985 The program accepts the following options. Also see @ref{Common options}.
2989 @item -l @var{lines}
2990 @itemx --lines=@var{lines}
2993 Put @var{lines} lines of @var{input} into each output file.
2995 For compatibility @command{split} also supports an obsolete
2996 option syntax @option{-@var{lines}}. New scripts should use
2997 @option{-l @var{lines}} instead.
3000 @itemx --bytes=@var{size}
3003 Put @var{size} bytes of @var{input} into each output file.
3004 @multiplierSuffixes{size}
3007 @itemx --line-bytes=@var{size}
3009 @opindex --line-bytes
3010 Put into each output file as many complete lines of @var{input} as
3011 possible without exceeding @var{size} bytes. Individual lines longer than
3012 @var{size} bytes are broken into multiple files.
3013 @var{size} has the same format as for the @option{--bytes} option.
3015 @item --filter=@var{command}
3017 With this option, rather than simply writing to each output file,
3018 write through a pipe to the specified shell @var{command} for each output file.
3019 @var{command} should use the $FILE environment variable, which is set
3020 to a different output file name for each invocation of the command.
3021 For example, imagine that you have a 1TiB compressed file
3022 that, if uncompressed, would be too large to reside on disk,
3023 yet you must split it into individually-compressed pieces
3024 of a more manageable size.
3025 To do that, you might run this command:
3028 xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
3031 Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
3032 with names @file{big-aa.xz}, @file{big-ab.xz}, @file{big-ac.xz}, etc.
3034 @item -n @var{chunks}
3035 @itemx --number=@var{chunks}
3039 Split @var{input} to @var{chunks} output files where @var{chunks} may be:
3042 @var{n} generate @var{n} files based on current size of @var{input}
3043 @var{k}/@var{n} only output @var{k}th of @var{n} to stdout
3044 l/@var{n} generate @var{n} files without splitting lines
3045 l/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3046 r/@var{n} like @samp{l} but use round robin distribution
3047 r/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3050 Any excess bytes remaining after dividing the @var{input}
3051 into @var{n} chunks, are assigned to the last chunk.
3052 Any excess bytes appearing after the initial calculation are discarded
3053 (except when using @samp{r} mode).
3055 All @var{n} files are created even if there are fewer than @var{n} lines,
3056 or the @var{input} is truncated.
3058 For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
3059 The @var{input} is partitioned into @var{n} equal sized portions, with
3060 the last assigned any excess. If a line @emph{starts} within a partition
3061 it is written completely to the corresponding file. Since lines
3062 are not split even if they overlap a partition, the files written
3063 can be larger or smaller than the partition size, and even empty
3064 if a line is so long as to completely overlap the partition.
3066 For @samp{r} mode, the size of @var{input} is irrelevant,
3067 and so can be a pipe for example.
3069 @item -a @var{length}
3070 @itemx --suffix-length=@var{length}
3072 @opindex --suffix-length
3073 Use suffixes of length @var{length}. If a @var{length} of 0 is specified,
3074 this is the same as if (any previous) @option{-a} was not specified, and
3075 thus enables the default behavior, which starts the suffix length at 2,
3076 and unless @option{-n} or @option{--numeric-suffixes=@var{from}} is
3077 specified, will auto increase the length by 2 as required.
3080 @itemx --numeric-suffixes[=@var{from}]
3082 @opindex --numeric-suffixes
3083 Use digits in suffixes rather than lower-case letters. The numerical
3084 suffix counts from @var{from} if specified, 0 otherwise.
3085 Note specifying a @var{from} value also disables the default
3086 auto suffix length expansion described above, and so you may also
3087 want to specify @option{-a} to allow suffixes beyond @samp{99}.
3089 @item --additional-suffix=@var{suffix}
3090 @opindex --additional-suffix
3091 Append an additional @var{suffix} to output file names. @var{suffix}
3092 must not contain slash.
3095 @itemx --elide-empty-files
3097 @opindex --elide-empty-files
3098 Suppress the generation of zero-length output files. This can happen
3099 with the @option{--number} option if a file is (truncated to be) shorter
3100 than the number requested, or if a line is so long as to completely
3101 span a chunk. The output file sequence numbers, always run consecutively
3102 even when this option is specified.
3107 @opindex --unbuffered
3108 Immediately copy input to output in @option{--number r/@dots{}} mode,
3109 which is a much slower mode of operation.
3113 Write a diagnostic just before each output file is opened.
3119 Here are a few examples to illustrate how the
3120 @option{--number} (@option{-n}) option works:
3122 Notice how, by default, one line may be split onto two or more:
3125 $ seq -w 6 10 > k; split -n3 k; head xa?
3138 Use the "l/" modifier to suppress that:
3141 $ seq -w 6 10 > k; split -nl/3 k; head xa?
3154 Use the "r/" modifier to distribute lines in a round-robin fashion:
3157 $ seq -w 6 10 > k; split -nr/3 k; head xa?
3170 You can also extract just the Kth chunk.
3171 This extracts and prints just the 7th "chunk" of 33:
3174 $ seq 100 > k; split -nl/7/33 k
3181 @node csplit invocation
3182 @section @command{csplit}: Split a file into context-determined pieces
3185 @cindex context splitting
3186 @cindex splitting a file into pieces by context
3188 @command{csplit} creates zero or more output files containing sections of
3189 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3192 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3195 The contents of the output files are determined by the @var{pattern}
3196 arguments, as detailed below. An error occurs if a @var{pattern}
3197 argument refers to a nonexistent line of the input file (e.g., if no
3198 remaining line matches a given regular expression). After every
3199 @var{pattern} has been matched, any remaining input is copied into one
3202 By default, @command{csplit} prints the number of bytes written to each
3203 output file after it has been created.
3205 The types of pattern arguments are:
3210 Create an output file containing the input up to but not including line
3211 @var{n} (a positive integer). If followed by a repeat count, also
3212 create an output file containing the next @var{n} lines of the input
3213 file once for each repeat.
3215 @item /@var{regexp}/[@var{offset}]
3216 Create an output file containing the current line up to (but not
3217 including) the next line of the input file that contains a match for
3218 @var{regexp}. The optional @var{offset} is an integer.
3219 If it is given, the input up to (but not including) the
3220 matching line plus or minus @var{offset} is put into the output file,
3221 and the line after that begins the next section of input.
3223 @item %@var{regexp}%[@var{offset}]
3224 Like the previous type, except that it does not create an output
3225 file, so that section of the input file is effectively ignored.
3227 @item @{@var{repeat-count}@}
3228 Repeat the previous pattern @var{repeat-count} additional
3229 times. The @var{repeat-count} can either be a positive integer or an
3230 asterisk, meaning repeat as many times as necessary until the input is
3235 The output files' names consist of a prefix (@samp{xx} by default)
3236 followed by a suffix. By default, the suffix is an ascending sequence
3237 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3238 concatenating the output files in sorted order by file name produces the
3239 original input file.
3241 By default, if @command{csplit} encounters an error or receives a hangup,
3242 interrupt, quit, or terminate signal, it removes any output files
3243 that it has created so far before it exits.
3245 The program accepts the following options. Also see @ref{Common options}.
3249 @item -f @var{prefix}
3250 @itemx --prefix=@var{prefix}
3253 @cindex output file name prefix
3254 Use @var{prefix} as the output file name prefix.
3256 @item -b @var{suffix}
3257 @itemx --suffix=@var{suffix}
3260 @cindex output file name suffix
3261 Use @var{suffix} as the output file name suffix. When this option is
3262 specified, the suffix string must include exactly one
3263 @code{printf(3)}-style conversion specification, possibly including
3264 format specification flags, a field width, a precision specifications,
3265 or all of these kinds of modifiers. The format letter must convert a
3266 binary unsigned integer argument to readable form. The format letters
3267 @samp{d} and @samp{i} are aliases for @samp{u}, and the
3268 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3269 entire @var{suffix} is given (with the current output file number) to
3270 @code{sprintf(3)} to form the file name suffixes for each of the
3271 individual output files in turn. If this option is used, the
3272 @option{--digits} option is ignored.
3274 @item -n @var{digits}
3275 @itemx --digits=@var{digits}
3278 Use output file names containing numbers that are @var{digits} digits
3279 long instead of the default 2.
3284 @opindex --keep-files
3285 Do not remove output files when errors are encountered.
3288 @itemx --elide-empty-files
3290 @opindex --elide-empty-files
3291 Suppress the generation of zero-length output files. (In cases where
3292 the section delimiters of the input file are supposed to mark the first
3293 lines of each of the sections, the first output file will generally be a
3294 zero-length file unless you use this option.) The output file sequence
3295 numbers always run consecutively starting from 0, even when this option
3306 Do not print counts of output file sizes.
3312 Here is an example of its usage.
3313 First, create an empty directory for the exercise,
3320 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3323 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3329 Each number printed above is the size of an output
3330 file that csplit has just created.
3331 List the names of those output files:
3338 Use @command{head} to show their contents:
3363 @node Summarizing files
3364 @chapter Summarizing files
3366 @cindex summarizing files
3368 These commands generate just a few numbers representing entire
3372 * wc invocation:: Print newline, word, and byte counts.
3373 * sum invocation:: Print checksum and block counts.
3374 * cksum invocation:: Print CRC checksum and byte counts.
3375 * md5sum invocation:: Print or check MD5 digests.
3376 * sha1sum invocation:: Print or check SHA-1 digests.
3377 * sha2 utilities:: Print or check SHA-2 digests.
3382 @section @command{wc}: Print newline, word, and byte counts
3386 @cindex character count
3390 @command{wc} counts the number of bytes, characters, whitespace-separated
3391 words, and newlines in each given @var{file}, or standard input if none
3392 are given or for a @var{file} of @samp{-}. Synopsis:
3395 wc [@var{option}]@dots{} [@var{file}]@dots{}
3398 @cindex total counts
3399 @command{wc} prints one line of counts for each file, and if the file was
3400 given as an argument, it prints the file name following the counts. If
3401 more than one @var{file} is given, @command{wc} prints a final line
3402 containing the cumulative counts, with the file name @file{total}. The
3403 counts are printed in this order: newlines, words, characters, bytes,
3404 maximum line length.
3405 Each count is printed right-justified in a field with at least one
3406 space between fields so that the numbers and file names normally line
3407 up nicely in columns. The width of the count fields varies depending
3408 on the inputs, so you should not depend on a particular field width.
3409 However, as a GNU extension, if only one count is printed,
3410 it is guaranteed to be printed without leading spaces.
3412 By default, @command{wc} prints three counts: the newline, words, and byte
3413 counts. Options can specify that only certain counts be printed.
3414 Options do not undo others previously given, so
3421 prints both the byte counts and the word counts.
3423 With the @option{--max-line-length} option, @command{wc} prints the length
3424 of the longest line per file, and if there is more than one file it
3425 prints the maximum (not the sum) of those lengths. The line lengths here
3426 are measured in screen columns, according to the current locale and
3427 assuming tab positions in every 8th column.
3429 The program accepts the following options. Also see @ref{Common options}.
3437 Print only the byte counts.
3443 Print only the character counts.
3449 Print only the word counts.
3455 Print only the newline counts.
3458 @itemx --max-line-length
3460 @opindex --max-line-length
3461 Print only the maximum line lengths.
3463 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3464 @item --files0-from=@var{file}
3465 @opindex --files0-from=@var{file}
3466 @c This is commented out to avoid a texi2dvi failure.
3467 @c texi2dvi (GNU Texinfo 4.11) 1.104
3468 @c @cindex including files from @command{\cmd\}
3469 Disallow processing files named on the command line, and instead process
3470 those named in file @var{file}; each name being terminated by a zero byte
3472 This is useful \withTotalOption\
3473 when the list of file names is so long that it may exceed a command line
3475 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3476 because it splits the list into pieces and makes @command{\cmd\} print
3477 \subListOutput\ for each sublist rather than for the entire list.
3478 One way to produce a list of ASCII NUL terminated file
3480 @command{find}, using its @option{-print0} predicate.
3481 If @var{file} is @samp{-} then the ASCII NUL terminated
3482 file names are read from standard input.
3484 @filesZeroFromOption{wc,,a total}
3486 For example, to find the length of the longest line in any @file{.c} or
3487 @file{.h} file in the current hierarchy, do this:
3490 find . -name '*.[ch]' -print0 |
3491 wc -L --files0-from=- | tail -n1
3499 @node sum invocation
3500 @section @command{sum}: Print checksum and block counts
3503 @cindex 16-bit checksum
3504 @cindex checksum, 16-bit
3506 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3507 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3510 sum [@var{option}]@dots{} [@var{file}]@dots{}
3513 @command{sum} prints the checksum for each @var{file} followed by the
3514 number of blocks in the file (rounded up). If more than one @var{file}
3515 is given, file names are also printed (by default). (With the
3516 @option{--sysv} option, corresponding file names are printed when there is
3517 at least one file argument.)
3519 By default, GNU @command{sum} computes checksums using an algorithm
3520 compatible with BSD @command{sum} and prints file sizes in units of
3523 The program accepts the following options. Also see @ref{Common options}.
3529 @cindex BSD @command{sum}
3530 Use the default (BSD compatible) algorithm. This option is included for
3531 compatibility with the System V @command{sum}. Unless @option{-s} was also
3532 given, it has no effect.
3538 @cindex System V @command{sum}
3539 Compute checksums using an algorithm compatible with System V
3540 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3544 @command{sum} is provided for compatibility; the @command{cksum} program (see
3545 next section) is preferable in new applications.
3550 @node cksum invocation
3551 @section @command{cksum}: Print CRC checksum and byte counts
3554 @cindex cyclic redundancy check
3555 @cindex CRC checksum
3557 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3558 given @var{file}, or standard input if none are given or for a
3559 @var{file} of @samp{-}. Synopsis:
3562 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3565 @command{cksum} prints the CRC checksum for each file along with the number
3566 of bytes in the file, and the file name unless no arguments were given.
3568 @command{cksum} is typically used to ensure that files
3569 transferred by unreliable means (e.g., netnews) have not been corrupted,
3570 by comparing the @command{cksum} output for the received files with the
3571 @command{cksum} output for the original files (typically given in the
3574 The CRC algorithm is specified by the POSIX standard. It is not
3575 compatible with the BSD or System V @command{sum} algorithms (see the
3576 previous section); it is more robust.
3578 The only options are @option{--help} and @option{--version}. @xref{Common
3584 @node md5sum invocation
3585 @section @command{md5sum}: Print or check MD5 digests
3589 @cindex 128-bit checksum
3590 @cindex checksum, 128-bit
3591 @cindex fingerprint, 128-bit
3592 @cindex message-digest, 128-bit
3594 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3595 @dfn{message-digest}) for each specified @var{file}.
3597 Note: The MD5 digest is more reliable than a simple CRC (provided by
3598 the @command{cksum} command) for detecting accidental file corruption,
3599 as the chances of accidentally having two files with identical MD5
3600 are vanishingly small. However, it should not be considered secure
3601 against malicious tampering: although finding a file with a given MD5
3602 fingerprint is considered infeasible at the moment, it is known how
3603 to modify certain files, including digital certificates, so that they
3604 appear valid when signed with an MD5 digest.
3605 For more secure hashes, consider using SHA-2. @xref{sha2 utilities}.
3607 If a @var{file} is specified as @samp{-} or if no files are given
3608 @command{md5sum} computes the checksum for the standard input.
3609 @command{md5sum} can also determine whether a file and checksum are
3610 consistent. Synopsis:
3613 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3616 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3617 indicating binary or text input mode, and the file name.
3618 If @var{file} contains a backslash or newline, the
3619 line is started with a backslash, and each problematic character in
3620 the file name is escaped with a backslash, making the output
3621 unambiguous even in the presence of arbitrary file names.
3622 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3624 The program accepts the following options. Also see @ref{Common options}.
3632 @cindex binary input files
3633 Treat each input file as binary, by reading it in binary mode and
3634 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3635 On systems like GNU that do not distinguish between binary
3636 and text files, this option merely flags each input mode as binary:
3637 the MD5 checksum is unaffected. This option is the default on systems
3638 like MS-DOS that distinguish between binary and text files, except
3639 for reading standard input when standard input is a terminal.
3643 Read file names and checksum information (not data) from each
3644 @var{file} (or from stdin if no @var{file} was specified) and report
3645 whether the checksums match the contents of the named files.
3646 The input to this mode of @command{md5sum} is usually the output of
3647 a prior, checksum-generating run of @samp{md5sum}.
3648 Each valid line of input consists of an MD5 checksum, a binary/text
3649 flag, and then a file name.
3650 Binary mode is indicated with @samp{*}, text with @samp{ } (space).
3651 For each such line, @command{md5sum} reads the named file and computes its
3652 MD5 checksum. Then, if the computed message digest does not match the
3653 one on the line with the file name, the file is noted as having
3654 failed the test. Otherwise, the file passes the test.
3655 By default, for each valid line, one line is written to standard
3656 output indicating whether the named file passed the test.
3657 After all checks have been performed, if there were any failures,
3658 a warning is issued to standard error.
3659 Use the @option{--status} option to inhibit that output.
3660 If any listed file cannot be opened or read, if any valid line has
3661 an MD5 checksum inconsistent with the associated file, or if no valid
3662 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3663 it exits successfully.
3667 @cindex verifying MD5 checksums
3668 This option is useful only when verifying checksums.
3669 When verifying checksums, don't generate an 'OK' message per successfully
3670 checked file. Files that fail the verification are reported in the
3671 default one-line-per-file format. If there is any checksum mismatch,
3672 print a warning summarizing the failures to standard error.
3676 @cindex verifying MD5 checksums
3677 This option is useful only when verifying checksums.
3678 When verifying checksums, don't generate the default one-line-per-file
3679 diagnostic and don't output the warning summarizing any failures.
3680 Failures to open or read a file still evoke individual diagnostics to
3682 If all listed files are readable and are consistent with the associated
3683 MD5 checksums, exit successfully. Otherwise exit with a status code
3684 indicating there was a failure.
3689 Output BSD style checksums, which indicate the checksum algorithm used.
3690 As a GNU extension, file names with problematic characters
3691 are escaped as described above, with the same escaping indicator of @samp{\}
3692 at the start of the line, being used.
3693 The @option{--tag} option implies binary mode, and is disallowed with
3694 @option{--text} mode as supporting that would unnecessarily complicate
3695 the output format, while providing little benefit.
3701 @cindex text input files
3702 Treat each input file as text, by reading it in text mode and
3703 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3704 This option is the default on systems like GNU that do not
3705 distinguish between binary and text files. On other systems, it is
3706 the default for reading standard input when standard input is a
3707 terminal. This mode is never defaulted to if @option{--tag} is used.
3713 @cindex verifying MD5 checksums
3714 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3715 This option is useful only if all but a few lines in the checked input
3720 @cindex verifying MD5 checksums
3721 When verifying checksums,
3722 if one or more input line is invalid,
3723 exit nonzero after all warnings have been issued.
3730 @node sha1sum invocation
3731 @section @command{sha1sum}: Print or check SHA-1 digests
3735 @cindex 160-bit checksum
3736 @cindex checksum, 160-bit
3737 @cindex fingerprint, 160-bit
3738 @cindex message-digest, 160-bit
3740 @command{sha1sum} computes a 160-bit checksum for each specified
3741 @var{file}. The usage and options of this command are precisely the
3742 same as for @command{md5sum}. @xref{md5sum invocation}.
3744 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3745 it are known (different files having the same fingerprint). However,
3746 it is known that they can be produced with considerable, but not
3747 unreasonable, resources. For this reason, it is generally considered
3748 that SHA-1 should be gradually phased out in favor of the more secure
3749 SHA-2 hash algorithms. @xref{sha2 utilities}.
3752 @node sha2 utilities
3753 @section sha2 utilities: Print or check SHA-2 digests
3760 @cindex 224-bit checksum
3761 @cindex 256-bit checksum
3762 @cindex 384-bit checksum
3763 @cindex 512-bit checksum
3764 @cindex checksum, 224-bit
3765 @cindex checksum, 256-bit
3766 @cindex checksum, 384-bit
3767 @cindex checksum, 512-bit
3768 @cindex fingerprint, 224-bit
3769 @cindex fingerprint, 256-bit
3770 @cindex fingerprint, 384-bit
3771 @cindex fingerprint, 512-bit
3772 @cindex message-digest, 224-bit
3773 @cindex message-digest, 256-bit
3774 @cindex message-digest, 384-bit
3775 @cindex message-digest, 512-bit
3777 The commands @command{sha224sum}, @command{sha256sum},
3778 @command{sha384sum} and @command{sha512sum} compute checksums of
3779 various lengths (respectively 224, 256, 384 and 512 bits),
3780 collectively known as the SHA-2 hashes. The usage and options of
3781 these commands are precisely the same as for @command{md5sum}.
3782 @xref{md5sum invocation}.
3784 Note: The SHA384 and SHA512 digests are considerably slower to
3785 compute, especially on 32-bit computers, than SHA224 or SHA256.
3788 @node Operating on sorted files
3789 @chapter Operating on sorted files
3791 @cindex operating on sorted files
3792 @cindex sorted files, operations on
3794 These commands work with (or produce) sorted files.
3797 * sort invocation:: Sort text files.
3798 * shuf invocation:: Shuffle text files.
3799 * uniq invocation:: Uniquify files.
3800 * comm invocation:: Compare two sorted files line by line.
3801 * ptx invocation:: Produce a permuted index of file contents.
3802 * tsort invocation:: Topological sort.
3806 @node sort invocation
3807 @section @command{sort}: Sort text files
3810 @cindex sorting files
3812 @command{sort} sorts, merges, or compares all the lines from the given
3813 files, or standard input if none are given or for a @var{file} of
3814 @samp{-}. By default, @command{sort} writes the results to standard
3818 sort [@var{option}]@dots{} [@var{file}]@dots{}
3821 @command{sort} has three modes of operation: sort (the default), merge,
3822 and check for sortedness. The following options change the operation
3829 @itemx --check=diagnose-first
3832 @cindex checking for sortedness
3833 Check whether the given file is already sorted: if it is not all
3834 sorted, print a diagnostic containing the first out-of-order line and
3835 exit with a status of 1.
3836 Otherwise, exit successfully.
3837 At most one input file can be given.
3840 @itemx --check=quiet
3841 @itemx --check=silent
3844 @cindex checking for sortedness
3845 Exit successfully if the given file is already sorted, and
3846 exit with status 1 otherwise.
3847 At most one input file can be given.
3848 This is like @option{-c}, except it does not print a diagnostic.
3854 @cindex merging sorted files
3855 Merge the given files by sorting them as a group. Each input file must
3856 always be individually sorted. It always works to sort instead of
3857 merge; merging is provided because it is faster, in the case where it
3862 @cindex sort stability
3863 @cindex sort's last-resort comparison
3864 A pair of lines is compared as follows:
3865 @command{sort} compares each pair of fields, in the
3866 order specified on the command line, according to the associated
3867 ordering options, until a difference is found or no fields are left.
3868 If no key fields are specified, @command{sort} uses a default key of
3869 the entire line. Finally, as a last resort when all keys compare
3870 equal, @command{sort} compares entire lines as if no ordering options
3871 other than @option{--reverse} (@option{-r}) were specified. The
3872 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3873 comparison} so that lines in which all fields compare equal are left
3874 in their original relative order. The @option{--unique}
3875 (@option{-u}) option also disables the last-resort comparison.
3879 Unless otherwise specified, all comparisons use the character collating
3880 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3881 use a non-POSIX locale (e.g., by setting @env{LC_ALL}
3882 to @samp{en_US}), then @command{sort} may produce output that is sorted
3883 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3884 environment variable to @samp{C}@. Note that setting only @env{LC_COLLATE}
3885 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3886 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3887 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3888 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3889 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3891 GNU @command{sort} (as specified for all GNU utilities) has no
3892 limit on input line length or restrictions on bytes allowed within lines.
3893 In addition, if the final byte of an input file is not a newline, GNU
3894 @command{sort} silently supplies one. A line's trailing newline is not
3895 part of the line for comparison purposes.
3897 @cindex exit status of @command{sort}
3901 0 if no error occurred
3902 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3903 2 if an error occurred
3907 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3908 value as the directory for temporary files instead of @file{/tmp}. The
3909 @option{--temporary-directory} (@option{-T}) option in turn overrides
3910 the environment variable.
3912 The following options affect the ordering of output lines. They may be
3913 specified globally or as part of a specific key field. If no key
3914 fields are specified, global options apply to comparison of entire
3915 lines; otherwise the global options are inherited by key fields that do
3916 not specify any special options of their own. In pre-POSIX
3917 versions of @command{sort}, global options affect only later key fields,
3918 so portable shell scripts should specify global options first.
3923 @itemx --ignore-leading-blanks
3925 @opindex --ignore-leading-blanks
3926 @cindex blanks, ignoring leading
3928 Ignore leading blanks when finding sort keys in each line.
3929 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3930 can change this. Note blanks may be ignored by your locale's collating
3931 rules, but without this option they will be significant for character
3932 positions specified in keys with the @option{-k} option.
3935 @itemx --dictionary-order
3937 @opindex --dictionary-order
3938 @cindex dictionary order
3939 @cindex phone directory order
3940 @cindex telephone directory order
3942 Sort in @dfn{phone directory} order: ignore all characters except
3943 letters, digits and blanks when sorting.
3944 By default letters and digits are those of ASCII and a blank
3945 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3948 @itemx --ignore-case
3950 @opindex --ignore-case
3951 @cindex ignoring case
3952 @cindex case folding
3954 Fold lowercase characters into the equivalent uppercase characters when
3955 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3956 The @env{LC_CTYPE} locale determines character types.
3957 When used with @option{--unique} those lower case equivalent lines are
3958 thrown away. (There is currently no way to throw away the upper case
3959 equivalent instead. (Any @option{--reverse} given would only affect
3960 the final result, after the throwing away.))
3963 @itemx --general-numeric-sort
3964 @itemx --sort=general-numeric
3966 @opindex --general-numeric-sort
3968 @cindex general numeric sort
3970 Sort numerically, converting a prefix of each line to a long
3971 double-precision floating point number. @xref{Floating point}.
3972 Do not report overflow, underflow, or conversion errors.
3973 Use the following collating sequence:
3977 Lines that do not start with numbers (all considered to be equal).
3979 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3980 in a consistent but machine-dependent order.
3984 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3989 Use this option only if there is no alternative; it is much slower than
3990 @option{--numeric-sort} (@option{-n}) and it can lose information when
3991 converting to floating point.
3994 @itemx --human-numeric-sort
3995 @itemx --sort=human-numeric
3997 @opindex --human-numeric-sort
3999 @cindex human numeric sort
4001 Sort numerically, first by numeric sign (negative, zero, or positive);
4002 then by SI suffix (either empty, or @samp{k} or @samp{K}, or
4003 one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
4004 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
4005 because @samp{M} (mega) precedes @samp{G} (giga) as an SI
4006 suffix. This option sorts values that are consistently scaled to the
4007 nearest suffix, regardless of whether suffixes denote powers of 1000
4008 or 1024, and it therefore sorts the output of any single invocation of
4009 the @command{df}, @command{du}, or @command{ls} commands that are
4010 invoked with their @option{--human-readable} or @option{--si} options.
4011 The syntax for numbers is the same as for the @option{--numeric-sort}
4012 option; the SI suffix must immediately follow the number.
4015 @itemx --ignore-nonprinting
4017 @opindex --ignore-nonprinting
4018 @cindex nonprinting characters, ignoring
4019 @cindex unprintable characters, ignoring
4021 Ignore nonprinting characters.
4022 The @env{LC_CTYPE} locale determines character types.
4023 This option has no effect if the stronger @option{--dictionary-order}
4024 (@option{-d}) option is also given.
4030 @opindex --month-sort
4032 @cindex months, sorting by
4034 An initial string, consisting of any amount of blanks, followed
4035 by a month name abbreviation, is folded to UPPER case and
4036 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}@.
4037 Invalid names compare low to valid names. The @env{LC_TIME} locale
4038 category determines the month spellings.
4039 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4043 @itemx --numeric-sort
4044 @itemx --sort=numeric
4046 @opindex --numeric-sort
4048 @cindex numeric sort
4050 Sort numerically. The number begins each line and consists
4051 of optional blanks, an optional @samp{-} sign, and zero or more
4052 digits possibly separated by thousands separators, optionally followed
4053 by a decimal-point character and zero or more digits. An empty
4054 number is treated as @samp{0}. The @env{LC_NUMERIC}
4055 locale specifies the decimal-point character and thousands separator.
4056 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4059 Comparison is exact; there is no rounding error.
4061 Neither a leading @samp{+} nor exponential notation is recognized.
4062 To compare such strings numerically, use the
4063 @option{--general-numeric-sort} (@option{-g}) option.
4066 @itemx --version-sort
4068 @opindex --version-sort
4069 @cindex version number sort
4070 Sort by version name and number. It behaves like a standard sort,
4071 except that each sequence of decimal digits is treated numerically
4072 as an index/version number. (@xref{Details about version sort}.)
4078 @cindex reverse sorting
4079 Reverse the result of comparison, so that lines with greater key values
4080 appear earlier in the output instead of later.
4083 @itemx --random-sort
4084 @itemx --sort=random
4086 @opindex --random-sort
4089 Sort by hashing the input keys and then sorting the hash values.
4090 Choose the hash function at random, ensuring that it is free of
4091 collisions so that differing keys have differing hash values. This is
4092 like a random permutation of the inputs (@pxref{shuf invocation}),
4093 except that keys with the same value sort together.
4095 If multiple random sort fields are specified, the same random hash
4096 function is used for all fields. To use different random hash
4097 functions for different fields, you can invoke @command{sort} more
4100 The choice of hash function is affected by the
4101 @option{--random-source} option.
4109 @item --compress-program=@var{prog}
4110 Compress any temporary files with the program @var{prog}.
4112 With no arguments, @var{prog} must compress standard input to standard
4113 output, and when given the @option{-d} option it must decompress
4114 standard input to standard output.
4116 Terminate with an error if @var{prog} exits with nonzero status.
4118 White space and the backslash character should not appear in
4119 @var{prog}; they are reserved for future use.
4121 @filesZeroFromOption{sort,,sorted output}
4123 @item -k @var{pos1}[,@var{pos2}]
4124 @itemx --key=@var{pos1}[,@var{pos2}]
4128 Specify a sort field that consists of the part of the line between
4129 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
4130 omitted), @emph{inclusive}.
4132 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
4133 where @var{f} is the number of the field to use, and @var{c} is the number
4134 of the first character from the beginning of the field. Fields and character
4135 positions are numbered starting with 1; a character position of zero in
4136 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
4137 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
4138 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
4139 @var{opts} are ordering options, allowing individual keys to be sorted
4140 according to different rules; see below for details. Keys can span
4143 Example: To sort on the second field, use @option{--key=2,2}
4144 (@option{-k 2,2}). See below for more notes on keys and more examples.
4145 See also the @option{--debug} option to help determine the part
4146 of the line being used in the sort.
4149 Highlight the portion of each line used for sorting.
4150 Also issue warnings about questionable usage to stderr.
4152 @item --batch-size=@var{nmerge}
4153 @opindex --batch-size
4154 @cindex number of inputs to merge, nmerge
4155 Merge at most @var{nmerge} inputs at once.
4157 When @command{sort} has to merge more than @var{nmerge} inputs,
4158 it merges them in groups of @var{nmerge}, saving the result in
4159 a temporary file, which is then used as an input in a subsequent merge.
4161 A large value of @var{nmerge} may improve merge performance and decrease
4162 temporary storage utilization at the expense of increased memory usage
4163 and I/O@. Conversely a small value of @var{nmerge} may reduce memory
4164 requirements and I/O at the expense of temporary storage consumption and
4167 The value of @var{nmerge} must be at least 2. The default value is
4168 currently 16, but this is implementation-dependent and may change in
4171 The value of @var{nmerge} may be bounded by a resource limit for open
4172 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
4173 OPEN_MAX} may display limits for your systems; these limits may be
4174 modified further if your program already has some files open, or if
4175 the operating system has other limits on the number of open files. If
4176 the value of @var{nmerge} exceeds the resource limit, @command{sort}
4177 silently uses a smaller value.
4179 @item -o @var{output-file}
4180 @itemx --output=@var{output-file}
4183 @cindex overwriting of input, allowed
4184 Write output to @var{output-file} instead of standard output.
4185 Normally, @command{sort} reads all input before opening
4186 @var{output-file}, so you can safely sort a file in place by using
4187 commands like @code{sort -o F F} and @code{cat F | sort -o F}@.
4188 However, @command{sort} with @option{--merge} (@option{-m}) can open
4189 the output file before reading all input, so a command like @code{cat
4190 F | sort -m -o F - G} is not safe as @command{sort} might start
4191 writing @file{F} before @command{cat} is done reading it.
4193 @vindex POSIXLY_CORRECT
4194 On newer systems, @option{-o} cannot appear after an input file if
4195 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}@. Portable
4196 scripts should specify @option{-o @var{output-file}} before any input
4199 @item --random-source=@var{file}
4200 @opindex --random-source
4201 @cindex random source for sorting
4202 Use @var{file} as a source of random data used to determine which
4203 random hash function to use with the @option{-R} option. @xref{Random
4210 @cindex sort stability
4211 @cindex sort's last-resort comparison
4213 Make @command{sort} stable by disabling its last-resort comparison.
4214 This option has no effect if no fields or global ordering options
4215 other than @option{--reverse} (@option{-r}) are specified.
4218 @itemx --buffer-size=@var{size}
4220 @opindex --buffer-size
4221 @cindex size for main memory sorting
4222 Use a main-memory sort buffer of the given @var{size}. By default,
4223 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4224 @var{size} to be interpreted as a percentage of physical memory.
4225 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4226 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4227 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}@. Appending
4228 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4231 This option can improve the performance of @command{sort} by causing it
4232 to start with a larger or smaller sort buffer than the default.
4233 However, this option affects only the initial buffer size. The buffer
4234 grows beyond @var{size} if @command{sort} encounters input lines larger
4237 @item -t @var{separator}
4238 @itemx --field-separator=@var{separator}
4240 @opindex --field-separator
4241 @cindex field separator character
4242 Use character @var{separator} as the field separator when finding the
4243 sort keys in each line. By default, fields are separated by the empty
4244 string between a non-blank character and a blank character.
4245 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4248 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4249 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4250 not considered to be part of either the field preceding or the field
4251 following, so with @samp{sort @w{-t " "}} the same input line has
4252 three fields: an empty field, @samp{foo}, and @samp{bar}.
4253 However, fields that extend to the end of the line,
4254 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4255 retain the field separators present between the endpoints of the range.
4257 To specify ASCII NUL as the field separator,
4258 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4260 @item -T @var{tempdir}
4261 @itemx --temporary-directory=@var{tempdir}
4263 @opindex --temporary-directory
4264 @cindex temporary directory
4266 Use directory @var{tempdir} to store temporary files, overriding the
4267 @env{TMPDIR} environment variable. If this option is given more than
4268 once, temporary files are stored in all the directories given. If you
4269 have a large sort or merge that is I/O-bound, you can often improve
4270 performance by using this option to specify directories on different
4271 disks and controllers.
4273 @item --parallel=@var{n}
4275 @cindex multithreaded sort
4276 Set the number of sorts run in parallel to @var{n}. By default,
4277 @var{n} is set to the number of available processors, but limited
4278 to 8, as there are diminishing performance gains after that.
4279 Note also that using @var{n} threads increases the memory usage by
4280 a factor of log @var{n}. Also see @ref{nproc invocation}.
4286 @cindex uniquifying output
4288 Normally, output only the first of a sequence of lines that compare
4289 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4290 check that no pair of consecutive lines compares equal.
4292 This option also disables the default last-resort comparison.
4294 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4295 this equivalence does not extend to arbitrary @command{sort} options.
4296 For example, @code{sort -n -u} inspects only the value of the initial
4297 numeric string when checking for uniqueness, whereas @code{sort -n |
4298 uniq} inspects the entire line. @xref{uniq invocation}.
4300 @macro zeroTerminatedOption
4302 @itemx --zero-terminated
4304 @opindex --zero-terminated
4305 @cindex process zero-terminated items
4306 Delimit items with a zero byte rather than a newline (ASCII LF).
4307 I.e., treat input as items separated by ASCII NUL
4308 and terminate output items with ASCII NUL.
4309 This option can be useful in conjunction with @samp{perl -0} or
4310 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4311 reliably handle arbitrary file names (even those containing blanks
4312 or other special characters).
4314 @zeroTerminatedOption
4318 Historical (BSD and System V) implementations of @command{sort} have
4319 differed in their interpretation of some options, particularly
4320 @option{-b}, @option{-f}, and @option{-n}.
4321 GNU sort follows the POSIX
4322 behavior, which is usually (but not always!) like the System V behavior.
4323 According to POSIX, @option{-n} no longer implies @option{-b}. For
4324 consistency, @option{-M} has been changed in the same way. This may
4325 affect the meaning of character positions in field specifications in
4326 obscure cases. The only fix is to add an explicit @option{-b}.
4328 A position in a sort field specified with @option{-k} may have any
4329 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4330 global ordering options are inherited by that particular field. The
4331 @option{-b} option may be independently attached to either or both of
4332 the start and end positions of a field specification, and if it is
4333 inherited from the global options it will be attached to both.
4334 If input lines can contain leading or adjacent blanks and @option{-t}
4335 is not used, then @option{-k} is typically combined with @option{-b} or
4336 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4337 the varying numbers of leading blanks in fields can cause confusing results.
4339 If the start position in a sort field specifier falls after the end of
4340 the line or after the end field, the field is empty. If the @option{-b}
4341 option was specified, the @samp{.@var{c}} part of a field specification
4342 is counted from the first nonblank character of the field.
4344 @vindex _POSIX2_VERSION
4345 @vindex POSIXLY_CORRECT
4346 On older systems, @command{sort} supports an obsolete origin-zero
4347 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4348 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4349 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4350 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4351 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4353 This obsolete behavior can be enabled or disabled with the
4354 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4355 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4356 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4358 Scripts intended for use on standard hosts should avoid obsolete
4359 syntax and should use @option{-k} instead. For example, avoid
4360 @samp{sort +2}, since it might be interpreted as either @samp{sort
4361 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4362 support only the obsolete syntax, it can use a test like @samp{if sort
4363 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4366 Here are some examples to illustrate various combinations of options.
4371 Sort in descending (reverse) numeric order.
4378 Run no more than 4 sorts concurrently, using a buffer size of 10M.
4381 sort --parallel=4 -S 10M
4385 Sort alphabetically, omitting the first and second fields
4386 and the blanks at the start of the third field.
4387 This uses a single key composed of the characters beginning
4388 at the start of the first nonblank character in field three
4389 and extending to the end of each line.
4396 Sort numerically on the second field and resolve ties by sorting
4397 alphabetically on the third and fourth characters of field five.
4398 Use @samp{:} as the field delimiter.
4401 sort -t : -k 2,2n -k 5.3,5.4
4404 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4405 @command{sort} would have used all characters beginning in the second field
4406 and extending to the end of the line as the primary @emph{numeric}
4407 key. For the large majority of applications, treating keys spanning
4408 more than one field as numeric will not do what you expect.
4410 Also note that the @samp{n} modifier was applied to the field-end
4411 specifier for the first key. It would have been equivalent to
4412 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4413 @samp{b} apply to the associated @emph{field}, regardless of whether
4414 the modifier character is attached to the field-start and/or the
4415 field-end part of the key specifier.
4418 Sort the password file on the fifth field and ignore any
4419 leading blanks. Sort lines with equal values in field five
4420 on the numeric user ID in field three. Fields are separated
4424 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4425 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4426 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4429 These three commands have equivalent effect. The first specifies that
4430 the first key's start position ignores leading blanks and the second
4431 key is sorted numerically. The other two commands rely on global
4432 options being inherited by sort keys that lack modifiers. The inheritance
4433 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4434 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4435 character position is not affected by whether initial blanks are
4439 Sort a set of log files, primarily by IPv4 address and secondarily by
4440 time stamp. If two lines' primary and secondary keys are identical,
4441 output the lines in the same order that they were input. The log
4442 files contain lines that look like this:
4445 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4446 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4449 Fields are separated by exactly one space. Sort IPv4 addresses
4450 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4451 because 61 is less than 129.
4454 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4455 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4458 This example cannot be done with a single @command{sort} invocation,
4459 since IPv4 address components are separated by @samp{.} while dates
4460 come just after a space. So it is broken down into two invocations of
4461 @command{sort}: the first sorts by time stamp and the second by IPv4
4462 address. The time stamp is sorted by year, then month, then day, and
4463 finally by hour-minute-second field, using @option{-k} to isolate each
4464 field. Except for hour-minute-second there's no need to specify the
4465 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4466 based on leading prefixes that cannot cross field boundaries. The
4467 IPv4 addresses are sorted lexicographically. The second sort uses
4468 @samp{-s} so that ties in the primary key are broken by the secondary
4469 key; the first sort uses @samp{-s} so that the combination of the two
4473 Generate a tags file in case-insensitive sorted order.
4476 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4479 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4480 that file names that contain blanks or other special characters are
4482 by the sort operation.
4484 @c This example is a bit contrived and needs more explanation.
4486 @c Sort records separated by an arbitrary string by using a pipe to convert
4487 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4488 @c and converting each @samp{\0} back to the original record delimiter.
4491 @c printf 'c\n\nb\n\na\n' |
4492 @c perl -0pe 's/\n\n/\n\0/g' |
4494 @c perl -0pe 's/\0/\n/g'
4498 Use the common DSU, Decorate Sort Undecorate idiom to
4499 sort lines according to their length.
4502 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4505 In general this technique can be used to sort data that the @command{sort}
4506 command does not support, or is inefficient at, sorting directly.
4509 Shuffle a list of directories, but preserve the order of files within
4510 each directory. For instance, one could use this to generate a music
4511 playlist in which albums are shuffled but the songs of each album are
4515 ls */* | sort -t / -k 1,1R -k 2,2
4521 @node shuf invocation
4522 @section @command{shuf}: Shuffling text
4525 @cindex shuffling files
4527 @command{shuf} shuffles its input by outputting a random permutation
4528 of its input lines. Each output permutation is equally likely.
4532 shuf [@var{option}]@dots{} [@var{file}]
4533 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4534 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4537 @command{shuf} has three modes of operation that affect where it
4538 obtains its input lines. By default, it reads lines from standard
4539 input. The following options change the operation mode:
4547 @cindex command-line operands to shuffle
4548 Treat each command-line operand as an input line.
4550 @item -i @var{lo}-@var{hi}
4551 @itemx --input-range=@var{lo}-@var{hi}
4553 @opindex --input-range
4554 @cindex input range to shuffle
4555 Act as if input came from a file containing the range of unsigned
4556 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4560 @command{shuf}'s other options can affect its behavior in all
4565 @item -n @var{lines}
4566 @itemx --head-count=@var{count}
4568 @opindex --head-count
4569 @cindex head of output
4570 Output at most @var{count} lines. By default, all input lines are
4573 @item -o @var{output-file}
4574 @itemx --output=@var{output-file}
4577 @cindex overwriting of input, allowed
4578 Write output to @var{output-file} instead of standard output.
4579 @command{shuf} reads all input before opening
4580 @var{output-file}, so you can safely shuffle a file in place by using
4581 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4583 @item --random-source=@var{file}
4584 @opindex --random-source
4585 @cindex random source for shuffling
4586 Use @var{file} as a source of random data used to determine which
4587 permutation to generate. @xref{Random sources}.
4589 @zeroTerminatedOption
4605 might produce the output
4615 Similarly, the command:
4618 shuf -e clubs hearts diamonds spades
4632 and the command @samp{shuf -i 1-4} might output:
4642 These examples all have four input lines, so @command{shuf} might
4643 produce any of the twenty-four possible permutations of the input. In
4644 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4645 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4646 output permutations.
4651 @node uniq invocation
4652 @section @command{uniq}: Uniquify files
4655 @cindex uniquify files
4657 @command{uniq} writes the unique lines in the given @file{input}, or
4658 standard input if nothing is given or for an @var{input} name of
4662 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4665 By default, @command{uniq} prints its input lines, except that
4666 it discards all but the first of adjacent repeated lines, so that
4667 no output lines are repeated. Optionally, it can instead discard
4668 lines that are not repeated, or all repeated lines.
4670 The input need not be sorted, but repeated input lines are detected
4671 only if they are adjacent. If you want to discard non-adjacent
4672 duplicate lines, perhaps you want to use @code{sort -u}.
4673 @xref{sort invocation}.
4676 Comparisons honor the rules specified by the @env{LC_COLLATE}
4679 If no @var{output} file is specified, @command{uniq} writes to standard
4682 The program accepts the following options. Also see @ref{Common options}.
4687 @itemx --skip-fields=@var{n}
4689 @opindex --skip-fields
4690 Skip @var{n} fields on each line before checking for uniqueness. Use
4691 a null string for comparison if a line has fewer than @var{n} fields. Fields
4692 are sequences of non-space non-tab characters that are separated from
4693 each other by at least one space or tab.
4695 For compatibility @command{uniq} supports an obsolete option syntax
4696 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4699 @itemx --skip-chars=@var{n}
4701 @opindex --skip-chars
4702 Skip @var{n} characters before checking for uniqueness. Use a null string
4703 for comparison if a line has fewer than @var{n} characters. If you use both
4704 the field and character skipping options, fields are skipped over first.
4706 @vindex _POSIX2_VERSION
4707 On older systems, @command{uniq} supports an obsolete option syntax
4709 This obsolete behavior can be enabled or disabled with the
4710 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4711 conformance}), but portable scripts should avoid commands whose
4712 behavior depends on this variable.
4713 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4714 the ambiguous @samp{uniq +10}.
4720 Print the number of times each line occurred along with the line.
4723 @itemx --ignore-case
4725 @opindex --ignore-case
4726 Ignore differences in case when comparing lines.
4732 @cindex repeated lines, outputting
4733 Discard lines that are not repeated. When used by itself, this option
4734 causes @command{uniq} to print the first copy of each repeated line,
4738 @itemx --all-repeated[=@var{delimit-method}]
4740 @opindex --all-repeated
4741 @cindex all repeated lines, outputting
4742 Do not discard the second and subsequent repeated input lines,
4743 but discard lines that are not repeated.
4744 This option is useful mainly in conjunction with other options e.g.,
4745 to ignore case or to compare only selected fields.
4746 The optional @var{delimit-method} tells how to delimit
4747 groups of repeated lines, and must be one of the following:
4752 Do not delimit groups of repeated lines.
4753 This is equivalent to @option{--all-repeated} (@option{-D}).
4756 Output a newline before each group of repeated lines.
4757 With @option{--zero-terminated} (@option{-z}), use a zero
4758 byte (ASCII NUL) instead of a newline.
4761 Separate groups of repeated lines with a single newline.
4762 With @option{--zero-terminated} (@option{-z}), use a zero
4763 byte (ASCII NUL) instead of a newline.
4764 This is the same as using @samp{prepend}, except that
4765 no delimiter is inserted before the first group, and hence
4766 may be better suited for output direct to users.
4769 Note that when groups are delimited and the input stream contains
4770 two or more consecutive blank lines, then the output is ambiguous.
4771 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4772 each sequence of consecutive newlines with a single newline.
4774 This is a GNU extension.
4775 @c FIXME: give an example showing *how* it's useful
4781 @cindex unique lines, outputting
4782 Discard the first repeated line. When used by itself, this option
4783 causes @command{uniq} to print unique lines, and nothing else.
4786 @itemx --check-chars=@var{n}
4788 @opindex --check-chars
4789 Compare at most @var{n} characters on each line (after skipping any specified
4790 fields and characters). By default the entire rest of the lines are
4793 @zeroTerminatedOption
4800 @node comm invocation
4801 @section @command{comm}: Compare two sorted files line by line
4804 @cindex line-by-line comparison
4805 @cindex comparing sorted files
4807 @command{comm} writes to standard output lines that are common, and lines
4808 that are unique, to two input files; a file name of @samp{-} means
4809 standard input. Synopsis:
4812 comm [@var{option}]@dots{} @var{file1} @var{file2}
4816 Before @command{comm} can be used, the input files must be sorted using the
4817 collating sequence specified by the @env{LC_COLLATE} locale.
4818 If an input file ends in a non-newline
4819 character, a newline is silently appended. The @command{sort} command with
4820 no options always outputs a file that is suitable input to @command{comm}.
4822 @cindex differing lines
4823 @cindex common lines
4824 With no options, @command{comm} produces three-column output. Column one
4825 contains lines unique to @var{file1}, column two contains lines unique
4826 to @var{file2}, and column three contains lines common to both files.
4827 Columns are separated by a single TAB character.
4828 @c FIXME: when there's an option to supply an alternative separator
4829 @c string, append "by default" to the above sentence.
4834 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4835 the corresponding columns (and separators). Also see @ref{Common options}.
4837 Unlike some other comparison utilities, @command{comm} has an exit
4838 status that does not depend on the result of the comparison.
4839 Upon normal completion @command{comm} produces an exit code of zero.
4840 If there is an error it exits with nonzero status.
4842 @macro checkOrderOption{cmd}
4843 If the @option{--check-order} option is given, unsorted inputs will
4844 cause a fatal error message. If the option @option{--nocheck-order}
4845 is given, unsorted inputs will never cause an error message. If neither
4846 of these options is given, wrongly sorted inputs are diagnosed
4847 only if an input file is found to contain unpairable
4849 lines, and when both input files are non empty.
4851 @ifclear JOIN_COMMAND
4854 If an input file is diagnosed as being unsorted, the @command{\cmd\}
4855 command will exit with a nonzero status (and the output should not be used).
4857 Forcing @command{\cmd\} to process wrongly sorted input files
4858 containing unpairable lines by specifying @option{--nocheck-order} is
4859 not guaranteed to produce any particular output. The output will
4860 probably not correspond with whatever you hoped it would be.
4862 @checkOrderOption{comm}
4867 Fail with an error message if either input file is wrongly ordered.
4869 @item --nocheck-order
4870 Do not check that both input files are in sorted order.
4874 @item --output-delimiter=@var{str}
4875 Print @var{str} between adjacent output columns,
4876 rather than the default of a single TAB character.
4878 The delimiter @var{str} may not be empty.
4882 @node ptx invocation
4883 @section @command{ptx}: Produce permuted indexes
4887 @command{ptx} reads a text file and essentially produces a permuted index, with
4888 each keyword in its context. The calling sketch is either one of:
4891 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4892 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4895 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4896 all GNU extensions and reverts to traditional mode, thus introducing some
4897 limitations and changing several of the program's default option values.
4898 When @option{-G} is not specified, GNU extensions are always enabled.
4899 GNU extensions to @command{ptx} are documented wherever appropriate in this
4900 document. @xref{Compatibility in ptx}, for the full list.
4902 Individual options are explained in the following sections.
4904 When GNU extensions are enabled, there may be zero, one or several
4905 @var{file}s after the options. If there is no @var{file}, the program
4906 reads the standard input. If there is one or several @var{file}s, they
4907 give the name of input files which are all read in turn, as if all the
4908 input files were concatenated. However, there is a full contextual
4909 break between each file and, when automatic referencing is requested,
4910 file names and line numbers refer to individual text input files. In
4911 all cases, the program outputs the permuted index to the standard
4914 When GNU extensions are @emph{not} enabled, that is, when the program
4915 operates in traditional mode, there may be zero, one or two parameters
4916 besides the options. If there are no parameters, the program reads the
4917 standard input and outputs the permuted index to the standard output.
4918 If there is only one parameter, it names the text @var{input} to be read
4919 instead of the standard input. If two parameters are given, they give
4920 respectively the name of the @var{input} file to read and the name of
4921 the @var{output} file to produce. @emph{Be very careful} to note that,
4922 in this case, the contents of file given by the second parameter is
4923 destroyed. This behavior is dictated by System V @command{ptx}
4924 compatibility; GNU Standards normally discourage output parameters not
4925 introduced by an option.
4927 Note that for @emph{any} file named as the value of an option or as an
4928 input text file, a single dash @kbd{-} may be used, in which case
4929 standard input is assumed. However, it would not make sense to use this
4930 convention more than once per program invocation.
4933 * General options in ptx:: Options which affect general program behavior.
4934 * Charset selection in ptx:: Underlying character set considerations.
4935 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4936 * Output formatting in ptx:: Types of output format, and sizing the fields.
4937 * Compatibility in ptx::
4941 @node General options in ptx
4942 @subsection General options
4947 @itemx --traditional
4948 As already explained, this option disables all GNU extensions to
4949 @command{ptx} and switches to traditional mode.
4952 Print a short help on standard output, then exit without further
4956 Print the program version on standard output, then exit without further
4964 @node Charset selection in ptx
4965 @subsection Charset selection
4967 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4968 As it is set up now, the program assumes that the input file is coded
4969 using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
4970 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4971 character set of the IBM-PC@. (GNU @command{ptx} is not known to work on
4972 smaller MS-DOS machines anymore.) Compared to 7-bit ASCII, the set
4973 of characters which are letters is different; this alters the behavior
4974 of regular expression matching. Thus, the default regular expression
4975 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4976 however, is still crude; it obeys the underlying character set ordering
4982 @itemx --ignore-case
4983 Fold lower case letters to upper case for sorting.
4988 @node Input processing in ptx
4989 @subsection Word selection and input processing
4994 @itemx --break-file=@var{file}
4996 This option provides an alternative (to @option{-W}) method of describing
4997 which characters make up words. It introduces the name of a
4998 file which contains a list of characters which can@emph{not} be part of
4999 one word; this file is called the @dfn{Break file}. Any character which
5000 is not part of the Break file is a word constituent. If both options
5001 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
5002 @option{-b} is ignored.
5004 When GNU extensions are enabled, the only way to avoid newline as a
5005 break character is to write all the break characters in the file with no
5006 newline at all, not even at the end of the file. When GNU extensions
5007 are disabled, spaces, tabs and newlines are always considered as break
5008 characters even if not included in the Break file.
5011 @itemx --ignore-file=@var{file}
5013 The file associated with this option contains a list of words which will
5014 never be taken as keywords in concordance output. It is called the
5015 @dfn{Ignore file}. The file contains exactly one word in each line; the
5016 end of line separation of words is not subject to the value of the
5020 @itemx --only-file=@var{file}
5022 The file associated with this option contains a list of words which will
5023 be retained in concordance output; any word not mentioned in this file
5024 is ignored. The file is called the @dfn{Only file}. The file contains
5025 exactly one word in each line; the end of line separation of words is
5026 not subject to the value of the @option{-S} option.
5028 There is no default for the Only file. When both an Only file and an
5029 Ignore file are specified, a word is considered a keyword only
5030 if it is listed in the Only file and not in the Ignore file.
5035 On each input line, the leading sequence of non-white space characters will be
5036 taken to be a reference that has the purpose of identifying this input
5037 line in the resulting permuted index.
5038 @xref{Output formatting in ptx},
5039 for more information about reference production.
5040 Using this option changes the default value for option @option{-S}.
5042 Using this option, the program does not try very hard to remove
5043 references from contexts in output, but it succeeds in doing so
5044 @emph{when} the context ends exactly at the newline. If option
5045 @option{-r} is used with @option{-S} default value, or when GNU extensions
5046 are disabled, this condition is always met and references are completely
5047 excluded from the output contexts.
5049 @item -S @var{regexp}
5050 @itemx --sentence-regexp=@var{regexp}
5052 This option selects which regular expression will describe the end of a
5053 line or the end of a sentence. In fact, this regular expression is not
5054 the only distinction between end of lines or end of sentences, and input
5055 line boundaries have no special significance outside this option. By
5056 default, when GNU extensions are enabled and if @option{-r} option is not
5057 used, end of sentences are used. In this case, this @var{regex} is
5058 imported from GNU Emacs:
5061 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
5064 Whenever GNU extensions are disabled or if @option{-r} option is used, end
5065 of lines are used; in this case, the default @var{regexp} is just:
5071 Using an empty @var{regexp} is equivalent to completely disabling end of
5072 line or end of sentence recognition. In this case, the whole file is
5073 considered to be a single big line or sentence. The user might want to
5074 disallow all truncation flag generation as well, through option @option{-F
5075 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5078 When the keywords happen to be near the beginning of the input line or
5079 sentence, this often creates an unused area at the beginning of the
5080 output context line; when the keywords happen to be near the end of the
5081 input line or sentence, this often creates an unused area at the end of
5082 the output context line. The program tries to fill those unused areas
5083 by wrapping around context in them; the tail of the input line or
5084 sentence is used to fill the unused area on the left of the output line;
5085 the head of the input line or sentence is used to fill the unused area
5086 on the right of the output line.
5088 As a matter of convenience to the user, many usual backslashed escape
5089 sequences from the C language are recognized and converted to the
5090 corresponding characters by @command{ptx} itself.
5092 @item -W @var{regexp}
5093 @itemx --word-regexp=@var{regexp}
5095 This option selects which regular expression will describe each keyword.
5096 By default, if GNU extensions are enabled, a word is a sequence of
5097 letters; the @var{regexp} used is @samp{\w+}. When GNU extensions are
5098 disabled, a word is by default anything which ends with a space, a tab
5099 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
5101 An empty @var{regexp} is equivalent to not using this option.
5102 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5105 As a matter of convenience to the user, many usual backslashed escape
5106 sequences, as found in the C language, are recognized and converted to
5107 the corresponding characters by @command{ptx} itself.
5112 @node Output formatting in ptx
5113 @subsection Output formatting
5115 Output format is mainly controlled by the @option{-O} and @option{-T} options
5116 described in the table below. When neither @option{-O} nor @option{-T} are
5117 selected, and if GNU extensions are enabled, the program chooses an
5118 output format suitable for a dumb terminal. Each keyword occurrence is
5119 output to the center of one line, surrounded by its left and right
5120 contexts. Each field is properly justified, so the concordance output
5121 can be readily observed. As a special feature, if automatic
5122 references are selected by option @option{-A} and are output before the
5123 left context, that is, if option @option{-R} is @emph{not} selected, then
5124 a colon is added after the reference; this nicely interfaces with GNU
5125 Emacs @code{next-error} processing. In this default output format, each
5126 white space character, like newline and tab, is merely changed to
5127 exactly one space, with no special attempt to compress consecutive
5128 spaces. This might change in the future. Except for those white space
5129 characters, every other character of the underlying set of 256
5130 characters is transmitted verbatim.
5132 Output format is further controlled by the following options.
5136 @item -g @var{number}
5137 @itemx --gap-size=@var{number}
5139 Select the size of the minimum white space gap between the fields on the
5142 @item -w @var{number}
5143 @itemx --width=@var{number}
5145 Select the maximum output width of each final line. If references are
5146 used, they are included or excluded from the maximum output width
5147 depending on the value of option @option{-R}@. If this option is not
5148 selected, that is, when references are output before the left context,
5149 the maximum output width takes into account the maximum length of all
5150 references. If this option is selected, that is, when references are
5151 output after the right context, the maximum output width does not take
5152 into account the space taken by references, nor the gap that precedes
5156 @itemx --auto-reference
5158 Select automatic references. Each input line will have an automatic
5159 reference made up of the file name and the line ordinal, with a single
5160 colon between them. However, the file name will be empty when standard
5161 input is being read. If both @option{-A} and @option{-r} are selected, then
5162 the input reference is still read and skipped, but the automatic
5163 reference is used at output time, overriding the input reference.
5166 @itemx --right-side-refs
5168 In the default output format, when option @option{-R} is not used, any
5169 references produced by the effect of options @option{-r} or @option{-A} are
5170 placed to the far right of output lines, after the right context. With
5171 default output format, when the @option{-R} option is specified, references
5172 are rather placed at the beginning of each output line, before the left
5173 context. For any other output format, option @option{-R} is
5174 ignored, with one exception: with @option{-R} the width of references
5175 is @emph{not} taken into account in total output width given by @option{-w}.
5177 This option is automatically selected whenever GNU extensions are
5180 @item -F @var{string}
5181 @itemx --flac-truncation=@var{string}
5183 This option will request that any truncation in the output be reported
5184 using the string @var{string}. Most output fields theoretically extend
5185 towards the beginning or the end of the current line, or current
5186 sentence, as selected with option @option{-S}@. But there is a maximum
5187 allowed output line width, changeable through option @option{-w}, which is
5188 further divided into space for various output fields. When a field has
5189 to be truncated because it cannot extend beyond the beginning or the end of
5190 the current line to fit in, then a truncation occurs. By default,
5191 the string used is a single slash, as in @option{-F /}.
5193 @var{string} may have more than one character, as in @option{-F @dots{}}.
5194 Also, in the particular case when @var{string} is empty (@option{-F ""}),
5195 truncation flagging is disabled, and no truncation marks are appended in
5198 As a matter of convenience to the user, many usual backslashed escape
5199 sequences, as found in the C language, are recognized and converted to
5200 the corresponding characters by @command{ptx} itself.
5202 @item -M @var{string}
5203 @itemx --macro-name=@var{string}
5205 Select another @var{string} to be used instead of @samp{xx}, while
5206 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5209 @itemx --format=roff
5211 Choose an output format suitable for @command{nroff} or @command{troff}
5212 processing. Each output line will look like:
5215 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
5216 "@var{head}" "@var{ref}"
5219 so it will be possible to write a @samp{.xx} roff macro to take care of
5220 the output typesetting. This is the default output format when GNU
5221 extensions are disabled. Option @option{-M} can be used to change
5222 @samp{xx} to another macro name.
5224 In this output format, each non-graphical character, like newline and
5225 tab, is merely changed to exactly one space, with no special attempt to
5226 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5227 so it will be correctly processed by @command{nroff} or @command{troff}.
5232 Choose an output format suitable for @TeX{} processing. Each output
5233 line will look like:
5236 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
5237 @{@var{after}@}@{@var{head}@}@{@var{ref}@}
5241 so it will be possible to write a @code{\xx} definition to take care of
5242 the output typesetting. Note that when references are not being
5243 produced, that is, neither option @option{-A} nor option @option{-r} is
5244 selected, the last parameter of each @code{\xx} call is inhibited.
5245 Option @option{-M} can be used to change @samp{xx} to another macro
5248 In this output format, some special characters, like @kbd{$}, @kbd{%},
5249 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5250 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5251 backslash and a pair of dollar signs (to force mathematical mode). The
5252 backslash itself produces the sequence @code{\backslash@{@}}.
5253 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5254 @code{~\@{ @}} respectively. Other diacriticized characters of the
5255 underlying character set produce an appropriate @TeX{} sequence as far
5256 as possible. The other non-graphical characters, like newline and tab,
5257 and all other characters which are not part of ASCII, are merely
5258 changed to exactly one space, with no special attempt to compress
5259 consecutive spaces. Let me know how to improve this special character
5260 processing for @TeX{}.
5265 @node Compatibility in ptx
5266 @subsection The GNU extensions to @command{ptx}
5268 This version of @command{ptx} contains a few features which do not exist in
5269 System V @command{ptx}. These extra features are suppressed by using the
5270 @option{-G} command line option, unless overridden by other command line
5271 options. Some GNU extensions cannot be recovered by overriding, so the
5272 simple rule is to avoid @option{-G} if you care about GNU extensions.
5273 Here are the differences between this program and System V @command{ptx}.
5278 This program can read many input files at once, it always writes the
5279 resulting concordance on standard output. On the other hand, System V
5280 @command{ptx} reads only one file and sends the result to standard output
5281 or, if a second @var{file} parameter is given on the command, to that
5284 Having output parameters not introduced by options is a dangerous
5285 practice which GNU avoids as far as possible. So, for using @command{ptx}
5286 portably between GNU and System V, you should always use it with a
5287 single input file, and always expect the result on standard output. You
5288 might also want to automatically configure in a @option{-G} option to
5289 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5290 that the installed @command{ptx} accepts @option{-G}.
5293 The only options available in System V @command{ptx} are options @option{-b},
5294 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5295 @option{-w}. All other options are GNU extensions and are not repeated in
5296 this enumeration. Moreover, some options have a slightly different
5297 meaning when GNU extensions are enabled, as explained below.
5300 By default, concordance output is not formatted for @command{troff} or
5301 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5302 or @command{nroff} output may still be selected through option @option{-O}.
5305 Unless @option{-R} option is used, the maximum reference width is
5306 subtracted from the total output line width. With GNU extensions
5307 disabled, width of references is not taken into account in the output
5308 line width computations.
5311 All 256 bytes, even ASCII NUL bytes, are always read and
5312 processed from input file with no adverse effect, even if GNU extensions
5313 are disabled. However, System V @command{ptx} does not accept 8-bit
5314 characters, a few control characters are rejected, and the tilde
5315 @kbd{~} is also rejected.
5318 Input line length is only limited by available memory, even if GNU
5319 extensions are disabled. However, System V @command{ptx} processes only
5320 the first 200 characters in each line.
5323 The break (non-word) characters default to be every character except all
5324 letters of the underlying character set, diacriticized or not. When GNU
5325 extensions are disabled, the break characters default to space, tab and
5329 The program makes better use of output line width. If GNU extensions
5330 are disabled, the program rather tries to imitate System V @command{ptx},
5331 but still, there are some slight disposition glitches this program does
5332 not completely reproduce.
5335 The user can specify both an Ignore file and an Only file. This is not
5336 allowed with System V @command{ptx}.
5341 @node tsort invocation
5342 @section @command{tsort}: Topological sort
5345 @cindex topological sort
5347 @command{tsort} performs a topological sort on the given @var{file}, or
5348 standard input if no input file is given or for a @var{file} of
5349 @samp{-}. For more details and some history, see @ref{tsort background}.
5353 tsort [@var{option}] [@var{file}]
5356 @command{tsort} reads its input as pairs of strings, separated by blanks,
5357 indicating a partial ordering. The output is a total ordering that
5358 corresponds to the given partial ordering.
5372 will produce the output
5383 Consider a more realistic example.
5384 You have a large set of functions all in one file, and they may all be
5385 declared static except one. Currently that one (say @code{main}) is the
5386 first function defined in the file, and the ones it calls directly follow
5387 it, followed by those they call, etc. Let's say that you are determined
5388 to take advantage of prototypes, so you have to choose between declaring
5389 all of those functions (which means duplicating a lot of information from
5390 the definitions) and rearranging the functions so that as many as possible
5391 are defined before they are used. One way to automate the latter process
5392 is to get a list for each function of the functions it calls directly.
5393 Many programs can generate such lists. They describe a call graph.
5394 Consider the following list, in which a given line indicates that the
5395 function on the left calls the one on the right directly.
5401 tail_file pretty_name
5402 tail_file write_header
5404 tail_forever recheck
5405 tail_forever pretty_name
5406 tail_forever write_header
5407 tail_forever dump_remainder
5410 tail_lines start_lines
5411 tail_lines dump_remainder
5412 tail_lines file_lines
5413 tail_lines pipe_lines
5415 tail_bytes start_bytes
5416 tail_bytes dump_remainder
5417 tail_bytes pipe_bytes
5418 file_lines dump_remainder
5422 then you can use @command{tsort} to produce an ordering of those
5423 functions that satisfies your requirement.
5426 example$ tsort call-graph | tac
5446 @command{tsort} detects any cycles in the input and writes the first cycle
5447 encountered to standard error.
5449 Note that for a given partial ordering, generally there is no unique
5450 total ordering. In the context of the call graph above, the function
5451 @code{parse_options} may be placed anywhere in the list as long as it
5452 precedes @code{main}.
5454 The only options are @option{--help} and @option{--version}. @xref{Common
5460 * tsort background:: Where tsort came from.
5463 @node tsort background
5464 @subsection @command{tsort}: Background
5466 @command{tsort} exists because very early versions of the Unix linker processed
5467 an archive file exactly once, and in order. As @command{ld} read each object
5468 in the archive, it decided whether it was needed in the program based on
5469 whether it defined any symbols which were undefined at that point in
5472 This meant that dependencies within the archive had to be handled
5473 specially. For example, @code{scanf} probably calls @code{read}. That means
5474 that in a single pass through an archive, it was important for @code{scanf.o}
5475 to appear before read.o, because otherwise a program which calls
5476 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5477 reference to @code{read}.
5479 The way to address this problem was to first generate a set of
5480 dependencies of one object file on another. This was done by a shell
5481 script called @command{lorder}. The GNU tools don't provide a version of
5482 lorder, as far as I know, but you can still find it in BSD
5485 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5486 resulting sort to define the order in which you added objects to the archive.
5488 This whole procedure has been obsolete since about 1980, because
5489 Unix archives now contain a symbol table (traditionally built by
5490 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5491 linker uses the symbol table to effectively make multiple passes over
5494 Anyhow, that's where tsort came from. To solve an old problem with
5495 the way the linker handled archive files, which has since been solved
5499 @node Operating on fields
5500 @chapter Operating on fields
5503 * cut invocation:: Print selected parts of lines.
5504 * paste invocation:: Merge lines of files.
5505 * join invocation:: Join lines on a common field.
5509 @node cut invocation
5510 @section @command{cut}: Print selected parts of lines
5513 @command{cut} writes to standard output selected parts of each line of each
5514 input file, or standard input if no files are given or for a file name of
5518 cut @var{option}@dots{} [@var{file}]@dots{}
5521 In the table which follows, the @var{byte-list}, @var{character-list},
5522 and @var{field-list} are one or more numbers or ranges (two numbers
5523 separated by a dash) separated by commas. Bytes, characters, and
5524 fields are numbered starting at 1. Incomplete ranges may be
5525 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5526 @samp{@var{n}} through end of line or last field. The list elements
5527 can be repeated, can overlap, and can be specified in any order; but
5528 the selected input is written in the same order that it is read, and
5529 is written exactly once.
5531 The program accepts the following options. Also see @ref{Common
5536 @item -b @var{byte-list}
5537 @itemx --bytes=@var{byte-list}
5540 Select for printing only the bytes in positions listed in
5541 @var{byte-list}. Tabs and backspaces are treated like any other
5542 character; they take up 1 byte. If an output delimiter is specified,
5543 (see the description of @option{--output-delimiter}), then output that
5544 string between ranges of selected bytes.
5546 @item -c @var{character-list}
5547 @itemx --characters=@var{character-list}
5549 @opindex --characters
5550 Select for printing only the characters in positions listed in
5551 @var{character-list}. The same as @option{-b} for now, but
5552 internationalization will change that. Tabs and backspaces are
5553 treated like any other character; they take up 1 character. If an
5554 output delimiter is specified, (see the description of
5555 @option{--output-delimiter}), then output that string between ranges
5558 @item -f @var{field-list}
5559 @itemx --fields=@var{field-list}
5562 Select for printing only the fields listed in @var{field-list}.
5563 Fields are separated by a TAB character by default. Also print any
5564 line that contains no delimiter character, unless the
5565 @option{--only-delimited} (@option{-s}) option is specified.
5567 Note @command{awk} supports more sophisticated field processing,
5568 and by default will use (and discard) runs of blank characters to
5569 separate fields, and ignore leading and trailing blanks.
5572 awk '{print $2}' # print the second field
5573 awk '{print $NF-1}' # print the penultimate field
5574 awk '{print $2,$1}' # reorder the first two fields
5578 In the unlikely event that @command{awk} is unavailable,
5579 one can use the @command{join} command, to process blank
5580 characters as @command{awk} does above.
5583 join -a1 -o 1.2 - /dev/null # print the second field
5584 join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
5588 @item -d @var{input_delim_byte}
5589 @itemx --delimiter=@var{input_delim_byte}
5591 @opindex --delimiter
5592 With @option{-f}, use the first byte of @var{input_delim_byte} as
5593 the input fields separator (default is TAB).
5597 Do not split multi-byte characters (no-op for now).
5600 @itemx --only-delimited
5602 @opindex --only-delimited
5603 For @option{-f}, do not print lines that do not contain the field separator
5604 character. Normally, any line without a field separator is printed verbatim.
5606 @item --output-delimiter=@var{output_delim_string}
5607 @opindex --output-delimiter
5608 With @option{-f}, output fields are separated by @var{output_delim_string}.
5609 The default with @option{-f} is to use the input delimiter.
5610 When using @option{-b} or @option{-c} to select ranges of byte or
5611 character offsets (as opposed to ranges of fields),
5612 output @var{output_delim_string} between non-overlapping
5613 ranges of selected bytes.
5616 @opindex --complement
5617 This option is a GNU extension.
5618 Select for printing the complement of the bytes, characters or fields
5619 selected with the @option{-b}, @option{-c} or @option{-f} options.
5620 In other words, do @emph{not} print the bytes, characters or fields
5621 specified via those options. This option is useful when you have
5622 many fields and want to print all but a few of them.
5629 @node paste invocation
5630 @section @command{paste}: Merge lines of files
5633 @cindex merging files
5635 @command{paste} writes to standard output lines consisting of sequentially
5636 corresponding lines of each given file, separated by a TAB character.
5637 Standard input is used for a file name of @samp{-} or if no input files
5659 paste [@var{option}]@dots{} [@var{file}]@dots{}
5662 The program accepts the following options. Also see @ref{Common options}.
5670 Paste the lines of one file at a time rather than one line from each
5671 file. Using the above example data:
5674 $ paste -s num2 let3
5679 @item -d @var{delim-list}
5680 @itemx --delimiters=@var{delim-list}
5682 @opindex --delimiters
5683 Consecutively use the characters in @var{delim-list} instead of
5684 TAB to separate merged lines. When @var{delim-list} is
5685 exhausted, start again at its beginning. Using the above example data:
5688 $ paste -d '%_' num2 let3 num2
5699 @node join invocation
5700 @section @command{join}: Join lines on a common field
5703 @cindex common field, joining on
5705 @command{join} writes to standard output a line for each pair of input
5706 lines that have identical join fields. Synopsis:
5709 join [@var{option}]@dots{} @var{file1} @var{file2}
5712 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5713 meaning standard input. @var{file1} and @var{file2} should be
5714 sorted on the join fields.
5717 Normally, the sort order is that of the
5718 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5719 the @option{-t} option is given, the sort comparison ignores blanks at
5720 the start of the join field, as in @code{sort -b}. If the
5721 @option{--ignore-case} option is given, the sort comparison ignores
5722 the case of characters in the join field, as in @code{sort -f}.
5724 The @command{sort} and @command{join} commands should use consistent
5725 locales and options if the output of @command{sort} is fed to
5726 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5727 sort a file on its default join field, but if you select a non-default
5728 locale, join field, separator, or comparison options, then you should
5729 do so consistently between @command{join} and @command{sort}.
5730 If @samp{join -t ''} is specified then the whole line is considered which
5731 matches the default operation of sort.
5733 If the input has no unpairable lines, a GNU extension is
5734 available; the sort order can be any order that considers two fields
5735 to be equal if and only if the sort comparison described above
5736 considers them to be equal. For example:
5754 @checkOrderOption{join}
5759 @item the join field is the first field in each line;
5760 @item fields in the input are separated by one or more blanks, with leading
5761 blanks on the line ignored;
5762 @item fields in the output are separated by a space;
5763 @item each output line consists of the join field, the remaining
5764 fields from @var{file1}, then the remaining fields from @var{file2}.
5767 The program accepts the following options. Also see @ref{Common options}.
5771 @item -a @var{file-number}
5773 Print a line for each unpairable line in file @var{file-number} (either
5774 @samp{1} or @samp{2}), in addition to the normal output.
5777 Fail with an error message if either input file is wrongly ordered.
5779 @item --nocheck-order
5780 Do not check that both input files are in sorted order. This is the default.
5782 @item -e @var{string}
5784 Replace those output fields that are missing in the input with @var{string}.
5785 I.e., missing fields specified with the @option{-12jo} options.
5789 Treat the first line of each input file as a header line. The header lines
5790 will be joined and printed as the first output line. If @option{-o} is used to
5791 specify output format, the header line will be printed according to the
5792 specified format. The header lines will not be checked for ordering even if
5793 @option{--check-order} is specified. Also if the header lines from each file
5794 do not match, the heading fields from the first file will be used.
5797 @itemx --ignore-case
5799 @opindex --ignore-case
5800 Ignore differences in case when comparing keys.
5801 With this option, the lines of the input files must be ordered in the same way.
5802 Use @samp{sort -f} to produce this ordering.
5804 @item -1 @var{field}
5806 Join on field @var{field} (a positive integer) of file 1.
5808 @item -2 @var{field}
5810 Join on field @var{field} (a positive integer) of file 2.
5812 @item -j @var{field}
5813 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5815 @item -o @var{field-list}
5817 If the keyword @samp{auto} is specified, infer the output format from
5818 the first line in each file. This is the same as the default output format
5819 but also ensures the same number of fields are output for each line.
5820 Missing fields are replaced with the @option{-e} option and extra fields
5823 Otherwise, construct each output line according to the format in
5824 @var{field-list}. Each element in @var{field-list} is either the single
5825 character @samp{0} or has the form @var{m.n} where the file number, @var{m},
5826 is @samp{1} or @samp{2} and @var{n} is a positive field number.
5828 A field specification of @samp{0} denotes the join field.
5829 In most cases, the functionality of the @samp{0} field spec
5830 may be reproduced using the explicit @var{m.n} that corresponds
5831 to the join field. However, when printing unpairable lines
5832 (using either of the @option{-a} or @option{-v} options), there is no way
5833 to specify the join field using @var{m.n} in @var{field-list}
5834 if there are unpairable lines in both files.
5835 To give @command{join} that functionality, POSIX invented the @samp{0}
5836 field specification notation.
5838 The elements in @var{field-list}
5839 are separated by commas or blanks.
5840 Blank separators typically need to be quoted for the shell. For
5841 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5842 2.2'} are equivalent.
5844 All output lines---including those printed because of any -a or -v
5845 option---are subject to the specified @var{field-list}.
5848 Use character @var{char} as the input and output field separator.
5849 Treat as significant each occurrence of @var{char} in the input file.
5850 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5851 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5852 the whole line is considered, matching the default operation of sort.
5853 If @samp{-t '\0'} is specified then the ASCII NUL
5854 character is used to delimit the fields.
5856 @item -v @var{file-number}
5857 Print a line for each unpairable line in file @var{file-number}
5858 (either @samp{1} or @samp{2}), instead of the normal output.
5865 @node Operating on characters
5866 @chapter Operating on characters
5868 @cindex operating on characters
5870 This commands operate on individual characters.
5873 * tr invocation:: Translate, squeeze, and/or delete characters.
5874 * expand invocation:: Convert tabs to spaces.
5875 * unexpand invocation:: Convert spaces to tabs.
5880 @section @command{tr}: Translate, squeeze, and/or delete characters
5887 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5890 @command{tr} copies standard input to standard output, performing
5891 one of the following operations:
5895 translate, and optionally squeeze repeated characters in the result,
5897 squeeze repeated characters,
5901 delete characters, then squeeze repeated characters from the result.
5904 The @var{set1} and (if given) @var{set2} arguments define ordered
5905 sets of characters, referred to below as @var{set1} and @var{set2}. These
5906 sets are the characters of the input that @command{tr} operates on.
5907 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5909 complement (all of the characters that are not in @var{set1}).
5911 Currently @command{tr} fully supports only single-byte characters.
5912 Eventually it will support multibyte characters; when it does, the
5913 @option{-C} option will cause it to complement the set of characters,
5914 whereas @option{-c} will cause it to complement the set of values.
5915 This distinction will matter only when some values are not characters,
5916 and this is possible only in locales using multibyte encodings when
5917 the input contains encoding errors.
5919 The program accepts the @option{--help} and @option{--version}
5920 options. @xref{Common options}. Options must precede operands.
5925 * Character sets:: Specifying sets of characters.
5926 * Translating:: Changing one set of characters to another.
5927 * Squeezing:: Squeezing repeats and deleting.
5931 @node Character sets
5932 @subsection Specifying sets of characters
5934 @cindex specifying sets of characters
5936 The format of the @var{set1} and @var{set2} arguments resembles
5937 the format of regular expressions; however, they are not regular
5938 expressions, only lists of characters. Most characters simply
5939 represent themselves in these strings, but the strings can contain
5940 the shorthands listed below, for convenience. Some of them can be
5941 used only in @var{set1} or @var{set2}, as noted below.
5945 @item Backslash escapes
5946 @cindex backslash escapes
5948 The following backslash escape sequences are recognized:
5966 The 8-bit character with the value given by @var{ooo}, which is 1 to 3
5967 octal digits. Note that @samp{\400} is interpreted as the two-byte
5968 sequence, @samp{\040} @samp{0}.
5973 While a backslash followed by a character not listed above is
5974 interpreted as that character, the backslash also effectively
5975 removes any special significance, so it is useful to escape
5976 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5981 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5982 from @var{m} through @var{n}, in ascending order. @var{m} should
5983 collate before @var{n}; if it doesn't, an error results. As an example,
5984 @samp{0-9} is the same as @samp{0123456789}.
5986 GNU @command{tr} does not support the System V syntax that uses square
5987 brackets to enclose ranges. Translations specified in that format
5988 sometimes work as expected, since the brackets are often transliterated
5989 to themselves. However, they should be avoided because they sometimes
5990 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5993 Many historically common and even accepted uses of ranges are not
5994 portable. For example, on EBCDIC hosts using the @samp{A-Z}
5995 range will not do what most would expect because @samp{A} through @samp{Z}
5996 are not contiguous as they are in ASCII@.
5997 If you can rely on a POSIX compliant version of @command{tr}, then
5998 the best way to work around this is to use character classes (see below).
5999 Otherwise, it is most portable (and most ugly) to enumerate the members
6002 @item Repeated characters
6003 @cindex repeated characters
6005 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
6006 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
6007 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
6008 to as many copies of @var{c} as are needed to make @var{set2} as long as
6009 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
6010 octal, otherwise in decimal.
6012 @item Character classes
6013 @cindex character classes
6015 The notation @samp{[:@var{class}:]} expands to all of the characters in
6016 the (predefined) class @var{class}. The characters expand in no
6017 particular order, except for the @code{upper} and @code{lower} classes,
6018 which expand in ascending order. When the @option{--delete} (@option{-d})
6019 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
6020 character class can be used in @var{set2}. Otherwise, only the
6021 character classes @code{lower} and @code{upper} are accepted in
6022 @var{set2}, and then only if the corresponding character class
6023 (@code{upper} and @code{lower}, respectively) is specified in the same
6024 relative position in @var{set1}. Doing this specifies case conversion.
6025 The class names are given below; an error results when an invalid class
6037 Horizontal whitespace.
6046 Printable characters, not including space.
6052 Printable characters, including space.
6055 Punctuation characters.
6058 Horizontal or vertical whitespace.
6067 @item Equivalence classes
6068 @cindex equivalence classes
6070 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
6071 equivalent to @var{c}, in no particular order. Equivalence classes are
6072 a relatively recent invention intended to support non-English alphabets.
6073 But there seems to be no standard way to define them or determine their
6074 contents. Therefore, they are not fully implemented in GNU @command{tr};
6075 each character's equivalence class consists only of that character,
6076 which is of no particular use.
6082 @subsection Translating
6084 @cindex translating characters
6086 @command{tr} performs translation when @var{set1} and @var{set2} are
6087 both given and the @option{--delete} (@option{-d}) option is not given.
6088 @command{tr} translates each character of its input that is in @var{set1}
6089 to the corresponding character in @var{set2}. Characters not in
6090 @var{set1} are passed through unchanged. When a character appears more
6091 than once in @var{set1} and the corresponding characters in @var{set2}
6092 are not all the same, only the final one is used. For example, these
6093 two commands are equivalent:
6100 A common use of @command{tr} is to convert lowercase characters to
6101 uppercase. This can be done in many ways. Here are three of them:
6104 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
6106 tr '[:lower:]' '[:upper:]'
6110 But note that using ranges like @code{a-z} above is not portable.
6112 When @command{tr} is performing translation, @var{set1} and @var{set2}
6113 typically have the same length. If @var{set1} is shorter than
6114 @var{set2}, the extra characters at the end of @var{set2} are ignored.
6116 On the other hand, making @var{set1} longer than @var{set2} is not
6117 portable; POSIX says that the result is undefined. In this situation,
6118 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
6119 the last character of @var{set2} as many times as necessary. System V
6120 @command{tr} truncates @var{set1} to the length of @var{set2}.
6122 By default, GNU @command{tr} handles this case like BSD @command{tr}.
6123 When the @option{--truncate-set1} (@option{-t}) option is given,
6124 GNU @command{tr} handles this case like the System V @command{tr}
6125 instead. This option is ignored for operations other than translation.
6127 Acting like System V @command{tr} in this case breaks the relatively common
6131 tr -cs A-Za-z0-9 '\012'
6135 because it converts only zero bytes (the first element in the
6136 complement of @var{set1}), rather than all non-alphanumerics, to
6140 By the way, the above idiom is not portable because it uses ranges, and
6141 it assumes that the octal code for newline is 012.
6142 Assuming a POSIX compliant @command{tr}, here is a better
6146 tr -cs '[:alnum:]' '[\n*]'
6151 @subsection Squeezing repeats and deleting
6153 @cindex squeezing repeat characters
6154 @cindex deleting characters
6156 When given just the @option{--delete} (@option{-d}) option, @command{tr}
6157 removes any input characters that are in @var{set1}.
6159 When given just the @option{--squeeze-repeats} (@option{-s}) option,
6160 @command{tr} replaces each input sequence of a repeated character that
6161 is in @var{set1} with a single occurrence of that character.
6163 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
6164 first performs any deletions using @var{set1}, then squeezes repeats
6165 from any remaining characters using @var{set2}.
6167 The @option{--squeeze-repeats} option may also be used when translating,
6168 in which case @command{tr} first performs translation, then squeezes
6169 repeats from any remaining characters using @var{set2}.
6171 Here are some examples to illustrate various combinations of options:
6176 Remove all zero bytes:
6183 Put all words on lines by themselves. This converts all
6184 non-alphanumeric characters to newlines, then squeezes each string
6185 of repeated newlines into a single newline:
6188 tr -cs '[:alnum:]' '[\n*]'
6192 Convert each sequence of repeated newlines to a single newline:
6199 Find doubled occurrences of words in a document.
6200 @c Separate the following two "the"s, so typo checkers don't complain.
6201 For example, people often write ``the @w{}the'' with the repeated words
6202 separated by a newline. The Bourne shell script below works first
6203 by converting each sequence of punctuation and blank characters to a
6204 single newline. That puts each ``word'' on a line by itself.
6205 Next it maps all uppercase characters to lower case, and finally it
6206 runs @command{uniq} with the @option{-d} option to print out only the words
6212 | tr -s '[:punct:][:blank:]' '[\n*]' \
6213 | tr '[:upper:]' '[:lower:]' \
6218 Deleting a small set of characters is usually straightforward. For example,
6219 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
6225 However, when @samp{-} is one of those characters, it can be tricky because
6226 @samp{-} has special meanings. Performing the same task as above but also
6227 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
6228 that would fail because @command{tr} would try to interpret @option{-a} as
6229 a command-line option. Alternatively, we could try putting the hyphen
6230 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
6231 it would make @command{tr} interpret @code{a-x} as the range of characters
6232 @samp{a}@dots{}@samp{x} rather than the three.
6233 One way to solve the problem is to put the hyphen at the end of the list
6240 Or you can use @samp{--} to terminate option processing:
6246 More generally, use the character class notation @code{[=c=]}
6247 with @samp{-} (or any other character) in place of the @samp{c}:
6253 Note how single quotes are used in the above example to protect the
6254 square brackets from interpretation by a shell.
6259 @node expand invocation
6260 @section @command{expand}: Convert tabs to spaces
6263 @cindex tabs to spaces, converting
6264 @cindex converting tabs to spaces
6266 @command{expand} writes the contents of each given @var{file}, or standard
6267 input if none are given or for a @var{file} of @samp{-}, to standard
6268 output, with tab characters converted to the appropriate number of
6272 expand [@var{option}]@dots{} [@var{file}]@dots{}
6275 By default, @command{expand} converts all tabs to spaces. It preserves
6276 backspace characters in the output; they decrement the column count for
6277 tab calculations. The default action is equivalent to @option{-t 8} (set
6278 tabs every 8 columns).
6280 The program accepts the following options. Also see @ref{Common options}.
6284 @item -t @var{tab1}[,@var{tab2}]@dots{}
6285 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6288 @cindex tab stops, setting
6289 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6290 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6291 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6292 last tab stop given with single spaces. Tab stops can be separated by
6293 blanks as well as by commas.
6295 For compatibility, GNU @command{expand} also accepts the obsolete
6296 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6297 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6303 @cindex initial tabs, converting
6304 Only convert initial tabs (those that precede all non-space or non-tab
6305 characters) on each line to spaces.
6312 @node unexpand invocation
6313 @section @command{unexpand}: Convert spaces to tabs
6317 @command{unexpand} writes the contents of each given @var{file}, or
6318 standard input if none are given or for a @var{file} of @samp{-}, to
6319 standard output, converting blanks at the beginning of each line into
6320 as many tab characters as needed. In the default POSIX
6321 locale, a @dfn{blank} is a space or a tab; other locales may specify
6322 additional blank characters. Synopsis:
6325 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6328 By default, @command{unexpand} converts only initial blanks (those
6329 that precede all non-blank characters) on each line. It
6330 preserves backspace characters in the output; they decrement the column
6331 count for tab calculations. By default, tabs are set at every 8th
6334 The program accepts the following options. Also see @ref{Common options}.
6338 @item -t @var{tab1}[,@var{tab2}]@dots{}
6339 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6342 If only one tab stop is given, set the tabs @var{tab1} columns apart
6343 instead of the default 8. Otherwise, set the tabs at columns
6344 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6345 beyond the tab stops given unchanged. Tab stops can be separated by
6346 blanks as well as by commas. This option implies the @option{-a} option.
6348 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6349 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6350 separated by commas. (Unlike @option{-t}, this obsolete option does
6351 not imply @option{-a}.) New scripts should use @option{--first-only -t
6352 @var{tab1}[,@var{tab2}]@dots{}} instead.
6358 Also convert all sequences of two or more blanks just before a tab stop,
6359 even if they occur after non-blank characters in a line.
6366 @node Directory listing
6367 @chapter Directory listing
6369 This chapter describes the @command{ls} command and its variants @command{dir}
6370 and @command{vdir}, which list information about files.
6373 * ls invocation:: List directory contents.
6374 * dir invocation:: Briefly ls.
6375 * vdir invocation:: Verbosely ls.
6376 * dircolors invocation:: Color setup for ls, etc.
6381 @section @command{ls}: List directory contents
6384 @cindex directory listing
6386 The @command{ls} program lists information about files (of any type,
6387 including directories). Options and file arguments can be intermixed
6388 arbitrarily, as usual.
6390 For non-option command-line arguments that are directories, by default
6391 @command{ls} lists the contents of directories, not recursively, and
6392 omitting files with names beginning with @samp{.}. For other non-option
6393 arguments, by default @command{ls} lists just the file name. If no
6394 non-option argument is specified, @command{ls} operates on the current
6395 directory, acting as if it had been invoked with a single argument of @samp{.}.
6398 By default, the output is sorted alphabetically, according to the locale
6399 settings in effect.@footnote{If you use a non-POSIX
6400 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6401 produce output that is sorted differently than you're accustomed to.
6402 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6403 If standard output is
6404 a terminal, the output is in columns (sorted vertically) and control
6405 characters are output as question marks; otherwise, the output is listed
6406 one per line and control characters are output as-is.
6408 Because @command{ls} is such a fundamental program, it has accumulated many
6409 options over the years. They are described in the subsections below;
6410 within each section, options are listed alphabetically (ignoring case).
6411 The division of options into the subsections is not absolute, since some
6412 options affect more than one aspect of @command{ls}'s operation.
6414 @cindex exit status of @command{ls}
6419 1 minor problems (e.g., failure to access a file or directory not
6420 specified as a command line argument. This happens when listing a
6421 directory in which entries are actively being removed or renamed.)
6422 2 serious trouble (e.g., memory exhausted, invalid option, failure
6423 to access a file or directory specified as a command line argument
6424 or a directory loop)
6427 Also see @ref{Common options}.
6430 * Which files are listed::
6431 * What information is listed::
6432 * Sorting the output::
6433 * Details about version sort::
6434 * General output formatting::
6435 * Formatting file timestamps::
6436 * Formatting the file names::
6440 @node Which files are listed
6441 @subsection Which files are listed
6443 These options determine which files @command{ls} lists information for.
6444 By default, @command{ls} lists files and the contents of any
6445 directories on the command line, except that in directories it ignores
6446 files whose names start with @samp{.}.
6454 In directories, do not ignore file names that start with @samp{.}.
6459 @opindex --almost-all
6460 In directories, do not ignore all file names that start with @samp{.};
6461 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6462 option overrides this option.
6465 @itemx --ignore-backups
6467 @opindex --ignore-backups
6468 @cindex backup files, ignoring
6469 In directories, ignore files that end with @samp{~}. This option is
6470 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6475 @opindex --directory
6476 List just the names of directories, as with other types of files, rather
6477 than listing their contents.
6478 @c The following sentence is the same as the one for -F.
6479 Do not follow symbolic links listed on the
6480 command line unless the @option{--dereference-command-line} (@option{-H}),
6481 @option{--dereference} (@option{-L}), or
6482 @option{--dereference-command-line-symlink-to-dir} options are specified.
6485 @itemx --dereference-command-line
6487 @opindex --dereference-command-line
6488 @cindex symbolic links, dereferencing
6489 If a command line argument specifies a symbolic link, show information
6490 for the file the link references rather than for the link itself.
6492 @item --dereference-command-line-symlink-to-dir
6493 @opindex --dereference-command-line-symlink-to-dir
6494 @cindex symbolic links, dereferencing
6495 Do not dereference symbolic links, with one exception:
6496 if a command line argument specifies a symbolic link that refers to
6497 a directory, show information for that directory rather than for the
6499 This is the default behavior when no other dereferencing-related
6500 option has been specified (@option{--classify} (@option{-F}),
6501 @option{--directory} (@option{-d}),
6503 @option{--dereference} (@option{-L}), or
6504 @option{--dereference-command-line} (@option{-H})).
6506 @item --group-directories-first
6507 @opindex --group-directories-first
6508 Group all the directories before the files and then sort the
6509 directories and the files separately using the selected sort key
6510 (see --sort option).
6511 That is, this option specifies a primary sort key,
6512 and the --sort option specifies a secondary key.
6513 However, any use of @option{--sort=none}
6514 (@option{-U}) disables this option altogether.
6516 @item --hide=PATTERN
6517 @opindex --hide=@var{pattern}
6518 In directories, ignore files whose names match the shell pattern
6519 @var{pattern}, unless the @option{--all} (@option{-a}) or
6520 @option{--almost-all} (@option{-A}) is also given. This
6521 option acts like @option{--ignore=@var{pattern}} except that it has no
6522 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6523 (@option{-A}) is also given.
6525 This option can be useful in shell aliases. For example, if
6526 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6527 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6528 lists the file @file{README~} even though @samp{ly -A} would not.
6530 @item -I @var{pattern}
6531 @itemx --ignore=@var{pattern}
6533 @opindex --ignore=@var{pattern}
6534 In directories, ignore files whose names match the shell pattern
6535 (not regular expression) @var{pattern}. As
6536 in the shell, an initial @samp{.} in a file name does not match a
6537 wildcard at the start of @var{pattern}. Sometimes it is useful
6538 to give this option several times. For example,
6541 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6544 The first option ignores names of length 3 or more that start with @samp{.},
6545 the second ignores all two-character names that start with @samp{.}
6546 except @samp{..}, and the third ignores names that start with @samp{#}.
6549 @itemx --dereference
6551 @opindex --dereference
6552 @cindex symbolic links, dereferencing
6553 When showing file information for a symbolic link, show information
6554 for the file the link references rather than the link itself.
6555 However, even with this option, @command{ls} still prints the name
6556 of the link itself, not the name of the file that the link points to.
6561 @opindex --recursive
6562 @cindex recursive directory listing
6563 @cindex directory listing, recursive
6564 List the contents of all directories recursively.
6569 @node What information is listed
6570 @subsection What information is listed
6572 These options affect the information that @command{ls} displays. By
6573 default, only file names are shown.
6579 @cindex hurd, author, printing
6580 List each file's author when producing long format directory listings.
6581 In GNU/Hurd, file authors can differ from their owners, but in other
6582 operating systems the two are the same.
6588 @cindex dired Emacs mode support
6589 With the long listing (@option{-l}) format, print an additional line after
6593 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6597 The @var{begn} and @var{endn} are unsigned integers that record the
6598 byte position of the beginning and end of each file name in the output.
6599 This makes it easy for Emacs to find the names, even when they contain
6600 unusual characters such as space or newline, without fancy searching.
6602 If directories are being listed recursively (@option{-R}), output a similar
6603 line with offsets for each subdirectory name:
6606 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6609 Finally, output a line of the form:
6612 //DIRED-OPTIONS// --quoting-style=@var{word}
6616 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6618 Here is an actual example:
6621 $ mkdir -p a/sub/deeper a/sub2
6623 $ touch a/sub/deeper/file
6624 $ ls -gloRF --dired a
6627 -rw-r--r-- 1 0 Jun 10 12:27 f1
6628 -rw-r--r-- 1 0 Jun 10 12:27 f2
6629 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6630 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6634 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6638 -rw-r--r-- 1 0 Jun 10 12:27 file
6642 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6643 //SUBDIRED// 2 3 167 172 228 240 290 296
6644 //DIRED-OPTIONS// --quoting-style=literal
6647 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6648 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6650 The offsets on the @samp{//SUBDIRED//} line delimit the following
6651 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6653 Here is an example of how to extract the fifth entry name, @samp{deeper},
6654 corresponding to the pair of offsets, 222 and 228:
6657 $ ls -gloRF --dired a > out
6658 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6662 Note that although the listing above includes a trailing slash
6663 for the @samp{deeper} entry, the offsets select the name without
6664 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6665 along with an option like @option{--escape} (aka @option{-b}) and operate
6666 on a file whose name contains special characters, notice that the backslash
6671 $ ls -blog --dired 'a b'
6672 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6674 //DIRED-OPTIONS// --quoting-style=escape
6677 If you use a quoting style that adds quote marks
6678 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6679 So beware that the user may select the quoting style via the environment
6680 variable @env{QUOTING_STYLE}@. Hence, applications using @option{--dired}
6681 should either specify an explicit @option{--quoting-style=literal} option
6682 (aka @option{-N} or @option{--literal}) on the command line, or else be
6683 prepared to parse the escaped names.
6686 @opindex --full-time
6687 Produce long format directory listings, and list times in full. It is
6688 equivalent to using @option{--format=long} with
6689 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6693 Produce long format directory listings, but don't display owner information.
6699 Inhibit display of group information in a long format directory listing.
6700 (This is the default in some non-GNU versions of @command{ls}, so we
6701 provide this option for compatibility.)
6709 @cindex inode number, printing
6710 Print the inode number (also called the file serial number and index
6711 number) of each file to the left of the file name. (This number
6712 uniquely identifies each file within a particular file system.)
6715 @itemx --format=long
6716 @itemx --format=verbose
6719 @opindex long ls @r{format}
6720 @opindex verbose ls @r{format}
6721 In addition to the name of each file, print the file type, file mode bits,
6722 number of hard links, owner name, group name, size, and
6723 timestamp (@pxref{Formatting file timestamps}), normally
6724 the modification time. Print question marks for information that
6725 cannot be determined.
6727 Normally the size is printed as a byte count without punctuation, but
6728 this can be overridden (@pxref{Block size}). For example, @option{-h}
6729 prints an abbreviated, human-readable count, and
6730 @samp{--block-size="'1"} prints a byte count with the thousands
6731 separator of the current locale.
6733 For each directory that is listed, preface the files with a line
6734 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6735 for all files in that directory. The block size currently defaults to 1024
6736 bytes, but this can be overridden (@pxref{Block size}).
6737 The @var{blocks} computed counts each hard link separately;
6738 this is arguably a deficiency.
6740 The file type is one of the following characters:
6742 @c The commented-out entries are ones we're not sure about.
6750 character special file
6752 high performance (``contiguous data'') file
6756 door (Solaris 2.5 and up)
6758 @c semaphore, if this is a distinct file type
6762 @c multiplexed file (7th edition Unix; obsolete)
6764 off-line (``migrated'') file (Cray DMF)
6766 network special file (HP-UX)
6770 port (Solaris 10 and up)
6772 @c message queue, if this is a distinct file type
6776 @c shared memory object, if this is a distinct file type
6778 @c typed memory object, if this is a distinct file type
6780 @c whiteout (4.4BSD; not implemented)
6782 some other file type
6785 @cindex permissions, output by @command{ls}
6786 The file mode bits listed are similar to symbolic mode specifications
6787 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6788 third character of each set of permissions as follows:
6792 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6796 If the set-user-ID or set-group-ID bit is set but the corresponding
6797 executable bit is not set.
6800 If the restricted deletion flag or sticky bit, and the
6801 other-executable bit, are both set. The restricted deletion flag is
6802 another name for the sticky bit. @xref{Mode Structure}.
6805 If the restricted deletion flag or sticky bit is set but the
6806 other-executable bit is not set.
6809 If the executable bit is set and none of the above apply.
6815 Following the file mode bits is a single character that specifies
6816 whether an alternate access method such as an access control list
6817 applies to the file. When the character following the file mode bits is a
6818 space, there is no alternate access method. When it is a printing
6819 character, then there is such a method.
6821 GNU @command{ls} uses a @samp{.} character to indicate a file
6822 with an SELinux security context, but no other alternate access method.
6824 A file with any other combination of alternate access methods
6825 is marked with a @samp{+} character.
6828 @itemx --numeric-uid-gid
6830 @opindex --numeric-uid-gid
6831 @cindex numeric uid and gid
6832 @cindex numeric user and group IDs
6833 Produce long format directory listings, but
6834 display numeric user and group IDs instead of the owner and group names.
6838 Produce long format directory listings, but don't display group information.
6839 It is equivalent to using @option{--format=long} with @option{--no-group} .
6845 @cindex disk allocation
6846 @cindex size of files, reporting
6847 Print the disk allocation of each file to the left of the file name.
6848 This is the amount of disk space used by the file, which is usually a
6849 bit more than the file's size, but it can be less if the file has holes.
6851 Normally the disk allocation is printed in units of
6852 1024 bytes, but this can be overridden (@pxref{Block size}).
6854 @cindex NFS mounts from BSD to HP-UX
6855 For files that are NFS-mounted from an HP-UX system to a BSD system,
6856 this option reports sizes that are half the correct values. On HP-UX
6857 systems, it reports sizes that are twice the correct values for files
6858 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6859 it also affects the HP-UX @command{ls} program.
6868 @cindex security context
6869 Display the SELinux security context or @samp{?} if none is found.
6870 When used with the @option{-l} option, print the security context
6871 to the left of the size column.
6876 @node Sorting the output
6877 @subsection Sorting the output
6879 @cindex sorting @command{ls} output
6880 These options change the order in which @command{ls} sorts the information
6881 it outputs. By default, sorting is done by character code
6882 (e.g., ASCII order).
6888 @itemx --time=status
6891 @opindex ctime@r{, printing or sorting by}
6892 @opindex status time@r{, printing or sorting by}
6893 @opindex use time@r{, printing or sorting files by}
6894 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6895 print the status change time (the @samp{ctime} in the inode) instead of
6896 the modification time.
6897 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6898 or when not using a long listing format,
6899 sort according to the status change time.
6903 @cindex unsorted directory listing
6904 @cindex directory order, listing by
6905 Primarily, like @option{-U}---do not sort; list the files in whatever
6906 order they are stored in the directory. But also enable @option{-a} (list
6907 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6908 were specified before the @option{-f}).
6914 @cindex reverse sorting
6915 Reverse whatever the sorting method is---e.g., list files in reverse
6916 alphabetical order, youngest first, smallest first, or whatever.
6922 @opindex size of files@r{, sorting files by}
6923 Sort by file size, largest first.
6929 @opindex modification time@r{, sorting files by}
6930 Sort by modification time (the @samp{mtime} in the inode), newest first.
6934 @itemx --time=access
6938 @opindex use time@r{, printing or sorting files by}
6939 @opindex atime@r{, printing or sorting files by}
6940 @opindex access time@r{, printing or sorting files by}
6941 If the long listing format (e.g., @option{--format=long}) is being used,
6942 print the last access time (the @samp{atime} in the inode).
6943 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6944 or when not using a long listing format, sort according to the access time.
6950 @opindex none@r{, sorting option for @command{ls}}
6951 Do not sort; list the files in whatever order they are
6952 stored in the directory. (Do not do any of the other unrelated things
6953 that @option{-f} does.) This is especially useful when listing very large
6954 directories, since not doing any sorting can be noticeably faster.
6957 @itemx --sort=version
6960 @opindex version@r{, sorting option for @command{ls}}
6961 Sort by version name and number, lowest first. It behaves like a default
6962 sort, except that each sequence of decimal digits is treated numerically
6963 as an index/version number. (@xref{Details about version sort}.)
6966 @itemx --sort=extension
6969 @opindex extension@r{, sorting files by}
6970 Sort directory contents alphabetically by file extension (characters
6971 after the last @samp{.}); files with no extension are sorted first.
6976 @node Details about version sort
6977 @subsection Details about version sort
6979 Version sorting handles the fact that file names frequently include indices or
6980 version numbers. Standard sorting usually does not produce the order that one
6981 expects because comparisons are made on a character-by-character basis.
6982 Version sorting is especially useful when browsing directories that contain
6983 many files with indices/version numbers in their names:
6987 abc.zml-1.gz abc.zml-1.gz
6988 abc.zml-12.gz abc.zml-2.gz
6989 abc.zml-2.gz abc.zml-12.gz
6992 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6993 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6994 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6995 @var{ver1} < @var{ver2} implies that the name composed of
6996 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6997 ``@var{prefix} @var{ver2} @var{suffix}''.
6999 Note also that leading zeros of numeric parts are ignored:
7003 abc-1.007.tgz abc-1.01a.tgz
7004 abc-1.012b.tgz abc-1.007.tgz
7005 abc-1.01a.tgz abc-1.012b.tgz
7008 This functionality is implemented using gnulib's @code{filevercmp} function,
7009 which has some caveats worth noting.
7012 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
7013 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
7014 was set to @samp{C}@.
7015 @item Some suffixes will not be matched by the regular
7016 expression mentioned above. Consequently these examples may
7017 not sort as you expect:
7025 abc-1.2.3.4.x86_64.rpm
7026 abc-1.2.3.x86_64.rpm
7030 @node General output formatting
7031 @subsection General output formatting
7033 These options affect the appearance of the overall output.
7038 @itemx --format=single-column
7041 @opindex single-column @r{output of files}
7042 List one file per line. This is the default for @command{ls} when standard
7043 output is not a terminal.
7046 @itemx --format=vertical
7049 @opindex vertical @r{sorted files in columns}
7050 List files in columns, sorted vertically. This is the default for
7051 @command{ls} if standard output is a terminal. It is always the default
7052 for the @command{dir} program.
7053 GNU @command{ls} uses variable width columns to display as many files as
7054 possible in the fewest lines.
7056 @item --color [=@var{when}]
7058 @cindex color, distinguishing file types with
7059 Specify whether to use color for distinguishing file types. @var{when}
7060 may be omitted, or one of:
7063 @vindex none @r{color option}
7064 - Do not use color at all. This is the default.
7066 @vindex auto @r{color option}
7067 @cindex terminal, using color iff
7068 - Only use color if standard output is a terminal.
7070 @vindex always @r{color option}
7073 Specifying @option{--color} and no @var{when} is equivalent to
7074 @option{--color=always}.
7075 Piping a colorized listing through a pager like @command{more} or
7076 @command{less} usually produces unreadable results. However, using
7077 @code{more -f} does seem to work.
7080 @vindex SHELL @r{environment variable, and color}
7081 Note that using the @option{--color} option may incur a noticeable
7082 performance penalty when run in a directory with very many entries,
7083 because the default settings require that @command{ls} @code{stat} every
7084 single file it lists.
7085 However, if you would like most of the file-type coloring
7086 but can live without the other coloring options (e.g.,
7087 executable, orphan, sticky, other-writable, capability), use
7088 @command{dircolors} to set the @env{LS_COLORS} environment variable like this,
7090 eval $(dircolors -p | perl -pe \
7091 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
7093 and on a @code{dirent.d_type}-capable file system, @command{ls}
7094 will perform only one @code{stat} call per command line argument.
7098 @itemx --indicator-style=classify
7101 @opindex --indicator-style
7102 @cindex file type and executables, marking
7103 @cindex executables and file type, marking
7104 Append a character to each file name indicating the file type. Also,
7105 for regular files that are executable, append @samp{*}. The file type
7106 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
7107 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
7108 and nothing for regular files.
7109 @c The following sentence is the same as the one for -d.
7110 Do not follow symbolic links listed on the
7111 command line unless the @option{--dereference-command-line} (@option{-H}),
7112 @option{--dereference} (@option{-L}), or
7113 @option{--dereference-command-line-symlink-to-dir} options are specified.
7116 @itemx --indicator-style=file-type
7117 @opindex --file-type
7118 @opindex --indicator-style
7119 @cindex file type, marking
7120 Append a character to each file name indicating the file type. This is
7121 like @option{-F}, except that executables are not marked.
7123 @item --indicator-style=@var{word}
7124 @opindex --indicator-style
7125 Append a character indicator with style @var{word} to entry names,
7130 Do not append any character indicator; this is the default.
7132 Append @samp{/} for directories. This is the same as the @option{-p}
7135 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
7136 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
7137 the same as the @option{--file-type} option.
7139 Append @samp{*} for executable regular files, otherwise behave as for
7140 @samp{file-type}. This is the same as the @option{-F} or
7141 @option{--classify} option.
7147 @opindex --kibibytes
7148 Set the default block size to its normal value of 1024 bytes,
7149 overriding any contrary specification in environment variables
7150 (@pxref{Block size}). This option is in turn overridden by the
7151 @option{--block-size}, @option{-h} or @option{--human-readable}, and
7152 @option{--si} options.
7154 The @option{-k} or @option{--kibibytes} option affects the
7155 per-directory block count written by the @option{-l} and similar
7156 options, and the size written by the @option{-s} or @option{--size}
7157 option. It does not affect the file size written by @option{-l}.
7160 @itemx --format=commas
7163 @opindex commas@r{, outputting between files}
7164 List files horizontally, with as many as will fit on each line,
7165 separated by @samp{, } (a comma and a space).
7168 @itemx --indicator-style=slash
7170 @opindex --indicator-style
7171 @cindex file type, marking
7172 Append a @samp{/} to directory names.
7175 @itemx --format=across
7176 @itemx --format=horizontal
7179 @opindex across@r{, listing files}
7180 @opindex horizontal@r{, listing files}
7181 List the files in columns, sorted horizontally.
7184 @itemx --tabsize=@var{cols}
7187 Assume that each tab stop is @var{cols} columns wide. The default is 8.
7188 @command{ls} uses tabs where possible in the output, for efficiency. If
7189 @var{cols} is zero, do not use tabs at all.
7191 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
7192 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
7193 do not properly align columns to the right of a TAB following a
7194 non-ASCII byte. If you use such a terminal emulator, use the
7195 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
7196 @command{ls} to align using spaces, not tabs.
7199 @itemx --width=@var{cols}
7203 Assume the screen is @var{cols} columns wide. The default is taken
7204 from the terminal settings if possible; otherwise the environment
7205 variable @env{COLUMNS} is used if it is set; otherwise the default
7211 @node Formatting file timestamps
7212 @subsection Formatting file timestamps
7214 By default, file timestamps are listed in abbreviated form, using
7215 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
7216 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
7217 This format can change depending on the current locale as detailed below.
7220 A timestamp is considered to be @dfn{recent} if it is less than six
7221 months old, and is not dated in the future. If a timestamp dated
7222 today is not listed in recent form, the timestamp is in the future,
7223 which means you probably have clock skew problems which may break
7224 programs like @command{make} that rely on file timestamps.
7227 Time stamps are listed according to the time zone rules specified by
7228 the @env{TZ} environment variable, or by the system default rules if
7229 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
7230 with @env{TZ}, libc, The GNU C Library Reference Manual}.
7232 The following option changes how file timestamps are printed.
7235 @item --time-style=@var{style}
7236 @opindex --time-style
7238 List timestamps in style @var{style}. The @var{style} should
7239 be one of the following:
7244 List timestamps using @var{format}, where @var{format} is interpreted
7245 like the format argument of @command{date} (@pxref{date invocation}).
7246 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
7247 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
7248 with @command{date}, @var{format}'s interpretation is affected by the
7249 @env{LC_TIME} locale category.
7251 If @var{format} contains two format strings separated by a newline,
7252 the former is used for non-recent files and the latter for recent
7253 files; if you want output columns to line up, you may need to insert
7254 spaces in one of the two formats.
7257 List timestamps in full using ISO 8601 date, time, and time zone
7258 format with nanosecond precision, e.g., @samp{2002-03-30
7259 23:45:56.477817180 -0700}. This style is equivalent to
7260 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
7262 This is useful because the time output includes all the information that
7263 is available from the operating system. For example, this can help
7264 explain @command{make}'s behavior, since GNU @command{make}
7265 uses the full timestamp to determine whether a file is out of date.
7268 List ISO 8601 date and time in minutes, e.g.,
7269 @samp{2002-03-30 23:45}. These timestamps are shorter than
7270 @samp{full-iso} timestamps, and are usually good enough for everyday
7271 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7274 List ISO 8601 dates for non-recent timestamps (e.g.,
7275 @samp{2002-03-30@ }), and ISO 8601 month, day, hour, and
7276 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7277 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7278 nearly the same information in a smaller space and their brevity helps
7279 @command{ls} output fit within traditional 80-column output lines.
7280 The following two @command{ls} invocations are equivalent:
7285 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7286 ls -l --time-style="iso"
7291 List timestamps in a locale-dependent form. For example, a Finnish
7292 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7293 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7294 timestamps typically consume more space than @samp{iso} timestamps and
7295 are harder for programs to parse because locale conventions vary so
7296 widely, but they are easier for many people to read.
7298 The @env{LC_TIME} locale category specifies the timestamp format. The
7299 default POSIX locale uses timestamps like @samp{Mar 30@
7300 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7301 @command{ls} invocations are equivalent:
7306 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7307 ls -l --time-style="locale"
7310 Other locales behave differently. For example, in a German locale,
7311 @option{--time-style="locale"} might be equivalent to
7312 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7313 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7314 @samp{30. M@"ar 23:45}.
7316 @item posix-@var{style}
7318 List POSIX-locale timestamps if the @env{LC_TIME} locale
7319 category is POSIX, @var{style} timestamps otherwise. For
7320 example, the @samp{posix-long-iso} style lists
7321 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7322 the POSIX locale, and like @samp{2002-03-30 23:45} otherwise.
7327 You can specify the default value of the @option{--time-style} option
7328 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7329 the default style is @samp{locale}. GNU Emacs 21.3 and
7330 later use the @option{--dired} option and therefore can parse any date
7331 format, but if you are using Emacs 21.1 or 21.2 and specify a
7332 non-POSIX locale you may need to set
7333 @samp{TIME_STYLE="posix-long-iso"}.
7335 To avoid certain denial-of-service attacks, timestamps that would be
7336 longer than 1000 bytes may be treated as errors.
7339 @node Formatting the file names
7340 @subsection Formatting the file names
7342 These options change how file names themselves are printed.
7348 @itemx --quoting-style=escape
7351 @opindex --quoting-style
7352 @cindex backslash sequences for file names
7353 Quote nongraphic characters in file names using alphabetic and octal
7354 backslash sequences like those used in C.
7358 @itemx --quoting-style=literal
7361 @opindex --quoting-style
7362 Do not quote file names. However, with @command{ls} nongraphic
7363 characters are still printed as question marks if the output is a
7364 terminal and you do not specify the @option{--show-control-chars}
7368 @itemx --hide-control-chars
7370 @opindex --hide-control-chars
7371 Print question marks instead of nongraphic characters in file names.
7372 This is the default if the output is a terminal and the program is
7377 @itemx --quoting-style=c
7379 @opindex --quote-name
7380 @opindex --quoting-style
7381 Enclose file names in double quotes and quote nongraphic characters as
7384 @item --quoting-style=@var{word}
7385 @opindex --quoting-style
7386 @cindex quoting style
7387 Use style @var{word} to quote file names and other strings that may
7388 contain arbitrary characters. The @var{word} should
7389 be one of the following:
7393 Output strings as-is; this is the same as the @option{-N} or
7394 @option{--literal} option.
7396 Quote strings for the shell if they contain shell metacharacters or would
7397 cause ambiguous output.
7398 The quoting is suitable for POSIX-compatible shells like
7399 @command{bash}, but it does not always work for incompatible shells
7402 Quote strings for the shell, even if they would normally not require quoting.
7404 Quote strings as for C character string literals, including the
7405 surrounding double-quote characters; this is the same as the
7406 @option{-Q} or @option{--quote-name} option.
7408 Quote strings as for C character string literals, except omit the
7409 surrounding double-quote
7410 characters; this is the same as the @option{-b} or @option{--escape} option.
7412 Quote strings as for C character string literals, except use
7413 surrounding quotation marks appropriate for the
7416 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7417 Quote strings as for C character string literals, except use
7418 surrounding quotation marks appropriate for the locale, and quote
7419 @t{'like this'} instead of @t{"like
7420 this"} in the default C locale. This looks nicer on many displays.
7423 You can specify the default value of the @option{--quoting-style} option
7424 with the environment variable @env{QUOTING_STYLE}@. If that environment
7425 variable is not set, the default value is @samp{literal}, but this
7426 default may change to @samp{shell} in a future version of this package.
7428 @item --show-control-chars
7429 @opindex --show-control-chars
7430 Print nongraphic characters as-is in file names.
7431 This is the default unless the output is a terminal and the program is
7437 @node dir invocation
7438 @section @command{dir}: Briefly list directory contents
7441 @cindex directory listing, brief
7443 @command{dir} is equivalent to @code{ls -C
7444 -b}; that is, by default files are listed in columns, sorted vertically,
7445 and special characters are represented by backslash escape sequences.
7447 @xref{ls invocation, @command{ls}}.
7450 @node vdir invocation
7451 @section @command{vdir}: Verbosely list directory contents
7454 @cindex directory listing, verbose
7456 @command{vdir} is equivalent to @code{ls -l
7457 -b}; that is, by default files are listed in long format and special
7458 characters are represented by backslash escape sequences.
7460 @node dircolors invocation
7461 @section @command{dircolors}: Color setup for @command{ls}
7465 @cindex setup for color
7467 @command{dircolors} outputs a sequence of shell commands to set up the
7468 terminal for color output from @command{ls} (and @command{dir}, etc.).
7472 eval "$(dircolors [@var{option}]@dots{} [@var{file}])"
7475 If @var{file} is specified, @command{dircolors} reads it to determine which
7476 colors to use for which file types and extensions. Otherwise, a
7477 precompiled database is used. For details on the format of these files,
7478 run @samp{dircolors --print-database}.
7480 To make @command{dircolors} read a @file{~/.dircolors} file if it
7481 exists, you can put the following lines in your @file{~/.bashrc} (or
7482 adapt them to your favorite shell):
7486 test -r $d && eval "$(dircolors $d)"
7490 @vindex SHELL @r{environment variable, and color}
7491 The output is a shell command to set the @env{LS_COLORS} environment
7492 variable. You can specify the shell syntax to use on the command line,
7493 or @command{dircolors} will guess it from the value of the @env{SHELL}
7494 environment variable.
7496 The program accepts the following options. Also see @ref{Common options}.
7501 @itemx --bourne-shell
7504 @opindex --bourne-shell
7505 @cindex Bourne shell syntax for color setup
7506 @cindex @command{sh} syntax for color setup
7507 Output Bourne shell commands. This is the default if the @env{SHELL}
7508 environment variable is set and does not end with @samp{csh} or
7517 @cindex C shell syntax for color setup
7518 @cindex @command{csh} syntax for color setup
7519 Output C shell commands. This is the default if @code{SHELL} ends with
7520 @command{csh} or @command{tcsh}.
7523 @itemx --print-database
7525 @opindex --print-database
7526 @cindex color database, printing
7527 @cindex database for color setup, printing
7528 @cindex printing color database
7529 Print the (compiled-in) default color configuration database. This
7530 output is itself a valid configuration file, and is fairly descriptive
7531 of the possibilities.
7538 @node Basic operations
7539 @chapter Basic operations
7541 @cindex manipulating files
7543 This chapter describes the commands for basic file manipulation:
7544 copying, moving (renaming), and deleting (removing).
7547 * cp invocation:: Copy files.
7548 * dd invocation:: Convert and copy a file.
7549 * install invocation:: Copy files and set attributes.
7550 * mv invocation:: Move (rename) files.
7551 * rm invocation:: Remove files or directories.
7552 * shred invocation:: Remove files more securely.
7557 @section @command{cp}: Copy files and directories
7560 @cindex copying files and directories
7561 @cindex files, copying
7562 @cindex directories, copying
7564 @command{cp} copies files (or, optionally, directories). The copy is
7565 completely independent of the original. You can either copy one file to
7566 another, or copy arbitrarily many files to a destination directory.
7570 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7571 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7572 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7577 If two file names are given, @command{cp} copies the first file to the
7581 If the @option{--target-directory} (@option{-t}) option is given, or
7582 failing that if the last file is a directory and the
7583 @option{--no-target-directory} (@option{-T}) option is not given,
7584 @command{cp} copies each @var{source} file to the specified directory,
7585 using the @var{source}s' names.
7588 Generally, files are written just as they are read. For exceptions,
7589 see the @option{--sparse} option below.
7591 By default, @command{cp} does not copy directories. However, the
7592 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7593 copy recursively by descending into source directories and copying files
7594 to corresponding destination directories.
7596 When copying from a symbolic link, @command{cp} normally follows the
7597 link only when not copying
7598 recursively. This default can be overridden with the
7599 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7600 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7601 @option{-H} options. If more than one of these options is specified,
7602 the last one silently overrides the others.
7604 When copying to a symbolic link, @command{cp} follows the
7605 link only when it refers to an existing regular file.
7606 However, when copying to a dangling symbolic link, @command{cp}
7607 refuses by default, and fails with a diagnostic, since the operation
7608 is inherently dangerous. This behavior is contrary to historical
7609 practice and to POSIX@.
7610 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7611 the target of a dangling destination symlink, in spite of the possible risk.
7612 Also, when an option like
7613 @option{--backup} or @option{--link} acts to rename or remove the
7614 destination before copying, @command{cp} renames or removes the
7615 symbolic link rather than the file it points to.
7617 By default, @command{cp} copies the contents of special files only
7618 when not copying recursively. This default can be overridden with the
7619 @option{--copy-contents} option.
7621 @cindex self-backups
7622 @cindex backups, making only
7623 @command{cp} generally refuses to copy a file onto itself, with the
7624 following exception: if @option{--force --backup} is specified with
7625 @var{source} and @var{dest} identical, and referring to a regular file,
7626 @command{cp} will make a backup file, either regular or numbered, as
7627 specified in the usual ways (@pxref{Backup options}). This is useful when
7628 you simply want to make a backup of an existing file before changing it.
7630 The program accepts the following options. Also see @ref{Common options}.
7637 Preserve as much as possible of the structure and attributes of the
7638 original files in the copy (but do not attempt to preserve internal
7639 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7640 directory in a different order).
7641 Try to preserve SELinux security context and extended attributes (xattr),
7642 but ignore any failure to do that and print no corresponding diagnostic.
7643 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7645 @item --attributes-only
7646 @opindex --attributes-only
7647 Copy only the specified attributes of the source file to the destination.
7648 If the destination already exists, do not alter its contents.
7649 See the @option{--preserve} option for controlling which attributes to copy.
7652 @itemx @w{@kbd{--backup}[=@var{method}]}
7655 @vindex VERSION_CONTROL
7656 @cindex backups, making
7657 @xref{Backup options}.
7658 Make a backup of each file that would otherwise be overwritten or removed.
7659 As a special case, @command{cp} makes a backup of @var{source} when the force
7660 and backup options are given and @var{source} and @var{dest} are the same
7661 name for an existing, regular file. One useful application of this
7662 combination of options is this tiny Bourne shell script:
7666 # Usage: backup FILE...
7667 # Create a GNU-style backup of each listed FILE.
7670 cp --backup --force --preserve=all -- "$i" "$i" || fail=1
7675 @item --copy-contents
7676 @cindex directories, copying recursively
7677 @cindex copying directories recursively
7678 @cindex recursively copying directories
7679 @cindex non-directories, copying as special files
7680 If copying recursively, copy the contents of any special files (e.g.,
7681 FIFOs and device files) as if they were regular files. This means
7682 trying to read the data in each source file and writing it to the
7683 destination. It is usually a mistake to use this option, as it
7684 normally has undesirable effects on special files like FIFOs and the
7685 ones typically found in the @file{/dev} directory. In most cases,
7686 @code{cp -R --copy-contents} will hang indefinitely trying to read
7687 from FIFOs and special files like @file{/dev/console}, and it will
7688 fill up your destination disk if you use it to copy @file{/dev/zero}.
7689 This option has no effect unless copying recursively, and it does not
7690 affect the copying of symbolic links.
7694 @cindex symbolic links, copying
7695 @cindex hard links, preserving
7696 Copy symbolic links as symbolic links rather than copying the files that
7697 they point to, and preserve hard links between source files in the copies.
7698 Equivalent to @option{--no-dereference --preserve=links}.
7704 When copying without this option and an existing destination file cannot
7705 be opened for writing, the copy fails. However, with @option{--force},
7706 when a destination file cannot be opened, @command{cp} then removes it and
7707 tries to open it again. Contrast this behavior with that enabled by
7708 @option{--link} and @option{--symbolic-link}, whereby the destination file
7709 is never opened but rather is removed unconditionally. Also see the
7710 description of @option{--remove-destination}.
7712 This option is independent of the @option{--interactive} or
7713 @option{-i} option: neither cancels the effect of the other.
7715 This option is ignored when the @option{--no-clobber} or @option{-n} option
7720 If a command line argument specifies a symbolic link, then copy the
7721 file it points to rather than the symbolic link itself. However,
7722 copy (preserving its nature) any symbolic link that is encountered
7723 via recursive traversal.
7726 @itemx --interactive
7728 @opindex --interactive
7729 When copying a file other than a directory, prompt whether to
7730 overwrite an existing destination file. The @option{-i} option overrides
7731 a previous @option{-n} option.
7737 Make hard links instead of copies of non-directories.
7740 @itemx --dereference
7742 @opindex --dereference
7743 Follow symbolic links when copying from them.
7744 With this option, @command{cp} cannot create a symbolic link.
7745 For example, a symlink (to regular file) in the source tree will be copied to
7746 a regular file in the destination tree.
7751 @opindex --no-clobber
7752 Do not overwrite an existing file. The @option{-n} option overrides a previous
7753 @option{-i} option. This option is mutually exclusive with @option{-b} or
7754 @option{--backup} option.
7757 @itemx --no-dereference
7759 @opindex --no-dereference
7760 @cindex symbolic links, copying
7761 Copy symbolic links as symbolic links rather than copying the files that
7762 they point to. This option affects only symbolic links in the source;
7763 symbolic links in the destination are always followed if possible.
7766 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7769 @cindex file information, preserving, extended attributes, xattr
7770 Preserve the specified attributes of the original files.
7771 If specified, the @var{attribute_list} must be a comma-separated list
7772 of one or more of the following strings:
7776 Preserve the file mode bits and access control lists.
7778 Preserve the owner and group. On most modern systems,
7779 only users with appropriate privileges may change the owner of a file,
7781 may preserve the group ownership of a file only if they happen to be
7782 a member of the desired group.
7784 Preserve the times of last access and last modification, when possible.
7785 On older systems, it is not possible to preserve these attributes
7786 when the affected file is a symbolic link.
7787 However, many systems now provide the @code{utimensat} function,
7788 which makes it possible even for symbolic links.
7790 Preserve in the destination files
7791 any links between corresponding source files.
7792 Note that with @option{-L} or @option{-H}, this option can convert
7793 symbolic links to hard links. For example,
7795 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7800 Note the inputs: @file{b} is a symlink to regular file @file{a},
7801 yet the files in destination directory, @file{c/}, are hard-linked.
7802 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7803 tells @command{cp} to dereference command line arguments, it sees two files
7804 with the same inode number, and preserves the perceived hard link.
7806 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7808 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7814 Preserve SELinux security context of the file, or fail with full diagnostics.
7816 Preserve extended attributes of the file, or fail with full diagnostics.
7817 If @command{cp} is built without xattr support, ignore this option.
7818 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7819 they are preserved implicitly by this option as well, i.e., even without
7820 specifying @option{--preserve=mode} or @option{--preserve=context}.
7822 Preserve all file attributes.
7823 Equivalent to specifying all of the above, but with the difference
7824 that failure to preserve SELinux security context or extended attributes
7825 does not change @command{cp}'s exit status. In contrast to @option{-a},
7826 all but @samp{Operation not supported} warnings are output.
7829 Using @option{--preserve} with no @var{attribute_list} is equivalent
7830 to @option{--preserve=mode,ownership,timestamps}.
7832 In the absence of this option, each destination file is created with the
7833 mode bits of the corresponding source file, minus the bits set in the
7834 umask and minus the set-user-ID and set-group-ID bits.
7835 @xref{File permissions}.
7837 @item @w{@kbd{--no-preserve}=@var{attribute_list}}
7838 @cindex file information, preserving
7839 Do not preserve the specified attributes. The @var{attribute_list}
7840 has the same form as for @option{--preserve}.
7844 @cindex parent directories and @command{cp}
7845 Form the name of each destination file by appending to the target
7846 directory a slash and the specified name of the source file. The last
7847 argument given to @command{cp} must be the name of an existing directory.
7848 For example, the command:
7851 cp --parents a/b/c existing_dir
7855 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7856 any missing intermediate directories.
7863 @opindex --recursive
7864 @cindex directories, copying recursively
7865 @cindex copying directories recursively
7866 @cindex recursively copying directories
7867 @cindex non-directories, copying as special files
7868 Copy directories recursively. By default, do not follow symbolic
7869 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7870 @option{--dereference} (@option{-L}), @option{--no-dereference}
7871 (@option{-P}), and @option{-H} options. Special files are copied by
7872 creating a destination file of the same type as the source; see the
7873 @option{--copy-contents} option. It is not portable to use
7874 @option{-r} to copy symbolic links or special files. On some
7875 non-GNU systems, @option{-r} implies the equivalent of
7876 @option{-L} and @option{--copy-contents} for historical reasons.
7877 Also, it is not portable to use @option{-R} to copy symbolic links
7878 unless you also specify @option{-P}, as POSIX allows
7879 implementations that dereference symbolic links by default.
7881 @item --reflink[=@var{when}]
7882 @opindex --reflink[=@var{when}]
7885 @cindex copy on write
7886 Perform a lightweight, copy-on-write (COW) copy, if supported by the
7887 file system. Once it has succeeded, beware that the source and destination
7888 files share the same disk data blocks as long as they remain unmodified.
7889 Thus, if a disk I/O error affects data blocks of one of the files,
7890 the other suffers the same fate.
7892 The @var{when} value can be one of the following:
7896 The default behavior: if the copy-on-write operation is not supported
7897 then report the failure for each file and exit with a failure status.
7900 If the copy-on-write operation is not supported then fall back
7901 to the standard copy behaviour.
7904 This option is overridden by the @option{--link}, @option{--symbolic-link}
7905 and @option{--attributes-only} options, thus allowing it to be used
7906 to configure the default data copying behavior for @command{cp}.
7907 For example, with the following alias, @command{cp} will use the
7908 minimum amount of space supported by the file system.
7911 alias cp='cp --reflink=auto --sparse=always'
7914 @item --remove-destination
7915 @opindex --remove-destination
7916 Remove each existing destination file before attempting to open it
7917 (contrast with @option{-f} above).
7919 @item --sparse=@var{when}
7920 @opindex --sparse=@var{when}
7921 @cindex sparse files, copying
7922 @cindex holes, copying files with
7923 @findex read @r{system call, and holes}
7924 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7925 does not occupy any physical disk blocks; the @samp{read} system call
7926 reads these as zeros. This can both save considerable disk space and
7927 increase speed, since many binary files contain lots of consecutive zero
7928 bytes. By default, @command{cp} detects holes in input source files via a crude
7929 heuristic and makes the corresponding output file sparse as well.
7930 Only regular files may be sparse.
7932 The @var{when} value can be one of the following:
7936 The default behavior: if the input file is sparse, attempt to make
7937 the output file sparse, too. However, if an output file exists but
7938 refers to a non-regular file, then do not attempt to make it sparse.
7941 For each sufficiently long sequence of zero bytes in the input file,
7942 attempt to create a corresponding hole in the output file, even if the
7943 input file does not appear to be sparse.
7944 This is useful when the input file resides on a file system
7945 that does not support sparse files
7946 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7947 but the output file is on a type of file system that does support them.
7948 Holes may be created only in regular files, so if the destination file
7949 is of some other type, @command{cp} does not even try to make it sparse.
7952 Never make the output file sparse.
7953 This is useful in creating a file for use with the @command{mkswap} command,
7954 since such a file must not have any holes.
7957 @optStripTrailingSlashes
7960 @itemx --symbolic-link
7962 @opindex --symbolic-link
7963 @cindex symbolic links, copying with
7964 Make symbolic links instead of copies of non-directories. All source
7965 file names must be absolute (starting with @samp{/}) unless the
7966 destination files are in the current directory. This option merely
7967 results in an error message on systems that do not support symbolic links.
7973 @optNoTargetDirectory
7979 @cindex newer files, copying only
7980 Do not copy a non-directory that has an existing destination with the
7981 same or newer modification time. If time stamps are being preserved,
7982 the comparison is to the source time stamp truncated to the
7983 resolutions of the destination file system and of the system calls
7984 used to update time stamps; this avoids duplicate work if several
7985 @samp{cp -pu} commands are executed with the same source and destination.
7986 If @option{--preserve=links} is also specified (like with @samp{cp -au}
7987 for example), that will take precedence. Consequently, depending on the
7988 order that files are processed from the source, newer files in the destination
7989 may be replaced, to mirror hard links in the source.
7995 Print the name of each file before copying it.
7998 @itemx --one-file-system
8000 @opindex --one-file-system
8001 @cindex file systems, omitting copying to different
8002 Skip subdirectories that are on different file systems from the one that
8003 the copy started on.
8004 However, mount point directories @emph{are} copied.
8012 @section @command{dd}: Convert and copy a file
8015 @cindex converting while copying a file
8017 @command{dd} copies a file (from standard input to standard output, by
8018 default) with a changeable I/O block size, while optionally performing
8019 conversions on it. Synopses:
8022 dd [@var{operand}]@dots{}
8026 The only options are @option{--help} and @option{--version}.
8027 @xref{Common options}. @command{dd} accepts the following operands,
8028 whose syntax was inspired by the DD (data definition) statement of
8035 Read from @var{file} instead of standard input.
8039 Write to @var{file} instead of standard output. Unless
8040 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
8041 bytes (or the size specified with @samp{seek=}).
8043 @item ibs=@var{bytes}
8045 @cindex block size of input
8046 @cindex input block size
8047 Set the input block size to @var{bytes}.
8048 This makes @command{dd} read @var{bytes} per block.
8049 The default is 512 bytes.
8051 @item obs=@var{bytes}
8053 @cindex block size of output
8054 @cindex output block size
8055 Set the output block size to @var{bytes}.
8056 This makes @command{dd} write @var{bytes} per block.
8057 The default is 512 bytes.
8059 @item bs=@var{bytes}
8062 Set both input and output block sizes to @var{bytes}.
8063 This makes @command{dd} read and write @var{bytes} per block,
8064 overriding any @samp{ibs} and @samp{obs} settings.
8065 In addition, if no data-transforming @option{conv} option is specified,
8066 input is copied to the output as soon as it's read,
8067 even if it is smaller than the block size.
8069 @item cbs=@var{bytes}
8071 @cindex block size of conversion
8072 @cindex conversion block size
8073 @cindex fixed-length records, converting to variable-length
8074 @cindex variable-length records, converting to fixed-length
8075 Set the conversion block size to @var{bytes}.
8076 When converting variable-length records to fixed-length ones
8077 (@option{conv=block}) or the reverse (@option{conv=unblock}),
8078 use @var{bytes} as the fixed record length.
8082 Skip @var{n} @samp{ibs}-byte blocks in the input file before copying.
8083 If @samp{iflag=skip_bytes} is specified, @var{n} is interpreted
8084 as a byte count rather than a block count.
8088 Skip @var{n} @samp{obs}-byte blocks in the output file before copying.
8089 if @samp{oflag=seek_bytes} is specified, @var{n} is interpreted
8090 as a byte count rather than a block count.
8094 Copy @var{n} @samp{ibs}-byte blocks from the input file, instead
8095 of everything until the end of the file.
8096 if @samp{iflag=count_bytes} is specified, @var{n} is interpreted
8097 as a byte count rather than a block count.
8098 Note if the input may return short reads as could be the case
8099 when reading from a pipe for example, @samp{iflag=fullblock}
8100 will ensure that @samp{count=} corresponds to complete input blocks
8101 rather than the traditional POSIX specified behavior of counting
8102 input read operations.
8104 @item status=@var{which}
8106 Transfer information is normally output to stderr upon
8107 receipt of the @samp{INFO} signal or when @command{dd} exits.
8108 Specifying @var{which} will identify which information to suppress.
8113 @opindex noxfer @r{dd status=}
8114 Do not print the transfer rate and volume statistics
8115 that normally make up the last status line.
8118 @opindex none @r{dd status=}
8119 Do not print any informational messages to stderr.
8120 Error messages are output as normal.
8124 @item conv=@var{conversion}[,@var{conversion}]@dots{}
8126 Convert the file as specified by the @var{conversion} argument(s).
8127 (No spaces around any comma(s).)
8134 @opindex ascii@r{, converting to}
8135 Convert EBCDIC to ASCII,
8136 using the conversion table specified by POSIX@.
8137 This provides a 1:1 translation for all 256 bytes.
8140 @opindex ebcdic@r{, converting to}
8141 Convert ASCII to EBCDIC@.
8142 This is the inverse of the @samp{ascii} conversion.
8145 @opindex alternate ebcdic@r{, converting to}
8146 Convert ASCII to alternate EBCDIC,
8147 using the alternate conversion table specified by POSIX@.
8148 This is not a 1:1 translation, but reflects common historical practice
8149 for @samp{~}, @samp{[}, and @samp{]}.
8151 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
8155 @opindex block @r{(space-padding)}
8156 For each line in the input, output @samp{cbs} bytes, replacing the
8157 input newline with a space and padding with spaces as necessary.
8161 Remove any trailing spaces in each @samp{cbs}-sized input block,
8162 and append a newline.
8164 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
8167 @opindex lcase@r{, converting to}
8168 Change uppercase letters to lowercase.
8171 @opindex ucase@r{, converting to}
8172 Change lowercase letters to uppercase.
8174 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
8178 Try to seek rather than write NUL output blocks.
8179 On a file system that supports sparse files, this will create
8180 sparse output when extending the output file.
8181 Be careful when using this option in conjunction with
8182 @samp{conv=notrunc} or @samp{oflag=append}.
8183 With @samp{conv=notrunc}, existing data in the output file
8184 corresponding to NUL blocks from the input, will be untouched.
8185 With @samp{oflag=append} the seeks performed will be ineffective.
8186 Similarly, when the output is a device rather than a file,
8187 NUL input blocks are not copied, and therefore this option
8188 is most useful with virtual or pre zeroed devices.
8191 @opindex swab @r{(byte-swapping)}
8192 @cindex byte-swapping
8193 Swap every pair of input bytes. GNU @command{dd}, unlike others, works
8194 when an odd number of bytes are read---the last byte is simply copied
8195 (since there is nothing to swap it with).
8198 @opindex sync @r{(padding with ASCII NULs)}
8199 Pad every input block to size of @samp{ibs} with trailing zero bytes.
8200 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
8205 The following ``conversions'' are really file flags
8206 and don't affect internal processing:
8211 @cindex creating output file, requiring
8212 Fail if the output file already exists; @command{dd} must create the
8217 @cindex creating output file, avoiding
8218 Do not create the output file; the output file must already exist.
8220 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
8224 @cindex truncating output file, avoiding
8225 Do not truncate the output file.
8229 @cindex read errors, ignoring
8230 Continue after read errors.
8234 @cindex synchronized data writes, before finishing
8235 Synchronize output data just before finishing. This forces a physical
8236 write of output data.
8240 @cindex synchronized data and metadata writes, before finishing
8241 Synchronize output data and metadata just before finishing. This
8242 forces a physical write of output data and metadata.
8246 @item iflag=@var{flag}[,@var{flag}]@dots{}
8248 Access the input file using the flags specified by the @var{flag}
8249 argument(s). (No spaces around any comma(s).)
8251 @item oflag=@var{flag}[,@var{flag}]@dots{}
8253 Access the output file using the flags specified by the @var{flag}
8254 argument(s). (No spaces around any comma(s).)
8256 Here are the flags. Not every flag is supported on every operating
8263 @cindex appending to the output file
8264 Write in append mode, so that even if some other process is writing to
8265 this file, every @command{dd} write will append to the current
8266 contents of the file. This flag makes sense only for output.
8267 If you combine this flag with the @samp{of=@var{file}} operand,
8268 you should also specify @samp{conv=notrunc} unless you want the
8269 output file to be truncated before being appended to.
8273 @cindex concurrent I/O
8274 Use concurrent I/O mode for data. This mode performs direct I/O
8275 and drops the POSIX requirement to serialize all I/O to the same file.
8276 A file cannot be opened in CIO mode and with a standard open at the
8282 Use direct I/O for data, avoiding the buffer cache.
8283 Note that the kernel may impose restrictions on read or write buffer sizes.
8284 For example, with an ext4 destination file system and a linux-based kernel,
8285 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
8286 output buffer size is not a multiple of 512.
8290 @cindex directory I/O
8292 Fail unless the file is a directory. Most operating systems do not
8293 allow I/O to a directory, so this flag has limited utility.
8297 @cindex synchronized data reads
8298 Use synchronized I/O for data. For the output file, this forces a
8299 physical write of output data on each write. For the input file,
8300 this flag can matter when reading from a remote file that has been
8301 written to synchronously by some other process. Metadata (e.g.,
8302 last-access and last-modified time) is not necessarily synchronized.
8306 @cindex synchronized data and metadata I/O
8307 Use synchronized I/O for both data and metadata.
8311 @cindex discarding file cache
8312 Discard the data cache for a file.
8313 When count=0 all cache is discarded,
8314 otherwise the cache is dropped for the processed
8315 portion of the file. Also when count=0
8316 failure to discard the cache is diagnosed
8317 and reflected in the exit status.
8318 Here as some usage examples:
8321 # Advise to drop cache for whole file
8322 dd if=ifile iflag=nocache count=0
8324 # Ensure drop cache for the whole file
8325 dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
8327 # Drop cache for part of file
8328 dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
8330 # Stream data using just the read-ahead cache
8331 dd if=ifile of=ofile iflag=nocache oflag=nocache
8336 @cindex nonblocking I/O
8337 Use non-blocking I/O.
8342 Do not update the file's access time.
8343 Some older file systems silently ignore this flag, so it is a good
8344 idea to test it on your files before relying on it.
8348 @cindex controlling terminal
8349 Do not assign the file to be a controlling terminal for @command{dd}.
8350 This has no effect when the file is not a terminal.
8351 On many hosts (e.g., GNU/Linux hosts), this option has no effect
8356 @cindex symbolic links, following
8357 Do not follow symbolic links.
8362 Fail if the file has multiple hard links.
8367 Use binary I/O@. This option has an effect only on nonstandard
8368 platforms that distinguish binary from text I/O.
8373 Use text I/O@. Like @samp{binary}, this option has no effect on
8378 Accumulate full blocks from input. The @code{read} system call
8379 may return early if a full block is not available.
8380 When that happens, continue calling @code{read} to fill the remainder
8382 This flag can be used only with @code{iflag}.
8383 This flag is useful with pipes for example
8384 as they may return short reads. In that case,
8385 this flag is needed to ensure that a @samp{count=} argument is
8386 interpreted as a block count rather than a count of read operations.
8389 @opindex count_bytes
8390 Interpret the @samp{count=} operand as a byte count,
8391 rather than a block count, which allows specifying
8392 a length that is not a multiple of the I/O block size.
8393 This flag can be used only with @code{iflag}.
8397 Interpret the @samp{skip=} operand as a byte count,
8398 rather than a block count, which allows specifying
8399 an offset that is not a multiple of the I/O block size.
8400 This flag can be used only with @code{iflag}.
8404 Interpret the @samp{seek=} operand as a byte count,
8405 rather than a block count, which allows specifying
8406 an offset that is not a multiple of the I/O block size.
8407 This flag can be used only with @code{oflag}.
8411 These flags are not supported on all systems, and @samp{dd} rejects
8412 attempts to use them when they are not supported. When reading from
8413 standard input or writing to standard output, the @samp{nofollow} and
8414 @samp{noctty} flags should not be specified, and the other flags
8415 (e.g., @samp{nonblock}) can affect how other processes behave with the
8416 affected file descriptors, even after @command{dd} exits.
8420 @cindex multipliers after numbers
8421 The numeric-valued strings above (@var{n} and @var{bytes})
8422 can be followed by a multiplier: @samp{b}=512, @samp{c}=1,
8423 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8424 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8426 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8427 should not be too large---values larger than a few megabytes
8428 are generally wasteful or (as in the gigabyte..exabyte case) downright
8429 counterproductive or error-inducing.
8431 To process data that is at an offset or size that is not a
8432 multiple of the I/O@ block size, you can use the @samp{skip_bytes},
8433 @samp{seek_bytes} and @samp{count_bytes} flags. Alternatively
8434 the traditional method of separate @command{dd} invocations can be used.
8435 For example, the following shell commands copy data
8436 in 512 KiB blocks between a disk and a tape, but do not save
8437 or restore a 4 KiB label at the start of the disk:
8440 disk=/dev/rdsk/c0t1d0s2
8443 # Copy all but the label from disk to tape.
8444 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8446 # Copy from tape back to disk, but leave the disk label alone.
8447 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8450 Sending an @samp{INFO} signal to a running @command{dd}
8451 process makes it print I/O statistics to standard error
8452 and then resume copying. In the example below,
8453 @command{dd} is run in the background to copy 10 million blocks.
8454 The @command{kill} command makes it output intermediate I/O statistics,
8455 and when @command{dd} completes normally or is killed by the
8456 @code{SIGINT} signal, it outputs the final statistics.
8459 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8460 $ kill -s INFO $pid; wait $pid
8461 3385223+0 records in
8462 3385223+0 records out
8463 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8464 10000000+0 records in
8465 10000000+0 records out
8466 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8469 @vindex POSIXLY_CORRECT
8470 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8471 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8472 environment variable is set.
8477 @node install invocation
8478 @section @command{install}: Copy files and set attributes
8481 @cindex copying files and setting attributes
8483 @command{install} copies files while setting their file mode bits and, if
8484 possible, their owner and group. Synopses:
8487 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8488 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8489 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8490 install [@var{option}]@dots{} -d @var{directory}@dots{}
8495 If two file names are given, @command{install} copies the first file to the
8499 If the @option{--target-directory} (@option{-t}) option is given, or
8500 failing that if the last file is a directory and the
8501 @option{--no-target-directory} (@option{-T}) option is not given,
8502 @command{install} copies each @var{source} file to the specified
8503 directory, using the @var{source}s' names.
8506 If the @option{--directory} (@option{-d}) option is given,
8507 @command{install} creates each @var{directory} and any missing parent
8508 directories. Parent directories are created with mode
8509 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8510 current umask. @xref{Directory Setuid and Setgid}, for how the
8511 set-user-ID and set-group-ID bits of parent directories are inherited.
8514 @cindex Makefiles, installing programs in
8515 @command{install} is similar to @command{cp}, but allows you to control the
8516 attributes of destination files. It is typically used in Makefiles to
8517 copy programs into their destination directories. It refuses to copy
8518 files onto themselves.
8520 @cindex extended attributes, xattr
8521 @command{install} never preserves extended attributes (xattr).
8523 The program accepts the following options. Also see @ref{Common options}.
8533 Compare each pair of source and destination files, and if the destination has
8534 identical content and any specified owner, group, permissions, and possibly
8535 SELinux context, then do not modify the destination at all.
8539 Ignored; for compatibility with old Unix versions of @command{install}.
8543 Create any missing parent directories of @var{dest},
8544 then copy @var{source} to @var{dest}.
8545 This option is ignored if a destination directory is specified
8546 via @option{--target-directory=DIR}.
8551 @opindex --directory
8552 @cindex directories, creating with given attributes
8553 @cindex parent directories, creating missing
8554 @cindex leading directories, creating missing
8555 Create any missing parent directories, giving them the default
8556 attributes. Then create each given directory, setting their owner,
8557 group and mode as given on the command line or to the defaults.
8559 @item -g @var{group}
8560 @itemx --group=@var{group}
8563 @cindex group ownership of installed files, setting
8564 Set the group ownership of installed files or directories to
8565 @var{group}. The default is the process's current group. @var{group}
8566 may be either a group name or a numeric group ID.
8569 @itemx --mode=@var{mode}
8572 @cindex permissions of installed files, setting
8573 Set the file mode bits for the installed file or directory to @var{mode},
8574 which can be either an octal number, or a symbolic mode as in
8575 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8576 point of departure (@pxref{File permissions}).
8577 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8578 execute for the owner, read and execute for group and other, and with
8579 set-user-ID and set-group-ID disabled.
8580 This default is not quite the same as @samp{755}, since it disables
8581 instead of preserving set-user-ID and set-group-ID on directories.
8582 @xref{Directory Setuid and Setgid}.
8584 @item -o @var{owner}
8585 @itemx --owner=@var{owner}
8588 @cindex ownership of installed files, setting
8589 @cindex appropriate privileges
8590 @vindex root @r{as default owner}
8591 If @command{install} has appropriate privileges (is run as root), set the
8592 ownership of installed files or directories to @var{owner}. The default
8593 is @code{root}. @var{owner} may be either a user name or a numeric user
8596 @item --preserve-context
8597 @opindex --preserve-context
8599 @cindex security context
8600 Preserve the SELinux security context of files and directories.
8601 Failure to preserve the context in all of the files or directories
8602 will result in an exit status of 1. If SELinux is disabled then
8603 print a warning and ignore the option.
8606 @itemx --preserve-timestamps
8608 @opindex --preserve-timestamps
8609 @cindex timestamps of installed files, preserving
8610 Set the time of last access and the time of last modification of each
8611 installed file to match those of each corresponding original file.
8612 When a file is installed without this option, its last access and
8613 last modification times are both set to the time of installation.
8614 This option is useful if you want to use the last modification times
8615 of installed files to keep track of when they were last built as opposed
8616 to when they were last installed.
8622 @cindex symbol table information, stripping
8623 @cindex stripping symbol table information
8624 Strip the symbol tables from installed binary executables.
8626 @item --strip-program=@var{program}
8627 @opindex --strip-program
8628 @cindex symbol table information, stripping, program
8629 Program used to strip binaries.
8635 @optNoTargetDirectory
8641 Print the name of each file before copying it.
8643 @item -Z @var{context}
8644 @itemx --context=@var{context}
8648 @cindex security context
8649 Set the default SELinux security context to be used for any
8650 created files and directories. If SELinux is disabled then
8651 print a warning and ignore the option.
8659 @section @command{mv}: Move (rename) files
8663 @command{mv} moves or renames files (or directories). Synopses:
8666 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8667 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8668 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8673 If two file names are given, @command{mv} moves the first file to the
8677 If the @option{--target-directory} (@option{-t}) option is given, or
8678 failing that if the last file is a directory and the
8679 @option{--no-target-directory} (@option{-T}) option is not given,
8680 @command{mv} moves each @var{source} file to the specified
8681 directory, using the @var{source}s' names.
8684 @command{mv} can move any type of file from one file system to another.
8685 Prior to version @code{4.0} of the fileutils,
8686 @command{mv} could move only regular files between file systems.
8687 For example, now @command{mv} can move an entire directory hierarchy
8688 including special device files from one partition to another. It first
8689 uses some of the same code that's used by @code{cp -a} to copy the
8690 requested directories and files, then (assuming the copy succeeded)
8691 it removes the originals. If the copy fails, then the part that was
8692 copied to the destination partition is removed. If you were to copy
8693 three directories from one partition to another and the copy of the first
8694 directory succeeded, but the second didn't, the first would be left on
8695 the destination partition and the second and third would be left on the
8698 @cindex extended attributes, xattr
8699 @command{mv} always tries to copy extended attributes (xattr), which may
8700 include SELinux context, ACLs or Capabilities.
8701 Upon failure all but @samp{Operation not supported} warnings are output.
8703 @cindex prompting, and @command{mv}
8704 If a destination file exists but is normally unwritable, standard input
8705 is a terminal, and the @option{-f} or @option{--force} option is not given,
8706 @command{mv} prompts the user for whether to replace the file. (You might
8707 own the file, or have write permission on its directory.) If the
8708 response is not affirmative, the file is skipped.
8710 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8711 when it might be a symlink to a directory.
8712 Otherwise, @command{mv} may do something very surprising, since
8713 its behavior depends on the underlying rename system call.
8714 On a system with a modern Linux-based kernel, it fails with
8715 @code{errno=ENOTDIR}@.
8716 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8717 renames not the symlink but rather the directory referenced by the symlink.
8718 @xref{Trailing slashes}.
8720 The program accepts the following options. Also see @ref{Common options}.
8730 @cindex prompts, omitting
8731 Do not prompt the user before removing a destination file.
8733 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8734 options, only the final one takes effect.
8739 @itemx --interactive
8741 @opindex --interactive
8742 @cindex prompts, forcing
8743 Prompt whether to overwrite each existing destination file, regardless
8745 If the response is not affirmative, the file is skipped.
8751 @opindex --no-clobber
8752 @cindex prompts, omitting
8753 Do not overwrite an existing file.
8755 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8761 @cindex newer files, moving only
8762 Do not move a non-directory that has an existing destination with the
8763 same or newer modification time.
8764 If the move is across file system boundaries, the comparison is to the
8765 source time stamp truncated to the resolutions of the destination file
8766 system and of the system calls used to update time stamps; this avoids
8767 duplicate work if several @samp{mv -u} commands are executed with the
8768 same source and destination.
8774 Print the name of each file before moving it.
8776 @optStripTrailingSlashes
8782 @optNoTargetDirectory
8790 @section @command{rm}: Remove files or directories
8793 @cindex removing files or directories
8795 @command{rm} removes each given @var{file}. By default, it does not remove
8796 directories. Synopsis:
8799 rm [@var{option}]@dots{} [@var{file}]@dots{}
8802 @cindex prompting, and @command{rm}
8803 If the @option{-I} or @option{--interactive=once} option is given,
8804 and there are more than three files or the @option{-r}, @option{-R},
8805 or @option{--recursive} are given, then @command{rm} prompts the user
8806 for whether to proceed with the entire operation. If the response is
8807 not affirmative, the entire command is aborted.
8809 Otherwise, if a file is unwritable, standard input is a terminal, and
8810 the @option{-f} or @option{--force} option is not given, or the
8811 @option{-i} or @option{--interactive=always} option @emph{is} given,
8812 @command{rm} prompts the user for whether to remove the file.
8813 If the response is not affirmative, the file is skipped.
8815 Any attempt to remove a file whose last file name component is
8816 @file{.} or @file{..} is rejected without any prompting.
8818 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8819 possible to recover the contents of that file. If you want more assurance
8820 that the contents are truly unrecoverable, consider using @command{shred}.
8822 The program accepts the following options. Also see @ref{Common options}.
8830 @cindex directories, removing
8831 Remove the listed directories if they are empty.
8837 Ignore nonexistent files and missing operands, and never prompt the user.
8838 Ignore any previous @option{--interactive} (@option{-i}) option.
8842 Prompt whether to remove each file.
8843 If the response is not affirmative, the file is skipped.
8844 Ignore any previous @option{--force} (@option{-f}) option.
8845 Equivalent to @option{--interactive=always}.
8849 Prompt once whether to proceed with the command, if more than three
8850 files are named or if a recursive removal is requested. Ignore any
8851 previous @option{--force} (@option{-f}) option. Equivalent to
8852 @option{--interactive=once}.
8854 @item --interactive [=@var{when}]
8855 @opindex --interactive
8856 Specify when to issue an interactive prompt. @var{when} may be
8860 @vindex never @r{interactive option}
8861 - Do not prompt at all.
8863 @vindex once @r{interactive option}
8864 - Prompt once if more than three files are named or if a recursive
8865 removal is requested. Equivalent to @option{-I}.
8867 @vindex always @r{interactive option}
8868 - Prompt for every file being removed. Equivalent to @option{-i}.
8870 @option{--interactive} with no @var{when} is equivalent to
8871 @option{--interactive=always}.
8873 @item --one-file-system
8874 @opindex --one-file-system
8875 @cindex one file system, restricting @command{rm} to
8876 When removing a hierarchy recursively, skip any directory that is on a
8877 file system different from that of the corresponding command line argument.
8880 This option is useful when removing a build ``chroot'' hierarchy,
8881 which normally contains no valuable data. However, it is not uncommon
8882 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8883 use one's start-up file. The catch is that it's easy to forget to
8884 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8885 your normally throw-away chroot, that command will remove everything
8886 under @file{/home}, too.
8887 Use the @option{--one-file-system} option, and it will
8888 warn about and skip directories on other file systems.
8889 Of course, this will not save your @file{/home} if it and your
8890 chroot happen to be on the same file system.
8892 @item --preserve-root
8893 @opindex --preserve-root
8894 @cindex root directory, disallow recursive destruction
8895 Fail upon any attempt to remove the root directory, @file{/},
8896 when used with the @option{--recursive} option.
8897 This is the default behavior.
8898 @xref{Treating / specially}.
8900 @item --no-preserve-root
8901 @opindex --no-preserve-root
8902 @cindex root directory, allow recursive destruction
8903 Do not treat @file{/} specially when removing recursively.
8904 This option is not recommended unless you really want to
8905 remove all the files on your computer.
8906 @xref{Treating / specially}.
8913 @opindex --recursive
8914 @cindex directories, removing (recursively)
8915 Remove the listed directories and their contents recursively.
8921 Print the name of each file before removing it.
8925 @cindex files beginning with @samp{-}, removing
8926 @cindex @samp{-}, removing files beginning with
8927 One common question is how to remove files whose names begin with a
8928 @samp{-}. GNU @command{rm}, like every program that uses the @code{getopt}
8929 function to parse its arguments, lets you use the @samp{--} option to
8930 indicate that all following arguments are non-options. To remove a file
8931 called @file{-f} in the current directory, you could type either:
8944 @opindex - @r{and Unix @command{rm}}
8945 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8946 predates the development of the getopt standard syntax.
8951 @node shred invocation
8952 @section @command{shred}: Remove files more securely
8955 @cindex data, erasing
8956 @cindex erasing data
8958 @command{shred} overwrites devices or files, to help prevent even
8959 very expensive hardware from recovering the data.
8961 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8962 not actually destroyed. Only the index listing where the file is
8963 stored is destroyed, and the storage is made available for reuse.
8964 There are undelete utilities that will attempt to reconstruct the index
8965 and can bring the file back if the parts were not reused.
8967 On a busy system with a nearly-full drive, space can get reused in a few
8968 seconds. But there is no way to know for sure. If you have sensitive
8969 data, you may want to be sure that recovery is not possible by actually
8970 overwriting the file with non-sensitive data.
8972 However, even after doing that, it is possible to take the disk back
8973 to a laboratory and use a lot of sensitive (and expensive) equipment
8974 to look for the faint ``echoes'' of the original data underneath the
8975 overwritten data. If the data has only been overwritten once, it's not
8978 The best way to remove something irretrievably is to destroy the media
8979 it's on with acid, melt it down, or the like. For cheap removable media
8980 like floppy disks, this is the preferred method. However, hard drives
8981 are expensive and hard to melt, so the @command{shred} utility tries
8982 to achieve a similar effect non-destructively.
8984 This uses many overwrite passes, with the data patterns chosen to
8985 maximize the damage they do to the old data. While this will work on
8986 floppies, the patterns are designed for best effect on hard drives.
8987 For more details, see the source code and Peter Gutmann's paper
8988 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8989 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8990 from the proceedings of the Sixth USENIX Security Symposium (San Jose,
8991 California, July 22--25, 1996).
8993 @strong{Please note} that @command{shred} relies on a very important assumption:
8994 that the file system overwrites data in place. This is the traditional
8995 way to do things, but many modern file system designs do not satisfy this
8996 assumption. Exceptions include:
9001 Log-structured or journaled file systems, such as those supplied with
9002 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
9003 BFS, NTFS, etc., when they are configured to journal @emph{data}.
9006 File systems that write redundant data and carry on even if some writes
9007 fail, such as RAID-based file systems.
9010 File systems that make snapshots, such as Network Appliance's NFS server.
9013 File systems that cache in temporary locations, such as NFS version 3
9017 Compressed file systems.
9020 In the particular case of ext3 file systems, the above disclaimer applies (and
9021 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
9022 mode, which journals file data in addition to just metadata. In both
9023 the @code{data=ordered} (default) and @code{data=writeback} modes,
9024 @command{shred} works as usual. Ext3 journaling modes can be changed
9025 by adding the @code{data=something} option to the mount options for a
9026 particular file system in the @file{/etc/fstab} file, as documented in
9027 the mount man page (man mount).
9029 If you are not sure how your file system operates, then you should assume
9030 that it does not overwrite data in place, which means that shred cannot
9031 reliably operate on regular files in your file system.
9033 Generally speaking, it is more reliable to shred a device than a file,
9034 since this bypasses the problem of file system design mentioned above.
9035 However, even shredding devices is not always completely reliable. For
9036 example, most disks map out bad sectors invisibly to the application; if
9037 the bad sectors contain sensitive data, @command{shred} won't be able to
9040 @command{shred} makes no attempt to detect or report this problem, just as
9041 it makes no attempt to do anything about backups. However, since it is
9042 more reliable to shred devices than files, @command{shred} by default does
9043 not truncate or remove the output file. This default is more suitable
9044 for devices, which typically cannot be truncated and should not be
9047 Finally, consider the risk of backups and mirrors.
9048 File system backups and remote mirrors may contain copies of the
9049 file that cannot be removed, and that will allow a shredded file
9050 to be recovered later. So if you keep any data you may later want
9051 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
9054 shred [@var{option}]@dots{} @var{file}[@dots{}]
9057 The program accepts the following options. Also see @ref{Common options}.
9065 @cindex force deletion
9066 Override file permissions if necessary to allow overwriting.
9069 @itemx -n @var{number}
9070 @itemx --iterations=@var{number}
9071 @opindex -n @var{number}
9072 @opindex --iterations=@var{number}
9073 @cindex iterations, selecting the number of
9074 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
9075 overwrite. You can reduce this to save time, or increase it if you think it's
9076 appropriate. After 25 passes all of the internal overwrite patterns will have
9077 been used at least once.
9079 @item --random-source=@var{file}
9080 @opindex --random-source
9081 @cindex random source for shredding
9082 Use @var{file} as a source of random data used to overwrite and to
9083 choose pass ordering. @xref{Random sources}.
9085 @item -s @var{bytes}
9086 @itemx --size=@var{bytes}
9087 @opindex -s @var{bytes}
9088 @opindex --size=@var{bytes}
9089 @cindex size of file to shred
9090 Shred the first @var{bytes} bytes of the file. The default is to shred
9091 the whole file. @var{bytes} can be followed by a size specification like
9092 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
9098 @cindex removing files after shredding
9099 After shredding a file, truncate it (if possible) and then remove it.
9100 If a file has multiple links, only the named links will be removed.
9106 Display to standard error all status updates as sterilization proceeds.
9112 By default, @command{shred} rounds the size of a regular file up to the next
9113 multiple of the file system block size to fully erase the last block
9115 Use @option{--exact} to suppress that behavior.
9116 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
9117 blocks, the resulting file will be 512 bytes long. With this option,
9118 shred does not increase the apparent size of the file.
9124 Normally, the last pass that @command{shred} writes is made up of
9125 random data. If this would be conspicuous on your hard drive (for
9126 example, because it looks like encrypted data), or you just think
9127 it's tidier, the @option{--zero} option adds an additional overwrite pass with
9128 all zero bits. This is in addition to the number of passes specified
9129 by the @option{--iterations} option.
9133 You might use the following command to erase all trace of the
9134 file system you'd created on the floppy disk in your first drive.
9135 That command takes about 20 minutes to erase a ``1.44MB'' (actually
9139 shred --verbose /dev/fd0
9142 Similarly, to erase all data on a selected partition of
9143 your hard disk, you could give a command like this:
9146 shred --verbose /dev/sda5
9149 On modern disks, a single pass should be adequate,
9150 and it will take one third the time of the default three-pass approach.
9153 # 1 pass, write pseudo-random data; 3x faster than the default
9154 shred --verbose -n1 /dev/sda5
9157 To be on the safe side, use at least one pass that overwrites using
9158 pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
9159 in case some disk controller optimizes the process of writing blocks
9160 of all zeros, and thereby does not clear all bytes in a block.
9161 Some SSDs may do just that.
9163 A @var{file} of @samp{-} denotes standard output.
9164 The intended use of this is to shred a removed temporary file.
9171 echo "Hello, world" >&3
9176 However, the command @samp{shred - >file} does not shred the contents
9177 of @var{file}, since the shell truncates @var{file} before invoking
9178 @command{shred}. Use the command @samp{shred file} or (if using a
9179 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
9184 @node Special file types
9185 @chapter Special file types
9187 @cindex special file types
9188 @cindex file types, special
9190 This chapter describes commands which create special types of files (and
9191 @command{rmdir}, which removes directories, one special file type).
9193 @cindex special file types
9195 Although Unix-like operating systems have markedly fewer special file
9196 types than others, not @emph{everything} can be treated only as the
9197 undifferentiated byte stream of @dfn{normal files}. For example, when a
9198 file is created or removed, the system must record this information,
9199 which it does in a @dfn{directory}---a special type of file. Although
9200 you can read directories as normal files, if you're curious, in order
9201 for the system to do its job it must impose a structure, a certain
9202 order, on the bytes of the file. Thus it is a ``special'' type of file.
9204 Besides directories, other special file types include named pipes
9205 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
9208 * link invocation:: Make a hard link via the link syscall
9209 * ln invocation:: Make links between files.
9210 * mkdir invocation:: Make directories.
9211 * mkfifo invocation:: Make FIFOs (named pipes).
9212 * mknod invocation:: Make block or character special files.
9213 * readlink invocation:: Print value of a symlink or canonical file name.
9214 * rmdir invocation:: Remove empty directories.
9215 * unlink invocation:: Remove files via the unlink syscall
9219 @node link invocation
9220 @section @command{link}: Make a hard link via the link syscall
9223 @cindex links, creating
9224 @cindex hard links, creating
9225 @cindex creating links (hard only)
9227 @command{link} creates a single hard link at a time.
9228 It is a minimalist interface to the system-provided
9229 @code{link} function. @xref{Hard Links, , , libc,
9230 The GNU C Library Reference Manual}.
9231 It avoids the bells and whistles of the more commonly-used
9232 @command{ln} command (@pxref{ln invocation}).
9236 link @var{filename} @var{linkname}
9239 @var{filename} must specify an existing file, and @var{linkname}
9240 must specify a nonexistent entry in an existing directory.
9241 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
9244 On a GNU system, this command acts like @samp{ln --directory
9245 --no-target-directory @var{filename} @var{linkname}}. However, the
9246 @option{--directory} and @option{--no-target-directory} options are
9247 not specified by POSIX, and the @command{link} command is
9248 more portable in practice.
9250 If @var{filename} is a symbolic link, it is unspecified whether
9251 @var{linkname} will be a hard link to the symbolic link or to the
9252 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
9253 to specify which behavior is desired.
9259 @section @command{ln}: Make links between files
9262 @cindex links, creating
9263 @cindex hard links, creating
9264 @cindex symbolic (soft) links, creating
9265 @cindex creating links (hard or soft)
9267 @cindex file systems and hard links
9268 @command{ln} makes links between files. By default, it makes hard links;
9269 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
9273 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
9274 ln [@var{option}]@dots{} @var{target}
9275 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
9276 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
9282 If two file names are given, @command{ln} creates a link to the first
9283 file from the second.
9286 If one @var{target} is given, @command{ln} creates a link to that file
9287 in the current directory.
9290 If the @option{--target-directory} (@option{-t}) option is given, or
9291 failing that if the last file is a directory and the
9292 @option{--no-target-directory} (@option{-T}) option is not given,
9293 @command{ln} creates a link to each @var{target} file in the specified
9294 directory, using the @var{target}s' names.
9298 Normally @command{ln} does not remove existing files. Use the
9299 @option{--force} (@option{-f}) option to remove them unconditionally,
9300 the @option{--interactive} (@option{-i}) option to remove them
9301 conditionally, and the @option{--backup} (@option{-b}) option to
9304 @cindex hard link, defined
9305 @cindex inode, and hard links
9306 A @dfn{hard link} is another name for an existing file; the link and the
9307 original are indistinguishable. Technically speaking, they share the
9308 same inode, and the inode contains all the information about a
9309 file---indeed, it is not incorrect to say that the inode @emph{is} the
9310 file. Most systems prohibit making a hard link to
9311 a directory; on those where it is allowed, only the super-user can do
9312 so (and with caution, since creating a cycle will cause problems to many
9313 other utilities). Hard links cannot cross file system boundaries. (These
9314 restrictions are not mandated by POSIX, however.)
9316 @cindex dereferencing symbolic links
9317 @cindex symbolic link, defined
9318 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
9319 a special file type (which not all kernels support: System V release 3
9320 (and older) systems lack symlinks) in which the link file actually
9321 refers to a different file, by name. When most operations (opening,
9322 reading, writing, and so on) are passed the symbolic link file, the
9323 kernel automatically @dfn{dereferences} the link and operates on the
9324 target of the link. But some operations (e.g., removing) work on the
9325 link file itself, rather than on its target. The owner and group of a
9326 symlink are not significant to file access performed through
9327 the link, but do have implications on deleting a symbolic link from a
9328 directory with the restricted deletion bit set. On the GNU system,
9329 the mode of a symlink has no significance and cannot be changed, but
9330 on some BSD systems, the mode can be changed and will affect whether
9331 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
9332 libc, The GNU C Library Reference Manual}.
9334 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
9335 occurs when the string in the symlink does not resolve to a file.
9336 There are no restrictions against creating dangling symbolic links.
9337 There are trade-offs to using absolute or relative symlinks. An
9338 absolute symlink always points to the same file, even if the directory
9339 containing the link is moved. However, if the symlink is visible from
9340 more than one machine (such as on a networked file system), the file
9341 pointed to might not always be the same. A relative symbolic link is
9342 resolved in relation to the directory that contains the link, and is
9343 often useful in referring to files on the same device without regards
9344 to what name that device is mounted on when accessed via networked
9347 When creating a relative symlink in a different location than the
9348 current directory, the resolution of the symlink will be different
9349 than the resolution of the same string from the current directory.
9350 Therefore, many users prefer to first change directories to the
9351 location where the relative symlink will be created, so that
9352 tab-completion or other file resolution will find the same target as
9353 what will be placed in the symlink.
9355 The program accepts the following options. Also see @ref{Common options}.
9366 @opindex --directory
9367 @cindex hard links to directories
9368 Allow users with appropriate privileges to attempt to make hard links
9370 However, note that this will probably fail due to
9371 system restrictions, even for the super-user.
9377 Remove existing destination files.
9380 @itemx --interactive
9382 @opindex --interactive
9383 @cindex prompting, and @command{ln}
9384 Prompt whether to remove existing destination files.
9390 If @option{-s} is not in effect, and the source file is a symbolic
9391 link, create the hard link to the file referred to by the symbolic
9392 link, rather than the symbolic link itself.
9395 @itemx --no-dereference
9397 @opindex --no-dereference
9398 Do not treat the last operand specially when it is a symbolic link to
9399 a directory. Instead, treat it as if it were a normal file.
9401 When the destination is an actual directory (not a symlink to one),
9402 there is no ambiguity. The link is created in that directory.
9403 But when the specified destination is a symlink to a directory,
9404 there are two ways to treat the user's request. @command{ln} can
9405 treat the destination just as it would a normal directory and create
9406 the link in it. On the other hand, the destination can be viewed as a
9407 non-directory---as the symlink itself. In that case, @command{ln}
9408 must delete or backup that symlink before creating the new link.
9409 The default is to treat a destination that is a symlink to a directory
9410 just like a directory.
9412 This option is weaker than the @option{--no-target-directory}
9413 (@option{-T}) option, so it has no effect if both options are given.
9419 If @option{-s} is not in effect, and the source file is a symbolic
9420 link, create the hard link to the symbolic link itself. On platforms
9421 where this is not supported by the kernel, this option creates a
9422 symbolic link with identical contents; since symbolic link contents
9423 cannot be edited, any file name resolution performed through either
9424 link will be the same as if a hard link had been created.
9430 Make symbolic links relative to the link location.
9435 ln -srv /a/file /tmp
9436 '/tmp/file' -> '../a/file'
9439 @xref{realpath invocation}, which gives greater control
9440 over relative file name generation.
9446 Make symbolic links instead of hard links. This option merely produces
9447 an error message on systems that do not support symbolic links.
9453 @optNoTargetDirectory
9459 Print the name of each file after linking it successfully.
9463 @cindex hard links to symbolic links
9464 @cindex symbolic links and @command{ln}
9465 If @option{-L} and @option{-P} are both given, the last one takes
9466 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9467 are silently ignored. If neither option is given, then this
9468 implementation defaults to @option{-P} if the system @code{link} supports
9469 hard links to symbolic links (such as the GNU system), and @option{-L}
9470 if @code{link} follows symbolic links (such as on BSD).
9479 # Create link ../a pointing to a in that directory.
9480 # Not really useful because it points to itself.
9485 # Change to the target before creating symlinks to avoid being confused.
9491 # Hard coded file names don't move well.
9492 ln -s $(pwd)/a /some/dir/
9496 # Relative file names survive directory moves and also
9497 # work across networked file systems.
9498 ln -s afile anotherfile
9499 ln -s ../adir/afile yetanotherfile
9503 @node mkdir invocation
9504 @section @command{mkdir}: Make directories
9507 @cindex directories, creating
9508 @cindex creating directories
9510 @command{mkdir} creates directories with the specified names. Synopsis:
9513 mkdir [@var{option}]@dots{} @var{name}@dots{}
9516 @command{mkdir} creates each directory @var{name} in the order given.
9517 It reports an error if @var{name} already exists, unless the
9518 @option{-p} option is given and @var{name} is a directory.
9520 The program accepts the following options. Also see @ref{Common options}.
9525 @itemx --mode=@var{mode}
9528 @cindex modes of created directories, setting
9529 Set the file permission bits of created directories to @var{mode},
9530 which uses the same syntax as
9531 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9532 everyone) for the point of the departure. @xref{File permissions}.
9534 Normally the directory has the desired file mode bits at the moment it
9535 is created. As a GNU extension, @var{mode} may also mention
9536 special mode bits, but in this case there may be a temporary window
9537 during which the directory exists but its special mode bits are
9538 incorrect. @xref{Directory Setuid and Setgid}, for how the
9539 set-user-ID and set-group-ID bits of directories are inherited unless
9540 overridden in this way.
9546 @cindex parent directories, creating
9547 Make any missing parent directories for each argument, setting their
9548 file permission bits to the umask modified by @samp{u+wx}. Ignore
9549 existing parent directories, and do not change their file permission
9552 To set the file permission bits of any newly-created parent
9553 directories to a value that includes @samp{u+wx}, you can set the
9554 umask before invoking @command{mkdir}. For example, if the shell
9555 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9556 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9557 To set a parent's special mode bits as well, you can invoke
9558 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9559 Setgid}, for how the set-user-ID and set-group-ID bits of
9560 newly-created parent directories are inherited.
9566 Print a message for each created directory. This is most useful with
9569 @item -Z @var{context}
9570 @itemx --context=@var{context}
9574 @cindex security context
9575 Set the default SELinux security context to be used for created directories.
9582 @node mkfifo invocation
9583 @section @command{mkfifo}: Make FIFOs (named pipes)
9586 @cindex FIFOs, creating
9587 @cindex named pipes, creating
9588 @cindex creating FIFOs (named pipes)
9590 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9591 specified names. Synopsis:
9594 mkfifo [@var{option}] @var{name}@dots{}
9597 A @dfn{FIFO} is a special file type that permits independent processes
9598 to communicate. One process opens the FIFO file for writing, and
9599 another for reading, after which data can flow as with the usual
9600 anonymous pipe in shells or elsewhere.
9602 The program accepts the following option. Also see @ref{Common options}.
9607 @itemx --mode=@var{mode}
9610 @cindex modes of created FIFOs, setting
9611 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9612 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9613 for the point of departure. @var{mode} should specify only file
9614 permission bits. @xref{File permissions}.
9616 @item -Z @var{context}
9617 @itemx --context=@var{context}
9621 @cindex security context
9622 Set the default SELinux security context to be used for created FIFOs.
9629 @node mknod invocation
9630 @section @command{mknod}: Make block or character special files
9633 @cindex block special files, creating
9634 @cindex character special files, creating
9636 @command{mknod} creates a FIFO, character special file, or block special
9637 file with the specified name. Synopsis:
9640 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9643 @cindex special files
9644 @cindex block special files
9645 @cindex character special files
9646 Unlike the phrase ``special file type'' above, the term @dfn{special
9647 file} has a technical meaning on Unix: something that can generate or
9648 receive data. Usually this corresponds to a physical piece of hardware,
9649 e.g., a printer or a disk. (These files are typically created at
9650 system-configuration time.) The @command{mknod} command is what creates
9651 files of this type. Such devices can be read either a character at a
9652 time or a ``block'' (many characters) at a time, hence we say there are
9653 @dfn{block special} files and @dfn{character special} files.
9655 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9656 @mayConflictWithShellBuiltIn{mknod}
9658 The arguments after @var{name} specify the type of file to make:
9663 @opindex p @r{for FIFO file}
9667 @opindex b @r{for block special file}
9668 for a block special file
9671 @c Don't document the 'u' option -- it's just a synonym for 'c'.
9672 @c Do *any* versions of mknod still use it?
9674 @opindex c @r{for character special file}
9675 @c @opindex u @r{for character special file}
9676 for a character special file
9680 When making a block or character special file, the major and minor
9681 device numbers must be given after the file type.
9682 If a major or minor device number begins with @samp{0x} or @samp{0X},
9683 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9684 as octal; otherwise, as decimal.
9686 The program accepts the following option. Also see @ref{Common options}.
9691 @itemx --mode=@var{mode}
9694 Set the mode of created files to @var{mode}, which is symbolic as in
9695 @command{chmod} and uses @samp{a=rw} as the point of departure.
9696 @var{mode} should specify only file permission bits.
9697 @xref{File permissions}.
9699 @item -Z @var{context}
9700 @itemx --context=@var{context}
9704 @cindex security context
9705 Set the default SELinux security context to be used for created files.
9712 @node readlink invocation
9713 @section @command{readlink}: Print value of a symlink or canonical file name
9716 @cindex displaying value of a symbolic link
9717 @cindex canonical file name
9718 @cindex canonicalize a file name
9721 @command{readlink} may work in one of two supported modes:
9727 @command{readlink} outputs the value of the given symbolic links.
9728 If @command{readlink} is invoked with an argument other than the name
9729 of a symbolic link, it produces no output and exits with a nonzero exit code.
9731 @item Canonicalize mode
9733 @command{readlink} outputs the absolute name of the given files which contain
9734 no @file{.}, @file{..} components nor any repeated separators
9735 (@file{/}) or symbolic links.
9740 readlink [@var{option}]@dots{} @var{file}@dots{}
9743 By default, @command{readlink} operates in readlink mode.
9745 The program accepts the following options. Also see @ref{Common options}.
9750 @itemx --canonicalize
9752 @opindex --canonicalize
9753 Activate canonicalize mode.
9754 If any component of the file name except the last one is missing or unavailable,
9755 @command{readlink} produces no output and exits with a nonzero exit
9756 code. A trailing slash is ignored.
9759 @itemx --canonicalize-existing
9761 @opindex --canonicalize-existing
9762 Activate canonicalize mode.
9763 If any component is missing or unavailable, @command{readlink} produces
9764 no output and exits with a nonzero exit code. A trailing slash
9765 requires that the name resolve to a directory.
9768 @itemx --canonicalize-missing
9770 @opindex --canonicalize-missing
9771 Activate canonicalize mode.
9772 If any component is missing or unavailable, @command{readlink} treats it
9778 @opindex --no-newline
9779 Do not print the output delimiter, when a single @var{file} is specified.
9780 Print a warning if specified along with multiple @var{file}s.
9790 Suppress most error messages.
9796 Report error messages.
9802 Separate output items with NUL characters.
9806 The @command{readlink} utility first appeared in OpenBSD 2.1.
9808 The @command{realpath} command without options, operates like
9809 @command{readlink} in canonicalize mode.
9814 @node rmdir invocation
9815 @section @command{rmdir}: Remove empty directories
9818 @cindex removing empty directories
9819 @cindex directories, removing empty
9821 @command{rmdir} removes empty directories. Synopsis:
9824 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9827 If any @var{directory} argument does not refer to an existing empty
9828 directory, it is an error.
9830 The program accepts the following options. Also see @ref{Common options}.
9834 @item --ignore-fail-on-non-empty
9835 @opindex --ignore-fail-on-non-empty
9836 @cindex directory deletion, ignoring failures
9837 Ignore each failure to remove a directory that is solely because
9838 the directory is non-empty.
9844 @cindex parent directories, removing
9845 Remove @var{directory}, then try to remove each component of @var{directory}.
9846 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9847 As such, it fails if any of those directories turns out not to be empty.
9848 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9849 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9850 exit unsuccessfully.
9856 @cindex directory deletion, reporting
9857 Give a diagnostic for each successful removal.
9858 @var{directory} is removed.
9862 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9867 @node unlink invocation
9868 @section @command{unlink}: Remove files via the unlink syscall
9871 @cindex removing files or directories (via the unlink syscall)
9873 @command{unlink} deletes a single specified file name.
9874 It is a minimalist interface to the system-provided
9875 @code{unlink} function. @xref{Deleting Files, , , libc,
9876 The GNU C Library Reference Manual}. Synopsis:
9877 It avoids the bells and whistles of the more commonly-used
9878 @command{rm} command (@pxref{rm invocation}).
9881 unlink @var{filename}
9884 On some systems @code{unlink} can be used to delete the name of a
9885 directory. On others, it can be used that way only by a privileged user.
9886 In the GNU system @code{unlink} can never delete the name of a directory.
9888 The @command{unlink} command honors the @option{--help} and
9889 @option{--version} options. To remove a file whose name begins with
9890 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9895 @node Changing file attributes
9896 @chapter Changing file attributes
9898 @cindex changing file attributes
9899 @cindex file attributes, changing
9900 @cindex attributes, file
9902 A file is not merely its contents, a name, and a file type
9903 (@pxref{Special file types}). A file also has an owner (a user ID), a
9904 group (a group ID), permissions (what the owner can do with the file,
9905 what people in the group can do, and what everyone else can do), various
9906 timestamps, and other information. Collectively, we call these a file's
9909 These commands change file attributes.
9912 * chown invocation:: Change file owners and groups.
9913 * chgrp invocation:: Change file groups.
9914 * chmod invocation:: Change access permissions.
9915 * touch invocation:: Change file timestamps.
9919 @node chown invocation
9920 @section @command{chown}: Change file owner and group
9923 @cindex file ownership, changing
9924 @cindex group ownership, changing
9925 @cindex changing file ownership
9926 @cindex changing group ownership
9928 @command{chown} changes the user and/or group ownership of each given @var{file}
9929 to @var{new-owner} or to the user and group of an existing reference file.
9933 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
9937 If used, @var{new-owner} specifies the new owner and/or group as follows
9938 (with no embedded white space):
9941 [@var{owner}] [ : [@var{group}] ]
9948 If only an @var{owner} (a user name or numeric user ID) is given, that
9949 user is made the owner of each given file, and the files' group is not
9952 @item owner@samp{:}group
9953 If the @var{owner} is followed by a colon and a @var{group} (a
9954 group name or numeric group ID), with no spaces between them, the group
9955 ownership of the files is changed as well (to @var{group}).
9958 If a colon but no group name follows @var{owner}, that user is
9959 made the owner of the files and the group of the files is changed to
9960 @var{owner}'s login group.
9963 If the colon and following @var{group} are given, but the owner
9964 is omitted, only the group of the files is changed; in this case,
9965 @command{chown} performs the same function as @command{chgrp}.
9968 If only a colon is given, or if @var{new-owner} is empty, neither the
9969 owner nor the group is changed.
9973 If @var{owner} or @var{group} is intended to represent a numeric user
9974 or group ID, then you may specify it with a leading @samp{+}.
9975 @xref{Disambiguating names and IDs}.
9977 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9978 POSIX 1003.1-2001 (@pxref{Standards conformance}) does not
9979 require support for that, but for backward compatibility GNU
9980 @command{chown} supports @samp{.} so long as no ambiguity results.
9981 New scripts should avoid the use of @samp{.} because it is not
9982 portable, and because it has undesirable results if the entire
9983 @var{owner@samp{.}group} happens to identify a user whose name
9986 The @command{chown} command sometimes clears the set-user-ID or
9987 set-group-ID permission bits. This behavior depends on the policy and
9988 functionality of the underlying @code{chown} system call, which may
9989 make system-dependent file mode modifications outside the control of
9990 the @command{chown} command. For example, the @command{chown} command
9991 might not affect those bits when invoked by a user with appropriate
9992 privileges, or when the
9993 bits signify some function other than executable permission (e.g.,
9995 When in doubt, check the underlying system behavior.
9997 The program accepts the following options. Also see @ref{Common options}.
10005 @cindex changed owners, verbosely describing
10006 Verbosely describe the action for each @var{file} whose ownership
10015 @cindex error messages, omitting
10016 Do not print error messages about files whose ownership cannot be
10019 @item @w{@kbd{--from}=@var{old-owner}}
10021 @cindex symbolic links, changing owner
10022 Change a @var{file}'s ownership only if it has current attributes specified
10023 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
10025 This option is useful primarily from a security standpoint in that
10026 it narrows considerably the window of potential abuse.
10027 For example, to reflect a user ID numbering change for one user's files
10028 without an option like this, @code{root} might run
10031 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
10034 But that is dangerous because the interval between when the @command{find}
10035 tests the existing file's owner and when the @command{chown} is actually run
10036 may be quite large.
10037 One way to narrow the gap would be to invoke chown for each file
10041 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
10044 But that is very slow if there are many affected files.
10045 With this option, it is safer (the gap is narrower still)
10046 though still not perfect:
10049 chown -h -R --from=OLDUSER NEWUSER /
10052 @item --dereference
10053 @opindex --dereference
10054 @cindex symbolic links, changing owner
10056 Do not act on symbolic links themselves but rather on what they point to.
10057 This is the default.
10060 @itemx --no-dereference
10062 @opindex --no-dereference
10063 @cindex symbolic links, changing owner
10065 Act on symbolic links themselves instead of what they point to.
10066 This mode relies on the @code{lchown} system call.
10067 On systems that do not provide the @code{lchown} system call,
10068 @command{chown} fails when a file specified on the command line
10069 is a symbolic link.
10070 By default, no diagnostic is issued for symbolic links encountered
10071 during a recursive traversal, but see @option{--verbose}.
10073 @item --preserve-root
10074 @opindex --preserve-root
10075 @cindex root directory, disallow recursive modification
10076 Fail upon any attempt to recursively change the root directory, @file{/}.
10077 Without @option{--recursive}, this option has no effect.
10078 @xref{Treating / specially}.
10080 @item --no-preserve-root
10081 @opindex --no-preserve-root
10082 @cindex root directory, allow recursive modification
10083 Cancel the effect of any preceding @option{--preserve-root} option.
10084 @xref{Treating / specially}.
10086 @item --reference=@var{ref_file}
10087 @opindex --reference
10088 Change the user and group of each @var{file} to be the same as those of
10089 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10090 user and group of the symbolic link, but rather those of the file it
10097 Output a diagnostic for every file processed.
10098 If a symbolic link is encountered during a recursive traversal
10099 on a system without the @code{lchown} system call, and @option{--no-dereference}
10100 is in effect, then issue a diagnostic saying neither the symbolic link nor
10101 its referent is being changed.
10106 @opindex --recursive
10107 @cindex recursively changing file ownership
10108 Recursively change ownership of directories and their contents.
10111 @xref{Traversing symlinks}.
10114 @xref{Traversing symlinks}.
10117 @xref{Traversing symlinks}.
10126 # Change the owner of /u to "root".
10129 # Likewise, but also change its group to "staff".
10130 chown root:staff /u
10132 # Change the owner of /u and subfiles to "root".
10137 @node chgrp invocation
10138 @section @command{chgrp}: Change group ownership
10141 @cindex group ownership, changing
10142 @cindex changing group ownership
10144 @command{chgrp} changes the group ownership of each given @var{file}
10145 to @var{group} (which can be either a group name or a numeric group ID)
10146 or to the group of an existing reference file. Synopsis:
10149 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
10153 If @var{group} is intended to represent a
10154 numeric group ID, then you may specify it with a leading @samp{+}.
10155 @xref{Disambiguating names and IDs}.
10157 The program accepts the following options. Also see @ref{Common options}.
10165 @cindex changed files, verbosely describing
10166 Verbosely describe the action for each @var{file} whose group actually
10175 @cindex error messages, omitting
10176 Do not print error messages about files whose group cannot be
10179 @item --dereference
10180 @opindex --dereference
10181 @cindex symbolic links, changing owner
10183 Do not act on symbolic links themselves but rather on what they point to.
10184 This is the default.
10187 @itemx --no-dereference
10189 @opindex --no-dereference
10190 @cindex symbolic links, changing group
10192 Act on symbolic links themselves instead of what they point to.
10193 This mode relies on the @code{lchown} system call.
10194 On systems that do not provide the @code{lchown} system call,
10195 @command{chgrp} fails when a file specified on the command line
10196 is a symbolic link.
10197 By default, no diagnostic is issued for symbolic links encountered
10198 during a recursive traversal, but see @option{--verbose}.
10200 @item --preserve-root
10201 @opindex --preserve-root
10202 @cindex root directory, disallow recursive modification
10203 Fail upon any attempt to recursively change the root directory, @file{/}.
10204 Without @option{--recursive}, this option has no effect.
10205 @xref{Treating / specially}.
10207 @item --no-preserve-root
10208 @opindex --no-preserve-root
10209 @cindex root directory, allow recursive modification
10210 Cancel the effect of any preceding @option{--preserve-root} option.
10211 @xref{Treating / specially}.
10213 @item --reference=@var{ref_file}
10214 @opindex --reference
10215 Change the group of each @var{file} to be the same as that of
10216 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10217 group of the symbolic link, but rather that of the file it refers to.
10223 Output a diagnostic for every file processed.
10224 If a symbolic link is encountered during a recursive traversal
10225 on a system without the @code{lchown} system call, and @option{--no-dereference}
10226 is in effect, then issue a diagnostic saying neither the symbolic link nor
10227 its referent is being changed.
10232 @opindex --recursive
10233 @cindex recursively changing group ownership
10234 Recursively change the group ownership of directories and their contents.
10237 @xref{Traversing symlinks}.
10240 @xref{Traversing symlinks}.
10243 @xref{Traversing symlinks}.
10252 # Change the group of /u to "staff".
10255 # Change the group of /u and subfiles to "staff".
10260 @node chmod invocation
10261 @section @command{chmod}: Change access permissions
10264 @cindex changing access permissions
10265 @cindex access permissions, changing
10266 @cindex permissions, changing access
10268 @command{chmod} changes the access permissions of the named files. Synopsis:
10271 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
10275 @cindex symbolic links, permissions of
10276 @command{chmod} never changes the permissions of symbolic links, since
10277 the @command{chmod} system call cannot change their permissions.
10278 This is not a problem since the permissions of symbolic links are
10279 never used. However, for each symbolic link listed on the command
10280 line, @command{chmod} changes the permissions of the pointed-to file.
10281 In contrast, @command{chmod} ignores symbolic links encountered during
10282 recursive directory traversals.
10284 A successful use of @command{chmod} clears the set-group-ID bit of a
10285 regular file if the file's group ID does not match the user's
10286 effective group ID or one of the user's supplementary group IDs,
10287 unless the user has appropriate privileges. Additional restrictions
10288 may cause the set-user-ID and set-group-ID bits of @var{mode} or
10289 @var{ref_file} to be ignored. This behavior depends on the policy and
10290 functionality of the underlying @code{chmod} system call. When in
10291 doubt, check the underlying system behavior.
10293 If used, @var{mode} specifies the new file mode bits.
10294 For details, see the section on @ref{File permissions}.
10295 If you really want @var{mode} to have a leading @samp{-}, you should
10296 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
10297 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
10298 file} (without the @option{--}) complains if it behaves differently
10299 from what @samp{chmod a-w file} would do.
10301 The program accepts the following options. Also see @ref{Common options}.
10309 Verbosely describe the action for each @var{file} whose permissions
10318 @cindex error messages, omitting
10319 Do not print error messages about files whose permissions cannot be
10322 @item --preserve-root
10323 @opindex --preserve-root
10324 @cindex root directory, disallow recursive modification
10325 Fail upon any attempt to recursively change the root directory, @file{/}.
10326 Without @option{--recursive}, this option has no effect.
10327 @xref{Treating / specially}.
10329 @item --no-preserve-root
10330 @opindex --no-preserve-root
10331 @cindex root directory, allow recursive modification
10332 Cancel the effect of any preceding @option{--preserve-root} option.
10333 @xref{Treating / specially}.
10339 Verbosely describe the action or non-action taken for every @var{file}.
10341 @item --reference=@var{ref_file}
10342 @opindex --reference
10343 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
10344 @xref{File permissions}.
10345 If @var{ref_file} is a symbolic link, do not use the mode
10346 of the symbolic link, but rather that of the file it refers to.
10351 @opindex --recursive
10352 @cindex recursively changing access permissions
10353 Recursively change permissions of directories and their contents.
10360 @node touch invocation
10361 @section @command{touch}: Change file timestamps
10364 @cindex changing file timestamps
10365 @cindex file timestamps, changing
10366 @cindex timestamps, changing file
10368 @command{touch} changes the access and/or modification times of the
10369 specified files. Synopsis:
10372 touch [@var{option}]@dots{} @var{file}@dots{}
10375 @cindex empty files, creating
10376 Any @var{file} argument that does not exist is created empty, unless
10377 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
10378 (@option{-h}) was in effect.
10380 A @var{file} argument string of @samp{-} is handled specially and
10381 causes @command{touch} to change the times of the file associated with
10385 By default, @command{touch} sets file timestamps to the current time.
10386 Because @command{touch} acts on its operands left to right, the
10387 resulting timestamps of earlier and later operands may disagree.
10388 Also, the determination of what time is ``current'' depends on the
10389 platform. Platforms with network file systems often use different
10390 clocks for the operating system and for file systems; because
10391 @command{touch} typically uses file systems' clocks by default, clock
10392 skew can cause the resulting file timestamps to appear to be in a
10393 program's ``future'' or ``past''.
10395 @cindex file timestamp resolution
10396 The @command{touch} command sets the file's timestamp to the greatest
10397 representable value that is not greater than the requested time. This
10398 can differ from the requested time for several reasons. First, the
10399 requested time may have a higher resolution than supported. Second, a
10400 file system may use different resolutions for different types of
10401 times. Third, file timestamps may use a different resolution than
10402 operating system timestamps. Fourth, the operating system primitives
10403 used to update timestamps may employ yet a different resolution. For
10404 example, in theory a file system might use 10-microsecond resolution
10405 for access time and 100-nanosecond resolution for modification time,
10406 and the operating system might use nanosecond resolution for the
10407 current time and microsecond resolution for the primitive that
10408 @command{touch} uses to set a file's timestamp to an arbitrary value.
10410 @cindex permissions, for changing file timestamps
10411 When setting file timestamps to the current time, @command{touch} can
10412 change the timestamps for files that the user does not own but has
10413 write permission for. Otherwise, the user must own the files. Some
10414 older systems have a further restriction: the user must own the files
10415 unless both the access and modification times are being set to the
10418 Although @command{touch} provides options for changing two of the times---the
10419 times of last access and modification---of a file, there is actually
10420 a standard third one as well: the inode change time. This is often
10421 referred to as a file's @code{ctime}.
10422 The inode change time represents the time when the file's meta-information
10423 last changed. One common example of this is when the permissions of a
10424 file change. Changing the permissions doesn't access the file, so
10425 the atime doesn't change, nor does it modify the file, so the mtime
10426 doesn't change. Yet, something about the file itself has changed,
10427 and this must be noted somewhere. This is the job of the ctime field.
10428 This is necessary, so that, for example, a backup program can make a
10429 fresh copy of the file, including the new permissions value.
10430 Another operation that modifies a file's ctime without affecting
10431 the others is renaming. In any case, it is not possible, in normal
10432 operations, for a user to change the ctime field to a user-specified value.
10433 Some operating systems and file systems support a fourth time: the
10434 birth time, when the file was first created; by definition, this
10435 timestamp never changes.
10438 Time stamps assume the time zone rules specified by the @env{TZ}
10439 environment variable, or by the system default rules if @env{TZ} is
10440 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
10441 libc, The GNU C Library Reference Manual}.
10442 You can avoid ambiguities during
10443 daylight saving transitions by using UTC time stamps.
10445 The program accepts the following options. Also see @ref{Common options}.
10450 @itemx --time=atime
10451 @itemx --time=access
10455 @opindex atime@r{, changing}
10456 @opindex access @r{time, changing}
10457 @opindex use @r{time, changing}
10458 Change the access time only.
10463 @opindex --no-create
10464 Do not warn about or create files that do not exist.
10467 @itemx --date=@var{time}
10471 Use @var{time} instead of the current time. It can contain month names,
10472 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10473 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10474 specifies the instant of time that is 489,392,193 nanoseconds after
10475 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10476 minutes east of UTC@. @xref{Date input formats}.
10477 File systems that do not support high-resolution time stamps
10478 silently ignore any excess precision here.
10482 @cindex BSD @command{touch} compatibility
10483 Ignored; for compatibility with BSD versions of @command{touch}.
10486 @itemx --no-dereference
10488 @opindex --no-dereference
10489 @cindex symbolic links, changing time
10491 Attempt to change the timestamps of a symbolic link, rather than what
10492 the link refers to. When using this option, empty files are not
10493 created, but option @option{-c} must also be used to avoid warning
10494 about files that do not exist. Not all systems support changing the
10495 timestamps of symlinks, since underlying system support for this
10496 action was not required until POSIX 2008. Also, on some
10497 systems, the mere act of examining a symbolic link changes the access
10498 time, such that only changes to the modification time will persist
10499 long enough to be observable. When coupled with option @option{-r}, a
10500 reference timestamp is taken from a symbolic link rather than the file
10504 @itemx --time=mtime
10505 @itemx --time=modify
10508 @opindex mtime@r{, changing}
10509 @opindex modify @r{time, changing}
10510 Change the modification time only.
10512 @item -r @var{file}
10513 @itemx --reference=@var{file}
10515 @opindex --reference
10516 Use the times of the reference @var{file} instead of the current time.
10517 If this option is combined with the @option{--date=@var{time}}
10518 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10519 the origin for any relative @var{time}s given, but is otherwise ignored.
10520 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10521 equal to five seconds before the corresponding time stamp for @file{foo}.
10522 If @var{file} is a symbolic link, the reference timestamp is taken
10523 from the target of the symlink, unless @option{-h} was also in effect.
10525 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10526 @cindex leap seconds
10527 Use the argument (optional four-digit or two-digit years, months,
10528 days, hours, minutes, optional seconds) instead of the current time.
10529 If the year is specified with only two digits, then @var{cc}
10530 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10531 69 @dots{} 99. If no digits of the year are specified,
10532 the argument is interpreted as a date in the current year.
10533 On the atypical systems that support leap seconds, @var{ss} may be
10538 @vindex _POSIX2_VERSION
10539 On older systems, @command{touch} supports an obsolete syntax, as follows.
10540 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10541 @option{-t} options, and if there are two or more @var{file}s and the
10542 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10543 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10544 any, were moved to the front), and if the represented year
10545 is in the range 1969--1999, that argument is interpreted as the time
10546 for the other files instead of as a file name.
10547 This obsolete behavior can be enabled or disabled with the
10548 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10549 conformance}), but portable scripts should avoid commands whose
10550 behavior depends on this variable.
10551 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10552 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10558 @chapter Disk usage
10562 No disk can hold an infinite amount of data. These commands report
10563 how much disk storage is in use or available, report other file and
10564 file status information, and write buffers to disk.
10567 * df invocation:: Report file system disk space usage.
10568 * du invocation:: Estimate file space usage.
10569 * stat invocation:: Report file or file system status.
10570 * sync invocation:: Synchronize memory and disk.
10571 * truncate invocation:: Shrink or extend the size of a file.
10575 @node df invocation
10576 @section @command{df}: Report file system disk space usage
10579 @cindex file system disk usage
10580 @cindex disk usage by file system
10582 @command{df} reports the amount of disk space used and available on
10583 file systems. Synopsis:
10586 df [@var{option}]@dots{} [@var{file}]@dots{}
10589 With no arguments, @command{df} reports the space used and available on all
10590 currently mounted file systems (of all types). Otherwise, @command{df}
10591 reports on the file system containing each argument @var{file}.
10593 Normally the disk space is printed in units of
10594 1024 bytes, but this can be overridden (@pxref{Block size}).
10595 Non-integer quantities are rounded up to the next higher unit.
10597 For bind mounts and without arguments, @command{df} only outputs the statistics
10598 for that device with the shortest mount point name in the list of file systems
10599 (@var{mtab}), i.e., it hides duplicate entries, unless the @option{-a} option is
10602 With the same logic, @command{df} elides a mount entry of a dummy pseude device
10603 if there is another mount entry of a real block device for that mount point with
10604 the same device number, e.g. the early-boot pseudo file system @samp{rootfs} is
10605 not shown per default when already the real root device has been mounted.
10607 @cindex disk device file
10608 @cindex device file, disk
10609 If an argument @var{file} is a disk device file containing a mounted
10610 file system, @command{df} shows the space available on that file system
10611 rather than on the file system containing the device node (i.e., the root
10612 file system). GNU @command{df} does not attempt to determine the
10614 on unmounted file systems, because on most kinds of systems doing so
10615 requires extremely nonportable intimate knowledge of file system
10618 The program accepts the following options. Also see @ref{Common options}.
10626 @cindex automounter file systems
10627 @cindex ignore file systems
10628 Include in the listing dummy file systems, which
10629 are omitted by default. Such file systems are typically special-purpose
10630 pseudo-file-systems, such as automounter entries.
10632 @item -B @var{size}
10633 @itemx --block-size=@var{size}
10635 @opindex --block-size
10636 @cindex file system sizes
10637 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10638 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10642 @cindex grand total of disk size, usage and available space
10643 Print a grand total of all arguments after all arguments have
10644 been processed. This can be used to find out the total disk size, usage
10645 and available space of all listed devices.
10647 For the grand total line, @command{df} prints @samp{"total"} into the
10648 @var{source} column, and @samp{"-"} into the @var{target} column.
10649 If there is no @var{source} column (see @option{--output}), then
10650 @command{df} prints @samp{"total"} into the @var{target} column,
10657 Equivalent to @option{--si}.
10663 @cindex inode usage
10664 List inode usage information instead of block usage. An inode (short
10665 for index node) contains information about a file such as its owner,
10666 permissions, timestamps, and location on the disk.
10670 @cindex kibibytes for file system sizes
10671 Print sizes in 1024-byte blocks, overriding the default block size
10672 (@pxref{Block size}).
10673 This option is equivalent to @option{--block-size=1K}.
10679 @cindex file system types, limiting output to certain
10680 Limit the listing to local file systems. By default, remote file systems
10685 @cindex file system space, retrieving old data more quickly
10686 Do not invoke the @code{sync} system call before getting any usage data.
10687 This may make @command{df} run significantly faster on systems with many
10688 disks, but on some systems (notably SunOS) the results may be slightly
10689 out of date. This is the default.
10692 @itemx @w{@kbd{--output}[=@var{field_list}]}
10694 Use the output format defined by @var{field_list}, or print all fields if
10695 @var{field_list} is omitted. In the latter case, the order of the columns
10696 conforms to the order of the field descriptions below.
10698 The use of the @option{--output} together with each of the options @option{-i},
10699 @option{-P}, and @option{-T} is mutually exclusive.
10701 FIELD_LIST is a comma-separated list of columns to be included in @command{df}'s
10702 output and therefore effectively controls the order of output columns.
10703 Each field can thus be used at the place of choice, but yet must only be
10706 Valid field names in the @var{field_list} are:
10709 The source of the mount point, usually a device.
10714 Total number of inodes.
10716 Number of used inodes.
10718 Number of available inodes.
10720 Percentage of @var{iused} divided by @var{itotal}.
10723 Total number of blocks.
10725 Number of used blocks.
10727 Number of available blocks.
10729 Percentage of @var{used} divided by @var{size}.
10735 The fields for block and inodes statistics are affected by the scaling
10736 options like @option{-h} as usual.
10738 The definition of the @var{field_list} can even be splitted among several
10739 @option{--output} uses.
10743 # Print the TARGET (i.e., the mount point) along with their percentage
10744 # statistic regarding the blocks and the inodes.
10745 df --out=target --output=pcent,ipcent
10747 # Print all available fields.
10753 @itemx --portability
10755 @opindex --portability
10756 @cindex one-line output format
10757 @cindex POSIX output format
10758 @cindex portable output format
10759 @cindex output format, portable
10760 Use the POSIX output format. This is like the default format except
10765 The information about each file system is always printed on exactly
10766 one line; a mount device is never put on a line by itself. This means
10767 that if the mount device name is more than 20 characters long (e.g., for
10768 some network mounts), the columns are misaligned.
10771 The labels in the header output line are changed to conform to POSIX.
10774 The default block size and output format are unaffected by the
10775 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10776 variables. However, the default block size is still affected by
10777 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10778 otherwise. @xref{Block size}.
10785 @cindex file system space, retrieving current data more slowly
10786 Invoke the @code{sync} system call before getting any usage data. On
10787 some systems (notably SunOS), doing this yields more up to date results,
10788 but in general this option makes @command{df} much slower, especially when
10789 there are many or very busy file systems.
10791 @item -t @var{fstype}
10792 @itemx --type=@var{fstype}
10795 @cindex file system types, limiting output to certain
10796 Limit the listing to file systems of type @var{fstype}. Multiple
10797 file system types can be specified by giving multiple @option{-t} options.
10798 By default, nothing is omitted.
10801 @itemx --print-type
10803 @opindex --print-type
10804 @cindex file system types, printing
10805 Print each file system's type. The types printed here are the same ones
10806 you can include or exclude with @option{-t} and @option{-x}. The particular
10807 types printed are whatever is supported by the system. Here are some of
10808 the common names (this list is certainly not exhaustive):
10813 @cindex NFS file system type
10814 An NFS file system, i.e., one mounted over a network from another
10815 machine. This is the one type name which seems to be used uniformly by
10818 @item 4.2@r{, }ufs@r{, }efs@dots{}
10819 @cindex Linux file system types
10820 @cindex local file system types
10821 @opindex 4.2 @r{file system type}
10822 @opindex ufs @r{file system type}
10823 @opindex efs @r{file system type}
10824 A file system on a locally-mounted hard disk. (The system might even
10825 support more than one type here; Linux does.)
10827 @item hsfs@r{, }cdfs
10828 @cindex CD-ROM file system type
10829 @cindex High Sierra file system
10830 @opindex hsfs @r{file system type}
10831 @opindex cdfs @r{file system type}
10832 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10833 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10836 @cindex PC file system
10837 @cindex DOS file system
10838 @cindex MS-DOS file system
10839 @cindex diskette file system
10841 An MS-DOS file system, usually on a diskette.
10845 @item -x @var{fstype}
10846 @itemx --exclude-type=@var{fstype}
10848 @opindex --exclude-type
10849 Limit the listing to file systems not of type @var{fstype}.
10850 Multiple file system types can be eliminated by giving multiple
10851 @option{-x} options. By default, no file system types are omitted.
10854 Ignored; for compatibility with System V versions of @command{df}.
10859 Failure includes the case where no output is generated, so you can
10860 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10861 @var{dir}} to test whether @var{dir} is on a file system of type
10862 @samp{ext3} or @samp{reiserfs}.
10864 Since the list of file systems (@var{mtab}) is needed to determine the
10865 file system type, failure includes the cases when that list cannot
10866 be read and one or more of the options @option{-a}, @option{-l}, @option{-t}
10867 or @option{-x} is used together with a file name argument.
10870 @node du invocation
10871 @section @command{du}: Estimate file space usage
10874 @cindex file space usage
10875 @cindex disk usage for files
10877 @command{du} reports the amount of disk space used by the specified files
10878 and for each subdirectory (of directory arguments). Synopsis:
10881 du [@var{option}]@dots{} [@var{file}]@dots{}
10884 With no arguments, @command{du} reports the disk space for the current
10885 directory. Normally the disk space is printed in units of
10886 1024 bytes, but this can be overridden (@pxref{Block size}).
10887 Non-integer quantities are rounded up to the next higher unit.
10889 If two or more hard links point to the same file, only one of the hard
10890 links is counted. The @var{file} argument order affects which links
10891 are counted, and changing the argument order may change the numbers
10892 that @command{du} outputs.
10894 The program accepts the following options. Also see @ref{Common options}.
10904 Show counts for all files, not just directories.
10906 @item --apparent-size
10907 @opindex --apparent-size
10908 Print apparent sizes, rather than disk usage. The apparent size of a
10909 file is the number of bytes reported by @code{wc -c} on regular files,
10910 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10911 For example, a file containing the word @samp{zoo} with no newline would,
10912 of course, have an apparent size of 3. Such a small file may require
10913 anywhere from 0 to 16 KiB or more of disk space, depending on
10914 the type and configuration of the file system on which the file resides.
10915 However, a sparse file created with this command:
10918 dd bs=1 seek=2GiB if=/dev/null of=big
10922 has an apparent size of 2 GiB, yet on most modern
10923 systems, it actually uses almost no disk space.
10925 @item -B @var{size}
10926 @itemx --block-size=@var{size}
10928 @opindex --block-size
10930 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10931 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10937 Equivalent to @code{--apparent-size --block-size=1}.
10943 @cindex grand total of disk space
10944 Print a grand total of all arguments after all arguments have
10945 been processed. This can be used to find out the total disk usage of
10946 a given set of files or directories.
10949 @itemx --dereference-args
10951 @opindex --dereference-args
10952 Dereference symbolic links that are command line arguments.
10953 Does not affect other symbolic links. This is helpful for finding
10954 out the disk usage of directories, such as @file{/usr/tmp}, which
10955 are often symbolic links.
10957 @item -d @var{depth}
10958 @itemx --max-depth=@var{depth}
10959 @opindex -d @var{depth}
10960 @opindex --max-depth=@var{depth}
10961 @cindex limiting output of @command{du}
10962 Show the total for each directory (and file if --all) that is at
10963 most MAX_DEPTH levels down from the root of the hierarchy. The root
10964 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10966 @c --files0-from=FILE
10967 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10971 Equivalent to @option{--dereference-args} (@option{-D}).
10977 @cindex kibibytes for file sizes
10978 Print sizes in 1024-byte blocks, overriding the default block size
10979 (@pxref{Block size}).
10980 This option is equivalent to @option{--block-size=1K}.
10983 @itemx --dereference
10985 @opindex --dereference
10986 @cindex symbolic links, dereferencing in @command{du}
10987 Dereference symbolic links (show the disk space used by the file
10988 or directory that the link points to instead of the space used by
10992 @itemx --count-links
10994 @opindex --count-links
10995 @cindex hard links, counting in @command{du}
10996 Count the size of all files, even if they have appeared already (as a
11001 @cindex mebibytes for file sizes
11002 Print sizes in 1,048,576-byte blocks, overriding the default block size
11003 (@pxref{Block size}).
11004 This option is equivalent to @option{--block-size=1M}.
11007 @itemx --no-dereference
11009 @opindex --no-dereference
11010 @cindex symbolic links, dereferencing in @command{du}
11011 For each symbolic links encountered by @command{du},
11012 consider the disk space used by the symbolic link.
11015 @itemx --separate-dirs
11017 @opindex --separate-dirs
11018 Normally, in the output of @command{du} (when not using @option{--summarize}),
11019 the size listed next to a directory name, @var{d}, represents the sum
11020 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
11021 With @option{--separate-dirs}, the size reported for a directory name,
11022 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
11030 @opindex --summarize
11031 Display only a total for each argument.
11033 @item -t @var{size}
11034 @itemx --threshold=@var{size}
11036 @opindex --threshold
11037 Exclude entries based on a given @var{size} (@pxref{Block size}).
11039 If @var{size} is positive, then @command{du} will only print entries with a size
11040 greater than or equal to that.
11042 If @var{size} is negative, then @command{du} will only print entries with a size
11043 smaller than or equal to that.
11045 Although GNU @command{find} can be used to find files of a certain size,
11046 @command{du}'s @option{--threshold} option can be used to also filter
11047 directories based on a given size.
11049 Please note that the @option{--threshold} option can be combined with the
11050 @option{--apparent-size} option, and in this case would elide entries based on
11053 Here's how you would use @option{--threshold} to find directories with a size
11054 greater than or equal to 200 megabytes:
11057 du --threshold=200MB
11060 Here's how you would use @option{--threshold} to find directories and files -
11061 note the @option{-a} - with an apparent size smaller than or equal to 500 bytes:
11064 du -a -t -500 --apparent-size
11070 @cindex last modified dates, displaying in @command{du}
11071 Show time of the most recent modification of any file in the directory,
11072 or any of its subdirectories.
11075 @itemx --time=status
11078 @opindex ctime@r{, show the most recent}
11079 @opindex status time@r{, show the most recent}
11080 @opindex use time@r{, show the most recent}
11081 Show the most recent status change time (the @samp{ctime} in the inode) of
11082 any file in the directory, instead of the modification time.
11085 @itemx --time=access
11087 @opindex atime@r{, show the most recent}
11088 @opindex access time@r{, show the most recent}
11089 Show the most recent access time (the @samp{atime} in the inode) of
11090 any file in the directory, instead of the modification time.
11092 @item --time-style=@var{style}
11093 @opindex --time-style
11095 List timestamps in style @var{style}. This option has an effect only if
11096 the @option{--time} option is also specified. The @var{style} should
11097 be one of the following:
11100 @item +@var{format}
11102 List timestamps using @var{format}, where @var{format} is interpreted
11103 like the format argument of @command{date} (@pxref{date invocation}).
11104 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
11105 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
11106 with @command{date}, @var{format}'s interpretation is affected by the
11107 @env{LC_TIME} locale category.
11110 List timestamps in full using ISO 8601 date, time, and time zone
11111 format with nanosecond precision, e.g., @samp{2002-03-30
11112 23:45:56.477817180 -0700}. This style is equivalent to
11113 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
11116 List ISO 8601 date and time in minutes, e.g.,
11117 @samp{2002-03-30 23:45}. These timestamps are shorter than
11118 @samp{full-iso} timestamps, and are usually good enough for everyday
11119 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
11122 List ISO 8601 dates for timestamps, e.g., @samp{2002-03-30}.
11123 This style is equivalent to @samp{+%Y-%m-%d}.
11127 You can specify the default value of the @option{--time-style} option
11128 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
11129 the default style is @samp{long-iso}. For compatibility with @command{ls},
11130 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
11131 the newline and any later characters are ignored; if @env{TIME_STYLE}
11132 begins with @samp{posix-} the @samp{posix-} is ignored; and if
11133 @env{TIME_STYLE} is @samp{locale} it is ignored.
11135 @item -X @var{file}
11136 @itemx --exclude-from=@var{file}
11137 @opindex -X @var{file}
11138 @opindex --exclude-from=@var{file}
11139 @cindex excluding files from @command{du}
11140 Like @option{--exclude}, except take the patterns to exclude from @var{file},
11141 one per line. If @var{file} is @samp{-}, take the patterns from standard
11144 @item --exclude=@var{pattern}
11145 @opindex --exclude=@var{pattern}
11146 @cindex excluding files from @command{du}
11147 When recursing, skip subdirectories or files matching @var{pattern}.
11148 For example, @code{du --exclude='*.o'} excludes files whose names
11152 @itemx --one-file-system
11154 @opindex --one-file-system
11155 @cindex one file system, restricting @command{du} to
11156 Skip directories that are on different file systems from the one that
11157 the argument being processed is on.
11161 @cindex NFS mounts from BSD to HP-UX
11162 On BSD systems, @command{du} reports sizes that are half the correct
11163 values for files that are NFS-mounted from HP-UX systems. On HP-UX
11164 systems, it reports sizes that are twice the correct values for
11165 files that are NFS-mounted from BSD systems. This is due to a flaw
11166 in HP-UX; it also affects the HP-UX @command{du} program.
11171 @node stat invocation
11172 @section @command{stat}: Report file or file system status
11175 @cindex file status
11176 @cindex file system status
11178 @command{stat} displays information about the specified file(s). Synopsis:
11181 stat [@var{option}]@dots{} [@var{file}]@dots{}
11184 With no option, @command{stat} reports all information about the given files.
11185 But it also can be used to report the information of the file systems the
11186 given files are located on. If the files are links, @command{stat} can
11187 also give information about the files the links point to.
11189 @mayConflictWithShellBuiltIn{stat}
11194 @itemx --dereference
11196 @opindex --dereference
11197 @cindex symbolic links, dereferencing in @command{stat}
11198 Change how @command{stat} treats symbolic links.
11199 With this option, @command{stat} acts on the file referenced
11200 by each symbolic link argument.
11201 Without it, @command{stat} acts on any symbolic link argument directly.
11204 @itemx --file-system
11206 @opindex --file-system
11207 @cindex file systems
11208 Report information about the file systems where the given files are located
11209 instead of information about the files themselves.
11210 This option implies the @option{-L} option.
11213 @itemx --format=@var{format}
11215 @opindex --format=@var{format}
11216 @cindex output format
11217 Use @var{format} rather than the default format.
11218 @var{format} is automatically newline-terminated, so
11219 running a command like the following with two or more @var{file}
11220 operands produces a line of output for each operand:
11222 $ stat --format=%d:%i / /usr
11227 @item --printf=@var{format}
11228 @opindex --printf=@var{format}
11229 @cindex output format
11230 Use @var{format} rather than the default format.
11231 Like @option{--format}, but interpret backslash escapes,
11232 and do not output a mandatory trailing newline.
11233 If you want a newline, include @samp{\n} in the @var{format}.
11234 Here's how you would use @option{--printf} to print the device
11235 and inode numbers of @file{/} and @file{/usr}:
11237 $ stat --printf='%d:%i\n' / /usr
11246 @cindex terse output
11247 Print the information in terse form, suitable for parsing by other programs.
11251 The valid @var{format} directives for files with @option{--format} and
11252 @option{--printf} are:
11255 @item %a - Access rights in octal
11256 @item %A - Access rights in human readable form
11257 @item %b - Number of blocks allocated (see @samp{%B})
11258 @item %B - The size in bytes of each block reported by @samp{%b}
11259 @item %C - The SELinux security context of a file, if available
11260 @item %d - Device number in decimal
11261 @item %D - Device number in hex
11262 @item %f - Raw mode in hex
11263 @item %F - File type
11264 @item %g - Group ID of owner
11265 @item %G - Group name of owner
11266 @item %h - Number of hard links
11267 @item %i - Inode number
11268 @item %m - Mount point (See note below)
11269 @item %n - File name
11270 @item %N - Quoted file name with dereference if symbolic link
11271 @item %o - Optimal I/O transfer size hint
11272 @item %s - Total size, in bytes
11273 @item %t - Major device type in hex
11274 @item %T - Minor device type in hex
11275 @item %u - User ID of owner
11276 @item %U - User name of owner
11277 @item %w - Time of file birth, or @samp{-} if unknown
11278 @item %W - Time of file birth as seconds since Epoch, or @samp{0}
11279 @item %x - Time of last access
11280 @item %X - Time of last access as seconds since Epoch
11281 @item %y - Time of last modification
11282 @item %Y - Time of last modification as seconds since Epoch
11283 @item %z - Time of last change
11284 @item %Z - Time of last change as seconds since Epoch
11287 The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
11288 precision preceded by a period to specify the number of digits to
11289 print after the decimal point. For example, @samp{%.3X} outputs the
11290 last access time to millisecond precision. If a period is given but no
11291 precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
11292 @samp{%.9X}@. When discarding excess precision, time stamps are truncated
11293 toward minus infinity.
11297 $ stat -c '[%015Y]' /usr
11300 $ stat -c '[%15Y]' /usr
11302 $ stat -c '[%-15Y]' /usr
11305 $ stat -c '[%.3Y]' /usr
11307 $ stat -c '[%.Y]' /usr
11308 [1288929712.114951834]
11311 The mount point printed by @samp{%m} is similar to that output
11312 by @command{df}, except that:
11315 stat does not dereference symlinks by default
11316 (unless @option{-L} is specified)
11318 stat does not search for specified device nodes in the
11319 file system list, instead operating on them directly
11322 stat outputs the alias for a bind mounted file, rather than
11323 the initial mount point of its backing device.
11324 One can recursively call stat until there is no change in output,
11325 to get the current base mount point
11328 When listing file system information (@option{--file-system} (@option{-f})),
11329 you must use a different set of @var{format} directives:
11332 @item %a - Free blocks available to non-super-user
11333 @item %b - Total data blocks in file system
11334 @item %c - Total file nodes in file system
11335 @item %d - Free file nodes in file system
11336 @item %f - Free blocks in file system
11337 @item %i - File System ID in hex
11338 @item %l - Maximum length of file names
11339 @item %n - File name
11340 @item %s - Block size (for faster transfers)
11341 @item %S - Fundamental block size (for block counts)
11342 @item %t - Type in hex
11343 @item %T - Type in human readable form
11347 Time stamps are listed according to the time zone rules specified by
11348 the @env{TZ} environment variable, or by the system default rules if
11349 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11350 with @env{TZ}, libc, The GNU C Library Reference Manual}.
11355 @node sync invocation
11356 @section @command{sync}: Synchronize data on disk with memory
11359 @cindex synchronize disk and memory
11361 @cindex superblock, writing
11362 @cindex inodes, written buffered
11363 @command{sync} writes any data buffered in memory out to disk. This can
11364 include (but is not limited to) modified superblocks, modified inodes,
11365 and delayed reads and writes. This must be implemented by the kernel;
11366 The @command{sync} program does nothing but exercise the @code{sync} system
11369 @cindex crashes and corruption
11370 The kernel keeps data in memory to avoid doing (relatively slow) disk
11371 reads and writes. This improves performance, but if the computer
11372 crashes, data may be lost or the file system corrupted as a
11373 result. The @command{sync} command ensures everything in memory
11374 is written to disk.
11376 Any arguments are ignored, except for a lone @option{--help} or
11377 @option{--version} (@pxref{Common options}).
11382 @node truncate invocation
11383 @section @command{truncate}: Shrink or extend the size of a file
11386 @cindex truncating, file sizes
11388 @command{truncate} shrinks or extends the size of each @var{file} to the
11389 specified size. Synopsis:
11392 truncate @var{option}@dots{} @var{file}@dots{}
11395 @cindex files, creating
11396 Any @var{file} that does not exist is created.
11398 @cindex sparse files, creating
11399 @cindex holes, creating files with
11400 If a @var{file} is larger than the specified size, the extra data is lost.
11401 If a @var{file} is shorter, it is extended and the extended part (or hole)
11402 reads as zero bytes.
11404 The program accepts the following options. Also see @ref{Common options}.
11411 @opindex --no-create
11412 Do not create files that do not exist.
11417 @opindex --io-blocks
11418 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
11420 @item -r @var{rfile}
11421 @itemx --reference=@var{rfile}
11423 @opindex --reference
11424 Base the size of each @var{file} on the size of @var{rfile}.
11426 @item -s @var{size}
11427 @itemx --size=@var{size}
11430 Set or adjust the size of each @var{file} according to @var{size}.
11431 @multiplierSuffixesNoBlocks{size}
11433 @var{size} may also be prefixed by one of the following to adjust
11434 the size of each @var{file} based on their current size:
11436 @samp{+} => extend by
11437 @samp{-} => reduce by
11438 @samp{<} => at most
11439 @samp{>} => at least
11440 @samp{/} => round down to multiple of
11441 @samp{%} => round up to multiple of
11449 @node Printing text
11450 @chapter Printing text
11452 @cindex printing text, commands for
11453 @cindex commands for printing text
11455 This section describes commands that display text strings.
11458 * echo invocation:: Print a line of text.
11459 * printf invocation:: Format and print data.
11460 * yes invocation:: Print a string until interrupted.
11464 @node echo invocation
11465 @section @command{echo}: Print a line of text
11468 @cindex displaying text
11469 @cindex printing text
11470 @cindex text, displaying
11471 @cindex arbitrary text, displaying
11473 @command{echo} writes each given @var{string} to standard output, with a
11474 space between each and a newline after the last one. Synopsis:
11477 echo [@var{option}]@dots{} [@var{string}]@dots{}
11480 @mayConflictWithShellBuiltIn{echo}
11482 The program accepts the following options. Also see @ref{Common options}.
11483 Options must precede operands, and the normally-special argument
11484 @samp{--} has no special meaning and is treated like any other
11490 Do not output the trailing newline.
11494 @cindex backslash escapes
11495 Enable interpretation of the following backslash-escaped characters in
11504 produce no further output
11520 the eight-bit value that is the octal number @var{nnn}
11521 (zero to three octal digits), if @var{nnn} is
11522 a nine-bit value, the ninth bit is ignored
11524 the eight-bit value that is the octal number @var{nnn}
11525 (one to three octal digits), if @var{nnn} is
11526 a nine-bit value, the ninth bit is ignored
11528 the eight-bit value that is the hexadecimal number @var{hh}
11529 (one or two hexadecimal digits)
11534 @cindex backslash escapes
11535 Disable interpretation of backslash escapes in each @var{string}.
11536 This is the default. If @option{-e} and @option{-E} are both
11537 specified, the last one given takes effect.
11541 @vindex POSIXLY_CORRECT
11542 If the @env{POSIXLY_CORRECT} environment variable is set, then when
11543 @command{echo}'s first argument is not @option{-n} it outputs
11544 option-like arguments instead of treating them as options. For
11545 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
11546 plain @samp{hello}.
11548 POSIX does not require support for any options, and says
11549 that the behavior of @command{echo} is implementation-defined if any
11550 @var{string} contains a backslash or if the first argument is
11551 @option{-n}. Portable programs can use the @command{printf} command
11552 if they need to omit trailing newlines or output control characters or
11553 backslashes. @xref{printf invocation}.
11558 @node printf invocation
11559 @section @command{printf}: Format and print data
11562 @command{printf} does formatted printing of text. Synopsis:
11565 printf @var{format} [@var{argument}]@dots{}
11568 @command{printf} prints the @var{format} string, interpreting @samp{%}
11569 directives and @samp{\} escapes to format numeric and string arguments
11570 in a way that is mostly similar to the C @samp{printf} function.
11571 @xref{Output Conversion Syntax,, @command{printf} format directives,
11572 libc, The GNU C Library Reference Manual}, for details.
11573 The differences are listed below.
11575 @mayConflictWithShellBuiltIn{printf}
11580 The @var{format} argument is reused as necessary to convert all the
11581 given @var{argument}s. For example, the command @samp{printf %s a b}
11585 Missing @var{argument}s are treated as null strings or as zeros,
11586 depending on whether the context expects a string or a number. For
11587 example, the command @samp{printf %sx%d} prints @samp{x0}.
11591 An additional escape, @samp{\c}, causes @command{printf} to produce no
11592 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
11593 E} prints @samp{ABC}.
11596 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
11597 digits, as opposed to C where it can have an unlimited number of
11598 digits. For example, the command @samp{printf '\x07e'} prints two
11599 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
11604 @command{printf} has an additional directive, @samp{%b}, which prints its
11605 argument string with @samp{\} escapes interpreted in the same way as in
11606 the @var{format} string, except that octal escapes are of the form
11607 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If
11608 @samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
11609 If a precision is also given, it limits the number of bytes printed
11610 from the converted string.
11613 Numeric arguments must be single C constants, possibly with leading
11614 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
11618 @vindex POSIXLY_CORRECT
11619 If the leading character of a numeric argument is @samp{"} or @samp{'}
11620 then its value is the numeric value of the immediately following
11621 character. Any remaining characters are silently ignored if the
11622 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
11623 warning is printed. For example, @samp{printf "%d" "'a"} outputs
11624 @samp{97} on hosts that use the ASCII character set, since
11625 @samp{a} has the numeric value 97 in ASCII.
11630 A floating-point argument must use a period before any fractional
11631 digits, but is printed according to the @env{LC_NUMERIC} category of the
11632 current locale. For example, in a locale whose radix character is a
11633 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11634 the command @samp{printf %g 3,14} is an error.
11635 @xref{Floating point}.
11639 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11640 (if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
11641 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11642 digits) specifying a character to print.
11643 Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
11644 @command{printf} ignores the ninth bit.
11645 For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.
11650 @cindex ISO/IEC 10646
11652 @command{printf} interprets two character syntaxes introduced in
11654 @samp{\u} for 16-bit Unicode (ISO/IEC 10646)
11655 characters, specified as
11656 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11657 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11658 @command{printf} outputs the Unicode characters
11659 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11660 U+0000@dots{}U+009F, U+D800@dots{}U+DFFF cannot be specified by this syntax,
11661 except for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11663 The processing of @samp{\u} and @samp{\U} requires a full-featured
11664 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11665 or when @code{libiconv} is installed prior to this package. Otherwise
11666 @samp{\u} and @samp{\U} will print as-is.
11668 The only options are a lone @option{--help} or
11669 @option{--version}. @xref{Common options}.
11670 Options must precede operands.
11672 The Unicode character syntaxes are useful for writing strings in a locale
11673 independent way. For example, a string containing the Euro currency symbol
11676 $ env printf '\u20AC 14.95'
11680 will be output correctly in all locales supporting the Euro symbol
11681 (ISO-8859-15, UTF-8, and others). Similarly, a Chinese string
11684 $ env printf '\u4e2d\u6587'
11688 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11690 Note that in these examples, the @command{printf} command has been
11691 invoked via @command{env} to ensure that we run the program found via
11692 your shell's search path, and not a shell alias or a built-in function.
11694 For larger strings, you don't need to look up the hexadecimal code
11695 values of each character one by one. ASCII characters mixed with \u
11696 escape sequences is also known as the JAVA source file encoding. You can
11697 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11698 is how to convert a piece of text into a shell script which will output
11699 this text in a locale-independent way:
11702 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11703 '\u4e2d\u6587\n' > sample.txt
11704 $ recode BIG5..JAVA < sample.txt \
11705 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11712 @node yes invocation
11713 @section @command{yes}: Print a string until interrupted
11716 @cindex repeated output of a string
11718 @command{yes} prints the command line arguments, separated by spaces and
11719 followed by a newline, forever until it is killed. If no arguments are
11720 given, it prints @samp{y} followed by a newline forever until killed.
11722 Upon a write error, @command{yes} exits with status @samp{1}.
11724 The only options are a lone @option{--help} or @option{--version}.
11725 To output an argument that begins with
11726 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11727 @xref{Common options}.
11731 @chapter Conditions
11734 @cindex commands for exit status
11735 @cindex exit status commands
11737 This section describes commands that are primarily useful for their exit
11738 status, rather than their output. Thus, they are often used as the
11739 condition of shell @code{if} statements, or as the last command in a
11743 * false invocation:: Do nothing, unsuccessfully.
11744 * true invocation:: Do nothing, successfully.
11745 * test invocation:: Check file types and compare values.
11746 * expr invocation:: Evaluate expressions.
11750 @node false invocation
11751 @section @command{false}: Do nothing, unsuccessfully
11754 @cindex do nothing, unsuccessfully
11755 @cindex failure exit status
11756 @cindex exit status of @command{false}
11758 @command{false} does nothing except return an exit status of 1, meaning
11759 @dfn{failure}. It can be used as a place holder in shell scripts
11760 where an unsuccessful command is needed.
11761 In most modern shells, @command{false} is a built-in command, so when
11762 you use @samp{false} in a script, you're probably using the built-in
11763 command, not the one documented here.
11765 @command{false} honors the @option{--help} and @option{--version} options.
11767 This version of @command{false} is implemented as a C program, and is thus
11768 more secure and faster than a shell script implementation, and may safely
11769 be used as a dummy shell for the purpose of disabling accounts.
11771 Note that @command{false} (unlike all other programs documented herein)
11772 exits unsuccessfully, even when invoked with
11773 @option{--help} or @option{--version}.
11775 Portable programs should not assume that the exit status of
11776 @command{false} is 1, as it is greater than 1 on some
11780 @node true invocation
11781 @section @command{true}: Do nothing, successfully
11784 @cindex do nothing, successfully
11786 @cindex successful exit
11787 @cindex exit status of @command{true}
11789 @command{true} does nothing except return an exit status of 0, meaning
11790 @dfn{success}. It can be used as a place holder in shell scripts
11791 where a successful command is needed, although the shell built-in
11792 command @code{:} (colon) may do the same thing faster.
11793 In most modern shells, @command{true} is a built-in command, so when
11794 you use @samp{true} in a script, you're probably using the built-in
11795 command, not the one documented here.
11797 @command{true} honors the @option{--help} and @option{--version} options.
11799 Note, however, that it is possible to cause @command{true}
11800 to exit with nonzero status: with the @option{--help} or @option{--version}
11801 option, and with standard
11802 output already closed or redirected to a file that evokes an I/O error.
11803 For example, using a Bourne-compatible shell:
11806 $ ./true --version >&-
11807 ./true: write error: Bad file number
11808 $ ./true --version > /dev/full
11809 ./true: write error: No space left on device
11812 This version of @command{true} is implemented as a C program, and is thus
11813 more secure and faster than a shell script implementation, and may safely
11814 be used as a dummy shell for the purpose of disabling accounts.
11816 @node test invocation
11817 @section @command{test}: Check file types and compare values
11820 @cindex check file types
11821 @cindex compare values
11822 @cindex expression evaluation
11824 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11825 evaluation of the conditional expression @var{expr}. Each part of the
11826 expression must be a separate argument.
11828 @command{test} has file status checks, string operators, and numeric
11829 comparison operators.
11831 @command{test} has an alternate form that uses opening and closing
11832 square brackets instead a leading @samp{test}. For example, instead
11833 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11834 brackets must be separate arguments; for example, @samp{[-d /]} does
11835 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11836 @var{expr} ]} have the same meaning, only the former form is discussed
11842 test @var{expression}
11844 [ @var{expression} ]
11849 @mayConflictWithShellBuiltIn{test}
11851 If @var{expression} is omitted, @command{test} returns false.
11852 If @var{expression} is a single argument,
11853 @command{test} returns false if the argument is null and true
11854 otherwise. The argument
11855 can be any string, including strings like @samp{-d}, @samp{-1},
11856 @samp{--}, @samp{--help}, and @samp{--version} that most other
11857 programs would treat as options. To get help and version information,
11858 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11859 the usual closing brackets. @xref{Common options}.
11861 @cindex exit status of @command{test}
11865 0 if the expression is true,
11866 1 if the expression is false,
11867 2 if an error occurred.
11871 * File type tests:: -[bcdfhLpSt]
11872 * Access permission tests:: -[gkruwxOG]
11873 * File characteristic tests:: -e -s -nt -ot -ef
11874 * String tests:: -z -n = == !=
11875 * Numeric tests:: -eq -ne -lt -le -gt -ge
11876 * Connectives for test:: ! -a -o
11880 @node File type tests
11881 @subsection File type tests
11883 @cindex file type tests
11885 These options test for particular types of files. (Everything's a file,
11886 but not all files are the same!)
11890 @item -b @var{file}
11892 @cindex block special check
11893 True if @var{file} exists and is a block special device.
11895 @item -c @var{file}
11897 @cindex character special check
11898 True if @var{file} exists and is a character special device.
11900 @item -d @var{file}
11902 @cindex directory check
11903 True if @var{file} exists and is a directory.
11905 @item -f @var{file}
11907 @cindex regular file check
11908 True if @var{file} exists and is a regular file.
11910 @item -h @var{file}
11911 @itemx -L @var{file}
11914 @cindex symbolic link check
11915 True if @var{file} exists and is a symbolic link.
11916 Unlike all other file-related tests, this test does not dereference
11917 @var{file} if it is a symbolic link.
11919 @item -p @var{file}
11921 @cindex named pipe check
11922 True if @var{file} exists and is a named pipe.
11924 @item -S @var{file}
11926 @cindex socket check
11927 True if @var{file} exists and is a socket.
11931 @cindex terminal check
11932 True if @var{fd} is a file descriptor that is associated with a
11938 @node Access permission tests
11939 @subsection Access permission tests
11941 @cindex access permission tests
11942 @cindex permission tests
11944 These options test for particular access permissions.
11948 @item -g @var{file}
11950 @cindex set-group-ID check
11951 True if @var{file} exists and has its set-group-ID bit set.
11953 @item -k @var{file}
11955 @cindex sticky bit check
11956 True if @var{file} exists and has its @dfn{sticky} bit set.
11958 @item -r @var{file}
11960 @cindex readable file check
11961 True if @var{file} exists and read permission is granted.
11963 @item -u @var{file}
11965 @cindex set-user-ID check
11966 True if @var{file} exists and has its set-user-ID bit set.
11968 @item -w @var{file}
11970 @cindex writable file check
11971 True if @var{file} exists and write permission is granted.
11973 @item -x @var{file}
11975 @cindex executable file check
11976 True if @var{file} exists and execute permission is granted
11977 (or search permission, if it is a directory).
11979 @item -O @var{file}
11981 @cindex owned by effective user ID check
11982 True if @var{file} exists and is owned by the current effective user ID.
11984 @item -G @var{file}
11986 @cindex owned by effective group ID check
11987 True if @var{file} exists and is owned by the current effective group ID.
11991 @node File characteristic tests
11992 @subsection File characteristic tests
11994 @cindex file characteristic tests
11996 These options test other file characteristics.
12000 @item -e @var{file}
12002 @cindex existence-of-file check
12003 True if @var{file} exists.
12005 @item -s @var{file}
12007 @cindex nonempty file check
12008 True if @var{file} exists and has a size greater than zero.
12010 @item @var{file1} -nt @var{file2}
12012 @cindex newer-than file check
12013 True if @var{file1} is newer (according to modification date) than
12014 @var{file2}, or if @var{file1} exists and @var{file2} does not.
12016 @item @var{file1} -ot @var{file2}
12018 @cindex older-than file check
12019 True if @var{file1} is older (according to modification date) than
12020 @var{file2}, or if @var{file2} exists and @var{file1} does not.
12022 @item @var{file1} -ef @var{file2}
12024 @cindex same file check
12025 @cindex hard link check
12026 True if @var{file1} and @var{file2} have the same device and inode
12027 numbers, i.e., if they are hard links to each other.
12033 @subsection String tests
12035 @cindex string tests
12037 These options test string characteristics. You may need to quote
12038 @var{string} arguments for the shell. For example:
12044 The quotes here prevent the wrong arguments from being passed to
12045 @command{test} if @samp{$V} is empty or contains special characters.
12049 @item -z @var{string}
12051 @cindex zero-length string check
12052 True if the length of @var{string} is zero.
12054 @item -n @var{string}
12055 @itemx @var{string}
12057 @cindex nonzero-length string check
12058 True if the length of @var{string} is nonzero.
12060 @item @var{string1} = @var{string2}
12062 @cindex equal string check
12063 True if the strings are equal.
12065 @item @var{string1} == @var{string2}
12067 @cindex equal string check
12068 True if the strings are equal (synonym for =).
12070 @item @var{string1} != @var{string2}
12072 @cindex not-equal string check
12073 True if the strings are not equal.
12078 @node Numeric tests
12079 @subsection Numeric tests
12081 @cindex numeric tests
12082 @cindex arithmetic tests
12084 Numeric relational operators. The arguments must be entirely numeric
12085 (possibly negative), or the special expression @w{@code{-l @var{string}}},
12086 which evaluates to the length of @var{string}.
12090 @item @var{arg1} -eq @var{arg2}
12091 @itemx @var{arg1} -ne @var{arg2}
12092 @itemx @var{arg1} -lt @var{arg2}
12093 @itemx @var{arg1} -le @var{arg2}
12094 @itemx @var{arg1} -gt @var{arg2}
12095 @itemx @var{arg1} -ge @var{arg2}
12102 These arithmetic binary operators return true if @var{arg1} is equal,
12103 not-equal, less-than, less-than-or-equal, greater-than, or
12104 greater-than-or-equal than @var{arg2}, respectively.
12111 test -1 -gt -2 && echo yes
12113 test -l abc -gt 1 && echo yes
12116 @error{} test: integer expression expected before -eq
12120 @node Connectives for test
12121 @subsection Connectives for @command{test}
12123 @cindex logical connectives
12124 @cindex connectives, logical
12126 The usual logical connectives.
12132 True if @var{expr} is false.
12134 @item @var{expr1} -a @var{expr2}
12136 @cindex logical and operator
12137 @cindex and operator
12138 True if both @var{expr1} and @var{expr2} are true.
12140 @item @var{expr1} -o @var{expr2}
12142 @cindex logical or operator
12143 @cindex or operator
12144 True if either @var{expr1} or @var{expr2} is true.
12149 @node expr invocation
12150 @section @command{expr}: Evaluate expressions
12153 @cindex expression evaluation
12154 @cindex evaluation of expressions
12156 @command{expr} evaluates an expression and writes the result on standard
12157 output. Each token of the expression must be a separate argument.
12159 Operands are either integers or strings. Integers consist of one or
12160 more decimal digits, with an optional leading @samp{-}.
12161 @command{expr} converts
12162 anything appearing in an operand position to an integer or a string
12163 depending on the operation being applied to it.
12165 Strings are not quoted for @command{expr} itself, though you may need to
12166 quote them to protect characters with special meaning to the shell,
12167 e.g., spaces. However, regardless of whether it is quoted, a string
12168 operand should not be a parenthesis or any of @command{expr}'s
12169 operators like @code{+}, so you cannot safely pass an arbitrary string
12170 @code{$str} to expr merely by quoting it to the shell. One way to
12171 work around this is to use the GNU extension @code{+},
12172 (e.g., @code{+ "$str" = foo}); a more portable way is to use
12173 @code{@w{" $str"}} and to adjust the rest of the expression to take
12174 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
12176 You should not pass a negative integer or a string with leading
12177 @samp{-} as @command{expr}'s first argument, as it might be
12178 misinterpreted as an option; this can be avoided by parenthesization.
12179 Also, portable scripts should not use a string operand that happens to
12180 take the form of an integer; this can be worked around by inserting
12181 leading spaces as mentioned above.
12183 @cindex parentheses for grouping
12184 Operators may be given as infix symbols or prefix keywords. Parentheses
12185 may be used for grouping in the usual manner. You must quote
12186 parentheses and many operators to avoid the shell evaluating them,
12189 When built with support for the GNU MP library, @command{expr} uses
12190 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
12191 types and may fail due to arithmetic overflow.
12193 The only options are @option{--help} and @option{--version}. @xref{Common
12194 options}. Options must precede operands.
12196 @cindex exit status of @command{expr}
12200 0 if the expression is neither null nor 0,
12201 1 if the expression is null or 0,
12202 2 if the expression is invalid,
12203 3 if an internal error occurred (e.g., arithmetic overflow).
12207 * String expressions:: + : match substr index length
12208 * Numeric expressions:: + - * / %
12209 * Relations for expr:: | & < <= = == != >= >
12210 * Examples of expr:: Examples.
12214 @node String expressions
12215 @subsection String expressions
12217 @cindex string expressions
12218 @cindex expressions, string
12220 @command{expr} supports pattern matching and other string operators. These
12221 have higher precedence than both the numeric and relational operators (in
12222 the next sections).
12226 @item @var{string} : @var{regex}
12227 @cindex pattern matching
12228 @cindex regular expression matching
12229 @cindex matching patterns
12230 Perform pattern matching. The arguments are converted to strings and the
12231 second is considered to be a (basic, a la GNU @code{grep}) regular
12232 expression, with a @code{^} implicitly prepended. The first argument is
12233 then matched against this regular expression.
12235 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
12236 @code{:} expression returns the part of @var{string} that matched the
12237 subexpression; otherwise, it returns the number of characters matched.
12239 If the match fails, the @code{:} operator returns the null string if
12240 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
12242 @kindex \( @r{regexp operator}
12243 Only the first @samp{\( @dots{} \)} pair is relevant to the return
12244 value; additional pairs are meaningful only for grouping the regular
12245 expression operators.
12247 @kindex \+ @r{regexp operator}
12248 @kindex \? @r{regexp operator}
12249 @kindex \| @r{regexp operator}
12250 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
12251 operators which respectively match one or more, zero or one, or separate
12252 alternatives. SunOS and other @command{expr}'s treat these as regular
12253 characters. (POSIX allows either behavior.)
12254 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
12255 regular expression syntax. Some examples are in @ref{Examples of expr}.
12257 @item match @var{string} @var{regex}
12259 An alternative way to do pattern matching. This is the same as
12260 @w{@samp{@var{string} : @var{regex}}}.
12262 @item substr @var{string} @var{position} @var{length}
12264 Returns the substring of @var{string} beginning at @var{position}
12265 with length at most @var{length}. If either @var{position} or
12266 @var{length} is negative, zero, or non-numeric, returns the null string.
12268 @item index @var{string} @var{charset}
12270 Returns the first position in @var{string} where the first character in
12271 @var{charset} was found. If no character in @var{charset} is found in
12272 @var{string}, return 0.
12274 @item length @var{string}
12276 Returns the length of @var{string}.
12278 @item + @var{token}
12280 Interpret @var{token} as a string, even if it is a keyword like @var{match}
12281 or an operator like @code{/}.
12282 This makes it possible to test @code{expr length + "$x"} or
12283 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
12284 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
12285 This operator is a GNU extension. Portable shell scripts should use
12286 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
12290 To make @command{expr} interpret keywords as strings, you must use the
12291 @code{quote} operator.
12294 @node Numeric expressions
12295 @subsection Numeric expressions
12297 @cindex numeric expressions
12298 @cindex expressions, numeric
12300 @command{expr} supports the usual numeric operators, in order of increasing
12301 precedence. These numeric operators have lower precedence than the
12302 string operators described in the previous section, and higher precedence
12303 than the connectives (next section).
12311 @cindex subtraction
12312 Addition and subtraction. Both arguments are converted to integers;
12313 an error occurs if this cannot be done.
12319 @cindex multiplication
12322 Multiplication, division, remainder. Both arguments are converted to
12323 integers; an error occurs if this cannot be done.
12328 @node Relations for expr
12329 @subsection Relations for @command{expr}
12331 @cindex connectives, logical
12332 @cindex logical connectives
12333 @cindex relations, numeric or string
12335 @command{expr} supports the usual logical connectives and relations. These
12336 have lower precedence than the string and numeric operators
12337 (previous sections). Here is the list, lowest-precedence operator first.
12343 @cindex logical or operator
12344 @cindex or operator
12345 Returns its first argument if that is neither null nor zero, otherwise
12346 its second argument if it is neither null nor zero, otherwise 0. It
12347 does not evaluate its second argument if its first argument is neither
12352 @cindex logical and operator
12353 @cindex and operator
12354 Return its first argument if neither argument is null or zero, otherwise
12355 0. It does not evaluate its second argument if its first argument is
12358 @item < <= = == != >= >
12365 @cindex comparison operators
12367 Compare the arguments and return 1 if the relation is true, 0 otherwise.
12368 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
12369 both arguments to integers and do a numeric comparison; if either
12370 conversion fails, it does a lexicographic comparison using the character
12371 collating sequence specified by the @env{LC_COLLATE} locale.
12376 @node Examples of expr
12377 @subsection Examples of using @command{expr}
12379 @cindex examples of @command{expr}
12380 Here are a few examples, including quoting for shell metacharacters.
12382 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
12385 foo=$(expr $foo + 1)
12388 To print the non-directory part of the file name stored in
12389 @code{$fname}, which need not contain a @code{/}:
12392 expr $fname : '.*/\(.*\)' '|' $fname
12395 An example showing that @code{\+} is an operator:
12403 expr abc : 'a\(.\)c'
12405 expr index abcdef cz
12408 @error{} expr: syntax error
12409 expr index + index a
12415 @chapter Redirection
12417 @cindex redirection
12418 @cindex commands for redirection
12420 Unix shells commonly provide several forms of @dfn{redirection}---ways
12421 to change the input source or output destination of a command. But one
12422 useful redirection is performed by a separate command, not by the shell;
12423 it's described here.
12426 * tee invocation:: Redirect output to multiple files or processes.
12430 @node tee invocation
12431 @section @command{tee}: Redirect output to multiple files or processes
12434 @cindex pipe fitting
12435 @cindex destinations, multiple output
12436 @cindex read from stdin and write to stdout and files
12438 The @command{tee} command copies standard input to standard output and also
12439 to any files given as arguments. This is useful when you want not only
12440 to send some data down a pipe, but also to save a copy. Synopsis:
12443 tee [@var{option}]@dots{} [@var{file}]@dots{}
12446 If a file being written to does not already exist, it is created. If a
12447 file being written to already exists, the data it previously contained
12448 is overwritten unless the @option{-a} option is used.
12450 A @var{file} of @samp{-} causes @command{tee} to send another copy of
12451 input to standard output, but this is typically not that useful as the
12452 copies are interleaved.
12454 The program accepts the following options. Also see @ref{Common options}.
12461 Append standard input to the given files rather than overwriting
12465 @itemx --ignore-interrupts
12467 @opindex --ignore-interrupts
12468 Ignore interrupt signals.
12472 The @command{tee} command is useful when you happen to be transferring a large
12473 amount of data and also want to summarize that data without reading
12474 it a second time. For example, when you are downloading a DVD image,
12475 you often want to verify its signature or checksum right away.
12476 The inefficient way to do it is simply:
12479 wget http://example.com/some.iso && sha1sum some.iso
12482 One problem with the above is that it makes you wait for the
12483 download to complete before starting the time-consuming SHA1 computation.
12484 Perhaps even more importantly, the above requires reading
12485 the DVD image a second time (the first was from the network).
12487 The efficient way to do it is to interleave the download
12488 and SHA1 computation. Then, you'll get the checksum for
12489 free, because the entire process parallelizes so well:
12492 # slightly contrived, to demonstrate process substitution
12493 wget -O - http://example.com/dvd.iso \
12494 | tee >(sha1sum > dvd.sha1) > dvd.iso
12497 That makes @command{tee} write not just to the expected output file,
12498 but also to a pipe running @command{sha1sum} and saving the final
12499 checksum in a file named @file{dvd.sha1}.
12501 Note, however, that this example relies on a feature of modern shells
12502 called @dfn{process substitution}
12503 (the @samp{>(command)} syntax, above;
12504 @xref{Process Substitution,,Process Substitution, bash,
12505 The Bash Reference Manual}.),
12506 so it works with @command{zsh}, @command{bash}, and @command{ksh},
12507 but not with @command{/bin/sh}. So if you write code like this
12508 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
12510 Since the above example writes to one file and one process,
12511 a more conventional and portable use of @command{tee} is even better:
12514 wget -O - http://example.com/dvd.iso \
12515 | tee dvd.iso | sha1sum > dvd.sha1
12518 You can extend this example to make @command{tee} write to two processes,
12519 computing MD5 and SHA1 checksums in parallel. In this case,
12520 process substitution is required:
12523 wget -O - http://example.com/dvd.iso \
12524 | tee >(sha1sum > dvd.sha1) \
12525 >(md5sum > dvd.md5) \
12529 This technique is also useful when you want to make a @emph{compressed}
12530 copy of the contents of a pipe.
12531 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
12532 For a large hierarchy, @samp{du -ak} can run for a long time,
12533 and can easily produce terabytes of data, so you won't want to
12534 rerun the command unnecessarily. Nor will you want to save
12535 the uncompressed output.
12537 Doing it the inefficient way, you can't even start the GUI
12538 until after you've compressed all of the @command{du} output:
12541 du -ak | gzip -9 > /tmp/du.gz
12542 gzip -d /tmp/du.gz | xdiskusage -a
12545 With @command{tee} and process substitution, you start the GUI
12546 right away and eliminate the decompression completely:
12549 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
12552 Finally, if you regularly create more than one type of
12553 compressed tarball at once, for example when @code{make dist} creates
12554 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
12555 there may be a better way.
12556 Typical @command{automake}-generated @file{Makefile} rules create
12557 the two compressed tar archives with commands in sequence, like this
12558 (slightly simplified):
12561 tardir=your-pkg-M.N
12562 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
12563 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12566 However, if the hierarchy you are archiving and compressing is larger
12567 than a couple megabytes, and especially if you are using a multi-processor
12568 system with plenty of memory, then you can do much better by reading the
12569 directory contents only once and running the compression programs in parallel:
12572 tardir=your-pkg-M.N
12573 tar chof - "$tardir" \
12574 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
12575 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12581 @node File name manipulation
12582 @chapter File name manipulation
12584 @cindex file name manipulation
12585 @cindex manipulation of file names
12586 @cindex commands for file name manipulation
12588 This section describes commands that manipulate file names.
12591 * basename invocation:: Strip directory and suffix from a file name.
12592 * dirname invocation:: Strip last file name component.
12593 * pathchk invocation:: Check file name validity and portability.
12594 * mktemp invocation:: Create temporary file or directory.
12595 * realpath invocation:: Print resolved file names.
12599 @node basename invocation
12600 @section @command{basename}: Strip directory and suffix from a file name
12603 @cindex strip directory and suffix from file names
12604 @cindex directory, stripping from file names
12605 @cindex suffix, stripping from file names
12606 @cindex file names, stripping directory and suffix
12607 @cindex leading directory components, stripping
12609 @command{basename} removes any leading directory components from
12610 @var{name}. Synopsis:
12613 basename @var{name} [@var{suffix}]
12614 basename @var{option}@dots{} @var{name}@dots{}
12617 If @var{suffix} is specified and is identical to the end of @var{name},
12618 it is removed from @var{name} as well. Note that since trailing slashes
12619 are removed prior to suffix matching, @var{suffix} will do nothing if it
12620 contains slashes. @command{basename} prints the result on standard
12623 @c This test is used both here and in the section on dirname.
12624 @macro basenameAndDirname
12625 Together, @command{basename} and @command{dirname} are designed such
12626 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
12627 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
12628 for everything except file names containing a trailing newline.
12630 @basenameAndDirname
12632 POSIX allows the implementation to define the results if
12633 @var{name} is empty or @samp{//}. In the former case, GNU
12634 @command{basename} returns the empty string. In the latter case, the
12635 result is @samp{//} on platforms where @var{//} is distinct from
12636 @var{/}, and @samp{/} on platforms where there is no difference.
12638 The program accepts the following options. Also see @ref{Common options}.
12639 Options must precede operands.
12646 @opindex --multiple
12647 Support more than one argument. Treat every argument as a @var{name}.
12648 With this, an optional @var{suffix} must be specified using the
12649 @option{-s} option.
12651 @item -s @var{suffix}
12652 @itemx --suffix=@var{suffix}
12655 Remove a trailing @var{suffix}.
12656 This option implies the @option{-a} option.
12662 Separate output items with NUL characters.
12672 basename /usr/bin/sort
12675 basename include/stdio.h .h
12678 basename -s .h include/stdio.h
12680 # Output "stdio" followed by "stdlib"
12681 basename -a -s .h include/stdio.h include/stdlib.h
12685 @node dirname invocation
12686 @section @command{dirname}: Strip last file name component
12689 @cindex directory components, printing
12690 @cindex stripping non-directory suffix
12691 @cindex non-directory suffix, stripping
12693 @command{dirname} prints all but the final slash-delimited component
12694 of each @var{name}. Slashes on either side of the final component are
12695 also removed. If the string contains no slash, @command{dirname}
12696 prints @samp{.} (meaning the current directory). Synopsis:
12699 dirname [@var{option}] @var{name}@dots{}
12702 @var{name} need not be a file name, but if it is, this operation
12703 effectively lists the directory that contains the final component,
12704 including the case when the final component is itself a directory.
12706 @basenameAndDirname
12708 POSIX allows the implementation to define the results if
12709 @var{name} is @samp{//}. With GNU @command{dirname}, the
12710 result is @samp{//} on platforms where @var{//} is distinct from
12711 @var{/}, and @samp{/} on platforms where there is no difference.
12713 The program accepts the following option. Also see @ref{Common options}.
12721 Separate output items with NUL characters.
12730 # Output "/usr/bin".
12731 dirname /usr/bin/sort
12732 dirname /usr/bin//.//
12734 # Output "dir1" followed by "dir2"
12735 dirname dir1/str dir2/str
12742 @node pathchk invocation
12743 @section @command{pathchk}: Check file name validity and portability
12746 @cindex file names, checking validity and portability
12747 @cindex valid file names, checking for
12748 @cindex portable file names, checking for
12750 @command{pathchk} checks validity and portability of file names. Synopsis:
12753 pathchk [@var{option}]@dots{} @var{name}@dots{}
12756 For each @var{name}, @command{pathchk} prints an error message if any of
12757 these conditions is true:
12761 One of the existing directories in @var{name} does not have search
12762 (execute) permission,
12764 The length of @var{name} is larger than the maximum supported by the
12767 The length of one component of @var{name} is longer than
12768 its file system's maximum.
12771 A nonexistent @var{name} is not an error, so long a file with that
12772 name could be created under the above conditions.
12774 The program accepts the following options. Also see @ref{Common options}.
12775 Options must precede operands.
12781 Instead of performing checks based on the underlying file system,
12782 print an error message if any of these conditions is true:
12786 A file name is empty.
12789 A file name contains a character outside the POSIX portable file
12790 name character set, namely, the ASCII letters and digits, @samp{.},
12791 @samp{_}, @samp{-}, and @samp{/}.
12794 The length of a file name or one of its components exceeds the
12795 POSIX minimum limits for portability.
12800 Print an error message if a file name is empty, or if it contains a component
12801 that begins with @samp{-}.
12803 @item --portability
12804 @opindex --portability
12805 Print an error message if a file name is not portable to all POSIX
12806 hosts. This option is equivalent to @samp{-p -P}.
12810 @cindex exit status of @command{pathchk}
12814 0 if all specified file names passed all checks,
12818 @node mktemp invocation
12819 @section @command{mktemp}: Create temporary file or directory
12822 @cindex file names, creating temporary
12823 @cindex directory, creating temporary
12824 @cindex temporary files and directories
12826 @command{mktemp} manages the creation of temporary files and
12827 directories. Synopsis:
12830 mktemp [@var{option}]@dots{} [@var{template}]
12833 Safely create a temporary file or directory based on @var{template},
12834 and print its name. If given, @var{template} must include at least
12835 three consecutive @samp{X}s in the last component. If omitted, the template
12836 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12837 implied. The final run of @samp{X}s in the @var{template} will be replaced
12838 by alpha-numeric characters; thus, on a case-sensitive file system,
12839 and with a @var{template} including a run of @var{n} instances of @samp{X},
12840 there are @samp{62**@var{n}} potential file names.
12842 Older scripts used to create temporary files by simply joining the
12843 name of the program with the process id (@samp{$$}) as a suffix.
12844 However, that naming scheme is easily predictable, and suffers from a
12845 race condition where the attacker can create an appropriately named
12846 symbolic link, such that when the script then opens a handle to what
12847 it thought was an unused file, it is instead modifying an existing
12848 file. Using the same scheme to create a directory is slightly safer,
12849 since the @command{mkdir} will fail if the target already exists, but
12850 it is still inferior because it allows for denial of service attacks.
12851 Therefore, modern scripts should use the @command{mktemp} command to
12852 guarantee that the generated name will be unpredictable, and that
12853 knowledge of the temporary file name implies that the file was created
12854 by the current script and cannot be modified by other users.
12856 When creating a file, the resulting file has read and write
12857 permissions for the current user, but no permissions for the group or
12858 others; these permissions are reduced if the current umask is more
12861 Here are some examples (although note that if you repeat them, you
12862 will most likely get different file names):
12867 Create a temporary file in the current directory.
12874 Create a temporary file with a known suffix.
12876 $ mktemp --suffix=.txt file-XXXX
12878 $ mktemp file-XXXX-XXXX.txt
12883 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12884 but falling back to the current directory rather than @file{/tmp}.
12885 Note that @command{mktemp} does not create fifos, but can create a
12886 secure directory in which the fifo can live. Exit the shell if the
12887 directory or fifo could not be created.
12889 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12891 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12895 Create and use a temporary file if possible, but ignore failure. The
12896 file will reside in the directory named by @env{TMPDIR}, if specified,
12897 or else in @file{/tmp}.
12899 $ file=$(mktemp -q) && @{
12900 > # Safe to use $file only within this block. Use quotes,
12901 > # since $TMPDIR, and thus $file, may contain whitespace.
12902 > echo ... > "$file"
12908 Act as a semi-random character generator (it is not fully random,
12909 since it is impacted by the contents of the current directory). To
12910 avoid security holes, do not use the resulting names to create a file.
12920 The program accepts the following options. Also see @ref{Common options}.
12927 @opindex --directory
12928 Create a directory rather than a file. The directory will have read,
12929 write, and search permissions for the current user, but no permissions
12930 for the group or others; these permissions are reduced if the current
12931 umask is more restrictive.
12937 Suppress diagnostics about failure to create a file or directory. The
12938 exit status will still reflect whether a file was created.
12944 Generate a temporary name that does not name an existing file, without
12945 changing the file system contents. Using the output of this command
12946 to create a new file is inherently unsafe, as there is a window of
12947 time between generating the name and using it where another process
12948 can create an object by the same name.
12951 @itemx --tmpdir[=@var{dir}]
12954 Treat @var{template} relative to the directory @var{dir}. If
12955 @var{dir} is not specified (only possible with the long option
12956 @option{--tmpdir}) or is the empty string, use the value of
12957 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12958 specified, @var{template} must not be absolute. However,
12959 @var{template} can still contain slashes, although intermediate
12960 directories must already exist.
12962 @item --suffix=@var{suffix}
12964 Append @var{suffix} to the @var{template}. @var{suffix} must not
12965 contain slash. If @option{--suffix} is specified, @var{template} must
12966 end in @samp{X}; if it is not specified, then an appropriate
12967 @option{--suffix} is inferred by finding the last @samp{X} in
12968 @var{template}. This option exists for use with the default
12969 @var{template} and for the creation of a @var{suffix} that starts with
12974 Treat @var{template} as a single file relative to the value of
12975 @env{TMPDIR} if available, or to the directory specified by
12976 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12977 contain slashes. This option is deprecated; the use of @option{-p}
12978 without @option{-t} offers better defaults (by favoring the command
12979 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12984 @cindex exit status of @command{mktemp}
12988 0 if the file was created,
12993 @node realpath invocation
12994 @section @command{realpath}: Print the resolved file name.
12997 @cindex file names, canonicalization
12998 @cindex symlinks, resolution
12999 @cindex canonical file name
13000 @cindex canonicalize a file name
13004 @command{realpath} expands all symbolic links and resolves references to
13005 @samp{/./}, @samp{/../} and extra @samp{/} characters. By default,
13006 all but the last component of the specified files must exist. Synopsis:
13009 realpath [@var{option}]@dots{} @var{file}@dots{}
13012 The program accepts the following options. Also see @ref{Common options}.
13017 @itemx --canonicalize-existing
13019 @opindex --canonicalize-existing
13020 Ensure that all components of the specified file names exist.
13021 If any component is missing or unavailable, @command{realpath} will output
13022 a diagnostic unless the @option{-q} option is specified, and exit with a
13023 nonzero exit code. A trailing slash requires that the name resolve to a
13027 @itemx --canonicalize-missing
13029 @opindex --canonicalize-missing
13030 If any component of a specified file name is missing or unavailable,
13031 treat it as a directory.
13037 Symbolic links are resolved in the specified file names,
13038 but they are resolved after any subsequent @samp{..} components are processed.
13043 @opindex --physical
13044 Symbolic links are resolved in the specified file names,
13045 and they are resolved before any subsequent @samp{..} components are processed.
13046 This is the default mode of operation.
13052 Suppress diagnostic messages for specified file names.
13056 @itemx --no-symlinks
13059 @opindex --no-symlinks
13060 Do not resolve symbolic links. Only resolve references to
13061 @samp{/./}, @samp{/../} and remove extra @samp{/} characters.
13062 When combined with the @option{-m} option, realpath operates
13063 only on the file name, and does not touch any actual file.
13069 Separate output items with NUL characters.
13071 @item --relative-to=@var{file}
13072 @opindex --relative-to
13074 Print the resolved file names relative to the specified file.
13075 Note this option honors the @option{-m} and @option{-e} options
13076 pertaining to file existence.
13078 @item --relative-base=@var{base}
13079 @opindex --relative-base
13080 This option is valid when used with @option{--relative-to}, and will restrict
13081 the output of @option{--relative-to} so that relative names are output,
13082 only when @var{file}s are descendants of @var{base}. Otherwise output the
13083 absolute file name. If @option{--relative-to} was not specified, then
13084 the descendants of @var{base} are printed relative to @var{base}. If
13085 @option{--relative-to} is specified, then that directory must be a
13086 descendant of @var{base} for this option to have an effect.
13087 Note: this option honors the @option{-m} and @option{-e}
13088 options pertaining to file existence. For example:
13091 realpath --relative-to=/usr /tmp /usr/bin
13094 realpath --relative-base=/usr /tmp /usr/bin
13101 @cindex exit status of @command{realpath}
13105 0 if all file names were printed without issue.
13110 @node Working context
13111 @chapter Working context
13113 @cindex working context
13114 @cindex commands for printing the working context
13116 This section describes commands that display or alter the context in
13117 which you are working: the current directory, the terminal settings, and
13118 so forth. See also the user-related commands in the next section.
13121 * pwd invocation:: Print working directory.
13122 * stty invocation:: Print or change terminal characteristics.
13123 * printenv invocation:: Print environment variables.
13124 * tty invocation:: Print file name of terminal on standard input.
13128 @node pwd invocation
13129 @section @command{pwd}: Print working directory
13132 @cindex print name of current directory
13133 @cindex current working directory, printing
13134 @cindex working directory, printing
13137 @command{pwd} prints the name of the current directory. Synopsis:
13140 pwd [@var{option}]@dots{}
13143 The program accepts the following options. Also see @ref{Common options}.
13150 If the contents of the environment variable @env{PWD} provide an
13151 absolute name of the current directory with no @samp{.} or @samp{..}
13152 components, but possibly with symbolic links, then output those
13153 contents. Otherwise, fall back to default @option{-P} handling.
13158 @opindex --physical
13159 Print a fully resolved name for the current directory. That is, all
13160 components of the printed name will be actual directory names---none
13161 will be symbolic links.
13164 @cindex symbolic links and @command{pwd}
13165 If @option{-L} and @option{-P} are both given, the last one takes
13166 precedence. If neither option is given, then this implementation uses
13167 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
13168 environment variable is set.
13170 @mayConflictWithShellBuiltIn{pwd}
13175 @node stty invocation
13176 @section @command{stty}: Print or change terminal characteristics
13179 @cindex change or print terminal settings
13180 @cindex terminal settings
13181 @cindex line settings of terminal
13183 @command{stty} prints or changes terminal characteristics, such as baud rate.
13187 stty [@var{option}] [@var{setting}]@dots{}
13188 stty [@var{option}]
13191 If given no line settings, @command{stty} prints the baud rate, line
13192 discipline number (on systems that support it), and line settings
13193 that have been changed from the values set by @samp{stty sane}.
13194 By default, mode reading and setting are performed on the tty line
13195 connected to standard input, although this can be modified by the
13196 @option{--file} option.
13198 @command{stty} accepts many non-option arguments that change aspects of
13199 the terminal line operation, as described below.
13201 The program accepts the following options. Also see @ref{Common options}.
13208 Print all current settings in human-readable form. This option may not
13209 be used in combination with any line settings.
13211 @item -F @var{device}
13212 @itemx --file=@var{device}
13215 Set the line opened by the file name specified in @var{device} instead of
13216 the tty line connected to standard input. This option is necessary
13217 because opening a POSIX tty requires use of the
13218 @code{O_NONDELAY} flag to prevent a POSIX tty from blocking
13219 until the carrier detect line is high if
13220 the @code{clocal} flag is not set. Hence, it is not always possible
13221 to allow the shell to open the device in the traditional manner.
13227 @cindex machine-readable @command{stty} output
13228 Print all current settings in a form that can be used as an argument to
13229 another @command{stty} command to restore the current settings. This option
13230 may not be used in combination with any line settings.
13234 Many settings can be turned off by preceding them with a @samp{-}.
13235 Such arguments are marked below with ``May be negated'' in their
13236 description. The descriptions themselves refer to the positive
13237 case, that is, when @emph{not} negated (unless stated otherwise,
13240 Some settings are not available on all POSIX systems, since they use
13241 extensions. Such arguments are marked below with
13242 ``Non-POSIX'' in their description. On non-POSIX
13243 systems, those or other settings also may not
13244 be available, but it's not feasible to document all the variations: just
13250 * Control:: Control settings
13251 * Input:: Input settings
13252 * Output:: Output settings
13253 * Local:: Local settings
13254 * Combination:: Combination settings
13255 * Characters:: Special characters
13256 * Special:: Special settings
13261 @subsection Control settings
13263 @cindex control settings
13269 @cindex two-way parity
13270 Generate parity bit in output and expect parity bit in input.
13276 @cindex even parity
13277 Set odd parity (even if negated). May be negated.
13284 @cindex character size
13285 @cindex eight-bit characters
13286 Set character size to 5, 6, 7, or 8 bits.
13291 Send a hangup signal when the last process closes the tty. May be
13297 Use two stop bits per character (one if negated). May be negated.
13301 Allow input to be received. May be negated.
13305 @cindex modem control
13306 Disable modem control signals. May be negated.
13310 @cindex hardware flow control
13311 @cindex flow control, hardware
13312 @cindex RTS/CTS flow control
13313 Enable RTS/CTS flow control. Non-POSIX@. May be negated.
13318 @subsection Input settings
13320 @cindex input settings
13321 These settings control operations on data received from the terminal.
13326 @cindex breaks, ignoring
13327 Ignore break characters. May be negated.
13331 @cindex breaks, cause interrupts
13332 Make breaks cause an interrupt signal. May be negated.
13336 @cindex parity, ignoring
13337 Ignore characters with parity errors. May be negated.
13341 @cindex parity errors, marking
13342 Mark parity errors (with a 255-0-character sequence). May be negated.
13346 Enable input parity checking. May be negated.
13350 @cindex eight-bit input
13351 Clear high (8th) bit of input characters. May be negated.
13355 @cindex newline, translating to return
13356 Translate newline to carriage return. May be negated.
13360 @cindex return, ignoring
13361 Ignore carriage return. May be negated.
13365 @cindex return, translating to newline
13366 Translate carriage return to newline. May be negated.
13370 @cindex input encoding, UTF-8
13371 Assume input characters are UTF-8 encoded. May be negated.
13375 @kindex C-s/C-q flow control
13376 @cindex XON/XOFF flow control
13377 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
13384 @cindex software flow control
13385 @cindex flow control, software
13386 Enable sending of @code{stop} character when the system input buffer
13387 is almost full, and @code{start} character when it becomes almost
13388 empty again. May be negated.
13392 @cindex uppercase, translating to lowercase
13393 Translate uppercase characters to lowercase. Non-POSIX@. May be
13394 negated. Note ilcuc is not implemented, as one would not be able to issue
13395 almost any (lowercase) Unix command, after invoking it.
13399 Allow any character to restart output (only the start character
13400 if negated). Non-POSIX@. May be negated.
13404 @cindex beeping at input buffer full
13405 Enable beeping and not flushing input buffer if a character arrives
13406 when the input buffer is full. Non-POSIX@. May be negated.
13411 @subsection Output settings
13413 @cindex output settings
13414 These settings control operations on data sent to the terminal.
13419 Postprocess output. May be negated.
13423 @cindex lowercase, translating to output
13424 Translate lowercase characters to uppercase. Non-POSIX@. May be
13425 negated. (Note ouclc is not currently implemented.)
13429 @cindex return, translating to newline
13430 Translate carriage return to newline. Non-POSIX@. May be negated.
13434 @cindex newline, translating to crlf
13435 Translate newline to carriage return-newline. Non-POSIX@. May be
13440 Do not print carriage returns in the first column. Non-POSIX@.
13445 Newline performs a carriage return. Non-POSIX@. May be negated.
13449 @cindex pad instead of timing for delaying
13450 Use fill (padding) characters instead of timing for delays.
13456 @cindex pad character
13457 Use ASCII DEL characters for fill instead of
13458 ASCII NUL characters. Non-POSIX@.
13464 Newline delay style. Non-POSIX.
13471 Carriage return delay style. Non-POSIX.
13477 @opindex tab@var{n}
13478 Horizontal tab delay style. Non-POSIX.
13483 Backspace delay style. Non-POSIX.
13488 Vertical tab delay style. Non-POSIX.
13493 Form feed delay style. Non-POSIX.
13498 @subsection Local settings
13500 @cindex local settings
13505 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
13506 characters. May be negated.
13510 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
13511 special characters. May be negated.
13515 Enable non-POSIX special characters. May be negated.
13519 Echo input characters. May be negated.
13525 Echo @code{erase} characters as backspace-space-backspace. May be
13530 @cindex newline echoing after @code{kill}
13531 Echo a newline after a @code{kill} character. May be negated.
13535 @cindex newline, echoing
13536 Echo newline even if not echoing other characters. May be negated.
13540 @cindex flushing, disabling
13541 Disable flushing after @code{interrupt} and @code{quit} special
13542 characters. May be negated.
13546 @cindex case translation
13547 Enable input and output of uppercase characters by preceding their
13548 lowercase equivalents with @samp{\}, when @code{icanon} is set.
13549 Non-POSIX@. May be negated.
13553 @cindex background jobs, stopping at terminal write
13554 Stop background jobs that try to write to the terminal. Non-POSIX@.
13561 Echo erased characters backward, between @samp{\} and @samp{/}.
13562 Non-POSIX@. May be negated.
13568 @cindex control characters, using @samp{^@var{c}}
13569 @cindex hat notation for control characters
13570 Echo control characters in hat notation (@samp{^@var{c}}) instead
13571 of literally. Non-POSIX@. May be negated.
13577 Echo the @code{kill} special character by erasing each character on
13578 the line as indicated by the @code{echoprt} and @code{echoe} settings,
13579 instead of by the @code{echoctl} and @code{echok} settings.
13586 @subsection Combination settings
13588 @cindex combination settings
13589 Combination settings:
13596 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
13597 as @code{-parenb cs8}.
13601 Same as @code{parenb parodd cs7}. May be negated. If negated, same
13602 as @code{-parenb cs8}.
13606 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
13607 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
13611 Reset the @code{erase} and @code{kill} special characters to their default
13618 @c This is too long to write inline.
13620 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
13621 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
13622 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
13623 ff0 isig icanon iexten echo echoe echok -echonl
13624 -noflsh -xcase -tostop -echoprt echoctl echoke
13628 and also sets all special characters to their default values.
13632 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
13633 sets the @code{eof} and @code{eol} characters to their default values
13634 if they are the same as the @code{min} and @code{time} characters.
13635 May be negated. If negated, same as @code{raw}.
13642 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
13643 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
13644 -imaxbel -opost -isig -icanon -xcase min 1 time 0
13648 May be negated. If negated, same as @code{cooked}.
13652 Same as @option{-icanon}. May be negated. If negated, same as
13657 @cindex eight-bit characters
13658 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
13659 same as @code{parenb istrip cs7}.
13663 Same as @option{-parenb -istrip -opost cs8}. May be negated.
13664 If negated, same as @code{parenb istrip opost cs7}.
13668 Same as @option{-ixany}. Non-POSIX@. May be negated.
13672 Same as @code{tab0}. Non-POSIX@. May be negated. If negated, same
13679 Same as @code{xcase iuclc olcuc}. Non-POSIX@. May be negated.
13680 (Used for terminals with uppercase characters only.)
13684 Same as @code{echoe echoctl echoke}.
13688 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
13693 @subsection Special characters
13695 @cindex special characters
13696 @cindex characters, special
13698 The special characters' default values vary from system to system.
13699 They are set with the syntax @samp{name value}, where the names are
13700 listed below and the value can be given either literally, in hat
13701 notation (@samp{^@var{c}}), or as an integer which may start with
13702 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
13703 any other digit to indicate decimal.
13705 @cindex disabling special characters
13706 @kindex u@r{, and disabling special characters}
13707 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
13708 special character. (This is incompatible with Ultrix @command{stty},
13709 which uses a value of @samp{u} to disable a special character. GNU
13710 @command{stty} treats a value @samp{u} like any other, namely to set that
13711 special character to @key{U}.)
13717 Send an interrupt signal.
13721 Send a quit signal.
13725 Erase the last character typed.
13729 Erase the current line.
13733 Send an end of file (terminate the input).
13741 Alternate character to end the line. Non-POSIX.
13745 Switch to a different shell layer. Non-POSIX.
13749 Restart the output after stopping it.
13757 Send a terminal stop signal.
13761 Send a terminal stop signal after flushing the input. Non-POSIX.
13765 Redraw the current line. Non-POSIX.
13769 Erase the last word typed. Non-POSIX.
13773 Enter the next character typed literally, even if it is a special
13774 character. Non-POSIX.
13779 @subsection Special settings
13781 @cindex special settings
13786 Set the minimum number of characters that will satisfy a read until
13787 the time value has expired, when @option{-icanon} is set.
13791 Set the number of tenths of a second before reads time out if the minimum
13792 number of characters have not been read, when @option{-icanon} is set.
13794 @item ispeed @var{n}
13796 Set the input speed to @var{n}.
13798 @item ospeed @var{n}
13800 Set the output speed to @var{n}.
13804 Tell the tty kernel driver that the terminal has @var{n} rows.
13808 @itemx columns @var{n}
13811 Tell the kernel that the terminal has @var{n} columns. Non-POSIX.
13817 Print the number of rows and columns that the kernel thinks the
13818 terminal has. (Systems that don't support rows and columns in the kernel
13819 typically use the environment variables @env{LINES} and @env{COLUMNS}
13820 instead; however, GNU @command{stty} does not know anything about them.)
13825 Use line discipline @var{n}. Non-POSIX.
13829 Print the terminal speed.
13832 @cindex baud rate, setting
13833 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13834 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13835 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13836 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13837 support higher speeds. The @command{stty} command includes support
13854 4000000 where the system supports these.
13855 0 hangs up the line if @option{-clocal} is set.
13859 @node printenv invocation
13860 @section @command{printenv}: Print all or some environment variables
13863 @cindex printing all or some environment variables
13864 @cindex environment variables, printing
13866 @command{printenv} prints environment variable values. Synopsis:
13869 printenv [@var{option}] [@var{variable}]@dots{}
13872 If no @var{variable}s are specified, @command{printenv} prints the value of
13873 every environment variable. Otherwise, it prints the value of each
13874 @var{variable} that is set, and nothing for those that are not set.
13876 The program accepts the following option. Also see @ref{Common options}.
13884 @cindex exit status of @command{printenv}
13888 0 if all variables specified were found
13889 1 if at least one specified variable was not found
13890 2 if a write error occurred
13894 @node tty invocation
13895 @section @command{tty}: Print file name of terminal on standard input
13898 @cindex print terminal file name
13899 @cindex terminal file name, printing
13901 @command{tty} prints the file name of the terminal connected to its standard
13902 input. It prints @samp{not a tty} if standard input is not a terminal.
13906 tty [@var{option}]@dots{}
13909 The program accepts the following option. Also see @ref{Common options}.
13919 Print nothing; only return an exit status.
13923 @cindex exit status of @command{tty}
13927 0 if standard input is a terminal
13928 1 if standard input is not a terminal
13929 2 if given incorrect arguments
13930 3 if a write error occurs
13934 @node User information
13935 @chapter User information
13937 @cindex user information, commands for
13938 @cindex commands for printing user information
13940 This section describes commands that print user-related information:
13941 logins, groups, and so forth.
13944 * id invocation:: Print user identity.
13945 * logname invocation:: Print current login name.
13946 * whoami invocation:: Print effective user ID.
13947 * groups invocation:: Print group names a user is in.
13948 * users invocation:: Print login names of users currently logged in.
13949 * who invocation:: Print who is currently logged in.
13953 @node id invocation
13954 @section @command{id}: Print user identity
13957 @cindex real user and group IDs, printing
13958 @cindex effective user and group IDs, printing
13959 @cindex printing real and effective user and group IDs
13961 @command{id} prints information about the given user, or the process
13962 running it if no user is specified. Synopsis:
13965 id [@var{option}]@dots{} [@var{username}]
13968 @vindex POSIXLY_CORRECT
13969 By default, it prints the real user ID, real group ID, effective user ID
13970 if different from the real user ID, effective group ID if different from
13971 the real group ID, and supplemental group IDs.
13972 In addition, if SELinux
13973 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13974 then print @samp{context=@var{c}}, where @var{c} is the security context.
13976 Each of these numeric values is preceded by an identifying string and
13977 followed by the corresponding user or group name in parentheses.
13979 The options cause @command{id} to print only part of the above information.
13980 Also see @ref{Common options}.
13987 Print only the group ID.
13993 Print only the group ID and the supplementary groups.
13999 Print the user or group name instead of the ID number. Requires
14000 @option{-u}, @option{-g}, or @option{-G}.
14006 Print the real, instead of effective, user or group ID@. Requires
14007 @option{-u}, @option{-g}, or @option{-G}.
14013 Print only the user ID.
14020 @cindex security context
14021 Print only the security context of the current user.
14022 If SELinux is disabled then print a warning and
14023 set the exit status to 1.
14029 @macro primaryAndSupplementaryGroups{cmd,arg}
14030 Primary and supplementary groups for a process are normally inherited
14031 from its parent and are usually unchanged since login. This means
14032 that if you change the group database after logging in, @command{\cmd\}
14033 will not reflect your changes within your existing login session.
14034 Running @command{\cmd\} with a \arg\ causes the user and group
14035 database to be consulted afresh, and so will give a different result.
14037 @primaryAndSupplementaryGroups{id,user argument}
14039 @node logname invocation
14040 @section @command{logname}: Print current login name
14043 @cindex printing user's login name
14044 @cindex login name, printing
14045 @cindex user name, printing
14048 @command{logname} prints the calling user's name, as found in a
14049 system-maintained file (often @file{/var/run/utmp} or
14050 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
14051 for the calling process, @command{logname} prints
14052 an error message and exits with a status of 1.
14054 The only options are @option{--help} and @option{--version}. @xref{Common
14060 @node whoami invocation
14061 @section @command{whoami}: Print effective user ID
14064 @cindex effective user ID, printing
14065 @cindex printing the effective user ID
14067 @command{whoami} prints the user name associated with the current
14068 effective user ID@. It is equivalent to the command @samp{id -un}.
14070 The only options are @option{--help} and @option{--version}. @xref{Common
14076 @node groups invocation
14077 @section @command{groups}: Print group names a user is in
14080 @cindex printing groups a user is in
14081 @cindex supplementary groups, printing
14083 @command{groups} prints the names of the primary and any supplementary
14084 groups for each given @var{username}, or the current process if no names
14085 are given. If more than one name is given, the name of each user is
14087 the list of that user's groups and the user name is separated from the
14088 group list by a colon. Synopsis:
14091 groups [@var{username}]@dots{}
14094 The group lists are equivalent to the output of the command @samp{id -Gn}.
14096 @primaryAndSupplementaryGroups{groups,list of users}
14098 The only options are @option{--help} and @option{--version}. @xref{Common
14104 @node users invocation
14105 @section @command{users}: Print login names of users currently logged in
14108 @cindex printing current usernames
14109 @cindex usernames, printing current
14111 @cindex login sessions, printing users with
14112 @command{users} prints on a single line a blank-separated list of user
14113 names of users currently logged in to the current host. Each user name
14114 corresponds to a login session, so if a user has more than one login
14115 session, that user's name will appear the same number of times in the
14124 With no @var{file} argument, @command{users} extracts its information from
14125 a system-maintained file (often @file{/var/run/utmp} or
14126 @file{/etc/utmp}). If a file argument is given, @command{users} uses
14127 that file instead. A common choice is @file{/var/log/wtmp}.
14129 The only options are @option{--help} and @option{--version}. @xref{Common
14135 @node who invocation
14136 @section @command{who}: Print who is currently logged in
14139 @cindex printing current user information
14140 @cindex information, about current users
14142 @command{who} prints information about users who are currently logged on.
14146 @command{who} [@var{option}] [@var{file}] [am i]
14149 @cindex terminal lines, currently used
14151 @cindex remote hostname
14152 If given no non-option arguments, @command{who} prints the following
14153 information for each user currently logged on: login name, terminal
14154 line, login time, and remote hostname or X display.
14158 If given one non-option argument, @command{who} uses that instead of
14159 a default system-maintained file (often @file{/var/run/utmp} or
14160 @file{/etc/utmp}) as the name of the file containing the record of
14161 users logged on. @file{/var/log/wtmp} is commonly given as an argument
14162 to @command{who} to look at who has previously logged on.
14166 If given two non-option arguments, @command{who} prints only the entry
14167 for the user running it (determined from its standard input), preceded
14168 by the hostname. Traditionally, the two arguments given are @samp{am
14169 i}, as in @samp{who am i}.
14172 Time stamps are listed according to the time zone rules specified by
14173 the @env{TZ} environment variable, or by the system default rules if
14174 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
14175 with @env{TZ}, libc, The GNU C Library Reference Manual}.
14177 The program accepts the following options. Also see @ref{Common options}.
14185 Same as @samp{-b -d --login -p -r -t -T -u}.
14191 Print the date and time of last system boot.
14197 Print information corresponding to dead processes.
14203 Print a line of column headings.
14209 List only the entries that correspond to processes via which the
14210 system is waiting for a user to login. The user name is always @samp{LOGIN}.
14214 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
14215 is not the default because it can cause significant delays on systems with
14216 automatic dial-up internet access.
14220 Same as @samp{who am i}.
14226 List active processes spawned by init.
14232 Print only the login names and the number of users logged on.
14233 Overrides all other options.
14238 @opindex --runlevel
14239 Print the current (and maybe previous) run-level of the init process.
14243 Ignored; for compatibility with other versions of @command{who}.
14249 Print last system clock change.
14254 After the login time, print the number of hours and minutes that the
14255 user has been idle. @samp{.} means the user was active in the last minute.
14256 @samp{old} means the user has been idle for more than 24 hours.
14267 @opindex --writable
14268 @cindex message status
14269 @pindex write@r{, allowed}
14270 After each login name print a character indicating the user's message status:
14273 @samp{+} allowing @code{write} messages
14274 @samp{-} disallowing @code{write} messages
14275 @samp{?} cannot find terminal device
14283 @node System context
14284 @chapter System context
14286 @cindex system context
14287 @cindex context, system
14288 @cindex commands for system context
14290 This section describes commands that print or change system-wide
14294 * date invocation:: Print or set system date and time.
14295 * arch invocation:: Print machine hardware name.
14296 * nproc invocation:: Print the number of processors.
14297 * uname invocation:: Print system information.
14298 * hostname invocation:: Print or set system name.
14299 * hostid invocation:: Print numeric host identifier.
14300 * uptime invocation:: Print system uptime and load.
14303 @node date invocation
14304 @section @command{date}: Print or set system date and time
14307 @cindex time, printing or setting
14308 @cindex printing the current time
14313 date [@var{option}]@dots{} [+@var{format}]
14314 date [-u|--utc|--universal] @c this avoids a newline in the output
14315 [ MMDDhhmm[[CC]YY][.ss] ]
14319 Invoking @command{date} with no @var{format} argument is equivalent to invoking
14320 it with a default format that depends on the @env{LC_TIME} locale category.
14321 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
14322 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
14325 Normally, @command{date} uses the time zone rules indicated by the
14326 @env{TZ} environment variable, or the system default rules if @env{TZ}
14327 is not set. @xref{TZ Variable,, Specifying the Time Zone with
14328 @env{TZ}, libc, The GNU C Library Reference Manual}.
14330 @findex strftime @r{and @command{date}}
14331 @cindex time formats
14332 @cindex formatting times
14333 If given an argument that starts with a @samp{+}, @command{date} prints the
14334 current date and time (or the date and time specified by the
14335 @option{--date} option, see below) in the format defined by that argument,
14336 which is similar to that of the @code{strftime} function. Except for
14337 conversion specifiers, which start with @samp{%}, characters in the
14338 format string are printed unchanged. The conversion specifiers are
14344 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
14345 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
14346 * Literal conversion specifiers:: %[%nt]
14347 * Padding and other flags:: Pad with zeros, spaces, etc.
14348 * Setting the time:: Changing the system clock.
14349 * Options for date:: Instead of the current time.
14351 * Date input formats:: Specifying date strings.
14353 * Examples of date:: Examples.
14356 @node Time conversion specifiers
14357 @subsection Time conversion specifiers
14359 @cindex time conversion specifiers
14360 @cindex conversion specifiers, time
14362 @command{date} conversion specifiers related to times.
14366 hour (@samp{00}@dots{}@samp{23})
14368 hour (@samp{01}@dots{}@samp{12})
14370 hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}@.
14371 This is a GNU extension.
14373 hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}@.
14374 This is a GNU extension.
14376 minute (@samp{00}@dots{}@samp{59})
14378 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
14379 This is a GNU extension.
14381 locale's equivalent of either @samp{AM} or @samp{PM};
14382 blank in many locales.
14383 Noon is treated as @samp{PM} and midnight as @samp{AM}.
14385 like @samp{%p}, except lower case.
14386 This is a GNU extension.
14388 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
14390 24-hour hour and minute. Same as @samp{%H:%M}.
14392 @cindex epoch, seconds since
14393 @cindex seconds since the epoch
14394 @cindex beginning of time
14395 @cindex leap seconds
14396 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC@.
14397 Leap seconds are not counted unless leap second support is available.
14398 @xref{%s-examples}, for examples.
14399 This is a GNU extension.
14401 @cindex leap seconds
14402 second (@samp{00}@dots{}@samp{60}).
14403 This may be @samp{60} if leap seconds are supported.
14405 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
14407 locale's time representation (e.g., @samp{23:13:48})
14409 @w{RFC 2822/ISO 8601} style numeric time zone
14410 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
14411 time zone is determinable. This value reflects the numeric time zone
14412 appropriate for the current time, using the time zone rules specified
14413 by the @env{TZ} environment variable.
14414 The time (and optionally, the time zone rules) can be overridden
14415 by the @option{--date} option.
14417 @w{RFC 3339/ISO 8601} style numeric time zone with
14418 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
14419 zone is determinable.
14420 This is a GNU extension.
14422 Numeric time zone to the nearest second with @samp{:} (e.g.,
14423 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
14425 This is a GNU extension.
14427 Numeric time zone with @samp{:} using the minimum necessary precision
14428 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
14429 no time zone is determinable.
14430 This is a GNU extension.
14432 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
14433 time zone is determinable. See @samp{%z} for how it is determined.
14437 @node Date conversion specifiers
14438 @subsection Date conversion specifiers
14440 @cindex date conversion specifiers
14441 @cindex conversion specifiers, date
14443 @command{date} conversion specifiers related to dates.
14447 locale's abbreviated weekday name (e.g., @samp{Sun})
14449 locale's full weekday name, variable length (e.g., @samp{Sunday})
14451 locale's abbreviated month name (e.g., @samp{Jan})
14453 locale's full month name, variable length (e.g., @samp{January})
14455 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
14457 century. This is like @samp{%Y}, except the last two digits are omitted.
14458 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
14459 and is @samp{-0} if @samp{%Y} is @samp{-001}.
14460 It is normally at least two characters, but it may be more.
14462 day of month (e.g., @samp{01})
14464 date; same as @samp{%m/%d/%y}
14466 day of month, space padded; same as @samp{%_d}
14468 full date in ISO 8601 format; same as @samp{%Y-%m-%d}.
14469 This is a good choice for a date format, as it is standard and
14470 is easy to sort in the usual case where years are in the range
14473 year corresponding to the ISO week number, but without the century
14474 (range @samp{00} through @samp{99}). This has the same format and value
14475 as @samp{%y}, except that if the ISO week number (see
14477 to the previous or next year, that year is used instead.
14479 year corresponding to the ISO week number. This has the
14480 same format and value as @samp{%Y}, except that if the ISO
14482 @samp{%V}) belongs to the previous or next year, that year is used
14484 It is normally useful only if @samp{%V} is also used;
14485 for example, the format @samp{%G-%m-%d} is probably a mistake,
14486 since it combines the ISO week number year with the conventional month and day.
14490 day of year (@samp{001}@dots{}@samp{366})
14492 month (@samp{01}@dots{}@samp{12})
14494 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
14496 week number of year, with Sunday as the first day of the week
14497 (@samp{00}@dots{}@samp{53}).
14498 Days in a new year preceding the first Sunday are in week zero.
14500 ISO week number, that is, the
14501 week number of year, with Monday as the first day of the week
14502 (@samp{01}@dots{}@samp{53}).
14503 If the week containing January 1 has four or more days in
14504 the new year, then it is considered week 1; otherwise, it is week 53 of
14505 the previous year, and the next week is week 1. (See the ISO 8601
14508 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
14510 week number of year, with Monday as first day of week
14511 (@samp{00}@dots{}@samp{53}).
14512 Days in a new year preceding the first Monday are in week zero.
14514 locale's date representation (e.g., @samp{12/31/99})
14516 last two digits of year (@samp{00}@dots{}@samp{99})
14518 year. This is normally at least four characters, but it may be more.
14519 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
14520 precedes year @samp{0000}.
14524 @node Literal conversion specifiers
14525 @subsection Literal conversion specifiers
14527 @cindex literal conversion specifiers
14528 @cindex conversion specifiers, literal
14530 @command{date} conversion specifiers that produce literal strings.
14542 @node Padding and other flags
14543 @subsection Padding and other flags
14545 @cindex numeric field padding
14546 @cindex padding of numeric fields
14547 @cindex fields, padding numeric
14549 Unless otherwise specified, @command{date} normally pads numeric fields
14550 with zeros, so that, for
14551 example, numeric months are always output as two digits.
14552 Seconds since the epoch are not padded, though,
14553 since there is no natural width for them.
14555 As a GNU extension, @command{date} recognizes any of the
14556 following optional flags after the @samp{%}:
14560 (hyphen) Do not pad the field; useful if the output is intended for
14563 (underscore) Pad with spaces; useful if you need a fixed
14564 number of characters in the output, but zeros are too distracting.
14566 (zero) Pad with zeros even if the conversion specifier
14567 would normally pad with spaces.
14569 Use upper case characters if possible.
14571 Use opposite case characters if possible.
14572 A field that is normally upper case becomes lower case, and vice versa.
14576 Here are some examples of padding:
14579 date +%d/%m -d "Feb 1"
14581 date +%-d/%-m -d "Feb 1"
14583 date +%_d/%_m -d "Feb 1"
14587 As a GNU extension, you can specify the field width
14588 (after any flag, if present) as a decimal number. If the natural size of the
14589 output of the field has less than the specified number of characters,
14590 the result is written right adjusted and padded to the given
14591 size. For example, @samp{%9B} prints the right adjusted month name in
14592 a field of width 9.
14594 An optional modifier can follow the optional flag and width
14595 specification. The modifiers are:
14599 Use the locale's alternate representation for date and time. This
14600 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
14601 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
14602 example, @samp{%Ex} might yield a date format based on the Japanese
14606 Use the locale's alternate numeric symbols for numbers. This modifier
14607 applies only to numeric conversion specifiers.
14610 If the format supports the modifier but no alternate representation
14611 is available, it is ignored.
14614 @node Setting the time
14615 @subsection Setting the time
14617 @cindex setting the time
14618 @cindex time setting
14619 @cindex appropriate privileges
14621 If given an argument that does not start with @samp{+}, @command{date} sets
14622 the system clock to the date and time specified by that argument (as
14623 described below). You must have appropriate privileges to set the
14624 system clock. Note for changes to persist across a reboot, the
14625 hardware clock may need to be updated from the system clock, which
14626 might not happen automatically on your system.
14628 The argument must consist entirely of digits, which have the following
14641 first two digits of year (optional)
14643 last two digits of year (optional)
14648 Note, the @option{--date} and @option{--set} options may not be used with an
14649 argument in the above format. The @option{--universal} option may be used
14650 with such an argument to indicate that the specified date and time are
14651 relative to Coordinated Universal Time rather than to the local time zone.
14654 @node Options for date
14655 @subsection Options for @command{date}
14657 @cindex @command{date} options
14658 @cindex options for @command{date}
14660 The program accepts the following options. Also see @ref{Common options}.
14664 @item -d @var{datestr}
14665 @itemx --date=@var{datestr}
14668 @cindex parsing date strings
14669 @cindex date strings, parsing
14670 @cindex arbitrary date strings, parsing
14673 @opindex next @var{day}
14674 @opindex last @var{day}
14675 Display the date and time specified in @var{datestr} instead of the
14676 current date and time. @var{datestr} can be in almost any common
14677 format. It can contain month names, time zones, @samp{am} and @samp{pm},
14678 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
14679 14:19:13.489392193 +0530"} specifies the instant of time that is
14680 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
14681 time zone that is 5 hours and 30 minutes east of UTC.@*
14682 Note: input currently must be in locale independent format. E.g., the
14683 LC_TIME=C below is needed to print back the correct date in many locales:
14685 date -d "$(LC_TIME=C date)"
14687 @xref{Date input formats}.
14689 @item -f @var{datefile}
14690 @itemx --file=@var{datefile}
14693 Parse each line in @var{datefile} as with @option{-d} and display the
14694 resulting date and time. If @var{datefile} is @samp{-}, use standard
14695 input. This is useful when you have many dates to process, because the
14696 system overhead of starting up the @command{date} executable many times can
14699 @item -I[@var{timespec}]
14700 @itemx --iso-8601[=@var{timespec}]
14701 @opindex -I[@var{timespec}]
14702 @opindex --iso-8601[=@var{timespec}]
14703 Display the date using the ISO 8601 format, @samp{%Y-%m-%d}.
14705 The argument @var{timespec} specifies the number of additional
14706 terms of the time to include. It can be one of the following:
14709 Print just the date. This is the default if @var{timespec} is omitted.
14712 Append the hour of the day to the date.
14715 Append the hours and minutes.
14718 Append the hours, minutes and seconds.
14721 Append the hours, minutes, seconds and nanoseconds.
14724 If showing any time terms, then include the time zone using the format
14727 @item -r @var{file}
14728 @itemx --reference=@var{file}
14730 @opindex --reference
14731 Display the date and time of the last modification of @var{file},
14732 instead of the current date and time.
14739 @opindex --rfc-2822
14740 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
14741 %z}, evaluated in the C locale so abbreviations are always in English.
14745 Fri, 09 Sep 2005 13:51:39 -0700
14748 This format conforms to
14749 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
14751 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
14752 current and previous standards for Internet email.
14754 @item --rfc-3339=@var{timespec}
14755 @opindex --rfc-3339=@var{timespec}
14756 Display the date using a format specified by
14757 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
14758 RFC 3339}. This is a subset of the ISO 8601
14759 format, except that it also permits applications to use a space rather
14760 than a @samp{T} to separate dates from times. Unlike the other
14761 standard formats, RFC 3339 format is always suitable as
14762 input for the @option{--date} (@option{-d}) and @option{--file}
14763 (@option{-f}) options, regardless of the current locale.
14765 The argument @var{timespec} specifies how much of the time to include.
14766 It can be one of the following:
14770 Print just the full-date, e.g., @samp{2005-09-14}.
14771 This is equivalent to the format @samp{%Y-%m-%d}.
14774 Print the full-date and full-time separated by a space, e.g.,
14775 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
14776 time-offset; here the @samp{+05:30} means that local time is five
14777 hours and thirty minutes east of UTC@. This is equivalent to
14778 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
14781 Like @samp{seconds}, but also print nanoseconds, e.g.,
14782 @samp{2005-09-14 00:56:06.998458565+05:30}.
14783 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
14787 @item -s @var{datestr}
14788 @itemx --set=@var{datestr}
14791 Set the date and time to @var{datestr}. See @option{-d} above.
14792 See also @ref{Setting the time}.
14799 @opindex --universal
14800 @cindex Coordinated Universal Time
14802 @cindex Greenwich Mean Time
14804 @cindex leap seconds
14806 Use Coordinated Universal Time (UTC) by operating as if the
14807 @env{TZ} environment variable were set to the string @samp{UTC0}.
14809 Universal Time is often called ``Greenwich Mean Time'' (GMT) for
14810 historical reasons.
14811 Typically, systems ignore leap seconds and thus implement an
14812 approximation to UTC rather than true UTC.
14816 @node Examples of date
14817 @subsection Examples of @command{date}
14819 @cindex examples of @command{date}
14821 Here are a few examples. Also see the documentation for the @option{-d}
14822 option in the previous section.
14827 To print the date of the day before yesterday:
14830 date --date='2 days ago'
14834 To print the date of the day three months and one day hence:
14837 date --date='3 months 1 day'
14841 To print the day of year of Christmas in the current year:
14844 date --date='25 Dec' +%j
14848 To print the current full month name and the day of the month:
14854 But this may not be what you want because for the first nine days of
14855 the month, the @samp{%d} expands to a zero-padded two-digit field,
14856 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14859 To print a date without the leading zero for one-digit days
14860 of the month, you can use the (GNU extension)
14861 @samp{-} flag to suppress
14862 the padding altogether:
14865 date -d 1may '+%B %-d
14869 To print the current date and time in the format required by many
14870 non-GNU versions of @command{date} when setting the system clock:
14873 date +%m%d%H%M%Y.%S
14877 To set the system clock forward by two minutes:
14880 date --set='+2 minutes'
14884 To print the date in RFC 2822 format,
14885 use @samp{date --rfc-2822}. Here is some example output:
14888 Fri, 09 Sep 2005 13:51:39 -0700
14891 @anchor{%s-examples}
14893 To convert a date string to the number of seconds since the epoch
14894 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14895 the @samp{%s} format. That can be useful in sorting and/or graphing
14896 and/or comparing data by date. The following command outputs the
14897 number of the seconds since the epoch for the time two minutes after the
14901 date --date='1970-01-01 00:02:00 +0000' +%s
14905 If you do not specify time zone information in the date string,
14906 @command{date} uses your computer's idea of the time zone when
14907 interpreting the string. For example, if your computer's time zone is
14908 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14909 seconds) behind UTC:
14912 # local time zone used
14913 date --date='1970-01-01 00:02:00' +%s
14918 If you're sorting or graphing dated data, your raw date values may be
14919 represented as seconds since the epoch. But few people can look at
14920 the date @samp{946684800} and casually note ``Oh, that's the first second
14921 of the year 2000 in Greenwich, England.''
14924 date --date='2000-01-01 UTC' +%s
14928 An alternative is to use the @option{--utc} (@option{-u}) option.
14929 Then you may omit @samp{UTC} from the date string. Although this
14930 produces the same result for @samp{%s} and many other format sequences,
14931 with a time zone offset different from zero, it would give a different
14932 result for zone-dependent formats like @samp{%z}.
14935 date -u --date=2000-01-01 +%s
14939 To convert such an unwieldy number of seconds back to
14940 a more readable form, use a command like this:
14943 # local time zone used
14944 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14945 1999-12-31 19:00:00 -0500
14948 Or if you do not mind depending on the @samp{@@} feature present since
14949 coreutils 5.3.0, you could shorten this to:
14952 date -d @@946684800 +"%F %T %z"
14953 1999-12-31 19:00:00 -0500
14956 Often it is better to output UTC-relative date and time:
14959 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14960 2000-01-01 00:00:00 +0000
14964 @cindex leap seconds
14965 Typically the seconds count omits leap seconds, but some systems are
14966 exceptions. Because leap seconds are not predictable, the mapping
14967 between the seconds count and a future timestamp is not reliable on
14968 the atypical systems that include leap seconds in their counts.
14970 Here is how the two kinds of systems handle the leap second at
14971 2012-06-30 23:59:60 UTC:
14974 # Typical systems ignore leap seconds:
14975 date --date='2012-06-30 23:59:59 +0000' +%s
14977 date --date='2012-06-30 23:59:60 +0000' +%s
14978 date: invalid date '2012-06-30 23:59:60 +0000'
14979 date --date='2012-07-01 00:00:00 +0000' +%s
14984 # Atypical systems count leap seconds:
14985 date --date='2012-06-30 23:59:59 +0000' +%s
14987 date --date='2012-06-30 23:59:60 +0000' +%s
14989 date --date='2012-07-01 00:00:00 +0000' +%s
14996 @node arch invocation
14997 @section @command{arch}: Print machine hardware name
15000 @cindex print machine hardware name
15001 @cindex system information, printing
15003 @command{arch} prints the machine hardware name,
15004 and is equivalent to @samp{uname -m}.
15008 arch [@var{option}]
15011 The program accepts the @ref{Common options} only.
15016 @node nproc invocation
15017 @section @command{nproc}: Print the number of available processors
15020 @cindex Print the number of processors
15021 @cindex system information, printing
15023 Print the number of processing units available to the current process,
15024 which may be less than the number of online processors.
15025 If this information is not accessible, then print the number of
15026 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
15027 set, then it will determine the returned value. The result is guaranteed to be
15028 greater than zero. Synopsis:
15031 nproc [@var{option}]
15034 The program accepts the following options. Also see @ref{Common options}.
15040 Print the number of installed processors on the system, which may
15041 be greater than the number online or available to the current process.
15042 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
15044 @item --ignore=@var{number}
15046 If possible, exclude this @var{number} of processing units.
15053 @node uname invocation
15054 @section @command{uname}: Print system information
15057 @cindex print system information
15058 @cindex system information, printing
15060 @command{uname} prints information about the machine and operating system
15061 it is run on. If no options are given, @command{uname} acts as if the
15062 @option{-s} option were given. Synopsis:
15065 uname [@var{option}]@dots{}
15068 If multiple options or @option{-a} are given, the selected information is
15069 printed in this order:
15072 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
15073 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
15076 The information may contain internal spaces, so such output cannot be
15077 parsed reliably. In the following example, @var{release} is
15078 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
15082 @result{} Linux dumdum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
15083 unknown unknown GNU/Linux
15087 The program accepts the following options. Also see @ref{Common options}.
15095 Print all of the below information, except omit the processor type
15096 and the hardware platform name if they are unknown.
15099 @itemx --hardware-platform
15101 @opindex --hardware-platform
15102 @cindex implementation, hardware
15103 @cindex hardware platform
15104 @cindex platform, hardware
15105 Print the hardware platform name
15106 (sometimes called the hardware implementation).
15107 Print @samp{unknown} if the kernel does not make this information
15108 easily available, as is the case with Linux kernels.
15114 @cindex machine type
15115 @cindex hardware class
15116 @cindex hardware type
15117 Print the machine hardware name (sometimes called the hardware class
15123 @opindex --nodename
15126 @cindex network node name
15127 Print the network node hostname.
15132 @opindex --processor
15133 @cindex host processor type
15134 Print the processor type (sometimes called the instruction set
15135 architecture or ISA).
15136 Print @samp{unknown} if the kernel does not make this information
15137 easily available, as is the case with Linux kernels.
15140 @itemx --operating-system
15142 @opindex --operating-system
15143 @cindex operating system name
15144 Print the name of the operating system.
15147 @itemx --kernel-release
15149 @opindex --kernel-release
15150 @cindex kernel release
15151 @cindex release of kernel
15152 Print the kernel release.
15155 @itemx --kernel-name
15157 @opindex --kernel-name
15158 @cindex kernel name
15159 @cindex name of kernel
15160 Print the kernel name.
15161 POSIX 1003.1-2001 (@pxref{Standards conformance}) calls this
15162 ``the implementation of the operating system'', because the
15163 POSIX specification itself has no notion of ``kernel''.
15164 The kernel name might be the same as the operating system name printed
15165 by the @option{-o} or @option{--operating-system} option, but it might
15166 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
15167 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
15171 @itemx --kernel-version
15173 @opindex --kernel-version
15174 @cindex kernel version
15175 @cindex version of kernel
15176 Print the kernel version.
15183 @node hostname invocation
15184 @section @command{hostname}: Print or set system name
15187 @cindex setting the hostname
15188 @cindex printing the hostname
15189 @cindex system name, printing
15190 @cindex appropriate privileges
15192 With no arguments, @command{hostname} prints the name of the current host
15193 system. With one argument, it sets the current host name to the
15194 specified string. You must have appropriate privileges to set the host
15198 hostname [@var{name}]
15201 The only options are @option{--help} and @option{--version}. @xref{Common
15207 @node hostid invocation
15208 @section @command{hostid}: Print numeric host identifier
15211 @cindex printing the host identifier
15213 @command{hostid} prints the numeric identifier of the current host
15214 in hexadecimal. This command accepts no arguments.
15215 The only options are @option{--help} and @option{--version}.
15216 @xref{Common options}.
15218 For example, here's what it prints on one system I use:
15225 On that system, the 32-bit quantity happens to be closely
15226 related to the system's Internet address, but that isn't always
15231 @node uptime invocation
15232 @section @command{uptime}: Print system uptime and load
15235 @cindex printing the system uptime and load
15237 @command{uptime} prints the current time, the system's uptime, the
15238 number of logged-in users and the current load average.
15240 If an argument is specified, it is used as the file to be read
15241 to discover how many users are logged in. If no argument is
15242 specified, a system default is used (@command{uptime --help} indicates
15243 the default setting).
15245 The only options are @option{--help} and @option{--version}.
15246 @xref{Common options}.
15248 For example, here's what it prints right now on one system I use:
15252 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
15255 The precise method of calculation of load average varies somewhat
15256 between systems. Some systems calculate it as the average number of
15257 runnable processes over the last 1, 5 and 15 minutes, but some systems
15258 also include processes in the uninterruptible sleep state (that is,
15259 those processes which are waiting for disk I/O). The Linux kernel
15260 includes uninterruptible processes.
15262 @node SELinux context
15263 @chapter SELinux context
15265 @cindex SELinux context
15266 @cindex SELinux, context
15267 @cindex commands for SELinux context
15269 This section describes commands for operations with SELinux
15273 * chcon invocation:: Change SELinux context of file
15274 * runcon invocation:: Run a command in specified SELinux context
15277 @node chcon invocation
15278 @section @command{chcon}: Change SELinux context of file
15281 @cindex changing security context
15282 @cindex change SELinux context
15284 @command{chcon} changes the SELinux security context of the selected files.
15288 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
15289 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
15290 [-t @var{type}] @var{file}@dots{}
15291 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
15294 Change the SELinux security context of each @var{file} to @var{context}.
15295 With @option{--reference}, change the security context of each @var{file}
15296 to that of @var{rfile}.
15298 The program accepts the following options. Also see @ref{Common options}.
15302 @item --dereference
15303 @opindex --dereference
15304 Do not affect symbolic links but what they refer to; this is the default.
15307 @itemx --no-dereference
15309 @opindex --no-dereference
15310 @cindex no dereference
15311 Affect the symbolic links themselves instead of any referenced file.
15313 @item --reference=@var{rfile}
15314 @opindex --reference
15315 @cindex reference file
15316 Use @var{rfile}'s security context rather than specifying a @var{context} value.
15321 @opindex --recursive
15322 Operate on files and directories recursively.
15324 @item --preserve-root
15325 @opindex --preserve-root
15326 Refuse to operate recursively on the root directory, @file{/},
15327 when used together with the @option{--recursive} option.
15328 @xref{Treating / specially}.
15330 @item --no-preserve-root
15331 @opindex --no-preserve-root
15332 Do not treat the root directory, @file{/}, specially when operating
15333 recursively; this is the default.
15334 @xref{Treating / specially}.
15337 @xref{Traversing symlinks}.
15340 @xref{Traversing symlinks}.
15343 @xref{Traversing symlinks}.
15350 Output a diagnostic for every file processed.
15352 @item -u @var{user}
15353 @itemx --user=@var{user}
15356 Set user @var{user} in the target security context.
15358 @item -r @var{role}
15359 @itemx --role=@var{role}
15362 Set role @var{role} in the target security context.
15364 @item -t @var{type}
15365 @itemx --type=@var{type}
15368 Set type @var{type} in the target security context.
15370 @item -l @var{range}
15371 @itemx --range=@var{range}
15374 Set range @var{range} in the target security context.
15380 @node runcon invocation
15381 @section @command{runcon}: Run a command in specified SELinux context
15384 @cindex run with security context
15387 @command{runcon} runs file in specified SELinux security context.
15391 runcon @var{context} @var{command} [@var{args}]
15392 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
15393 [-l @var{range}] @var{command} [@var{args}]
15396 Run @var{command} with completely-specified @var{context}, or with
15397 current or transitioned security context modified by one or more of @var{level},
15398 @var{role}, @var{type} and @var{user}.
15400 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
15401 is specified, the first argument is used as the complete context.
15402 Any additional arguments after @var{command}
15403 are interpreted as arguments to the command.
15405 With neither @var{context} nor @var{command}, print the current
15408 The program accepts the following options. Also see @ref{Common options}.
15416 Compute process transition context before modifying.
15418 @item -u @var{user}
15419 @itemx --user=@var{user}
15422 Set user @var{user} in the target security context.
15424 @item -r @var{role}
15425 @itemx --role=@var{role}
15428 Set role @var{role} in the target security context.
15430 @item -t @var{type}
15431 @itemx --type=@var{type}
15434 Set type @var{type} in the target security context.
15436 @item -l @var{range}
15437 @itemx --range=@var{range}
15440 Set range @var{range} in the target security context.
15444 @cindex exit status of @command{runcon}
15448 126 if @var{command} is found but cannot be invoked
15449 127 if @command{runcon} itself fails or if @var{command} cannot be found
15450 the exit status of @var{command} otherwise
15453 @node Modified command invocation
15454 @chapter Modified command invocation
15456 @cindex modified command invocation
15457 @cindex invocation of commands, modified
15458 @cindex commands for invoking other commands
15460 This section describes commands that run other commands in some context
15461 different than the current one: a modified environment, as a different
15465 * chroot invocation:: Modify the root directory.
15466 * env invocation:: Modify environment variables.
15467 * nice invocation:: Modify niceness.
15468 * nohup invocation:: Immunize to hangups.
15469 * stdbuf invocation:: Modify buffering of standard streams.
15470 * timeout invocation:: Run with time limit.
15474 @node chroot invocation
15475 @section @command{chroot}: Run a command with a different root directory
15478 @cindex running a program in a specified root directory
15479 @cindex root directory, running a program in a specified
15481 @command{chroot} runs a command with a specified root directory.
15482 On many systems, only the super-user can do this.@footnote{However,
15483 some systems (e.g., FreeBSD) can be configured to allow certain regular
15484 users to use the @code{chroot} system call, and hence to run this program.
15485 Also, on Cygwin, anyone can run the @command{chroot} command, because the
15486 underlying function is non-privileged due to lack of support in MS-Windows.}
15490 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
15491 chroot @var{option}
15494 Ordinarily, file names are looked up starting at the root of the
15495 directory structure, i.e., @file{/}. @command{chroot} changes the root to
15496 the directory @var{newroot} (which must exist) and then runs
15497 @var{command} with optional @var{args}. If @var{command} is not
15498 specified, the default is the value of the @env{SHELL} environment
15499 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
15500 @var{command} must not be a special built-in utility
15501 (@pxref{Special built-in utilities}).
15503 The program accepts the following options. Also see @ref{Common options}.
15504 Options must precede operands.
15508 @item --userspec=@var{user}[:@var{group}]
15509 @opindex --userspec
15510 By default, @var{command} is run with the same credentials
15511 as the invoking process.
15512 Use this option to run it as a different @var{user} and/or with a
15513 different primary @var{group}.
15515 @item --groups=@var{groups}
15517 Use this option to specify the supplementary @var{groups} to be
15518 used by the new process.
15519 The items in the list (names or numeric IDs) must be separated by commas.
15523 Here are a few tips to help avoid common problems in using chroot.
15524 To start with a simple example, make @var{command} refer to a statically
15525 linked binary. If you were to use a dynamically linked executable, then
15526 you'd have to arrange to have the shared libraries in the right place under
15527 your new root directory.
15529 For example, if you create a statically linked @command{ls} executable,
15530 and put it in @file{/tmp/empty}, you can run this command as root:
15533 $ chroot /tmp/empty /ls -Rl /
15536 Then you'll see output like this:
15541 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
15544 If you want to use a dynamically linked executable, say @command{bash},
15545 then first run @samp{ldd bash} to see what shared objects it needs.
15546 Then, in addition to copying the actual binary, also copy the listed
15547 files to the required positions under your intended new root directory.
15548 Finally, if the executable requires any other files (e.g., data, state,
15549 device files), copy them into place, too.
15551 @cindex exit status of @command{chroot}
15555 125 if @command{chroot} itself fails
15556 126 if @var{command} is found but cannot be invoked
15557 127 if @var{command} cannot be found
15558 the exit status of @var{command} otherwise
15562 @node env invocation
15563 @section @command{env}: Run a command in a modified environment
15566 @cindex environment, running a program in a modified
15567 @cindex modified environment, running a program in a
15568 @cindex running a program in a modified environment
15570 @command{env} runs a command with a modified environment. Synopses:
15573 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
15574 [@var{command} [@var{args}]@dots{}]
15578 Operands of the form @samp{@var{variable}=@var{value}} set
15579 the environment variable @var{variable} to value @var{value}.
15580 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
15581 to an empty value is different from unsetting it.
15582 These operands are evaluated left-to-right, so if two operands
15583 mention the same variable the earlier is ignored.
15585 Environment variable names can be empty, and can contain any
15586 characters other than @samp{=} and ASCII NUL.
15587 However, it is wise to limit yourself to names that
15588 consist solely of underscores, digits, and ASCII letters,
15589 and that begin with a non-digit, as applications like the shell do not
15590 work well with other names.
15593 The first operand that does not contain the character @samp{=}
15594 specifies the program to invoke; it is
15595 searched for according to the @env{PATH} environment variable. Any
15596 remaining arguments are passed as arguments to that program.
15597 The program should not be a special built-in utility
15598 (@pxref{Special built-in utilities}).
15600 Modifications to @env{PATH} take effect prior to searching for
15601 @var{command}. Use caution when reducing @env{PATH}; behavior is
15602 not portable when @env{PATH} is undefined or omits key directories
15603 such as @file{/bin}.
15605 In the rare case that a utility contains a @samp{=} in the name, the
15606 only way to disambiguate it from a variable assignment is to use an
15607 intermediate command for @var{command}, and pass the problematic
15608 program name via @var{args}. For example, if @file{./prog=} is an
15609 executable in the current @env{PATH}:
15612 env prog= true # runs 'true', with prog= in environment
15613 env ./prog= true # runs 'true', with ./prog= in environment
15614 env -- prog= true # runs 'true', with prog= in environment
15615 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
15616 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
15619 @cindex environment, printing
15621 If no command name is specified following the environment
15622 specifications, the resulting environment is printed. This is like
15623 specifying the @command{printenv} program.
15625 For some examples, suppose the environment passed to @command{env}
15626 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
15627 @samp{PATH=.:/gnubin:/hacks}:
15632 Output the current environment.
15634 $ env | LC_ALL=C sort
15637 PATH=.:/gnubin:/hacks
15641 Run @command{foo} with a reduced environment, preserving only the
15642 original @env{PATH} to avoid problems in locating @command{foo}.
15644 env - PATH="$PATH" foo
15648 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
15649 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
15650 that @command{foo} was found in the file system rather than as a shell
15657 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
15658 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
15659 @samp{DISPLAY=gnu:0}.
15661 env DISPLAY=gnu:0 LOGNAME=foo nemacs
15665 Attempt to run the program @command{/energy/--} (as that is the only
15666 possible path search result); if the command exists, the environment
15667 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
15668 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
15670 env -u EDITOR PATH=/energy -- e=mc2 bar baz
15676 The program accepts the following options. Also see @ref{Common options}.
15677 Options must precede operands.
15683 @item -u @var{name}
15684 @itemx --unset=@var{name}
15687 Remove variable @var{name} from the environment, if it was in the
15692 @itemx --ignore-environment
15695 @opindex --ignore-environment
15696 Start with an empty environment, ignoring the inherited environment.
15700 @cindex exit status of @command{env}
15704 0 if no @var{command} is specified and the environment is output
15705 125 if @command{env} itself fails
15706 126 if @var{command} is found but cannot be invoked
15707 127 if @var{command} cannot be found
15708 the exit status of @var{command} otherwise
15712 @node nice invocation
15713 @section @command{nice}: Run a command with modified niceness
15717 @cindex scheduling, affecting
15718 @cindex appropriate privileges
15720 @command{nice} prints a process's @dfn{niceness}, or runs
15721 a command with modified niceness. @dfn{niceness} affects how
15722 favorably the process is scheduled in the system.
15726 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
15729 If no arguments are given, @command{nice} prints the current niceness.
15730 Otherwise, @command{nice} runs the given @var{command} with its
15731 niceness adjusted. By default, its niceness is incremented by 10.
15733 Niceness values range at least from @minus{}20 (process has high priority
15734 and gets more resources, thus slowing down other processes) through 19
15735 (process has lower priority and runs slowly itself, but has less impact
15736 on the speed of other running processes). Some systems
15737 may have a wider range of niceness values; conversely, other systems may
15738 enforce more restrictive limits. An attempt to set the niceness
15739 outside the supported range is treated as an attempt to use the
15740 minimum or maximum supported value.
15742 A niceness should not be confused with a scheduling priority, which
15743 lets applications determine the order in which threads are scheduled
15744 to run. Unlike a priority, a niceness is merely advice to the
15745 scheduler, which the scheduler is free to ignore. Also, as a point of
15746 terminology, POSIX defines the behavior of @command{nice} in
15747 terms of a @dfn{nice value}, which is the nonnegative difference
15748 between a niceness and the minimum niceness. Though @command{nice}
15749 conforms to POSIX, its documentation and diagnostics use the
15750 term ``niceness'' for compatibility with historical practice.
15752 @var{command} must not be a special built-in utility (@pxref{Special
15753 built-in utilities}).
15755 @mayConflictWithShellBuiltIn{nice}
15757 Note to change the @dfn{niceness} of an existing process,
15758 one needs to use the @command{renice} command.
15760 The program accepts the following option. Also see @ref{Common options}.
15761 Options must precede operands.
15764 @item -n @var{adjustment}
15765 @itemx --adjustment=@var{adjustment}
15767 @opindex --adjustment
15768 Add @var{adjustment} instead of 10 to the command's niceness. If
15769 @var{adjustment} is negative and you lack appropriate privileges,
15770 @command{nice} issues a warning but otherwise acts as if you specified
15773 For compatibility @command{nice} also supports an obsolete
15774 option syntax @option{-@var{adjustment}}. New scripts should use
15775 @option{-n @var{adjustment}} instead.
15779 @cindex exit status of @command{nice}
15783 0 if no @var{command} is specified and the niceness is output
15784 125 if @command{nice} itself fails
15785 126 if @var{command} is found but cannot be invoked
15786 127 if @var{command} cannot be found
15787 the exit status of @var{command} otherwise
15790 It is sometimes useful to run a non-interactive program with reduced niceness.
15793 $ nice factor 4611686018427387903
15796 Since @command{nice} prints the current niceness,
15797 you can invoke it through itself to demonstrate how it works.
15799 The default behavior is to increase the niceness by @samp{10}:
15810 The @var{adjustment} is relative to the current niceness. In the
15811 next example, the first @command{nice} invocation runs the second one
15812 with niceness 10, and it in turn runs the final one with a niceness
15816 $ nice nice -n 3 nice
15820 Specifying a niceness larger than the supported range
15821 is the same as specifying the maximum supported value:
15824 $ nice -n 10000000000 nice
15828 Only a privileged user may run a process with lower niceness:
15832 nice: cannot set niceness: Permission denied
15834 $ sudo nice -n -1 nice
15839 @node nohup invocation
15840 @section @command{nohup}: Run a command immune to hangups
15843 @cindex hangups, immunity to
15844 @cindex immunity to hangups
15845 @cindex logging out and continuing to run
15848 @command{nohup} runs the given @var{command} with hangup signals ignored,
15849 so that the command can continue running in the background after you log
15853 nohup @var{command} [@var{arg}]@dots{}
15856 If standard input is a terminal, it is redirected from
15857 @file{/dev/null} so that terminal sessions do not mistakenly consider
15858 the terminal to be used by the command. This is a GNU
15859 extension; programs intended to be portable to non-GNU hosts
15860 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
15864 If standard output is a terminal, the command's standard output is appended
15865 to the file @file{nohup.out}; if that cannot be written to, it is appended
15866 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
15867 command is not run.
15868 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
15869 @command{nohup} is made readable and writable only to the user,
15870 regardless of the current umask settings.
15872 If standard error is a terminal, it is normally redirected to the same file
15873 descriptor as the (possibly-redirected) standard output.
15874 However, if standard output is closed, standard error terminal output
15875 is instead appended to the file @file{nohup.out} or
15876 @file{$HOME/nohup.out} as above.
15878 To capture the command's output to a file other than @file{nohup.out}
15879 you can redirect it. For example, to capture the output of
15883 nohup make > make.log
15886 @command{nohup} does not automatically put the command it runs in the
15887 background; you must do that explicitly, by ending the command line
15888 with an @samp{&}. Also, @command{nohup} does not alter the
15889 niceness of @var{command}; use @command{nice} for that,
15890 e.g., @samp{nohup nice @var{command}}.
15892 @var{command} must not be a special built-in utility (@pxref{Special
15893 built-in utilities}).
15895 The only options are @option{--help} and @option{--version}. @xref{Common
15896 options}. Options must precede operands.
15898 @cindex exit status of @command{nohup}
15902 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15903 126 if @var{command} is found but cannot be invoked
15904 127 if @var{command} cannot be found
15905 the exit status of @var{command} otherwise
15908 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15912 @node stdbuf invocation
15913 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15916 @cindex standard streams, buffering
15917 @cindex line buffered
15919 @command{stdbuf} allows one to modify the buffering operations of the
15920 three standard I/O streams associated with a program. Synopsis:
15923 stdbuf @var{option}@dots{} @var{command}
15926 @var{command} must start with the name of a program that
15929 uses the ISO C @code{FILE} streams for input/output (note the
15930 programs @command{dd} and @command{cat} don't do that),
15933 does not adjust the buffering of its standard streams (note the
15934 program @command{tee} is not in this category).
15937 Any additional @var{arg}s are passed as additional arguments to the
15940 The program accepts the following options. Also see @ref{Common options}.
15944 @item -i @var{mode}
15945 @itemx --input=@var{mode}
15948 Adjust the standard input stream buffering.
15950 @item -o @var{mode}
15951 @itemx --output=@var{mode}
15954 Adjust the standard output stream buffering.
15956 @item -e @var{mode}
15957 @itemx --error=@var{mode}
15960 Adjust the standard error stream buffering.
15964 The @var{mode} can be specified as follows:
15969 Set the stream to line buffered mode.
15970 In this mode data is coalesced until a newline is output or
15971 input is read from any stream attached to a terminal device.
15972 This option is invalid with standard input.
15975 Disable buffering of the selected stream.
15976 In this mode, data is output immediately and only the
15977 amount of data requested is read from input.
15978 Note the difference in function for input and output.
15979 Disabling buffering for input will not influence the responsiveness
15980 or blocking behavior of the stream input functions.
15981 For example @code{fread} will still block until @code{EOF} or error,
15982 even if the underlying @code{read} returns less data than requested.
15985 Specify the size of the buffer to use in fully buffered mode.
15986 @multiplierSuffixesNoBlocks{size}
15990 @cindex exit status of @command{stdbuf}
15994 125 if @command{stdbuf} itself fails
15995 126 if @var{command} is found but cannot be invoked
15996 127 if @var{command} cannot be found
15997 the exit status of @var{command} otherwise
16001 @node timeout invocation
16002 @section @command{timeout}: Run a command with a time limit
16006 @cindex run commands with bounded time
16008 @command{timeout} runs the given @var{command} and kills it if it is
16009 still running after the specified time interval. Synopsis:
16012 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
16015 @var{command} must not be a special built-in utility (@pxref{Special
16016 built-in utilities}).
16018 The program accepts the following options. Also see @ref{Common options}.
16019 Options must precede operands.
16022 @item --preserve-status
16023 @opindex --preserve-status
16024 Return the exit status of the managed @var{command} on timeout, rather than
16025 a specific exit status indicating a timeout. This is useful if the
16026 managed @var{command} supports running for an indeterminite amount of time.
16029 @opindex --foreground
16030 Don't create a separate background program group, so that
16031 the managed @var{command} can use the foreground TTY normally.
16032 This is needed to support timing out commands not started
16033 directly from an interactive shell, in two situations.
16036 @var{command} is interactive and needs to read from the terminal for example
16038 the user wants to support sending signals directly to @var{command}
16039 from the terminal (like Ctrl-C for example)
16042 Note in this mode of operation, any children of @var{command}
16043 will not be timed out.
16045 @item -k @var{duration}
16046 @itemx --kill-after=@var{duration}
16048 @opindex --kill-after
16049 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
16050 signal, after the specified @var{duration}. Without this option, if the
16051 selected signal proves not to be fatal, @command{timeout} does not kill
16054 @item -s @var{signal}
16055 @itemx --signal=@var{signal}
16058 Send this @var{signal} to @var{command} on timeout, rather than the
16059 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
16060 or a number. @xref{Signal specifications}.
16064 @var{duration} is a floating point number followed by an optional unit:
16066 @samp{s} for seconds (the default)
16067 @samp{m} for minutes
16071 A duration of 0 disables the associated timeout.
16072 Note that the actual timeout duration is dependent on system conditions,
16073 which should be especially considered when specifying sub-second timeouts.
16075 @cindex exit status of @command{timeout}
16079 124 if @var{command} times out
16080 125 if @command{timeout} itself fails
16081 126 if @var{command} is found but cannot be invoked
16082 127 if @var{command} cannot be found
16083 137 if @var{command} is sent the KILL(9) signal (128+9)
16084 the exit status of @var{command} otherwise
16088 @node Process control
16089 @chapter Process control
16091 @cindex processes, commands for controlling
16092 @cindex commands for controlling processes
16095 * kill invocation:: Sending a signal to processes.
16099 @node kill invocation
16100 @section @command{kill}: Send a signal to processes
16103 @cindex send a signal to processes
16105 The @command{kill} command sends a signal to processes, causing them
16106 to terminate or otherwise act upon receiving the signal in some way.
16107 Alternatively, it lists information about signals. Synopses:
16110 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
16111 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
16114 @mayConflictWithShellBuiltIn{kill}
16116 The first form of the @command{kill} command sends a signal to all
16117 @var{pid} arguments. The default signal to send if none is specified
16118 is @samp{TERM}@. The special signal number @samp{0} does not denote a
16119 valid signal, but can be used to test whether the @var{pid} arguments
16120 specify processes to which a signal could be sent.
16122 If @var{pid} is positive, the signal is sent to the process with the
16123 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
16124 processes in the process group of the current process. If @var{pid}
16125 is @minus{}1, the signal is sent to all processes for which the user has
16126 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
16127 is sent to all processes in the process group that equals the absolute
16128 value of @var{pid}.
16130 If @var{pid} is not positive, a system-dependent set of system
16131 processes is excluded from the list of processes to which the signal
16134 If a negative @var{pid} argument is desired as the first one, it
16135 should be preceded by @option{--}. However, as a common extension to
16136 POSIX, @option{--} is not required with @samp{kill
16137 -@var{signal} -@var{pid}}. The following commands are equivalent:
16146 The first form of the @command{kill} command succeeds if every @var{pid}
16147 argument specifies at least one process that the signal was sent to.
16149 The second form of the @command{kill} command lists signal information.
16150 Either the @option{-l} or @option{--list} option, or the @option{-t}
16151 or @option{--table} option must be specified. Without any
16152 @var{signal} argument, all supported signals are listed. The output
16153 of @option{-l} or @option{--list} is a list of the signal names, one
16154 per line; if @var{signal} is already a name, the signal number is
16155 printed instead. The output of @option{-t} or @option{--table} is a
16156 table of signal numbers, names, and descriptions. This form of the
16157 @command{kill} command succeeds if all @var{signal} arguments are valid
16158 and if there is no output error.
16160 The @command{kill} command also supports the @option{--help} and
16161 @option{--version} options. @xref{Common options}.
16163 A @var{signal} may be a signal name like @samp{HUP}, or a signal
16164 number like @samp{1}, or an exit status of a process terminated by the
16165 signal. A signal name can be given in canonical form or prefixed by
16166 @samp{SIG}@. The case of the letters is ignored, except for the
16167 @option{-@var{signal}} option which must use upper case to avoid
16168 ambiguity with lower case option letters.
16169 @xref{Signal specifications}, for a list of supported
16170 signal names and numbers.
16175 @cindex delaying commands
16176 @cindex commands for delaying
16178 @c Perhaps @command{wait} or other commands should be described here also?
16181 * sleep invocation:: Delay for a specified time.
16185 @node sleep invocation
16186 @section @command{sleep}: Delay for a specified time
16189 @cindex delay for a specified time
16191 @command{sleep} pauses for an amount of time specified by the sum of
16192 the values of the command line arguments.
16196 sleep @var{number}[smhd]@dots{}
16200 Each argument is a number followed by an optional unit; the default
16201 is seconds. The units are:
16214 Historical implementations of @command{sleep} have required that
16215 @var{number} be an integer, and only accepted a single argument
16216 without a suffix. However, GNU @command{sleep} accepts
16217 arbitrary floating point numbers. @xref{Floating point}.
16219 The only options are @option{--help} and @option{--version}. @xref{Common
16222 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
16223 @mayConflictWithShellBuiltIn{sleep}
16228 @node Numeric operations
16229 @chapter Numeric operations
16231 @cindex numeric operations
16232 These programs do numerically-related operations.
16235 * factor invocation:: Show factors of numbers.
16236 * seq invocation:: Print sequences of numbers.
16240 @node factor invocation
16241 @section @command{factor}: Print prime factors
16244 @cindex prime factors
16246 @command{factor} prints prime factors. Synopses:
16249 factor [@var{number}]@dots{}
16250 factor @var{option}
16253 If no @var{number} is specified on the command line, @command{factor} reads
16254 numbers from standard input, delimited by newlines, tabs, or spaces.
16256 The @command{factor} command supports only a small number of options:
16260 Print a short help on standard output, then exit without further
16264 Print the program version on standard output, then exit without further
16268 Factoring the product of the eighth and ninth Mersenne primes
16269 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
16272 M8=$(echo 2^31-1|bc)
16273 M9=$(echo 2^61-1|bc)
16274 n=$(echo "$M8 * $M9" | bc)
16275 /usr/bin/time -f %U factor $n
16276 4951760154835678088235319297: 2147483647 2305843009213693951
16280 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
16281 about 20 seconds on the same machine.
16283 Factoring large numbers is, in general, hard. The Pollard Rho
16284 algorithm used by @command{factor} is particularly effective for
16285 numbers with relatively small factors. If you wish to factor large
16286 numbers which do not have small factors (for example, numbers which
16287 are the product of two large primes), other methods are far better.
16289 If @command{factor} is built without using GNU MP, only
16290 single-precision arithmetic is available, and so large numbers
16291 (typically @math{2^{64}} and above) will not be supported. The single-precision
16292 code uses an algorithm which is designed for factoring smaller
16298 @node seq invocation
16299 @section @command{seq}: Print numeric sequences
16302 @cindex numeric sequences
16303 @cindex sequence of numbers
16305 @command{seq} prints a sequence of numbers to standard output. Synopses:
16308 seq [@var{option}]@dots{} @var{last}
16309 seq [@var{option}]@dots{} @var{first} @var{last}
16310 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
16313 @command{seq} prints the numbers from @var{first} to @var{last} by
16314 @var{increment}. By default, each number is printed on a separate line.
16315 When @var{increment} is not specified, it defaults to @samp{1},
16316 even when @var{first} is larger than @var{last}.
16317 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
16318 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
16319 Floating-point numbers may be specified. @xref{Floating point}.
16321 The program accepts the following options. Also see @ref{Common options}.
16322 Options must precede operands.
16325 @item -f @var{format}
16326 @itemx --format=@var{format}
16327 @opindex -f @var{format}
16328 @opindex --format=@var{format}
16329 @cindex formatting of numbers in @command{seq}
16330 Print all numbers using @var{format}.
16331 @var{format} must contain exactly one of the @samp{printf}-style
16332 floating point conversion specifications @samp{%a}, @samp{%e},
16333 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}@.
16334 The @samp{%} may be followed by zero or more flags taken from the set
16335 @samp{-+#0 '}, then an optional width containing one or more digits,
16336 then an optional precision consisting of a @samp{.} followed by zero
16337 or more digits. @var{format} may also contain any number of @samp{%%}
16338 conversion specifications. All conversion specifications have the
16339 same meaning as with @samp{printf}.
16341 The default format is derived from @var{first}, @var{step}, and
16342 @var{last}. If these all use a fixed point decimal representation,
16343 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
16344 precision that can represent the output numbers exactly. Otherwise,
16345 the default format is @samp{%g}.
16347 @item -s @var{string}
16348 @itemx --separator=@var{string}
16349 @cindex separator for numbers in @command{seq}
16350 Separate numbers with @var{string}; default is a newline.
16351 The output always terminates with a newline.
16354 @itemx --equal-width
16355 Print all numbers with the same width, by padding with leading zeros.
16356 @var{first}, @var{step}, and @var{last} should all use a fixed point
16357 decimal representation.
16358 (To have other kinds of padding, use @option{--format}).
16362 You can get finer-grained control over output with @option{-f}:
16365 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
16371 If you want hexadecimal integer output, you can use @command{printf}
16372 to perform the conversion:
16375 $ printf '%x\n' $(seq 1048575 1024 1050623)
16381 For very long lists of numbers, use xargs to avoid
16382 system limitations on the length of an argument list:
16385 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
16391 To generate octal output, use the printf @code{%o} format instead
16394 On most systems, seq can produce whole-number output for values up to
16395 at least @math{2^{53}}. Larger integers are approximated. The details
16396 differ depending on your floating-point implementation.
16397 @xref{Floating point}. A common
16398 case is that @command{seq} works with integers through @math{2^{64}},
16399 and larger integers may not be numerically correct:
16402 $ seq 50000000000000000000 2 50000000000000000004
16403 50000000000000000000
16404 50000000000000000000
16405 50000000000000000004
16408 However, note that when limited to non-negative whole numbers,
16409 an increment of 1 and no format-specifying option, seq can print
16410 arbitrarily large numbers.
16412 Be careful when using @command{seq} with outlandish values: otherwise
16413 you may see surprising results, as @command{seq} uses floating point
16414 internally. For example, on the x86 platform, where the internal
16415 representation uses a 64-bit fraction, the command:
16418 seq 1 0.0000000000000000001 1.0000000000000000009
16421 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
16426 @node File permissions
16427 @chapter File permissions
16430 @include parse-datetime.texi
16434 @node Opening the software toolbox
16435 @chapter Opening the Software Toolbox
16437 An earlier version of this chapter appeared in
16438 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
16439 @cite{What's GNU@?} column of the June 1994 @cite{Linux Journal}}.
16440 It was written by Arnold Robbins.
16443 * Toolbox introduction:: Toolbox introduction
16444 * I/O redirection:: I/O redirection
16445 * The who command:: The @command{who} command
16446 * The cut command:: The @command{cut} command
16447 * The sort command:: The @command{sort} command
16448 * The uniq command:: The @command{uniq} command
16449 * Putting the tools together:: Putting the tools together
16453 @node Toolbox introduction
16454 @unnumberedsec Toolbox Introduction
16456 This month's column is only peripherally related to the GNU Project, in
16457 that it describes a number of the GNU tools on your GNU/Linux system
16459 might be used. What it's really about is the ``Software Tools'' philosophy
16460 of program development and usage.
16462 The software tools philosophy was an important and integral concept
16463 in the initial design and development of Unix (of which Linux and GNU are
16464 essentially clones). Unfortunately, in the modern day press of
16465 Internetworking and flashy GUIs, it seems to have fallen by the
16466 wayside. This is a shame, since it provides a powerful mental model
16467 for solving many kinds of problems.
16469 Many people carry a Swiss Army knife around in their pants pockets (or
16470 purse). A Swiss Army knife is a handy tool to have: it has several knife
16471 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
16472 a number of other things on it. For the everyday, small miscellaneous jobs
16473 where you need a simple, general purpose tool, it's just the thing.
16475 On the other hand, an experienced carpenter doesn't build a house using
16476 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
16477 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
16478 exactly when and where to use each tool; you won't catch him hammering nails
16479 with the handle of his screwdriver.
16481 The Unix developers at Bell Labs were all professional programmers and trained
16482 computer scientists. They had found that while a one-size-fits-all program
16483 might appeal to a user because there's only one program to use, in practice
16488 difficult to write,
16491 difficult to maintain and
16495 difficult to extend to meet new situations.
16498 Instead, they felt that programs should be specialized tools. In short, each
16499 program ``should do one thing well.'' No more and no less. Such programs are
16500 simpler to design, write, and get right---they only do one thing.
16502 Furthermore, they found that with the right machinery for hooking programs
16503 together, that the whole was greater than the sum of the parts. By combining
16504 several special purpose programs, you could accomplish a specific task
16505 that none of the programs was designed for, and accomplish it much more
16506 quickly and easily than if you had to write a special purpose program.
16507 We will see some (classic) examples of this further on in the column.
16508 (An important additional point was that, if necessary, take a detour
16509 and build any software tools you may need first, if you don't already
16510 have something appropriate in the toolbox.)
16512 @node I/O redirection
16513 @unnumberedsec I/O Redirection
16515 Hopefully, you are familiar with the basics of I/O redirection in the
16516 shell, in particular the concepts of ``standard input,'' ``standard output,''
16517 and ``standard error''. Briefly, ``standard input'' is a data source, where
16518 data comes from. A program should not need to either know or care if the
16519 data source is a disk file, a keyboard, a magnetic tape, or even a punched
16520 card reader. Similarly, ``standard output'' is a data sink, where data goes
16521 to. The program should neither know nor care where this might be.
16522 Programs that only read their standard input, do something to the data,
16523 and then send it on, are called @dfn{filters}, by analogy to filters in a
16526 With the Unix shell, it's very easy to set up data pipelines:
16529 program_to_create_data | filter1 | ... | filterN > final.pretty.data
16532 We start out by creating the raw data; each filter applies some successive
16533 transformation to the data, until by the time it comes out of the pipeline,
16534 it is in the desired form.
16536 This is fine and good for standard input and standard output. Where does the
16537 standard error come in to play? Well, think about @command{filter1} in
16538 the pipeline above. What happens if it encounters an error in the data it
16539 sees? If it writes an error message to standard output, it will just
16540 disappear down the pipeline into @command{filter2}'s input, and the
16541 user will probably never see it. So programs need a place where they can send
16542 error messages so that the user will notice them. This is standard error,
16543 and it is usually connected to your console or window, even if you have
16544 redirected standard output of your program away from your screen.
16546 For filter programs to work together, the format of the data has to be
16547 agreed upon. The most straightforward and easiest format to use is simply
16548 lines of text. Unix data files are generally just streams of bytes, with
16549 lines delimited by the ASCII LF (Line Feed) character,
16550 conventionally called a ``newline'' in the Unix literature. (This is
16551 @code{'\n'} if you're a C programmer.) This is the format used by all
16552 the traditional filtering programs. (Many earlier operating systems
16553 had elaborate facilities and special purpose programs for managing
16554 binary data. Unix has always shied away from such things, under the
16555 philosophy that it's easiest to simply be able to view and edit your
16556 data with a text editor.)
16558 OK, enough introduction. Let's take a look at some of the tools, and then
16559 we'll see how to hook them together in interesting ways. In the following
16560 discussion, we will only present those command line options that interest
16561 us. As you should always do, double check your system documentation
16562 for the full story.
16564 @node The who command
16565 @unnumberedsec The @command{who} Command
16567 The first program is the @command{who} command. By itself, it generates a
16568 list of the users who are currently logged in. Although I'm writing
16569 this on a single-user system, we'll pretend that several people are
16574 @print{} arnold console Jan 22 19:57
16575 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
16576 @print{} bill ttyp1 Jan 21 09:32(:0.0)
16577 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
16580 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
16581 There are three people logged in, and I am logged in twice. On traditional
16582 Unix systems, user names are never more than eight characters long. This
16583 little bit of trivia will be useful later. The output of @command{who} is nice,
16584 but the data is not all that exciting.
16586 @node The cut command
16587 @unnumberedsec The @command{cut} Command
16589 The next program we'll look at is the @command{cut} command. This program
16590 cuts out columns or fields of input data. For example, we can tell it
16591 to print just the login name and full name from the @file{/etc/passwd}
16592 file. The @file{/etc/passwd} file has seven fields, separated by
16596 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
16599 To get the first and fifth fields, we would use @command{cut} like this:
16602 $ cut -d: -f1,5 /etc/passwd
16603 @print{} root:Operator
16605 @print{} arnold:Arnold D. Robbins
16606 @print{} miriam:Miriam A. Robbins
16610 With the @option{-c} option, @command{cut} will cut out specific characters
16611 (i.e., columns) in the input lines. This is useful for input data
16612 that has fixed width fields, and does not have a field separator. For
16613 example, list the Monday dates for the current month:
16615 @c Is using cal ok? Looked at gcal, but I don't like it.
16626 @node The sort command
16627 @unnumberedsec The @command{sort} Command
16629 Next we'll look at the @command{sort} command. This is one of the most
16630 powerful commands on a Unix-style system; one that you will often find
16631 yourself using when setting up fancy data plumbing.
16634 command reads and sorts each file named on the command line. It then
16635 merges the sorted data and writes it to standard output. It will read
16636 standard input if no files are given on the command line (thus
16637 making it into a filter). The sort is based on the character collating
16638 sequence or based on user-supplied ordering criteria.
16641 @node The uniq command
16642 @unnumberedsec The @command{uniq} Command
16644 Finally (at least for now), we'll look at the @command{uniq} program. When
16645 sorting data, you will often end up with duplicate lines, lines that
16646 are identical. Usually, all you need is one instance of each line.
16647 This is where @command{uniq} comes in. The @command{uniq} program reads its
16648 standard input. It prints only one
16649 copy of each repeated line. It does have several options. Later on,
16650 we'll use the @option{-c} option, which prints each unique line, preceded
16651 by a count of the number of times that line occurred in the input.
16654 @node Putting the tools together
16655 @unnumberedsec Putting the Tools Together
16657 Now, let's suppose this is a large ISP server system with dozens of users
16658 logged in. The management wants the system administrator to write a
16660 generate a sorted list of logged in users. Furthermore, even if a user
16661 is logged in multiple times, his or her name should only show up in the
16664 The administrator could sit down with the system documentation and write a C
16665 program that did this. It would take perhaps a couple of hundred lines
16666 of code and about two hours to write it, test it, and debug it.
16667 However, knowing the software toolbox, the administrator can instead start out
16668 by generating just a list of logged on users:
16678 Next, sort the list:
16681 $ who | cut -c1-8 | sort
16688 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
16691 $ who | cut -c1-8 | sort | uniq
16697 The @command{sort} command actually has a @option{-u} option that does what
16698 @command{uniq} does. However, @command{uniq} has other uses for which one
16699 cannot substitute @samp{sort -u}.
16701 The administrator puts this pipeline into a shell script, and makes it
16703 all the users on the system (@samp{#} is the system administrator,
16704 or @code{root}, prompt):
16707 # cat > /usr/local/bin/listusers
16708 who | cut -c1-8 | sort | uniq
16710 # chmod +x /usr/local/bin/listusers
16713 There are four major points to note here. First, with just four
16714 programs, on one command line, the administrator was able to save about two
16715 hours worth of work. Furthermore, the shell pipeline is just about as
16716 efficient as the C program would be, and it is much more efficient in
16717 terms of programmer time. People time is much more expensive than
16718 computer time, and in our modern ``there's never enough time to do
16719 everything'' society, saving two hours of programmer time is no mean
16722 Second, it is also important to emphasize that with the
16723 @emph{combination} of the tools, it is possible to do a special
16724 purpose job never imagined by the authors of the individual programs.
16726 Third, it is also valuable to build up your pipeline in stages, as we did here.
16727 This allows you to view the data at each stage in the pipeline, which helps
16728 you acquire the confidence that you are indeed using these tools correctly.
16730 Finally, by bundling the pipeline in a shell script, other users can use
16731 your command, without having to remember the fancy plumbing you set up for
16732 them. In terms of how you run them, shell scripts and compiled programs are
16735 After the previous warm-up exercise, we'll look at two additional, more
16736 complicated pipelines. For them, we need to introduce two more tools.
16738 The first is the @command{tr} command, which stands for ``transliterate.''
16739 The @command{tr} command works on a character-by-character basis, changing
16740 characters. Normally it is used for things like mapping upper case to
16744 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
16745 @print{} this example has mixed case!
16748 There are several options of interest:
16752 work on the complement of the listed characters, i.e.,
16753 operations apply to characters not in the given set
16756 delete characters in the first set from the output
16759 squeeze repeated characters in the output into just one character.
16762 We will be using all three options in a moment.
16764 The other command we'll look at is @command{comm}. The @command{comm}
16765 command takes two sorted input files as input data, and prints out the
16766 files' lines in three columns. The output columns are the data lines
16767 unique to the first file, the data lines unique to the second file, and
16768 the data lines that are common to both. The @option{-1}, @option{-2}, and
16769 @option{-3} command line options @emph{omit} the respective columns. (This is
16770 non-intuitive and takes a little getting used to.) For example:
16792 The file name @file{-} tells @command{comm} to read standard input
16793 instead of a regular file.
16795 Now we're ready to build a fancy pipeline. The first application is a word
16796 frequency counter. This helps an author determine if he or she is over-using
16799 The first step is to change the case of all the letters in our input file
16800 to one case. ``The'' and ``the'' are the same word when doing counting.
16803 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16806 The next step is to get rid of punctuation. Quoted words and unquoted words
16807 should be treated identically; it's easiest to just get the punctuation out of
16811 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16814 The second @command{tr} command operates on the complement of the listed
16815 characters, which are all the letters, the digits, the underscore, and
16816 the blank. The @samp{\n} represents the newline character; it has to
16817 be left alone. (The ASCII tab character should also be included for
16818 good measure in a production script.)
16820 At this point, we have data consisting of words separated by blank space.
16821 The words only contain alphanumeric characters (and the underscore). The
16822 next step is break the data apart so that we have one word per line. This
16823 makes the counting operation much easier, as we will see shortly.
16826 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16827 > tr -s ' ' '\n' | ...
16830 This command turns blanks into newlines. The @option{-s} option squeezes
16831 multiple newline characters in the output into just one. This helps us
16832 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16833 This is what the shell prints when it notices you haven't finished
16834 typing in all of a command.)
16836 We now have data consisting of one word per line, no punctuation, all one
16837 case. We're ready to count each word:
16840 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16841 > tr -s ' ' '\n' | sort | uniq -c | ...
16844 At this point, the data might look something like this:
16857 The output is sorted by word, not by count! What we want is the most
16858 frequently used words first. Fortunately, this is easy to accomplish,
16859 with the help of two more @command{sort} options:
16863 do a numeric sort, not a textual one
16866 reverse the order of the sort
16869 The final pipeline looks like this:
16872 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16873 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16882 Whew! That's a lot to digest. Yet, the same principles apply. With six
16883 commands, on two lines (really one long one split for convenience), we've
16884 created a program that does something interesting and useful, in much
16885 less time than we could have written a C program to do the same thing.
16887 A minor modification to the above pipeline can give us a simple spelling
16888 checker! To determine if you've spelled a word correctly, all you have to
16889 do is look it up in a dictionary. If it is not there, then chances are
16890 that your spelling is incorrect. So, we need a dictionary.
16891 The conventional location for a dictionary is @file{/usr/dict/words}.
16892 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16893 revision of this article.}
16894 this is a sorted, 45,402 word dictionary.
16896 Now, how to compare our file with the dictionary? As before, we generate
16897 a sorted list of words, one per line:
16900 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16901 > tr -s ' ' '\n' | sort -u | ...
16904 Now, all we need is a list of words that are @emph{not} in the
16905 dictionary. Here is where the @command{comm} command comes in.
16908 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16909 > tr -s ' ' '\n' | sort -u |
16910 > comm -23 - /usr/dict/words
16913 The @option{-2} and @option{-3} options eliminate lines that are only in the
16914 dictionary (the second file), and lines that are in both files. Lines
16915 only in the first file (standard input, our stream of words), are
16916 words that are not in the dictionary. These are likely candidates for
16917 spelling errors. This pipeline was the first cut at a production
16918 spelling checker on Unix.
16920 There are some other tools that deserve brief mention.
16924 search files for text that matches a regular expression
16927 count lines, words, characters
16930 a T-fitting for data pipes, copies data to files and to standard output
16933 the stream editor, an advanced tool
16936 a data manipulation language, another advanced tool
16939 The software tools philosophy also espoused the following bit of
16940 advice: ``Let someone else do the hard part.'' This means, take
16941 something that gives you most of what you need, and then massage it the
16942 rest of the way until it's in the form that you want.
16948 Each program should do one thing well. No more, no less.
16951 Combining programs with appropriate plumbing leads to results where
16952 the whole is greater than the sum of the parts. It also leads to novel
16953 uses of programs that the authors might never have imagined.
16956 Programs should never print extraneous header or trailer data, since these
16957 could get sent on down a pipeline. (A point we didn't mention earlier.)
16960 Let someone else do the hard part.
16963 Know your toolbox! Use each program appropriately. If you don't have an
16964 appropriate tool, build one.
16967 As of this writing, all the programs we've discussed are available via
16968 anonymous @command{ftp} from: @*
16969 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16970 be more recent versions available now.)
16972 None of what I have presented in this column is new. The Software Tools
16973 philosophy was first introduced in the book @cite{Software Tools}, by
16974 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16975 This book showed how to write and use software tools. It was written in
16976 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16977 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16978 was. The last chapter presented a @command{ratfor} to FORTRAN
16979 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16980 lot like C; if you know C, you won't have any problem following the
16983 In 1981, the book was updated and made available as @cite{Software Tools
16984 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16985 still in print and are well worth
16986 reading if you're a programmer. They certainly made a major change in
16987 how I view programming.
16989 The programs in both books are available from
16990 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16991 For a number of years, there was an active
16992 Software Tools Users Group, whose members had ported the original
16993 @command{ratfor} programs to essentially every computer system with a
16994 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16995 as Unix began to spread beyond universities.
16997 With the current proliferation of GNU code and other clones of Unix programs,
16998 these programs now receive little attention; modern C versions are
16999 much more efficient and do more than these programs do. Nevertheless, as
17000 exposition of good programming style, and evangelism for a still-valuable
17001 philosophy, these books are unparalleled, and I recommend them highly.
17003 Acknowledgment: I would like to express my gratitude to Brian Kernighan
17004 of Bell Labs, the original Software Toolsmith, for reviewing this column.
17006 @node GNU Free Documentation License
17007 @appendix GNU Free Documentation License
17011 @node Concept index
17018 @c Local variables:
17019 @c texinfo-column-for-description: 32