3 @setfilename coreutils.info
4 @settitle @sc{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 @sc{gnu} core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-2012 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 @sc{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:: @sc{est}, @sc{pdt}, @sc{gmt}
473 * Day of week items:: Monday and others
474 * Relative items in date strings:: next tuesday, 2 years ago
475 * Pure numbers in date strings:: 19931219, 1440
476 * Seconds since the Epoch:: @@1078100502
477 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
478 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al
480 Opening the software toolbox
482 * Toolbox introduction:: Toolbox introduction
483 * I/O redirection:: I/O redirection
484 * The who command:: The @command{who} command
485 * The cut command:: The @command{cut} command
486 * The sort command:: The @command{sort} command
487 * The uniq command:: The @command{uniq} command
488 * Putting the tools together:: Putting the tools together
492 * GNU Free Documentation License:: Copying and sharing this manual
499 @chapter Introduction
501 This manual is a work in progress: many sections make no attempt to explain
502 basic concepts in a way suitable for novices. Thus, if you are interested,
503 please get involved in improving this manual. The entire @sc{gnu} community
507 The @sc{gnu} utilities documented here are mostly compatible with the
509 @cindex bugs, reporting
510 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
511 to include the version number, machine architecture, input files, and
512 any other information needed to reproduce the bug: your input, what you
513 expected, what you got, and why it is wrong. Diffs are welcome, but
514 please include a description of the problem as well, since this is
515 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
521 @cindex MacKenzie, D.
524 This manual was originally derived from the Unix man pages in the
525 distributions, which were written by David MacKenzie and updated by Jim
526 Meyering. What you are reading now is the authoritative documentation
527 for these utilities; the man pages are no longer being maintained. The
528 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
529 Pinard did the initial conversion to Texinfo format. Karl Berry did the
530 indexing, some reorganization, and editing of the results. Brian
531 Youmans of the Free Software Foundation office staff combined the
532 manuals for textutils, fileutils, and sh-utils to produce the present
533 omnibus manual. Richard Stallman contributed his usual invaluable
534 insights to the overall process.
537 @chapter Common options
541 @itemx @w{@kbd{--backup}[=@var{method}]}
544 @vindex VERSION_CONTROL
545 @cindex backups, making
546 @xref{Backup options}.
547 Make a backup of each file that would otherwise be overwritten or removed.
550 @macro optBackupSuffix
551 @item -S @var{suffix}
552 @itemx --suffix=@var{suffix}
555 Append @var{suffix} to each backup file made with @option{-b}.
556 @xref{Backup options}.
559 @macro optTargetDirectory
560 @item -t @var{directory}
561 @itemx @w{@kbd{--target-directory}=@var{directory}}
563 @opindex --target-directory
564 @cindex target directory
565 @cindex destination directory
566 Specify the destination @var{directory}.
567 @xref{Target directory}.
570 @macro optNoTargetDirectory
572 @itemx --no-target-directory
574 @opindex --no-target-directory
575 @cindex target directory
576 @cindex destination directory
577 Do not treat the last operand specially when it is a directory or a
578 symbolic link to a directory. @xref{Target directory}.
586 @cindex output @sc{nul}-byte-terminated lines
587 Output a zero byte (ASCII @sc{nul}) at the end of each line,
588 rather than a newline. This option enables other programs to parse the
589 output of @command{\cmd\} even when that output would contain data
590 with embedded newlines.
597 Append an SI-style abbreviation to each size, such as @samp{M} for
598 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
599 1,000,000 bytes. This option is equivalent to
600 @option{--block-size=si}. Use the @option{-h} or
601 @option{--human-readable} option if
602 you prefer powers of 1024.
605 @macro optHumanReadable
607 @itemx --human-readable
609 @opindex --human-readable
610 @cindex human-readable output
611 Append a size letter to each size, such as @samp{M} for mebibytes.
612 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
613 This option is equivalent to @option{--block-size=human-readable}.
614 Use the @option{--si} option if you prefer powers of 1000.
617 @macro optStripTrailingSlashes
618 @item @w{@kbd{--strip-trailing-slashes}}
619 @opindex --strip-trailing-slashes
620 @cindex stripping trailing slashes
621 Remove any trailing slashes from each @var{source} argument.
622 @xref{Trailing slashes}.
625 @macro mayConflictWithShellBuiltIn{cmd}
626 @cindex conflicts with shell built-ins
627 @cindex built-in shell commands, conflicts with
628 Due to shell aliases and built-in @command{\cmd\} functions, using an
629 unadorned @command{\cmd\} interactively or in a script may get you
630 different functionality than that described here. Invoke it via
631 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
636 @macro multiplierSuffixes{varName}
637 @var{\varName\} may be, or may be an integer optionally followed by,
638 one of the following multiplicative suffixes:
640 @samp{b} => 512 ("blocks")
641 @samp{KB} => 1000 (KiloBytes)
642 @samp{K} => 1024 (KibiBytes)
643 @samp{MB} => 1000*1000 (MegaBytes)
644 @samp{M} => 1024*1024 (MebiBytes)
645 @samp{GB} => 1000*1000*1000 (GigaBytes)
646 @samp{G} => 1024*1024*1024 (GibiBytes)
648 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
651 @c FIXME: same as above, but no ``blocks'' line.
652 @macro multiplierSuffixesNoBlocks{varName}
653 @var{\varName\} may be, or may be an integer optionally followed by,
654 one of the following multiplicative suffixes:
656 @samp{KB} => 1000 (KiloBytes)
657 @samp{K} => 1024 (KibiBytes)
658 @samp{MB} => 1000*1000 (MegaBytes)
659 @samp{M} => 1024*1024 (MebiBytes)
660 @samp{GB} => 1000*1000*1000 (GigaBytes)
661 @samp{G} => 1024*1024*1024 (GibiBytes)
663 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
666 @cindex common options
668 Certain options are available in all of these programs. Rather than
669 writing identical descriptions for each of the programs, they are
670 described here. (In fact, every @sc{gnu} program accepts (or should accept)
673 @vindex POSIXLY_CORRECT
674 Normally options and operands can appear in any order, and programs act
675 as if all the options appear before any operands. For example,
676 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
677 @samp{:} is an option-argument of @option{-t}. However, if the
678 @env{POSIXLY_CORRECT} environment variable is set, options must appear
679 before operands, unless otherwise specified for a particular command.
681 A few programs can usefully have trailing operands with leading
682 @samp{-}. With such a program, options must precede operands even if
683 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
684 program description. For example, the @command{env} command's options
685 must appear before its operands, since in some cases the operands
686 specify a command that itself contains options.
688 Most programs that accept long options recognize unambiguous
689 abbreviations of those options. For example, @samp{rmdir
690 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
691 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
692 @samp{ls --h}, are identified as such.
694 Some of these programs recognize the @option{--help} and @option{--version}
695 options only when one of them is the sole command line argument. For
696 these programs, abbreviations of the long options are not always recognized.
703 Print a usage message listing all available options, then exit successfully.
707 @cindex version number, finding
708 Print the version number, then exit successfully.
712 @cindex option delimiter
713 Delimit the option list. Later arguments, if any, are treated as
714 operands even if they begin with @samp{-}. For example, @samp{sort --
715 -r} reads from the file named @file{-r}.
719 @cindex standard input
720 @cindex standard output
721 A single @samp{-} operand is not really an option, though it looks like one. It
722 stands for standard input, or for standard output if that is clear from
723 the context. For example, @samp{sort -} reads from standard input,
724 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
725 extra copy of its input to standard output. Unless otherwise
726 specified, @samp{-} can appear as any operand that requires a file
730 * Exit status:: Indicating program success or failure.
731 * Backup options:: -b -S, in some programs.
732 * Block size:: BLOCK_SIZE and --block-size, in some programs.
733 * Floating point:: Floating point number representation.
734 * Signal specifications:: Specifying signals using the --signal option.
735 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
736 * Random sources:: --random-source, in some programs.
737 * Target directory:: Specifying a target directory, in some programs.
738 * Trailing slashes:: --strip-trailing-slashes, in some programs.
739 * Traversing symlinks:: -H, -L, or -P, in some programs.
740 * Treating / specially:: --preserve-root and --no-preserve-root.
741 * Special built-in utilities:: @command{break}, @command{:}, @dots{}
742 * Standards conformance:: Conformance to the POSIX standard.
750 An exit status of zero indicates success,
751 and a nonzero value indicates failure.
754 Nearly every command invocation yields an integral @dfn{exit status}
755 that can be used to change how other commands work.
756 For the vast majority of commands, an exit status of zero indicates
757 success. Failure is indicated by a nonzero value---typically
758 @samp{1}, though it may differ on unusual platforms as POSIX
759 requires only that it be nonzero.
761 However, some of the programs documented here do produce
762 other exit status values and a few associate different
763 meanings with the values @samp{0} and @samp{1}.
764 Here are some of the exceptions:
765 @command{chroot}, @command{env}, @command{expr}, @command{nice},
766 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
767 @command{test}, @command{timeout}, @command{tty}.
771 @section Backup options
773 @cindex backup options
775 Some @sc{gnu} programs (at least @command{cp}, @command{install},
776 @command{ln}, and @command{mv}) optionally make backups of files
777 before writing new versions.
778 These options control the details of these backups. The options are also
779 briefly mentioned in the descriptions of the particular programs.
784 @itemx @w{@kbd{--backup}[=@var{method}]}
787 @vindex VERSION_CONTROL
788 @cindex backups, making
789 Make a backup of each file that would otherwise be overwritten or removed.
790 Without this option, the original versions are destroyed.
791 Use @var{method} to determine the type of backups to make.
792 When this option is used but @var{method} is not specified,
793 then the value of the @env{VERSION_CONTROL}
794 environment variable is used. And if @env{VERSION_CONTROL} is not set,
795 the default backup type is @samp{existing}.
797 Note that the short form of this option, @option{-b} does not accept any
798 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
800 @vindex version-control @r{Emacs variable}
801 This option corresponds to the Emacs variable @samp{version-control};
802 the values for @var{method} are the same as those used in Emacs.
803 This option also accepts more descriptive names.
804 The valid @var{method}s are (unique abbreviations are accepted):
809 @opindex none @r{backup method}
814 @opindex numbered @r{backup method}
815 Always make numbered backups.
819 @opindex existing @r{backup method}
820 Make numbered backups of files that already have them, simple backups
825 @opindex simple @r{backup method}
826 Always make simple backups. Please note @samp{never} is not to be
827 confused with @samp{none}.
831 @item -S @var{suffix}
832 @itemx --suffix=@var{suffix}
835 @cindex backup suffix
836 @vindex SIMPLE_BACKUP_SUFFIX
837 Append @var{suffix} to each backup file made with @option{-b}. If this
838 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
839 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
840 set, the default is @samp{~}, just as in Emacs.
849 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
850 @command{ls}) display sizes in ``blocks''. You can adjust the block size
851 and method of display to make sizes easier to read. The block size
852 used for display is independent of any file system block size.
853 Fractional block counts are rounded up to the nearest integer.
855 @opindex --block-size=@var{size}
858 @vindex DF_BLOCK_SIZE
859 @vindex DU_BLOCK_SIZE
860 @vindex LS_BLOCK_SIZE
861 @vindex POSIXLY_CORRECT@r{, and block size}
863 The default block size is chosen by examining the following environment
864 variables in turn; the first one that is set determines the block size.
869 This specifies the default block size for the @command{df} command.
870 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
871 @env{LS_BLOCK_SIZE} for @command{ls}.
874 This specifies the default block size for all three commands, if the
875 above command-specific environment variables are not set.
878 This specifies the default block size for all values that are normally
879 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
880 command-specific environment variables are set. Unlike the other
881 environment variables, @env{BLOCKSIZE} does not affect values that are
882 normally printed as byte counts, e.g., the file sizes contained in
885 @item POSIXLY_CORRECT
886 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
887 @env{BLOCKSIZE} is set, but this variable is set, the block size
892 If none of the above environment variables are set, the block size
893 currently defaults to 1024 bytes in most contexts, but this number may
894 change in the future. For @command{ls} file sizes, the block size
897 @cindex human-readable output
900 A block size specification can be a positive integer specifying the number
901 of bytes per block, or it can be @code{human-readable} or @code{si} to
902 select a human-readable format. Integers may be followed by suffixes
903 that are upward compatible with the
904 @uref{http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html, SI prefixes}
905 for decimal multiples and with the
906 @uref{http://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13
907 (formerly IEC 60027-2) prefixes} for binary multiples.
909 With human-readable formats, output sizes are followed by a size letter
910 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
911 powers of 1024; @samp{M} stands for 1,048,576 bytes.
912 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
913 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
916 A block size specification preceded by @samp{'} causes output sizes to
917 be displayed with thousands separators. The @env{LC_NUMERIC} locale
918 specifies the thousands separator and grouping. For example, in an
919 American English locale, @samp{--block-size="'1kB"} would cause a size
920 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
921 locale, there is no thousands separator so a leading @samp{'} has no
924 An integer block size can be followed by a suffix to specify a
925 multiple of that size. A bare size letter,
926 or one followed by @samp{iB}, specifies
927 a multiple using powers of 1024. A size letter followed by @samp{B}
928 specifies powers of 1000 instead. For example, @samp{1M} and
929 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
930 equivalent to @samp{1000000}.
932 A plain suffix without a preceding integer acts as if @samp{1} were
933 prepended, except that it causes a size indication to be appended to
934 the output. For example, @samp{--block-size="kB"} displays 3000 as
937 The following suffixes are defined. Large sizes like @code{1Y}
938 may be rejected by your computer due to limitations of its arithmetic.
942 @cindex kilobyte, definition of
943 kilobyte: @math{10^3 = 1000}.
947 @cindex kibibyte, definition of
948 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
949 @samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and
950 POSIX use @samp{k} to mean @samp{KiB}.
952 @cindex megabyte, definition of
953 megabyte: @math{10^6 = 1,000,000}.
956 @cindex mebibyte, definition of
957 mebibyte: @math{2^{20} = 1,048,576}.
959 @cindex gigabyte, definition of
960 gigabyte: @math{10^9 = 1,000,000,000}.
963 @cindex gibibyte, definition of
964 gibibyte: @math{2^{30} = 1,073,741,824}.
966 @cindex terabyte, definition of
967 terabyte: @math{10^{12} = 1,000,000,000,000}.
970 @cindex tebibyte, definition of
971 tebibyte: @math{2^{40} = 1,099,511,627,776}.
973 @cindex petabyte, definition of
974 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
977 @cindex pebibyte, definition of
978 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
980 @cindex exabyte, definition of
981 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
984 @cindex exbibyte, definition of
985 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
987 @cindex zettabyte, definition of
988 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
991 @math{2^{70} = 1,180,591,620,717,411,303,424}.
993 @cindex yottabyte, definition of
994 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
997 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
1002 @opindex --block-size
1003 @opindex --human-readable
1006 Block size defaults can be overridden by an explicit
1007 @option{--block-size=@var{size}} option. The @option{-k}
1008 option is equivalent to @option{--block-size=1K}, which
1009 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1010 set. The @option{-h} or @option{--human-readable} option is equivalent to
1011 @option{--block-size=human-readable}. The @option{--si} option is
1012 equivalent to @option{--block-size=si}.
1014 @node Floating point
1015 @section Floating point numbers
1016 @cindex floating point
1017 @cindex IEEE floating point
1019 Commands that accept or produce floating point numbers employ the
1020 floating point representation of the underlying system, and suffer
1021 from rounding error, overflow, and similar floating-point issues.
1022 Almost all modern systems use IEEE-754 floating point, and it is
1023 typically portable to assume IEEE-754 behavior these days. IEEE-754
1024 has positive and negative infinity, distinguishes positive from
1025 negative zero, and uses special values called NaNs to represent
1026 invalid computations such as dividing zero by itself. For more
1027 information, please see David Goldberg's paper
1028 @uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
1029 Computer Scientist Should Know About Floating-Point Arithmetic}.
1032 Commands that accept floating point numbers as options, operands or
1033 input use the standard C functions @code{strtod} and @code{strtold} to
1034 convert from text to floating point numbers. These floating point
1035 numbers therefore can use scientific notation like @code{1.0e-34} and
1036 @code{-10e100}. Modern C implementations also accept hexadecimal
1037 floating point numbers such as @code{-0x.ep-3}, which stands for
1038 @minus{}14/16 times @math{2^-3}, which equals @minus{}0.109375. The
1039 @env{LC_NUMERIC} locale determines the decimal-point character.
1040 @xref{Parsing of Floats,,, libc, The GNU C Library Reference Manual}.
1042 @node Signal specifications
1043 @section Signal specifications
1044 @cindex signals, specifying
1046 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1047 number like @samp{1}, or an exit status of a process terminated by the
1048 signal. A signal name can be given in canonical form or prefixed by
1049 @samp{SIG}@. The case of the letters is ignored. The following signal names
1050 and numbers are supported on all POSIX compliant systems:
1056 2. Terminal interrupt.
1062 9. Kill (cannot be caught or ignored).
1070 Other supported signal names have system-dependent corresponding
1071 numbers. All systems conforming to POSIX 1003.1-2001 also
1072 support the following signals:
1076 Access to an undefined portion of a memory object.
1078 Child process terminated, stopped, or continued.
1080 Continue executing, if stopped.
1082 Erroneous arithmetic operation.
1084 Illegal Instruction.
1086 Write on a pipe with no one to read it.
1088 Invalid memory reference.
1090 Stop executing (cannot be caught or ignored).
1094 Background process attempting read.
1096 Background process attempting write.
1098 High bandwidth data is available at a socket.
1100 User-defined signal 1.
1102 User-defined signal 2.
1106 POSIX 1003.1-2001 systems that support the XSI extension
1107 also support the following signals:
1113 Profiling timer expired.
1117 Trace/breakpoint trap.
1119 Virtual timer expired.
1121 CPU time limit exceeded.
1123 File size limit exceeded.
1127 POSIX 1003.1-2001 systems that support the XRT extension
1128 also support at least eight real-time signals called @samp{RTMIN},
1129 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1131 @node Disambiguating names and IDs
1132 @section chown and chgrp: Disambiguating user names and IDs
1133 @cindex user names, disambiguating
1134 @cindex user IDs, disambiguating
1135 @cindex group names, disambiguating
1136 @cindex group IDs, disambiguating
1137 @cindex disambiguating group names and IDs
1139 Since the @var{owner} and @var{group} arguments to @command{chown} and
1140 @command{chgrp} may be specified as names or numeric IDs, there is an
1142 What if a user or group @emph{name} is a string of digits?
1143 @footnote{Using a number as a user name is common in some environments.}
1144 Should the command interpret it as a user name or as an ID@?
1145 POSIX requires that @command{chown} and @command{chgrp}
1146 first attempt to resolve the specified string as a name, and
1147 only once that fails, then try to interpret it as an ID@.
1148 This is troublesome when you want to specify a numeric ID, say 42,
1149 and it must work even in a pathological situation where
1150 @samp{42} is a user name that maps to some other user ID, say 1000.
1151 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1152 1000---not what you intended.
1154 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1155 that at the same time may result in a significant performance improvement
1156 by eliminating a database look-up.
1157 Simply precede each numeric user ID and/or group ID with a @samp{+},
1158 in order to force its interpretation as an integer:
1162 chgrp +$numeric_group_id another-file
1166 GNU @command{chown} and @command{chgrp}
1167 skip the name look-up process for each @samp{+}-prefixed string,
1168 because a string containing @samp{+} is never a valid user or group name.
1169 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1171 @node Random sources
1172 @section Sources of random data
1174 @cindex random sources
1176 The @command{shuf}, @command{shred}, and @command{sort} commands
1177 sometimes need random data to do their work. For example, @samp{sort
1178 -R} must choose a hash function at random, and it needs random data to
1179 make this selection.
1181 By default these commands use an internal pseudorandom generator
1182 initialized by a small amount of entropy, but can be directed to use
1183 an external source with the @option{--random-source=@var{file}} option.
1184 An error is reported if @var{file} does not contain enough bytes.
1186 For example, the device file @file{/dev/urandom} could be used as the
1187 source of random data. Typically, this device gathers environmental
1188 noise from device drivers and other sources into an entropy pool, and
1189 uses the pool to generate random bits. If the pool is short of data,
1190 the device reuses the internal pool to produce more bits, using a
1191 cryptographically secure pseudorandom number generator. But be aware
1192 that this device is not designed for bulk random data generation
1193 and is relatively slow.
1195 @file{/dev/urandom} suffices for most practical uses, but applications
1196 requiring high-value or long-term protection of private data may
1197 require an alternate data source like @file{/dev/random} or
1198 @file{/dev/arandom}. The set of available sources depends on your
1201 To reproduce the results of an earlier invocation of a command, you
1202 can save some random data into a file and then use that file as the
1203 random source in earlier and later invocations of the command.
1205 @node Target directory
1206 @section Target directory
1208 @cindex target directory
1210 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1211 commands normally treat the last operand specially when it is a
1212 directory or a symbolic link to a directory. For example, @samp{cp
1213 source dest} is equivalent to @samp{cp source dest/source} if
1214 @file{dest} is a directory. Sometimes this behavior is not exactly
1215 what is wanted, so these commands support the following options to
1216 allow more fine-grained control:
1221 @itemx --no-target-directory
1222 @opindex --no-target-directory
1223 @cindex target directory
1224 @cindex destination directory
1225 Do not treat the last operand specially when it is a directory or a
1226 symbolic link to a directory. This can help avoid race conditions in
1227 programs that operate in a shared area. For example, when the command
1228 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1229 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1230 renamed to @file{/tmp/dest/source} instead, if some other process
1231 created @file{/tmp/dest} as a directory. However, if @file{mv
1232 -T /tmp/source /tmp/dest} succeeds, there is no
1233 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1235 In the opposite situation, where you want the last operand to be
1236 treated as a directory and want a diagnostic otherwise, you can use
1237 the @option{--target-directory} (@option{-t}) option.
1239 @item -t @var{directory}
1240 @itemx @w{@kbd{--target-directory}=@var{directory}}
1241 @opindex --target-directory
1242 @cindex target directory
1243 @cindex destination directory
1244 Use @var{directory} as the directory component of each destination
1247 The interface for most programs is that after processing options and a
1248 finite (possibly zero) number of fixed-position arguments, the remaining
1249 argument list is either expected to be empty, or is a list of items
1250 (usually files) that will all be handled identically. The @command{xargs}
1251 program is designed to work well with this convention.
1253 The commands in the @command{mv}-family are unusual in that they take
1254 a variable number of arguments with a special case at the @emph{end}
1255 (namely, the target directory). This makes it nontrivial to perform some
1256 operations, e.g., ``move all files from here to ../d/'', because
1257 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1258 doesn't have a clean way to specify an extra final argument for each
1259 invocation of the subject command. (It can be done by going through a
1260 shell command, but that requires more human labor and brain power than
1263 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1264 @command{install}, @command{ln}, and @command{mv} programs to be used
1265 conveniently with @command{xargs}. For example, you can move the files
1266 from the current directory to a sibling directory, @code{d} like this:
1269 ls | xargs mv -t ../d --
1272 However, this doesn't move files whose names begin with @samp{.}.
1273 If you use the @sc{gnu} @command{find} program, you can move those
1274 files too, with this command:
1277 find . -mindepth 1 -maxdepth 1 \
1281 But both of the above approaches fail if there are no files in the
1282 current directory, or if any file has a name containing a blank or
1283 some other special characters.
1284 The following example removes those limitations and requires both
1285 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1288 find . -mindepth 1 -maxdepth 1 -print0 \
1289 | xargs --null --no-run-if-empty \
1296 The @option{--target-directory} (@option{-t}) and
1297 @option{--no-target-directory} (@option{-T})
1298 options cannot be combined.
1300 @node Trailing slashes
1301 @section Trailing slashes
1303 @cindex trailing slashes
1305 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1306 remove any trailing slashes from each @var{source} argument before
1307 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1310 This is useful when a @var{source} argument may have a trailing slash and
1311 @c FIXME: mv's behavior in this case is system-dependent
1312 specify a symbolic link to a directory. This scenario is in fact rather
1313 common because some shells can automatically append a trailing slash when
1314 performing file name completion on such symbolic links. Without this
1315 option, @command{mv}, for example, (via the system's rename function) must
1316 interpret a trailing slash as a request to dereference the symbolic link
1317 and so must rename the indirectly referenced @emph{directory} and not
1318 the symbolic link. Although it may seem surprising that such behavior
1319 be the default, it is required by POSIX and is consistent with
1320 other parts of that standard.
1322 @node Traversing symlinks
1323 @section Traversing symlinks
1325 @cindex symbolic link to directory, controlling traversal of
1327 The following options modify how @command{chown} and @command{chgrp}
1328 @c FIXME: note that 'du' has these options, too, but they have slightly
1329 @c different meaning.
1330 traverse a hierarchy when the @option{--recursive} (@option{-R})
1331 option is also specified.
1332 If more than one of the following options is specified, only the final
1334 These options specify whether processing a symbolic link to a directory
1335 entails operating on just the symbolic link or on all files in the
1336 hierarchy rooted at that directory.
1338 These options are independent of @option{--dereference} and
1339 @option{--no-dereference} (@option{-h}), which control whether to modify
1340 a symlink or its referent.
1347 @cindex symbolic link to directory, traverse if on the command line
1348 If @option{--recursive} (@option{-R}) is specified and
1349 a command line argument is a symbolic link to a directory, traverse it.
1356 @cindex symbolic link to directory, traverse each that is encountered
1357 In a recursive traversal, traverse every symbolic link to a directory
1358 that is encountered.
1365 @cindex symbolic link to directory, never traverse
1366 Do not traverse any symbolic links.
1367 This is the default if none of @option{-H}, @option{-L},
1368 or @option{-P} is specified.
1375 @node Treating / specially
1376 @section Treating @file{/} specially
1378 Certain commands can operate destructively on entire hierarchies.
1379 For example, if a user with appropriate privileges mistakenly runs
1380 @samp{rm -rf / tmp/junk}, that may remove
1381 all files on the entire system. Since there are so few
1382 legitimate uses for such a command,
1383 @sc{gnu} @command{rm} normally declines to operate on any directory
1384 that resolves to @file{/}. If you really want to try to remove all
1385 the files on your system, you can use the @option{--no-preserve-root}
1386 option, but the default behavior, specified by the
1387 @option{--preserve-option}, is safer for most purposes.
1389 The commands @command{chgrp}, @command{chmod} and @command{chown}
1390 can also operate destructively on entire hierarchies, so they too
1391 support these options. Although, unlike @command{rm}, they don't
1392 actually unlink files, these commands are arguably more dangerous
1393 when operating recursively on @file{/}, since they often work much
1394 more quickly, and hence damage more files before an alert user can
1395 interrupt them. Tradition and POSIX require these commands
1396 to operate recursively on @file{/}, so they default to
1397 @option{--no-preserve-root}, but using the @option{--preserve-root}
1398 option makes them safer for most purposes. For convenience you can
1399 specify @option{--preserve-root} in an alias or in a shell function.
1401 Note that the @option{--preserve-root} option also ensures
1402 that @command{chgrp} and @command{chown} do not modify @file{/}
1403 even when dereferencing a symlink pointing to @file{/}.
1405 @node Special built-in utilities
1406 @section Special built-in utilities
1408 Some programs like @command{nice} can invoke other programs; for
1409 example, the command @samp{nice cat file} invokes the program
1410 @command{cat} by executing the command @samp{cat file}. However,
1411 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1412 this way. For example, the command @samp{nice exit} does not have a
1413 well-defined behavior: it may generate an error message instead of
1416 Here is a list of the special built-in utilities that are standardized
1417 by POSIX 1003.1-2004.
1420 @t{.@: : break continue eval exec exit export readonly
1421 return set shift times trap unset}
1424 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1425 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1426 pwd} do not work as you might expect.
1428 Many shells extend this list. For example, Bash has several extra
1429 special built-in utilities like @command{history}, and
1430 @command{suspend}, and with Bash the command @samp{nice suspend}
1431 generates an error message instead of suspending.
1433 @node Standards conformance
1434 @section Standards conformance
1436 @vindex POSIXLY_CORRECT
1437 In a few cases, the @sc{gnu} utilities' default behavior is
1438 incompatible with the POSIX standard. To suppress these
1439 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1440 variable. Unless you are checking for POSIX conformance, you
1441 probably do not need to define @env{POSIXLY_CORRECT}.
1443 Newer versions of POSIX are occasionally incompatible with older
1444 versions. For example, older versions of POSIX required the
1445 command @samp{sort +1} to sort based on the second and succeeding
1446 fields in each input line, but starting with POSIX 1003.1-2001
1447 the same command is required to sort the file named @file{+1}, and you
1448 must instead use the command @samp{sort -k 2} to get the field-based
1451 @vindex _POSIX2_VERSION
1452 The @sc{gnu} utilities normally conform to the version of POSIX
1453 that is standard for your system. To cause them to conform to a
1454 different version of POSIX, define the @env{_POSIX2_VERSION}
1455 environment variable to a value of the form @var{yyyymm} specifying
1456 the year and month the standard was adopted. Three values are currently
1457 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1458 POSIX 1003.2-1992, @samp{200112} stands for POSIX
1459 1003.1-2001, and @samp{200809} stands for POSIX 1003.1-2008.
1460 For example, if you have a newer system but are running software
1461 that assumes an older version of POSIX and uses @samp{sort +1}
1462 or @samp{tail +10}, you can work around any compatibility problems by setting
1463 @samp{_POSIX2_VERSION=199209} in your environment.
1465 @node Output of entire files
1466 @chapter Output of entire files
1468 @cindex output of entire files
1469 @cindex entire files, output of
1471 These commands read and write entire files, possibly transforming them
1475 * cat invocation:: Concatenate and write files.
1476 * tac invocation:: Concatenate and write files in reverse.
1477 * nl invocation:: Number lines and write files.
1478 * od invocation:: Write files in octal or other formats.
1479 * base64 invocation:: Transform data into printable data.
1482 @node cat invocation
1483 @section @command{cat}: Concatenate and write files
1486 @cindex concatenate and write files
1487 @cindex copying files
1489 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1490 standard input if none are given, to standard output. Synopsis:
1493 cat [@var{option}] [@var{file}]@dots{}
1496 The program accepts the following options. Also see @ref{Common options}.
1504 Equivalent to @option{-vET}.
1507 @itemx --number-nonblank
1509 @opindex --number-nonblank
1510 Number all nonempty output lines, starting with 1.
1514 Equivalent to @option{-vE}.
1519 @opindex --show-ends
1520 Display a @samp{$} after the end of each line.
1526 Number all output lines, starting with 1. This option is ignored
1527 if @option{-b} is in effect.
1530 @itemx --squeeze-blank
1532 @opindex --squeeze-blank
1533 @cindex squeezing empty lines
1534 Suppress repeated adjacent empty lines; output just one empty line
1539 Equivalent to @option{-vT}.
1544 @opindex --show-tabs
1545 Display TAB characters as @samp{^I}.
1549 Ignored; for POSIX compatibility.
1552 @itemx --show-nonprinting
1554 @opindex --show-nonprinting
1555 Display control characters except for LFD and TAB using
1556 @samp{^} notation and precede characters that have the high bit set with
1561 On systems like MS-DOS that distinguish between text and binary files,
1562 @command{cat} normally reads and writes in binary mode. However,
1563 @command{cat} reads in text mode if one of the options
1564 @option{-bensAE} is used or if @command{cat} is reading from standard
1565 input and standard input is a terminal. Similarly, @command{cat}
1566 writes in text mode if one of the options @option{-bensAE} is used or
1567 if standard output is a terminal.
1574 # Output f's contents, then standard input, then g's contents.
1577 # Copy standard input to standard output.
1582 @node tac invocation
1583 @section @command{tac}: Concatenate and write files in reverse
1586 @cindex reversing files
1588 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1589 standard input if none are given, to standard output, reversing the
1590 records (lines by default) in each separately. Synopsis:
1593 tac [@var{option}]@dots{} [@var{file}]@dots{}
1596 @dfn{Records} are separated by instances of a string (newline by
1597 default). By default, this separator string is attached to the end of
1598 the record that it follows in the file.
1600 The program accepts the following options. Also see @ref{Common options}.
1608 The separator is attached to the beginning of the record that it
1609 precedes in the file.
1615 Treat the separator string as a regular expression. Users of @command{tac}
1616 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1617 binary mode, each line of a text file might end with a CR/LF pair
1618 instead of the Unix-style LF.
1620 @item -s @var{separator}
1621 @itemx --separator=@var{separator}
1623 @opindex --separator
1624 Use @var{separator} as the record separator, instead of newline.
1632 @section @command{nl}: Number lines and write files
1635 @cindex numbering lines
1636 @cindex line numbering
1638 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1639 standard input if none are given, to standard output, with line numbers
1640 added to some or all of the lines. Synopsis:
1643 nl [@var{option}]@dots{} [@var{file}]@dots{}
1646 @cindex logical pages, numbering on
1647 @command{nl} decomposes its input into (logical) pages; by default, the
1648 line number is reset to 1 at the top of each logical page. @command{nl}
1649 treats all of the input files as a single document; it does not reset
1650 line numbers or logical pages between files.
1652 @cindex headers, numbering
1653 @cindex body, numbering
1654 @cindex footers, numbering
1655 A logical page consists of three sections: header, body, and footer.
1656 Any of the sections can be empty. Each can be numbered in a different
1657 style from the others.
1659 The beginnings of the sections of logical pages are indicated in the
1660 input file by a line containing exactly one of these delimiter strings:
1671 The two characters from which these strings are made can be changed from
1672 @samp{\} and @samp{:} via options (see below), but the pattern and
1673 length of each string cannot be changed.
1675 A section delimiter is replaced by an empty line on output. Any text
1676 that comes before the first section delimiter string in the input file
1677 is considered to be part of a body section, so @command{nl} treats a
1678 file that contains no section delimiters as a single body section.
1680 The program accepts the following options. Also see @ref{Common options}.
1684 @item -b @var{style}
1685 @itemx --body-numbering=@var{style}
1687 @opindex --body-numbering
1688 Select the numbering style for lines in the body section of each
1689 logical page. When a line is not numbered, the current line number
1690 is not incremented, but the line number separator character is still
1691 prepended to the line. The styles are:
1697 number only nonempty lines (default for body),
1699 do not number lines (default for header and footer),
1701 number only lines that contain a match for the basic regular
1702 expression @var{bre}.
1703 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1707 @itemx --section-delimiter=@var{cd}
1709 @opindex --section-delimiter
1710 @cindex section delimiters of pages
1711 Set the section delimiter characters to @var{cd}; default is
1712 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1713 (Remember to protect @samp{\} or other metacharacters from shell
1714 expansion with quotes or extra backslashes.)
1716 @item -f @var{style}
1717 @itemx --footer-numbering=@var{style}
1719 @opindex --footer-numbering
1720 Analogous to @option{--body-numbering}.
1722 @item -h @var{style}
1723 @itemx --header-numbering=@var{style}
1725 @opindex --header-numbering
1726 Analogous to @option{--body-numbering}.
1728 @item -i @var{number}
1729 @itemx --line-increment=@var{number}
1731 @opindex --line-increment
1732 Increment line numbers by @var{number} (default 1).
1734 @item -l @var{number}
1735 @itemx --join-blank-lines=@var{number}
1737 @opindex --join-blank-lines
1738 @cindex empty lines, numbering
1739 @cindex blank lines, numbering
1740 Consider @var{number} (default 1) consecutive empty lines to be one
1741 logical line for numbering, and only number the last one. Where fewer
1742 than @var{number} consecutive empty lines occur, do not number them.
1743 An empty line is one that contains no characters, not even spaces
1746 @item -n @var{format}
1747 @itemx --number-format=@var{format}
1749 @opindex --number-format
1750 Select the line numbering format (default is @code{rn}):
1754 @opindex ln @r{format for @command{nl}}
1755 left justified, no leading zeros;
1757 @opindex rn @r{format for @command{nl}}
1758 right justified, no leading zeros;
1760 @opindex rz @r{format for @command{nl}}
1761 right justified, leading zeros.
1765 @itemx --no-renumber
1767 @opindex --no-renumber
1768 Do not reset the line number at the start of a logical page.
1770 @item -s @var{string}
1771 @itemx --number-separator=@var{string}
1773 @opindex --number-separator
1774 Separate the line number from the text line in the output with
1775 @var{string} (default is the TAB character).
1777 @item -v @var{number}
1778 @itemx --starting-line-number=@var{number}
1780 @opindex --starting-line-number
1781 Set the initial line number on each logical page to @var{number} (default 1).
1783 @item -w @var{number}
1784 @itemx --number-width=@var{number}
1786 @opindex --number-width
1787 Use @var{number} characters for line numbers (default 6).
1795 @section @command{od}: Write files in octal or other formats
1798 @cindex octal dump of files
1799 @cindex hex dump of files
1800 @cindex ASCII dump of files
1801 @cindex file contents, dumping unambiguously
1803 @command{od} writes an unambiguous representation of each @var{file}
1804 (@samp{-} means standard input), or standard input if none are given.
1808 od [@var{option}]@dots{} [@var{file}]@dots{}
1809 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1810 od [@var{option}]@dots{} --traditional [@var{file}]@c
1811 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1814 Each line of output consists of the offset in the input, followed by
1815 groups of data from the file. By default, @command{od} prints the offset in
1816 octal, and each group of file data is a C @code{short int}'s worth of input
1817 printed as a single octal number.
1819 If @var{offset} is given, it specifies how many input bytes to skip
1820 before formatting and writing. By default, it is interpreted as an
1821 octal number, but the optional trailing decimal point causes it to be
1822 interpreted as decimal. If no decimal is specified and the offset
1823 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1824 number. If there is a trailing @samp{b}, the number of bytes skipped
1825 will be @var{offset} multiplied by 512.
1827 If a command is of both the first and second forms, the second form is
1828 assumed if the last operand begins with @samp{+} or (if there are two
1829 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1830 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1833 The program accepts the following options. Also see @ref{Common options}.
1837 @item -A @var{radix}
1838 @itemx --address-radix=@var{radix}
1840 @opindex --address-radix
1841 @cindex radix for file offsets
1842 @cindex file offset radix
1843 Select the base in which file offsets are printed. @var{radix} can
1844 be one of the following:
1854 none (do not print offsets).
1857 The default is octal.
1859 @item -j @var{bytes}
1860 @itemx --skip-bytes=@var{bytes}
1862 @opindex --skip-bytes
1863 Skip @var{bytes} input bytes before formatting and writing. If
1864 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1865 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1867 @multiplierSuffixes{bytes}
1869 @item -N @var{bytes}
1870 @itemx --read-bytes=@var{bytes}
1872 @opindex --read-bytes
1873 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1874 @code{bytes} are interpreted as for the @option{-j} option.
1876 @item -S @var{bytes}
1877 @itemx --strings[=@var{bytes}]
1880 @cindex string constants, outputting
1881 Instead of the normal output, output only @dfn{string constants}: at
1882 least @var{bytes} consecutive ASCII graphic characters,
1883 followed by a zero byte (ASCII @sc{nul}).
1884 Prefixes and suffixes on @var{bytes} are interpreted as for the
1887 If @var{n} is omitted with @option{--strings}, the default is 3.
1890 @itemx --format=@var{type}
1893 Select the format in which to output the file data. @var{type} is a
1894 string of one or more of the below type indicator characters. If you
1895 include more than one type indicator character in a single @var{type}
1896 string, or use this option more than once, @command{od} writes one copy
1897 of each output line using each of the data types that you specified,
1898 in the order that you specified.
1900 Adding a trailing ``z'' to any type specification appends a display
1901 of the ASCII character representation of the printable characters
1902 to the output line generated by the type specification.
1906 named character, ignoring high-order bit
1908 ASCII character or backslash escape,
1912 floating point (@pxref{Floating point})
1921 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1922 newline, and @samp{nul} for a zero byte. Only the least significant
1923 seven bits of each byte is used; the high-order bit is ignored.
1924 Type @code{c} outputs
1925 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1928 Except for types @samp{a} and @samp{c}, you can specify the number
1929 of bytes to use in interpreting each number in the given data type
1930 by following the type indicator character with a decimal integer.
1931 Alternately, you can specify the size of one of the C compiler's
1932 built-in data types by following the type indicator character with
1933 one of the following characters. For integers (@samp{d}, @samp{o},
1934 @samp{u}, @samp{x}):
1947 For floating point (@code{f}):
1959 @itemx --output-duplicates
1961 @opindex --output-duplicates
1962 Output consecutive lines that are identical. By default, when two or
1963 more consecutive output lines would be identical, @command{od} outputs only
1964 the first line, and puts just an asterisk on the following line to
1965 indicate the elision.
1968 @itemx --width[=@var{n}]
1971 Dump @code{n} input bytes per output line. This must be a multiple of
1972 the least common multiple of the sizes associated with the specified
1975 If this option is not given at all, the default is 16. If @var{n} is
1976 omitted, the default is 32.
1980 The next several options are shorthands for format specifications.
1981 @sc{gnu} @command{od} accepts any combination of shorthands and format
1982 specification options. These options accumulate.
1988 Output as named characters. Equivalent to @samp{-t a}.
1992 Output as octal bytes. Equivalent to @samp{-t o1}.
1996 Output as ASCII characters or backslash escapes. Equivalent to
2001 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
2005 Output as floats. Equivalent to @samp{-t fF}.
2009 Output as decimal ints. Equivalent to @samp{-t dI}.
2013 Output as decimal long ints. Equivalent to @samp{-t dL}.
2017 Output as octal two-byte units. Equivalent to @option{-t o2}.
2021 Output as decimal two-byte units. Equivalent to @option{-t d2}.
2025 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
2028 @opindex --traditional
2029 Recognize the non-option label argument that traditional @command{od}
2030 accepted. The following syntax:
2033 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2037 can be used to specify at most one file and optional arguments
2038 specifying an offset and a pseudo-start address, @var{label}.
2039 The @var{label} argument is interpreted
2040 just like @var{offset}, but it specifies an initial pseudo-address. The
2041 pseudo-addresses are displayed in parentheses following any normal
2048 @node base64 invocation
2049 @section @command{base64}: Transform data into printable data
2052 @cindex base64 encoding
2054 @command{base64} transforms data read from a file, or standard input,
2055 into (or from) base64 encoded form. The base64 encoded form uses
2056 printable ASCII characters to represent binary data.
2060 base64 [@var{option}]@dots{} [@var{file}]
2061 base64 --decode [@var{option}]@dots{} [@var{file}]
2064 The base64 encoding expands data to roughly 133% of the original.
2065 The format conforms to
2066 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2068 The program accepts the following options. Also see @ref{Common options}.
2073 @itemx --wrap=@var{cols}
2077 @cindex column to wrap data after
2078 During encoding, wrap lines after @var{cols} characters. This must be
2081 The default is to wrap after 76 characters. Use the value 0 to
2082 disable line wrapping altogether.
2088 @cindex Decode base64 data
2089 @cindex Base64 decoding
2090 Change the mode of operation, from the default of encoding data, to
2091 decoding data. Input is expected to be base64 encoded data, and the
2092 output will be the original data.
2095 @itemx --ignore-garbage
2097 @opindex --ignore-garbage
2098 @cindex Ignore garbage in base64 stream
2099 When decoding, newlines are always accepted.
2100 During decoding, ignore unrecognized bytes,
2101 to permit distorted data to be decoded.
2108 @node Formatting file contents
2109 @chapter Formatting file contents
2111 @cindex formatting file contents
2113 These commands reformat the contents of files.
2116 * fmt invocation:: Reformat paragraph text.
2117 * pr invocation:: Paginate or columnate files for printing.
2118 * fold invocation:: Wrap input lines to fit in specified width.
2122 @node fmt invocation
2123 @section @command{fmt}: Reformat paragraph text
2126 @cindex reformatting paragraph text
2127 @cindex paragraphs, reformatting
2128 @cindex text, reformatting
2130 @command{fmt} fills and joins lines to produce output lines of (at most)
2131 a given number of characters (75 by default). Synopsis:
2134 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2137 @command{fmt} reads from the specified @var{file} arguments (or standard
2138 input if none are given), and writes to standard output.
2140 By default, blank lines, spaces between words, and indentation are
2141 preserved in the output; successive input lines with different
2142 indentation are not joined; tabs are expanded on input and introduced on
2145 @cindex line-breaking
2146 @cindex sentences and line-breaking
2147 @cindex Knuth, Donald E.
2148 @cindex Plass, Michael F.
2149 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2150 avoid line breaks after the first word of a sentence or before the last
2151 word of a sentence. A @dfn{sentence break} is defined as either the end
2152 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2153 spaces or end of line, ignoring any intervening parentheses or quotes.
2154 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2155 breaks; the algorithm is a variant of that given by Donald E. Knuth
2156 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2157 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2160 The program accepts the following options. Also see @ref{Common options}.
2165 @itemx --crown-margin
2167 @opindex --crown-margin
2168 @cindex crown margin
2169 @dfn{Crown margin} mode: preserve the indentation of the first two
2170 lines within a paragraph, and align the left margin of each subsequent
2171 line with that of the second line.
2174 @itemx --tagged-paragraph
2176 @opindex --tagged-paragraph
2177 @cindex tagged paragraphs
2178 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2179 indentation of the first line of a paragraph is the same as the
2180 indentation of the second, the first line is treated as a one-line
2186 @opindex --split-only
2187 Split lines only. Do not join short lines to form longer ones. This
2188 prevents sample lines of code, and other such ``formatted'' text from
2189 being unduly combined.
2192 @itemx --uniform-spacing
2194 @opindex --uniform-spacing
2195 Uniform spacing. Reduce spacing between words to one space, and spacing
2196 between sentences to two spaces.
2199 @itemx -w @var{width}
2200 @itemx --width=@var{width}
2201 @opindex -@var{width}
2204 Fill output lines up to @var{width} characters (default 75 or @var{goal}
2205 plus 10, if @var{goal} is provided).
2208 @itemx --goal=@var{goal}
2211 @command{fmt} initially tries to make lines @var{goal} characters wide.
2212 By default, this is 7% shorter than @var{width}.
2214 @item -p @var{prefix}
2215 @itemx --prefix=@var{prefix}
2216 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2217 are subject to formatting. The prefix and any preceding whitespace are
2218 stripped for the formatting and then re-attached to each formatted output
2219 line. One use is to format certain kinds of program comments, while
2220 leaving the code unchanged.
2228 @section @command{pr}: Paginate or columnate files for printing
2231 @cindex printing, preparing files for
2232 @cindex multicolumn output, generating
2233 @cindex merging files in parallel
2235 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2236 standard input if none are given, to standard output, paginating and
2237 optionally outputting in multicolumn format; optionally merges all
2238 @var{file}s, printing all in parallel, one per column. Synopsis:
2241 pr [@var{option}]@dots{} [@var{file}]@dots{}
2245 By default, a 5-line header is printed at each page: two blank lines;
2246 a line with the date, the file name, and the page count; and two more
2247 blank lines. A footer of five blank lines is also printed.
2248 The default @var{page_length} is 66
2249 lines. The default number of text lines is therefore 56.
2250 The text line of the header takes the form
2251 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2252 @var{string} so that the line takes up the full @var{page_width}. Here,
2253 @var{date} is the date (see the @option{-D} or @option{--date-format}
2254 option for details), @var{string} is the centered header string, and
2255 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2256 category affects the spelling of @var{page}; in the default C locale, it
2257 is @samp{Page @var{number}} where @var{number} is the decimal page
2260 Form feeds in the input cause page breaks in the output. Multiple form
2261 feeds produce empty pages.
2263 Columns are of equal width, separated by an optional string (default
2264 is @samp{space}). For multicolumn output, lines will always be truncated to
2265 @var{page_width} (default 72), unless you use the @option{-J} option.
2267 column output no line truncation occurs by default. Use @option{-W} option to
2268 truncate lines in that case.
2270 The following changes were made in version 1.22i and apply to later
2271 versions of @command{pr}:
2272 @c FIXME: this whole section here sounds very awkward to me. I
2273 @c made a few small changes, but really it all needs to be redone. - Brian
2274 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2279 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2280 redefined for better POSIX compliance. The output of some further
2281 cases has been adapted to other Unix systems. These changes are not
2282 compatible with earlier versions of the program.
2285 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2286 have been introduced to turn off unexpected interferences of small letter
2287 options. The @option{-N} option and the second argument @var{last_page}
2288 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2289 form feeds set in the input files requires the @option{-T} option.
2292 Capital letter options override small letter ones.
2295 Some of the option-arguments (compare @option{-s}, @option{-e},
2296 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2297 preceding option letter (already stated in the POSIX specification).
2300 The program accepts the following options. Also see @ref{Common options}.
2304 @item +@var{first_page}[:@var{last_page}]
2305 @itemx --pages=@var{first_page}[:@var{last_page}]
2306 @c The two following @opindex lines evoke warnings because they contain ':'
2307 @c The 'info' spec does not permit that. If we use those lines, we end
2308 @c up with truncated index entries that don't work.
2309 @c @opindex +@var{first_page}[:@var{last_page}]
2310 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2311 @opindex +@var{page_range}
2312 @opindex --pages=@var{page_range}
2313 Begin printing with page @var{first_page} and stop with @var{last_page}.
2314 Missing @samp{:@var{last_page}} implies end of file. While estimating
2315 the number of skipped pages each form feed in the input file results
2316 in a new page. Page counting with and without @samp{+@var{first_page}}
2317 is identical. By default, counting starts with the first page of input
2318 file (not first page printed). Line numbering may be altered by @option{-N}
2322 @itemx --columns=@var{column}
2323 @opindex -@var{column}
2325 @cindex down columns
2326 With each single @var{file}, produce @var{column} columns of output
2327 (default is 1) and print columns down, unless @option{-a} is used. The
2328 column width is automatically decreased as @var{column} increases; unless
2329 you use the @option{-W/-w} option to increase @var{page_width} as well.
2330 This option might well cause some lines to be truncated. The number of
2331 lines in the columns on each page are balanced. The options @option{-e}
2332 and @option{-i} are on for multiple text-column output. Together with
2333 @option{-J} option column alignment and line truncation is turned off.
2334 Lines of full length are joined in a free field format and @option{-S}
2335 option may set field separators. @option{-@var{column}} may not be used
2336 with @option{-m} option.
2342 @cindex across columns
2343 With each single @var{file}, print columns across rather than down. The
2344 @option{-@var{column}} option must be given with @var{column} greater than one.
2345 If a line is too long to fit in a column, it is truncated.
2348 @itemx --show-control-chars
2350 @opindex --show-control-chars
2351 Print control characters using hat notation (e.g., @samp{^G}); print
2352 other nonprinting characters in octal backslash notation. By default,
2353 nonprinting characters are not changed.
2356 @itemx --double-space
2358 @opindex --double-space
2359 @cindex double spacing
2360 Double space the output.
2362 @item -D @var{format}
2363 @itemx --date-format=@var{format}
2364 @cindex time formats
2365 @cindex formatting times
2366 Format header dates using @var{format}, using the same conventions as
2367 for the command @samp{date +@var{format}}. @xref{date invocation}.
2368 Except for directives, which start with
2369 @samp{%}, characters in @var{format} are printed unchanged. You can use
2370 this option to specify an arbitrary string in place of the header date,
2371 e.g., @option{--date-format="Monday morning"}.
2373 @vindex POSIXLY_CORRECT
2375 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2376 @samp{2001-12-04 23:59});
2377 but if the @env{POSIXLY_CORRECT} environment variable is set
2378 and the @env{LC_TIME} locale category specifies the POSIX
2379 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2380 @samp{Dec@ @ 4 23:59 2001}.
2383 Time stamps are listed according to the time zone rules specified by
2384 the @env{TZ} environment variable, or by the system default rules if
2385 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2386 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2388 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2389 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2391 @opindex --expand-tabs
2393 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2394 the input tab character (default is the TAB character). Second optional
2395 argument @var{in-tabwidth} is the input tab character's width (default
2403 @opindex --form-feed
2404 Use a form feed instead of newlines to separate output pages. This does
2405 not alter the default page length of 66 lines.
2407 @item -h @var{header}
2408 @itemx --header=@var{header}
2411 Replace the file name in the header with the centered string @var{header}.
2412 When using the shell, @var{header} should be quoted and should be
2413 separated from @option{-h} by a space.
2415 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2416 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2418 @opindex --output-tabs
2420 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2421 is the output tab character (default is the TAB character). Second optional
2422 argument @var{out-tabwidth} is the output tab character's width (default
2428 @opindex --join-lines
2429 Merge lines of full length. Used together with the column options
2430 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2431 @option{-W/-w} line truncation;
2432 no column alignment used; may be used with
2433 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2434 (together with @option{-W} and @option{--sep-string})
2435 to disentangle the old (POSIX-compliant) options @option{-w} and
2436 @option{-s} along with the three column options.
2439 @item -l @var{page_length}
2440 @itemx --length=@var{page_length}
2443 Set the page length to @var{page_length} (default 66) lines, including
2444 the lines of the header [and the footer]. If @var{page_length} is less
2445 than or equal to 10, the header and footer are omitted, as if the
2446 @option{-t} option had been given.
2452 Merge and print all @var{file}s in parallel, one in each column. If a
2453 line is too long to fit in a column, it is truncated, unless the @option{-J}
2454 option is used. @option{--sep-string[=@var{string}]} may be used.
2456 some @var{file}s (form feeds set) produce empty columns, still marked
2457 by @var{string}. The result is a continuous line numbering and column
2458 marking throughout the whole merged file. Completely empty merged pages
2459 show no separators or line numbers. The default header becomes
2460 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2461 may be used with the @option{-h} or @option{--header} option to fill up
2462 the middle blank part.
2464 @item -n[@var{number-separator}[@var{digits}]]
2465 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2467 @opindex --number-lines
2468 Provide @var{digits} digit line numbering (default for @var{digits} is
2469 5). With multicolumn output the number occupies the first @var{digits}
2470 column positions of each text column or only each line of @option{-m}
2471 output. With single column output the number precedes each line just as
2472 @option{-m} does. Default counting of the line numbers starts with the
2473 first line of the input file (not the first line printed, compare the
2474 @option{--page} option and @option{-N} option).
2475 Optional argument @var{number-separator} is the character appended to
2476 the line number to separate it from the text followed. The default
2477 separator is the TAB character. In a strict sense a TAB is always
2478 printed with single column output only. The TAB width varies
2479 with the TAB position, e.g., with the left @var{margin} specified
2480 by @option{-o} option. With multicolumn output priority is given to
2481 @samp{equal width of output columns} (a POSIX specification).
2482 The TAB width is fixed to the value of the first column and does
2483 not change with different values of left @var{margin}. That means a
2484 fixed number of spaces is always printed in the place of the
2485 @var{number-separator} TAB@. The tabification depends upon the output
2488 @item -N @var{line_number}
2489 @itemx --first-line-number=@var{line_number}
2491 @opindex --first-line-number
2492 Start line counting with the number @var{line_number} at first line of
2493 first page printed (in most cases not the first line of the input file).
2495 @item -o @var{margin}
2496 @itemx --indent=@var{margin}
2499 @cindex indenting lines
2501 Indent each line with a margin @var{margin} spaces wide (default is zero).
2502 The total page width is the size of the margin plus the @var{page_width}
2503 set with the @option{-W/-w} option. A limited overflow may occur with
2504 numbered single column output (compare @option{-n} option).
2507 @itemx --no-file-warnings
2509 @opindex --no-file-warnings
2510 Do not print a warning message when an argument @var{file} cannot be
2511 opened. (The exit status will still be nonzero, however.)
2513 @item -s[@var{char}]
2514 @itemx --separator[=@var{char}]
2516 @opindex --separator
2517 Separate columns by a single character @var{char}. The default for
2518 @var{char} is the TAB character without @option{-w} and @samp{no
2519 character} with @option{-w}. Without @option{-s} the default separator
2520 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2521 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2522 @option{-w} is set. This is a POSIX-compliant formulation.
2525 @item -S[@var{string}]
2526 @itemx --sep-string[=@var{string}]
2528 @opindex --sep-string
2529 Use @var{string} to separate output columns. The @option{-S} option doesn't
2530 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2531 does not affect line truncation or column alignment.
2532 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2534 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2535 (same as @option{-S"@w{ }"}).
2536 If no @samp{@var{string}} argument is specified, @samp{""} is assumed.
2539 @itemx --omit-header
2541 @opindex --omit-header
2542 Do not print the usual header [and footer] on each page, and do not fill
2543 out the bottom of pages (with blank lines or a form feed). No page
2544 structure is produced, but form feeds set in the input files are retained.
2545 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2546 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2547 in the input file to 4 spaces but don't make any other changes. Use of
2548 @option{-t} overrides @option{-h}.
2551 @itemx --omit-pagination
2553 @opindex --omit-pagination
2554 Do not print header [and footer]. In addition eliminate all form feeds
2555 set in the input files.
2558 @itemx --show-nonprinting
2560 @opindex --show-nonprinting
2561 Print nonprinting characters in octal backslash notation.
2563 @item -w @var{page_width}
2564 @itemx --width=@var{page_width}
2567 Set page width to @var{page_width} characters for multiple text-column
2568 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2569 off the default page width and any line truncation and column alignment.
2570 Lines of full length are merged, regardless of the column options
2571 set. No @var{page_width} setting is possible with single column output.
2572 A POSIX-compliant formulation.
2574 @item -W @var{page_width}
2575 @itemx --page_width=@var{page_width}
2577 @opindex --page_width
2578 Set the page width to @var{page_width} characters. That's valid with and
2579 without a column option. Text lines are truncated, unless @option{-J}
2580 is used. Together with one of the three column options
2581 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2582 alignment is always used. The separator options @option{-S} or @option{-s}
2583 don't affect the @option{-W} option. Default is 72 characters. Without
2584 @option{-W @var{page_width}} and without any of the column options NO line
2585 truncation is used (defined to keep downward compatibility and to meet
2586 most frequent tasks). That's equivalent to @option{-W 72 -J}@. The header
2587 line is never truncated.
2594 @node fold invocation
2595 @section @command{fold}: Wrap input lines to fit in specified width
2598 @cindex wrapping long input lines
2599 @cindex folding long input lines
2601 @command{fold} writes each @var{file} (@option{-} means standard input), or
2602 standard input if none are given, to standard output, breaking long
2606 fold [@var{option}]@dots{} [@var{file}]@dots{}
2609 By default, @command{fold} breaks lines wider than 80 columns. The output
2610 is split into as many lines as necessary.
2612 @cindex screen columns
2613 @command{fold} counts screen columns by default; thus, a tab may count more
2614 than one column, backspace decreases the column count, and carriage
2615 return sets the column to zero.
2617 The program accepts the following options. Also see @ref{Common options}.
2625 Count bytes rather than columns, so that tabs, backspaces, and carriage
2626 returns are each counted as taking up one column, just like other
2633 Break at word boundaries: the line is broken after the last blank before
2634 the maximum line length. If the line contains no such blanks, the line
2635 is broken at the maximum line length as usual.
2637 @item -w @var{width}
2638 @itemx --width=@var{width}
2641 Use a maximum line length of @var{width} columns instead of 80.
2643 For compatibility @command{fold} supports an obsolete option syntax
2644 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2652 @node Output of parts of files
2653 @chapter Output of parts of files
2655 @cindex output of parts of files
2656 @cindex parts of files, output of
2658 These commands output pieces of the input.
2661 * head invocation:: Output the first part of files.
2662 * tail invocation:: Output the last part of files.
2663 * split invocation:: Split a file into pieces.
2664 * csplit invocation:: Split a file into context-determined pieces.
2667 @node head invocation
2668 @section @command{head}: Output the first part of files
2671 @cindex initial part of files, outputting
2672 @cindex first part of files, outputting
2674 @command{head} prints the first part (10 lines by default) of each
2675 @var{file}; it reads from standard input if no files are given or
2676 when given a @var{file} of @option{-}. Synopsis:
2679 head [@var{option}]@dots{} [@var{file}]@dots{}
2682 If more than one @var{file} is specified, @command{head} prints a
2683 one-line header consisting of:
2686 ==> @var{file name} <==
2690 before the output for each @var{file}.
2692 The program accepts the following options. Also see @ref{Common options}.
2697 @itemx --bytes=@var{k}
2700 Print the first @var{k} bytes, instead of initial lines.
2701 However, if @var{k} starts with a @samp{-},
2702 print all but the last @var{k} bytes of each file.
2703 @multiplierSuffixes{k}
2706 @itemx --lines=@var{k}
2709 Output the first @var{k} lines.
2710 However, if @var{k} starts with a @samp{-},
2711 print all but the last @var{k} lines of each file.
2712 Size multiplier suffixes are the same as with the @option{-c} option.
2720 Never print file name headers.
2726 Always print file name headers.
2730 For compatibility @command{head} also supports an obsolete option syntax
2731 @option{-@var{count}@var{options}}, which is recognized only if it is
2732 specified first. @var{count} is a decimal number optionally followed
2733 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2734 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2735 Scripts intended for standard hosts should use @option{-c @var{count}}
2736 or @option{-n @var{count}} instead. If your script must also run on
2737 hosts that support only the obsolete syntax, it is usually simpler to
2738 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2744 @node tail invocation
2745 @section @command{tail}: Output the last part of files
2748 @cindex last part of files, outputting
2750 @command{tail} prints the last part (10 lines by default) of each
2751 @var{file}; it reads from standard input if no files are given or
2752 when given a @var{file} of @samp{-}. Synopsis:
2755 tail [@var{option}]@dots{} [@var{file}]@dots{}
2758 If more than one @var{file} is specified, @command{tail} prints a
2759 one-line header consisting of:
2762 ==> @var{file name} <==
2766 before the output for each @var{file}.
2768 @cindex BSD @command{tail}
2769 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2770 @command{tail} cannot). It also has no @option{-r} option (print in
2771 reverse), since reversing a file is really a different job from printing
2772 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2773 only reverse files that are at most as large as its buffer, which is
2774 typically 32 KiB@. A more reliable and versatile way to reverse files is
2775 the @sc{gnu} @command{tac} command.
2777 The program accepts the following options. Also see @ref{Common options}.
2782 @itemx --bytes=@var{k}
2785 Output the last @var{k} bytes, instead of final lines.
2786 However, if @var{k} starts with a @samp{+}, start printing with the
2787 @var{k}th byte from the start of each file, instead of from the end.
2788 @multiplierSuffixes{k}
2791 @itemx --follow[=@var{how}]
2794 @cindex growing files
2795 @vindex name @r{follow option}
2796 @vindex descriptor @r{follow option}
2797 Loop forever trying to read more characters at the end of the file,
2798 presumably because the file is growing.
2799 If more than one file is given, @command{tail} prints a header whenever it
2800 gets output from a different file, to indicate which file that output is
2803 There are two ways to specify how you'd like to track files with this option,
2804 but that difference is noticeable only when a followed file is removed or
2806 If you'd like to continue to track the end of a growing file even after
2807 it has been unlinked, use @option{--follow=descriptor}. This is the default
2808 behavior, but it is not useful if you're tracking a log file that may be
2809 rotated (removed or renamed, then reopened). In that case, use
2810 @option{--follow=name} to track the named file, perhaps by reopening it
2811 periodically to see if it has been removed and recreated by some other program.
2812 Note that the inotify-based implementation handles this case without
2813 the need for any periodic reopening.
2815 No matter which method you use, if the tracked file is determined to have
2816 shrunk, @command{tail} prints a message saying the file has been truncated
2817 and resumes tracking the end of the file from the newly-determined endpoint.
2819 When a file is removed, @command{tail}'s behavior depends on whether it is
2820 following the name or the descriptor. When following by name, tail can
2821 detect that a file has been removed and gives a message to that effect,
2822 and if @option{--retry} has been specified it will continue checking
2823 periodically to see if the file reappears.
2824 When following a descriptor, tail does not detect that the file has
2825 been unlinked or renamed and issues no message; even though the file
2826 may no longer be accessible via its original name, it may still be
2829 The option values @samp{descriptor} and @samp{name} may be specified only
2830 with the long form of the option, not with @option{-f}.
2832 The @option{-f} option is ignored if
2833 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2834 Likewise, the @option{-f} option has no effect for any
2835 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2837 With kernel inotify support, output is triggered by file changes
2838 and is generally very prompt.
2839 Otherwise, @command{tail} sleeps for one second between checks---
2840 use @option{--sleep-interval=@var{n}} to change that default---which can
2841 make the output appear slightly less responsive or bursty.
2842 When using tail without inotify support, you can make it more responsive
2843 by using a sub-second sleep interval, e.g., via an alias like this:
2846 alias tail='tail -s.1'
2851 This option is the same as @option{--follow=name --retry}. That is, tail
2852 will attempt to reopen a file when it is removed. Should this fail, tail
2853 will keep trying until it becomes accessible again.
2857 This option is useful mainly when following by name (i.e., with
2858 @option{--follow=name}).
2859 Without this option, when tail encounters a file that doesn't
2860 exist or is otherwise inaccessible, it reports that fact and
2861 never checks it again.
2863 @item --sleep-interval=@var{number}
2864 @opindex --sleep-interval
2865 Change the number of seconds to wait between iterations (the default is 1.0).
2866 During one iteration, every specified file is checked to see if it has
2868 Historical implementations of @command{tail} have required that
2869 @var{number} be an integer. However, GNU @command{tail} accepts
2870 an arbitrary floating point number. @xref{Floating point}.
2871 When @command{tail} uses inotify, this polling-related option
2872 is usually ignored. However, if you also specify @option{--pid=@var{p}},
2873 @command{tail} checks whether process @var{p} is alive at least
2874 every @var{number} seconds.
2876 @item --pid=@var{pid}
2878 When following by name or by descriptor, you may specify the process ID,
2879 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2880 after that process terminates, tail will also terminate. This will
2881 work properly only if the writer and the tailing process are running on
2882 the same machine. For example, to save the output of a build in a file
2883 and to watch the file grow, if you invoke @command{make} and @command{tail}
2884 like this then the tail process will stop when your build completes.
2885 Without this option, you would have had to kill the @code{tail -f}
2889 $ make >& makerr & tail --pid=$! -f makerr
2892 If you specify a @var{pid} that is not in use or that does not correspond
2893 to the process that is writing to the tailed files, then @command{tail}
2894 may terminate long before any @var{file}s stop growing or it may not
2895 terminate until long after the real writer has terminated.
2896 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2897 will print a warning if this is the case.
2899 @item --max-unchanged-stats=@var{n}
2900 @opindex --max-unchanged-stats
2901 When tailing a file by name, if there have been @var{n} (default
2902 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2903 iterations for which the file has not changed, then
2904 @code{open}/@code{fstat} the file to determine if that file name is
2905 still associated with the same device/inode-number pair as before.
2906 When following a log file that is rotated, this is approximately the
2907 number of seconds between when tail prints the last pre-rotation lines
2908 and when it prints the lines that have accumulated in the new log file.
2909 This option is meaningful only when polling (i.e., without inotify)
2910 and when following by name.
2913 @itemx --lines=@var{k}
2916 Output the last @var{k} lines.
2917 However, if @var{k} starts with a @samp{+}, start printing with the
2918 @var{k}th line from the start of each file, instead of from the end.
2919 Size multiplier suffixes are the same as with the @option{-c} option.
2927 Never print file name headers.
2933 Always print file name headers.
2937 For compatibility @command{tail} also supports an obsolete usage
2938 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2939 only if it does not conflict with the usage described
2940 above. This obsolete form uses exactly one option and at most one
2941 file. In the option, @var{count} is an optional decimal number optionally
2942 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2943 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2944 which has the same meaning as @option{-f}.
2946 @vindex _POSIX2_VERSION
2947 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2948 the obsolete option syntax with the same meaning as in counts, and
2949 obsolete usage overrides normal usage when the two conflict.
2950 This obsolete behavior can be enabled or disabled with the
2951 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2954 Scripts intended for use on standard hosts should avoid obsolete
2955 syntax and should use @option{-c @var{count}[b]}, @option{-n
2956 @var{count}}, and/or @option{-f} instead. If your script must also
2957 run on hosts that support only the obsolete syntax, you can often
2958 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2959 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2960 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2961 then @dots{}} to decide which syntax to use.
2963 Even if your script assumes the standard behavior, you should still
2964 beware usages whose behaviors differ depending on the POSIX
2965 version. For example, avoid @samp{tail - main.c}, since it might be
2966 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2967 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2968 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2969 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2974 @node split invocation
2975 @section @command{split}: Split a file into pieces.
2978 @cindex splitting a file into pieces
2979 @cindex pieces, splitting a file into
2981 @command{split} creates output files containing consecutive or interleaved
2982 sections of @var{input} (standard input if none is given or @var{input}
2983 is @samp{-}). Synopsis:
2986 split [@var{option}] [@var{input} [@var{prefix}]]
2989 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2990 left over for the last section), into each output file.
2992 @cindex output file name prefix
2993 The output files' names consist of @var{prefix} (@samp{x} by default)
2994 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2995 default), such that concatenating the output files in traditional
2996 sorted order by file name produces the original input file (except
2997 @option{-nr/@var{n}}). By default split will initially create files
2998 with two generated suffix characters, and will increase this width by two
2999 when the next most significant position reaches the last character.
3000 (@samp{yz}, @samp{zaaa}, @samp{zaab}, @dots{}). In this way an arbitrary
3001 number of output files are supported, which sort as described above,
3002 even in the presence of an @option{--additional-suffix} option.
3003 If the @option{-a} option is specified and the output file names are
3004 exhausted, @command{split} reports an error without deleting the
3005 output files that it did create.
3007 The program accepts the following options. Also see @ref{Common options}.
3011 @item -l @var{lines}
3012 @itemx --lines=@var{lines}
3015 Put @var{lines} lines of @var{input} into each output file.
3017 For compatibility @command{split} also supports an obsolete
3018 option syntax @option{-@var{lines}}. New scripts should use
3019 @option{-l @var{lines}} instead.
3022 @itemx --bytes=@var{size}
3025 Put @var{size} bytes of @var{input} into each output file.
3026 @multiplierSuffixes{size}
3029 @itemx --line-bytes=@var{size}
3031 @opindex --line-bytes
3032 Put into each output file as many complete lines of @var{input} as
3033 possible without exceeding @var{size} bytes. Individual lines longer than
3034 @var{size} bytes are broken into multiple files.
3035 @var{size} has the same format as for the @option{--bytes} option.
3037 @item --filter=@var{command}
3039 With this option, rather than simply writing to each output file,
3040 write through a pipe to the specified shell @var{command} for each output file.
3041 @var{command} should use the $FILE environment variable, which is set
3042 to a different output file name for each invocation of the command.
3043 For example, imagine that you have a 1TiB compressed file
3044 that, if uncompressed, would be too large to reside on disk,
3045 yet you must split it into individually-compressed pieces
3046 of a more manageable size.
3047 To do that, you might run this command:
3050 xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
3053 Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
3054 with names @file{big-aa.xz}, @file{big-ab.xz}, @file{big-ac.xz}, etc.
3056 @item -n @var{chunks}
3057 @itemx --number=@var{chunks}
3061 Split @var{input} to @var{chunks} output files where @var{chunks} may be:
3064 @var{n} generate @var{n} files based on current size of @var{input}
3065 @var{k}/@var{n} only output @var{k}th of @var{n} to stdout
3066 l/@var{n} generate @var{n} files without splitting lines
3067 l/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3068 r/@var{n} like @samp{l} but use round robin distribution
3069 r/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3072 Any excess bytes remaining after dividing the @var{input}
3073 into @var{n} chunks, are assigned to the last chunk.
3074 Any excess bytes appearing after the initial calculation are discarded
3075 (except when using @samp{r} mode).
3077 All @var{n} files are created even if there are fewer than @var{n} lines,
3078 or the @var{input} is truncated.
3080 For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
3081 The @var{input} is partitioned into @var{n} equal sized portions, with
3082 the last assigned any excess. If a line @emph{starts} within a partition
3083 it is written completely to the corresponding file. Since lines
3084 are not split even if they overlap a partition, the files written
3085 can be larger or smaller than the partition size, and even empty
3086 if a line is so long as to completely overlap the partition.
3088 For @samp{r} mode, the size of @var{input} is irrelevant,
3089 and so can be a pipe for example.
3091 @item -a @var{length}
3092 @itemx --suffix-length=@var{length}
3094 @opindex --suffix-length
3095 Use suffixes of length @var{length}. If a @var{length} of 0 is specified,
3096 this is the same as if (any previous) @option{-a} was not specified, and
3097 thus enables the default behavior, which starts the suffix length at 2,
3098 and unless @option{-n} or @option{--numeric-suffixes=@var{from}} is
3099 specified, will auto increase the length by 2 as required.
3102 @itemx --numeric-suffixes[=@var{from}]
3104 @opindex --numeric-suffixes
3105 Use digits in suffixes rather than lower-case letters. The numerical
3106 suffix counts from @var{from} if specified, 0 otherwise.
3107 Note specifying a @var{from} value also disables the default
3108 auto suffix length expansion described above, and so you may also
3109 want to specify @option{-a} to allow suffixes beyond @samp{99}.
3111 @item --additional-suffix=@var{suffix}
3112 @opindex --additional-suffix
3113 Append an additional @var{suffix} to output file names. @var{suffix}
3114 must not contain slash.
3117 @itemx --elide-empty-files
3119 @opindex --elide-empty-files
3120 Suppress the generation of zero-length output files. This can happen
3121 with the @option{--number} option if a file is (truncated to be) shorter
3122 than the number requested, or if a line is so long as to completely
3123 span a chunk. The output file sequence numbers, always run consecutively
3124 even when this option is specified.
3129 @opindex --unbuffered
3130 Immediately copy input to output in @option{--number r/...} mode,
3131 which is a much slower mode of operation.
3135 Write a diagnostic just before each output file is opened.
3141 Here are a few examples to illustrate how the
3142 @option{--number} (@option{-n}) option works:
3144 Notice how, by default, one line may be split onto two or more:
3147 $ seq -w 6 10 > k; split -n3 k; head xa?
3160 Use the "l/" modifier to suppress that:
3163 $ seq -w 6 10 > k; split -nl/3 k; head xa?
3176 Use the "r/" modifier to distribute lines in a round-robin fashion:
3179 $ seq -w 6 10 > k; split -nr/3 k; head xa?
3192 You can also extract just the Kth chunk.
3193 This extracts and prints just the 7th "chunk" of 33:
3196 $ seq 100 > k; split -nl/7/33 k
3203 @node csplit invocation
3204 @section @command{csplit}: Split a file into context-determined pieces
3207 @cindex context splitting
3208 @cindex splitting a file into pieces by context
3210 @command{csplit} creates zero or more output files containing sections of
3211 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3214 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3217 The contents of the output files are determined by the @var{pattern}
3218 arguments, as detailed below. An error occurs if a @var{pattern}
3219 argument refers to a nonexistent line of the input file (e.g., if no
3220 remaining line matches a given regular expression). After every
3221 @var{pattern} has been matched, any remaining input is copied into one
3224 By default, @command{csplit} prints the number of bytes written to each
3225 output file after it has been created.
3227 The types of pattern arguments are:
3232 Create an output file containing the input up to but not including line
3233 @var{n} (a positive integer). If followed by a repeat count, also
3234 create an output file containing the next @var{n} lines of the input
3235 file once for each repeat.
3237 @item /@var{regexp}/[@var{offset}]
3238 Create an output file containing the current line up to (but not
3239 including) the next line of the input file that contains a match for
3240 @var{regexp}. The optional @var{offset} is an integer.
3241 If it is given, the input up to (but not including) the
3242 matching line plus or minus @var{offset} is put into the output file,
3243 and the line after that begins the next section of input.
3245 @item %@var{regexp}%[@var{offset}]
3246 Like the previous type, except that it does not create an output
3247 file, so that section of the input file is effectively ignored.
3249 @item @{@var{repeat-count}@}
3250 Repeat the previous pattern @var{repeat-count} additional
3251 times. The @var{repeat-count} can either be a positive integer or an
3252 asterisk, meaning repeat as many times as necessary until the input is
3257 The output files' names consist of a prefix (@samp{xx} by default)
3258 followed by a suffix. By default, the suffix is an ascending sequence
3259 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3260 concatenating the output files in sorted order by file name produces the
3261 original input file.
3263 By default, if @command{csplit} encounters an error or receives a hangup,
3264 interrupt, quit, or terminate signal, it removes any output files
3265 that it has created so far before it exits.
3267 The program accepts the following options. Also see @ref{Common options}.
3271 @item -f @var{prefix}
3272 @itemx --prefix=@var{prefix}
3275 @cindex output file name prefix
3276 Use @var{prefix} as the output file name prefix.
3278 @item -b @var{suffix}
3279 @itemx --suffix=@var{suffix}
3282 @cindex output file name suffix
3283 Use @var{suffix} as the output file name suffix. When this option is
3284 specified, the suffix string must include exactly one
3285 @code{printf(3)}-style conversion specification, possibly including
3286 format specification flags, a field width, a precision specifications,
3287 or all of these kinds of modifiers. The format letter must convert a
3288 binary unsigned integer argument to readable form. The format letters
3289 @samp{d} and @samp{i} are aliases for @samp{u}, and the
3290 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3291 entire @var{suffix} is given (with the current output file number) to
3292 @code{sprintf(3)} to form the file name suffixes for each of the
3293 individual output files in turn. If this option is used, the
3294 @option{--digits} option is ignored.
3296 @item -n @var{digits}
3297 @itemx --digits=@var{digits}
3300 Use output file names containing numbers that are @var{digits} digits
3301 long instead of the default 2.
3306 @opindex --keep-files
3307 Do not remove output files when errors are encountered.
3310 @itemx --elide-empty-files
3312 @opindex --elide-empty-files
3313 Suppress the generation of zero-length output files. (In cases where
3314 the section delimiters of the input file are supposed to mark the first
3315 lines of each of the sections, the first output file will generally be a
3316 zero-length file unless you use this option.) The output file sequence
3317 numbers always run consecutively starting from 0, even when this option
3328 Do not print counts of output file sizes.
3334 Here is an example of its usage.
3335 First, create an empty directory for the exercise,
3342 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3345 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3351 Each number printed above is the size of an output
3352 file that csplit has just created.
3353 List the names of those output files:
3360 Use @command{head} to show their contents:
3385 @node Summarizing files
3386 @chapter Summarizing files
3388 @cindex summarizing files
3390 These commands generate just a few numbers representing entire
3394 * wc invocation:: Print newline, word, and byte counts.
3395 * sum invocation:: Print checksum and block counts.
3396 * cksum invocation:: Print CRC checksum and byte counts.
3397 * md5sum invocation:: Print or check MD5 digests.
3398 * sha1sum invocation:: Print or check SHA-1 digests.
3399 * sha2 utilities:: Print or check SHA-2 digests.
3404 @section @command{wc}: Print newline, word, and byte counts
3408 @cindex character count
3412 @command{wc} counts the number of bytes, characters, whitespace-separated
3413 words, and newlines in each given @var{file}, or standard input if none
3414 are given or for a @var{file} of @samp{-}. Synopsis:
3417 wc [@var{option}]@dots{} [@var{file}]@dots{}
3420 @cindex total counts
3421 @command{wc} prints one line of counts for each file, and if the file was
3422 given as an argument, it prints the file name following the counts. If
3423 more than one @var{file} is given, @command{wc} prints a final line
3424 containing the cumulative counts, with the file name @file{total}. The
3425 counts are printed in this order: newlines, words, characters, bytes,
3426 maximum line length.
3427 Each count is printed right-justified in a field with at least one
3428 space between fields so that the numbers and file names normally line
3429 up nicely in columns. The width of the count fields varies depending
3430 on the inputs, so you should not depend on a particular field width.
3431 However, as a GNU extension, if only one count is printed,
3432 it is guaranteed to be printed without leading spaces.
3434 By default, @command{wc} prints three counts: the newline, words, and byte
3435 counts. Options can specify that only certain counts be printed.
3436 Options do not undo others previously given, so
3443 prints both the byte counts and the word counts.
3445 With the @option{--max-line-length} option, @command{wc} prints the length
3446 of the longest line per file, and if there is more than one file it
3447 prints the maximum (not the sum) of those lengths. The line lengths here
3448 are measured in screen columns, according to the current locale and
3449 assuming tab positions in every 8th column.
3451 The program accepts the following options. Also see @ref{Common options}.
3459 Print only the byte counts.
3465 Print only the character counts.
3471 Print only the word counts.
3477 Print only the newline counts.
3480 @itemx --max-line-length
3482 @opindex --max-line-length
3483 Print only the maximum line lengths.
3485 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3486 @item --files0-from=@var{file}
3487 @opindex --files0-from=@var{file}
3488 @c This is commented out to avoid a texi2dvi failure.
3489 @c texi2dvi (GNU Texinfo 4.11) 1.104
3490 @c @cindex including files from @command{\cmd\}
3491 Disallow processing files named on the command line, and instead process
3492 those named in file @var{file}; each name being terminated by a zero byte
3494 This is useful \withTotalOption\
3495 when the list of file names is so long that it may exceed a command line
3497 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3498 because it splits the list into pieces and makes @command{\cmd\} print
3499 \subListOutput\ for each sublist rather than for the entire list.
3500 One way to produce a list of ASCII @sc{nul} terminated file
3501 names is with @sc{gnu}
3502 @command{find}, using its @option{-print0} predicate.
3503 If @var{file} is @samp{-} then the ASCII @sc{nul} terminated
3504 file names are read from standard input.
3506 @filesZeroFromOption{wc,,a total}
3508 For example, to find the length of the longest line in any @file{.c} or
3509 @file{.h} file in the current hierarchy, do this:
3512 find . -name '*.[ch]' -print0 |
3513 wc -L --files0-from=- | tail -n1
3521 @node sum invocation
3522 @section @command{sum}: Print checksum and block counts
3525 @cindex 16-bit checksum
3526 @cindex checksum, 16-bit
3528 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3529 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3532 sum [@var{option}]@dots{} [@var{file}]@dots{}
3535 @command{sum} prints the checksum for each @var{file} followed by the
3536 number of blocks in the file (rounded up). If more than one @var{file}
3537 is given, file names are also printed (by default). (With the
3538 @option{--sysv} option, corresponding file names are printed when there is
3539 at least one file argument.)
3541 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3542 compatible with BSD @command{sum} and prints file sizes in units of
3545 The program accepts the following options. Also see @ref{Common options}.
3551 @cindex BSD @command{sum}
3552 Use the default (BSD compatible) algorithm. This option is included for
3553 compatibility with the System V @command{sum}. Unless @option{-s} was also
3554 given, it has no effect.
3560 @cindex System V @command{sum}
3561 Compute checksums using an algorithm compatible with System V
3562 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3566 @command{sum} is provided for compatibility; the @command{cksum} program (see
3567 next section) is preferable in new applications.
3572 @node cksum invocation
3573 @section @command{cksum}: Print CRC checksum and byte counts
3576 @cindex cyclic redundancy check
3577 @cindex CRC checksum
3579 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3580 given @var{file}, or standard input if none are given or for a
3581 @var{file} of @samp{-}. Synopsis:
3584 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3587 @command{cksum} prints the CRC checksum for each file along with the number
3588 of bytes in the file, and the file name unless no arguments were given.
3590 @command{cksum} is typically used to ensure that files
3591 transferred by unreliable means (e.g., netnews) have not been corrupted,
3592 by comparing the @command{cksum} output for the received files with the
3593 @command{cksum} output for the original files (typically given in the
3596 The CRC algorithm is specified by the POSIX standard. It is not
3597 compatible with the BSD or System V @command{sum} algorithms (see the
3598 previous section); it is more robust.
3600 The only options are @option{--help} and @option{--version}. @xref{Common
3606 @node md5sum invocation
3607 @section @command{md5sum}: Print or check MD5 digests
3611 @cindex 128-bit checksum
3612 @cindex checksum, 128-bit
3613 @cindex fingerprint, 128-bit
3614 @cindex message-digest, 128-bit
3616 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3617 @dfn{message-digest}) for each specified @var{file}.
3619 Note: The MD5 digest is more reliable than a simple CRC (provided by
3620 the @command{cksum} command) for detecting accidental file corruption,
3621 as the chances of accidentally having two files with identical MD5
3622 are vanishingly small. However, it should not be considered secure
3623 against malicious tampering: although finding a file with a given MD5
3624 fingerprint is considered infeasible at the moment, it is known how
3625 to modify certain files, including digital certificates, so that they
3626 appear valid when signed with an MD5 digest.
3627 For more secure hashes, consider using SHA-2. @xref{sha2 utilities}.
3629 If a @var{file} is specified as @samp{-} or if no files are given
3630 @command{md5sum} computes the checksum for the standard input.
3631 @command{md5sum} can also determine whether a file and checksum are
3632 consistent. Synopsis:
3635 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3638 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3639 indicating binary or text input mode, and the file name.
3640 If @var{file} contains a backslash or newline, the
3641 line is started with a backslash, and each problematic character in
3642 the file name is escaped with a backslash, making the output
3643 unambiguous even in the presence of arbitrary file names.
3644 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3646 The program accepts the following options. Also see @ref{Common options}.
3654 @cindex binary input files
3655 Treat each input file as binary, by reading it in binary mode and
3656 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3657 On systems like GNU that do not distinguish between binary
3658 and text files, this option merely flags each input mode as binary:
3659 the MD5 checksum is unaffected. This option is the default on systems
3660 like MS-DOS that distinguish between binary and text files, except
3661 for reading standard input when standard input is a terminal.
3665 Read file names and checksum information (not data) from each
3666 @var{file} (or from stdin if no @var{file} was specified) and report
3667 whether the checksums match the contents of the named files.
3668 The input to this mode of @command{md5sum} is usually the output of
3669 a prior, checksum-generating run of @samp{md5sum}.
3670 Each valid line of input consists of an MD5 checksum, a binary/text
3671 flag, and then a file name.
3672 Binary mode is indicated with @samp{*}, text with @samp{ } (space).
3673 For each such line, @command{md5sum} reads the named file and computes its
3674 MD5 checksum. Then, if the computed message digest does not match the
3675 one on the line with the file name, the file is noted as having
3676 failed the test. Otherwise, the file passes the test.
3677 By default, for each valid line, one line is written to standard
3678 output indicating whether the named file passed the test.
3679 After all checks have been performed, if there were any failures,
3680 a warning is issued to standard error.
3681 Use the @option{--status} option to inhibit that output.
3682 If any listed file cannot be opened or read, if any valid line has
3683 an MD5 checksum inconsistent with the associated file, or if no valid
3684 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3685 it exits successfully.
3689 @cindex verifying MD5 checksums
3690 This option is useful only when verifying checksums.
3691 When verifying checksums, don't generate an 'OK' message per successfully
3692 checked file. Files that fail the verification are reported in the
3693 default one-line-per-file format. If there is any checksum mismatch,
3694 print a warning summarizing the failures to standard error.
3698 @cindex verifying MD5 checksums
3699 This option is useful only when verifying checksums.
3700 When verifying checksums, don't generate the default one-line-per-file
3701 diagnostic and don't output the warning summarizing any failures.
3702 Failures to open or read a file still evoke individual diagnostics to
3704 If all listed files are readable and are consistent with the associated
3705 MD5 checksums, exit successfully. Otherwise exit with a status code
3706 indicating there was a failure.
3711 Output BSD style checksums, which indicate the checksum algorithm used.
3712 As a GNU extension, file names with problematic characters
3713 are escaped as described above, with the same escaping indicator of @samp{\}
3714 at the start of the line, being used.
3715 The @option{--tag} option implies binary mode, and is disallowed with
3716 @option{--text} mode as supporting that would unnecessarily complicate
3717 the output format, while providing little benefit.
3723 @cindex text input files
3724 Treat each input file as text, by reading it in text mode and
3725 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3726 This option is the default on systems like GNU that do not
3727 distinguish between binary and text files. On other systems, it is
3728 the default for reading standard input when standard input is a
3729 terminal. This mode is never defaulted to if @option{--tag} is used.
3735 @cindex verifying MD5 checksums
3736 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3737 This option is useful only if all but a few lines in the checked input
3742 @cindex verifying MD5 checksums
3743 When verifying checksums,
3744 if one or more input line is invalid,
3745 exit nonzero after all warnings have been issued.
3752 @node sha1sum invocation
3753 @section @command{sha1sum}: Print or check SHA-1 digests
3757 @cindex 160-bit checksum
3758 @cindex checksum, 160-bit
3759 @cindex fingerprint, 160-bit
3760 @cindex message-digest, 160-bit
3762 @command{sha1sum} computes a 160-bit checksum for each specified
3763 @var{file}. The usage and options of this command are precisely the
3764 same as for @command{md5sum}. @xref{md5sum invocation}.
3766 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3767 it are known (different files having the same fingerprint). However,
3768 it is known that they can be produced with considerable, but not
3769 unreasonable, resources. For this reason, it is generally considered
3770 that SHA-1 should be gradually phased out in favor of the more secure
3771 SHA-2 hash algorithms. @xref{sha2 utilities}.
3774 @node sha2 utilities
3775 @section sha2 utilities: Print or check SHA-2 digests
3782 @cindex 224-bit checksum
3783 @cindex 256-bit checksum
3784 @cindex 384-bit checksum
3785 @cindex 512-bit checksum
3786 @cindex checksum, 224-bit
3787 @cindex checksum, 256-bit
3788 @cindex checksum, 384-bit
3789 @cindex checksum, 512-bit
3790 @cindex fingerprint, 224-bit
3791 @cindex fingerprint, 256-bit
3792 @cindex fingerprint, 384-bit
3793 @cindex fingerprint, 512-bit
3794 @cindex message-digest, 224-bit
3795 @cindex message-digest, 256-bit
3796 @cindex message-digest, 384-bit
3797 @cindex message-digest, 512-bit
3799 The commands @command{sha224sum}, @command{sha256sum},
3800 @command{sha384sum} and @command{sha512sum} compute checksums of
3801 various lengths (respectively 224, 256, 384 and 512 bits),
3802 collectively known as the SHA-2 hashes. The usage and options of
3803 these commands are precisely the same as for @command{md5sum}.
3804 @xref{md5sum invocation}.
3806 Note: The SHA384 and SHA512 digests are considerably slower to
3807 compute, especially on 32-bit computers, than SHA224 or SHA256.
3810 @node Operating on sorted files
3811 @chapter Operating on sorted files
3813 @cindex operating on sorted files
3814 @cindex sorted files, operations on
3816 These commands work with (or produce) sorted files.
3819 * sort invocation:: Sort text files.
3820 * shuf invocation:: Shuffle text files.
3821 * uniq invocation:: Uniquify files.
3822 * comm invocation:: Compare two sorted files line by line.
3823 * ptx invocation:: Produce a permuted index of file contents.
3824 * tsort invocation:: Topological sort.
3828 @node sort invocation
3829 @section @command{sort}: Sort text files
3832 @cindex sorting files
3834 @command{sort} sorts, merges, or compares all the lines from the given
3835 files, or standard input if none are given or for a @var{file} of
3836 @samp{-}. By default, @command{sort} writes the results to standard
3840 sort [@var{option}]@dots{} [@var{file}]@dots{}
3843 @command{sort} has three modes of operation: sort (the default), merge,
3844 and check for sortedness. The following options change the operation
3851 @itemx --check=diagnose-first
3854 @cindex checking for sortedness
3855 Check whether the given file is already sorted: if it is not all
3856 sorted, print a diagnostic containing the first out-of-order line and
3857 exit with a status of 1.
3858 Otherwise, exit successfully.
3859 At most one input file can be given.
3862 @itemx --check=quiet
3863 @itemx --check=silent
3866 @cindex checking for sortedness
3867 Exit successfully if the given file is already sorted, and
3868 exit with status 1 otherwise.
3869 At most one input file can be given.
3870 This is like @option{-c}, except it does not print a diagnostic.
3876 @cindex merging sorted files
3877 Merge the given files by sorting them as a group. Each input file must
3878 always be individually sorted. It always works to sort instead of
3879 merge; merging is provided because it is faster, in the case where it
3884 @cindex sort stability
3885 @cindex sort's last-resort comparison
3886 A pair of lines is compared as follows:
3887 @command{sort} compares each pair of fields, in the
3888 order specified on the command line, according to the associated
3889 ordering options, until a difference is found or no fields are left.
3890 If no key fields are specified, @command{sort} uses a default key of
3891 the entire line. Finally, as a last resort when all keys compare
3892 equal, @command{sort} compares entire lines as if no ordering options
3893 other than @option{--reverse} (@option{-r}) were specified. The
3894 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3895 comparison} so that lines in which all fields compare equal are left
3896 in their original relative order. The @option{--unique}
3897 (@option{-u}) option also disables the last-resort comparison.
3901 Unless otherwise specified, all comparisons use the character collating
3902 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3903 use a non-POSIX locale (e.g., by setting @env{LC_ALL}
3904 to @samp{en_US}), then @command{sort} may produce output that is sorted
3905 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3906 environment variable to @samp{C}@. Note that setting only @env{LC_COLLATE}
3907 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3908 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3909 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3910 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3911 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3913 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3914 limit on input line length or restrictions on bytes allowed within lines.
3915 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3916 @command{sort} silently supplies one. A line's trailing newline is not
3917 part of the line for comparison purposes.
3919 @cindex exit status of @command{sort}
3923 0 if no error occurred
3924 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3925 2 if an error occurred
3929 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3930 value as the directory for temporary files instead of @file{/tmp}. The
3931 @option{--temporary-directory} (@option{-T}) option in turn overrides
3932 the environment variable.
3934 The following options affect the ordering of output lines. They may be
3935 specified globally or as part of a specific key field. If no key
3936 fields are specified, global options apply to comparison of entire
3937 lines; otherwise the global options are inherited by key fields that do
3938 not specify any special options of their own. In pre-POSIX
3939 versions of @command{sort}, global options affect only later key fields,
3940 so portable shell scripts should specify global options first.
3945 @itemx --ignore-leading-blanks
3947 @opindex --ignore-leading-blanks
3948 @cindex blanks, ignoring leading
3950 Ignore leading blanks when finding sort keys in each line.
3951 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3952 can change this. Note blanks may be ignored by your locale's collating
3953 rules, but without this option they will be significant for character
3954 positions specified in keys with the @option{-k} option.
3957 @itemx --dictionary-order
3959 @opindex --dictionary-order
3960 @cindex dictionary order
3961 @cindex phone directory order
3962 @cindex telephone directory order
3964 Sort in @dfn{phone directory} order: ignore all characters except
3965 letters, digits and blanks when sorting.
3966 By default letters and digits are those of ASCII and a blank
3967 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3970 @itemx --ignore-case
3972 @opindex --ignore-case
3973 @cindex ignoring case
3974 @cindex case folding
3976 Fold lowercase characters into the equivalent uppercase characters when
3977 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3978 The @env{LC_CTYPE} locale determines character types.
3979 When used with @option{--unique} those lower case equivalent lines are
3980 thrown away. (There is currently no way to throw away the upper case
3981 equivalent instead. (Any @option{--reverse} given would only affect
3982 the final result, after the throwing away.))
3985 @itemx --general-numeric-sort
3986 @itemx --sort=general-numeric
3988 @opindex --general-numeric-sort
3990 @cindex general numeric sort
3992 Sort numerically, converting a prefix of each line to a long
3993 double-precision floating point number. @xref{Floating point}.
3994 Do not report overflow, underflow, or conversion errors.
3995 Use the following collating sequence:
3999 Lines that do not start with numbers (all considered to be equal).
4001 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
4002 in a consistent but machine-dependent order.
4006 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
4011 Use this option only if there is no alternative; it is much slower than
4012 @option{--numeric-sort} (@option{-n}) and it can lose information when
4013 converting to floating point.
4016 @itemx --human-numeric-sort
4017 @itemx --sort=human-numeric
4019 @opindex --human-numeric-sort
4021 @cindex human numeric sort
4023 Sort numerically, first by numeric sign (negative, zero, or positive);
4024 then by SI suffix (either empty, or @samp{k} or @samp{K}, or
4025 one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
4026 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
4027 because @samp{M} (mega) precedes @samp{G} (giga) as an SI
4028 suffix. This option sorts values that are consistently scaled to the
4029 nearest suffix, regardless of whether suffixes denote powers of 1000
4030 or 1024, and it therefore sorts the output of any single invocation of
4031 the @command{df}, @command{du}, or @command{ls} commands that are
4032 invoked with their @option{--human-readable} or @option{--si} options.
4033 The syntax for numbers is the same as for the @option{--numeric-sort}
4034 option; the SI suffix must immediately follow the number.
4037 @itemx --ignore-nonprinting
4039 @opindex --ignore-nonprinting
4040 @cindex nonprinting characters, ignoring
4041 @cindex unprintable characters, ignoring
4043 Ignore nonprinting characters.
4044 The @env{LC_CTYPE} locale determines character types.
4045 This option has no effect if the stronger @option{--dictionary-order}
4046 (@option{-d}) option is also given.
4052 @opindex --month-sort
4054 @cindex months, sorting by
4056 An initial string, consisting of any amount of blanks, followed
4057 by a month name abbreviation, is folded to UPPER case and
4058 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}@.
4059 Invalid names compare low to valid names. The @env{LC_TIME} locale
4060 category determines the month spellings.
4061 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4065 @itemx --numeric-sort
4066 @itemx --sort=numeric
4068 @opindex --numeric-sort
4070 @cindex numeric sort
4072 Sort numerically. The number begins each line and consists
4073 of optional blanks, an optional @samp{-} sign, and zero or more
4074 digits possibly separated by thousands separators, optionally followed
4075 by a decimal-point character and zero or more digits. An empty
4076 number is treated as @samp{0}. The @env{LC_NUMERIC}
4077 locale specifies the decimal-point character and thousands separator.
4078 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4081 Comparison is exact; there is no rounding error.
4083 Neither a leading @samp{+} nor exponential notation is recognized.
4084 To compare such strings numerically, use the
4085 @option{--general-numeric-sort} (@option{-g}) option.
4088 @itemx --version-sort
4090 @opindex --version-sort
4091 @cindex version number sort
4092 Sort by version name and number. It behaves like a standard sort,
4093 except that each sequence of decimal digits is treated numerically
4094 as an index/version number. (@xref{Details about version sort}.)
4100 @cindex reverse sorting
4101 Reverse the result of comparison, so that lines with greater key values
4102 appear earlier in the output instead of later.
4105 @itemx --random-sort
4106 @itemx --sort=random
4108 @opindex --random-sort
4111 Sort by hashing the input keys and then sorting the hash values.
4112 Choose the hash function at random, ensuring that it is free of
4113 collisions so that differing keys have differing hash values. This is
4114 like a random permutation of the inputs (@pxref{shuf invocation}),
4115 except that keys with the same value sort together.
4117 If multiple random sort fields are specified, the same random hash
4118 function is used for all fields. To use different random hash
4119 functions for different fields, you can invoke @command{sort} more
4122 The choice of hash function is affected by the
4123 @option{--random-source} option.
4131 @item --compress-program=@var{prog}
4132 Compress any temporary files with the program @var{prog}.
4134 With no arguments, @var{prog} must compress standard input to standard
4135 output, and when given the @option{-d} option it must decompress
4136 standard input to standard output.
4138 Terminate with an error if @var{prog} exits with nonzero status.
4140 White space and the backslash character should not appear in
4141 @var{prog}; they are reserved for future use.
4143 @filesZeroFromOption{sort,,sorted output}
4145 @item -k @var{pos1}[,@var{pos2}]
4146 @itemx --key=@var{pos1}[,@var{pos2}]
4150 Specify a sort field that consists of the part of the line between
4151 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
4152 omitted), @emph{inclusive}.
4154 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
4155 where @var{f} is the number of the field to use, and @var{c} is the number
4156 of the first character from the beginning of the field. Fields and character
4157 positions are numbered starting with 1; a character position of zero in
4158 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
4159 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
4160 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
4161 @var{opts} are ordering options, allowing individual keys to be sorted
4162 according to different rules; see below for details. Keys can span
4165 Example: To sort on the second field, use @option{--key=2,2}
4166 (@option{-k 2,2}). See below for more notes on keys and more examples.
4167 See also the @option{--debug} option to help determine the part
4168 of the line being used in the sort.
4171 Highlight the portion of each line used for sorting.
4172 Also issue warnings about questionable usage to stderr.
4174 @item --batch-size=@var{nmerge}
4175 @opindex --batch-size
4176 @cindex number of inputs to merge, nmerge
4177 Merge at most @var{nmerge} inputs at once.
4179 When @command{sort} has to merge more than @var{nmerge} inputs,
4180 it merges them in groups of @var{nmerge}, saving the result in
4181 a temporary file, which is then used as an input in a subsequent merge.
4183 A large value of @var{nmerge} may improve merge performance and decrease
4184 temporary storage utilization at the expense of increased memory usage
4185 and I/O@. Conversely a small value of @var{nmerge} may reduce memory
4186 requirements and I/O at the expense of temporary storage consumption and
4189 The value of @var{nmerge} must be at least 2. The default value is
4190 currently 16, but this is implementation-dependent and may change in
4193 The value of @var{nmerge} may be bounded by a resource limit for open
4194 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
4195 OPEN_MAX} may display limits for your systems; these limits may be
4196 modified further if your program already has some files open, or if
4197 the operating system has other limits on the number of open files. If
4198 the value of @var{nmerge} exceeds the resource limit, @command{sort}
4199 silently uses a smaller value.
4201 @item -o @var{output-file}
4202 @itemx --output=@var{output-file}
4205 @cindex overwriting of input, allowed
4206 Write output to @var{output-file} instead of standard output.
4207 Normally, @command{sort} reads all input before opening
4208 @var{output-file}, so you can safely sort a file in place by using
4209 commands like @code{sort -o F F} and @code{cat F | sort -o F}@.
4210 However, @command{sort} with @option{--merge} (@option{-m}) can open
4211 the output file before reading all input, so a command like @code{cat
4212 F | sort -m -o F - G} is not safe as @command{sort} might start
4213 writing @file{F} before @command{cat} is done reading it.
4215 @vindex POSIXLY_CORRECT
4216 On newer systems, @option{-o} cannot appear after an input file if
4217 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}@. Portable
4218 scripts should specify @option{-o @var{output-file}} before any input
4221 @item --random-source=@var{file}
4222 @opindex --random-source
4223 @cindex random source for sorting
4224 Use @var{file} as a source of random data used to determine which
4225 random hash function to use with the @option{-R} option. @xref{Random
4232 @cindex sort stability
4233 @cindex sort's last-resort comparison
4235 Make @command{sort} stable by disabling its last-resort comparison.
4236 This option has no effect if no fields or global ordering options
4237 other than @option{--reverse} (@option{-r}) are specified.
4240 @itemx --buffer-size=@var{size}
4242 @opindex --buffer-size
4243 @cindex size for main memory sorting
4244 Use a main-memory sort buffer of the given @var{size}. By default,
4245 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4246 @var{size} to be interpreted as a percentage of physical memory.
4247 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4248 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4249 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}@. Appending
4250 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4253 This option can improve the performance of @command{sort} by causing it
4254 to start with a larger or smaller sort buffer than the default.
4255 However, this option affects only the initial buffer size. The buffer
4256 grows beyond @var{size} if @command{sort} encounters input lines larger
4259 @item -t @var{separator}
4260 @itemx --field-separator=@var{separator}
4262 @opindex --field-separator
4263 @cindex field separator character
4264 Use character @var{separator} as the field separator when finding the
4265 sort keys in each line. By default, fields are separated by the empty
4266 string between a non-blank character and a blank character.
4267 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4270 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4271 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4272 not considered to be part of either the field preceding or the field
4273 following, so with @samp{sort @w{-t " "}} the same input line has
4274 three fields: an empty field, @samp{foo}, and @samp{bar}.
4275 However, fields that extend to the end of the line,
4276 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4277 retain the field separators present between the endpoints of the range.
4279 To specify ASCII @sc{nul} as the field separator,
4280 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4282 @item -T @var{tempdir}
4283 @itemx --temporary-directory=@var{tempdir}
4285 @opindex --temporary-directory
4286 @cindex temporary directory
4288 Use directory @var{tempdir} to store temporary files, overriding the
4289 @env{TMPDIR} environment variable. If this option is given more than
4290 once, temporary files are stored in all the directories given. If you
4291 have a large sort or merge that is I/O-bound, you can often improve
4292 performance by using this option to specify directories on different
4293 disks and controllers.
4295 @item --parallel=@var{n}
4297 @cindex multithreaded sort
4298 Set the number of sorts run in parallel to @var{n}. By default,
4299 @var{n} is set to the number of available processors, but limited
4300 to 8, as there are diminishing performance gains after that.
4301 Note also that using @var{n} threads increases the memory usage by
4302 a factor of log @var{n}. Also see @ref{nproc invocation}.
4308 @cindex uniquifying output
4310 Normally, output only the first of a sequence of lines that compare
4311 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4312 check that no pair of consecutive lines compares equal.
4314 This option also disables the default last-resort comparison.
4316 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4317 this equivalence does not extend to arbitrary @command{sort} options.
4318 For example, @code{sort -n -u} inspects only the value of the initial
4319 numeric string when checking for uniqueness, whereas @code{sort -n |
4320 uniq} inspects the entire line. @xref{uniq invocation}.
4322 @macro zeroTerminatedOption
4324 @itemx --zero-terminated
4326 @opindex --zero-terminated
4327 @cindex process zero-terminated items
4328 Delimit items with a zero byte rather than a newline (ASCII @sc{lf}).
4329 I.e., treat input as items separated by ASCII @sc{nul}
4330 and terminate output items with ASCII @sc{nul}.
4331 This option can be useful in conjunction with @samp{perl -0} or
4332 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4333 reliably handle arbitrary file names (even those containing blanks
4334 or other special characters).
4336 @zeroTerminatedOption
4340 Historical (BSD and System V) implementations of @command{sort} have
4341 differed in their interpretation of some options, particularly
4342 @option{-b}, @option{-f}, and @option{-n}.
4343 @sc{gnu} sort follows the POSIX
4344 behavior, which is usually (but not always!) like the System V behavior.
4345 According to POSIX, @option{-n} no longer implies @option{-b}. For
4346 consistency, @option{-M} has been changed in the same way. This may
4347 affect the meaning of character positions in field specifications in
4348 obscure cases. The only fix is to add an explicit @option{-b}.
4350 A position in a sort field specified with @option{-k} may have any
4351 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4352 global ordering options are inherited by that particular field. The
4353 @option{-b} option may be independently attached to either or both of
4354 the start and end positions of a field specification, and if it is
4355 inherited from the global options it will be attached to both.
4356 If input lines can contain leading or adjacent blanks and @option{-t}
4357 is not used, then @option{-k} is typically combined with @option{-b} or
4358 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4359 the varying numbers of leading blanks in fields can cause confusing results.
4361 If the start position in a sort field specifier falls after the end of
4362 the line or after the end field, the field is empty. If the @option{-b}
4363 option was specified, the @samp{.@var{c}} part of a field specification
4364 is counted from the first nonblank character of the field.
4366 @vindex _POSIX2_VERSION
4367 @vindex POSIXLY_CORRECT
4368 On older systems, @command{sort} supports an obsolete origin-zero
4369 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4370 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4371 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4372 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4373 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4375 This obsolete behavior can be enabled or disabled with the
4376 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4377 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4378 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4380 Scripts intended for use on standard hosts should avoid obsolete
4381 syntax and should use @option{-k} instead. For example, avoid
4382 @samp{sort +2}, since it might be interpreted as either @samp{sort
4383 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4384 support only the obsolete syntax, it can use a test like @samp{if sort
4385 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4388 Here are some examples to illustrate various combinations of options.
4393 Sort in descending (reverse) numeric order.
4400 Run no more than 4 sorts concurrently, using a buffer size of 10M.
4403 sort --parallel=4 -S 10M
4407 Sort alphabetically, omitting the first and second fields
4408 and the blanks at the start of the third field.
4409 This uses a single key composed of the characters beginning
4410 at the start of the first nonblank character in field three
4411 and extending to the end of each line.
4418 Sort numerically on the second field and resolve ties by sorting
4419 alphabetically on the third and fourth characters of field five.
4420 Use @samp{:} as the field delimiter.
4423 sort -t : -k 2,2n -k 5.3,5.4
4426 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4427 @command{sort} would have used all characters beginning in the second field
4428 and extending to the end of the line as the primary @emph{numeric}
4429 key. For the large majority of applications, treating keys spanning
4430 more than one field as numeric will not do what you expect.
4432 Also note that the @samp{n} modifier was applied to the field-end
4433 specifier for the first key. It would have been equivalent to
4434 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4435 @samp{b} apply to the associated @emph{field}, regardless of whether
4436 the modifier character is attached to the field-start and/or the
4437 field-end part of the key specifier.
4440 Sort the password file on the fifth field and ignore any
4441 leading blanks. Sort lines with equal values in field five
4442 on the numeric user ID in field three. Fields are separated
4446 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4447 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4448 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4451 These three commands have equivalent effect. The first specifies that
4452 the first key's start position ignores leading blanks and the second
4453 key is sorted numerically. The other two commands rely on global
4454 options being inherited by sort keys that lack modifiers. The inheritance
4455 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4456 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4457 character position is not affected by whether initial blanks are
4461 Sort a set of log files, primarily by IPv4 address and secondarily by
4462 time stamp. If two lines' primary and secondary keys are identical,
4463 output the lines in the same order that they were input. The log
4464 files contain lines that look like this:
4467 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4468 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4471 Fields are separated by exactly one space. Sort IPv4 addresses
4472 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4473 because 61 is less than 129.
4476 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4477 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4480 This example cannot be done with a single @command{sort} invocation,
4481 since IPv4 address components are separated by @samp{.} while dates
4482 come just after a space. So it is broken down into two invocations of
4483 @command{sort}: the first sorts by time stamp and the second by IPv4
4484 address. The time stamp is sorted by year, then month, then day, and
4485 finally by hour-minute-second field, using @option{-k} to isolate each
4486 field. Except for hour-minute-second there's no need to specify the
4487 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4488 based on leading prefixes that cannot cross field boundaries. The
4489 IPv4 addresses are sorted lexicographically. The second sort uses
4490 @samp{-s} so that ties in the primary key are broken by the secondary
4491 key; the first sort uses @samp{-s} so that the combination of the two
4495 Generate a tags file in case-insensitive sorted order.
4498 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4501 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4502 that file names that contain blanks or other special characters are
4504 by the sort operation.
4506 @c This example is a bit contrived and needs more explanation.
4508 @c Sort records separated by an arbitrary string by using a pipe to convert
4509 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4510 @c and converting each @samp{\0} back to the original record delimiter.
4513 @c printf 'c\n\nb\n\na\n' |
4514 @c perl -0pe 's/\n\n/\n\0/g' |
4516 @c perl -0pe 's/\0/\n/g'
4520 Use the common DSU, Decorate Sort Undecorate idiom to
4521 sort lines according to their length.
4524 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4527 In general this technique can be used to sort data that the @command{sort}
4528 command does not support, or is inefficient at, sorting directly.
4531 Shuffle a list of directories, but preserve the order of files within
4532 each directory. For instance, one could use this to generate a music
4533 playlist in which albums are shuffled but the songs of each album are
4537 ls */* | sort -t / -k 1,1R -k 2,2
4543 @node shuf invocation
4544 @section @command{shuf}: Shuffling text
4547 @cindex shuffling files
4549 @command{shuf} shuffles its input by outputting a random permutation
4550 of its input lines. Each output permutation is equally likely.
4554 shuf [@var{option}]@dots{} [@var{file}]
4555 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4556 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4559 @command{shuf} has three modes of operation that affect where it
4560 obtains its input lines. By default, it reads lines from standard
4561 input. The following options change the operation mode:
4569 @cindex command-line operands to shuffle
4570 Treat each command-line operand as an input line.
4572 @item -i @var{lo}-@var{hi}
4573 @itemx --input-range=@var{lo}-@var{hi}
4575 @opindex --input-range
4576 @cindex input range to shuffle
4577 Act as if input came from a file containing the range of unsigned
4578 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4582 @command{shuf}'s other options can affect its behavior in all
4587 @item -n @var{lines}
4588 @itemx --head-count=@var{count}
4590 @opindex --head-count
4591 @cindex head of output
4592 Output at most @var{count} lines. By default, all input lines are
4595 @item -o @var{output-file}
4596 @itemx --output=@var{output-file}
4599 @cindex overwriting of input, allowed
4600 Write output to @var{output-file} instead of standard output.
4601 @command{shuf} reads all input before opening
4602 @var{output-file}, so you can safely shuffle a file in place by using
4603 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4605 @item --random-source=@var{file}
4606 @opindex --random-source
4607 @cindex random source for shuffling
4608 Use @var{file} as a source of random data used to determine which
4609 permutation to generate. @xref{Random sources}.
4611 @zeroTerminatedOption
4627 might produce the output
4637 Similarly, the command:
4640 shuf -e clubs hearts diamonds spades
4654 and the command @samp{shuf -i 1-4} might output:
4664 These examples all have four input lines, so @command{shuf} might
4665 produce any of the twenty-four possible permutations of the input. In
4666 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4667 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4668 output permutations.
4673 @node uniq invocation
4674 @section @command{uniq}: Uniquify files
4677 @cindex uniquify files
4679 @command{uniq} writes the unique lines in the given @file{input}, or
4680 standard input if nothing is given or for an @var{input} name of
4684 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4687 By default, @command{uniq} prints its input lines, except that
4688 it discards all but the first of adjacent repeated lines, so that
4689 no output lines are repeated. Optionally, it can instead discard
4690 lines that are not repeated, or all repeated lines.
4692 The input need not be sorted, but repeated input lines are detected
4693 only if they are adjacent. If you want to discard non-adjacent
4694 duplicate lines, perhaps you want to use @code{sort -u}.
4695 @xref{sort invocation}.
4698 Comparisons honor the rules specified by the @env{LC_COLLATE}
4701 If no @var{output} file is specified, @command{uniq} writes to standard
4704 The program accepts the following options. Also see @ref{Common options}.
4709 @itemx --skip-fields=@var{n}
4711 @opindex --skip-fields
4712 Skip @var{n} fields on each line before checking for uniqueness. Use
4713 a null string for comparison if a line has fewer than @var{n} fields. Fields
4714 are sequences of non-space non-tab characters that are separated from
4715 each other by at least one space or tab.
4717 For compatibility @command{uniq} supports an obsolete option syntax
4718 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4721 @itemx --skip-chars=@var{n}
4723 @opindex --skip-chars
4724 Skip @var{n} characters before checking for uniqueness. Use a null string
4725 for comparison if a line has fewer than @var{n} characters. If you use both
4726 the field and character skipping options, fields are skipped over first.
4728 @vindex _POSIX2_VERSION
4729 On older systems, @command{uniq} supports an obsolete option syntax
4731 This obsolete behavior can be enabled or disabled with the
4732 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4733 conformance}), but portable scripts should avoid commands whose
4734 behavior depends on this variable.
4735 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4736 the ambiguous @samp{uniq +10}.
4742 Print the number of times each line occurred along with the line.
4745 @itemx --ignore-case
4747 @opindex --ignore-case
4748 Ignore differences in case when comparing lines.
4754 @cindex repeated lines, outputting
4755 Discard lines that are not repeated. When used by itself, this option
4756 causes @command{uniq} to print the first copy of each repeated line,
4760 @itemx --all-repeated[=@var{delimit-method}]
4762 @opindex --all-repeated
4763 @cindex all repeated lines, outputting
4764 Do not discard the second and subsequent repeated input lines,
4765 but discard lines that are not repeated.
4766 This option is useful mainly in conjunction with other options e.g.,
4767 to ignore case or to compare only selected fields.
4768 The optional @var{delimit-method} tells how to delimit
4769 groups of repeated lines, and must be one of the following:
4774 Do not delimit groups of repeated lines.
4775 This is equivalent to @option{--all-repeated} (@option{-D}).
4778 Output a newline before each group of repeated lines.
4779 With @option{--zero-terminated} (@option{-z}), use a zero
4780 byte (ASCII @sc{nul}) instead of a newline.
4783 Separate groups of repeated lines with a single newline.
4784 With @option{--zero-terminated} (@option{-z}), use a zero
4785 byte (ASCII @sc{nul}) instead of a newline.
4786 This is the same as using @samp{prepend}, except that
4787 no delimiter is inserted before the first group, and hence
4788 may be better suited for output direct to users.
4791 Note that when groups are delimited and the input stream contains
4792 two or more consecutive blank lines, then the output is ambiguous.
4793 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4794 each sequence of consecutive newlines with a single newline.
4796 This is a @sc{gnu} extension.
4797 @c FIXME: give an example showing *how* it's useful
4803 @cindex unique lines, outputting
4804 Discard the first repeated line. When used by itself, this option
4805 causes @command{uniq} to print unique lines, and nothing else.
4808 @itemx --check-chars=@var{n}
4810 @opindex --check-chars
4811 Compare at most @var{n} characters on each line (after skipping any specified
4812 fields and characters). By default the entire rest of the lines are
4815 @zeroTerminatedOption
4822 @node comm invocation
4823 @section @command{comm}: Compare two sorted files line by line
4826 @cindex line-by-line comparison
4827 @cindex comparing sorted files
4829 @command{comm} writes to standard output lines that are common, and lines
4830 that are unique, to two input files; a file name of @samp{-} means
4831 standard input. Synopsis:
4834 comm [@var{option}]@dots{} @var{file1} @var{file2}
4838 Before @command{comm} can be used, the input files must be sorted using the
4839 collating sequence specified by the @env{LC_COLLATE} locale.
4840 If an input file ends in a non-newline
4841 character, a newline is silently appended. The @command{sort} command with
4842 no options always outputs a file that is suitable input to @command{comm}.
4844 @cindex differing lines
4845 @cindex common lines
4846 With no options, @command{comm} produces three-column output. Column one
4847 contains lines unique to @var{file1}, column two contains lines unique
4848 to @var{file2}, and column three contains lines common to both files.
4849 Columns are separated by a single TAB character.
4850 @c FIXME: when there's an option to supply an alternative separator
4851 @c string, append "by default" to the above sentence.
4856 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4857 the corresponding columns (and separators). Also see @ref{Common options}.
4859 Unlike some other comparison utilities, @command{comm} has an exit
4860 status that does not depend on the result of the comparison.
4861 Upon normal completion @command{comm} produces an exit code of zero.
4862 If there is an error it exits with nonzero status.
4864 @macro checkOrderOption{cmd}
4865 If the @option{--check-order} option is given, unsorted inputs will
4866 cause a fatal error message. If the option @option{--nocheck-order}
4867 is given, unsorted inputs will never cause an error message. If neither
4868 of these options is given, wrongly sorted inputs are diagnosed
4869 only if an input file is found to contain unpairable
4871 lines, and when both input files are non empty.
4873 @ifclear JOIN_COMMAND
4876 If an input file is diagnosed as being unsorted, the @command{\cmd\}
4877 command will exit with a nonzero status (and the output should not be used).
4879 Forcing @command{\cmd\} to process wrongly sorted input files
4880 containing unpairable lines by specifying @option{--nocheck-order} is
4881 not guaranteed to produce any particular output. The output will
4882 probably not correspond with whatever you hoped it would be.
4884 @checkOrderOption{comm}
4889 Fail with an error message if either input file is wrongly ordered.
4891 @item --nocheck-order
4892 Do not check that both input files are in sorted order.
4896 @item --output-delimiter=@var{str}
4897 Print @var{str} between adjacent output columns,
4898 rather than the default of a single TAB character.
4900 The delimiter @var{str} may not be empty.
4904 @node ptx invocation
4905 @section @command{ptx}: Produce permuted indexes
4909 @command{ptx} reads a text file and essentially produces a permuted index, with
4910 each keyword in its context. The calling sketch is either one of:
4913 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4914 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4917 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4918 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4919 limitations and changing several of the program's default option values.
4920 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4921 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4922 document. @xref{Compatibility in ptx}, for the full list.
4924 Individual options are explained in the following sections.
4926 When @sc{gnu} extensions are enabled, there may be zero, one or several
4927 @var{file}s after the options. If there is no @var{file}, the program
4928 reads the standard input. If there is one or several @var{file}s, they
4929 give the name of input files which are all read in turn, as if all the
4930 input files were concatenated. However, there is a full contextual
4931 break between each file and, when automatic referencing is requested,
4932 file names and line numbers refer to individual text input files. In
4933 all cases, the program outputs the permuted index to the standard
4936 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4937 operates in traditional mode, there may be zero, one or two parameters
4938 besides the options. If there are no parameters, the program reads the
4939 standard input and outputs the permuted index to the standard output.
4940 If there is only one parameter, it names the text @var{input} to be read
4941 instead of the standard input. If two parameters are given, they give
4942 respectively the name of the @var{input} file to read and the name of
4943 the @var{output} file to produce. @emph{Be very careful} to note that,
4944 in this case, the contents of file given by the second parameter is
4945 destroyed. This behavior is dictated by System V @command{ptx}
4946 compatibility; @sc{gnu} Standards normally discourage output parameters not
4947 introduced by an option.
4949 Note that for @emph{any} file named as the value of an option or as an
4950 input text file, a single dash @kbd{-} may be used, in which case
4951 standard input is assumed. However, it would not make sense to use this
4952 convention more than once per program invocation.
4955 * General options in ptx:: Options which affect general program behavior.
4956 * Charset selection in ptx:: Underlying character set considerations.
4957 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4958 * Output formatting in ptx:: Types of output format, and sizing the fields.
4959 * Compatibility in ptx::
4963 @node General options in ptx
4964 @subsection General options
4969 @itemx --traditional
4970 As already explained, this option disables all @sc{gnu} extensions to
4971 @command{ptx} and switches to traditional mode.
4974 Print a short help on standard output, then exit without further
4978 Print the program version on standard output, then exit without further
4986 @node Charset selection in ptx
4987 @subsection Charset selection
4989 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4990 As it is set up now, the program assumes that the input file is coded
4991 using 8-bit ISO 8859-1 code, also known as Latin-1 character set,
4992 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4993 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4994 smaller MS-DOS machines anymore.) Compared to 7-bit ASCII, the set
4995 of characters which are letters is different; this alters the behavior
4996 of regular expression matching. Thus, the default regular expression
4997 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4998 however, is still crude; it obeys the underlying character set ordering
5004 @itemx --ignore-case
5005 Fold lower case letters to upper case for sorting.
5010 @node Input processing in ptx
5011 @subsection Word selection and input processing
5016 @itemx --break-file=@var{file}
5018 This option provides an alternative (to @option{-W}) method of describing
5019 which characters make up words. It introduces the name of a
5020 file which contains a list of characters which can@emph{not} be part of
5021 one word; this file is called the @dfn{Break file}. Any character which
5022 is not part of the Break file is a word constituent. If both options
5023 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
5024 @option{-b} is ignored.
5026 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
5027 break character is to write all the break characters in the file with no
5028 newline at all, not even at the end of the file. When @sc{gnu} extensions
5029 are disabled, spaces, tabs and newlines are always considered as break
5030 characters even if not included in the Break file.
5033 @itemx --ignore-file=@var{file}
5035 The file associated with this option contains a list of words which will
5036 never be taken as keywords in concordance output. It is called the
5037 @dfn{Ignore file}. The file contains exactly one word in each line; the
5038 end of line separation of words is not subject to the value of the
5042 @itemx --only-file=@var{file}
5044 The file associated with this option contains a list of words which will
5045 be retained in concordance output; any word not mentioned in this file
5046 is ignored. The file is called the @dfn{Only file}. The file contains
5047 exactly one word in each line; the end of line separation of words is
5048 not subject to the value of the @option{-S} option.
5050 There is no default for the Only file. When both an Only file and an
5051 Ignore file are specified, a word is considered a keyword only
5052 if it is listed in the Only file and not in the Ignore file.
5057 On each input line, the leading sequence of non-white space characters will be
5058 taken to be a reference that has the purpose of identifying this input
5059 line in the resulting permuted index.
5060 @xref{Output formatting in ptx},
5061 for more information about reference production.
5062 Using this option changes the default value for option @option{-S}.
5064 Using this option, the program does not try very hard to remove
5065 references from contexts in output, but it succeeds in doing so
5066 @emph{when} the context ends exactly at the newline. If option
5067 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
5068 are disabled, this condition is always met and references are completely
5069 excluded from the output contexts.
5071 @item -S @var{regexp}
5072 @itemx --sentence-regexp=@var{regexp}
5074 This option selects which regular expression will describe the end of a
5075 line or the end of a sentence. In fact, this regular expression is not
5076 the only distinction between end of lines or end of sentences, and input
5077 line boundaries have no special significance outside this option. By
5078 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
5079 used, end of sentences are used. In this case, this @var{regex} is
5080 imported from @sc{gnu} Emacs:
5083 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
5086 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
5087 of lines are used; in this case, the default @var{regexp} is just:
5093 Using an empty @var{regexp} is equivalent to completely disabling end of
5094 line or end of sentence recognition. In this case, the whole file is
5095 considered to be a single big line or sentence. The user might want to
5096 disallow all truncation flag generation as well, through option @option{-F
5097 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5100 When the keywords happen to be near the beginning of the input line or
5101 sentence, this often creates an unused area at the beginning of the
5102 output context line; when the keywords happen to be near the end of the
5103 input line or sentence, this often creates an unused area at the end of
5104 the output context line. The program tries to fill those unused areas
5105 by wrapping around context in them; the tail of the input line or
5106 sentence is used to fill the unused area on the left of the output line;
5107 the head of the input line or sentence is used to fill the unused area
5108 on the right of the output line.
5110 As a matter of convenience to the user, many usual backslashed escape
5111 sequences from the C language are recognized and converted to the
5112 corresponding characters by @command{ptx} itself.
5114 @item -W @var{regexp}
5115 @itemx --word-regexp=@var{regexp}
5117 This option selects which regular expression will describe each keyword.
5118 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
5119 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
5120 disabled, a word is by default anything which ends with a space, a tab
5121 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
5123 An empty @var{regexp} is equivalent to not using this option.
5124 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5127 As a matter of convenience to the user, many usual backslashed escape
5128 sequences, as found in the C language, are recognized and converted to
5129 the corresponding characters by @command{ptx} itself.
5134 @node Output formatting in ptx
5135 @subsection Output formatting
5137 Output format is mainly controlled by the @option{-O} and @option{-T} options
5138 described in the table below. When neither @option{-O} nor @option{-T} are
5139 selected, and if @sc{gnu} extensions are enabled, the program chooses an
5140 output format suitable for a dumb terminal. Each keyword occurrence is
5141 output to the center of one line, surrounded by its left and right
5142 contexts. Each field is properly justified, so the concordance output
5143 can be readily observed. As a special feature, if automatic
5144 references are selected by option @option{-A} and are output before the
5145 left context, that is, if option @option{-R} is @emph{not} selected, then
5146 a colon is added after the reference; this nicely interfaces with @sc{gnu}
5147 Emacs @code{next-error} processing. In this default output format, each
5148 white space character, like newline and tab, is merely changed to
5149 exactly one space, with no special attempt to compress consecutive
5150 spaces. This might change in the future. Except for those white space
5151 characters, every other character of the underlying set of 256
5152 characters is transmitted verbatim.
5154 Output format is further controlled by the following options.
5158 @item -g @var{number}
5159 @itemx --gap-size=@var{number}
5161 Select the size of the minimum white space gap between the fields on the
5164 @item -w @var{number}
5165 @itemx --width=@var{number}
5167 Select the maximum output width of each final line. If references are
5168 used, they are included or excluded from the maximum output width
5169 depending on the value of option @option{-R}@. If this option is not
5170 selected, that is, when references are output before the left context,
5171 the maximum output width takes into account the maximum length of all
5172 references. If this option is selected, that is, when references are
5173 output after the right context, the maximum output width does not take
5174 into account the space taken by references, nor the gap that precedes
5178 @itemx --auto-reference
5180 Select automatic references. Each input line will have an automatic
5181 reference made up of the file name and the line ordinal, with a single
5182 colon between them. However, the file name will be empty when standard
5183 input is being read. If both @option{-A} and @option{-r} are selected, then
5184 the input reference is still read and skipped, but the automatic
5185 reference is used at output time, overriding the input reference.
5188 @itemx --right-side-refs
5190 In the default output format, when option @option{-R} is not used, any
5191 references produced by the effect of options @option{-r} or @option{-A} are
5192 placed to the far right of output lines, after the right context. With
5193 default output format, when the @option{-R} option is specified, references
5194 are rather placed at the beginning of each output line, before the left
5195 context. For any other output format, option @option{-R} is
5196 ignored, with one exception: with @option{-R} the width of references
5197 is @emph{not} taken into account in total output width given by @option{-w}.
5199 This option is automatically selected whenever @sc{gnu} extensions are
5202 @item -F @var{string}
5203 @itemx --flac-truncation=@var{string}
5205 This option will request that any truncation in the output be reported
5206 using the string @var{string}. Most output fields theoretically extend
5207 towards the beginning or the end of the current line, or current
5208 sentence, as selected with option @option{-S}@. But there is a maximum
5209 allowed output line width, changeable through option @option{-w}, which is
5210 further divided into space for various output fields. When a field has
5211 to be truncated because it cannot extend beyond the beginning or the end of
5212 the current line to fit in, then a truncation occurs. By default,
5213 the string used is a single slash, as in @option{-F /}.
5215 @var{string} may have more than one character, as in @option{-F ...}.
5216 Also, in the particular case when @var{string} is empty (@option{-F ""}),
5217 truncation flagging is disabled, and no truncation marks are appended in
5220 As a matter of convenience to the user, many usual backslashed escape
5221 sequences, as found in the C language, are recognized and converted to
5222 the corresponding characters by @command{ptx} itself.
5224 @item -M @var{string}
5225 @itemx --macro-name=@var{string}
5227 Select another @var{string} to be used instead of @samp{xx}, while
5228 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5231 @itemx --format=roff
5233 Choose an output format suitable for @command{nroff} or @command{troff}
5234 processing. Each output line will look like:
5237 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
5238 "@var{head}" "@var{ref}"
5241 so it will be possible to write a @samp{.xx} roff macro to take care of
5242 the output typesetting. This is the default output format when @sc{gnu}
5243 extensions are disabled. Option @option{-M} can be used to change
5244 @samp{xx} to another macro name.
5246 In this output format, each non-graphical character, like newline and
5247 tab, is merely changed to exactly one space, with no special attempt to
5248 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5249 so it will be correctly processed by @command{nroff} or @command{troff}.
5254 Choose an output format suitable for @TeX{} processing. Each output
5255 line will look like:
5258 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
5259 @{@var{after}@}@{@var{head}@}@{@var{ref}@}
5263 so it will be possible to write a @code{\xx} definition to take care of
5264 the output typesetting. Note that when references are not being
5265 produced, that is, neither option @option{-A} nor option @option{-r} is
5266 selected, the last parameter of each @code{\xx} call is inhibited.
5267 Option @option{-M} can be used to change @samp{xx} to another macro
5270 In this output format, some special characters, like @kbd{$}, @kbd{%},
5271 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5272 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5273 backslash and a pair of dollar signs (to force mathematical mode). The
5274 backslash itself produces the sequence @code{\backslash@{@}}.
5275 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5276 @code{~\@{ @}} respectively. Other diacriticized characters of the
5277 underlying character set produce an appropriate @TeX{} sequence as far
5278 as possible. The other non-graphical characters, like newline and tab,
5279 and all other characters which are not part of ASCII, are merely
5280 changed to exactly one space, with no special attempt to compress
5281 consecutive spaces. Let me know how to improve this special character
5282 processing for @TeX{}.
5287 @node Compatibility in ptx
5288 @subsection The @sc{gnu} extensions to @command{ptx}
5290 This version of @command{ptx} contains a few features which do not exist in
5291 System V @command{ptx}. These extra features are suppressed by using the
5292 @option{-G} command line option, unless overridden by other command line
5293 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5294 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5295 Here are the differences between this program and System V @command{ptx}.
5300 This program can read many input files at once, it always writes the
5301 resulting concordance on standard output. On the other hand, System V
5302 @command{ptx} reads only one file and sends the result to standard output
5303 or, if a second @var{file} parameter is given on the command, to that
5306 Having output parameters not introduced by options is a dangerous
5307 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5308 portably between @sc{gnu} and System V, you should always use it with a
5309 single input file, and always expect the result on standard output. You
5310 might also want to automatically configure in a @option{-G} option to
5311 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5312 that the installed @command{ptx} accepts @option{-G}.
5315 The only options available in System V @command{ptx} are options @option{-b},
5316 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5317 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5318 this enumeration. Moreover, some options have a slightly different
5319 meaning when @sc{gnu} extensions are enabled, as explained below.
5322 By default, concordance output is not formatted for @command{troff} or
5323 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5324 or @command{nroff} output may still be selected through option @option{-O}.
5327 Unless @option{-R} option is used, the maximum reference width is
5328 subtracted from the total output line width. With @sc{gnu} extensions
5329 disabled, width of references is not taken into account in the output
5330 line width computations.
5333 All 256 bytes, even ASCII @sc{nul} bytes, are always read and
5334 processed from input file with no adverse effect, even if @sc{gnu} extensions
5335 are disabled. However, System V @command{ptx} does not accept 8-bit
5336 characters, a few control characters are rejected, and the tilde
5337 @kbd{~} is also rejected.
5340 Input line length is only limited by available memory, even if @sc{gnu}
5341 extensions are disabled. However, System V @command{ptx} processes only
5342 the first 200 characters in each line.
5345 The break (non-word) characters default to be every character except all
5346 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5347 extensions are disabled, the break characters default to space, tab and
5351 The program makes better use of output line width. If @sc{gnu} extensions
5352 are disabled, the program rather tries to imitate System V @command{ptx},
5353 but still, there are some slight disposition glitches this program does
5354 not completely reproduce.
5357 The user can specify both an Ignore file and an Only file. This is not
5358 allowed with System V @command{ptx}.
5363 @node tsort invocation
5364 @section @command{tsort}: Topological sort
5367 @cindex topological sort
5369 @command{tsort} performs a topological sort on the given @var{file}, or
5370 standard input if no input file is given or for a @var{file} of
5371 @samp{-}. For more details and some history, see @ref{tsort background}.
5375 tsort [@var{option}] [@var{file}]
5378 @command{tsort} reads its input as pairs of strings, separated by blanks,
5379 indicating a partial ordering. The output is a total ordering that
5380 corresponds to the given partial ordering.
5394 will produce the output
5405 Consider a more realistic example.
5406 You have a large set of functions all in one file, and they may all be
5407 declared static except one. Currently that one (say @code{main}) is the
5408 first function defined in the file, and the ones it calls directly follow
5409 it, followed by those they call, etc. Let's say that you are determined
5410 to take advantage of prototypes, so you have to choose between declaring
5411 all of those functions (which means duplicating a lot of information from
5412 the definitions) and rearranging the functions so that as many as possible
5413 are defined before they are used. One way to automate the latter process
5414 is to get a list for each function of the functions it calls directly.
5415 Many programs can generate such lists. They describe a call graph.
5416 Consider the following list, in which a given line indicates that the
5417 function on the left calls the one on the right directly.
5423 tail_file pretty_name
5424 tail_file write_header
5426 tail_forever recheck
5427 tail_forever pretty_name
5428 tail_forever write_header
5429 tail_forever dump_remainder
5432 tail_lines start_lines
5433 tail_lines dump_remainder
5434 tail_lines file_lines
5435 tail_lines pipe_lines
5437 tail_bytes start_bytes
5438 tail_bytes dump_remainder
5439 tail_bytes pipe_bytes
5440 file_lines dump_remainder
5444 then you can use @command{tsort} to produce an ordering of those
5445 functions that satisfies your requirement.
5448 example$ tsort call-graph | tac
5468 @command{tsort} detects any cycles in the input and writes the first cycle
5469 encountered to standard error.
5471 Note that for a given partial ordering, generally there is no unique
5472 total ordering. In the context of the call graph above, the function
5473 @code{parse_options} may be placed anywhere in the list as long as it
5474 precedes @code{main}.
5476 The only options are @option{--help} and @option{--version}. @xref{Common
5482 * tsort background:: Where tsort came from.
5485 @node tsort background
5486 @subsection @command{tsort}: Background
5488 @command{tsort} exists because very early versions of the Unix linker processed
5489 an archive file exactly once, and in order. As @command{ld} read each object
5490 in the archive, it decided whether it was needed in the program based on
5491 whether it defined any symbols which were undefined at that point in
5494 This meant that dependencies within the archive had to be handled
5495 specially. For example, @code{scanf} probably calls @code{read}. That means
5496 that in a single pass through an archive, it was important for @code{scanf.o}
5497 to appear before read.o, because otherwise a program which calls
5498 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5499 reference to @code{read}.
5501 The way to address this problem was to first generate a set of
5502 dependencies of one object file on another. This was done by a shell
5503 script called @command{lorder}. The GNU tools don't provide a version of
5504 lorder, as far as I know, but you can still find it in BSD
5507 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5508 resulting sort to define the order in which you added objects to the archive.
5510 This whole procedure has been obsolete since about 1980, because
5511 Unix archives now contain a symbol table (traditionally built by
5512 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5513 linker uses the symbol table to effectively make multiple passes over
5516 Anyhow, that's where tsort came from. To solve an old problem with
5517 the way the linker handled archive files, which has since been solved
5521 @node Operating on fields
5522 @chapter Operating on fields
5525 * cut invocation:: Print selected parts of lines.
5526 * paste invocation:: Merge lines of files.
5527 * join invocation:: Join lines on a common field.
5531 @node cut invocation
5532 @section @command{cut}: Print selected parts of lines
5535 @command{cut} writes to standard output selected parts of each line of each
5536 input file, or standard input if no files are given or for a file name of
5540 cut @var{option}@dots{} [@var{file}]@dots{}
5543 In the table which follows, the @var{byte-list}, @var{character-list},
5544 and @var{field-list} are one or more numbers or ranges (two numbers
5545 separated by a dash) separated by commas. Bytes, characters, and
5546 fields are numbered starting at 1. Incomplete ranges may be
5547 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5548 @samp{@var{n}} through end of line or last field. The list elements
5549 can be repeated, can overlap, and can be specified in any order; but
5550 the selected input is written in the same order that it is read, and
5551 is written exactly once.
5553 The program accepts the following options. Also see @ref{Common
5558 @item -b @var{byte-list}
5559 @itemx --bytes=@var{byte-list}
5562 Select for printing only the bytes in positions listed in
5563 @var{byte-list}. Tabs and backspaces are treated like any other
5564 character; they take up 1 byte. If an output delimiter is specified,
5565 (see the description of @option{--output-delimiter}), then output that
5566 string between ranges of selected bytes.
5568 @item -c @var{character-list}
5569 @itemx --characters=@var{character-list}
5571 @opindex --characters
5572 Select for printing only the characters in positions listed in
5573 @var{character-list}. The same as @option{-b} for now, but
5574 internationalization will change that. Tabs and backspaces are
5575 treated like any other character; they take up 1 character. If an
5576 output delimiter is specified, (see the description of
5577 @option{--output-delimiter}), then output that string between ranges
5580 @item -f @var{field-list}
5581 @itemx --fields=@var{field-list}
5584 Select for printing only the fields listed in @var{field-list}.
5585 Fields are separated by a TAB character by default. Also print any
5586 line that contains no delimiter character, unless the
5587 @option{--only-delimited} (@option{-s}) option is specified.
5589 Note @command{awk} supports more sophisticated field processing,
5590 and by default will use (and discard) runs of blank characters to
5591 separate fields, and ignore leading and trailing blanks.
5594 awk '{print $2}' # print the second field
5595 awk '{print $NF-1}' # print the penultimate field
5596 awk '{print $2,$1}' # reorder the first two fields
5600 In the unlikely event that @command{awk} is unavailable,
5601 one can use the @command{join} command, to process blank
5602 characters as @command{awk} does above.
5605 join -a1 -o 1.2 - /dev/null # print the second field
5606 join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
5610 @item -d @var{input_delim_byte}
5611 @itemx --delimiter=@var{input_delim_byte}
5613 @opindex --delimiter
5614 With @option{-f}, use the first byte of @var{input_delim_byte} as
5615 the input fields separator (default is TAB).
5619 Do not split multi-byte characters (no-op for now).
5622 @itemx --only-delimited
5624 @opindex --only-delimited
5625 For @option{-f}, do not print lines that do not contain the field separator
5626 character. Normally, any line without a field separator is printed verbatim.
5628 @item --output-delimiter=@var{output_delim_string}
5629 @opindex --output-delimiter
5630 With @option{-f}, output fields are separated by @var{output_delim_string}.
5631 The default with @option{-f} is to use the input delimiter.
5632 When using @option{-b} or @option{-c} to select ranges of byte or
5633 character offsets (as opposed to ranges of fields),
5634 output @var{output_delim_string} between non-overlapping
5635 ranges of selected bytes.
5638 @opindex --complement
5639 This option is a GNU extension.
5640 Select for printing the complement of the bytes, characters or fields
5641 selected with the @option{-b}, @option{-c} or @option{-f} options.
5642 In other words, do @emph{not} print the bytes, characters or fields
5643 specified via those options. This option is useful when you have
5644 many fields and want to print all but a few of them.
5651 @node paste invocation
5652 @section @command{paste}: Merge lines of files
5655 @cindex merging files
5657 @command{paste} writes to standard output lines consisting of sequentially
5658 corresponding lines of each given file, separated by a TAB character.
5659 Standard input is used for a file name of @samp{-} or if no input files
5681 paste [@var{option}]@dots{} [@var{file}]@dots{}
5684 The program accepts the following options. Also see @ref{Common options}.
5692 Paste the lines of one file at a time rather than one line from each
5693 file. Using the above example data:
5696 $ paste -s num2 let3
5701 @item -d @var{delim-list}
5702 @itemx --delimiters=@var{delim-list}
5704 @opindex --delimiters
5705 Consecutively use the characters in @var{delim-list} instead of
5706 TAB to separate merged lines. When @var{delim-list} is
5707 exhausted, start again at its beginning. Using the above example data:
5710 $ paste -d '%_' num2 let3 num2
5721 @node join invocation
5722 @section @command{join}: Join lines on a common field
5725 @cindex common field, joining on
5727 @command{join} writes to standard output a line for each pair of input
5728 lines that have identical join fields. Synopsis:
5731 join [@var{option}]@dots{} @var{file1} @var{file2}
5734 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5735 meaning standard input. @var{file1} and @var{file2} should be
5736 sorted on the join fields.
5739 Normally, the sort order is that of the
5740 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5741 the @option{-t} option is given, the sort comparison ignores blanks at
5742 the start of the join field, as in @code{sort -b}. If the
5743 @option{--ignore-case} option is given, the sort comparison ignores
5744 the case of characters in the join field, as in @code{sort -f}.
5746 The @command{sort} and @command{join} commands should use consistent
5747 locales and options if the output of @command{sort} is fed to
5748 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5749 sort a file on its default join field, but if you select a non-default
5750 locale, join field, separator, or comparison options, then you should
5751 do so consistently between @command{join} and @command{sort}.
5752 If @samp{join -t ''} is specified then the whole line is considered which
5753 matches the default operation of sort.
5755 If the input has no unpairable lines, a GNU extension is
5756 available; the sort order can be any order that considers two fields
5757 to be equal if and only if the sort comparison described above
5758 considers them to be equal. For example:
5776 @checkOrderOption{join}
5781 @item the join field is the first field in each line;
5782 @item fields in the input are separated by one or more blanks, with leading
5783 blanks on the line ignored;
5784 @item fields in the output are separated by a space;
5785 @item each output line consists of the join field, the remaining
5786 fields from @var{file1}, then the remaining fields from @var{file2}.
5789 The program accepts the following options. Also see @ref{Common options}.
5793 @item -a @var{file-number}
5795 Print a line for each unpairable line in file @var{file-number} (either
5796 @samp{1} or @samp{2}), in addition to the normal output.
5799 Fail with an error message if either input file is wrongly ordered.
5801 @item --nocheck-order
5802 Do not check that both input files are in sorted order. This is the default.
5804 @item -e @var{string}
5806 Replace those output fields that are missing in the input with @var{string}.
5807 I.e., missing fields specified with the @option{-12jo} options.
5811 Treat the first line of each input file as a header line. The header lines
5812 will be joined and printed as the first output line. If @option{-o} is used to
5813 specify output format, the header line will be printed according to the
5814 specified format. The header lines will not be checked for ordering even if
5815 @option{--check-order} is specified. Also if the header lines from each file
5816 do not match, the heading fields from the first file will be used.
5819 @itemx --ignore-case
5821 @opindex --ignore-case
5822 Ignore differences in case when comparing keys.
5823 With this option, the lines of the input files must be ordered in the same way.
5824 Use @samp{sort -f} to produce this ordering.
5826 @item -1 @var{field}
5828 Join on field @var{field} (a positive integer) of file 1.
5830 @item -2 @var{field}
5832 Join on field @var{field} (a positive integer) of file 2.
5834 @item -j @var{field}
5835 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5837 @item -o @var{field-list}
5839 If the keyword @samp{auto} is specified, infer the output format from
5840 the first line in each file. This is the same as the default output format
5841 but also ensures the same number of fields are output for each line.
5842 Missing fields are replaced with the @option{-e} option and extra fields
5845 Otherwise, construct each output line according to the format in
5846 @var{field-list}. Each element in @var{field-list} is either the single
5847 character @samp{0} or has the form @var{m.n} where the file number, @var{m},
5848 is @samp{1} or @samp{2} and @var{n} is a positive field number.
5850 A field specification of @samp{0} denotes the join field.
5851 In most cases, the functionality of the @samp{0} field spec
5852 may be reproduced using the explicit @var{m.n} that corresponds
5853 to the join field. However, when printing unpairable lines
5854 (using either of the @option{-a} or @option{-v} options), there is no way
5855 to specify the join field using @var{m.n} in @var{field-list}
5856 if there are unpairable lines in both files.
5857 To give @command{join} that functionality, POSIX invented the @samp{0}
5858 field specification notation.
5860 The elements in @var{field-list}
5861 are separated by commas or blanks.
5862 Blank separators typically need to be quoted for the shell. For
5863 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5864 2.2'} are equivalent.
5866 All output lines---including those printed because of any -a or -v
5867 option---are subject to the specified @var{field-list}.
5870 Use character @var{char} as the input and output field separator.
5871 Treat as significant each occurrence of @var{char} in the input file.
5872 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5873 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5874 the whole line is considered, matching the default operation of sort.
5875 If @samp{-t '\0'} is specified then the ASCII @sc{nul}
5876 character is used to delimit the fields.
5878 @item -v @var{file-number}
5879 Print a line for each unpairable line in file @var{file-number}
5880 (either @samp{1} or @samp{2}), instead of the normal output.
5887 @node Operating on characters
5888 @chapter Operating on characters
5890 @cindex operating on characters
5892 This commands operate on individual characters.
5895 * tr invocation:: Translate, squeeze, and/or delete characters.
5896 * expand invocation:: Convert tabs to spaces.
5897 * unexpand invocation:: Convert spaces to tabs.
5902 @section @command{tr}: Translate, squeeze, and/or delete characters
5909 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5912 @command{tr} copies standard input to standard output, performing
5913 one of the following operations:
5917 translate, and optionally squeeze repeated characters in the result,
5919 squeeze repeated characters,
5923 delete characters, then squeeze repeated characters from the result.
5926 The @var{set1} and (if given) @var{set2} arguments define ordered
5927 sets of characters, referred to below as @var{set1} and @var{set2}. These
5928 sets are the characters of the input that @command{tr} operates on.
5929 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5931 complement (all of the characters that are not in @var{set1}).
5933 Currently @command{tr} fully supports only single-byte characters.
5934 Eventually it will support multibyte characters; when it does, the
5935 @option{-C} option will cause it to complement the set of characters,
5936 whereas @option{-c} will cause it to complement the set of values.
5937 This distinction will matter only when some values are not characters,
5938 and this is possible only in locales using multibyte encodings when
5939 the input contains encoding errors.
5941 The program accepts the @option{--help} and @option{--version}
5942 options. @xref{Common options}. Options must precede operands.
5947 * Character sets:: Specifying sets of characters.
5948 * Translating:: Changing one set of characters to another.
5949 * Squeezing:: Squeezing repeats and deleting.
5953 @node Character sets
5954 @subsection Specifying sets of characters
5956 @cindex specifying sets of characters
5958 The format of the @var{set1} and @var{set2} arguments resembles
5959 the format of regular expressions; however, they are not regular
5960 expressions, only lists of characters. Most characters simply
5961 represent themselves in these strings, but the strings can contain
5962 the shorthands listed below, for convenience. Some of them can be
5963 used only in @var{set1} or @var{set2}, as noted below.
5967 @item Backslash escapes
5968 @cindex backslash escapes
5970 The following backslash escape sequences are recognized:
5988 The 8-bit character with the value given by @var{ooo}, which is 1 to 3
5989 octal digits. Note that @samp{\400} is interpreted as the two-byte
5990 sequence, @samp{\040} @samp{0}.
5995 While a backslash followed by a character not listed above is
5996 interpreted as that character, the backslash also effectively
5997 removes any special significance, so it is useful to escape
5998 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
6003 The notation @samp{@var{m}-@var{n}} expands to all of the characters
6004 from @var{m} through @var{n}, in ascending order. @var{m} should
6005 collate before @var{n}; if it doesn't, an error results. As an example,
6006 @samp{0-9} is the same as @samp{0123456789}.
6008 @sc{gnu} @command{tr} does not support the System V syntax that uses square
6009 brackets to enclose ranges. Translations specified in that format
6010 sometimes work as expected, since the brackets are often transliterated
6011 to themselves. However, they should be avoided because they sometimes
6012 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
6015 Many historically common and even accepted uses of ranges are not
6016 portable. For example, on EBCDIC hosts using the @samp{A-Z}
6017 range will not do what most would expect because @samp{A} through @samp{Z}
6018 are not contiguous as they are in ASCII@.
6019 If you can rely on a POSIX compliant version of @command{tr}, then
6020 the best way to work around this is to use character classes (see below).
6021 Otherwise, it is most portable (and most ugly) to enumerate the members
6024 @item Repeated characters
6025 @cindex repeated characters
6027 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
6028 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
6029 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
6030 to as many copies of @var{c} as are needed to make @var{set2} as long as
6031 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
6032 octal, otherwise in decimal.
6034 @item Character classes
6035 @cindex character classes
6037 The notation @samp{[:@var{class}:]} expands to all of the characters in
6038 the (predefined) class @var{class}. The characters expand in no
6039 particular order, except for the @code{upper} and @code{lower} classes,
6040 which expand in ascending order. When the @option{--delete} (@option{-d})
6041 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
6042 character class can be used in @var{set2}. Otherwise, only the
6043 character classes @code{lower} and @code{upper} are accepted in
6044 @var{set2}, and then only if the corresponding character class
6045 (@code{upper} and @code{lower}, respectively) is specified in the same
6046 relative position in @var{set1}. Doing this specifies case conversion.
6047 The class names are given below; an error results when an invalid class
6059 Horizontal whitespace.
6068 Printable characters, not including space.
6074 Printable characters, including space.
6077 Punctuation characters.
6080 Horizontal or vertical whitespace.
6089 @item Equivalence classes
6090 @cindex equivalence classes
6092 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
6093 equivalent to @var{c}, in no particular order. Equivalence classes are
6094 a relatively recent invention intended to support non-English alphabets.
6095 But there seems to be no standard way to define them or determine their
6096 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
6097 each character's equivalence class consists only of that character,
6098 which is of no particular use.
6104 @subsection Translating
6106 @cindex translating characters
6108 @command{tr} performs translation when @var{set1} and @var{set2} are
6109 both given and the @option{--delete} (@option{-d}) option is not given.
6110 @command{tr} translates each character of its input that is in @var{set1}
6111 to the corresponding character in @var{set2}. Characters not in
6112 @var{set1} are passed through unchanged. When a character appears more
6113 than once in @var{set1} and the corresponding characters in @var{set2}
6114 are not all the same, only the final one is used. For example, these
6115 two commands are equivalent:
6122 A common use of @command{tr} is to convert lowercase characters to
6123 uppercase. This can be done in many ways. Here are three of them:
6126 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
6128 tr '[:lower:]' '[:upper:]'
6132 But note that using ranges like @code{a-z} above is not portable.
6134 When @command{tr} is performing translation, @var{set1} and @var{set2}
6135 typically have the same length. If @var{set1} is shorter than
6136 @var{set2}, the extra characters at the end of @var{set2} are ignored.
6138 On the other hand, making @var{set1} longer than @var{set2} is not
6139 portable; POSIX says that the result is undefined. In this situation,
6140 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
6141 the last character of @var{set2} as many times as necessary. System V
6142 @command{tr} truncates @var{set1} to the length of @var{set2}.
6144 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
6145 When the @option{--truncate-set1} (@option{-t}) option is given,
6146 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
6147 instead. This option is ignored for operations other than translation.
6149 Acting like System V @command{tr} in this case breaks the relatively common
6153 tr -cs A-Za-z0-9 '\012'
6157 because it converts only zero bytes (the first element in the
6158 complement of @var{set1}), rather than all non-alphanumerics, to
6162 By the way, the above idiom is not portable because it uses ranges, and
6163 it assumes that the octal code for newline is 012.
6164 Assuming a POSIX compliant @command{tr}, here is a better
6168 tr -cs '[:alnum:]' '[\n*]'
6173 @subsection Squeezing repeats and deleting
6175 @cindex squeezing repeat characters
6176 @cindex deleting characters
6178 When given just the @option{--delete} (@option{-d}) option, @command{tr}
6179 removes any input characters that are in @var{set1}.
6181 When given just the @option{--squeeze-repeats} (@option{-s}) option,
6182 @command{tr} replaces each input sequence of a repeated character that
6183 is in @var{set1} with a single occurrence of that character.
6185 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
6186 first performs any deletions using @var{set1}, then squeezes repeats
6187 from any remaining characters using @var{set2}.
6189 The @option{--squeeze-repeats} option may also be used when translating,
6190 in which case @command{tr} first performs translation, then squeezes
6191 repeats from any remaining characters using @var{set2}.
6193 Here are some examples to illustrate various combinations of options:
6198 Remove all zero bytes:
6205 Put all words on lines by themselves. This converts all
6206 non-alphanumeric characters to newlines, then squeezes each string
6207 of repeated newlines into a single newline:
6210 tr -cs '[:alnum:]' '[\n*]'
6214 Convert each sequence of repeated newlines to a single newline:
6221 Find doubled occurrences of words in a document.
6222 @c Separate the following two "the"s, so typo checkers don't complain.
6223 For example, people often write ``the @w{}the'' with the repeated words
6224 separated by a newline. The Bourne shell script below works first
6225 by converting each sequence of punctuation and blank characters to a
6226 single newline. That puts each ``word'' on a line by itself.
6227 Next it maps all uppercase characters to lower case, and finally it
6228 runs @command{uniq} with the @option{-d} option to print out only the words
6234 | tr -s '[:punct:][:blank:]' '[\n*]' \
6235 | tr '[:upper:]' '[:lower:]' \
6240 Deleting a small set of characters is usually straightforward. For example,
6241 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
6247 However, when @samp{-} is one of those characters, it can be tricky because
6248 @samp{-} has special meanings. Performing the same task as above but also
6249 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
6250 that would fail because @command{tr} would try to interpret @option{-a} as
6251 a command-line option. Alternatively, we could try putting the hyphen
6252 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
6253 it would make @command{tr} interpret @code{a-x} as the range of characters
6254 @samp{a}@dots{}@samp{x} rather than the three.
6255 One way to solve the problem is to put the hyphen at the end of the list
6262 Or you can use @samp{--} to terminate option processing:
6268 More generally, use the character class notation @code{[=c=]}
6269 with @samp{-} (or any other character) in place of the @samp{c}:
6275 Note how single quotes are used in the above example to protect the
6276 square brackets from interpretation by a shell.
6281 @node expand invocation
6282 @section @command{expand}: Convert tabs to spaces
6285 @cindex tabs to spaces, converting
6286 @cindex converting tabs to spaces
6288 @command{expand} writes the contents of each given @var{file}, or standard
6289 input if none are given or for a @var{file} of @samp{-}, to standard
6290 output, with tab characters converted to the appropriate number of
6294 expand [@var{option}]@dots{} [@var{file}]@dots{}
6297 By default, @command{expand} converts all tabs to spaces. It preserves
6298 backspace characters in the output; they decrement the column count for
6299 tab calculations. The default action is equivalent to @option{-t 8} (set
6300 tabs every 8 columns).
6302 The program accepts the following options. Also see @ref{Common options}.
6306 @item -t @var{tab1}[,@var{tab2}]@dots{}
6307 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6310 @cindex tab stops, setting
6311 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6312 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6313 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6314 last tab stop given with single spaces. Tab stops can be separated by
6315 blanks as well as by commas.
6317 For compatibility, GNU @command{expand} also accepts the obsolete
6318 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6319 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6325 @cindex initial tabs, converting
6326 Only convert initial tabs (those that precede all non-space or non-tab
6327 characters) on each line to spaces.
6334 @node unexpand invocation
6335 @section @command{unexpand}: Convert spaces to tabs
6339 @command{unexpand} writes the contents of each given @var{file}, or
6340 standard input if none are given or for a @var{file} of @samp{-}, to
6341 standard output, converting blanks at the beginning of each line into
6342 as many tab characters as needed. In the default POSIX
6343 locale, a @dfn{blank} is a space or a tab; other locales may specify
6344 additional blank characters. Synopsis:
6347 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6350 By default, @command{unexpand} converts only initial blanks (those
6351 that precede all non-blank characters) on each line. It
6352 preserves backspace characters in the output; they decrement the column
6353 count for tab calculations. By default, tabs are set at every 8th
6356 The program accepts the following options. Also see @ref{Common options}.
6360 @item -t @var{tab1}[,@var{tab2}]@dots{}
6361 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6364 If only one tab stop is given, set the tabs @var{tab1} columns apart
6365 instead of the default 8. Otherwise, set the tabs at columns
6366 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6367 beyond the tab stops given unchanged. Tab stops can be separated by
6368 blanks as well as by commas. This option implies the @option{-a} option.
6370 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6371 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6372 separated by commas. (Unlike @option{-t}, this obsolete option does
6373 not imply @option{-a}.) New scripts should use @option{--first-only -t
6374 @var{tab1}[,@var{tab2}]@dots{}} instead.
6380 Also convert all sequences of two or more blanks just before a tab stop,
6381 even if they occur after non-blank characters in a line.
6388 @node Directory listing
6389 @chapter Directory listing
6391 This chapter describes the @command{ls} command and its variants @command{dir}
6392 and @command{vdir}, which list information about files.
6395 * ls invocation:: List directory contents.
6396 * dir invocation:: Briefly ls.
6397 * vdir invocation:: Verbosely ls.
6398 * dircolors invocation:: Color setup for ls, etc.
6403 @section @command{ls}: List directory contents
6406 @cindex directory listing
6408 The @command{ls} program lists information about files (of any type,
6409 including directories). Options and file arguments can be intermixed
6410 arbitrarily, as usual.
6412 For non-option command-line arguments that are directories, by default
6413 @command{ls} lists the contents of directories, not recursively, and
6414 omitting files with names beginning with @samp{.}. For other non-option
6415 arguments, by default @command{ls} lists just the file name. If no
6416 non-option argument is specified, @command{ls} operates on the current
6417 directory, acting as if it had been invoked with a single argument of @samp{.}.
6420 By default, the output is sorted alphabetically, according to the locale
6421 settings in effect.@footnote{If you use a non-POSIX
6422 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6423 produce output that is sorted differently than you're accustomed to.
6424 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6425 If standard output is
6426 a terminal, the output is in columns (sorted vertically) and control
6427 characters are output as question marks; otherwise, the output is listed
6428 one per line and control characters are output as-is.
6430 Because @command{ls} is such a fundamental program, it has accumulated many
6431 options over the years. They are described in the subsections below;
6432 within each section, options are listed alphabetically (ignoring case).
6433 The division of options into the subsections is not absolute, since some
6434 options affect more than one aspect of @command{ls}'s operation.
6436 @cindex exit status of @command{ls}
6441 1 minor problems (e.g., failure to access a file or directory not
6442 specified as a command line argument. This happens when listing a
6443 directory in which entries are actively being removed or renamed.)
6444 2 serious trouble (e.g., memory exhausted, invalid option, failure
6445 to access a file or directory specified as a command line argument
6446 or a directory loop)
6449 Also see @ref{Common options}.
6452 * Which files are listed::
6453 * What information is listed::
6454 * Sorting the output::
6455 * Details about version sort::
6456 * General output formatting::
6457 * Formatting file timestamps::
6458 * Formatting the file names::
6462 @node Which files are listed
6463 @subsection Which files are listed
6465 These options determine which files @command{ls} lists information for.
6466 By default, @command{ls} lists files and the contents of any
6467 directories on the command line, except that in directories it ignores
6468 files whose names start with @samp{.}.
6476 In directories, do not ignore file names that start with @samp{.}.
6481 @opindex --almost-all
6482 In directories, do not ignore all file names that start with @samp{.};
6483 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6484 option overrides this option.
6487 @itemx --ignore-backups
6489 @opindex --ignore-backups
6490 @cindex backup files, ignoring
6491 In directories, ignore files that end with @samp{~}. This option is
6492 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6497 @opindex --directory
6498 List just the names of directories, as with other types of files, rather
6499 than listing their contents.
6500 @c The following sentence is the same as the one for -F.
6501 Do not follow symbolic links listed on the
6502 command line unless the @option{--dereference-command-line} (@option{-H}),
6503 @option{--dereference} (@option{-L}), or
6504 @option{--dereference-command-line-symlink-to-dir} options are specified.
6507 @itemx --dereference-command-line
6509 @opindex --dereference-command-line
6510 @cindex symbolic links, dereferencing
6511 If a command line argument specifies a symbolic link, show information
6512 for the file the link references rather than for the link itself.
6514 @item --dereference-command-line-symlink-to-dir
6515 @opindex --dereference-command-line-symlink-to-dir
6516 @cindex symbolic links, dereferencing
6517 Do not dereference symbolic links, with one exception:
6518 if a command line argument specifies a symbolic link that refers to
6519 a directory, show information for that directory rather than for the
6521 This is the default behavior when no other dereferencing-related
6522 option has been specified (@option{--classify} (@option{-F}),
6523 @option{--directory} (@option{-d}),
6525 @option{--dereference} (@option{-L}), or
6526 @option{--dereference-command-line} (@option{-H})).
6528 @item --group-directories-first
6529 @opindex --group-directories-first
6530 Group all the directories before the files and then sort the
6531 directories and the files separately using the selected sort key
6532 (see --sort option).
6533 That is, this option specifies a primary sort key,
6534 and the --sort option specifies a secondary key.
6535 However, any use of @option{--sort=none}
6536 (@option{-U}) disables this option altogether.
6538 @item --hide=PATTERN
6539 @opindex --hide=@var{pattern}
6540 In directories, ignore files whose names match the shell pattern
6541 @var{pattern}, unless the @option{--all} (@option{-a}) or
6542 @option{--almost-all} (@option{-A}) is also given. This
6543 option acts like @option{--ignore=@var{pattern}} except that it has no
6544 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6545 (@option{-A}) is also given.
6547 This option can be useful in shell aliases. For example, if
6548 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6549 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6550 lists the file @file{README~} even though @samp{ly -A} would not.
6552 @item -I @var{pattern}
6553 @itemx --ignore=@var{pattern}
6555 @opindex --ignore=@var{pattern}
6556 In directories, ignore files whose names match the shell pattern
6557 (not regular expression) @var{pattern}. As
6558 in the shell, an initial @samp{.} in a file name does not match a
6559 wildcard at the start of @var{pattern}. Sometimes it is useful
6560 to give this option several times. For example,
6563 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6566 The first option ignores names of length 3 or more that start with @samp{.},
6567 the second ignores all two-character names that start with @samp{.}
6568 except @samp{..}, and the third ignores names that start with @samp{#}.
6571 @itemx --dereference
6573 @opindex --dereference
6574 @cindex symbolic links, dereferencing
6575 When showing file information for a symbolic link, show information
6576 for the file the link references rather than the link itself.
6577 However, even with this option, @command{ls} still prints the name
6578 of the link itself, not the name of the file that the link points to.
6583 @opindex --recursive
6584 @cindex recursive directory listing
6585 @cindex directory listing, recursive
6586 List the contents of all directories recursively.
6591 @node What information is listed
6592 @subsection What information is listed
6594 These options affect the information that @command{ls} displays. By
6595 default, only file names are shown.
6601 @cindex hurd, author, printing
6602 List each file's author when producing long format directory listings.
6603 In GNU/Hurd, file authors can differ from their owners, but in other
6604 operating systems the two are the same.
6610 @cindex dired Emacs mode support
6611 With the long listing (@option{-l}) format, print an additional line after
6615 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6619 The @var{begn} and @var{endn} are unsigned integers that record the
6620 byte position of the beginning and end of each file name in the output.
6621 This makes it easy for Emacs to find the names, even when they contain
6622 unusual characters such as space or newline, without fancy searching.
6624 If directories are being listed recursively (@option{-R}), output a similar
6625 line with offsets for each subdirectory name:
6628 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6631 Finally, output a line of the form:
6634 //DIRED-OPTIONS// --quoting-style=@var{word}
6638 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6640 Here is an actual example:
6643 $ mkdir -p a/sub/deeper a/sub2
6645 $ touch a/sub/deeper/file
6646 $ ls -gloRF --dired a
6649 -rw-r--r-- 1 0 Jun 10 12:27 f1
6650 -rw-r--r-- 1 0 Jun 10 12:27 f2
6651 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6652 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6656 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6660 -rw-r--r-- 1 0 Jun 10 12:27 file
6664 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6665 //SUBDIRED// 2 3 167 172 228 240 290 296
6666 //DIRED-OPTIONS// --quoting-style=literal
6669 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6670 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6672 The offsets on the @samp{//SUBDIRED//} line delimit the following
6673 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6675 Here is an example of how to extract the fifth entry name, @samp{deeper},
6676 corresponding to the pair of offsets, 222 and 228:
6679 $ ls -gloRF --dired a > out
6680 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6684 Note that although the listing above includes a trailing slash
6685 for the @samp{deeper} entry, the offsets select the name without
6686 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6687 along with an option like @option{--escape} (aka @option{-b}) and operate
6688 on a file whose name contains special characters, notice that the backslash
6693 $ ls -blog --dired 'a b'
6694 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6696 //DIRED-OPTIONS// --quoting-style=escape
6699 If you use a quoting style that adds quote marks
6700 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6701 So beware that the user may select the quoting style via the environment
6702 variable @env{QUOTING_STYLE}@. Hence, applications using @option{--dired}
6703 should either specify an explicit @option{--quoting-style=literal} option
6704 (aka @option{-N} or @option{--literal}) on the command line, or else be
6705 prepared to parse the escaped names.
6708 @opindex --full-time
6709 Produce long format directory listings, and list times in full. It is
6710 equivalent to using @option{--format=long} with
6711 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6715 Produce long format directory listings, but don't display owner information.
6721 Inhibit display of group information in a long format directory listing.
6722 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6723 provide this option for compatibility.)
6731 @cindex inode number, printing
6732 Print the inode number (also called the file serial number and index
6733 number) of each file to the left of the file name. (This number
6734 uniquely identifies each file within a particular file system.)
6737 @itemx --format=long
6738 @itemx --format=verbose
6741 @opindex long ls @r{format}
6742 @opindex verbose ls @r{format}
6743 In addition to the name of each file, print the file type, file mode bits,
6744 number of hard links, owner name, group name, size, and
6745 timestamp (@pxref{Formatting file timestamps}), normally
6746 the modification time. Print question marks for information that
6747 cannot be determined.
6749 Normally the size is printed as a byte count without punctuation, but
6750 this can be overridden (@pxref{Block size}). For example, @option{-h}
6751 prints an abbreviated, human-readable count, and
6752 @samp{--block-size="'1"} prints a byte count with the thousands
6753 separator of the current locale.
6755 For each directory that is listed, preface the files with a line
6756 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6757 for all files in that directory. The block size currently defaults to 1024
6758 bytes, but this can be overridden (@pxref{Block size}).
6759 The @var{blocks} computed counts each hard link separately;
6760 this is arguably a deficiency.
6762 The file type is one of the following characters:
6764 @c The commented-out entries are ones we're not sure about.
6772 character special file
6774 high performance (``contiguous data'') file
6778 door (Solaris 2.5 and up)
6780 @c semaphore, if this is a distinct file type
6784 @c multiplexed file (7th edition Unix; obsolete)
6786 off-line (``migrated'') file (Cray DMF)
6788 network special file (HP-UX)
6792 port (Solaris 10 and up)
6794 @c message queue, if this is a distinct file type
6798 @c shared memory object, if this is a distinct file type
6800 @c typed memory object, if this is a distinct file type
6802 @c whiteout (4.4BSD; not implemented)
6804 some other file type
6807 @cindex permissions, output by @command{ls}
6808 The file mode bits listed are similar to symbolic mode specifications
6809 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6810 third character of each set of permissions as follows:
6814 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6818 If the set-user-ID or set-group-ID bit is set but the corresponding
6819 executable bit is not set.
6822 If the restricted deletion flag or sticky bit, and the
6823 other-executable bit, are both set. The restricted deletion flag is
6824 another name for the sticky bit. @xref{Mode Structure}.
6827 If the restricted deletion flag or sticky bit is set but the
6828 other-executable bit is not set.
6831 If the executable bit is set and none of the above apply.
6837 Following the file mode bits is a single character that specifies
6838 whether an alternate access method such as an access control list
6839 applies to the file. When the character following the file mode bits is a
6840 space, there is no alternate access method. When it is a printing
6841 character, then there is such a method.
6843 GNU @command{ls} uses a @samp{.} character to indicate a file
6844 with an SELinux security context, but no other alternate access method.
6846 A file with any other combination of alternate access methods
6847 is marked with a @samp{+} character.
6850 @itemx --numeric-uid-gid
6852 @opindex --numeric-uid-gid
6853 @cindex numeric uid and gid
6854 @cindex numeric user and group IDs
6855 Produce long format directory listings, but
6856 display numeric user and group IDs instead of the owner and group names.
6860 Produce long format directory listings, but don't display group information.
6861 It is equivalent to using @option{--format=long} with @option{--no-group} .
6867 @cindex disk allocation
6868 @cindex size of files, reporting
6869 Print the disk allocation of each file to the left of the file name.
6870 This is the amount of disk space used by the file, which is usually a
6871 bit more than the file's size, but it can be less if the file has holes.
6873 Normally the disk allocation is printed in units of
6874 1024 bytes, but this can be overridden (@pxref{Block size}).
6876 @cindex NFS mounts from BSD to HP-UX
6877 For files that are NFS-mounted from an HP-UX system to a BSD system,
6878 this option reports sizes that are half the correct values. On HP-UX
6879 systems, it reports sizes that are twice the correct values for files
6880 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6881 it also affects the HP-UX @command{ls} program.
6890 @cindex security context
6891 Display the SELinux security context or @samp{?} if none is found.
6892 When used with the @option{-l} option, print the security context
6893 to the left of the size column.
6898 @node Sorting the output
6899 @subsection Sorting the output
6901 @cindex sorting @command{ls} output
6902 These options change the order in which @command{ls} sorts the information
6903 it outputs. By default, sorting is done by character code
6904 (e.g., ASCII order).
6910 @itemx --time=status
6913 @opindex ctime@r{, printing or sorting by}
6914 @opindex status time@r{, printing or sorting by}
6915 @opindex use time@r{, printing or sorting files by}
6916 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6917 print the status change time (the @samp{ctime} in the inode) instead of
6918 the modification time.
6919 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6920 or when not using a long listing format,
6921 sort according to the status change time.
6925 @cindex unsorted directory listing
6926 @cindex directory order, listing by
6927 Primarily, like @option{-U}---do not sort; list the files in whatever
6928 order they are stored in the directory. But also enable @option{-a} (list
6929 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6930 were specified before the @option{-f}).
6936 @cindex reverse sorting
6937 Reverse whatever the sorting method is---e.g., list files in reverse
6938 alphabetical order, youngest first, smallest first, or whatever.
6944 @opindex size of files@r{, sorting files by}
6945 Sort by file size, largest first.
6951 @opindex modification time@r{, sorting files by}
6952 Sort by modification time (the @samp{mtime} in the inode), newest first.
6956 @itemx --time=access
6960 @opindex use time@r{, printing or sorting files by}
6961 @opindex atime@r{, printing or sorting files by}
6962 @opindex access time@r{, printing or sorting files by}
6963 If the long listing format (e.g., @option{--format=long}) is being used,
6964 print the last access time (the @samp{atime} in the inode).
6965 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6966 or when not using a long listing format, sort according to the access time.
6972 @opindex none@r{, sorting option for @command{ls}}
6973 Do not sort; list the files in whatever order they are
6974 stored in the directory. (Do not do any of the other unrelated things
6975 that @option{-f} does.) This is especially useful when listing very large
6976 directories, since not doing any sorting can be noticeably faster.
6979 @itemx --sort=version
6982 @opindex version@r{, sorting option for @command{ls}}
6983 Sort by version name and number, lowest first. It behaves like a default
6984 sort, except that each sequence of decimal digits is treated numerically
6985 as an index/version number. (@xref{Details about version sort}.)
6988 @itemx --sort=extension
6991 @opindex extension@r{, sorting files by}
6992 Sort directory contents alphabetically by file extension (characters
6993 after the last @samp{.}); files with no extension are sorted first.
6998 @node Details about version sort
6999 @subsection Details about version sort
7001 Version sorting handles the fact that file names frequently include indices or
7002 version numbers. Standard sorting usually does not produce the order that one
7003 expects because comparisons are made on a character-by-character basis.
7004 Version sorting is especially useful when browsing directories that contain
7005 many files with indices/version numbers in their names:
7009 abc.zml-1.gz abc.zml-1.gz
7010 abc.zml-12.gz abc.zml-2.gz
7011 abc.zml-2.gz abc.zml-12.gz
7014 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
7015 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
7016 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
7017 @var{ver1} < @var{ver2} implies that the name composed of
7018 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
7019 ``@var{prefix} @var{ver2} @var{suffix}''.
7021 Note also that leading zeros of numeric parts are ignored:
7025 abc-1.007.tgz abc-1.01a.tgz
7026 abc-1.012b.tgz abc-1.007.tgz
7027 abc-1.01a.tgz abc-1.012b.tgz
7030 This functionality is implemented using gnulib's @code{filevercmp} function,
7031 which has some caveats worth noting.
7034 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
7035 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
7036 was set to @samp{C}@.
7037 @item Some suffixes will not be matched by the regular
7038 expression mentioned above. Consequently these examples may
7039 not sort as you expect:
7047 abc-1.2.3.4.x86_64.rpm
7048 abc-1.2.3.x86_64.rpm
7052 @node General output formatting
7053 @subsection General output formatting
7055 These options affect the appearance of the overall output.
7060 @itemx --format=single-column
7063 @opindex single-column @r{output of files}
7064 List one file per line. This is the default for @command{ls} when standard
7065 output is not a terminal.
7068 @itemx --format=vertical
7071 @opindex vertical @r{sorted files in columns}
7072 List files in columns, sorted vertically. This is the default for
7073 @command{ls} if standard output is a terminal. It is always the default
7074 for the @command{dir} program.
7075 @sc{gnu} @command{ls} uses variable width columns to display as many files as
7076 possible in the fewest lines.
7078 @item --color [=@var{when}]
7080 @cindex color, distinguishing file types with
7081 Specify whether to use color for distinguishing file types. @var{when}
7082 may be omitted, or one of:
7085 @vindex none @r{color option}
7086 - Do not use color at all. This is the default.
7088 @vindex auto @r{color option}
7089 @cindex terminal, using color iff
7090 - Only use color if standard output is a terminal.
7092 @vindex always @r{color option}
7095 Specifying @option{--color} and no @var{when} is equivalent to
7096 @option{--color=always}.
7097 Piping a colorized listing through a pager like @command{more} or
7098 @command{less} usually produces unreadable results. However, using
7099 @code{more -f} does seem to work.
7102 @vindex SHELL @r{environment variable, and color}
7103 Note that using the @option{--color} option may incur a noticeable
7104 performance penalty when run in a directory with very many entries,
7105 because the default settings require that @command{ls} @code{stat} every
7106 single file it lists.
7107 However, if you would like most of the file-type coloring
7108 but can live without the other coloring options (e.g.,
7109 executable, orphan, sticky, other-writable, capability), use
7110 @command{dircolors} to set the @env{LS_COLORS} environment variable like this,
7112 eval $(dircolors -p | perl -pe \
7113 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
7115 and on a @code{dirent.d_type}-capable file system, @command{ls}
7116 will perform only one @code{stat} call per command line argument.
7120 @itemx --indicator-style=classify
7123 @opindex --indicator-style
7124 @cindex file type and executables, marking
7125 @cindex executables and file type, marking
7126 Append a character to each file name indicating the file type. Also,
7127 for regular files that are executable, append @samp{*}. The file type
7128 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
7129 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
7130 and nothing for regular files.
7131 @c The following sentence is the same as the one for -d.
7132 Do not follow symbolic links listed on the
7133 command line unless the @option{--dereference-command-line} (@option{-H}),
7134 @option{--dereference} (@option{-L}), or
7135 @option{--dereference-command-line-symlink-to-dir} options are specified.
7138 @itemx --indicator-style=file-type
7139 @opindex --file-type
7140 @opindex --indicator-style
7141 @cindex file type, marking
7142 Append a character to each file name indicating the file type. This is
7143 like @option{-F}, except that executables are not marked.
7145 @item --indicator-style=@var{word}
7146 @opindex --indicator-style
7147 Append a character indicator with style @var{word} to entry names,
7152 Do not append any character indicator; this is the default.
7154 Append @samp{/} for directories. This is the same as the @option{-p}
7157 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
7158 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
7159 the same as the @option{--file-type} option.
7161 Append @samp{*} for executable regular files, otherwise behave as for
7162 @samp{file-type}. This is the same as the @option{-F} or
7163 @option{--classify} option.
7169 @opindex --kibibytes
7170 Set the default block size to its normal value of 1024 bytes,
7171 overriding any contrary specification in environment variables
7172 (@pxref{Block size}). This option is in turn overridden by the
7173 @option{--block-size}, @option{-h} or @option{--human-readable}, and
7174 @option{--si} options.
7176 The @option{-k} or @option{--kibibytes} option affects the
7177 per-directory block count written by the @option{-l} and similar
7178 options, and the size written by the @option{-s} or @option{--size}
7179 option. It does not affect the file size written by @option{-l}.
7182 @itemx --format=commas
7185 @opindex commas@r{, outputting between files}
7186 List files horizontally, with as many as will fit on each line,
7187 separated by @samp{, } (a comma and a space).
7190 @itemx --indicator-style=slash
7192 @opindex --indicator-style
7193 @cindex file type, marking
7194 Append a @samp{/} to directory names.
7197 @itemx --format=across
7198 @itemx --format=horizontal
7201 @opindex across@r{, listing files}
7202 @opindex horizontal@r{, listing files}
7203 List the files in columns, sorted horizontally.
7206 @itemx --tabsize=@var{cols}
7209 Assume that each tab stop is @var{cols} columns wide. The default is 8.
7210 @command{ls} uses tabs where possible in the output, for efficiency. If
7211 @var{cols} is zero, do not use tabs at all.
7213 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
7214 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
7215 do not properly align columns to the right of a TAB following a
7216 non-ASCII byte. If you use such a terminal emulator, use the
7217 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
7218 @command{ls} to align using spaces, not tabs.
7221 @itemx --width=@var{cols}
7225 Assume the screen is @var{cols} columns wide. The default is taken
7226 from the terminal settings if possible; otherwise the environment
7227 variable @env{COLUMNS} is used if it is set; otherwise the default
7233 @node Formatting file timestamps
7234 @subsection Formatting file timestamps
7236 By default, file timestamps are listed in abbreviated form, using
7237 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
7238 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
7239 This format can change depending on the current locale as detailed below.
7242 A timestamp is considered to be @dfn{recent} if it is less than six
7243 months old, and is not dated in the future. If a timestamp dated
7244 today is not listed in recent form, the timestamp is in the future,
7245 which means you probably have clock skew problems which may break
7246 programs like @command{make} that rely on file timestamps.
7249 Time stamps are listed according to the time zone rules specified by
7250 the @env{TZ} environment variable, or by the system default rules if
7251 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
7252 with @env{TZ}, libc, The GNU C Library Reference Manual}.
7254 The following option changes how file timestamps are printed.
7257 @item --time-style=@var{style}
7258 @opindex --time-style
7260 List timestamps in style @var{style}. The @var{style} should
7261 be one of the following:
7266 List timestamps using @var{format}, where @var{format} is interpreted
7267 like the format argument of @command{date} (@pxref{date invocation}).
7268 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
7269 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
7270 with @command{date}, @var{format}'s interpretation is affected by the
7271 @env{LC_TIME} locale category.
7273 If @var{format} contains two format strings separated by a newline,
7274 the former is used for non-recent files and the latter for recent
7275 files; if you want output columns to line up, you may need to insert
7276 spaces in one of the two formats.
7279 List timestamps in full using ISO 8601 date, time, and time zone
7280 format with nanosecond precision, e.g., @samp{2002-03-30
7281 23:45:56.477817180 -0700}. This style is equivalent to
7282 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
7284 This is useful because the time output includes all the information that
7285 is available from the operating system. For example, this can help
7286 explain @command{make}'s behavior, since GNU @command{make}
7287 uses the full timestamp to determine whether a file is out of date.
7290 List ISO 8601 date and time in minutes, e.g.,
7291 @samp{2002-03-30 23:45}. These timestamps are shorter than
7292 @samp{full-iso} timestamps, and are usually good enough for everyday
7293 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7296 List ISO 8601 dates for non-recent timestamps (e.g.,
7297 @samp{2002-03-30@ }), and ISO 8601 month, day, hour, and
7298 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7299 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7300 nearly the same information in a smaller space and their brevity helps
7301 @command{ls} output fit within traditional 80-column output lines.
7302 The following two @command{ls} invocations are equivalent:
7307 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7308 ls -l --time-style="iso"
7313 List timestamps in a locale-dependent form. For example, a Finnish
7314 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7315 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7316 timestamps typically consume more space than @samp{iso} timestamps and
7317 are harder for programs to parse because locale conventions vary so
7318 widely, but they are easier for many people to read.
7320 The @env{LC_TIME} locale category specifies the timestamp format. The
7321 default POSIX locale uses timestamps like @samp{Mar 30@
7322 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7323 @command{ls} invocations are equivalent:
7328 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7329 ls -l --time-style="locale"
7332 Other locales behave differently. For example, in a German locale,
7333 @option{--time-style="locale"} might be equivalent to
7334 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7335 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7336 @samp{30. M@"ar 23:45}.
7338 @item posix-@var{style}
7340 List POSIX-locale timestamps if the @env{LC_TIME} locale
7341 category is POSIX, @var{style} timestamps otherwise. For
7342 example, the @samp{posix-long-iso} style lists
7343 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7344 the POSIX locale, and like @samp{2002-03-30 23:45} otherwise.
7349 You can specify the default value of the @option{--time-style} option
7350 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7351 the default style is @samp{locale}. GNU Emacs 21.3 and
7352 later use the @option{--dired} option and therefore can parse any date
7353 format, but if you are using Emacs 21.1 or 21.2 and specify a
7354 non-POSIX locale you may need to set
7355 @samp{TIME_STYLE="posix-long-iso"}.
7357 To avoid certain denial-of-service attacks, timestamps that would be
7358 longer than 1000 bytes may be treated as errors.
7361 @node Formatting the file names
7362 @subsection Formatting the file names
7364 These options change how file names themselves are printed.
7370 @itemx --quoting-style=escape
7373 @opindex --quoting-style
7374 @cindex backslash sequences for file names
7375 Quote nongraphic characters in file names using alphabetic and octal
7376 backslash sequences like those used in C.
7380 @itemx --quoting-style=literal
7383 @opindex --quoting-style
7384 Do not quote file names. However, with @command{ls} nongraphic
7385 characters are still printed as question marks if the output is a
7386 terminal and you do not specify the @option{--show-control-chars}
7390 @itemx --hide-control-chars
7392 @opindex --hide-control-chars
7393 Print question marks instead of nongraphic characters in file names.
7394 This is the default if the output is a terminal and the program is
7399 @itemx --quoting-style=c
7401 @opindex --quote-name
7402 @opindex --quoting-style
7403 Enclose file names in double quotes and quote nongraphic characters as
7406 @item --quoting-style=@var{word}
7407 @opindex --quoting-style
7408 @cindex quoting style
7409 Use style @var{word} to quote file names and other strings that may
7410 contain arbitrary characters. The @var{word} should
7411 be one of the following:
7415 Output strings as-is; this is the same as the @option{-N} or
7416 @option{--literal} option.
7418 Quote strings for the shell if they contain shell metacharacters or would
7419 cause ambiguous output.
7420 The quoting is suitable for POSIX-compatible shells like
7421 @command{bash}, but it does not always work for incompatible shells
7424 Quote strings for the shell, even if they would normally not require quoting.
7426 Quote strings as for C character string literals, including the
7427 surrounding double-quote characters; this is the same as the
7428 @option{-Q} or @option{--quote-name} option.
7430 Quote strings as for C character string literals, except omit the
7431 surrounding double-quote
7432 characters; this is the same as the @option{-b} or @option{--escape} option.
7434 Quote strings as for C character string literals, except use
7435 surrounding quotation marks appropriate for the
7438 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7439 Quote strings as for C character string literals, except use
7440 surrounding quotation marks appropriate for the locale, and quote
7441 @t{'like this'} instead of @t{"like
7442 this"} in the default C locale. This looks nicer on many displays.
7445 You can specify the default value of the @option{--quoting-style} option
7446 with the environment variable @env{QUOTING_STYLE}@. If that environment
7447 variable is not set, the default value is @samp{literal}, but this
7448 default may change to @samp{shell} in a future version of this package.
7450 @item --show-control-chars
7451 @opindex --show-control-chars
7452 Print nongraphic characters as-is in file names.
7453 This is the default unless the output is a terminal and the program is
7459 @node dir invocation
7460 @section @command{dir}: Briefly list directory contents
7463 @cindex directory listing, brief
7465 @command{dir} is equivalent to @code{ls -C
7466 -b}; that is, by default files are listed in columns, sorted vertically,
7467 and special characters are represented by backslash escape sequences.
7469 @xref{ls invocation, @command{ls}}.
7472 @node vdir invocation
7473 @section @command{vdir}: Verbosely list directory contents
7476 @cindex directory listing, verbose
7478 @command{vdir} is equivalent to @code{ls -l
7479 -b}; that is, by default files are listed in long format and special
7480 characters are represented by backslash escape sequences.
7482 @node dircolors invocation
7483 @section @command{dircolors}: Color setup for @command{ls}
7487 @cindex setup for color
7489 @command{dircolors} outputs a sequence of shell commands to set up the
7490 terminal for color output from @command{ls} (and @command{dir}, etc.).
7494 eval "$(dircolors [@var{option}]@dots{} [@var{file}])"
7497 If @var{file} is specified, @command{dircolors} reads it to determine which
7498 colors to use for which file types and extensions. Otherwise, a
7499 precompiled database is used. For details on the format of these files,
7500 run @samp{dircolors --print-database}.
7502 To make @command{dircolors} read a @file{~/.dircolors} file if it
7503 exists, you can put the following lines in your @file{~/.bashrc} (or
7504 adapt them to your favorite shell):
7508 test -r $d && eval "$(dircolors $d)"
7512 @vindex SHELL @r{environment variable, and color}
7513 The output is a shell command to set the @env{LS_COLORS} environment
7514 variable. You can specify the shell syntax to use on the command line,
7515 or @command{dircolors} will guess it from the value of the @env{SHELL}
7516 environment variable.
7518 The program accepts the following options. Also see @ref{Common options}.
7523 @itemx --bourne-shell
7526 @opindex --bourne-shell
7527 @cindex Bourne shell syntax for color setup
7528 @cindex @command{sh} syntax for color setup
7529 Output Bourne shell commands. This is the default if the @env{SHELL}
7530 environment variable is set and does not end with @samp{csh} or
7539 @cindex C shell syntax for color setup
7540 @cindex @command{csh} syntax for color setup
7541 Output C shell commands. This is the default if @code{SHELL} ends with
7542 @command{csh} or @command{tcsh}.
7545 @itemx --print-database
7547 @opindex --print-database
7548 @cindex color database, printing
7549 @cindex database for color setup, printing
7550 @cindex printing color database
7551 Print the (compiled-in) default color configuration database. This
7552 output is itself a valid configuration file, and is fairly descriptive
7553 of the possibilities.
7560 @node Basic operations
7561 @chapter Basic operations
7563 @cindex manipulating files
7565 This chapter describes the commands for basic file manipulation:
7566 copying, moving (renaming), and deleting (removing).
7569 * cp invocation:: Copy files.
7570 * dd invocation:: Convert and copy a file.
7571 * install invocation:: Copy files and set attributes.
7572 * mv invocation:: Move (rename) files.
7573 * rm invocation:: Remove files or directories.
7574 * shred invocation:: Remove files more securely.
7579 @section @command{cp}: Copy files and directories
7582 @cindex copying files and directories
7583 @cindex files, copying
7584 @cindex directories, copying
7586 @command{cp} copies files (or, optionally, directories). The copy is
7587 completely independent of the original. You can either copy one file to
7588 another, or copy arbitrarily many files to a destination directory.
7592 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7593 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7594 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7599 If two file names are given, @command{cp} copies the first file to the
7603 If the @option{--target-directory} (@option{-t}) option is given, or
7604 failing that if the last file is a directory and the
7605 @option{--no-target-directory} (@option{-T}) option is not given,
7606 @command{cp} copies each @var{source} file to the specified directory,
7607 using the @var{source}s' names.
7610 Generally, files are written just as they are read. For exceptions,
7611 see the @option{--sparse} option below.
7613 By default, @command{cp} does not copy directories. However, the
7614 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7615 copy recursively by descending into source directories and copying files
7616 to corresponding destination directories.
7618 When copying from a symbolic link, @command{cp} normally follows the
7619 link only when not copying
7620 recursively. This default can be overridden with the
7621 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7622 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7623 @option{-H} options. If more than one of these options is specified,
7624 the last one silently overrides the others.
7626 When copying to a symbolic link, @command{cp} follows the
7627 link only when it refers to an existing regular file.
7628 However, when copying to a dangling symbolic link, @command{cp}
7629 refuses by default, and fails with a diagnostic, since the operation
7630 is inherently dangerous. This behavior is contrary to historical
7631 practice and to POSIX@.
7632 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7633 the target of a dangling destination symlink, in spite of the possible risk.
7634 Also, when an option like
7635 @option{--backup} or @option{--link} acts to rename or remove the
7636 destination before copying, @command{cp} renames or removes the
7637 symbolic link rather than the file it points to.
7639 By default, @command{cp} copies the contents of special files only
7640 when not copying recursively. This default can be overridden with the
7641 @option{--copy-contents} option.
7643 @cindex self-backups
7644 @cindex backups, making only
7645 @command{cp} generally refuses to copy a file onto itself, with the
7646 following exception: if @option{--force --backup} is specified with
7647 @var{source} and @var{dest} identical, and referring to a regular file,
7648 @command{cp} will make a backup file, either regular or numbered, as
7649 specified in the usual ways (@pxref{Backup options}). This is useful when
7650 you simply want to make a backup of an existing file before changing it.
7652 The program accepts the following options. Also see @ref{Common options}.
7659 Preserve as much as possible of the structure and attributes of the
7660 original files in the copy (but do not attempt to preserve internal
7661 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7662 directory in a different order).
7663 Try to preserve SELinux security context and extended attributes (xattr),
7664 but ignore any failure to do that and print no corresponding diagnostic.
7665 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7667 @item --attributes-only
7668 @opindex --attributes-only
7669 Copy only the specified attributes of the source file to the destination.
7670 If the destination already exists, do not alter its contents.
7671 See the @option{--preserve} option for controlling which attributes to copy.
7674 @itemx @w{@kbd{--backup}[=@var{method}]}
7677 @vindex VERSION_CONTROL
7678 @cindex backups, making
7679 @xref{Backup options}.
7680 Make a backup of each file that would otherwise be overwritten or removed.
7681 As a special case, @command{cp} makes a backup of @var{source} when the force
7682 and backup options are given and @var{source} and @var{dest} are the same
7683 name for an existing, regular file. One useful application of this
7684 combination of options is this tiny Bourne shell script:
7688 # Usage: backup FILE...
7689 # Create a @sc{gnu}-style backup of each listed FILE.
7692 cp --backup --force --preserve=all -- "$i" "$i" || fail=1
7697 @item --copy-contents
7698 @cindex directories, copying recursively
7699 @cindex copying directories recursively
7700 @cindex recursively copying directories
7701 @cindex non-directories, copying as special files
7702 If copying recursively, copy the contents of any special files (e.g.,
7703 FIFOs and device files) as if they were regular files. This means
7704 trying to read the data in each source file and writing it to the
7705 destination. It is usually a mistake to use this option, as it
7706 normally has undesirable effects on special files like FIFOs and the
7707 ones typically found in the @file{/dev} directory. In most cases,
7708 @code{cp -R --copy-contents} will hang indefinitely trying to read
7709 from FIFOs and special files like @file{/dev/console}, and it will
7710 fill up your destination disk if you use it to copy @file{/dev/zero}.
7711 This option has no effect unless copying recursively, and it does not
7712 affect the copying of symbolic links.
7716 @cindex symbolic links, copying
7717 @cindex hard links, preserving
7718 Copy symbolic links as symbolic links rather than copying the files that
7719 they point to, and preserve hard links between source files in the copies.
7720 Equivalent to @option{--no-dereference --preserve=links}.
7726 When copying without this option and an existing destination file cannot
7727 be opened for writing, the copy fails. However, with @option{--force},
7728 when a destination file cannot be opened, @command{cp} then removes it and
7729 tries to open it again. Contrast this behavior with that enabled by
7730 @option{--link} and @option{--symbolic-link}, whereby the destination file
7731 is never opened but rather is removed unconditionally. Also see the
7732 description of @option{--remove-destination}.
7734 This option is independent of the @option{--interactive} or
7735 @option{-i} option: neither cancels the effect of the other.
7737 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7742 If a command line argument specifies a symbolic link, then copy the
7743 file it points to rather than the symbolic link itself. However,
7744 copy (preserving its nature) any symbolic link that is encountered
7745 via recursive traversal.
7748 @itemx --interactive
7750 @opindex --interactive
7751 When copying a file other than a directory, prompt whether to
7752 overwrite an existing destination file. The @option{-i} option overrides
7753 a previous @option{-n} option.
7759 Make hard links instead of copies of non-directories.
7762 @itemx --dereference
7764 @opindex --dereference
7765 Follow symbolic links when copying from them.
7766 With this option, @command{cp} cannot create a symbolic link.
7767 For example, a symlink (to regular file) in the source tree will be copied to
7768 a regular file in the destination tree.
7773 @opindex --no-clobber
7774 Do not overwrite an existing file. The @option{-n} option overrides a previous
7775 @option{-i} option. This option is mutually exclusive with @option{-b} or
7776 @option{--backup} option.
7779 @itemx --no-dereference
7781 @opindex --no-dereference
7782 @cindex symbolic links, copying
7783 Copy symbolic links as symbolic links rather than copying the files that
7784 they point to. This option affects only symbolic links in the source;
7785 symbolic links in the destination are always followed if possible.
7788 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7791 @cindex file information, preserving, extended attributes, xattr
7792 Preserve the specified attributes of the original files.
7793 If specified, the @var{attribute_list} must be a comma-separated list
7794 of one or more of the following strings:
7798 Preserve the file mode bits and access control lists.
7800 Preserve the owner and group. On most modern systems,
7801 only users with appropriate privileges may change the owner of a file,
7803 may preserve the group ownership of a file only if they happen to be
7804 a member of the desired group.
7806 Preserve the times of last access and last modification, when possible.
7807 On older systems, it is not possible to preserve these attributes
7808 when the affected file is a symbolic link.
7809 However, many systems now provide the @code{utimensat} function,
7810 which makes it possible even for symbolic links.
7812 Preserve in the destination files
7813 any links between corresponding source files.
7814 Note that with @option{-L} or @option{-H}, this option can convert
7815 symbolic links to hard links. For example,
7817 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7822 Note the inputs: @file{b} is a symlink to regular file @file{a},
7823 yet the files in destination directory, @file{c/}, are hard-linked.
7824 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7825 tells @command{cp} to dereference command line arguments, it sees two files
7826 with the same inode number, and preserves the perceived hard link.
7828 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7830 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7836 Preserve SELinux security context of the file, or fail with full diagnostics.
7838 Preserve extended attributes of the file, or fail with full diagnostics.
7839 If @command{cp} is built without xattr support, ignore this option.
7840 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7841 they are preserved by this option as well.
7843 Preserve all file attributes.
7844 Equivalent to specifying all of the above, but with the difference
7845 that failure to preserve SELinux security context or extended attributes
7846 does not change @command{cp}'s exit status. In contrast to @option{-a},
7847 all but @samp{Operation not supported} warnings are output.
7850 Using @option{--preserve} with no @var{attribute_list} is equivalent
7851 to @option{--preserve=mode,ownership,timestamps}.
7853 In the absence of this option, each destination file is created with the
7854 mode bits of the corresponding source file, minus the bits set in the
7855 umask and minus the set-user-ID and set-group-ID bits.
7856 @xref{File permissions}.
7858 @item @w{@kbd{--no-preserve}=@var{attribute_list}}
7859 @cindex file information, preserving
7860 Do not preserve the specified attributes. The @var{attribute_list}
7861 has the same form as for @option{--preserve}.
7865 @cindex parent directories and @command{cp}
7866 Form the name of each destination file by appending to the target
7867 directory a slash and the specified name of the source file. The last
7868 argument given to @command{cp} must be the name of an existing directory.
7869 For example, the command:
7872 cp --parents a/b/c existing_dir
7876 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7877 any missing intermediate directories.
7884 @opindex --recursive
7885 @cindex directories, copying recursively
7886 @cindex copying directories recursively
7887 @cindex recursively copying directories
7888 @cindex non-directories, copying as special files
7889 Copy directories recursively. By default, do not follow symbolic
7890 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7891 @option{--dereference} (@option{-L}), @option{--no-dereference}
7892 (@option{-P}), and @option{-H} options. Special files are copied by
7893 creating a destination file of the same type as the source; see the
7894 @option{--copy-contents} option. It is not portable to use
7895 @option{-r} to copy symbolic links or special files. On some
7896 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7897 @option{-L} and @option{--copy-contents} for historical reasons.
7898 Also, it is not portable to use @option{-R} to copy symbolic links
7899 unless you also specify @option{-P}, as POSIX allows
7900 implementations that dereference symbolic links by default.
7902 @item --reflink[=@var{when}]
7903 @opindex --reflink[=@var{when}]
7906 @cindex copy on write
7907 Perform a lightweight, copy-on-write (COW) copy, if supported by the
7908 file system. Once it has succeeded, beware that the source and destination
7909 files share the same disk data blocks as long as they remain unmodified.
7910 Thus, if a disk I/O error affects data blocks of one of the files,
7911 the other suffers the same fate.
7913 The @var{when} value can be one of the following:
7917 The default behavior: if the copy-on-write operation is not supported
7918 then report the failure for each file and exit with a failure status.
7921 If the copy-on-write operation is not supported then fall back
7922 to the standard copy behaviour.
7925 This option is overridden by the @option{--link}, @option{--symbolic-link}
7926 and @option{--attributes-only} options, thus allowing it to be used
7927 to configure the default data copying behavior for @command{cp}.
7928 For example, with the following alias, @command{cp} will use the
7929 minimum amount of space supported by the file system.
7932 alias cp='cp --reflink=auto --sparse=always'
7935 @item --remove-destination
7936 @opindex --remove-destination
7937 Remove each existing destination file before attempting to open it
7938 (contrast with @option{-f} above).
7940 @item --sparse=@var{when}
7941 @opindex --sparse=@var{when}
7942 @cindex sparse files, copying
7943 @cindex holes, copying files with
7944 @findex read @r{system call, and holes}
7945 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7946 does not occupy any physical disk blocks; the @samp{read} system call
7947 reads these as zeros. This can both save considerable disk space and
7948 increase speed, since many binary files contain lots of consecutive zero
7949 bytes. By default, @command{cp} detects holes in input source files via a crude
7950 heuristic and makes the corresponding output file sparse as well.
7951 Only regular files may be sparse.
7953 The @var{when} value can be one of the following:
7957 The default behavior: if the input file is sparse, attempt to make
7958 the output file sparse, too. However, if an output file exists but
7959 refers to a non-regular file, then do not attempt to make it sparse.
7962 For each sufficiently long sequence of zero bytes in the input file,
7963 attempt to create a corresponding hole in the output file, even if the
7964 input file does not appear to be sparse.
7965 This is useful when the input file resides on a file system
7966 that does not support sparse files
7967 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7968 but the output file is on a type of file system that does support them.
7969 Holes may be created only in regular files, so if the destination file
7970 is of some other type, @command{cp} does not even try to make it sparse.
7973 Never make the output file sparse.
7974 This is useful in creating a file for use with the @command{mkswap} command,
7975 since such a file must not have any holes.
7978 @optStripTrailingSlashes
7981 @itemx --symbolic-link
7983 @opindex --symbolic-link
7984 @cindex symbolic links, copying with
7985 Make symbolic links instead of copies of non-directories. All source
7986 file names must be absolute (starting with @samp{/}) unless the
7987 destination files are in the current directory. This option merely
7988 results in an error message on systems that do not support symbolic links.
7994 @optNoTargetDirectory
8000 @cindex newer files, copying only
8001 Do not copy a non-directory that has an existing destination with the
8002 same or newer modification time. If time stamps are being preserved,
8003 the comparison is to the source time stamp truncated to the
8004 resolutions of the destination file system and of the system calls
8005 used to update time stamps; this avoids duplicate work if several
8006 @samp{cp -pu} commands are executed with the same source and destination.
8007 If @option{--preserve=links} is also specified (like with @samp{cp -au}
8008 for example), that will take precedence. Consequently, depending on the
8009 order that files are processed from the source, newer files in the destination
8010 may be replaced, to mirror hard links in the source.
8016 Print the name of each file before copying it.
8019 @itemx --one-file-system
8021 @opindex --one-file-system
8022 @cindex file systems, omitting copying to different
8023 Skip subdirectories that are on different file systems from the one that
8024 the copy started on.
8025 However, mount point directories @emph{are} copied.
8033 @section @command{dd}: Convert and copy a file
8036 @cindex converting while copying a file
8038 @command{dd} copies a file (from standard input to standard output, by
8039 default) with a changeable I/O block size, while optionally performing
8040 conversions on it. Synopses:
8043 dd [@var{operand}]@dots{}
8047 The only options are @option{--help} and @option{--version}.
8048 @xref{Common options}. @command{dd} accepts the following operands.
8054 Read from @var{file} instead of standard input.
8058 Write to @var{file} instead of standard output. Unless
8059 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
8060 bytes (or the size specified with @samp{seek=}).
8062 @item ibs=@var{bytes}
8064 @cindex block size of input
8065 @cindex input block size
8066 Set the input block size to @var{bytes}.
8067 This makes @command{dd} read @var{bytes} per block.
8068 The default is 512 bytes.
8070 @item obs=@var{bytes}
8072 @cindex block size of output
8073 @cindex output block size
8074 Set the output block size to @var{bytes}.
8075 This makes @command{dd} write @var{bytes} per block.
8076 The default is 512 bytes.
8078 @item bs=@var{bytes}
8081 Set both input and output block sizes to @var{bytes}.
8082 This makes @command{dd} read and write @var{bytes} per block,
8083 overriding any @samp{ibs} and @samp{obs} settings.
8084 In addition, if no data-transforming @option{conv} option is specified,
8085 input is copied to the output as soon as it's read,
8086 even if it is smaller than the block size.
8088 @item cbs=@var{bytes}
8090 @cindex block size of conversion
8091 @cindex conversion block size
8092 @cindex fixed-length records, converting to variable-length
8093 @cindex variable-length records, converting to fixed-length
8094 Set the conversion block size to @var{bytes}.
8095 When converting variable-length records to fixed-length ones
8096 (@option{conv=block}) or the reverse (@option{conv=unblock}),
8097 use @var{bytes} as the fixed record length.
8101 Skip @var{n} @samp{ibs}-byte blocks in the input file before copying.
8102 If @samp{iflag=skip_bytes} is specified, @var{n} is interpreted
8103 as a byte count rather than a block count.
8107 Skip @var{n} @samp{obs}-byte blocks in the output file before copying.
8108 if @samp{oflag=seek_bytes} is specified, @var{n} is interpreted
8109 as a byte count rather than a block count.
8113 Copy @var{n} @samp{ibs}-byte blocks from the input file, instead
8114 of everything until the end of the file.
8115 if @samp{iflag=count_bytes} is specified, @var{n} is interpreted
8116 as a byte count rather than a block count.
8118 @item status=@var{which}
8120 Transfer information is normally output to stderr upon
8121 receipt of the @samp{INFO} signal or when @command{dd} exits.
8122 Specifying @var{which} will identify which information to suppress.
8127 @opindex noxfer @r{dd status=}
8128 Do not print the transfer rate and volume statistics
8129 that normally make up the last status line.
8132 @opindex none @r{dd status=}
8133 Do not print any informational messages to stderr.
8134 Error messages are output as normal.
8138 @item conv=@var{conversion}[,@var{conversion}]@dots{}
8140 Convert the file as specified by the @var{conversion} argument(s).
8141 (No spaces around any comma(s).)
8148 @opindex ascii@r{, converting to}
8149 Convert EBCDIC to ASCII,
8150 using the conversion table specified by POSIX@.
8151 This provides a 1:1 translation for all 256 bytes.
8154 @opindex ebcdic@r{, converting to}
8155 Convert ASCII to EBCDIC@.
8156 This is the inverse of the @samp{ascii} conversion.
8159 @opindex alternate ebcdic@r{, converting to}
8160 Convert ASCII to alternate EBCDIC,
8161 using the alternate conversion table specified by POSIX@.
8162 This is not a 1:1 translation, but reflects common historical practice
8163 for @samp{~}, @samp{[}, and @samp{]}.
8165 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
8169 @opindex block @r{(space-padding)}
8170 For each line in the input, output @samp{cbs} bytes, replacing the
8171 input newline with a space and padding with spaces as necessary.
8175 Remove any trailing spaces in each @samp{cbs}-sized input block,
8176 and append a newline.
8178 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
8181 @opindex lcase@r{, converting to}
8182 Change uppercase letters to lowercase.
8185 @opindex ucase@r{, converting to}
8186 Change lowercase letters to uppercase.
8188 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
8192 Try to seek rather than write @sc{nul} output blocks.
8193 On a file system that supports sparse files, this will create
8194 sparse output when extending the output file.
8195 Be careful when using this option in conjunction with
8196 @samp{conv=notrunc} or @samp{oflag=append}.
8197 With @samp{conv=notrunc}, existing data in the output file
8198 corresponding to @sc{nul} blocks from the input, will be untouched.
8199 With @samp{oflag=append} the seeks performed will be ineffective.
8200 Similarly, when the output is a device rather than a file,
8201 @sc{nul} input blocks are not copied, and therefore this option
8202 is most useful with virtual or pre zeroed devices.
8205 @opindex swab @r{(byte-swapping)}
8206 @cindex byte-swapping
8207 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
8208 when an odd number of bytes are read---the last byte is simply copied
8209 (since there is nothing to swap it with).
8212 @opindex sync @r{(padding with ASCII @sc{nul}s)}
8213 Pad every input block to size of @samp{ibs} with trailing zero bytes.
8214 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
8219 The following ``conversions'' are really file flags
8220 and don't affect internal processing:
8225 @cindex creating output file, requiring
8226 Fail if the output file already exists; @command{dd} must create the
8231 @cindex creating output file, avoiding
8232 Do not create the output file; the output file must already exist.
8234 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
8238 @cindex truncating output file, avoiding
8239 Do not truncate the output file.
8243 @cindex read errors, ignoring
8244 Continue after read errors.
8248 @cindex synchronized data writes, before finishing
8249 Synchronize output data just before finishing. This forces a physical
8250 write of output data.
8254 @cindex synchronized data and metadata writes, before finishing
8255 Synchronize output data and metadata just before finishing. This
8256 forces a physical write of output data and metadata.
8260 @item iflag=@var{flag}[,@var{flag}]@dots{}
8262 Access the input file using the flags specified by the @var{flag}
8263 argument(s). (No spaces around any comma(s).)
8265 @item oflag=@var{flag}[,@var{flag}]@dots{}
8267 Access the output file using the flags specified by the @var{flag}
8268 argument(s). (No spaces around any comma(s).)
8270 Here are the flags. Not every flag is supported on every operating
8277 @cindex appending to the output file
8278 Write in append mode, so that even if some other process is writing to
8279 this file, every @command{dd} write will append to the current
8280 contents of the file. This flag makes sense only for output.
8281 If you combine this flag with the @samp{of=@var{file}} operand,
8282 you should also specify @samp{conv=notrunc} unless you want the
8283 output file to be truncated before being appended to.
8287 @cindex concurrent I/O
8288 Use concurrent I/O mode for data. This mode performs direct I/O
8289 and drops the POSIX requirement to serialize all I/O to the same file.
8290 A file cannot be opened in CIO mode and with a standard open at the
8296 Use direct I/O for data, avoiding the buffer cache.
8297 Note that the kernel may impose restrictions on read or write buffer sizes.
8298 For example, with an ext4 destination file system and a linux-based kernel,
8299 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
8300 output buffer size is not a multiple of 512.
8304 @cindex directory I/O
8306 Fail unless the file is a directory. Most operating systems do not
8307 allow I/O to a directory, so this flag has limited utility.
8311 @cindex synchronized data reads
8312 Use synchronized I/O for data. For the output file, this forces a
8313 physical write of output data on each write. For the input file,
8314 this flag can matter when reading from a remote file that has been
8315 written to synchronously by some other process. Metadata (e.g.,
8316 last-access and last-modified time) is not necessarily synchronized.
8320 @cindex synchronized data and metadata I/O
8321 Use synchronized I/O for both data and metadata.
8325 @cindex discarding file cache
8326 Discard the data cache for a file.
8327 When count=0 all cache is discarded,
8328 otherwise the cache is dropped for the processed
8329 portion of the file. Also when count=0
8330 failure to discard the cache is diagnosed
8331 and reflected in the exit status.
8332 Here as some usage examples:
8335 # Advise to drop cache for whole file
8336 dd if=ifile iflag=nocache count=0
8338 # Ensure drop cache for the whole file
8339 dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
8341 # Drop cache for part of file
8342 dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
8344 # Stream data using just the read-ahead cache
8345 dd if=ifile of=ofile iflag=nocache oflag=nocache
8350 @cindex nonblocking I/O
8351 Use non-blocking I/O.
8356 Do not update the file's access time.
8357 Some older file systems silently ignore this flag, so it is a good
8358 idea to test it on your files before relying on it.
8362 @cindex controlling terminal
8363 Do not assign the file to be a controlling terminal for @command{dd}.
8364 This has no effect when the file is not a terminal.
8365 On many hosts (e.g., GNU/Linux hosts), this option has no effect
8370 @cindex symbolic links, following
8371 Do not follow symbolic links.
8376 Fail if the file has multiple hard links.
8381 Use binary I/O@. This option has an effect only on nonstandard
8382 platforms that distinguish binary from text I/O.
8387 Use text I/O@. Like @samp{binary}, this option has no effect on
8392 Accumulate full blocks from input. The @code{read} system call
8393 may return early if a full block is not available.
8394 When that happens, continue calling @code{read} to fill the remainder
8396 This flag can be used only with @code{iflag}.
8399 @opindex count_bytes
8400 Interpret the @samp{count=} operand as a byte count,
8401 rather than a block count, which allows specifying
8402 a length that is not a multiple of the I/O block size.
8403 This flag can be used only with @code{iflag}.
8407 Interpret the @samp{skip=} operand as a byte count,
8408 rather than a block count, which allows specifying
8409 an offset that is not a multiple of the I/O block size.
8410 This flag can be used only with @code{iflag}.
8414 Interpret the @samp{seek=} operand as a byte count,
8415 rather than a block count, which allows specifying
8416 an offset that is not a multiple of the I/O block size.
8417 This flag can be used only with @code{oflag}.
8421 These flags are not supported on all systems, and @samp{dd} rejects
8422 attempts to use them when they are not supported. When reading from
8423 standard input or writing to standard output, the @samp{nofollow} and
8424 @samp{noctty} flags should not be specified, and the other flags
8425 (e.g., @samp{nonblock}) can affect how other processes behave with the
8426 affected file descriptors, even after @command{dd} exits.
8430 @cindex multipliers after numbers
8431 The numeric-valued strings above (@var{n} and @var{bytes})
8432 can be followed by a multiplier: @samp{b}=512, @samp{c}=1,
8433 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8434 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8436 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8437 should not be too large---values larger than a few megabytes
8438 are generally wasteful or (as in the gigabyte..exabyte case) downright
8439 counterproductive or error-inducing.
8441 To process data that is at an offset or size that is not a
8442 multiple of the I/O@ block size, you can use the @samp{skip_bytes},
8443 @samp{seek_bytes} and @samp{count_bytes} flags. Alternatively
8444 the traditional method of separate @command{dd} invocations can be used.
8445 For example, the following shell commands copy data
8446 in 512 KiB blocks between a disk and a tape, but do not save
8447 or restore a 4 KiB label at the start of the disk:
8450 disk=/dev/rdsk/c0t1d0s2
8453 # Copy all but the label from disk to tape.
8454 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8456 # Copy from tape back to disk, but leave the disk label alone.
8457 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8460 Sending an @samp{INFO} signal to a running @command{dd}
8461 process makes it print I/O statistics to standard error
8462 and then resume copying. In the example below,
8463 @command{dd} is run in the background to copy 10 million blocks.
8464 The @command{kill} command makes it output intermediate I/O statistics,
8465 and when @command{dd} completes normally or is killed by the
8466 @code{SIGINT} signal, it outputs the final statistics.
8469 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8470 $ kill -s INFO $pid; wait $pid
8471 3385223+0 records in
8472 3385223+0 records out
8473 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8474 10000000+0 records in
8475 10000000+0 records out
8476 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8479 @vindex POSIXLY_CORRECT
8480 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8481 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8482 environment variable is set.
8487 @node install invocation
8488 @section @command{install}: Copy files and set attributes
8491 @cindex copying files and setting attributes
8493 @command{install} copies files while setting their file mode bits and, if
8494 possible, their owner and group. Synopses:
8497 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8498 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8499 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8500 install [@var{option}]@dots{} -d @var{directory}@dots{}
8505 If two file names are given, @command{install} copies the first file to the
8509 If the @option{--target-directory} (@option{-t}) option is given, or
8510 failing that if the last file is a directory and the
8511 @option{--no-target-directory} (@option{-T}) option is not given,
8512 @command{install} copies each @var{source} file to the specified
8513 directory, using the @var{source}s' names.
8516 If the @option{--directory} (@option{-d}) option is given,
8517 @command{install} creates each @var{directory} and any missing parent
8518 directories. Parent directories are created with mode
8519 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8520 current umask. @xref{Directory Setuid and Setgid}, for how the
8521 set-user-ID and set-group-ID bits of parent directories are inherited.
8524 @cindex Makefiles, installing programs in
8525 @command{install} is similar to @command{cp}, but allows you to control the
8526 attributes of destination files. It is typically used in Makefiles to
8527 copy programs into their destination directories. It refuses to copy
8528 files onto themselves.
8530 @cindex extended attributes, xattr
8531 @command{install} never preserves extended attributes (xattr).
8533 The program accepts the following options. Also see @ref{Common options}.
8543 Compare each pair of source and destination files, and if the destination has
8544 identical content and any specified owner, group, permissions, and possibly
8545 SELinux context, then do not modify the destination at all.
8549 Ignored; for compatibility with old Unix versions of @command{install}.
8553 Create any missing parent directories of @var{dest},
8554 then copy @var{source} to @var{dest}.
8555 This option is ignored if a destination directory is specified
8556 via @option{--target-directory=DIR}.
8561 @opindex --directory
8562 @cindex directories, creating with given attributes
8563 @cindex parent directories, creating missing
8564 @cindex leading directories, creating missing
8565 Create any missing parent directories, giving them the default
8566 attributes. Then create each given directory, setting their owner,
8567 group and mode as given on the command line or to the defaults.
8569 @item -g @var{group}
8570 @itemx --group=@var{group}
8573 @cindex group ownership of installed files, setting
8574 Set the group ownership of installed files or directories to
8575 @var{group}. The default is the process's current group. @var{group}
8576 may be either a group name or a numeric group ID.
8579 @itemx --mode=@var{mode}
8582 @cindex permissions of installed files, setting
8583 Set the file mode bits for the installed file or directory to @var{mode},
8584 which can be either an octal number, or a symbolic mode as in
8585 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8586 point of departure (@pxref{File permissions}).
8587 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8588 execute for the owner, read and execute for group and other, and with
8589 set-user-ID and set-group-ID disabled.
8590 This default is not quite the same as @samp{755}, since it disables
8591 instead of preserving set-user-ID and set-group-ID on directories.
8592 @xref{Directory Setuid and Setgid}.
8594 @item -o @var{owner}
8595 @itemx --owner=@var{owner}
8598 @cindex ownership of installed files, setting
8599 @cindex appropriate privileges
8600 @vindex root @r{as default owner}
8601 If @command{install} has appropriate privileges (is run as root), set the
8602 ownership of installed files or directories to @var{owner}. The default
8603 is @code{root}. @var{owner} may be either a user name or a numeric user
8606 @item --preserve-context
8607 @opindex --preserve-context
8609 @cindex security context
8610 Preserve the SELinux security context of files and directories.
8611 Failure to preserve the context in all of the files or directories
8612 will result in an exit status of 1. If SELinux is disabled then
8613 print a warning and ignore the option.
8616 @itemx --preserve-timestamps
8618 @opindex --preserve-timestamps
8619 @cindex timestamps of installed files, preserving
8620 Set the time of last access and the time of last modification of each
8621 installed file to match those of each corresponding original file.
8622 When a file is installed without this option, its last access and
8623 last modification times are both set to the time of installation.
8624 This option is useful if you want to use the last modification times
8625 of installed files to keep track of when they were last built as opposed
8626 to when they were last installed.
8632 @cindex symbol table information, stripping
8633 @cindex stripping symbol table information
8634 Strip the symbol tables from installed binary executables.
8636 @item --strip-program=@var{program}
8637 @opindex --strip-program
8638 @cindex symbol table information, stripping, program
8639 Program used to strip binaries.
8645 @optNoTargetDirectory
8651 Print the name of each file before copying it.
8653 @item -Z @var{context}
8654 @itemx --context=@var{context}
8658 @cindex security context
8659 Set the default SELinux security context to be used for any
8660 created files and directories. If SELinux is disabled then
8661 print a warning and ignore the option.
8669 @section @command{mv}: Move (rename) files
8673 @command{mv} moves or renames files (or directories). Synopses:
8676 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8677 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8678 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8683 If two file names are given, @command{mv} moves the first file to the
8687 If the @option{--target-directory} (@option{-t}) option is given, or
8688 failing that if the last file is a directory and the
8689 @option{--no-target-directory} (@option{-T}) option is not given,
8690 @command{mv} moves each @var{source} file to the specified
8691 directory, using the @var{source}s' names.
8694 @command{mv} can move any type of file from one file system to another.
8695 Prior to version @code{4.0} of the fileutils,
8696 @command{mv} could move only regular files between file systems.
8697 For example, now @command{mv} can move an entire directory hierarchy
8698 including special device files from one partition to another. It first
8699 uses some of the same code that's used by @code{cp -a} to copy the
8700 requested directories and files, then (assuming the copy succeeded)
8701 it removes the originals. If the copy fails, then the part that was
8702 copied to the destination partition is removed. If you were to copy
8703 three directories from one partition to another and the copy of the first
8704 directory succeeded, but the second didn't, the first would be left on
8705 the destination partition and the second and third would be left on the
8708 @cindex extended attributes, xattr
8709 @command{mv} always tries to copy extended attributes (xattr), which may
8710 include SELinux context, ACLs or Capabilities.
8711 Upon failure all but @samp{Operation not supported} warnings are output.
8713 @cindex prompting, and @command{mv}
8714 If a destination file exists but is normally unwritable, standard input
8715 is a terminal, and the @option{-f} or @option{--force} option is not given,
8716 @command{mv} prompts the user for whether to replace the file. (You might
8717 own the file, or have write permission on its directory.) If the
8718 response is not affirmative, the file is skipped.
8720 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8721 when it might be a symlink to a directory.
8722 Otherwise, @command{mv} may do something very surprising, since
8723 its behavior depends on the underlying rename system call.
8724 On a system with a modern Linux-based kernel, it fails with
8725 @code{errno=ENOTDIR}@.
8726 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8727 renames not the symlink but rather the directory referenced by the symlink.
8728 @xref{Trailing slashes}.
8730 The program accepts the following options. Also see @ref{Common options}.
8740 @cindex prompts, omitting
8741 Do not prompt the user before removing a destination file.
8743 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8744 options, only the final one takes effect.
8749 @itemx --interactive
8751 @opindex --interactive
8752 @cindex prompts, forcing
8753 Prompt whether to overwrite each existing destination file, regardless
8755 If the response is not affirmative, the file is skipped.
8761 @opindex --no-clobber
8762 @cindex prompts, omitting
8763 Do not overwrite an existing file.
8765 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8771 @cindex newer files, moving only
8772 Do not move a non-directory that has an existing destination with the
8773 same or newer modification time.
8774 If the move is across file system boundaries, the comparison is to the
8775 source time stamp truncated to the resolutions of the destination file
8776 system and of the system calls used to update time stamps; this avoids
8777 duplicate work if several @samp{mv -u} commands are executed with the
8778 same source and destination.
8784 Print the name of each file before moving it.
8786 @optStripTrailingSlashes
8792 @optNoTargetDirectory
8800 @section @command{rm}: Remove files or directories
8803 @cindex removing files or directories
8805 @command{rm} removes each given @var{file}. By default, it does not remove
8806 directories. Synopsis:
8809 rm [@var{option}]@dots{} [@var{file}]@dots{}
8812 @cindex prompting, and @command{rm}
8813 If the @option{-I} or @option{--interactive=once} option is given,
8814 and there are more than three files or the @option{-r}, @option{-R},
8815 or @option{--recursive} are given, then @command{rm} prompts the user
8816 for whether to proceed with the entire operation. If the response is
8817 not affirmative, the entire command is aborted.
8819 Otherwise, if a file is unwritable, standard input is a terminal, and
8820 the @option{-f} or @option{--force} option is not given, or the
8821 @option{-i} or @option{--interactive=always} option @emph{is} given,
8822 @command{rm} prompts the user for whether to remove the file.
8823 If the response is not affirmative, the file is skipped.
8825 Any attempt to remove a file whose last file name component is
8826 @file{.} or @file{..} is rejected without any prompting.
8828 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8829 possible to recover the contents of that file. If you want more assurance
8830 that the contents are truly unrecoverable, consider using @command{shred}.
8832 The program accepts the following options. Also see @ref{Common options}.
8840 @cindex directories, removing
8841 Remove the listed directories if they are empty.
8847 Ignore nonexistent files and missing operands, and never prompt the user.
8848 Ignore any previous @option{--interactive} (@option{-i}) option.
8852 Prompt whether to remove each file.
8853 If the response is not affirmative, the file is skipped.
8854 Ignore any previous @option{--force} (@option{-f}) option.
8855 Equivalent to @option{--interactive=always}.
8859 Prompt once whether to proceed with the command, if more than three
8860 files are named or if a recursive removal is requested. Ignore any
8861 previous @option{--force} (@option{-f}) option. Equivalent to
8862 @option{--interactive=once}.
8864 @item --interactive [=@var{when}]
8865 @opindex --interactive
8866 Specify when to issue an interactive prompt. @var{when} may be
8870 @vindex never @r{interactive option}
8871 - Do not prompt at all.
8873 @vindex once @r{interactive option}
8874 - Prompt once if more than three files are named or if a recursive
8875 removal is requested. Equivalent to @option{-I}.
8877 @vindex always @r{interactive option}
8878 - Prompt for every file being removed. Equivalent to @option{-i}.
8880 @option{--interactive} with no @var{when} is equivalent to
8881 @option{--interactive=always}.
8883 @item --one-file-system
8884 @opindex --one-file-system
8885 @cindex one file system, restricting @command{rm} to
8886 When removing a hierarchy recursively, skip any directory that is on a
8887 file system different from that of the corresponding command line argument.
8890 This option is useful when removing a build ``chroot'' hierarchy,
8891 which normally contains no valuable data. However, it is not uncommon
8892 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8893 use one's start-up file. The catch is that it's easy to forget to
8894 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8895 your normally throw-away chroot, that command will remove everything
8896 under @file{/home}, too.
8897 Use the @option{--one-file-system} option, and it will
8898 warn about and skip directories on other file systems.
8899 Of course, this will not save your @file{/home} if it and your
8900 chroot happen to be on the same file system.
8902 @item --preserve-root
8903 @opindex --preserve-root
8904 @cindex root directory, disallow recursive destruction
8905 Fail upon any attempt to remove the root directory, @file{/},
8906 when used with the @option{--recursive} option.
8907 This is the default behavior.
8908 @xref{Treating / specially}.
8910 @item --no-preserve-root
8911 @opindex --no-preserve-root
8912 @cindex root directory, allow recursive destruction
8913 Do not treat @file{/} specially when removing recursively.
8914 This option is not recommended unless you really want to
8915 remove all the files on your computer.
8916 @xref{Treating / specially}.
8923 @opindex --recursive
8924 @cindex directories, removing (recursively)
8925 Remove the listed directories and their contents recursively.
8931 Print the name of each file before removing it.
8935 @cindex files beginning with @samp{-}, removing
8936 @cindex @samp{-}, removing files beginning with
8937 One common question is how to remove files whose names begin with a
8938 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8939 function to parse its arguments, lets you use the @samp{--} option to
8940 indicate that all following arguments are non-options. To remove a file
8941 called @file{-f} in the current directory, you could type either:
8954 @opindex - @r{and Unix @command{rm}}
8955 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8956 predates the development of the getopt standard syntax.
8961 @node shred invocation
8962 @section @command{shred}: Remove files more securely
8965 @cindex data, erasing
8966 @cindex erasing data
8968 @command{shred} overwrites devices or files, to help prevent even
8969 very expensive hardware from recovering the data.
8971 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8972 not actually destroyed. Only the index listing where the file is
8973 stored is destroyed, and the storage is made available for reuse.
8974 There are undelete utilities that will attempt to reconstruct the index
8975 and can bring the file back if the parts were not reused.
8977 On a busy system with a nearly-full drive, space can get reused in a few
8978 seconds. But there is no way to know for sure. If you have sensitive
8979 data, you may want to be sure that recovery is not possible by actually
8980 overwriting the file with non-sensitive data.
8982 However, even after doing that, it is possible to take the disk back
8983 to a laboratory and use a lot of sensitive (and expensive) equipment
8984 to look for the faint ``echoes'' of the original data underneath the
8985 overwritten data. If the data has only been overwritten once, it's not
8988 The best way to remove something irretrievably is to destroy the media
8989 it's on with acid, melt it down, or the like. For cheap removable media
8990 like floppy disks, this is the preferred method. However, hard drives
8991 are expensive and hard to melt, so the @command{shred} utility tries
8992 to achieve a similar effect non-destructively.
8994 This uses many overwrite passes, with the data patterns chosen to
8995 maximize the damage they do to the old data. While this will work on
8996 floppies, the patterns are designed for best effect on hard drives.
8997 For more details, see the source code and Peter Gutmann's paper
8998 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8999 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
9000 from the proceedings of the Sixth USENIX Security Symposium (San Jose,
9001 California, July 22--25, 1996).
9003 @strong{Please note} that @command{shred} relies on a very important assumption:
9004 that the file system overwrites data in place. This is the traditional
9005 way to do things, but many modern file system designs do not satisfy this
9006 assumption. Exceptions include:
9011 Log-structured or journaled file systems, such as those supplied with
9012 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
9013 BFS, NTFS, etc., when they are configured to journal @emph{data}.
9016 File systems that write redundant data and carry on even if some writes
9017 fail, such as RAID-based file systems.
9020 File systems that make snapshots, such as Network Appliance's NFS server.
9023 File systems that cache in temporary locations, such as NFS version 3
9027 Compressed file systems.
9030 In the particular case of ext3 file systems, the above disclaimer applies (and
9031 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
9032 mode, which journals file data in addition to just metadata. In both
9033 the @code{data=ordered} (default) and @code{data=writeback} modes,
9034 @command{shred} works as usual. Ext3 journaling modes can be changed
9035 by adding the @code{data=something} option to the mount options for a
9036 particular file system in the @file{/etc/fstab} file, as documented in
9037 the mount man page (man mount).
9039 If you are not sure how your file system operates, then you should assume
9040 that it does not overwrite data in place, which means that shred cannot
9041 reliably operate on regular files in your file system.
9043 Generally speaking, it is more reliable to shred a device than a file,
9044 since this bypasses the problem of file system design mentioned above.
9045 However, even shredding devices is not always completely reliable. For
9046 example, most disks map out bad sectors invisibly to the application; if
9047 the bad sectors contain sensitive data, @command{shred} won't be able to
9050 @command{shred} makes no attempt to detect or report this problem, just as
9051 it makes no attempt to do anything about backups. However, since it is
9052 more reliable to shred devices than files, @command{shred} by default does
9053 not truncate or remove the output file. This default is more suitable
9054 for devices, which typically cannot be truncated and should not be
9057 Finally, consider the risk of backups and mirrors.
9058 File system backups and remote mirrors may contain copies of the
9059 file that cannot be removed, and that will allow a shredded file
9060 to be recovered later. So if you keep any data you may later want
9061 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
9064 shred [@var{option}]@dots{} @var{file}[@dots{}]
9067 The program accepts the following options. Also see @ref{Common options}.
9075 @cindex force deletion
9076 Override file permissions if necessary to allow overwriting.
9079 @itemx -n @var{number}
9080 @itemx --iterations=@var{number}
9081 @opindex -n @var{number}
9082 @opindex --iterations=@var{number}
9083 @cindex iterations, selecting the number of
9084 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
9085 overwrite. You can reduce this to save time, or increase it if you think it's
9086 appropriate. After 25 passes all of the internal overwrite patterns will have
9087 been used at least once.
9089 @item --random-source=@var{file}
9090 @opindex --random-source
9091 @cindex random source for shredding
9092 Use @var{file} as a source of random data used to overwrite and to
9093 choose pass ordering. @xref{Random sources}.
9095 @item -s @var{bytes}
9096 @itemx --size=@var{bytes}
9097 @opindex -s @var{bytes}
9098 @opindex --size=@var{bytes}
9099 @cindex size of file to shred
9100 Shred the first @var{bytes} bytes of the file. The default is to shred
9101 the whole file. @var{bytes} can be followed by a size specification like
9102 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
9108 @cindex removing files after shredding
9109 After shredding a file, truncate it (if possible) and then remove it.
9110 If a file has multiple links, only the named links will be removed.
9116 Display to standard error all status updates as sterilization proceeds.
9122 By default, @command{shred} rounds the size of a regular file up to the next
9123 multiple of the file system block size to fully erase the last block
9125 Use @option{--exact} to suppress that behavior.
9126 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
9127 blocks, the resulting file will be 512 bytes long. With this option,
9128 shred does not increase the apparent size of the file.
9134 Normally, the last pass that @command{shred} writes is made up of
9135 random data. If this would be conspicuous on your hard drive (for
9136 example, because it looks like encrypted data), or you just think
9137 it's tidier, the @option{--zero} option adds an additional overwrite pass with
9138 all zero bits. This is in addition to the number of passes specified
9139 by the @option{--iterations} option.
9143 You might use the following command to erase all trace of the
9144 file system you'd created on the floppy disk in your first drive.
9145 That command takes about 20 minutes to erase a ``1.44MB'' (actually
9149 shred --verbose /dev/fd0
9152 Similarly, to erase all data on a selected partition of
9153 your hard disk, you could give a command like this:
9156 shred --verbose /dev/sda5
9159 On modern disks, a single pass should be adequate,
9160 and it will take one third the time of the default three-pass approach.
9163 # 1 pass, write pseudo-random data; 3x faster than the default
9164 shred --verbose -n1 /dev/sda5
9167 To be on the safe side, use at least one pass that overwrites using
9168 pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
9169 in case some disk controller optimizes the process of writing blocks
9170 of all zeros, and thereby does not clear all bytes in a block.
9171 Some SSDs may do just that.
9173 A @var{file} of @samp{-} denotes standard output.
9174 The intended use of this is to shred a removed temporary file.
9181 echo "Hello, world" >&3
9186 However, the command @samp{shred - >file} does not shred the contents
9187 of @var{file}, since the shell truncates @var{file} before invoking
9188 @command{shred}. Use the command @samp{shred file} or (if using a
9189 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
9194 @node Special file types
9195 @chapter Special file types
9197 @cindex special file types
9198 @cindex file types, special
9200 This chapter describes commands which create special types of files (and
9201 @command{rmdir}, which removes directories, one special file type).
9203 @cindex special file types
9205 Although Unix-like operating systems have markedly fewer special file
9206 types than others, not @emph{everything} can be treated only as the
9207 undifferentiated byte stream of @dfn{normal files}. For example, when a
9208 file is created or removed, the system must record this information,
9209 which it does in a @dfn{directory}---a special type of file. Although
9210 you can read directories as normal files, if you're curious, in order
9211 for the system to do its job it must impose a structure, a certain
9212 order, on the bytes of the file. Thus it is a ``special'' type of file.
9214 Besides directories, other special file types include named pipes
9215 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
9218 * link invocation:: Make a hard link via the link syscall
9219 * ln invocation:: Make links between files.
9220 * mkdir invocation:: Make directories.
9221 * mkfifo invocation:: Make FIFOs (named pipes).
9222 * mknod invocation:: Make block or character special files.
9223 * readlink invocation:: Print value of a symlink or canonical file name.
9224 * rmdir invocation:: Remove empty directories.
9225 * unlink invocation:: Remove files via the unlink syscall
9229 @node link invocation
9230 @section @command{link}: Make a hard link via the link syscall
9233 @cindex links, creating
9234 @cindex hard links, creating
9235 @cindex creating links (hard only)
9237 @command{link} creates a single hard link at a time.
9238 It is a minimalist interface to the system-provided
9239 @code{link} function. @xref{Hard Links, , , libc,
9240 The GNU C Library Reference Manual}.
9241 It avoids the bells and whistles of the more commonly-used
9242 @command{ln} command (@pxref{ln invocation}).
9246 link @var{filename} @var{linkname}
9249 @var{filename} must specify an existing file, and @var{linkname}
9250 must specify a nonexistent entry in an existing directory.
9251 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
9254 On a GNU system, this command acts like @samp{ln --directory
9255 --no-target-directory @var{filename} @var{linkname}}. However, the
9256 @option{--directory} and @option{--no-target-directory} options are
9257 not specified by POSIX, and the @command{link} command is
9258 more portable in practice.
9260 If @var{filename} is a symbolic link, it is unspecified whether
9261 @var{linkname} will be a hard link to the symbolic link or to the
9262 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
9263 to specify which behavior is desired.
9269 @section @command{ln}: Make links between files
9272 @cindex links, creating
9273 @cindex hard links, creating
9274 @cindex symbolic (soft) links, creating
9275 @cindex creating links (hard or soft)
9277 @cindex file systems and hard links
9278 @command{ln} makes links between files. By default, it makes hard links;
9279 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
9283 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
9284 ln [@var{option}]@dots{} @var{target}
9285 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
9286 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
9292 If two file names are given, @command{ln} creates a link to the first
9293 file from the second.
9296 If one @var{target} is given, @command{ln} creates a link to that file
9297 in the current directory.
9300 If the @option{--target-directory} (@option{-t}) option is given, or
9301 failing that if the last file is a directory and the
9302 @option{--no-target-directory} (@option{-T}) option is not given,
9303 @command{ln} creates a link to each @var{target} file in the specified
9304 directory, using the @var{target}s' names.
9308 Normally @command{ln} does not remove existing files. Use the
9309 @option{--force} (@option{-f}) option to remove them unconditionally,
9310 the @option{--interactive} (@option{-i}) option to remove them
9311 conditionally, and the @option{--backup} (@option{-b}) option to
9314 @cindex hard link, defined
9315 @cindex inode, and hard links
9316 A @dfn{hard link} is another name for an existing file; the link and the
9317 original are indistinguishable. Technically speaking, they share the
9318 same inode, and the inode contains all the information about a
9319 file---indeed, it is not incorrect to say that the inode @emph{is} the
9320 file. Most systems prohibit making a hard link to
9321 a directory; on those where it is allowed, only the super-user can do
9322 so (and with caution, since creating a cycle will cause problems to many
9323 other utilities). Hard links cannot cross file system boundaries. (These
9324 restrictions are not mandated by POSIX, however.)
9326 @cindex dereferencing symbolic links
9327 @cindex symbolic link, defined
9328 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
9329 a special file type (which not all kernels support: System V release 3
9330 (and older) systems lack symlinks) in which the link file actually
9331 refers to a different file, by name. When most operations (opening,
9332 reading, writing, and so on) are passed the symbolic link file, the
9333 kernel automatically @dfn{dereferences} the link and operates on the
9334 target of the link. But some operations (e.g., removing) work on the
9335 link file itself, rather than on its target. The owner and group of a
9336 symlink are not significant to file access performed through
9337 the link, but do have implications on deleting a symbolic link from a
9338 directory with the restricted deletion bit set. On the GNU system,
9339 the mode of a symlink has no significance and cannot be changed, but
9340 on some BSD systems, the mode can be changed and will affect whether
9341 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
9342 libc, The GNU C Library Reference Manual}.
9344 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
9345 occurs when the string in the symlink does not resolve to a file.
9346 There are no restrictions against creating dangling symbolic links.
9347 There are trade-offs to using absolute or relative symlinks. An
9348 absolute symlink always points to the same file, even if the directory
9349 containing the link is moved. However, if the symlink is visible from
9350 more than one machine (such as on a networked file system), the file
9351 pointed to might not always be the same. A relative symbolic link is
9352 resolved in relation to the directory that contains the link, and is
9353 often useful in referring to files on the same device without regards
9354 to what name that device is mounted on when accessed via networked
9357 When creating a relative symlink in a different location than the
9358 current directory, the resolution of the symlink will be different
9359 than the resolution of the same string from the current directory.
9360 Therefore, many users prefer to first change directories to the
9361 location where the relative symlink will be created, so that
9362 tab-completion or other file resolution will find the same target as
9363 what will be placed in the symlink.
9365 The program accepts the following options. Also see @ref{Common options}.
9376 @opindex --directory
9377 @cindex hard links to directories
9378 Allow users with appropriate privileges to attempt to make hard links
9380 However, note that this will probably fail due to
9381 system restrictions, even for the super-user.
9387 Remove existing destination files.
9390 @itemx --interactive
9392 @opindex --interactive
9393 @cindex prompting, and @command{ln}
9394 Prompt whether to remove existing destination files.
9400 If @option{-s} is not in effect, and the source file is a symbolic
9401 link, create the hard link to the file referred to by the symbolic
9402 link, rather than the symbolic link itself.
9405 @itemx --no-dereference
9407 @opindex --no-dereference
9408 Do not treat the last operand specially when it is a symbolic link to
9409 a directory. Instead, treat it as if it were a normal file.
9411 When the destination is an actual directory (not a symlink to one),
9412 there is no ambiguity. The link is created in that directory.
9413 But when the specified destination is a symlink to a directory,
9414 there are two ways to treat the user's request. @command{ln} can
9415 treat the destination just as it would a normal directory and create
9416 the link in it. On the other hand, the destination can be viewed as a
9417 non-directory---as the symlink itself. In that case, @command{ln}
9418 must delete or backup that symlink before creating the new link.
9419 The default is to treat a destination that is a symlink to a directory
9420 just like a directory.
9422 This option is weaker than the @option{--no-target-directory}
9423 (@option{-T}) option, so it has no effect if both options are given.
9429 If @option{-s} is not in effect, and the source file is a symbolic
9430 link, create the hard link to the symbolic link itself. On platforms
9431 where this is not supported by the kernel, this option creates a
9432 symbolic link with identical contents; since symbolic link contents
9433 cannot be edited, any file name resolution performed through either
9434 link will be the same as if a hard link had been created.
9440 Make symbolic links relative to the link location.
9445 ln -srv /a/file /tmp
9446 '/tmp/file' -> '../a/file'
9449 @xref{realpath invocation}, which gives greater control
9450 over relative file name generation.
9456 Make symbolic links instead of hard links. This option merely produces
9457 an error message on systems that do not support symbolic links.
9463 @optNoTargetDirectory
9469 Print the name of each file after linking it successfully.
9473 @cindex hard links to symbolic links
9474 @cindex symbolic links and @command{ln}
9475 If @option{-L} and @option{-P} are both given, the last one takes
9476 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9477 are silently ignored. If neither option is given, then this
9478 implementation defaults to @option{-P} if the system @code{link} supports
9479 hard links to symbolic links (such as the GNU system), and @option{-L}
9480 if @code{link} follows symbolic links (such as on BSD).
9489 # Create link ../a pointing to a in that directory.
9490 # Not really useful because it points to itself.
9495 # Change to the target before creating symlinks to avoid being confused.
9501 # Hard coded file names don't move well.
9502 ln -s $(pwd)/a /some/dir/
9506 # Relative file names survive directory moves and also
9507 # work across networked file systems.
9508 ln -s afile anotherfile
9509 ln -s ../adir/afile yetanotherfile
9513 @node mkdir invocation
9514 @section @command{mkdir}: Make directories
9517 @cindex directories, creating
9518 @cindex creating directories
9520 @command{mkdir} creates directories with the specified names. Synopsis:
9523 mkdir [@var{option}]@dots{} @var{name}@dots{}
9526 @command{mkdir} creates each directory @var{name} in the order given.
9527 It reports an error if @var{name} already exists, unless the
9528 @option{-p} option is given and @var{name} is a directory.
9530 The program accepts the following options. Also see @ref{Common options}.
9535 @itemx --mode=@var{mode}
9538 @cindex modes of created directories, setting
9539 Set the file permission bits of created directories to @var{mode},
9540 which uses the same syntax as
9541 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9542 everyone) for the point of the departure. @xref{File permissions}.
9544 Normally the directory has the desired file mode bits at the moment it
9545 is created. As a GNU extension, @var{mode} may also mention
9546 special mode bits, but in this case there may be a temporary window
9547 during which the directory exists but its special mode bits are
9548 incorrect. @xref{Directory Setuid and Setgid}, for how the
9549 set-user-ID and set-group-ID bits of directories are inherited unless
9550 overridden in this way.
9556 @cindex parent directories, creating
9557 Make any missing parent directories for each argument, setting their
9558 file permission bits to the umask modified by @samp{u+wx}. Ignore
9559 existing parent directories, and do not change their file permission
9562 To set the file permission bits of any newly-created parent
9563 directories to a value that includes @samp{u+wx}, you can set the
9564 umask before invoking @command{mkdir}. For example, if the shell
9565 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9566 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9567 To set a parent's special mode bits as well, you can invoke
9568 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9569 Setgid}, for how the set-user-ID and set-group-ID bits of
9570 newly-created parent directories are inherited.
9576 Print a message for each created directory. This is most useful with
9579 @item -Z @var{context}
9580 @itemx --context=@var{context}
9584 @cindex security context
9585 Set the default SELinux security context to be used for created directories.
9592 @node mkfifo invocation
9593 @section @command{mkfifo}: Make FIFOs (named pipes)
9596 @cindex FIFOs, creating
9597 @cindex named pipes, creating
9598 @cindex creating FIFOs (named pipes)
9600 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9601 specified names. Synopsis:
9604 mkfifo [@var{option}] @var{name}@dots{}
9607 A @dfn{FIFO} is a special file type that permits independent processes
9608 to communicate. One process opens the FIFO file for writing, and
9609 another for reading, after which data can flow as with the usual
9610 anonymous pipe in shells or elsewhere.
9612 The program accepts the following option. Also see @ref{Common options}.
9617 @itemx --mode=@var{mode}
9620 @cindex modes of created FIFOs, setting
9621 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9622 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9623 for the point of departure. @var{mode} should specify only file
9624 permission bits. @xref{File permissions}.
9626 @item -Z @var{context}
9627 @itemx --context=@var{context}
9631 @cindex security context
9632 Set the default SELinux security context to be used for created FIFOs.
9639 @node mknod invocation
9640 @section @command{mknod}: Make block or character special files
9643 @cindex block special files, creating
9644 @cindex character special files, creating
9646 @command{mknod} creates a FIFO, character special file, or block special
9647 file with the specified name. Synopsis:
9650 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9653 @cindex special files
9654 @cindex block special files
9655 @cindex character special files
9656 Unlike the phrase ``special file type'' above, the term @dfn{special
9657 file} has a technical meaning on Unix: something that can generate or
9658 receive data. Usually this corresponds to a physical piece of hardware,
9659 e.g., a printer or a disk. (These files are typically created at
9660 system-configuration time.) The @command{mknod} command is what creates
9661 files of this type. Such devices can be read either a character at a
9662 time or a ``block'' (many characters) at a time, hence we say there are
9663 @dfn{block special} files and @dfn{character special} files.
9665 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9666 @mayConflictWithShellBuiltIn{mknod}
9668 The arguments after @var{name} specify the type of file to make:
9673 @opindex p @r{for FIFO file}
9677 @opindex b @r{for block special file}
9678 for a block special file
9681 @c Don't document the 'u' option -- it's just a synonym for 'c'.
9682 @c Do *any* versions of mknod still use it?
9684 @opindex c @r{for character special file}
9685 @c @opindex u @r{for character special file}
9686 for a character special file
9690 When making a block or character special file, the major and minor
9691 device numbers must be given after the file type.
9692 If a major or minor device number begins with @samp{0x} or @samp{0X},
9693 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9694 as octal; otherwise, as decimal.
9696 The program accepts the following option. Also see @ref{Common options}.
9701 @itemx --mode=@var{mode}
9704 Set the mode of created files to @var{mode}, which is symbolic as in
9705 @command{chmod} and uses @samp{a=rw} as the point of departure.
9706 @var{mode} should specify only file permission bits.
9707 @xref{File permissions}.
9709 @item -Z @var{context}
9710 @itemx --context=@var{context}
9714 @cindex security context
9715 Set the default SELinux security context to be used for created files.
9722 @node readlink invocation
9723 @section @command{readlink}: Print value of a symlink or canonical file name
9726 @cindex displaying value of a symbolic link
9727 @cindex canonical file name
9728 @cindex canonicalize a file name
9731 @command{readlink} may work in one of two supported modes:
9737 @command{readlink} outputs the value of the given symbolic link.
9738 If @command{readlink} is invoked with an argument other than the name
9739 of a symbolic link, it produces no output and exits with a nonzero exit code.
9741 @item Canonicalize mode
9743 @command{readlink} outputs the absolute name of the given file which contains
9744 no @file{.}, @file{..} components nor any repeated separators
9745 (@file{/}) or symbolic links.
9750 readlink [@var{option}] @var{file}
9753 By default, @command{readlink} operates in readlink mode.
9755 The program accepts the following options. Also see @ref{Common options}.
9760 @itemx --canonicalize
9762 @opindex --canonicalize
9763 Activate canonicalize mode.
9764 If any component of the file name except the last one is missing or unavailable,
9765 @command{readlink} produces no output and exits with a nonzero exit
9766 code. A trailing slash is ignored.
9769 @itemx --canonicalize-existing
9771 @opindex --canonicalize-existing
9772 Activate canonicalize mode.
9773 If any component is missing or unavailable, @command{readlink} produces
9774 no output and exits with a nonzero exit code. A trailing slash
9775 requires that the name resolve to a directory.
9778 @itemx --canonicalize-missing
9780 @opindex --canonicalize-missing
9781 Activate canonicalize mode.
9782 If any component is missing or unavailable, @command{readlink} treats it
9788 @opindex --no-newline
9789 Do not output the trailing newline.
9799 Suppress most error messages.
9805 Report error messages.
9809 The @command{readlink} utility first appeared in OpenBSD 2.1.
9811 The @command{realpath} command without options, operates like
9812 @command{readlink} in canonicalize mode.
9817 @node rmdir invocation
9818 @section @command{rmdir}: Remove empty directories
9821 @cindex removing empty directories
9822 @cindex directories, removing empty
9824 @command{rmdir} removes empty directories. Synopsis:
9827 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9830 If any @var{directory} argument does not refer to an existing empty
9831 directory, it is an error.
9833 The program accepts the following options. Also see @ref{Common options}.
9837 @item --ignore-fail-on-non-empty
9838 @opindex --ignore-fail-on-non-empty
9839 @cindex directory deletion, ignoring failures
9840 Ignore each failure to remove a directory that is solely because
9841 the directory is non-empty.
9847 @cindex parent directories, removing
9848 Remove @var{directory}, then try to remove each component of @var{directory}.
9849 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9850 As such, it fails if any of those directories turns out not to be empty.
9851 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9852 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9853 exit unsuccessfully.
9859 @cindex directory deletion, reporting
9860 Give a diagnostic for each successful removal.
9861 @var{directory} is removed.
9865 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9870 @node unlink invocation
9871 @section @command{unlink}: Remove files via the unlink syscall
9874 @cindex removing files or directories (via the unlink syscall)
9876 @command{unlink} deletes a single specified file name.
9877 It is a minimalist interface to the system-provided
9878 @code{unlink} function. @xref{Deleting Files, , , libc,
9879 The GNU C Library Reference Manual}. Synopsis:
9880 It avoids the bells and whistles of the more commonly-used
9881 @command{rm} command (@pxref{rm invocation}).
9884 unlink @var{filename}
9887 On some systems @code{unlink} can be used to delete the name of a
9888 directory. On others, it can be used that way only by a privileged user.
9889 In the GNU system @code{unlink} can never delete the name of a directory.
9891 The @command{unlink} command honors the @option{--help} and
9892 @option{--version} options. To remove a file whose name begins with
9893 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9898 @node Changing file attributes
9899 @chapter Changing file attributes
9901 @cindex changing file attributes
9902 @cindex file attributes, changing
9903 @cindex attributes, file
9905 A file is not merely its contents, a name, and a file type
9906 (@pxref{Special file types}). A file also has an owner (a user ID), a
9907 group (a group ID), permissions (what the owner can do with the file,
9908 what people in the group can do, and what everyone else can do), various
9909 timestamps, and other information. Collectively, we call these a file's
9912 These commands change file attributes.
9915 * chown invocation:: Change file owners and groups.
9916 * chgrp invocation:: Change file groups.
9917 * chmod invocation:: Change access permissions.
9918 * touch invocation:: Change file timestamps.
9922 @node chown invocation
9923 @section @command{chown}: Change file owner and group
9926 @cindex file ownership, changing
9927 @cindex group ownership, changing
9928 @cindex changing file ownership
9929 @cindex changing group ownership
9931 @command{chown} changes the user and/or group ownership of each given @var{file}
9932 to @var{new-owner} or to the user and group of an existing reference file.
9936 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
9940 If used, @var{new-owner} specifies the new owner and/or group as follows
9941 (with no embedded white space):
9944 [@var{owner}] [ : [@var{group}] ]
9951 If only an @var{owner} (a user name or numeric user ID) is given, that
9952 user is made the owner of each given file, and the files' group is not
9955 @item owner@samp{:}group
9956 If the @var{owner} is followed by a colon and a @var{group} (a
9957 group name or numeric group ID), with no spaces between them, the group
9958 ownership of the files is changed as well (to @var{group}).
9961 If a colon but no group name follows @var{owner}, that user is
9962 made the owner of the files and the group of the files is changed to
9963 @var{owner}'s login group.
9966 If the colon and following @var{group} are given, but the owner
9967 is omitted, only the group of the files is changed; in this case,
9968 @command{chown} performs the same function as @command{chgrp}.
9971 If only a colon is given, or if @var{new-owner} is empty, neither the
9972 owner nor the group is changed.
9976 If @var{owner} or @var{group} is intended to represent a numeric user
9977 or group ID, then you may specify it with a leading @samp{+}.
9978 @xref{Disambiguating names and IDs}.
9980 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9981 POSIX 1003.1-2001 (@pxref{Standards conformance}) does not
9982 require support for that, but for backward compatibility GNU
9983 @command{chown} supports @samp{.} so long as no ambiguity results.
9984 New scripts should avoid the use of @samp{.} because it is not
9985 portable, and because it has undesirable results if the entire
9986 @var{owner@samp{.}group} happens to identify a user whose name
9989 The @command{chown} command sometimes clears the set-user-ID or
9990 set-group-ID permission bits. This behavior depends on the policy and
9991 functionality of the underlying @code{chown} system call, which may
9992 make system-dependent file mode modifications outside the control of
9993 the @command{chown} command. For example, the @command{chown} command
9994 might not affect those bits when invoked by a user with appropriate
9995 privileges, or when the
9996 bits signify some function other than executable permission (e.g.,
9998 When in doubt, check the underlying system behavior.
10000 The program accepts the following options. Also see @ref{Common options}.
10008 @cindex changed owners, verbosely describing
10009 Verbosely describe the action for each @var{file} whose ownership
10018 @cindex error messages, omitting
10019 Do not print error messages about files whose ownership cannot be
10022 @item @w{@kbd{--from}=@var{old-owner}}
10024 @cindex symbolic links, changing owner
10025 Change a @var{file}'s ownership only if it has current attributes specified
10026 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
10028 This option is useful primarily from a security standpoint in that
10029 it narrows considerably the window of potential abuse.
10030 For example, to reflect a user ID numbering change for one user's files
10031 without an option like this, @code{root} might run
10034 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
10037 But that is dangerous because the interval between when the @command{find}
10038 tests the existing file's owner and when the @command{chown} is actually run
10039 may be quite large.
10040 One way to narrow the gap would be to invoke chown for each file
10044 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
10047 But that is very slow if there are many affected files.
10048 With this option, it is safer (the gap is narrower still)
10049 though still not perfect:
10052 chown -h -R --from=OLDUSER NEWUSER /
10055 @item --dereference
10056 @opindex --dereference
10057 @cindex symbolic links, changing owner
10059 Do not act on symbolic links themselves but rather on what they point to.
10060 This is the default.
10063 @itemx --no-dereference
10065 @opindex --no-dereference
10066 @cindex symbolic links, changing owner
10068 Act on symbolic links themselves instead of what they point to.
10069 This mode relies on the @code{lchown} system call.
10070 On systems that do not provide the @code{lchown} system call,
10071 @command{chown} fails when a file specified on the command line
10072 is a symbolic link.
10073 By default, no diagnostic is issued for symbolic links encountered
10074 during a recursive traversal, but see @option{--verbose}.
10076 @item --preserve-root
10077 @opindex --preserve-root
10078 @cindex root directory, disallow recursive modification
10079 Fail upon any attempt to recursively change the root directory, @file{/}.
10080 Without @option{--recursive}, this option has no effect.
10081 @xref{Treating / specially}.
10083 @item --no-preserve-root
10084 @opindex --no-preserve-root
10085 @cindex root directory, allow recursive modification
10086 Cancel the effect of any preceding @option{--preserve-root} option.
10087 @xref{Treating / specially}.
10089 @item --reference=@var{ref_file}
10090 @opindex --reference
10091 Change the user and group of each @var{file} to be the same as those of
10092 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10093 user and group of the symbolic link, but rather those of the file it
10100 Output a diagnostic for every file processed.
10101 If a symbolic link is encountered during a recursive traversal
10102 on a system without the @code{lchown} system call, and @option{--no-dereference}
10103 is in effect, then issue a diagnostic saying neither the symbolic link nor
10104 its referent is being changed.
10109 @opindex --recursive
10110 @cindex recursively changing file ownership
10111 Recursively change ownership of directories and their contents.
10114 @xref{Traversing symlinks}.
10117 @xref{Traversing symlinks}.
10120 @xref{Traversing symlinks}.
10129 # Change the owner of /u to "root".
10132 # Likewise, but also change its group to "staff".
10133 chown root:staff /u
10135 # Change the owner of /u and subfiles to "root".
10140 @node chgrp invocation
10141 @section @command{chgrp}: Change group ownership
10144 @cindex group ownership, changing
10145 @cindex changing group ownership
10147 @command{chgrp} changes the group ownership of each given @var{file}
10148 to @var{group} (which can be either a group name or a numeric group ID)
10149 or to the group of an existing reference file. Synopsis:
10152 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
10156 If @var{group} is intended to represent a
10157 numeric group ID, then you may specify it with a leading @samp{+}.
10158 @xref{Disambiguating names and IDs}.
10160 The program accepts the following options. Also see @ref{Common options}.
10168 @cindex changed files, verbosely describing
10169 Verbosely describe the action for each @var{file} whose group actually
10178 @cindex error messages, omitting
10179 Do not print error messages about files whose group cannot be
10182 @item --dereference
10183 @opindex --dereference
10184 @cindex symbolic links, changing owner
10186 Do not act on symbolic links themselves but rather on what they point to.
10187 This is the default.
10190 @itemx --no-dereference
10192 @opindex --no-dereference
10193 @cindex symbolic links, changing group
10195 Act on symbolic links themselves instead of what they point to.
10196 This mode relies on the @code{lchown} system call.
10197 On systems that do not provide the @code{lchown} system call,
10198 @command{chgrp} fails when a file specified on the command line
10199 is a symbolic link.
10200 By default, no diagnostic is issued for symbolic links encountered
10201 during a recursive traversal, but see @option{--verbose}.
10203 @item --preserve-root
10204 @opindex --preserve-root
10205 @cindex root directory, disallow recursive modification
10206 Fail upon any attempt to recursively change the root directory, @file{/}.
10207 Without @option{--recursive}, this option has no effect.
10208 @xref{Treating / specially}.
10210 @item --no-preserve-root
10211 @opindex --no-preserve-root
10212 @cindex root directory, allow recursive modification
10213 Cancel the effect of any preceding @option{--preserve-root} option.
10214 @xref{Treating / specially}.
10216 @item --reference=@var{ref_file}
10217 @opindex --reference
10218 Change the group of each @var{file} to be the same as that of
10219 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10220 group of the symbolic link, but rather that of the file it refers to.
10226 Output a diagnostic for every file processed.
10227 If a symbolic link is encountered during a recursive traversal
10228 on a system without the @code{lchown} system call, and @option{--no-dereference}
10229 is in effect, then issue a diagnostic saying neither the symbolic link nor
10230 its referent is being changed.
10235 @opindex --recursive
10236 @cindex recursively changing group ownership
10237 Recursively change the group ownership of directories and their contents.
10240 @xref{Traversing symlinks}.
10243 @xref{Traversing symlinks}.
10246 @xref{Traversing symlinks}.
10255 # Change the group of /u to "staff".
10258 # Change the group of /u and subfiles to "staff".
10263 @node chmod invocation
10264 @section @command{chmod}: Change access permissions
10267 @cindex changing access permissions
10268 @cindex access permissions, changing
10269 @cindex permissions, changing access
10271 @command{chmod} changes the access permissions of the named files. Synopsis:
10274 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
10278 @cindex symbolic links, permissions of
10279 @command{chmod} never changes the permissions of symbolic links, since
10280 the @command{chmod} system call cannot change their permissions.
10281 This is not a problem since the permissions of symbolic links are
10282 never used. However, for each symbolic link listed on the command
10283 line, @command{chmod} changes the permissions of the pointed-to file.
10284 In contrast, @command{chmod} ignores symbolic links encountered during
10285 recursive directory traversals.
10287 A successful use of @command{chmod} clears the set-group-ID bit of a
10288 regular file if the file's group ID does not match the user's
10289 effective group ID or one of the user's supplementary group IDs,
10290 unless the user has appropriate privileges. Additional restrictions
10291 may cause the set-user-ID and set-group-ID bits of @var{mode} or
10292 @var{ref_file} to be ignored. This behavior depends on the policy and
10293 functionality of the underlying @code{chmod} system call. When in
10294 doubt, check the underlying system behavior.
10296 If used, @var{mode} specifies the new file mode bits.
10297 For details, see the section on @ref{File permissions}.
10298 If you really want @var{mode} to have a leading @samp{-}, you should
10299 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
10300 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
10301 file} (without the @option{--}) complains if it behaves differently
10302 from what @samp{chmod a-w file} would do.
10304 The program accepts the following options. Also see @ref{Common options}.
10312 Verbosely describe the action for each @var{file} whose permissions
10321 @cindex error messages, omitting
10322 Do not print error messages about files whose permissions cannot be
10325 @item --preserve-root
10326 @opindex --preserve-root
10327 @cindex root directory, disallow recursive modification
10328 Fail upon any attempt to recursively change the root directory, @file{/}.
10329 Without @option{--recursive}, this option has no effect.
10330 @xref{Treating / specially}.
10332 @item --no-preserve-root
10333 @opindex --no-preserve-root
10334 @cindex root directory, allow recursive modification
10335 Cancel the effect of any preceding @option{--preserve-root} option.
10336 @xref{Treating / specially}.
10342 Verbosely describe the action or non-action taken for every @var{file}.
10344 @item --reference=@var{ref_file}
10345 @opindex --reference
10346 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
10347 @xref{File permissions}.
10348 If @var{ref_file} is a symbolic link, do not use the mode
10349 of the symbolic link, but rather that of the file it refers to.
10354 @opindex --recursive
10355 @cindex recursively changing access permissions
10356 Recursively change permissions of directories and their contents.
10363 @node touch invocation
10364 @section @command{touch}: Change file timestamps
10367 @cindex changing file timestamps
10368 @cindex file timestamps, changing
10369 @cindex timestamps, changing file
10371 @command{touch} changes the access and/or modification times of the
10372 specified files. Synopsis:
10375 touch [@var{option}]@dots{} @var{file}@dots{}
10378 @cindex empty files, creating
10379 Any @var{file} argument that does not exist is created empty, unless
10380 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
10381 (@option{-h}) was in effect.
10383 A @var{file} argument string of @samp{-} is handled specially and
10384 causes @command{touch} to change the times of the file associated with
10388 By default, @command{touch} sets file timestamps to the current time.
10389 Because @command{touch} acts on its operands left to right, the
10390 resulting timestamps of earlier and later operands may disagree.
10391 Also, the determination of what time is ``current'' depends on the
10392 platform. Platforms with network file systems often use different
10393 clocks for the operating system and for file systems; because
10394 @command{touch} typically uses file systems' clocks by default, clock
10395 skew can cause the resulting file timestamps to appear to be in a
10396 program's ``future'' or ``past''.
10398 @cindex file timestamp resolution
10399 The @command{touch} command sets the file's timestamp to the greatest
10400 representable value that is not greater than the requested time. This
10401 can differ from the requested time for several reasons. First, the
10402 requested time may have a higher resolution than supported. Second, a
10403 file system may use different resolutions for different types of
10404 times. Third, file timestamps may use a different resolution than
10405 operating system timestamps. Fourth, the operating system primitives
10406 used to update timestamps may employ yet a different resolution. For
10407 example, in theory a file system might use 10-microsecond resolution
10408 for access time and 100-nanosecond resolution for modification time,
10409 and the operating system might use nanosecond resolution for the
10410 current time and microsecond resolution for the primitive that
10411 @command{touch} uses to set a file's timestamp to an arbitrary value.
10413 @cindex permissions, for changing file timestamps
10414 When setting file timestamps to the current time, @command{touch} can
10415 change the timestamps for files that the user does not own but has
10416 write permission for. Otherwise, the user must own the files. Some
10417 older systems have a further restriction: the user must own the files
10418 unless both the access and modification times are being set to the
10421 Although @command{touch} provides options for changing two of the times---the
10422 times of last access and modification---of a file, there is actually
10423 a standard third one as well: the inode change time. This is often
10424 referred to as a file's @code{ctime}.
10425 The inode change time represents the time when the file's meta-information
10426 last changed. One common example of this is when the permissions of a
10427 file change. Changing the permissions doesn't access the file, so
10428 the atime doesn't change, nor does it modify the file, so the mtime
10429 doesn't change. Yet, something about the file itself has changed,
10430 and this must be noted somewhere. This is the job of the ctime field.
10431 This is necessary, so that, for example, a backup program can make a
10432 fresh copy of the file, including the new permissions value.
10433 Another operation that modifies a file's ctime without affecting
10434 the others is renaming. In any case, it is not possible, in normal
10435 operations, for a user to change the ctime field to a user-specified value.
10436 Some operating systems and file systems support a fourth time: the
10437 birth time, when the file was first created; by definition, this
10438 timestamp never changes.
10441 Time stamps assume the time zone rules specified by the @env{TZ}
10442 environment variable, or by the system default rules if @env{TZ} is
10443 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
10444 libc, The GNU C Library Reference Manual}.
10445 You can avoid ambiguities during
10446 daylight saving transitions by using @sc{utc} time stamps.
10448 The program accepts the following options. Also see @ref{Common options}.
10453 @itemx --time=atime
10454 @itemx --time=access
10458 @opindex atime@r{, changing}
10459 @opindex access @r{time, changing}
10460 @opindex use @r{time, changing}
10461 Change the access time only.
10466 @opindex --no-create
10467 Do not warn about or create files that do not exist.
10470 @itemx --date=@var{time}
10474 Use @var{time} instead of the current time. It can contain month names,
10475 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10476 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10477 specifies the instant of time that is 489,392,193 nanoseconds after
10478 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10479 minutes east of UTC@. @xref{Date input formats}.
10480 File systems that do not support high-resolution time stamps
10481 silently ignore any excess precision here.
10485 @cindex BSD @command{touch} compatibility
10486 Ignored; for compatibility with BSD versions of @command{touch}.
10489 @itemx --no-dereference
10491 @opindex --no-dereference
10492 @cindex symbolic links, changing time
10494 Attempt to change the timestamps of a symbolic link, rather than what
10495 the link refers to. When using this option, empty files are not
10496 created, but option @option{-c} must also be used to avoid warning
10497 about files that do not exist. Not all systems support changing the
10498 timestamps of symlinks, since underlying system support for this
10499 action was not required until POSIX 2008. Also, on some
10500 systems, the mere act of examining a symbolic link changes the access
10501 time, such that only changes to the modification time will persist
10502 long enough to be observable. When coupled with option @option{-r}, a
10503 reference timestamp is taken from a symbolic link rather than the file
10507 @itemx --time=mtime
10508 @itemx --time=modify
10511 @opindex mtime@r{, changing}
10512 @opindex modify @r{time, changing}
10513 Change the modification time only.
10515 @item -r @var{file}
10516 @itemx --reference=@var{file}
10518 @opindex --reference
10519 Use the times of the reference @var{file} instead of the current time.
10520 If this option is combined with the @option{--date=@var{time}}
10521 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10522 the origin for any relative @var{time}s given, but is otherwise ignored.
10523 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10524 equal to five seconds before the corresponding time stamp for @file{foo}.
10525 If @var{file} is a symbolic link, the reference timestamp is taken
10526 from the target of the symlink, unless @option{-h} was also in effect.
10528 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10529 @cindex leap seconds
10530 Use the argument (optional four-digit or two-digit years, months,
10531 days, hours, minutes, optional seconds) instead of the current time.
10532 If the year is specified with only two digits, then @var{cc}
10533 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10534 69 @dots{} 99. If no digits of the year are specified,
10535 the argument is interpreted as a date in the current year.
10536 On the atypical systems that support leap seconds, @var{ss} may be
10541 @vindex _POSIX2_VERSION
10542 On older systems, @command{touch} supports an obsolete syntax, as follows.
10543 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10544 @option{-t} options, and if there are two or more @var{file}s and the
10545 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10546 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10547 any, were moved to the front), and if the represented year
10548 is in the range 1969--1999, that argument is interpreted as the time
10549 for the other files instead of as a file name.
10550 This obsolete behavior can be enabled or disabled with the
10551 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10552 conformance}), but portable scripts should avoid commands whose
10553 behavior depends on this variable.
10554 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10555 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10561 @chapter Disk usage
10565 No disk can hold an infinite amount of data. These commands report
10566 how much disk storage is in use or available, report other file and
10567 file status information, and write buffers to disk.
10570 * df invocation:: Report file system disk space usage.
10571 * du invocation:: Estimate file space usage.
10572 * stat invocation:: Report file or file system status.
10573 * sync invocation:: Synchronize memory and disk.
10574 * truncate invocation:: Shrink or extend the size of a file.
10578 @node df invocation
10579 @section @command{df}: Report file system disk space usage
10582 @cindex file system disk usage
10583 @cindex disk usage by file system
10585 @command{df} reports the amount of disk space used and available on
10586 file systems. Synopsis:
10589 df [@var{option}]@dots{} [@var{file}]@dots{}
10592 With no arguments, @command{df} reports the space used and available on all
10593 currently mounted file systems (of all types). Otherwise, @command{df}
10594 reports on the file system containing each argument @var{file}.
10596 Normally the disk space is printed in units of
10597 1024 bytes, but this can be overridden (@pxref{Block size}).
10598 Non-integer quantities are rounded up to the next higher unit.
10600 @cindex disk device file
10601 @cindex device file, disk
10602 If an argument @var{file} is a disk device file containing a mounted
10603 file system, @command{df} shows the space available on that file system
10604 rather than on the file system containing the device node (i.e., the root
10605 file system). @sc{gnu} @command{df} does not attempt to determine the
10607 on unmounted file systems, because on most kinds of systems doing so
10608 requires extremely nonportable intimate knowledge of file system
10611 The program accepts the following options. Also see @ref{Common options}.
10619 @cindex automounter file systems
10620 @cindex ignore file systems
10621 Include in the listing dummy file systems, which
10622 are omitted by default. Such file systems are typically special-purpose
10623 pseudo-file-systems, such as automounter entries.
10625 @item -B @var{size}
10626 @itemx --block-size=@var{size}
10628 @opindex --block-size
10629 @cindex file system sizes
10630 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10631 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10635 @cindex grand total of disk size, usage and available space
10636 Print a grand total of all arguments after all arguments have
10637 been processed. This can be used to find out the total disk size, usage
10638 and available space of all listed devices.
10644 Equivalent to @option{--si}.
10650 @cindex inode usage
10651 List inode usage information instead of block usage. An inode (short
10652 for index node) contains information about a file such as its owner,
10653 permissions, timestamps, and location on the disk.
10657 @cindex kibibytes for file system sizes
10658 Print sizes in 1024-byte blocks, overriding the default block size
10659 (@pxref{Block size}).
10660 This option is equivalent to @option{--block-size=1K}.
10666 @cindex file system types, limiting output to certain
10667 Limit the listing to local file systems. By default, remote file systems
10672 @cindex file system space, retrieving old data more quickly
10673 Do not invoke the @code{sync} system call before getting any usage data.
10674 This may make @command{df} run significantly faster on systems with many
10675 disks, but on some systems (notably SunOS) the results may be slightly
10676 out of date. This is the default.
10679 @itemx --portability
10681 @opindex --portability
10682 @cindex one-line output format
10683 @cindex POSIX output format
10684 @cindex portable output format
10685 @cindex output format, portable
10686 Use the POSIX output format. This is like the default format except
10691 The information about each file system is always printed on exactly
10692 one line; a mount device is never put on a line by itself. This means
10693 that if the mount device name is more than 20 characters long (e.g., for
10694 some network mounts), the columns are misaligned.
10697 The labels in the header output line are changed to conform to POSIX.
10700 The default block size and output format are unaffected by the
10701 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10702 variables. However, the default block size is still affected by
10703 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10704 otherwise. @xref{Block size}.
10711 @cindex file system space, retrieving current data more slowly
10712 Invoke the @code{sync} system call before getting any usage data. On
10713 some systems (notably SunOS), doing this yields more up to date results,
10714 but in general this option makes @command{df} much slower, especially when
10715 there are many or very busy file systems.
10717 @item -t @var{fstype}
10718 @itemx --type=@var{fstype}
10721 @cindex file system types, limiting output to certain
10722 Limit the listing to file systems of type @var{fstype}. Multiple
10723 file system types can be specified by giving multiple @option{-t} options.
10724 By default, nothing is omitted.
10727 @itemx --print-type
10729 @opindex --print-type
10730 @cindex file system types, printing
10731 Print each file system's type. The types printed here are the same ones
10732 you can include or exclude with @option{-t} and @option{-x}. The particular
10733 types printed are whatever is supported by the system. Here are some of
10734 the common names (this list is certainly not exhaustive):
10739 @cindex NFS file system type
10740 An NFS file system, i.e., one mounted over a network from another
10741 machine. This is the one type name which seems to be used uniformly by
10744 @item 4.2@r{, }ufs@r{, }efs@dots{}
10745 @cindex Linux file system types
10746 @cindex local file system types
10747 @opindex 4.2 @r{file system type}
10748 @opindex ufs @r{file system type}
10749 @opindex efs @r{file system type}
10750 A file system on a locally-mounted hard disk. (The system might even
10751 support more than one type here; Linux does.)
10753 @item hsfs@r{, }cdfs
10754 @cindex CD-ROM file system type
10755 @cindex High Sierra file system
10756 @opindex hsfs @r{file system type}
10757 @opindex cdfs @r{file system type}
10758 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10759 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10762 @cindex PC file system
10763 @cindex DOS file system
10764 @cindex MS-DOS file system
10765 @cindex diskette file system
10767 An MS-DOS file system, usually on a diskette.
10771 @item -x @var{fstype}
10772 @itemx --exclude-type=@var{fstype}
10774 @opindex --exclude-type
10775 Limit the listing to file systems not of type @var{fstype}.
10776 Multiple file system types can be eliminated by giving multiple
10777 @option{-x} options. By default, no file system types are omitted.
10780 Ignored; for compatibility with System V versions of @command{df}.
10785 Failure includes the case where no output is generated, so you can
10786 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10787 @var{dir}} to test whether @var{dir} is on a file system of type
10788 @samp{ext3} or @samp{reiserfs}.
10790 Since the list of file systems (@var{mtab}) is needed to determine the
10791 file system type, failure includes the cases when that list cannot
10792 be read and one or more of the options @option{-a}, @option{-l}, @option{-t}
10793 or @option{-x} is used together with a file name argument.
10796 @node du invocation
10797 @section @command{du}: Estimate file space usage
10800 @cindex file space usage
10801 @cindex disk usage for files
10803 @command{du} reports the amount of disk space used by the specified files
10804 and for each subdirectory (of directory arguments). Synopsis:
10807 du [@var{option}]@dots{} [@var{file}]@dots{}
10810 With no arguments, @command{du} reports the disk space for the current
10811 directory. Normally the disk space is printed in units of
10812 1024 bytes, but this can be overridden (@pxref{Block size}).
10813 Non-integer quantities are rounded up to the next higher unit.
10815 If two or more hard links point to the same file, only one of the hard
10816 links is counted. The @var{file} argument order affects which links
10817 are counted, and changing the argument order may change the numbers
10818 that @command{du} outputs.
10820 The program accepts the following options. Also see @ref{Common options}.
10828 Show counts for all files, not just directories.
10830 @item --apparent-size
10831 @opindex --apparent-size
10832 Print apparent sizes, rather than disk usage. The apparent size of a
10833 file is the number of bytes reported by @code{wc -c} on regular files,
10834 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10835 For example, a file containing the word @samp{zoo} with no newline would,
10836 of course, have an apparent size of 3. Such a small file may require
10837 anywhere from 0 to 16 KiB or more of disk space, depending on
10838 the type and configuration of the file system on which the file resides.
10839 However, a sparse file created with this command:
10842 dd bs=1 seek=2GiB if=/dev/null of=big
10846 has an apparent size of 2 GiB, yet on most modern
10847 systems, it actually uses almost no disk space.
10853 Equivalent to @code{--apparent-size --block-size=1}.
10855 @item -B @var{size}
10856 @itemx --block-size=@var{size}
10858 @opindex --block-size
10860 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10861 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10867 @cindex grand total of disk space
10868 Print a grand total of all arguments after all arguments have
10869 been processed. This can be used to find out the total disk usage of
10870 a given set of files or directories.
10873 @itemx --dereference-args
10875 @opindex --dereference-args
10876 Dereference symbolic links that are command line arguments.
10877 Does not affect other symbolic links. This is helpful for finding
10878 out the disk usage of directories, such as @file{/usr/tmp}, which
10879 are often symbolic links.
10881 @c --files0-from=FILE
10882 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10888 Equivalent to @option{--dereference-args} (@option{-D}).
10892 @cindex kibibytes for file sizes
10893 Print sizes in 1024-byte blocks, overriding the default block size
10894 (@pxref{Block size}).
10895 This option is equivalent to @option{--block-size=1K}.
10898 @itemx --count-links
10900 @opindex --count-links
10901 @cindex hard links, counting in @command{du}
10902 Count the size of all files, even if they have appeared already (as a
10906 @itemx --dereference
10908 @opindex --dereference
10909 @cindex symbolic links, dereferencing in @command{du}
10910 Dereference symbolic links (show the disk space used by the file
10911 or directory that the link points to instead of the space used by
10916 @cindex mebibytes for file sizes
10917 Print sizes in 1,048,576-byte blocks, overriding the default block size
10918 (@pxref{Block size}).
10919 This option is equivalent to @option{--block-size=1M}.
10922 @itemx --no-dereference
10924 @opindex --no-dereference
10925 @cindex symbolic links, dereferencing in @command{du}
10926 For each symbolic links encountered by @command{du},
10927 consider the disk space used by the symbolic link.
10929 @item -d @var{depth}
10930 @item --max-depth=@var{depth}
10931 @opindex -d @var{depth}
10932 @opindex --max-depth=@var{depth}
10933 @cindex limiting output of @command{du}
10934 Show the total for each directory (and file if --all) that is at
10935 most MAX_DEPTH levels down from the root of the hierarchy. The root
10936 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10945 @opindex --summarize
10946 Display only a total for each argument.
10949 @itemx --separate-dirs
10951 @opindex --separate-dirs
10952 Normally, in the output of @command{du} (when not using @option{--summarize}),
10953 the size listed next to a directory name, @var{d}, represents the sum
10954 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10955 With @option{--separate-dirs}, the size reported for a directory name,
10956 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10961 @cindex last modified dates, displaying in @command{du}
10962 Show time of the most recent modification of any file in the directory,
10963 or any of its subdirectories.
10966 @itemx --time=status
10969 @opindex ctime@r{, show the most recent}
10970 @opindex status time@r{, show the most recent}
10971 @opindex use time@r{, show the most recent}
10972 Show the most recent status change time (the @samp{ctime} in the inode) of
10973 any file in the directory, instead of the modification time.
10976 @itemx --time=access
10978 @opindex atime@r{, show the most recent}
10979 @opindex access time@r{, show the most recent}
10980 Show the most recent access time (the @samp{atime} in the inode) of
10981 any file in the directory, instead of the modification time.
10983 @item --time-style=@var{style}
10984 @opindex --time-style
10986 List timestamps in style @var{style}. This option has an effect only if
10987 the @option{--time} option is also specified. The @var{style} should
10988 be one of the following:
10991 @item +@var{format}
10993 List timestamps using @var{format}, where @var{format} is interpreted
10994 like the format argument of @command{date} (@pxref{date invocation}).
10995 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10996 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10997 with @command{date}, @var{format}'s interpretation is affected by the
10998 @env{LC_TIME} locale category.
11001 List timestamps in full using ISO 8601 date, time, and time zone
11002 format with nanosecond precision, e.g., @samp{2002-03-30
11003 23:45:56.477817180 -0700}. This style is equivalent to
11004 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
11007 List ISO 8601 date and time in minutes, e.g.,
11008 @samp{2002-03-30 23:45}. These timestamps are shorter than
11009 @samp{full-iso} timestamps, and are usually good enough for everyday
11010 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
11013 List ISO 8601 dates for timestamps, e.g., @samp{2002-03-30}.
11014 This style is equivalent to @samp{+%Y-%m-%d}.
11018 You can specify the default value of the @option{--time-style} option
11019 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
11020 the default style is @samp{long-iso}. For compatibility with @command{ls},
11021 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
11022 the newline and any later characters are ignored; if @env{TIME_STYLE}
11023 begins with @samp{posix-} the @samp{posix-} is ignored; and if
11024 @env{TIME_STYLE} is @samp{locale} it is ignored.
11027 @itemx --one-file-system
11029 @opindex --one-file-system
11030 @cindex one file system, restricting @command{du} to
11031 Skip directories that are on different file systems from the one that
11032 the argument being processed is on.
11034 @item --exclude=@var{pattern}
11035 @opindex --exclude=@var{pattern}
11036 @cindex excluding files from @command{du}
11037 When recursing, skip subdirectories or files matching @var{pattern}.
11038 For example, @code{du --exclude='*.o'} excludes files whose names
11041 @item -X @var{file}
11042 @itemx --exclude-from=@var{file}
11043 @opindex -X @var{file}
11044 @opindex --exclude-from=@var{file}
11045 @cindex excluding files from @command{du}
11046 Like @option{--exclude}, except take the patterns to exclude from @var{file},
11047 one per line. If @var{file} is @samp{-}, take the patterns from standard
11052 @cindex NFS mounts from BSD to HP-UX
11053 On BSD systems, @command{du} reports sizes that are half the correct
11054 values for files that are NFS-mounted from HP-UX systems. On HP-UX
11055 systems, it reports sizes that are twice the correct values for
11056 files that are NFS-mounted from BSD systems. This is due to a flaw
11057 in HP-UX; it also affects the HP-UX @command{du} program.
11062 @node stat invocation
11063 @section @command{stat}: Report file or file system status
11066 @cindex file status
11067 @cindex file system status
11069 @command{stat} displays information about the specified file(s). Synopsis:
11072 stat [@var{option}]@dots{} [@var{file}]@dots{}
11075 With no option, @command{stat} reports all information about the given files.
11076 But it also can be used to report the information of the file systems the
11077 given files are located on. If the files are links, @command{stat} can
11078 also give information about the files the links point to.
11080 @mayConflictWithShellBuiltIn{stat}
11085 @itemx --dereference
11087 @opindex --dereference
11088 @cindex symbolic links, dereferencing in @command{stat}
11089 Change how @command{stat} treats symbolic links.
11090 With this option, @command{stat} acts on the file referenced
11091 by each symbolic link argument.
11092 Without it, @command{stat} acts on any symbolic link argument directly.
11095 @itemx --file-system
11097 @opindex --file-system
11098 @cindex file systems
11099 Report information about the file systems where the given files are located
11100 instead of information about the files themselves.
11101 This option implies the @option{-L} option.
11104 @itemx --format=@var{format}
11106 @opindex --format=@var{format}
11107 @cindex output format
11108 Use @var{format} rather than the default format.
11109 @var{format} is automatically newline-terminated, so
11110 running a command like the following with two or more @var{file}
11111 operands produces a line of output for each operand:
11113 $ stat --format=%d:%i / /usr
11118 @item --printf=@var{format}
11119 @opindex --printf=@var{format}
11120 @cindex output format
11121 Use @var{format} rather than the default format.
11122 Like @option{--format}, but interpret backslash escapes,
11123 and do not output a mandatory trailing newline.
11124 If you want a newline, include @samp{\n} in the @var{format}.
11125 Here's how you would use @option{--printf} to print the device
11126 and inode numbers of @file{/} and @file{/usr}:
11128 $ stat --printf='%d:%i\n' / /usr
11137 @cindex terse output
11138 Print the information in terse form, suitable for parsing by other programs.
11142 The valid @var{format} directives for files with @option{--format} and
11143 @option{--printf} are:
11146 @item %a - Access rights in octal
11147 @item %A - Access rights in human readable form
11148 @item %b - Number of blocks allocated (see @samp{%B})
11149 @item %B - The size in bytes of each block reported by @samp{%b}
11150 @item %C - The SELinux security context of a file, if available
11151 @item %d - Device number in decimal
11152 @item %D - Device number in hex
11153 @item %f - Raw mode in hex
11154 @item %F - File type
11155 @item %g - Group ID of owner
11156 @item %G - Group name of owner
11157 @item %h - Number of hard links
11158 @item %i - Inode number
11159 @item %m - Mount point (See note below)
11160 @item %n - File name
11161 @item %N - Quoted file name with dereference if symbolic link
11162 @item %o - Optimal I/O transfer size hint
11163 @item %s - Total size, in bytes
11164 @item %t - Major device type in hex
11165 @item %T - Minor device type in hex
11166 @item %u - User ID of owner
11167 @item %U - User name of owner
11168 @item %w - Time of file birth, or @samp{-} if unknown
11169 @item %W - Time of file birth as seconds since Epoch, or @samp{0}
11170 @item %x - Time of last access
11171 @item %X - Time of last access as seconds since Epoch
11172 @item %y - Time of last modification
11173 @item %Y - Time of last modification as seconds since Epoch
11174 @item %z - Time of last change
11175 @item %Z - Time of last change as seconds since Epoch
11178 The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
11179 precision preceded by a period to specify the number of digits to
11180 print after the decimal point. For example, @samp{%.3X} outputs the
11181 last access time to millisecond precision. If a period is given but no
11182 precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
11183 @samp{%.9X}@. When discarding excess precision, time stamps are truncated
11184 toward minus infinity.
11188 $ stat -c '[%015Y]' /usr
11191 $ stat -c '[%15Y]' /usr
11193 $ stat -c '[%-15Y]' /usr
11196 $ stat -c '[%.3Y]' /usr
11198 $ stat -c '[%.Y]' /usr
11199 [1288929712.114951834]
11202 The mount point printed by @samp{%m} is similar to that output
11203 by @command{df}, except that:
11206 stat does not dereference symlinks by default
11207 (unless @option{-L} is specified)
11209 stat does not search for specified device nodes in the
11210 file system list, instead operating on them directly
11213 stat outputs the alias for a bind mounted file, rather than
11214 the initial mount point of its backing device.
11215 One can recursively call stat until there is no change in output,
11216 to get the current base mount point
11219 When listing file system information (@option{--file-system} (@option{-f})),
11220 you must use a different set of @var{format} directives:
11223 @item %a - Free blocks available to non-super-user
11224 @item %b - Total data blocks in file system
11225 @item %c - Total file nodes in file system
11226 @item %d - Free file nodes in file system
11227 @item %f - Free blocks in file system
11228 @item %i - File System ID in hex
11229 @item %l - Maximum length of file names
11230 @item %n - File name
11231 @item %s - Block size (for faster transfers)
11232 @item %S - Fundamental block size (for block counts)
11233 @item %t - Type in hex
11234 @item %T - Type in human readable form
11238 Time stamps are listed according to the time zone rules specified by
11239 the @env{TZ} environment variable, or by the system default rules if
11240 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11241 with @env{TZ}, libc, The GNU C Library Reference Manual}.
11246 @node sync invocation
11247 @section @command{sync}: Synchronize data on disk with memory
11250 @cindex synchronize disk and memory
11252 @cindex superblock, writing
11253 @cindex inodes, written buffered
11254 @command{sync} writes any data buffered in memory out to disk. This can
11255 include (but is not limited to) modified superblocks, modified inodes,
11256 and delayed reads and writes. This must be implemented by the kernel;
11257 The @command{sync} program does nothing but exercise the @code{sync} system
11260 @cindex crashes and corruption
11261 The kernel keeps data in memory to avoid doing (relatively slow) disk
11262 reads and writes. This improves performance, but if the computer
11263 crashes, data may be lost or the file system corrupted as a
11264 result. The @command{sync} command ensures everything in memory
11265 is written to disk.
11267 Any arguments are ignored, except for a lone @option{--help} or
11268 @option{--version} (@pxref{Common options}).
11273 @node truncate invocation
11274 @section @command{truncate}: Shrink or extend the size of a file
11277 @cindex truncating, file sizes
11279 @command{truncate} shrinks or extends the size of each @var{file} to the
11280 specified size. Synopsis:
11283 truncate @var{option}@dots{} @var{file}@dots{}
11286 @cindex files, creating
11287 Any @var{file} that does not exist is created.
11289 @cindex sparse files, creating
11290 @cindex holes, creating files with
11291 If a @var{file} is larger than the specified size, the extra data is lost.
11292 If a @var{file} is shorter, it is extended and the extended part (or hole)
11293 reads as zero bytes.
11295 The program accepts the following options. Also see @ref{Common options}.
11302 @opindex --no-create
11303 Do not create files that do not exist.
11308 @opindex --io-blocks
11309 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
11311 @item -r @var{rfile}
11312 @itemx --reference=@var{rfile}
11314 @opindex --reference
11315 Base the size of each @var{file} on the size of @var{rfile}.
11317 @item -s @var{size}
11318 @itemx --size=@var{size}
11321 Set or adjust the size of each @var{file} according to @var{size}.
11322 @multiplierSuffixesNoBlocks{size}
11324 @var{size} may also be prefixed by one of the following to adjust
11325 the size of each @var{file} based on their current size:
11327 @samp{+} => extend by
11328 @samp{-} => reduce by
11329 @samp{<} => at most
11330 @samp{>} => at least
11331 @samp{/} => round down to multiple of
11332 @samp{%} => round up to multiple of
11340 @node Printing text
11341 @chapter Printing text
11343 @cindex printing text, commands for
11344 @cindex commands for printing text
11346 This section describes commands that display text strings.
11349 * echo invocation:: Print a line of text.
11350 * printf invocation:: Format and print data.
11351 * yes invocation:: Print a string until interrupted.
11355 @node echo invocation
11356 @section @command{echo}: Print a line of text
11359 @cindex displaying text
11360 @cindex printing text
11361 @cindex text, displaying
11362 @cindex arbitrary text, displaying
11364 @command{echo} writes each given @var{string} to standard output, with a
11365 space between each and a newline after the last one. Synopsis:
11368 echo [@var{option}]@dots{} [@var{string}]@dots{}
11371 @mayConflictWithShellBuiltIn{echo}
11373 The program accepts the following options. Also see @ref{Common options}.
11374 Options must precede operands, and the normally-special argument
11375 @samp{--} has no special meaning and is treated like any other
11381 Do not output the trailing newline.
11385 @cindex backslash escapes
11386 Enable interpretation of the following backslash-escaped characters in
11395 produce no further output
11411 the eight-bit value that is the octal number @var{nnn}
11412 (zero to three octal digits), if @var{nnn} is
11413 a nine-bit value, the ninth bit is ignored
11415 the eight-bit value that is the octal number @var{nnn}
11416 (one to three octal digits), if @var{nnn} is
11417 a nine-bit value, the ninth bit is ignored
11419 the eight-bit value that is the hexadecimal number @var{hh}
11420 (one or two hexadecimal digits)
11425 @cindex backslash escapes
11426 Disable interpretation of backslash escapes in each @var{string}.
11427 This is the default. If @option{-e} and @option{-E} are both
11428 specified, the last one given takes effect.
11432 @vindex POSIXLY_CORRECT
11433 If the @env{POSIXLY_CORRECT} environment variable is set, then when
11434 @command{echo}'s first argument is not @option{-n} it outputs
11435 option-like arguments instead of treating them as options. For
11436 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
11437 plain @samp{hello}.
11439 POSIX does not require support for any options, and says
11440 that the behavior of @command{echo} is implementation-defined if any
11441 @var{string} contains a backslash or if the first argument is
11442 @option{-n}. Portable programs can use the @command{printf} command
11443 if they need to omit trailing newlines or output control characters or
11444 backslashes. @xref{printf invocation}.
11449 @node printf invocation
11450 @section @command{printf}: Format and print data
11453 @command{printf} does formatted printing of text. Synopsis:
11456 printf @var{format} [@var{argument}]@dots{}
11459 @command{printf} prints the @var{format} string, interpreting @samp{%}
11460 directives and @samp{\} escapes to format numeric and string arguments
11461 in a way that is mostly similar to the C @samp{printf} function.
11462 @xref{Output Conversion Syntax,, @command{printf} format directives,
11463 libc, The GNU C Library Reference Manual}, for details.
11464 The differences are listed below.
11466 @mayConflictWithShellBuiltIn{printf}
11471 The @var{format} argument is reused as necessary to convert all the
11472 given @var{argument}s. For example, the command @samp{printf %s a b}
11476 Missing @var{argument}s are treated as null strings or as zeros,
11477 depending on whether the context expects a string or a number. For
11478 example, the command @samp{printf %sx%d} prints @samp{x0}.
11482 An additional escape, @samp{\c}, causes @command{printf} to produce no
11483 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
11484 E} prints @samp{ABC}.
11487 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
11488 digits, as opposed to C where it can have an unlimited number of
11489 digits. For example, the command @samp{printf '\x07e'} prints two
11490 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
11495 @command{printf} has an additional directive, @samp{%b}, which prints its
11496 argument string with @samp{\} escapes interpreted in the same way as in
11497 the @var{format} string, except that octal escapes are of the form
11498 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If
11499 @samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
11500 If a precision is also given, it limits the number of bytes printed
11501 from the converted string.
11504 Numeric arguments must be single C constants, possibly with leading
11505 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
11509 @vindex POSIXLY_CORRECT
11510 If the leading character of a numeric argument is @samp{"} or @samp{'}
11511 then its value is the numeric value of the immediately following
11512 character. Any remaining characters are silently ignored if the
11513 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
11514 warning is printed. For example, @samp{printf "%d" "'a"} outputs
11515 @samp{97} on hosts that use the ASCII character set, since
11516 @samp{a} has the numeric value 97 in ASCII.
11521 A floating-point argument must use a period before any fractional
11522 digits, but is printed according to the @env{LC_NUMERIC} category of the
11523 current locale. For example, in a locale whose radix character is a
11524 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11525 the command @samp{printf %g 3,14} is an error.
11526 @xref{Floating point}.
11530 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11531 (if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
11532 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11533 digits) specifying a character to print.
11534 Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
11535 @command{printf} ignores the ninth bit.
11536 For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.
11541 @cindex ISO/IEC 10646
11543 @command{printf} interprets two character syntaxes introduced in
11545 @samp{\u} for 16-bit Unicode (ISO/IEC 10646)
11546 characters, specified as
11547 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11548 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11549 @command{printf} outputs the Unicode characters
11550 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11551 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11552 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11554 The processing of @samp{\u} and @samp{\U} requires a full-featured
11555 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11556 or when @code{libiconv} is installed prior to this package. Otherwise
11557 @samp{\u} and @samp{\U} will print as-is.
11559 The only options are a lone @option{--help} or
11560 @option{--version}. @xref{Common options}.
11561 Options must precede operands.
11563 The Unicode character syntaxes are useful for writing strings in a locale
11564 independent way. For example, a string containing the Euro currency symbol
11567 $ env printf '\u20AC 14.95'
11571 will be output correctly in all locales supporting the Euro symbol
11572 (ISO-8859-15, UTF-8, and others). Similarly, a Chinese string
11575 $ env printf '\u4e2d\u6587'
11579 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11581 Note that in these examples, the @command{printf} command has been
11582 invoked via @command{env} to ensure that we run the program found via
11583 your shell's search path, and not a shell alias or a built-in function.
11585 For larger strings, you don't need to look up the hexadecimal code
11586 values of each character one by one. ASCII characters mixed with \u
11587 escape sequences is also known as the JAVA source file encoding. You can
11588 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11589 is how to convert a piece of text into a shell script which will output
11590 this text in a locale-independent way:
11593 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11594 '\u4e2d\u6587\n' > sample.txt
11595 $ recode BIG5..JAVA < sample.txt \
11596 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11603 @node yes invocation
11604 @section @command{yes}: Print a string until interrupted
11607 @cindex repeated output of a string
11609 @command{yes} prints the command line arguments, separated by spaces and
11610 followed by a newline, forever until it is killed. If no arguments are
11611 given, it prints @samp{y} followed by a newline forever until killed.
11613 Upon a write error, @command{yes} exits with status @samp{1}.
11615 The only options are a lone @option{--help} or @option{--version}.
11616 To output an argument that begins with
11617 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11618 @xref{Common options}.
11622 @chapter Conditions
11625 @cindex commands for exit status
11626 @cindex exit status commands
11628 This section describes commands that are primarily useful for their exit
11629 status, rather than their output. Thus, they are often used as the
11630 condition of shell @code{if} statements, or as the last command in a
11634 * false invocation:: Do nothing, unsuccessfully.
11635 * true invocation:: Do nothing, successfully.
11636 * test invocation:: Check file types and compare values.
11637 * expr invocation:: Evaluate expressions.
11641 @node false invocation
11642 @section @command{false}: Do nothing, unsuccessfully
11645 @cindex do nothing, unsuccessfully
11646 @cindex failure exit status
11647 @cindex exit status of @command{false}
11649 @command{false} does nothing except return an exit status of 1, meaning
11650 @dfn{failure}. It can be used as a place holder in shell scripts
11651 where an unsuccessful command is needed.
11652 In most modern shells, @command{false} is a built-in command, so when
11653 you use @samp{false} in a script, you're probably using the built-in
11654 command, not the one documented here.
11656 @command{false} honors the @option{--help} and @option{--version} options.
11658 This version of @command{false} is implemented as a C program, and is thus
11659 more secure and faster than a shell script implementation, and may safely
11660 be used as a dummy shell for the purpose of disabling accounts.
11662 Note that @command{false} (unlike all other programs documented herein)
11663 exits unsuccessfully, even when invoked with
11664 @option{--help} or @option{--version}.
11666 Portable programs should not assume that the exit status of
11667 @command{false} is 1, as it is greater than 1 on some
11671 @node true invocation
11672 @section @command{true}: Do nothing, successfully
11675 @cindex do nothing, successfully
11677 @cindex successful exit
11678 @cindex exit status of @command{true}
11680 @command{true} does nothing except return an exit status of 0, meaning
11681 @dfn{success}. It can be used as a place holder in shell scripts
11682 where a successful command is needed, although the shell built-in
11683 command @code{:} (colon) may do the same thing faster.
11684 In most modern shells, @command{true} is a built-in command, so when
11685 you use @samp{true} in a script, you're probably using the built-in
11686 command, not the one documented here.
11688 @command{true} honors the @option{--help} and @option{--version} options.
11690 Note, however, that it is possible to cause @command{true}
11691 to exit with nonzero status: with the @option{--help} or @option{--version}
11692 option, and with standard
11693 output already closed or redirected to a file that evokes an I/O error.
11694 For example, using a Bourne-compatible shell:
11697 $ ./true --version >&-
11698 ./true: write error: Bad file number
11699 $ ./true --version > /dev/full
11700 ./true: write error: No space left on device
11703 This version of @command{true} is implemented as a C program, and is thus
11704 more secure and faster than a shell script implementation, and may safely
11705 be used as a dummy shell for the purpose of disabling accounts.
11707 @node test invocation
11708 @section @command{test}: Check file types and compare values
11711 @cindex check file types
11712 @cindex compare values
11713 @cindex expression evaluation
11715 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11716 evaluation of the conditional expression @var{expr}. Each part of the
11717 expression must be a separate argument.
11719 @command{test} has file status checks, string operators, and numeric
11720 comparison operators.
11722 @command{test} has an alternate form that uses opening and closing
11723 square brackets instead a leading @samp{test}. For example, instead
11724 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11725 brackets must be separate arguments; for example, @samp{[-d /]} does
11726 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11727 @var{expr} ]} have the same meaning, only the former form is discussed
11733 test @var{expression}
11735 [ @var{expression} ]
11740 @mayConflictWithShellBuiltIn{test}
11742 If @var{expression} is omitted, @command{test} returns false.
11743 If @var{expression} is a single argument,
11744 @command{test} returns false if the argument is null and true
11745 otherwise. The argument
11746 can be any string, including strings like @samp{-d}, @samp{-1},
11747 @samp{--}, @samp{--help}, and @samp{--version} that most other
11748 programs would treat as options. To get help and version information,
11749 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11750 the usual closing brackets. @xref{Common options}.
11752 @cindex exit status of @command{test}
11756 0 if the expression is true,
11757 1 if the expression is false,
11758 2 if an error occurred.
11762 * File type tests:: -[bcdfhLpSt]
11763 * Access permission tests:: -[gkruwxOG]
11764 * File characteristic tests:: -e -s -nt -ot -ef
11765 * String tests:: -z -n = == !=
11766 * Numeric tests:: -eq -ne -lt -le -gt -ge
11767 * Connectives for test:: ! -a -o
11771 @node File type tests
11772 @subsection File type tests
11774 @cindex file type tests
11776 These options test for particular types of files. (Everything's a file,
11777 but not all files are the same!)
11781 @item -b @var{file}
11783 @cindex block special check
11784 True if @var{file} exists and is a block special device.
11786 @item -c @var{file}
11788 @cindex character special check
11789 True if @var{file} exists and is a character special device.
11791 @item -d @var{file}
11793 @cindex directory check
11794 True if @var{file} exists and is a directory.
11796 @item -f @var{file}
11798 @cindex regular file check
11799 True if @var{file} exists and is a regular file.
11801 @item -h @var{file}
11802 @itemx -L @var{file}
11805 @cindex symbolic link check
11806 True if @var{file} exists and is a symbolic link.
11807 Unlike all other file-related tests, this test does not dereference
11808 @var{file} if it is a symbolic link.
11810 @item -p @var{file}
11812 @cindex named pipe check
11813 True if @var{file} exists and is a named pipe.
11815 @item -S @var{file}
11817 @cindex socket check
11818 True if @var{file} exists and is a socket.
11822 @cindex terminal check
11823 True if @var{fd} is a file descriptor that is associated with a
11829 @node Access permission tests
11830 @subsection Access permission tests
11832 @cindex access permission tests
11833 @cindex permission tests
11835 These options test for particular access permissions.
11839 @item -g @var{file}
11841 @cindex set-group-ID check
11842 True if @var{file} exists and has its set-group-ID bit set.
11844 @item -k @var{file}
11846 @cindex sticky bit check
11847 True if @var{file} exists and has its @dfn{sticky} bit set.
11849 @item -r @var{file}
11851 @cindex readable file check
11852 True if @var{file} exists and read permission is granted.
11854 @item -u @var{file}
11856 @cindex set-user-ID check
11857 True if @var{file} exists and has its set-user-ID bit set.
11859 @item -w @var{file}
11861 @cindex writable file check
11862 True if @var{file} exists and write permission is granted.
11864 @item -x @var{file}
11866 @cindex executable file check
11867 True if @var{file} exists and execute permission is granted
11868 (or search permission, if it is a directory).
11870 @item -O @var{file}
11872 @cindex owned by effective user ID check
11873 True if @var{file} exists and is owned by the current effective user ID.
11875 @item -G @var{file}
11877 @cindex owned by effective group ID check
11878 True if @var{file} exists and is owned by the current effective group ID.
11882 @node File characteristic tests
11883 @subsection File characteristic tests
11885 @cindex file characteristic tests
11887 These options test other file characteristics.
11891 @item -e @var{file}
11893 @cindex existence-of-file check
11894 True if @var{file} exists.
11896 @item -s @var{file}
11898 @cindex nonempty file check
11899 True if @var{file} exists and has a size greater than zero.
11901 @item @var{file1} -nt @var{file2}
11903 @cindex newer-than file check
11904 True if @var{file1} is newer (according to modification date) than
11905 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11907 @item @var{file1} -ot @var{file2}
11909 @cindex older-than file check
11910 True if @var{file1} is older (according to modification date) than
11911 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11913 @item @var{file1} -ef @var{file2}
11915 @cindex same file check
11916 @cindex hard link check
11917 True if @var{file1} and @var{file2} have the same device and inode
11918 numbers, i.e., if they are hard links to each other.
11924 @subsection String tests
11926 @cindex string tests
11928 These options test string characteristics. You may need to quote
11929 @var{string} arguments for the shell. For example:
11935 The quotes here prevent the wrong arguments from being passed to
11936 @command{test} if @samp{$V} is empty or contains special characters.
11940 @item -z @var{string}
11942 @cindex zero-length string check
11943 True if the length of @var{string} is zero.
11945 @item -n @var{string}
11946 @itemx @var{string}
11948 @cindex nonzero-length string check
11949 True if the length of @var{string} is nonzero.
11951 @item @var{string1} = @var{string2}
11953 @cindex equal string check
11954 True if the strings are equal.
11956 @item @var{string1} == @var{string2}
11958 @cindex equal string check
11959 True if the strings are equal (synonym for =).
11961 @item @var{string1} != @var{string2}
11963 @cindex not-equal string check
11964 True if the strings are not equal.
11969 @node Numeric tests
11970 @subsection Numeric tests
11972 @cindex numeric tests
11973 @cindex arithmetic tests
11975 Numeric relational operators. The arguments must be entirely numeric
11976 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11977 which evaluates to the length of @var{string}.
11981 @item @var{arg1} -eq @var{arg2}
11982 @itemx @var{arg1} -ne @var{arg2}
11983 @itemx @var{arg1} -lt @var{arg2}
11984 @itemx @var{arg1} -le @var{arg2}
11985 @itemx @var{arg1} -gt @var{arg2}
11986 @itemx @var{arg1} -ge @var{arg2}
11993 These arithmetic binary operators return true if @var{arg1} is equal,
11994 not-equal, less-than, less-than-or-equal, greater-than, or
11995 greater-than-or-equal than @var{arg2}, respectively.
12002 test -1 -gt -2 && echo yes
12004 test -l abc -gt 1 && echo yes
12007 @error{} test: integer expression expected before -eq
12011 @node Connectives for test
12012 @subsection Connectives for @command{test}
12014 @cindex logical connectives
12015 @cindex connectives, logical
12017 The usual logical connectives.
12023 True if @var{expr} is false.
12025 @item @var{expr1} -a @var{expr2}
12027 @cindex logical and operator
12028 @cindex and operator
12029 True if both @var{expr1} and @var{expr2} are true.
12031 @item @var{expr1} -o @var{expr2}
12033 @cindex logical or operator
12034 @cindex or operator
12035 True if either @var{expr1} or @var{expr2} is true.
12040 @node expr invocation
12041 @section @command{expr}: Evaluate expressions
12044 @cindex expression evaluation
12045 @cindex evaluation of expressions
12047 @command{expr} evaluates an expression and writes the result on standard
12048 output. Each token of the expression must be a separate argument.
12050 Operands are either integers or strings. Integers consist of one or
12051 more decimal digits, with an optional leading @samp{-}.
12052 @command{expr} converts
12053 anything appearing in an operand position to an integer or a string
12054 depending on the operation being applied to it.
12056 Strings are not quoted for @command{expr} itself, though you may need to
12057 quote them to protect characters with special meaning to the shell,
12058 e.g., spaces. However, regardless of whether it is quoted, a string
12059 operand should not be a parenthesis or any of @command{expr}'s
12060 operators like @code{+}, so you cannot safely pass an arbitrary string
12061 @code{$str} to expr merely by quoting it to the shell. One way to
12062 work around this is to use the @sc{gnu} extension @code{+},
12063 (e.g., @code{+ "$str" = foo}); a more portable way is to use
12064 @code{@w{" $str"}} and to adjust the rest of the expression to take
12065 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
12067 You should not pass a negative integer or a string with leading
12068 @samp{-} as @command{expr}'s first argument, as it might be
12069 misinterpreted as an option; this can be avoided by parenthesization.
12070 Also, portable scripts should not use a string operand that happens to
12071 take the form of an integer; this can be worked around by inserting
12072 leading spaces as mentioned above.
12074 @cindex parentheses for grouping
12075 Operators may be given as infix symbols or prefix keywords. Parentheses
12076 may be used for grouping in the usual manner. You must quote
12077 parentheses and many operators to avoid the shell evaluating them,
12080 When built with support for the GNU MP library, @command{expr} uses
12081 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
12082 types and may fail due to arithmetic overflow.
12084 The only options are @option{--help} and @option{--version}. @xref{Common
12085 options}. Options must precede operands.
12087 @cindex exit status of @command{expr}
12091 0 if the expression is neither null nor 0,
12092 1 if the expression is null or 0,
12093 2 if the expression is invalid,
12094 3 if an internal error occurred (e.g., arithmetic overflow).
12098 * String expressions:: + : match substr index length
12099 * Numeric expressions:: + - * / %
12100 * Relations for expr:: | & < <= = == != >= >
12101 * Examples of expr:: Examples.
12105 @node String expressions
12106 @subsection String expressions
12108 @cindex string expressions
12109 @cindex expressions, string
12111 @command{expr} supports pattern matching and other string operators. These
12112 have higher precedence than both the numeric and relational operators (in
12113 the next sections).
12117 @item @var{string} : @var{regex}
12118 @cindex pattern matching
12119 @cindex regular expression matching
12120 @cindex matching patterns
12121 Perform pattern matching. The arguments are converted to strings and the
12122 second is considered to be a (basic, a la GNU @code{grep}) regular
12123 expression, with a @code{^} implicitly prepended. The first argument is
12124 then matched against this regular expression.
12126 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
12127 @code{:} expression returns the part of @var{string} that matched the
12128 subexpression; otherwise, it returns the number of characters matched.
12130 If the match fails, the @code{:} operator returns the null string if
12131 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
12133 @kindex \( @r{regexp operator}
12134 Only the first @samp{\( @dots{} \)} pair is relevant to the return
12135 value; additional pairs are meaningful only for grouping the regular
12136 expression operators.
12138 @kindex \+ @r{regexp operator}
12139 @kindex \? @r{regexp operator}
12140 @kindex \| @r{regexp operator}
12141 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
12142 operators which respectively match one or more, zero or one, or separate
12143 alternatives. SunOS and other @command{expr}'s treat these as regular
12144 characters. (POSIX allows either behavior.)
12145 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
12146 regular expression syntax. Some examples are in @ref{Examples of expr}.
12148 @item match @var{string} @var{regex}
12150 An alternative way to do pattern matching. This is the same as
12151 @w{@samp{@var{string} : @var{regex}}}.
12153 @item substr @var{string} @var{position} @var{length}
12155 Returns the substring of @var{string} beginning at @var{position}
12156 with length at most @var{length}. If either @var{position} or
12157 @var{length} is negative, zero, or non-numeric, returns the null string.
12159 @item index @var{string} @var{charset}
12161 Returns the first position in @var{string} where the first character in
12162 @var{charset} was found. If no character in @var{charset} is found in
12163 @var{string}, return 0.
12165 @item length @var{string}
12167 Returns the length of @var{string}.
12169 @item + @var{token}
12171 Interpret @var{token} as a string, even if it is a keyword like @var{match}
12172 or an operator like @code{/}.
12173 This makes it possible to test @code{expr length + "$x"} or
12174 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
12175 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
12176 This operator is a GNU extension. Portable shell scripts should use
12177 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
12181 To make @command{expr} interpret keywords as strings, you must use the
12182 @code{quote} operator.
12185 @node Numeric expressions
12186 @subsection Numeric expressions
12188 @cindex numeric expressions
12189 @cindex expressions, numeric
12191 @command{expr} supports the usual numeric operators, in order of increasing
12192 precedence. These numeric operators have lower precedence than the
12193 string operators described in the previous section, and higher precedence
12194 than the connectives (next section).
12202 @cindex subtraction
12203 Addition and subtraction. Both arguments are converted to integers;
12204 an error occurs if this cannot be done.
12210 @cindex multiplication
12213 Multiplication, division, remainder. Both arguments are converted to
12214 integers; an error occurs if this cannot be done.
12219 @node Relations for expr
12220 @subsection Relations for @command{expr}
12222 @cindex connectives, logical
12223 @cindex logical connectives
12224 @cindex relations, numeric or string
12226 @command{expr} supports the usual logical connectives and relations. These
12227 have lower precedence than the string and numeric operators
12228 (previous sections). Here is the list, lowest-precedence operator first.
12234 @cindex logical or operator
12235 @cindex or operator
12236 Returns its first argument if that is neither null nor zero, otherwise
12237 its second argument if it is neither null nor zero, otherwise 0. It
12238 does not evaluate its second argument if its first argument is neither
12243 @cindex logical and operator
12244 @cindex and operator
12245 Return its first argument if neither argument is null or zero, otherwise
12246 0. It does not evaluate its second argument if its first argument is
12249 @item < <= = == != >= >
12256 @cindex comparison operators
12258 Compare the arguments and return 1 if the relation is true, 0 otherwise.
12259 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
12260 both arguments to integers and do a numeric comparison; if either
12261 conversion fails, it does a lexicographic comparison using the character
12262 collating sequence specified by the @env{LC_COLLATE} locale.
12267 @node Examples of expr
12268 @subsection Examples of using @command{expr}
12270 @cindex examples of @command{expr}
12271 Here are a few examples, including quoting for shell metacharacters.
12273 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
12276 foo=$(expr $foo + 1)
12279 To print the non-directory part of the file name stored in
12280 @code{$fname}, which need not contain a @code{/}:
12283 expr $fname : '.*/\(.*\)' '|' $fname
12286 An example showing that @code{\+} is an operator:
12294 expr abc : 'a\(.\)c'
12296 expr index abcdef cz
12299 @error{} expr: syntax error
12300 expr index + index a
12306 @chapter Redirection
12308 @cindex redirection
12309 @cindex commands for redirection
12311 Unix shells commonly provide several forms of @dfn{redirection}---ways
12312 to change the input source or output destination of a command. But one
12313 useful redirection is performed by a separate command, not by the shell;
12314 it's described here.
12317 * tee invocation:: Redirect output to multiple files or processes.
12321 @node tee invocation
12322 @section @command{tee}: Redirect output to multiple files or processes
12325 @cindex pipe fitting
12326 @cindex destinations, multiple output
12327 @cindex read from stdin and write to stdout and files
12329 The @command{tee} command copies standard input to standard output and also
12330 to any files given as arguments. This is useful when you want not only
12331 to send some data down a pipe, but also to save a copy. Synopsis:
12334 tee [@var{option}]@dots{} [@var{file}]@dots{}
12337 If a file being written to does not already exist, it is created. If a
12338 file being written to already exists, the data it previously contained
12339 is overwritten unless the @option{-a} option is used.
12341 A @var{file} of @samp{-} causes @command{tee} to send another copy of
12342 input to standard output, but this is typically not that useful as the
12343 copies are interleaved.
12345 The program accepts the following options. Also see @ref{Common options}.
12352 Append standard input to the given files rather than overwriting
12356 @itemx --ignore-interrupts
12358 @opindex --ignore-interrupts
12359 Ignore interrupt signals.
12363 The @command{tee} command is useful when you happen to be transferring a large
12364 amount of data and also want to summarize that data without reading
12365 it a second time. For example, when you are downloading a DVD image,
12366 you often want to verify its signature or checksum right away.
12367 The inefficient way to do it is simply:
12370 wget http://example.com/some.iso && sha1sum some.iso
12373 One problem with the above is that it makes you wait for the
12374 download to complete before starting the time-consuming SHA1 computation.
12375 Perhaps even more importantly, the above requires reading
12376 the DVD image a second time (the first was from the network).
12378 The efficient way to do it is to interleave the download
12379 and SHA1 computation. Then, you'll get the checksum for
12380 free, because the entire process parallelizes so well:
12383 # slightly contrived, to demonstrate process substitution
12384 wget -O - http://example.com/dvd.iso \
12385 | tee >(sha1sum > dvd.sha1) > dvd.iso
12388 That makes @command{tee} write not just to the expected output file,
12389 but also to a pipe running @command{sha1sum} and saving the final
12390 checksum in a file named @file{dvd.sha1}.
12392 Note, however, that this example relies on a feature of modern shells
12393 called @dfn{process substitution}
12394 (the @samp{>(command)} syntax, above;
12395 @xref{Process Substitution,,Process Substitution, bashref,
12396 The Bash Reference Manual}.),
12397 so it works with @command{zsh}, @command{bash}, and @command{ksh},
12398 but not with @command{/bin/sh}. So if you write code like this
12399 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
12401 Since the above example writes to one file and one process,
12402 a more conventional and portable use of @command{tee} is even better:
12405 wget -O - http://example.com/dvd.iso \
12406 | tee dvd.iso | sha1sum > dvd.sha1
12409 You can extend this example to make @command{tee} write to two processes,
12410 computing MD5 and SHA1 checksums in parallel. In this case,
12411 process substitution is required:
12414 wget -O - http://example.com/dvd.iso \
12415 | tee >(sha1sum > dvd.sha1) \
12416 >(md5sum > dvd.md5) \
12420 This technique is also useful when you want to make a @emph{compressed}
12421 copy of the contents of a pipe.
12422 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
12423 For a large hierarchy, @samp{du -ak} can run for a long time,
12424 and can easily produce terabytes of data, so you won't want to
12425 rerun the command unnecessarily. Nor will you want to save
12426 the uncompressed output.
12428 Doing it the inefficient way, you can't even start the GUI
12429 until after you've compressed all of the @command{du} output:
12432 du -ak | gzip -9 > /tmp/du.gz
12433 gzip -d /tmp/du.gz | xdiskusage -a
12436 With @command{tee} and process substitution, you start the GUI
12437 right away and eliminate the decompression completely:
12440 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
12443 Finally, if you regularly create more than one type of
12444 compressed tarball at once, for example when @code{make dist} creates
12445 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
12446 there may be a better way.
12447 Typical @command{automake}-generated @file{Makefile} rules create
12448 the two compressed tar archives with commands in sequence, like this
12449 (slightly simplified):
12452 tardir=your-pkg-M.N
12453 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
12454 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12457 However, if the hierarchy you are archiving and compressing is larger
12458 than a couple megabytes, and especially if you are using a multi-processor
12459 system with plenty of memory, then you can do much better by reading the
12460 directory contents only once and running the compression programs in parallel:
12463 tardir=your-pkg-M.N
12464 tar chof - "$tardir" \
12465 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
12466 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12472 @node File name manipulation
12473 @chapter File name manipulation
12475 @cindex file name manipulation
12476 @cindex manipulation of file names
12477 @cindex commands for file name manipulation
12479 This section describes commands that manipulate file names.
12482 * basename invocation:: Strip directory and suffix from a file name.
12483 * dirname invocation:: Strip last file name component.
12484 * pathchk invocation:: Check file name validity and portability.
12485 * mktemp invocation:: Create temporary file or directory.
12486 * realpath invocation:: Print resolved file names.
12490 @node basename invocation
12491 @section @command{basename}: Strip directory and suffix from a file name
12494 @cindex strip directory and suffix from file names
12495 @cindex directory, stripping from file names
12496 @cindex suffix, stripping from file names
12497 @cindex file names, stripping directory and suffix
12498 @cindex leading directory components, stripping
12500 @command{basename} removes any leading directory components from
12501 @var{name}. Synopsis:
12504 basename @var{name} [@var{suffix}]
12505 basename @var{option}... @var{name}...
12508 If @var{suffix} is specified and is identical to the end of @var{name},
12509 it is removed from @var{name} as well. Note that since trailing slashes
12510 are removed prior to suffix matching, @var{suffix} will do nothing if it
12511 contains slashes. @command{basename} prints the result on standard
12514 @c This test is used both here and in the section on dirname.
12515 @macro basenameAndDirname
12516 Together, @command{basename} and @command{dirname} are designed such
12517 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
12518 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
12519 for everything except file names containing a trailing newline.
12521 @basenameAndDirname
12523 POSIX allows the implementation to define the results if
12524 @var{name} is empty or @samp{//}. In the former case, GNU
12525 @command{basename} returns the empty string. In the latter case, the
12526 result is @samp{//} on platforms where @var{//} is distinct from
12527 @var{/}, and @samp{/} on platforms where there is no difference.
12529 The program accepts the following options. Also see @ref{Common options}.
12530 Options must precede operands.
12537 @opindex --multiple
12538 Support more than one argument. Treat every argument as a @var{name}.
12539 With this, an optional @var{suffix} must be specified using the
12540 @option{-s} option.
12542 @item -s @var{suffix}
12543 @itemx --suffix=@var{suffix}
12546 Remove a trailing @var{suffix}.
12547 This option implies the @option{-a} option.
12553 Separate output items with @sc{nul} characters.
12563 basename /usr/bin/sort
12566 basename include/stdio.h .h
12569 basename -s .h include/stdio.h
12571 # Output "stdio" followed by "stdlib"
12572 basename -a -s .h include/stdio.h include/stdlib.h
12576 @node dirname invocation
12577 @section @command{dirname}: Strip last file name component
12580 @cindex directory components, printing
12581 @cindex stripping non-directory suffix
12582 @cindex non-directory suffix, stripping
12584 @command{dirname} prints all but the final slash-delimited component
12585 of each @var{name}. Slashes on either side of the final component are
12586 also removed. If the string contains no slash, @command{dirname}
12587 prints @samp{.} (meaning the current directory). Synopsis:
12590 dirname [@var{option}] @var{name}...
12593 @var{name} need not be a file name, but if it is, this operation
12594 effectively lists the directory that contains the final component,
12595 including the case when the final component is itself a directory.
12597 @basenameAndDirname
12599 POSIX allows the implementation to define the results if
12600 @var{name} is @samp{//}. With GNU @command{dirname}, the
12601 result is @samp{//} on platforms where @var{//} is distinct from
12602 @var{/}, and @samp{/} on platforms where there is no difference.
12604 The program accepts the following option. Also see @ref{Common options}.
12612 Separate output items with @sc{nul} characters.
12621 # Output "/usr/bin".
12622 dirname /usr/bin/sort
12623 dirname /usr/bin//.//
12625 # Output "dir1" followed by "dir2"
12626 dirname dir1/str dir2/str
12633 @node pathchk invocation
12634 @section @command{pathchk}: Check file name validity and portability
12637 @cindex file names, checking validity and portability
12638 @cindex valid file names, checking for
12639 @cindex portable file names, checking for
12641 @command{pathchk} checks validity and portability of file names. Synopsis:
12644 pathchk [@var{option}]@dots{} @var{name}@dots{}
12647 For each @var{name}, @command{pathchk} prints an error message if any of
12648 these conditions is true:
12652 One of the existing directories in @var{name} does not have search
12653 (execute) permission,
12655 The length of @var{name} is larger than the maximum supported by the
12658 The length of one component of @var{name} is longer than
12659 its file system's maximum.
12662 A nonexistent @var{name} is not an error, so long a file with that
12663 name could be created under the above conditions.
12665 The program accepts the following options. Also see @ref{Common options}.
12666 Options must precede operands.
12672 Instead of performing checks based on the underlying file system,
12673 print an error message if any of these conditions is true:
12677 A file name is empty.
12680 A file name contains a character outside the POSIX portable file
12681 name character set, namely, the ASCII letters and digits, @samp{.},
12682 @samp{_}, @samp{-}, and @samp{/}.
12685 The length of a file name or one of its components exceeds the
12686 POSIX minimum limits for portability.
12691 Print an error message if a file name is empty, or if it contains a component
12692 that begins with @samp{-}.
12694 @item --portability
12695 @opindex --portability
12696 Print an error message if a file name is not portable to all POSIX
12697 hosts. This option is equivalent to @samp{-p -P}.
12701 @cindex exit status of @command{pathchk}
12705 0 if all specified file names passed all checks,
12709 @node mktemp invocation
12710 @section @command{mktemp}: Create temporary file or directory
12713 @cindex file names, creating temporary
12714 @cindex directory, creating temporary
12715 @cindex temporary files and directories
12717 @command{mktemp} manages the creation of temporary files and
12718 directories. Synopsis:
12721 mktemp [@var{option}]@dots{} [@var{template}]
12724 Safely create a temporary file or directory based on @var{template},
12725 and print its name. If given, @var{template} must include at least
12726 three consecutive @samp{X}s in the last component. If omitted, the template
12727 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12728 implied. The final run of @samp{X}s in the @var{template} will be replaced
12729 by alpha-numeric characters; thus, on a case-sensitive file system,
12730 and with a @var{template} including a run of @var{n} instances of @samp{X},
12731 there are @samp{62**@var{n}} potential file names.
12733 Older scripts used to create temporary files by simply joining the
12734 name of the program with the process id (@samp{$$}) as a suffix.
12735 However, that naming scheme is easily predictable, and suffers from a
12736 race condition where the attacker can create an appropriately named
12737 symbolic link, such that when the script then opens a handle to what
12738 it thought was an unused file, it is instead modifying an existing
12739 file. Using the same scheme to create a directory is slightly safer,
12740 since the @command{mkdir} will fail if the target already exists, but
12741 it is still inferior because it allows for denial of service attacks.
12742 Therefore, modern scripts should use the @command{mktemp} command to
12743 guarantee that the generated name will be unpredictable, and that
12744 knowledge of the temporary file name implies that the file was created
12745 by the current script and cannot be modified by other users.
12747 When creating a file, the resulting file has read and write
12748 permissions for the current user, but no permissions for the group or
12749 others; these permissions are reduced if the current umask is more
12752 Here are some examples (although note that if you repeat them, you
12753 will most likely get different file names):
12758 Create a temporary file in the current directory.
12765 Create a temporary file with a known suffix.
12767 $ mktemp --suffix=.txt file-XXXX
12769 $ mktemp file-XXXX-XXXX.txt
12774 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12775 but falling back to the current directory rather than @file{/tmp}.
12776 Note that @command{mktemp} does not create fifos, but can create a
12777 secure directory in which the fifo can live. Exit the shell if the
12778 directory or fifo could not be created.
12780 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12782 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12786 Create and use a temporary file if possible, but ignore failure. The
12787 file will reside in the directory named by @env{TMPDIR}, if specified,
12788 or else in @file{/tmp}.
12790 $ file=$(mktemp -q) && @{
12791 > # Safe to use $file only within this block. Use quotes,
12792 > # since $TMPDIR, and thus $file, may contain whitespace.
12793 > echo ... > "$file"
12799 Act as a semi-random character generator (it is not fully random,
12800 since it is impacted by the contents of the current directory). To
12801 avoid security holes, do not use the resulting names to create a file.
12811 The program accepts the following options. Also see @ref{Common options}.
12818 @opindex --directory
12819 Create a directory rather than a file. The directory will have read,
12820 write, and search permissions for the current user, but no permissions
12821 for the group or others; these permissions are reduced if the current
12822 umask is more restrictive.
12828 Suppress diagnostics about failure to create a file or directory. The
12829 exit status will still reflect whether a file was created.
12835 Generate a temporary name that does not name an existing file, without
12836 changing the file system contents. Using the output of this command
12837 to create a new file is inherently unsafe, as there is a window of
12838 time between generating the name and using it where another process
12839 can create an object by the same name.
12842 @itemx --tmpdir[=@var{dir}]
12845 Treat @var{template} relative to the directory @var{dir}. If
12846 @var{dir} is not specified (only possible with the long option
12847 @option{--tmpdir}) or is the empty string, use the value of
12848 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12849 specified, @var{template} must not be absolute. However,
12850 @var{template} can still contain slashes, although intermediate
12851 directories must already exist.
12853 @item --suffix=@var{suffix}
12855 Append @var{suffix} to the @var{template}. @var{suffix} must not
12856 contain slash. If @option{--suffix} is specified, @var{template} must
12857 end in @samp{X}; if it is not specified, then an appropriate
12858 @option{--suffix} is inferred by finding the last @samp{X} in
12859 @var{template}. This option exists for use with the default
12860 @var{template} and for the creation of a @var{suffix} that starts with
12865 Treat @var{template} as a single file relative to the value of
12866 @env{TMPDIR} if available, or to the directory specified by
12867 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12868 contain slashes. This option is deprecated; the use of @option{-p}
12869 without @option{-t} offers better defaults (by favoring the command
12870 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12875 @cindex exit status of @command{mktemp}
12879 0 if the file was created,
12884 @node realpath invocation
12885 @section @command{realpath}: Print the resolved file name.
12888 @cindex file names, canonicalization
12889 @cindex symlinks, resolution
12890 @cindex canonical file name
12891 @cindex canonicalize a file name
12895 @command{realpath} expands all symbolic links and resolves references to
12896 @samp{/./}, @samp{/../} and extra @samp{/} characters. By default,
12897 all but the last component of the specified files must exist. Synopsis:
12900 realpath [@var{option}]@dots{} @var{file}@dots{}
12903 The program accepts the following options. Also see @ref{Common options}.
12908 @itemx --canonicalize-existing
12910 @opindex --canonicalize-existing
12911 Ensure that all components of the specified file names exist.
12912 If any component is missing or unavailable, @command{realpath} will output
12913 a diagnostic unless the @option{-q} option is specified, and exit with a
12914 nonzero exit code. A trailing slash requires that the name resolve to a
12918 @itemx --canonicalize-missing
12920 @opindex --canonicalize-missing
12921 If any component of a specified file name is missing or unavailable,
12922 treat it as a directory.
12928 Symbolic links are resolved in the specified file names,
12929 but they are resolved after any subsequent @samp{..} components are processed.
12934 @opindex --physical
12935 Symbolic links are resolved in the specified file names,
12936 and they are resolved before any subsequent @samp{..} components are processed.
12937 This is the default mode of operation.
12943 Suppress diagnostic messages for specified file names.
12947 @itemx --no-symlinks
12950 @opindex --no-symlinks
12951 Do not resolve symbolic links. Only resolve references to
12952 @samp{/./}, @samp{/../} and remove extra @samp{/} characters.
12953 When combined with the @option{-m} option, realpath operates
12954 only on the file name, and does not touch any actual file.
12960 Separate output items with @sc{nul} characters.
12962 @item --relative-to=@var{file}
12963 @opindex --relative-to
12965 Print the resolved file names relative to the specified file.
12966 Note this option honors the @option{-m} and @option{-e} options
12967 pertaining to file existence.
12969 @item --relative-base=@var{base}
12970 @opindex --relative-base
12971 This option is valid when used with @option{--relative-to}, and will restrict
12972 the output of @option{--relative-to} so that relative names are output,
12973 only when @var{file}s are descendants of @var{base}. Otherwise output the
12974 absolute file name. If @option{--relative-to} was not specified, then
12975 the descendants of @var{base} are printed relative to @var{base}. If
12976 @option{--relative-to} is specified, then that directory must be a
12977 descendant of @var{base} for this option to have an effect.
12978 Note: this option honors the @option{-m} and @option{-e}
12979 options pertaining to file existence. For example:
12982 realpath --relative-to=/usr /tmp /usr/bin
12985 realpath --relative-base=/usr /tmp /usr/bin
12992 @cindex exit status of @command{realpath}
12996 0 if all file names were printed without issue.
13001 @node Working context
13002 @chapter Working context
13004 @cindex working context
13005 @cindex commands for printing the working context
13007 This section describes commands that display or alter the context in
13008 which you are working: the current directory, the terminal settings, and
13009 so forth. See also the user-related commands in the next section.
13012 * pwd invocation:: Print working directory.
13013 * stty invocation:: Print or change terminal characteristics.
13014 * printenv invocation:: Print environment variables.
13015 * tty invocation:: Print file name of terminal on standard input.
13019 @node pwd invocation
13020 @section @command{pwd}: Print working directory
13023 @cindex print name of current directory
13024 @cindex current working directory, printing
13025 @cindex working directory, printing
13028 @command{pwd} prints the name of the current directory. Synopsis:
13031 pwd [@var{option}]@dots{}
13034 The program accepts the following options. Also see @ref{Common options}.
13041 If the contents of the environment variable @env{PWD} provide an
13042 absolute name of the current directory with no @samp{.} or @samp{..}
13043 components, but possibly with symbolic links, then output those
13044 contents. Otherwise, fall back to default @option{-P} handling.
13049 @opindex --physical
13050 Print a fully resolved name for the current directory. That is, all
13051 components of the printed name will be actual directory names---none
13052 will be symbolic links.
13055 @cindex symbolic links and @command{pwd}
13056 If @option{-L} and @option{-P} are both given, the last one takes
13057 precedence. If neither option is given, then this implementation uses
13058 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
13059 environment variable is set.
13061 @mayConflictWithShellBuiltIn{pwd}
13066 @node stty invocation
13067 @section @command{stty}: Print or change terminal characteristics
13070 @cindex change or print terminal settings
13071 @cindex terminal settings
13072 @cindex line settings of terminal
13074 @command{stty} prints or changes terminal characteristics, such as baud rate.
13078 stty [@var{option}] [@var{setting}]@dots{}
13079 stty [@var{option}]
13082 If given no line settings, @command{stty} prints the baud rate, line
13083 discipline number (on systems that support it), and line settings
13084 that have been changed from the values set by @samp{stty sane}.
13085 By default, mode reading and setting are performed on the tty line
13086 connected to standard input, although this can be modified by the
13087 @option{--file} option.
13089 @command{stty} accepts many non-option arguments that change aspects of
13090 the terminal line operation, as described below.
13092 The program accepts the following options. Also see @ref{Common options}.
13099 Print all current settings in human-readable form. This option may not
13100 be used in combination with any line settings.
13102 @item -F @var{device}
13103 @itemx --file=@var{device}
13106 Set the line opened by the file name specified in @var{device} instead of
13107 the tty line connected to standard input. This option is necessary
13108 because opening a POSIX tty requires use of the
13109 @code{O_NONDELAY} flag to prevent a POSIX tty from blocking
13110 until the carrier detect line is high if
13111 the @code{clocal} flag is not set. Hence, it is not always possible
13112 to allow the shell to open the device in the traditional manner.
13118 @cindex machine-readable @command{stty} output
13119 Print all current settings in a form that can be used as an argument to
13120 another @command{stty} command to restore the current settings. This option
13121 may not be used in combination with any line settings.
13125 Many settings can be turned off by preceding them with a @samp{-}.
13126 Such arguments are marked below with ``May be negated'' in their
13127 description. The descriptions themselves refer to the positive
13128 case, that is, when @emph{not} negated (unless stated otherwise,
13131 Some settings are not available on all POSIX systems, since they use
13132 extensions. Such arguments are marked below with
13133 ``Non-POSIX'' in their description. On non-POSIX
13134 systems, those or other settings also may not
13135 be available, but it's not feasible to document all the variations: just
13141 * Control:: Control settings
13142 * Input:: Input settings
13143 * Output:: Output settings
13144 * Local:: Local settings
13145 * Combination:: Combination settings
13146 * Characters:: Special characters
13147 * Special:: Special settings
13152 @subsection Control settings
13154 @cindex control settings
13160 @cindex two-way parity
13161 Generate parity bit in output and expect parity bit in input.
13167 @cindex even parity
13168 Set odd parity (even if negated). May be negated.
13175 @cindex character size
13176 @cindex eight-bit characters
13177 Set character size to 5, 6, 7, or 8 bits.
13182 Send a hangup signal when the last process closes the tty. May be
13188 Use two stop bits per character (one if negated). May be negated.
13192 Allow input to be received. May be negated.
13196 @cindex modem control
13197 Disable modem control signals. May be negated.
13201 @cindex hardware flow control
13202 @cindex flow control, hardware
13203 @cindex RTS/CTS flow control
13204 Enable RTS/CTS flow control. Non-POSIX@. May be negated.
13209 @subsection Input settings
13211 @cindex input settings
13212 These settings control operations on data received from the terminal.
13217 @cindex breaks, ignoring
13218 Ignore break characters. May be negated.
13222 @cindex breaks, cause interrupts
13223 Make breaks cause an interrupt signal. May be negated.
13227 @cindex parity, ignoring
13228 Ignore characters with parity errors. May be negated.
13232 @cindex parity errors, marking
13233 Mark parity errors (with a 255-0-character sequence). May be negated.
13237 Enable input parity checking. May be negated.
13241 @cindex eight-bit input
13242 Clear high (8th) bit of input characters. May be negated.
13246 @cindex newline, translating to return
13247 Translate newline to carriage return. May be negated.
13251 @cindex return, ignoring
13252 Ignore carriage return. May be negated.
13256 @cindex return, translating to newline
13257 Translate carriage return to newline. May be negated.
13261 @cindex input encoding, UTF-8
13262 Assume input characters are UTF-8 encoded. May be negated.
13266 @kindex C-s/C-q flow control
13267 @cindex XON/XOFF flow control
13268 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
13275 @cindex software flow control
13276 @cindex flow control, software
13277 Enable sending of @code{stop} character when the system input buffer
13278 is almost full, and @code{start} character when it becomes almost
13279 empty again. May be negated.
13283 @cindex uppercase, translating to lowercase
13284 Translate uppercase characters to lowercase. Non-POSIX@. May be
13285 negated. Note ilcuc is not implemented, as one would not be able to issue
13286 almost any (lowercase) Unix command, after invoking it.
13290 Allow any character to restart output (only the start character
13291 if negated). Non-POSIX@. May be negated.
13295 @cindex beeping at input buffer full
13296 Enable beeping and not flushing input buffer if a character arrives
13297 when the input buffer is full. Non-POSIX@. May be negated.
13302 @subsection Output settings
13304 @cindex output settings
13305 These settings control operations on data sent to the terminal.
13310 Postprocess output. May be negated.
13314 @cindex lowercase, translating to output
13315 Translate lowercase characters to uppercase. Non-POSIX@. May be
13316 negated. (Note ouclc is not currently implemented.)
13320 @cindex return, translating to newline
13321 Translate carriage return to newline. Non-POSIX@. May be negated.
13325 @cindex newline, translating to crlf
13326 Translate newline to carriage return-newline. Non-POSIX@. May be
13331 Do not print carriage returns in the first column. Non-POSIX@.
13336 Newline performs a carriage return. Non-POSIX@. May be negated.
13340 @cindex pad instead of timing for delaying
13341 Use fill (padding) characters instead of timing for delays.
13347 @cindex pad character
13348 Use ASCII @sc{del} characters for fill instead of
13349 ASCII @sc{nul} characters. Non-POSIX@.
13355 Newline delay style. Non-POSIX.
13362 Carriage return delay style. Non-POSIX.
13368 @opindex tab@var{n}
13369 Horizontal tab delay style. Non-POSIX.
13374 Backspace delay style. Non-POSIX.
13379 Vertical tab delay style. Non-POSIX.
13384 Form feed delay style. Non-POSIX.
13389 @subsection Local settings
13391 @cindex local settings
13396 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
13397 characters. May be negated.
13401 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
13402 special characters. May be negated.
13406 Enable non-POSIX special characters. May be negated.
13410 Echo input characters. May be negated.
13416 Echo @code{erase} characters as backspace-space-backspace. May be
13421 @cindex newline echoing after @code{kill}
13422 Echo a newline after a @code{kill} character. May be negated.
13426 @cindex newline, echoing
13427 Echo newline even if not echoing other characters. May be negated.
13431 @cindex flushing, disabling
13432 Disable flushing after @code{interrupt} and @code{quit} special
13433 characters. May be negated.
13437 @cindex case translation
13438 Enable input and output of uppercase characters by preceding their
13439 lowercase equivalents with @samp{\}, when @code{icanon} is set.
13440 Non-POSIX@. May be negated.
13444 @cindex background jobs, stopping at terminal write
13445 Stop background jobs that try to write to the terminal. Non-POSIX@.
13452 Echo erased characters backward, between @samp{\} and @samp{/}.
13453 Non-POSIX@. May be negated.
13459 @cindex control characters, using @samp{^@var{c}}
13460 @cindex hat notation for control characters
13461 Echo control characters in hat notation (@samp{^@var{c}}) instead
13462 of literally. Non-POSIX@. May be negated.
13468 Echo the @code{kill} special character by erasing each character on
13469 the line as indicated by the @code{echoprt} and @code{echoe} settings,
13470 instead of by the @code{echoctl} and @code{echok} settings.
13477 @subsection Combination settings
13479 @cindex combination settings
13480 Combination settings:
13487 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
13488 as @code{-parenb cs8}.
13492 Same as @code{parenb parodd cs7}. May be negated. If negated, same
13493 as @code{-parenb cs8}.
13497 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
13498 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
13502 Reset the @code{erase} and @code{kill} special characters to their default
13509 @c This is too long to write inline.
13511 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
13512 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
13513 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
13514 ff0 isig icanon iexten echo echoe echok -echonl
13515 -noflsh -xcase -tostop -echoprt echoctl echoke
13519 and also sets all special characters to their default values.
13523 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
13524 sets the @code{eof} and @code{eol} characters to their default values
13525 if they are the same as the @code{min} and @code{time} characters.
13526 May be negated. If negated, same as @code{raw}.
13533 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
13534 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
13535 -imaxbel -opost -isig -icanon -xcase min 1 time 0
13539 May be negated. If negated, same as @code{cooked}.
13543 Same as @option{-icanon}. May be negated. If negated, same as
13548 @cindex eight-bit characters
13549 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
13550 same as @code{parenb istrip cs7}.
13554 Same as @option{-parenb -istrip -opost cs8}. May be negated.
13555 If negated, same as @code{parenb istrip opost cs7}.
13559 Same as @option{-ixany}. Non-POSIX@. May be negated.
13563 Same as @code{tab0}. Non-POSIX@. May be negated. If negated, same
13570 Same as @code{xcase iuclc olcuc}. Non-POSIX@. May be negated.
13571 (Used for terminals with uppercase characters only.)
13575 Same as @code{echoe echoctl echoke}.
13579 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
13584 @subsection Special characters
13586 @cindex special characters
13587 @cindex characters, special
13589 The special characters' default values vary from system to system.
13590 They are set with the syntax @samp{name value}, where the names are
13591 listed below and the value can be given either literally, in hat
13592 notation (@samp{^@var{c}}), or as an integer which may start with
13593 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
13594 any other digit to indicate decimal.
13596 @cindex disabling special characters
13597 @kindex u@r{, and disabling special characters}
13598 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
13599 special character. (This is incompatible with Ultrix @command{stty},
13600 which uses a value of @samp{u} to disable a special character. GNU
13601 @command{stty} treats a value @samp{u} like any other, namely to set that
13602 special character to @key{U}.)
13608 Send an interrupt signal.
13612 Send a quit signal.
13616 Erase the last character typed.
13620 Erase the current line.
13624 Send an end of file (terminate the input).
13632 Alternate character to end the line. Non-POSIX.
13636 Switch to a different shell layer. Non-POSIX.
13640 Restart the output after stopping it.
13648 Send a terminal stop signal.
13652 Send a terminal stop signal after flushing the input. Non-POSIX.
13656 Redraw the current line. Non-POSIX.
13660 Erase the last word typed. Non-POSIX.
13664 Enter the next character typed literally, even if it is a special
13665 character. Non-POSIX.
13670 @subsection Special settings
13672 @cindex special settings
13677 Set the minimum number of characters that will satisfy a read until
13678 the time value has expired, when @option{-icanon} is set.
13682 Set the number of tenths of a second before reads time out if the minimum
13683 number of characters have not been read, when @option{-icanon} is set.
13685 @item ispeed @var{n}
13687 Set the input speed to @var{n}.
13689 @item ospeed @var{n}
13691 Set the output speed to @var{n}.
13695 Tell the tty kernel driver that the terminal has @var{n} rows.
13699 @itemx columns @var{n}
13702 Tell the kernel that the terminal has @var{n} columns. Non-POSIX.
13708 Print the number of rows and columns that the kernel thinks the
13709 terminal has. (Systems that don't support rows and columns in the kernel
13710 typically use the environment variables @env{LINES} and @env{COLUMNS}
13711 instead; however, GNU @command{stty} does not know anything about them.)
13716 Use line discipline @var{n}. Non-POSIX.
13720 Print the terminal speed.
13723 @cindex baud rate, setting
13724 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13725 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13726 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13727 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13728 support higher speeds. The @command{stty} command includes support
13745 4000000 where the system supports these.
13746 0 hangs up the line if @option{-clocal} is set.
13750 @node printenv invocation
13751 @section @command{printenv}: Print all or some environment variables
13754 @cindex printing all or some environment variables
13755 @cindex environment variables, printing
13757 @command{printenv} prints environment variable values. Synopsis:
13760 printenv [@var{option}] [@var{variable}]@dots{}
13763 If no @var{variable}s are specified, @command{printenv} prints the value of
13764 every environment variable. Otherwise, it prints the value of each
13765 @var{variable} that is set, and nothing for those that are not set.
13767 The program accepts the following option. Also see @ref{Common options}.
13775 @cindex exit status of @command{printenv}
13779 0 if all variables specified were found
13780 1 if at least one specified variable was not found
13781 2 if a write error occurred
13785 @node tty invocation
13786 @section @command{tty}: Print file name of terminal on standard input
13789 @cindex print terminal file name
13790 @cindex terminal file name, printing
13792 @command{tty} prints the file name of the terminal connected to its standard
13793 input. It prints @samp{not a tty} if standard input is not a terminal.
13797 tty [@var{option}]@dots{}
13800 The program accepts the following option. Also see @ref{Common options}.
13810 Print nothing; only return an exit status.
13814 @cindex exit status of @command{tty}
13818 0 if standard input is a terminal
13819 1 if standard input is not a terminal
13820 2 if given incorrect arguments
13821 3 if a write error occurs
13825 @node User information
13826 @chapter User information
13828 @cindex user information, commands for
13829 @cindex commands for printing user information
13831 This section describes commands that print user-related information:
13832 logins, groups, and so forth.
13835 * id invocation:: Print user identity.
13836 * logname invocation:: Print current login name.
13837 * whoami invocation:: Print effective user ID.
13838 * groups invocation:: Print group names a user is in.
13839 * users invocation:: Print login names of users currently logged in.
13840 * who invocation:: Print who is currently logged in.
13844 @node id invocation
13845 @section @command{id}: Print user identity
13848 @cindex real user and group IDs, printing
13849 @cindex effective user and group IDs, printing
13850 @cindex printing real and effective user and group IDs
13852 @command{id} prints information about the given user, or the process
13853 running it if no user is specified. Synopsis:
13856 id [@var{option}]@dots{} [@var{username}]
13859 @vindex POSIXLY_CORRECT
13860 By default, it prints the real user ID, real group ID, effective user ID
13861 if different from the real user ID, effective group ID if different from
13862 the real group ID, and supplemental group IDs.
13863 In addition, if SELinux
13864 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13865 then print @samp{context=@var{c}}, where @var{c} is the security context.
13867 Each of these numeric values is preceded by an identifying string and
13868 followed by the corresponding user or group name in parentheses.
13870 The options cause @command{id} to print only part of the above information.
13871 Also see @ref{Common options}.
13878 Print only the group ID.
13884 Print only the group ID and the supplementary groups.
13890 Print the user or group name instead of the ID number. Requires
13891 @option{-u}, @option{-g}, or @option{-G}.
13897 Print the real, instead of effective, user or group ID@. Requires
13898 @option{-u}, @option{-g}, or @option{-G}.
13904 Print only the user ID.
13911 @cindex security context
13912 Print only the security context of the current user.
13913 If SELinux is disabled then print a warning and
13914 set the exit status to 1.
13920 @macro primaryAndSupplementaryGroups{cmd,arg}
13921 Primary and supplementary groups for a process are normally inherited
13922 from its parent and are usually unchanged since login. This means
13923 that if you change the group database after logging in, @command{\cmd\}
13924 will not reflect your changes within your existing login session.
13925 Running @command{\cmd\} with a \arg\ causes the user and group
13926 database to be consulted afresh, and so will give a different result.
13928 @primaryAndSupplementaryGroups{id,user argument}
13930 @node logname invocation
13931 @section @command{logname}: Print current login name
13934 @cindex printing user's login name
13935 @cindex login name, printing
13936 @cindex user name, printing
13939 @command{logname} prints the calling user's name, as found in a
13940 system-maintained file (often @file{/var/run/utmp} or
13941 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13942 for the calling process, @command{logname} prints
13943 an error message and exits with a status of 1.
13945 The only options are @option{--help} and @option{--version}. @xref{Common
13951 @node whoami invocation
13952 @section @command{whoami}: Print effective user ID
13955 @cindex effective user ID, printing
13956 @cindex printing the effective user ID
13958 @command{whoami} prints the user name associated with the current
13959 effective user ID@. It is equivalent to the command @samp{id -un}.
13961 The only options are @option{--help} and @option{--version}. @xref{Common
13967 @node groups invocation
13968 @section @command{groups}: Print group names a user is in
13971 @cindex printing groups a user is in
13972 @cindex supplementary groups, printing
13974 @command{groups} prints the names of the primary and any supplementary
13975 groups for each given @var{username}, or the current process if no names
13976 are given. If more than one name is given, the name of each user is
13978 the list of that user's groups and the user name is separated from the
13979 group list by a colon. Synopsis:
13982 groups [@var{username}]@dots{}
13985 The group lists are equivalent to the output of the command @samp{id -Gn}.
13987 @primaryAndSupplementaryGroups{groups,list of users}
13989 The only options are @option{--help} and @option{--version}. @xref{Common
13995 @node users invocation
13996 @section @command{users}: Print login names of users currently logged in
13999 @cindex printing current usernames
14000 @cindex usernames, printing current
14002 @cindex login sessions, printing users with
14003 @command{users} prints on a single line a blank-separated list of user
14004 names of users currently logged in to the current host. Each user name
14005 corresponds to a login session, so if a user has more than one login
14006 session, that user's name will appear the same number of times in the
14015 With no @var{file} argument, @command{users} extracts its information from
14016 a system-maintained file (often @file{/var/run/utmp} or
14017 @file{/etc/utmp}). If a file argument is given, @command{users} uses
14018 that file instead. A common choice is @file{/var/log/wtmp}.
14020 The only options are @option{--help} and @option{--version}. @xref{Common
14026 @node who invocation
14027 @section @command{who}: Print who is currently logged in
14030 @cindex printing current user information
14031 @cindex information, about current users
14033 @command{who} prints information about users who are currently logged on.
14037 @command{who} [@var{option}] [@var{file}] [am i]
14040 @cindex terminal lines, currently used
14042 @cindex remote hostname
14043 If given no non-option arguments, @command{who} prints the following
14044 information for each user currently logged on: login name, terminal
14045 line, login time, and remote hostname or X display.
14049 If given one non-option argument, @command{who} uses that instead of
14050 a default system-maintained file (often @file{/var/run/utmp} or
14051 @file{/etc/utmp}) as the name of the file containing the record of
14052 users logged on. @file{/var/log/wtmp} is commonly given as an argument
14053 to @command{who} to look at who has previously logged on.
14057 If given two non-option arguments, @command{who} prints only the entry
14058 for the user running it (determined from its standard input), preceded
14059 by the hostname. Traditionally, the two arguments given are @samp{am
14060 i}, as in @samp{who am i}.
14063 Time stamps are listed according to the time zone rules specified by
14064 the @env{TZ} environment variable, or by the system default rules if
14065 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
14066 with @env{TZ}, libc, The GNU C Library Reference Manual}.
14068 The program accepts the following options. Also see @ref{Common options}.
14076 Same as @samp{-b -d --login -p -r -t -T -u}.
14082 Print the date and time of last system boot.
14088 Print information corresponding to dead processes.
14094 Print a line of column headings.
14100 List only the entries that correspond to processes via which the
14101 system is waiting for a user to login. The user name is always @samp{LOGIN}.
14105 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
14106 is not the default because it can cause significant delays on systems with
14107 automatic dial-up internet access.
14111 Same as @samp{who am i}.
14117 List active processes spawned by init.
14123 Print only the login names and the number of users logged on.
14124 Overrides all other options.
14129 @opindex --runlevel
14130 Print the current (and maybe previous) run-level of the init process.
14134 Ignored; for compatibility with other versions of @command{who}.
14140 Print last system clock change.
14145 After the login time, print the number of hours and minutes that the
14146 user has been idle. @samp{.} means the user was active in the last minute.
14147 @samp{old} means the user has been idle for more than 24 hours.
14158 @opindex --writable
14159 @cindex message status
14160 @pindex write@r{, allowed}
14161 After each login name print a character indicating the user's message status:
14164 @samp{+} allowing @code{write} messages
14165 @samp{-} disallowing @code{write} messages
14166 @samp{?} cannot find terminal device
14174 @node System context
14175 @chapter System context
14177 @cindex system context
14178 @cindex context, system
14179 @cindex commands for system context
14181 This section describes commands that print or change system-wide
14185 * date invocation:: Print or set system date and time.
14186 * arch invocation:: Print machine hardware name.
14187 * nproc invocation:: Print the number of processors.
14188 * uname invocation:: Print system information.
14189 * hostname invocation:: Print or set system name.
14190 * hostid invocation:: Print numeric host identifier.
14191 * uptime invocation:: Print system uptime and load.
14194 @node date invocation
14195 @section @command{date}: Print or set system date and time
14198 @cindex time, printing or setting
14199 @cindex printing the current time
14204 date [@var{option}]@dots{} [+@var{format}]
14205 date [-u|--utc|--universal] @c this avoids a newline in the output
14206 [ MMDDhhmm[[CC]YY][.ss] ]
14210 Invoking @command{date} with no @var{format} argument is equivalent to invoking
14211 it with a default format that depends on the @env{LC_TIME} locale category.
14212 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
14213 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
14216 Normally, @command{date} uses the time zone rules indicated by the
14217 @env{TZ} environment variable, or the system default rules if @env{TZ}
14218 is not set. @xref{TZ Variable,, Specifying the Time Zone with
14219 @env{TZ}, libc, The GNU C Library Reference Manual}.
14221 @findex strftime @r{and @command{date}}
14222 @cindex time formats
14223 @cindex formatting times
14224 If given an argument that starts with a @samp{+}, @command{date} prints the
14225 current date and time (or the date and time specified by the
14226 @option{--date} option, see below) in the format defined by that argument,
14227 which is similar to that of the @code{strftime} function. Except for
14228 conversion specifiers, which start with @samp{%}, characters in the
14229 format string are printed unchanged. The conversion specifiers are
14235 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
14236 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
14237 * Literal conversion specifiers:: %[%nt]
14238 * Padding and other flags:: Pad with zeros, spaces, etc.
14239 * Setting the time:: Changing the system clock.
14240 * Options for date:: Instead of the current time.
14242 * Date input formats:: Specifying date strings.
14244 * Examples of date:: Examples.
14247 @node Time conversion specifiers
14248 @subsection Time conversion specifiers
14250 @cindex time conversion specifiers
14251 @cindex conversion specifiers, time
14253 @command{date} conversion specifiers related to times.
14257 hour (@samp{00}@dots{}@samp{23})
14259 hour (@samp{01}@dots{}@samp{12})
14261 hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}@.
14262 This is a GNU extension.
14264 hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}@.
14265 This is a GNU extension.
14267 minute (@samp{00}@dots{}@samp{59})
14269 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
14270 This is a GNU extension.
14272 locale's equivalent of either @samp{AM} or @samp{PM};
14273 blank in many locales.
14274 Noon is treated as @samp{PM} and midnight as @samp{AM}.
14276 like @samp{%p}, except lower case.
14277 This is a GNU extension.
14279 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
14281 24-hour hour and minute. Same as @samp{%H:%M}.
14283 @cindex epoch, seconds since
14284 @cindex seconds since the epoch
14285 @cindex beginning of time
14286 @cindex leap seconds
14287 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC@.
14288 Leap seconds are not counted unless leap second support is available.
14289 @xref{%s-examples}, for examples.
14290 This is a GNU extension.
14292 @cindex leap seconds
14293 second (@samp{00}@dots{}@samp{60}).
14294 This may be @samp{60} if leap seconds are supported.
14296 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
14298 locale's time representation (e.g., @samp{23:13:48})
14300 @w{RFC 2822/ISO 8601} style numeric time zone
14301 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
14302 time zone is determinable. This value reflects the numeric time zone
14303 appropriate for the current time, using the time zone rules specified
14304 by the @env{TZ} environment variable.
14305 The time (and optionally, the time zone rules) can be overridden
14306 by the @option{--date} option.
14308 @w{RFC 3339/ISO 8601} style numeric time zone with
14309 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
14310 zone is determinable.
14311 This is a GNU extension.
14313 Numeric time zone to the nearest second with @samp{:} (e.g.,
14314 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
14316 This is a GNU extension.
14318 Numeric time zone with @samp{:} using the minimum necessary precision
14319 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
14320 no time zone is determinable.
14321 This is a GNU extension.
14323 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
14324 time zone is determinable. See @samp{%z} for how it is determined.
14328 @node Date conversion specifiers
14329 @subsection Date conversion specifiers
14331 @cindex date conversion specifiers
14332 @cindex conversion specifiers, date
14334 @command{date} conversion specifiers related to dates.
14338 locale's abbreviated weekday name (e.g., @samp{Sun})
14340 locale's full weekday name, variable length (e.g., @samp{Sunday})
14342 locale's abbreviated month name (e.g., @samp{Jan})
14344 locale's full month name, variable length (e.g., @samp{January})
14346 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
14348 century. This is like @samp{%Y}, except the last two digits are omitted.
14349 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
14350 and is @samp{-0} if @samp{%Y} is @samp{-001}.
14351 It is normally at least two characters, but it may be more.
14353 day of month (e.g., @samp{01})
14355 date; same as @samp{%m/%d/%y}
14357 day of month, space padded; same as @samp{%_d}
14359 full date in ISO 8601 format; same as @samp{%Y-%m-%d}.
14360 This is a good choice for a date format, as it is standard and
14361 is easy to sort in the usual case where years are in the range
14364 year corresponding to the ISO week number, but without the century
14365 (range @samp{00} through @samp{99}). This has the same format and value
14366 as @samp{%y}, except that if the ISO week number (see
14368 to the previous or next year, that year is used instead.
14370 year corresponding to the ISO week number. This has the
14371 same format and value as @samp{%Y}, except that if the ISO
14373 @samp{%V}) belongs to the previous or next year, that year is used
14375 It is normally useful only if @samp{%V} is also used;
14376 for example, the format @samp{%G-%m-%d} is probably a mistake,
14377 since it combines the ISO week number year with the conventional month and day.
14381 day of year (@samp{001}@dots{}@samp{366})
14383 month (@samp{01}@dots{}@samp{12})
14385 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
14387 week number of year, with Sunday as the first day of the week
14388 (@samp{00}@dots{}@samp{53}).
14389 Days in a new year preceding the first Sunday are in week zero.
14391 ISO week number, that is, the
14392 week number of year, with Monday as the first day of the week
14393 (@samp{01}@dots{}@samp{53}).
14394 If the week containing January 1 has four or more days in
14395 the new year, then it is considered week 1; otherwise, it is week 53 of
14396 the previous year, and the next week is week 1. (See the ISO 8601
14399 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
14401 week number of year, with Monday as first day of week
14402 (@samp{00}@dots{}@samp{53}).
14403 Days in a new year preceding the first Monday are in week zero.
14405 locale's date representation (e.g., @samp{12/31/99})
14407 last two digits of year (@samp{00}@dots{}@samp{99})
14409 year. This is normally at least four characters, but it may be more.
14410 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
14411 precedes year @samp{0000}.
14415 @node Literal conversion specifiers
14416 @subsection Literal conversion specifiers
14418 @cindex literal conversion specifiers
14419 @cindex conversion specifiers, literal
14421 @command{date} conversion specifiers that produce literal strings.
14433 @node Padding and other flags
14434 @subsection Padding and other flags
14436 @cindex numeric field padding
14437 @cindex padding of numeric fields
14438 @cindex fields, padding numeric
14440 Unless otherwise specified, @command{date} normally pads numeric fields
14441 with zeros, so that, for
14442 example, numeric months are always output as two digits.
14443 Seconds since the epoch are not padded, though,
14444 since there is no natural width for them.
14446 As a GNU extension, @command{date} recognizes any of the
14447 following optional flags after the @samp{%}:
14451 (hyphen) Do not pad the field; useful if the output is intended for
14454 (underscore) Pad with spaces; useful if you need a fixed
14455 number of characters in the output, but zeros are too distracting.
14457 (zero) Pad with zeros even if the conversion specifier
14458 would normally pad with spaces.
14460 Use upper case characters if possible.
14462 Use opposite case characters if possible.
14463 A field that is normally upper case becomes lower case, and vice versa.
14467 Here are some examples of padding:
14470 date +%d/%m -d "Feb 1"
14472 date +%-d/%-m -d "Feb 1"
14474 date +%_d/%_m -d "Feb 1"
14478 As a GNU extension, you can specify the field width
14479 (after any flag, if present) as a decimal number. If the natural size of the
14480 output of the field has less than the specified number of characters,
14481 the result is written right adjusted and padded to the given
14482 size. For example, @samp{%9B} prints the right adjusted month name in
14483 a field of width 9.
14485 An optional modifier can follow the optional flag and width
14486 specification. The modifiers are:
14490 Use the locale's alternate representation for date and time. This
14491 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
14492 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
14493 example, @samp{%Ex} might yield a date format based on the Japanese
14497 Use the locale's alternate numeric symbols for numbers. This modifier
14498 applies only to numeric conversion specifiers.
14501 If the format supports the modifier but no alternate representation
14502 is available, it is ignored.
14505 @node Setting the time
14506 @subsection Setting the time
14508 @cindex setting the time
14509 @cindex time setting
14510 @cindex appropriate privileges
14512 If given an argument that does not start with @samp{+}, @command{date} sets
14513 the system clock to the date and time specified by that argument (as
14514 described below). You must have appropriate privileges to set the
14515 system clock. Note for changes to persist across a reboot, the
14516 hardware clock may need to be updated from the system clock, which
14517 might not happen automatically on your system.
14519 The argument must consist entirely of digits, which have the following
14532 first two digits of year (optional)
14534 last two digits of year (optional)
14539 Note, the @option{--date} and @option{--set} options may not be used with an
14540 argument in the above format. The @option{--universal} option may be used
14541 with such an argument to indicate that the specified date and time are
14542 relative to Coordinated Universal Time rather than to the local time zone.
14545 @node Options for date
14546 @subsection Options for @command{date}
14548 @cindex @command{date} options
14549 @cindex options for @command{date}
14551 The program accepts the following options. Also see @ref{Common options}.
14555 @item -d @var{datestr}
14556 @itemx --date=@var{datestr}
14559 @cindex parsing date strings
14560 @cindex date strings, parsing
14561 @cindex arbitrary date strings, parsing
14564 @opindex next @var{day}
14565 @opindex last @var{day}
14566 Display the date and time specified in @var{datestr} instead of the
14567 current date and time. @var{datestr} can be in almost any common
14568 format. It can contain month names, time zones, @samp{am} and @samp{pm},
14569 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
14570 14:19:13.489392193 +0530"} specifies the instant of time that is
14571 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
14572 time zone that is 5 hours and 30 minutes east of UTC.@*
14573 Note: input currently must be in locale independent format. E.g., the
14574 LC_TIME=C below is needed to print back the correct date in many locales:
14576 date -d "$(LC_TIME=C date)"
14578 @xref{Date input formats}.
14580 @item -f @var{datefile}
14581 @itemx --file=@var{datefile}
14584 Parse each line in @var{datefile} as with @option{-d} and display the
14585 resulting date and time. If @var{datefile} is @samp{-}, use standard
14586 input. This is useful when you have many dates to process, because the
14587 system overhead of starting up the @command{date} executable many times can
14590 @item -I[@var{timespec}]
14591 @itemx --iso-8601[=@var{timespec}]
14592 @opindex -I[@var{timespec}]
14593 @opindex --iso-8601[=@var{timespec}]
14594 Display the date using the ISO 8601 format, @samp{%Y-%m-%d}.
14596 The argument @var{timespec} specifies the number of additional
14597 terms of the time to include. It can be one of the following:
14600 Print just the date. This is the default if @var{timespec} is omitted.
14603 Append the hour of the day to the date.
14606 Append the hours and minutes.
14609 Append the hours, minutes and seconds.
14612 Append the hours, minutes, seconds and nanoseconds.
14615 If showing any time terms, then include the time zone using the format
14618 @item -r @var{file}
14619 @itemx --reference=@var{file}
14621 @opindex --reference
14622 Display the date and time of the last modification of @var{file},
14623 instead of the current date and time.
14630 @opindex --rfc-2822
14631 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
14632 %z}, evaluated in the C locale so abbreviations are always in English.
14636 Fri, 09 Sep 2005 13:51:39 -0700
14639 This format conforms to
14640 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
14642 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
14643 current and previous standards for Internet email.
14645 @item --rfc-3339=@var{timespec}
14646 @opindex --rfc-3339=@var{timespec}
14647 Display the date using a format specified by
14648 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
14649 RFC 3339}. This is a subset of the ISO 8601
14650 format, except that it also permits applications to use a space rather
14651 than a @samp{T} to separate dates from times. Unlike the other
14652 standard formats, RFC 3339 format is always suitable as
14653 input for the @option{--date} (@option{-d}) and @option{--file}
14654 (@option{-f}) options, regardless of the current locale.
14656 The argument @var{timespec} specifies how much of the time to include.
14657 It can be one of the following:
14661 Print just the full-date, e.g., @samp{2005-09-14}.
14662 This is equivalent to the format @samp{%Y-%m-%d}.
14665 Print the full-date and full-time separated by a space, e.g.,
14666 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
14667 time-offset; here the @samp{+05:30} means that local time is five
14668 hours and thirty minutes east of UTC@. This is equivalent to
14669 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
14672 Like @samp{seconds}, but also print nanoseconds, e.g.,
14673 @samp{2005-09-14 00:56:06.998458565+05:30}.
14674 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
14678 @item -s @var{datestr}
14679 @itemx --set=@var{datestr}
14682 Set the date and time to @var{datestr}. See @option{-d} above.
14683 See also @ref{Setting the time}.
14690 @opindex --universal
14691 @cindex Coordinated Universal Time
14693 @cindex Greenwich Mean Time
14695 @cindex leap seconds
14697 Use Coordinated Universal Time (UTC) by operating as if the
14698 @env{TZ} environment variable were set to the string @samp{UTC0}.
14700 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
14701 historical reasons.
14702 Typically, systems ignore leap seconds and thus implement an
14703 approximation to UTC rather than true UTC.
14707 @node Examples of date
14708 @subsection Examples of @command{date}
14710 @cindex examples of @command{date}
14712 Here are a few examples. Also see the documentation for the @option{-d}
14713 option in the previous section.
14718 To print the date of the day before yesterday:
14721 date --date='2 days ago'
14725 To print the date of the day three months and one day hence:
14728 date --date='3 months 1 day'
14732 To print the day of year of Christmas in the current year:
14735 date --date='25 Dec' +%j
14739 To print the current full month name and the day of the month:
14745 But this may not be what you want because for the first nine days of
14746 the month, the @samp{%d} expands to a zero-padded two-digit field,
14747 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14750 To print a date without the leading zero for one-digit days
14751 of the month, you can use the (GNU extension)
14752 @samp{-} flag to suppress
14753 the padding altogether:
14756 date -d 1may '+%B %-d
14760 To print the current date and time in the format required by many
14761 non-GNU versions of @command{date} when setting the system clock:
14764 date +%m%d%H%M%Y.%S
14768 To set the system clock forward by two minutes:
14771 date --set='+2 minutes'
14775 To print the date in RFC 2822 format,
14776 use @samp{date --rfc-2822}. Here is some example output:
14779 Fri, 09 Sep 2005 13:51:39 -0700
14782 @anchor{%s-examples}
14784 To convert a date string to the number of seconds since the epoch
14785 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14786 the @samp{%s} format. That can be useful in sorting and/or graphing
14787 and/or comparing data by date. The following command outputs the
14788 number of the seconds since the epoch for the time two minutes after the
14792 date --date='1970-01-01 00:02:00 +0000' +%s
14796 If you do not specify time zone information in the date string,
14797 @command{date} uses your computer's idea of the time zone when
14798 interpreting the string. For example, if your computer's time zone is
14799 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14800 seconds) behind UTC:
14803 # local time zone used
14804 date --date='1970-01-01 00:02:00' +%s
14809 If you're sorting or graphing dated data, your raw date values may be
14810 represented as seconds since the epoch. But few people can look at
14811 the date @samp{946684800} and casually note ``Oh, that's the first second
14812 of the year 2000 in Greenwich, England.''
14815 date --date='2000-01-01 UTC' +%s
14819 An alternative is to use the @option{--utc} (@option{-u}) option.
14820 Then you may omit @samp{UTC} from the date string. Although this
14821 produces the same result for @samp{%s} and many other format sequences,
14822 with a time zone offset different from zero, it would give a different
14823 result for zone-dependent formats like @samp{%z}.
14826 date -u --date=2000-01-01 +%s
14830 To convert such an unwieldy number of seconds back to
14831 a more readable form, use a command like this:
14834 # local time zone used
14835 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14836 1999-12-31 19:00:00 -0500
14839 Or if you do not mind depending on the @samp{@@} feature present since
14840 coreutils 5.3.0, you could shorten this to:
14843 date -d @@946684800 +"%F %T %z"
14844 1999-12-31 19:00:00 -0500
14847 Often it is better to output UTC-relative date and time:
14850 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14851 2000-01-01 00:00:00 +0000
14855 @cindex leap seconds
14856 Typically the seconds count omits leap seconds, but some systems are
14857 exceptions. Because leap seconds are not predictable, the mapping
14858 between the seconds count and a future timestamp is not reliable on
14859 the atypical systems that include leap seconds in their counts.
14861 Here is how the two kinds of systems handle the leap second at
14862 2012-06-30 23:59:60 UTC:
14865 # Typical systems ignore leap seconds:
14866 date --date='2012-06-30 23:59:59 +0000' +%s
14868 date --date='2012-06-30 23:59:60 +0000' +%s
14869 date: invalid date '2012-06-30 23:59:60 +0000'
14870 date --date='2012-07-01 00:00:00 +0000' +%s
14875 # Atypical systems count leap seconds:
14876 date --date='2012-06-30 23:59:59 +0000' +%s
14878 date --date='2012-06-30 23:59:60 +0000' +%s
14880 date --date='2012-07-01 00:00:00 +0000' +%s
14887 @node arch invocation
14888 @section @command{arch}: Print machine hardware name
14891 @cindex print machine hardware name
14892 @cindex system information, printing
14894 @command{arch} prints the machine hardware name,
14895 and is equivalent to @samp{uname -m}.
14899 arch [@var{option}]
14902 The program accepts the @ref{Common options} only.
14907 @node nproc invocation
14908 @section @command{nproc}: Print the number of available processors
14911 @cindex Print the number of processors
14912 @cindex system information, printing
14914 Print the number of processing units available to the current process,
14915 which may be less than the number of online processors.
14916 If this information is not accessible, then print the number of
14917 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14918 set, then it will determine the returned value. The result is guaranteed to be
14919 greater than zero. Synopsis:
14922 nproc [@var{option}]
14925 The program accepts the following options. Also see @ref{Common options}.
14931 Print the number of installed processors on the system, which may
14932 be greater than the number online or available to the current process.
14933 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14935 @item --ignore=@var{number}
14937 If possible, exclude this @var{number} of processing units.
14944 @node uname invocation
14945 @section @command{uname}: Print system information
14948 @cindex print system information
14949 @cindex system information, printing
14951 @command{uname} prints information about the machine and operating system
14952 it is run on. If no options are given, @command{uname} acts as if the
14953 @option{-s} option were given. Synopsis:
14956 uname [@var{option}]@dots{}
14959 If multiple options or @option{-a} are given, the selected information is
14960 printed in this order:
14963 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14964 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14967 The information may contain internal spaces, so such output cannot be
14968 parsed reliably. In the following example, @var{release} is
14969 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14973 @result{} Linux dumdum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
14974 unknown unknown GNU/Linux
14978 The program accepts the following options. Also see @ref{Common options}.
14986 Print all of the below information, except omit the processor type
14987 and the hardware platform name if they are unknown.
14990 @itemx --hardware-platform
14992 @opindex --hardware-platform
14993 @cindex implementation, hardware
14994 @cindex hardware platform
14995 @cindex platform, hardware
14996 Print the hardware platform name
14997 (sometimes called the hardware implementation).
14998 Print @samp{unknown} if the kernel does not make this information
14999 easily available, as is the case with Linux kernels.
15005 @cindex machine type
15006 @cindex hardware class
15007 @cindex hardware type
15008 Print the machine hardware name (sometimes called the hardware class
15014 @opindex --nodename
15017 @cindex network node name
15018 Print the network node hostname.
15023 @opindex --processor
15024 @cindex host processor type
15025 Print the processor type (sometimes called the instruction set
15026 architecture or ISA).
15027 Print @samp{unknown} if the kernel does not make this information
15028 easily available, as is the case with Linux kernels.
15031 @itemx --operating-system
15033 @opindex --operating-system
15034 @cindex operating system name
15035 Print the name of the operating system.
15038 @itemx --kernel-release
15040 @opindex --kernel-release
15041 @cindex kernel release
15042 @cindex release of kernel
15043 Print the kernel release.
15046 @itemx --kernel-name
15048 @opindex --kernel-name
15049 @cindex kernel name
15050 @cindex name of kernel
15051 Print the kernel name.
15052 POSIX 1003.1-2001 (@pxref{Standards conformance}) calls this
15053 ``the implementation of the operating system'', because the
15054 POSIX specification itself has no notion of ``kernel''.
15055 The kernel name might be the same as the operating system name printed
15056 by the @option{-o} or @option{--operating-system} option, but it might
15057 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
15058 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
15062 @itemx --kernel-version
15064 @opindex --kernel-version
15065 @cindex kernel version
15066 @cindex version of kernel
15067 Print the kernel version.
15074 @node hostname invocation
15075 @section @command{hostname}: Print or set system name
15078 @cindex setting the hostname
15079 @cindex printing the hostname
15080 @cindex system name, printing
15081 @cindex appropriate privileges
15083 With no arguments, @command{hostname} prints the name of the current host
15084 system. With one argument, it sets the current host name to the
15085 specified string. You must have appropriate privileges to set the host
15089 hostname [@var{name}]
15092 The only options are @option{--help} and @option{--version}. @xref{Common
15098 @node hostid invocation
15099 @section @command{hostid}: Print numeric host identifier
15102 @cindex printing the host identifier
15104 @command{hostid} prints the numeric identifier of the current host
15105 in hexadecimal. This command accepts no arguments.
15106 The only options are @option{--help} and @option{--version}.
15107 @xref{Common options}.
15109 For example, here's what it prints on one system I use:
15116 On that system, the 32-bit quantity happens to be closely
15117 related to the system's Internet address, but that isn't always
15122 @node uptime invocation
15123 @section @command{uptime}: Print system uptime and load
15126 @cindex printing the system uptime and load
15128 @command{uptime} prints the current time, the system's uptime, the
15129 number of logged-in users and the current load average.
15131 If an argument is specified, it is used as the file to be read
15132 to discover how many users are logged in. If no argument is
15133 specified, a system default is used (@command{uptime --help} indicates
15134 the default setting).
15136 The only options are @option{--help} and @option{--version}.
15137 @xref{Common options}.
15139 For example, here's what it prints right now on one system I use:
15143 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
15146 The precise method of calculation of load average varies somewhat
15147 between systems. Some systems calculate it as the average number of
15148 runnable processes over the last 1, 5 and 15 minutes, but some systems
15149 also include processes in the uninterruptible sleep state (that is,
15150 those processes which are waiting for disk I/O). The Linux kernel
15151 includes uninterruptible processes.
15153 @node SELinux context
15154 @chapter SELinux context
15156 @cindex SELinux context
15157 @cindex SELinux, context
15158 @cindex commands for SELinux context
15160 This section describes commands for operations with SELinux
15164 * chcon invocation:: Change SELinux context of file
15165 * runcon invocation:: Run a command in specified SELinux context
15168 @node chcon invocation
15169 @section @command{chcon}: Change SELinux context of file
15172 @cindex changing security context
15173 @cindex change SELinux context
15175 @command{chcon} changes the SELinux security context of the selected files.
15179 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
15180 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
15181 [-t @var{type}] @var{file}@dots{}
15182 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
15185 Change the SELinux security context of each @var{file} to @var{context}.
15186 With @option{--reference}, change the security context of each @var{file}
15187 to that of @var{rfile}.
15189 The program accepts the following options. Also see @ref{Common options}.
15194 @itemx --no-dereference
15196 @opindex --no-dereference
15197 @cindex no dereference
15198 Affect symbolic links instead of any referenced file.
15200 @item --reference=@var{rfile}
15201 @opindex --reference
15202 @cindex reference file
15203 Use @var{rfile}'s security context rather than specifying a @var{context} value.
15208 @opindex --recursive
15209 Operate on files and directories recursively.
15212 @xref{Traversing symlinks}.
15215 @xref{Traversing symlinks}.
15218 @xref{Traversing symlinks}.
15225 Output a diagnostic for every file processed.
15227 @item -u @var{user}
15228 @itemx --user=@var{user}
15231 Set user @var{user} in the target security context.
15233 @item -r @var{role}
15234 @itemx --role=@var{role}
15237 Set role @var{role} in the target security context.
15239 @item -t @var{type}
15240 @itemx --type=@var{type}
15243 Set type @var{type} in the target security context.
15245 @item -l @var{range}
15246 @itemx --range=@var{range}
15249 Set range @var{range} in the target security context.
15255 @node runcon invocation
15256 @section @command{runcon}: Run a command in specified SELinux context
15259 @cindex run with security context
15262 @command{runcon} runs file in specified SELinux security context.
15266 runcon @var{context} @var{command} [@var{args}]
15267 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
15268 [-l @var{range}] @var{command} [@var{args}]
15271 Run @var{command} with completely-specified @var{context}, or with
15272 current or transitioned security context modified by one or more of @var{level},
15273 @var{role}, @var{type} and @var{user}.
15275 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
15276 is specified, the first argument is used as the complete context.
15277 Any additional arguments after @var{command}
15278 are interpreted as arguments to the command.
15280 With neither @var{context} nor @var{command}, print the current
15283 The program accepts the following options. Also see @ref{Common options}.
15291 Compute process transition context before modifying.
15293 @item -u @var{user}
15294 @itemx --user=@var{user}
15297 Set user @var{user} in the target security context.
15299 @item -r @var{role}
15300 @itemx --role=@var{role}
15303 Set role @var{role} in the target security context.
15305 @item -t @var{type}
15306 @itemx --type=@var{type}
15309 Set type @var{type} in the target security context.
15311 @item -l @var{range}
15312 @itemx --range=@var{range}
15315 Set range @var{range} in the target security context.
15319 @cindex exit status of @command{runcon}
15323 126 if @var{command} is found but cannot be invoked
15324 127 if @command{runcon} itself fails or if @var{command} cannot be found
15325 the exit status of @var{command} otherwise
15328 @node Modified command invocation
15329 @chapter Modified command invocation
15331 @cindex modified command invocation
15332 @cindex invocation of commands, modified
15333 @cindex commands for invoking other commands
15335 This section describes commands that run other commands in some context
15336 different than the current one: a modified environment, as a different
15340 * chroot invocation:: Modify the root directory.
15341 * env invocation:: Modify environment variables.
15342 * nice invocation:: Modify niceness.
15343 * nohup invocation:: Immunize to hangups.
15344 * stdbuf invocation:: Modify buffering of standard streams.
15345 * timeout invocation:: Run with time limit.
15349 @node chroot invocation
15350 @section @command{chroot}: Run a command with a different root directory
15353 @cindex running a program in a specified root directory
15354 @cindex root directory, running a program in a specified
15356 @command{chroot} runs a command with a specified root directory.
15357 On many systems, only the super-user can do this.@footnote{However,
15358 some systems (e.g., FreeBSD) can be configured to allow certain regular
15359 users to use the @code{chroot} system call, and hence to run this program.
15360 Also, on Cygwin, anyone can run the @command{chroot} command, because the
15361 underlying function is non-privileged due to lack of support in MS-Windows.}
15365 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
15366 chroot @var{option}
15369 Ordinarily, file names are looked up starting at the root of the
15370 directory structure, i.e., @file{/}. @command{chroot} changes the root to
15371 the directory @var{newroot} (which must exist) and then runs
15372 @var{command} with optional @var{args}. If @var{command} is not
15373 specified, the default is the value of the @env{SHELL} environment
15374 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
15375 @var{command} must not be a special built-in utility
15376 (@pxref{Special built-in utilities}).
15378 The program accepts the following options. Also see @ref{Common options}.
15379 Options must precede operands.
15383 @item --userspec=@var{user}[:@var{group}]
15384 @opindex --userspec
15385 By default, @var{command} is run with the same credentials
15386 as the invoking process.
15387 Use this option to run it as a different @var{user} and/or with a
15388 different primary @var{group}.
15390 @item --groups=@var{groups}
15392 Use this option to specify the supplementary @var{groups} to be
15393 used by the new process.
15394 The items in the list (names or numeric IDs) must be separated by commas.
15398 Here are a few tips to help avoid common problems in using chroot.
15399 To start with a simple example, make @var{command} refer to a statically
15400 linked binary. If you were to use a dynamically linked executable, then
15401 you'd have to arrange to have the shared libraries in the right place under
15402 your new root directory.
15404 For example, if you create a statically linked @command{ls} executable,
15405 and put it in @file{/tmp/empty}, you can run this command as root:
15408 $ chroot /tmp/empty /ls -Rl /
15411 Then you'll see output like this:
15416 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
15419 If you want to use a dynamically linked executable, say @command{bash},
15420 then first run @samp{ldd bash} to see what shared objects it needs.
15421 Then, in addition to copying the actual binary, also copy the listed
15422 files to the required positions under your intended new root directory.
15423 Finally, if the executable requires any other files (e.g., data, state,
15424 device files), copy them into place, too.
15426 @cindex exit status of @command{chroot}
15430 125 if @command{chroot} itself fails
15431 126 if @var{command} is found but cannot be invoked
15432 127 if @var{command} cannot be found
15433 the exit status of @var{command} otherwise
15437 @node env invocation
15438 @section @command{env}: Run a command in a modified environment
15441 @cindex environment, running a program in a modified
15442 @cindex modified environment, running a program in a
15443 @cindex running a program in a modified environment
15445 @command{env} runs a command with a modified environment. Synopses:
15448 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
15449 [@var{command} [@var{args}]@dots{}]
15453 Operands of the form @samp{@var{variable}=@var{value}} set
15454 the environment variable @var{variable} to value @var{value}.
15455 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
15456 to an empty value is different from unsetting it.
15457 These operands are evaluated left-to-right, so if two operands
15458 mention the same variable the earlier is ignored.
15460 Environment variable names can be empty, and can contain any
15461 characters other than @samp{=} and ASCII @sc{nul}.
15462 However, it is wise to limit yourself to names that
15463 consist solely of underscores, digits, and ASCII letters,
15464 and that begin with a non-digit, as applications like the shell do not
15465 work well with other names.
15468 The first operand that does not contain the character @samp{=}
15469 specifies the program to invoke; it is
15470 searched for according to the @env{PATH} environment variable. Any
15471 remaining arguments are passed as arguments to that program.
15472 The program should not be a special built-in utility
15473 (@pxref{Special built-in utilities}).
15475 Modifications to @env{PATH} take effect prior to searching for
15476 @var{command}. Use caution when reducing @env{PATH}; behavior is
15477 not portable when @env{PATH} is undefined or omits key directories
15478 such as @file{/bin}.
15480 In the rare case that a utility contains a @samp{=} in the name, the
15481 only way to disambiguate it from a variable assignment is to use an
15482 intermediate command for @var{command}, and pass the problematic
15483 program name via @var{args}. For example, if @file{./prog=} is an
15484 executable in the current @env{PATH}:
15487 env prog= true # runs 'true', with prog= in environment
15488 env ./prog= true # runs 'true', with ./prog= in environment
15489 env -- prog= true # runs 'true', with prog= in environment
15490 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
15491 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
15494 @cindex environment, printing
15496 If no command name is specified following the environment
15497 specifications, the resulting environment is printed. This is like
15498 specifying the @command{printenv} program.
15500 For some examples, suppose the environment passed to @command{env}
15501 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
15502 @samp{PATH=.:/gnubin:/hacks}:
15507 Output the current environment.
15509 $ env | LC_ALL=C sort
15512 PATH=.:/gnubin:/hacks
15516 Run @command{foo} with a reduced environment, preserving only the
15517 original @env{PATH} to avoid problems in locating @command{foo}.
15519 env - PATH="$PATH" foo
15523 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
15524 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
15525 that @command{foo} was found in the file system rather than as a shell
15532 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
15533 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
15534 @samp{DISPLAY=gnu:0}.
15536 env DISPLAY=gnu:0 LOGNAME=foo nemacs
15540 Attempt to run the program @command{/energy/--} (as that is the only
15541 possible path search result); if the command exists, the environment
15542 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
15543 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
15545 env -u EDITOR PATH=/energy -- e=mc2 bar baz
15551 The program accepts the following options. Also see @ref{Common options}.
15552 Options must precede operands.
15558 @item -u @var{name}
15559 @itemx --unset=@var{name}
15562 Remove variable @var{name} from the environment, if it was in the
15567 @itemx --ignore-environment
15570 @opindex --ignore-environment
15571 Start with an empty environment, ignoring the inherited environment.
15575 @cindex exit status of @command{env}
15579 0 if no @var{command} is specified and the environment is output
15580 125 if @command{env} itself fails
15581 126 if @var{command} is found but cannot be invoked
15582 127 if @var{command} cannot be found
15583 the exit status of @var{command} otherwise
15587 @node nice invocation
15588 @section @command{nice}: Run a command with modified niceness
15592 @cindex scheduling, affecting
15593 @cindex appropriate privileges
15595 @command{nice} prints or modifies a process's @dfn{niceness},
15596 a parameter that affects whether the process is scheduled favorably.
15600 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
15603 If no arguments are given, @command{nice} prints the current niceness.
15604 Otherwise, @command{nice} runs the given @var{command} with its
15605 niceness adjusted. By default, its niceness is incremented by 10.
15607 Niceness values range at least from @minus{}20 (process has high priority
15608 and gets more resources, thus slowing down other processes) through 19
15609 (process has lower priority and runs slowly itself, but has less impact
15610 on the speed of other running processes). Some systems
15611 may have a wider range of niceness values; conversely, other systems may
15612 enforce more restrictive limits. An attempt to set the niceness
15613 outside the supported range is treated as an attempt to use the
15614 minimum or maximum supported value.
15616 A niceness should not be confused with a scheduling priority, which
15617 lets applications determine the order in which threads are scheduled
15618 to run. Unlike a priority, a niceness is merely advice to the
15619 scheduler, which the scheduler is free to ignore. Also, as a point of
15620 terminology, POSIX defines the behavior of @command{nice} in
15621 terms of a @dfn{nice value}, which is the nonnegative difference
15622 between a niceness and the minimum niceness. Though @command{nice}
15623 conforms to POSIX, its documentation and diagnostics use the
15624 term ``niceness'' for compatibility with historical practice.
15626 @var{command} must not be a special built-in utility (@pxref{Special
15627 built-in utilities}).
15629 @mayConflictWithShellBuiltIn{nice}
15631 The program accepts the following option. Also see @ref{Common options}.
15632 Options must precede operands.
15635 @item -n @var{adjustment}
15636 @itemx --adjustment=@var{adjustment}
15638 @opindex --adjustment
15639 Add @var{adjustment} instead of 10 to the command's niceness. If
15640 @var{adjustment} is negative and you lack appropriate privileges,
15641 @command{nice} issues a warning but otherwise acts as if you specified
15644 For compatibility @command{nice} also supports an obsolete
15645 option syntax @option{-@var{adjustment}}. New scripts should use
15646 @option{-n @var{adjustment}} instead.
15650 @cindex exit status of @command{nice}
15654 0 if no @var{command} is specified and the niceness is output
15655 125 if @command{nice} itself fails
15656 126 if @var{command} is found but cannot be invoked
15657 127 if @var{command} cannot be found
15658 the exit status of @var{command} otherwise
15661 It is sometimes useful to run a non-interactive program with reduced niceness.
15664 $ nice factor 4611686018427387903
15667 Since @command{nice} prints the current niceness,
15668 you can invoke it through itself to demonstrate how it works.
15670 The default behavior is to increase the niceness by @samp{10}:
15681 The @var{adjustment} is relative to the current niceness. In the
15682 next example, the first @command{nice} invocation runs the second one
15683 with niceness 10, and it in turn runs the final one with a niceness
15687 $ nice nice -n 3 nice
15691 Specifying a niceness larger than the supported range
15692 is the same as specifying the maximum supported value:
15695 $ nice -n 10000000000 nice
15699 Only a privileged user may run a process with lower niceness:
15703 nice: cannot set niceness: Permission denied
15705 $ sudo nice -n -1 nice
15710 @node nohup invocation
15711 @section @command{nohup}: Run a command immune to hangups
15714 @cindex hangups, immunity to
15715 @cindex immunity to hangups
15716 @cindex logging out and continuing to run
15719 @command{nohup} runs the given @var{command} with hangup signals ignored,
15720 so that the command can continue running in the background after you log
15724 nohup @var{command} [@var{arg}]@dots{}
15727 If standard input is a terminal, it is redirected from
15728 @file{/dev/null} so that terminal sessions do not mistakenly consider
15729 the terminal to be used by the command. This is a GNU
15730 extension; programs intended to be portable to non-GNU hosts
15731 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
15735 If standard output is a terminal, the command's standard output is appended
15736 to the file @file{nohup.out}; if that cannot be written to, it is appended
15737 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
15738 command is not run.
15739 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
15740 @command{nohup} is made readable and writable only to the user,
15741 regardless of the current umask settings.
15743 If standard error is a terminal, it is normally redirected to the same file
15744 descriptor as the (possibly-redirected) standard output.
15745 However, if standard output is closed, standard error terminal output
15746 is instead appended to the file @file{nohup.out} or
15747 @file{$HOME/nohup.out} as above.
15749 To capture the command's output to a file other than @file{nohup.out}
15750 you can redirect it. For example, to capture the output of
15754 nohup make > make.log
15757 @command{nohup} does not automatically put the command it runs in the
15758 background; you must do that explicitly, by ending the command line
15759 with an @samp{&}. Also, @command{nohup} does not alter the
15760 niceness of @var{command}; use @command{nice} for that,
15761 e.g., @samp{nohup nice @var{command}}.
15763 @var{command} must not be a special built-in utility (@pxref{Special
15764 built-in utilities}).
15766 The only options are @option{--help} and @option{--version}. @xref{Common
15767 options}. Options must precede operands.
15769 @cindex exit status of @command{nohup}
15773 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15774 126 if @var{command} is found but cannot be invoked
15775 127 if @var{command} cannot be found
15776 the exit status of @var{command} otherwise
15779 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15783 @node stdbuf invocation
15784 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15787 @cindex standard streams, buffering
15788 @cindex line buffered
15790 @command{stdbuf} allows one to modify the buffering operations of the
15791 three standard I/O streams associated with a program. Synopsis:
15794 stdbuf @var{option}@dots{} @var{command}
15797 @var{command} must start with the name of a program that
15800 uses the ISO C @code{FILE} streams for input/output (note the
15801 programs @command{dd} and @command{cat} don't do that),
15804 does not adjust the buffering of its standard streams (note the
15805 program @command{tee} is not in this category).
15808 Any additional @var{arg}s are passed as additional arguments to the
15811 The program accepts the following options. Also see @ref{Common options}.
15815 @item -i @var{mode}
15816 @itemx --input=@var{mode}
15819 Adjust the standard input stream buffering.
15821 @item -o @var{mode}
15822 @itemx --output=@var{mode}
15825 Adjust the standard output stream buffering.
15827 @item -e @var{mode}
15828 @itemx --error=@var{mode}
15831 Adjust the standard error stream buffering.
15835 The @var{mode} can be specified as follows:
15840 Set the stream to line buffered mode.
15841 In this mode data is coalesced until a newline is output or
15842 input is read from any stream attached to a terminal device.
15843 This option is invalid with standard input.
15846 Disable buffering of the selected stream.
15847 In this mode, data is output immediately and only the
15848 amount of data requested is read from input.
15849 Note the difference in function for input and output.
15850 Disabling buffering for input will not influence the responsiveness
15851 or blocking behavior of the stream input functions.
15852 For example @code{fread} will still block until @code{EOF} or error,
15853 even if the underlying @code{read} returns less data than requested.
15856 Specify the size of the buffer to use in fully buffered mode.
15857 @multiplierSuffixesNoBlocks{size}
15861 @cindex exit status of @command{stdbuf}
15865 125 if @command{stdbuf} itself fails
15866 126 if @var{command} is found but cannot be invoked
15867 127 if @var{command} cannot be found
15868 the exit status of @var{command} otherwise
15872 @node timeout invocation
15873 @section @command{timeout}: Run a command with a time limit
15877 @cindex run commands with bounded time
15879 @command{timeout} runs the given @var{command} and kills it if it is
15880 still running after the specified time interval. Synopsis:
15883 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15886 @var{command} must not be a special built-in utility (@pxref{Special
15887 built-in utilities}).
15889 The program accepts the following options. Also see @ref{Common options}.
15890 Options must precede operands.
15894 @opindex --foreground
15895 Don't create a separate background program group, so that
15896 the managed @var{command} can use the foreground TTY normally.
15897 This is needed to support timing out commands not started
15898 directly from an interactive shell, in two situations.
15901 @var{command} is interactive and needs to read from the terminal for example
15903 the user wants to support sending signals directly to @var{command}
15904 from the terminal (like Ctrl-C for example)
15907 Note in this mode of operation, any children of @var{command}
15908 will not be timed out.
15910 @item -k @var{duration}
15911 @itemx --kill-after=@var{duration}
15913 @opindex --kill-after
15914 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15915 signal, after the specified @var{duration}. Without this option, if the
15916 selected signal proves not to be fatal, @command{timeout} does not kill
15919 @item -s @var{signal}
15920 @itemx --signal=@var{signal}
15923 Send this @var{signal} to @var{command} on timeout, rather than the
15924 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15925 or a number. @xref{Signal specifications}.
15929 @var{duration} is a floating point number followed by an optional unit:
15931 @samp{s} for seconds (the default)
15932 @samp{m} for minutes
15936 A duration of 0 disables the associated timeout.
15937 Note that the actual timeout duration is dependent on system conditions,
15938 which should be especially considered when specifying sub-second timeouts.
15940 @cindex exit status of @command{timeout}
15944 124 if @var{command} times out
15945 125 if @command{timeout} itself fails
15946 126 if @var{command} is found but cannot be invoked
15947 127 if @var{command} cannot be found
15948 137 if @var{command} is sent the KILL(9) signal (128+9)
15949 the exit status of @var{command} otherwise
15953 @node Process control
15954 @chapter Process control
15956 @cindex processes, commands for controlling
15957 @cindex commands for controlling processes
15960 * kill invocation:: Sending a signal to processes.
15964 @node kill invocation
15965 @section @command{kill}: Send a signal to processes
15968 @cindex send a signal to processes
15970 The @command{kill} command sends a signal to processes, causing them
15971 to terminate or otherwise act upon receiving the signal in some way.
15972 Alternatively, it lists information about signals. Synopses:
15975 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15976 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15979 @mayConflictWithShellBuiltIn{kill}
15981 The first form of the @command{kill} command sends a signal to all
15982 @var{pid} arguments. The default signal to send if none is specified
15983 is @samp{TERM}@. The special signal number @samp{0} does not denote a
15984 valid signal, but can be used to test whether the @var{pid} arguments
15985 specify processes to which a signal could be sent.
15987 If @var{pid} is positive, the signal is sent to the process with the
15988 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15989 processes in the process group of the current process. If @var{pid}
15990 is @minus{}1, the signal is sent to all processes for which the user has
15991 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15992 is sent to all processes in the process group that equals the absolute
15993 value of @var{pid}.
15995 If @var{pid} is not positive, a system-dependent set of system
15996 processes is excluded from the list of processes to which the signal
15999 If a negative @var{pid} argument is desired as the first one, it
16000 should be preceded by @option{--}. However, as a common extension to
16001 POSIX, @option{--} is not required with @samp{kill
16002 -@var{signal} -@var{pid}}. The following commands are equivalent:
16011 The first form of the @command{kill} command succeeds if every @var{pid}
16012 argument specifies at least one process that the signal was sent to.
16014 The second form of the @command{kill} command lists signal information.
16015 Either the @option{-l} or @option{--list} option, or the @option{-t}
16016 or @option{--table} option must be specified. Without any
16017 @var{signal} argument, all supported signals are listed. The output
16018 of @option{-l} or @option{--list} is a list of the signal names, one
16019 per line; if @var{signal} is already a name, the signal number is
16020 printed instead. The output of @option{-t} or @option{--table} is a
16021 table of signal numbers, names, and descriptions. This form of the
16022 @command{kill} command succeeds if all @var{signal} arguments are valid
16023 and if there is no output error.
16025 The @command{kill} command also supports the @option{--help} and
16026 @option{--version} options. @xref{Common options}.
16028 A @var{signal} may be a signal name like @samp{HUP}, or a signal
16029 number like @samp{1}, or an exit status of a process terminated by the
16030 signal. A signal name can be given in canonical form or prefixed by
16031 @samp{SIG}@. The case of the letters is ignored, except for the
16032 @option{-@var{signal}} option which must use upper case to avoid
16033 ambiguity with lower case option letters.
16034 @xref{Signal specifications}, for a list of supported
16035 signal names and numbers.
16040 @cindex delaying commands
16041 @cindex commands for delaying
16043 @c Perhaps @command{wait} or other commands should be described here also?
16046 * sleep invocation:: Delay for a specified time.
16050 @node sleep invocation
16051 @section @command{sleep}: Delay for a specified time
16054 @cindex delay for a specified time
16056 @command{sleep} pauses for an amount of time specified by the sum of
16057 the values of the command line arguments.
16061 sleep @var{number}[smhd]@dots{}
16065 Each argument is a number followed by an optional unit; the default
16066 is seconds. The units are:
16079 Historical implementations of @command{sleep} have required that
16080 @var{number} be an integer, and only accepted a single argument
16081 without a suffix. However, GNU @command{sleep} accepts
16082 arbitrary floating point numbers. @xref{Floating point}.
16084 The only options are @option{--help} and @option{--version}. @xref{Common
16087 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
16088 @mayConflictWithShellBuiltIn{sleep}
16093 @node Numeric operations
16094 @chapter Numeric operations
16096 @cindex numeric operations
16097 These programs do numerically-related operations.
16100 * factor invocation:: Show factors of numbers.
16101 * seq invocation:: Print sequences of numbers.
16105 @node factor invocation
16106 @section @command{factor}: Print prime factors
16109 @cindex prime factors
16111 @command{factor} prints prime factors. Synopses:
16114 factor [@var{number}]@dots{}
16115 factor @var{option}
16118 If no @var{number} is specified on the command line, @command{factor} reads
16119 numbers from standard input, delimited by newlines, tabs, or spaces.
16121 The @command{factor} command supports only a small number of options:
16125 Print a short help on standard output, then exit without further
16129 Print the program version on standard output, then exit without further
16133 Factoring the product of the eighth and ninth Mersenne primes
16134 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
16137 M8=$(echo 2^31-1|bc)
16138 M9=$(echo 2^61-1|bc)
16139 n=$(echo "$M8 * $M9" | bc)
16140 /usr/bin/time -f %U factor $n
16141 4951760154835678088235319297: 2147483647 2305843009213693951
16145 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
16146 about 20 seconds on the same machine.
16148 Factoring large numbers is, in general, hard. The Pollard Rho
16149 algorithm used by @command{factor} is particularly effective for
16150 numbers with relatively small factors. If you wish to factor large
16151 numbers which do not have small factors (for example, numbers which
16152 are the product of two large primes), other methods are far better.
16154 If @command{factor} is built without using GNU MP, only
16155 single-precision arithmetic is available, and so large numbers
16156 (typically @math{2^{64}} and above) will not be supported. The single-precision
16157 code uses an algorithm which is designed for factoring smaller
16163 @node seq invocation
16164 @section @command{seq}: Print numeric sequences
16167 @cindex numeric sequences
16168 @cindex sequence of numbers
16170 @command{seq} prints a sequence of numbers to standard output. Synopses:
16173 seq [@var{option}]@dots{} @var{last}
16174 seq [@var{option}]@dots{} @var{first} @var{last}
16175 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
16178 @command{seq} prints the numbers from @var{first} to @var{last} by
16179 @var{increment}. By default, each number is printed on a separate line.
16180 When @var{increment} is not specified, it defaults to @samp{1},
16181 even when @var{first} is larger than @var{last}.
16182 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
16183 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
16184 Floating-point numbers may be specified. @xref{Floating point}.
16186 The program accepts the following options. Also see @ref{Common options}.
16187 Options must precede operands.
16190 @item -f @var{format}
16191 @itemx --format=@var{format}
16192 @opindex -f @var{format}
16193 @opindex --format=@var{format}
16194 @cindex formatting of numbers in @command{seq}
16195 Print all numbers using @var{format}.
16196 @var{format} must contain exactly one of the @samp{printf}-style
16197 floating point conversion specifications @samp{%a}, @samp{%e},
16198 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}@.
16199 The @samp{%} may be followed by zero or more flags taken from the set
16200 @samp{-+#0 '}, then an optional width containing one or more digits,
16201 then an optional precision consisting of a @samp{.} followed by zero
16202 or more digits. @var{format} may also contain any number of @samp{%%}
16203 conversion specifications. All conversion specifications have the
16204 same meaning as with @samp{printf}.
16206 The default format is derived from @var{first}, @var{step}, and
16207 @var{last}. If these all use a fixed point decimal representation,
16208 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
16209 precision that can represent the output numbers exactly. Otherwise,
16210 the default format is @samp{%g}.
16212 @item -s @var{string}
16213 @itemx --separator=@var{string}
16214 @cindex separator for numbers in @command{seq}
16215 Separate numbers with @var{string}; default is a newline.
16216 The output always terminates with a newline.
16219 @itemx --equal-width
16220 Print all numbers with the same width, by padding with leading zeros.
16221 @var{first}, @var{step}, and @var{last} should all use a fixed point
16222 decimal representation.
16223 (To have other kinds of padding, use @option{--format}).
16227 You can get finer-grained control over output with @option{-f}:
16230 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
16236 If you want hexadecimal integer output, you can use @command{printf}
16237 to perform the conversion:
16240 $ printf '%x\n' $(seq 1048575 1024 1050623)
16246 For very long lists of numbers, use xargs to avoid
16247 system limitations on the length of an argument list:
16250 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
16256 To generate octal output, use the printf @code{%o} format instead
16259 On most systems, seq can produce whole-number output for values up to
16260 at least @math{2^{53}}. Larger integers are approximated. The details
16261 differ depending on your floating-point implementation.
16262 @xref{Floating point}. A common
16263 case is that @command{seq} works with integers through @math{2^{64}},
16264 and larger integers may not be numerically correct:
16267 $ seq 50000000000000000000 2 50000000000000000004
16268 50000000000000000000
16269 50000000000000000000
16270 50000000000000000004
16273 However, note that when limited to non-negative whole numbers,
16274 an increment of 1 and no format-specifying option, seq can print
16275 arbitrarily large numbers.
16277 Be careful when using @command{seq} with outlandish values: otherwise
16278 you may see surprising results, as @command{seq} uses floating point
16279 internally. For example, on the x86 platform, where the internal
16280 representation uses a 64-bit fraction, the command:
16283 seq 1 0.0000000000000000001 1.0000000000000000009
16286 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
16291 @node File permissions
16292 @chapter File permissions
16295 @include parse-datetime.texi
16299 @node Opening the software toolbox
16300 @chapter Opening the Software Toolbox
16302 An earlier version of this chapter appeared in
16303 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
16304 @cite{What's GNU@?} column of the June 1994 @cite{Linux Journal}}.
16305 It was written by Arnold Robbins.
16308 * Toolbox introduction:: Toolbox introduction
16309 * I/O redirection:: I/O redirection
16310 * The who command:: The @command{who} command
16311 * The cut command:: The @command{cut} command
16312 * The sort command:: The @command{sort} command
16313 * The uniq command:: The @command{uniq} command
16314 * Putting the tools together:: Putting the tools together
16318 @node Toolbox introduction
16319 @unnumberedsec Toolbox Introduction
16321 This month's column is only peripherally related to the GNU Project, in
16322 that it describes a number of the GNU tools on your GNU/Linux system
16324 might be used. What it's really about is the ``Software Tools'' philosophy
16325 of program development and usage.
16327 The software tools philosophy was an important and integral concept
16328 in the initial design and development of Unix (of which Linux and GNU are
16329 essentially clones). Unfortunately, in the modern day press of
16330 Internetworking and flashy GUIs, it seems to have fallen by the
16331 wayside. This is a shame, since it provides a powerful mental model
16332 for solving many kinds of problems.
16334 Many people carry a Swiss Army knife around in their pants pockets (or
16335 purse). A Swiss Army knife is a handy tool to have: it has several knife
16336 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
16337 a number of other things on it. For the everyday, small miscellaneous jobs
16338 where you need a simple, general purpose tool, it's just the thing.
16340 On the other hand, an experienced carpenter doesn't build a house using
16341 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
16342 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
16343 exactly when and where to use each tool; you won't catch him hammering nails
16344 with the handle of his screwdriver.
16346 The Unix developers at Bell Labs were all professional programmers and trained
16347 computer scientists. They had found that while a one-size-fits-all program
16348 might appeal to a user because there's only one program to use, in practice
16353 difficult to write,
16356 difficult to maintain and
16360 difficult to extend to meet new situations.
16363 Instead, they felt that programs should be specialized tools. In short, each
16364 program ``should do one thing well.'' No more and no less. Such programs are
16365 simpler to design, write, and get right---they only do one thing.
16367 Furthermore, they found that with the right machinery for hooking programs
16368 together, that the whole was greater than the sum of the parts. By combining
16369 several special purpose programs, you could accomplish a specific task
16370 that none of the programs was designed for, and accomplish it much more
16371 quickly and easily than if you had to write a special purpose program.
16372 We will see some (classic) examples of this further on in the column.
16373 (An important additional point was that, if necessary, take a detour
16374 and build any software tools you may need first, if you don't already
16375 have something appropriate in the toolbox.)
16377 @node I/O redirection
16378 @unnumberedsec I/O Redirection
16380 Hopefully, you are familiar with the basics of I/O redirection in the
16381 shell, in particular the concepts of ``standard input,'' ``standard output,''
16382 and ``standard error''. Briefly, ``standard input'' is a data source, where
16383 data comes from. A program should not need to either know or care if the
16384 data source is a disk file, a keyboard, a magnetic tape, or even a punched
16385 card reader. Similarly, ``standard output'' is a data sink, where data goes
16386 to. The program should neither know nor care where this might be.
16387 Programs that only read their standard input, do something to the data,
16388 and then send it on, are called @dfn{filters}, by analogy to filters in a
16391 With the Unix shell, it's very easy to set up data pipelines:
16394 program_to_create_data | filter1 | ... | filterN > final.pretty.data
16397 We start out by creating the raw data; each filter applies some successive
16398 transformation to the data, until by the time it comes out of the pipeline,
16399 it is in the desired form.
16401 This is fine and good for standard input and standard output. Where does the
16402 standard error come in to play? Well, think about @command{filter1} in
16403 the pipeline above. What happens if it encounters an error in the data it
16404 sees? If it writes an error message to standard output, it will just
16405 disappear down the pipeline into @command{filter2}'s input, and the
16406 user will probably never see it. So programs need a place where they can send
16407 error messages so that the user will notice them. This is standard error,
16408 and it is usually connected to your console or window, even if you have
16409 redirected standard output of your program away from your screen.
16411 For filter programs to work together, the format of the data has to be
16412 agreed upon. The most straightforward and easiest format to use is simply
16413 lines of text. Unix data files are generally just streams of bytes, with
16414 lines delimited by the ASCII @sc{lf} (Line Feed) character,
16415 conventionally called a ``newline'' in the Unix literature. (This is
16416 @code{'\n'} if you're a C programmer.) This is the format used by all
16417 the traditional filtering programs. (Many earlier operating systems
16418 had elaborate facilities and special purpose programs for managing
16419 binary data. Unix has always shied away from such things, under the
16420 philosophy that it's easiest to simply be able to view and edit your
16421 data with a text editor.)
16423 OK, enough introduction. Let's take a look at some of the tools, and then
16424 we'll see how to hook them together in interesting ways. In the following
16425 discussion, we will only present those command line options that interest
16426 us. As you should always do, double check your system documentation
16427 for the full story.
16429 @node The who command
16430 @unnumberedsec The @command{who} Command
16432 The first program is the @command{who} command. By itself, it generates a
16433 list of the users who are currently logged in. Although I'm writing
16434 this on a single-user system, we'll pretend that several people are
16439 @print{} arnold console Jan 22 19:57
16440 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
16441 @print{} bill ttyp1 Jan 21 09:32(:0.0)
16442 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
16445 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
16446 There are three people logged in, and I am logged in twice. On traditional
16447 Unix systems, user names are never more than eight characters long. This
16448 little bit of trivia will be useful later. The output of @command{who} is nice,
16449 but the data is not all that exciting.
16451 @node The cut command
16452 @unnumberedsec The @command{cut} Command
16454 The next program we'll look at is the @command{cut} command. This program
16455 cuts out columns or fields of input data. For example, we can tell it
16456 to print just the login name and full name from the @file{/etc/passwd}
16457 file. The @file{/etc/passwd} file has seven fields, separated by
16461 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
16464 To get the first and fifth fields, we would use @command{cut} like this:
16467 $ cut -d: -f1,5 /etc/passwd
16468 @print{} root:Operator
16470 @print{} arnold:Arnold D. Robbins
16471 @print{} miriam:Miriam A. Robbins
16475 With the @option{-c} option, @command{cut} will cut out specific characters
16476 (i.e., columns) in the input lines. This is useful for input data
16477 that has fixed width fields, and does not have a field separator. For
16478 example, list the Monday dates for the current month:
16480 @c Is using cal ok? Looked at gcal, but I don't like it.
16491 @node The sort command
16492 @unnumberedsec The @command{sort} Command
16494 Next we'll look at the @command{sort} command. This is one of the most
16495 powerful commands on a Unix-style system; one that you will often find
16496 yourself using when setting up fancy data plumbing.
16499 command reads and sorts each file named on the command line. It then
16500 merges the sorted data and writes it to standard output. It will read
16501 standard input if no files are given on the command line (thus
16502 making it into a filter). The sort is based on the character collating
16503 sequence or based on user-supplied ordering criteria.
16506 @node The uniq command
16507 @unnumberedsec The @command{uniq} Command
16509 Finally (at least for now), we'll look at the @command{uniq} program. When
16510 sorting data, you will often end up with duplicate lines, lines that
16511 are identical. Usually, all you need is one instance of each line.
16512 This is where @command{uniq} comes in. The @command{uniq} program reads its
16513 standard input. It prints only one
16514 copy of each repeated line. It does have several options. Later on,
16515 we'll use the @option{-c} option, which prints each unique line, preceded
16516 by a count of the number of times that line occurred in the input.
16519 @node Putting the tools together
16520 @unnumberedsec Putting the Tools Together
16522 Now, let's suppose this is a large ISP server system with dozens of users
16523 logged in. The management wants the system administrator to write a
16525 generate a sorted list of logged in users. Furthermore, even if a user
16526 is logged in multiple times, his or her name should only show up in the
16529 The administrator could sit down with the system documentation and write a C
16530 program that did this. It would take perhaps a couple of hundred lines
16531 of code and about two hours to write it, test it, and debug it.
16532 However, knowing the software toolbox, the administrator can instead start out
16533 by generating just a list of logged on users:
16543 Next, sort the list:
16546 $ who | cut -c1-8 | sort
16553 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
16556 $ who | cut -c1-8 | sort | uniq
16562 The @command{sort} command actually has a @option{-u} option that does what
16563 @command{uniq} does. However, @command{uniq} has other uses for which one
16564 cannot substitute @samp{sort -u}.
16566 The administrator puts this pipeline into a shell script, and makes it
16568 all the users on the system (@samp{#} is the system administrator,
16569 or @code{root}, prompt):
16572 # cat > /usr/local/bin/listusers
16573 who | cut -c1-8 | sort | uniq
16575 # chmod +x /usr/local/bin/listusers
16578 There are four major points to note here. First, with just four
16579 programs, on one command line, the administrator was able to save about two
16580 hours worth of work. Furthermore, the shell pipeline is just about as
16581 efficient as the C program would be, and it is much more efficient in
16582 terms of programmer time. People time is much more expensive than
16583 computer time, and in our modern ``there's never enough time to do
16584 everything'' society, saving two hours of programmer time is no mean
16587 Second, it is also important to emphasize that with the
16588 @emph{combination} of the tools, it is possible to do a special
16589 purpose job never imagined by the authors of the individual programs.
16591 Third, it is also valuable to build up your pipeline in stages, as we did here.
16592 This allows you to view the data at each stage in the pipeline, which helps
16593 you acquire the confidence that you are indeed using these tools correctly.
16595 Finally, by bundling the pipeline in a shell script, other users can use
16596 your command, without having to remember the fancy plumbing you set up for
16597 them. In terms of how you run them, shell scripts and compiled programs are
16600 After the previous warm-up exercise, we'll look at two additional, more
16601 complicated pipelines. For them, we need to introduce two more tools.
16603 The first is the @command{tr} command, which stands for ``transliterate.''
16604 The @command{tr} command works on a character-by-character basis, changing
16605 characters. Normally it is used for things like mapping upper case to
16609 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
16610 @print{} this example has mixed case!
16613 There are several options of interest:
16617 work on the complement of the listed characters, i.e.,
16618 operations apply to characters not in the given set
16621 delete characters in the first set from the output
16624 squeeze repeated characters in the output into just one character.
16627 We will be using all three options in a moment.
16629 The other command we'll look at is @command{comm}. The @command{comm}
16630 command takes two sorted input files as input data, and prints out the
16631 files' lines in three columns. The output columns are the data lines
16632 unique to the first file, the data lines unique to the second file, and
16633 the data lines that are common to both. The @option{-1}, @option{-2}, and
16634 @option{-3} command line options @emph{omit} the respective columns. (This is
16635 non-intuitive and takes a little getting used to.) For example:
16657 The file name @file{-} tells @command{comm} to read standard input
16658 instead of a regular file.
16660 Now we're ready to build a fancy pipeline. The first application is a word
16661 frequency counter. This helps an author determine if he or she is over-using
16664 The first step is to change the case of all the letters in our input file
16665 to one case. ``The'' and ``the'' are the same word when doing counting.
16668 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16671 The next step is to get rid of punctuation. Quoted words and unquoted words
16672 should be treated identically; it's easiest to just get the punctuation out of
16676 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16679 The second @command{tr} command operates on the complement of the listed
16680 characters, which are all the letters, the digits, the underscore, and
16681 the blank. The @samp{\n} represents the newline character; it has to
16682 be left alone. (The ASCII tab character should also be included for
16683 good measure in a production script.)
16685 At this point, we have data consisting of words separated by blank space.
16686 The words only contain alphanumeric characters (and the underscore). The
16687 next step is break the data apart so that we have one word per line. This
16688 makes the counting operation much easier, as we will see shortly.
16691 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16692 > tr -s ' ' '\n' | ...
16695 This command turns blanks into newlines. The @option{-s} option squeezes
16696 multiple newline characters in the output into just one. This helps us
16697 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16698 This is what the shell prints when it notices you haven't finished
16699 typing in all of a command.)
16701 We now have data consisting of one word per line, no punctuation, all one
16702 case. We're ready to count each word:
16705 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16706 > tr -s ' ' '\n' | sort | uniq -c | ...
16709 At this point, the data might look something like this:
16722 The output is sorted by word, not by count! What we want is the most
16723 frequently used words first. Fortunately, this is easy to accomplish,
16724 with the help of two more @command{sort} options:
16728 do a numeric sort, not a textual one
16731 reverse the order of the sort
16734 The final pipeline looks like this:
16737 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16738 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16747 Whew! That's a lot to digest. Yet, the same principles apply. With six
16748 commands, on two lines (really one long one split for convenience), we've
16749 created a program that does something interesting and useful, in much
16750 less time than we could have written a C program to do the same thing.
16752 A minor modification to the above pipeline can give us a simple spelling
16753 checker! To determine if you've spelled a word correctly, all you have to
16754 do is look it up in a dictionary. If it is not there, then chances are
16755 that your spelling is incorrect. So, we need a dictionary.
16756 The conventional location for a dictionary is @file{/usr/dict/words}.
16757 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16758 revision of this article.}
16759 this is a sorted, 45,402 word dictionary.
16761 Now, how to compare our file with the dictionary? As before, we generate
16762 a sorted list of words, one per line:
16765 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16766 > tr -s ' ' '\n' | sort -u | ...
16769 Now, all we need is a list of words that are @emph{not} in the
16770 dictionary. Here is where the @command{comm} command comes in.
16773 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16774 > tr -s ' ' '\n' | sort -u |
16775 > comm -23 - /usr/dict/words
16778 The @option{-2} and @option{-3} options eliminate lines that are only in the
16779 dictionary (the second file), and lines that are in both files. Lines
16780 only in the first file (standard input, our stream of words), are
16781 words that are not in the dictionary. These are likely candidates for
16782 spelling errors. This pipeline was the first cut at a production
16783 spelling checker on Unix.
16785 There are some other tools that deserve brief mention.
16789 search files for text that matches a regular expression
16792 count lines, words, characters
16795 a T-fitting for data pipes, copies data to files and to standard output
16798 the stream editor, an advanced tool
16801 a data manipulation language, another advanced tool
16804 The software tools philosophy also espoused the following bit of
16805 advice: ``Let someone else do the hard part.'' This means, take
16806 something that gives you most of what you need, and then massage it the
16807 rest of the way until it's in the form that you want.
16813 Each program should do one thing well. No more, no less.
16816 Combining programs with appropriate plumbing leads to results where
16817 the whole is greater than the sum of the parts. It also leads to novel
16818 uses of programs that the authors might never have imagined.
16821 Programs should never print extraneous header or trailer data, since these
16822 could get sent on down a pipeline. (A point we didn't mention earlier.)
16825 Let someone else do the hard part.
16828 Know your toolbox! Use each program appropriately. If you don't have an
16829 appropriate tool, build one.
16832 As of this writing, all the programs we've discussed are available via
16833 anonymous @command{ftp} from: @*
16834 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16835 be more recent versions available now.)
16837 None of what I have presented in this column is new. The Software Tools
16838 philosophy was first introduced in the book @cite{Software Tools}, by
16839 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16840 This book showed how to write and use software tools. It was written in
16841 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16842 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16843 was. The last chapter presented a @command{ratfor} to FORTRAN
16844 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16845 lot like C; if you know C, you won't have any problem following the
16848 In 1981, the book was updated and made available as @cite{Software Tools
16849 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16850 still in print and are well worth
16851 reading if you're a programmer. They certainly made a major change in
16852 how I view programming.
16854 The programs in both books are available from
16855 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16856 For a number of years, there was an active
16857 Software Tools Users Group, whose members had ported the original
16858 @command{ratfor} programs to essentially every computer system with a
16859 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16860 as Unix began to spread beyond universities.
16862 With the current proliferation of GNU code and other clones of Unix programs,
16863 these programs now receive little attention; modern C versions are
16864 much more efficient and do more than these programs do. Nevertheless, as
16865 exposition of good programming style, and evangelism for a still-valuable
16866 philosophy, these books are unparalleled, and I recommend them highly.
16868 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16869 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16871 @node GNU Free Documentation License
16872 @appendix GNU Free Documentation License
16876 @node Concept index
16883 @c Local variables:
16884 @c texinfo-column-for-description: 32