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. 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 file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/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 * rm: (coreutils)rm invocation. Remove files.
98 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
99 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
100 * seq: (coreutils)seq invocation. Print numeric sequences
101 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
102 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
103 * shred: (coreutils)shred invocation. Remove files more securely.
104 * shuf: (coreutils)shuf invocation. Shuffling text files.
105 * sleep: (coreutils)sleep invocation. Delay for a specified time.
106 * sort: (coreutils)sort invocation. Sort text files.
107 * split: (coreutils)split invocation. Split into pieces.
108 * stat: (coreutils)stat invocation. Report file(system) status.
109 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
110 * stty: (coreutils)stty invocation. Print/change terminal settings.
111 * su: (coreutils)su invocation. Modify user and group ID.
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{} 1994-1996, 2000-2011 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
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 su 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 @acronym{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
387 * pwd invocation:: Print working directory
388 * stty invocation:: Print or change terminal characteristics
389 * printenv invocation:: Print all or some environment variables
390 * tty invocation:: Print file name of terminal on standard input
392 @command{stty}: Print or change terminal characteristics
394 * Control:: Control settings
395 * Input:: Input settings
396 * Output:: Output settings
397 * Local:: Local settings
398 * Combination:: Combination settings
399 * Characters:: Special characters
400 * Special:: Special settings
404 * id invocation:: Print user identity
405 * logname invocation:: Print current login name
406 * whoami invocation:: Print effective user ID
407 * groups invocation:: Print group names a user is in
408 * users invocation:: Print login names of users currently logged in
409 * who invocation:: Print who is currently logged in
413 * arch invocation:: Print machine hardware name
414 * date invocation:: Print or set system date and time
415 * nproc invocation:: Print the number of processors
416 * uname invocation:: Print system information
417 * hostname invocation:: Print or set system name
418 * hostid invocation:: Print numeric host identifier
419 * uptime invocation:: Print system uptime and load
421 @command{date}: Print or set system date and time
423 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
424 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
425 * Literal conversion specifiers:: %[%nt]
426 * Padding and other flags:: Pad with zeros, spaces, etc.
427 * Setting the time:: Changing the system clock
428 * Options for date:: Instead of the current time
429 * Date input formats:: Specifying date strings
430 * Examples of date:: Examples
434 * chcon invocation:: Change SELinux context of file
435 * runcon invocation:: Run a command in specified SELinux context
437 Modified command invocation
439 * chroot invocation:: Run a command with a different root directory
440 * env invocation:: Run a command in a modified environment
441 * nice invocation:: Run a command with modified niceness
442 * nohup invocation:: Run a command immune to hangups
443 * stdbuf invocation:: Run a command with modified I/O buffering
444 * su invocation:: Run a command with substitute user and group ID
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
506 @cindex @acronym{POSIX}
507 The @sc{gnu} utilities documented here are mostly compatible with the
508 @acronym{POSIX} standard.
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 (@acronym{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 @itemx @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 @acronym{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 @acronym{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{su}, @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.fr/enus/3_SI/si-prefixes.html, SI prefixes}
905 for decimal multiples and with the
906 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
907 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 IEC 60027-2 prefix is @samp{Ki}, but tradition and
950 @acronym{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}.
992 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
994 @cindex yottabyte, definition of
995 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
998 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
999 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
1004 @opindex --block-size
1005 @opindex --human-readable
1008 Block size defaults can be overridden by an explicit
1009 @option{--block-size=@var{size}} option. The @option{-k}
1010 option is equivalent to @option{--block-size=1K}, which
1011 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1012 set. The @option{-h} or @option{--human-readable} option is equivalent to
1013 @option{--block-size=human-readable}. The @option{--si} option is
1014 equivalent to @option{--block-size=si}.
1016 @node Floating point
1017 @section Floating point numbers
1018 @cindex floating point
1019 @cindex IEEE floating point
1021 Commands that accept or produce floating point numbers employ the
1022 floating point representation of the underlying system, and suffer
1023 from rounding error, overflow, and similar floating-point issues.
1024 Almost all modern systems use IEEE-754 floating point, and it is
1025 typically portable to assume IEEE-754 behavior these days. IEEE-754
1026 has positive and negative infinity, distinguishes positive from
1027 negative zero, and uses special values called NaNs to represent
1028 invalid computations such as dividing zero by itself. For more
1029 information, please see David Goldberg's paper
1030 @uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
1031 Computer Scientist Should Know About Floating-Point Arithmetic}.
1034 Commands that accept floating point numbers as options, operands or
1035 input use the standard C functions @code{strtod} and @code{strtold} to
1036 convert from text to floating point numbers. These floating point
1037 numbers therefore can use scientific notation like @code{1.0e-34} and
1038 @code{-10e100}. Modern C implementations also accept hexadecimal
1039 floating point numbers such as @code{-0x.ep-3}, which stands for
1040 @minus{}14/16 times @math{2^-3}, which equals @minus{}0.109375. The
1041 @env{LC_NUMERIC} locale determines the decimal-point character.
1042 @xref{Parsing of Floats,,, libc, The GNU C Library Reference Manual}.
1044 @node Signal specifications
1045 @section Signal specifications
1046 @cindex signals, specifying
1048 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1049 number like @samp{1}, or an exit status of a process terminated by the
1050 signal. A signal name can be given in canonical form or prefixed by
1051 @samp{SIG}. The case of the letters is ignored. The following signal names
1052 and numbers are supported on all @acronym{POSIX} compliant systems:
1058 2. Terminal interrupt.
1064 9. Kill (cannot be caught or ignored).
1072 Other supported signal names have system-dependent corresponding
1073 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1074 support the following signals:
1078 Access to an undefined portion of a memory object.
1080 Child process terminated, stopped, or continued.
1082 Continue executing, if stopped.
1084 Erroneous arithmetic operation.
1086 Illegal Instruction.
1088 Write on a pipe with no one to read it.
1090 Invalid memory reference.
1092 Stop executing (cannot be caught or ignored).
1096 Background process attempting read.
1098 Background process attempting write.
1100 High bandwidth data is available at a socket.
1102 User-defined signal 1.
1104 User-defined signal 2.
1108 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1109 also support the following signals:
1115 Profiling timer expired.
1119 Trace/breakpoint trap.
1121 Virtual timer expired.
1123 CPU time limit exceeded.
1125 File size limit exceeded.
1129 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1130 also support at least eight real-time signals called @samp{RTMIN},
1131 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1133 @node Disambiguating names and IDs
1134 @section chown and chgrp: Disambiguating user names and IDs
1135 @cindex user names, disambiguating
1136 @cindex user IDs, disambiguating
1137 @cindex group names, disambiguating
1138 @cindex group IDs, disambiguating
1139 @cindex disambiguating group names and IDs
1141 Since the @var{owner} and @var{group} arguments to @command{chown} and
1142 @command{chgrp} may be specified as names or numeric IDs, there is an
1144 What if a user or group @emph{name} is a string of digits?
1145 @footnote{Using a number as a user name is common in some environments.}
1146 Should the command interpret it as a user name or as an ID?
1147 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1148 first attempt to resolve the specified string as a name, and
1149 only once that fails, then try to interpret it as an ID.
1150 This is troublesome when you want to specify a numeric ID, say 42,
1151 and it must work even in a pathological situation where
1152 @samp{42} is a user name that maps to some other user ID, say 1000.
1153 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1154 1000---not what you intended.
1156 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1157 that at the same time may result in a significant performance improvement
1158 by eliminating a database look-up.
1159 Simply precede each numeric user ID and/or group ID with a @samp{+},
1160 in order to force its interpretation as an integer:
1164 chgrp +$numeric_group_id another-file
1168 GNU @command{chown} and @command{chgrp}
1169 skip the name look-up process for each @samp{+}-prefixed string,
1170 because a string containing @samp{+} is never a valid user or group name.
1171 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1173 @node Random sources
1174 @section Sources of random data
1176 @cindex random sources
1178 The @command{shuf}, @command{shred}, and @command{sort} commands
1179 sometimes need random data to do their work. For example, @samp{sort
1180 -R} must choose a hash function at random, and it needs random data to
1181 make this selection.
1183 By default these commands use an internal pseudorandom generator
1184 initialized by a small amount of entropy, but can be directed to use
1185 an external source with the @option{--random-source=@var{file}} option.
1186 An error is reported if @var{file} does not contain enough bytes.
1188 For example, the device file @file{/dev/urandom} could be used as the
1189 source of random data. Typically, this device gathers environmental
1190 noise from device drivers and other sources into an entropy pool, and
1191 uses the pool to generate random bits. If the pool is short of data,
1192 the device reuses the internal pool to produce more bits, using a
1193 cryptographically secure pseudorandom number generator. But be aware
1194 that this device is not designed for bulk random data generation
1195 and is relatively slow.
1197 @file{/dev/urandom} suffices for most practical uses, but applications
1198 requiring high-value or long-term protection of private data may
1199 require an alternate data source like @file{/dev/random} or
1200 @file{/dev/arandom}. The set of available sources depends on your
1203 To reproduce the results of an earlier invocation of a command, you
1204 can save some random data into a file and then use that file as the
1205 random source in earlier and later invocations of the command.
1207 @node Target directory
1208 @section Target directory
1210 @cindex target directory
1212 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1213 commands normally treat the last operand specially when it is a
1214 directory or a symbolic link to a directory. For example, @samp{cp
1215 source dest} is equivalent to @samp{cp source dest/source} if
1216 @file{dest} is a directory. Sometimes this behavior is not exactly
1217 what is wanted, so these commands support the following options to
1218 allow more fine-grained control:
1223 @itemx --no-target-directory
1224 @opindex --no-target-directory
1225 @cindex target directory
1226 @cindex destination directory
1227 Do not treat the last operand specially when it is a directory or a
1228 symbolic link to a directory. This can help avoid race conditions in
1229 programs that operate in a shared area. For example, when the command
1230 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1231 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1232 renamed to @file{/tmp/dest/source} instead, if some other process
1233 created @file{/tmp/dest} as a directory. However, if @file{mv
1234 -T /tmp/source /tmp/dest} succeeds, there is no
1235 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1237 In the opposite situation, where you want the last operand to be
1238 treated as a directory and want a diagnostic otherwise, you can use
1239 the @option{--target-directory} (@option{-t}) option.
1241 @item -t @var{directory}
1242 @itemx @w{@kbd{--target-directory}=@var{directory}}
1243 @opindex --target-directory
1244 @cindex target directory
1245 @cindex destination directory
1246 Use @var{directory} as the directory component of each destination
1249 The interface for most programs is that after processing options and a
1250 finite (possibly zero) number of fixed-position arguments, the remaining
1251 argument list is either expected to be empty, or is a list of items
1252 (usually files) that will all be handled identically. The @command{xargs}
1253 program is designed to work well with this convention.
1255 The commands in the @command{mv}-family are unusual in that they take
1256 a variable number of arguments with a special case at the @emph{end}
1257 (namely, the target directory). This makes it nontrivial to perform some
1258 operations, e.g., ``move all files from here to ../d/'', because
1259 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1260 doesn't have a clean way to specify an extra final argument for each
1261 invocation of the subject command. (It can be done by going through a
1262 shell command, but that requires more human labor and brain power than
1265 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1266 @command{install}, @command{ln}, and @command{mv} programs to be used
1267 conveniently with @command{xargs}. For example, you can move the files
1268 from the current directory to a sibling directory, @code{d} like this:
1271 ls | xargs mv -t ../d --
1274 However, this doesn't move files whose names begin with @samp{.}.
1275 If you use the @sc{gnu} @command{find} program, you can move those
1276 files too, with this command:
1279 find . -mindepth 1 -maxdepth 1 \
1283 But both of the above approaches fail if there are no files in the
1284 current directory, or if any file has a name containing a blank or
1285 some other special characters.
1286 The following example removes those limitations and requires both
1287 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1290 find . -mindepth 1 -maxdepth 1 -print0 \
1291 | xargs --null --no-run-if-empty \
1298 The @option{--target-directory} (@option{-t}) and
1299 @option{--no-target-directory} (@option{-T})
1300 options cannot be combined.
1302 @node Trailing slashes
1303 @section Trailing slashes
1305 @cindex trailing slashes
1307 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1308 remove any trailing slashes from each @var{source} argument before
1309 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1312 This is useful when a @var{source} argument may have a trailing slash and
1313 @c FIXME: mv's behavior in this case is system-dependent
1314 specify a symbolic link to a directory. This scenario is in fact rather
1315 common because some shells can automatically append a trailing slash when
1316 performing file name completion on such symbolic links. Without this
1317 option, @command{mv}, for example, (via the system's rename function) must
1318 interpret a trailing slash as a request to dereference the symbolic link
1319 and so must rename the indirectly referenced @emph{directory} and not
1320 the symbolic link. Although it may seem surprising that such behavior
1321 be the default, it is required by @acronym{POSIX} and is consistent with
1322 other parts of that standard.
1324 @node Traversing symlinks
1325 @section Traversing symlinks
1327 @cindex symbolic link to directory, controlling traversal of
1329 The following options modify how @command{chown} and @command{chgrp}
1330 @c FIXME: note that `du' has these options, too, but they have slightly
1331 @c different meaning.
1332 traverse a hierarchy when the @option{--recursive} (@option{-R})
1333 option is also specified.
1334 If more than one of the following options is specified, only the final
1336 These options specify whether processing a symbolic link to a directory
1337 entails operating on just the symbolic link or on all files in the
1338 hierarchy rooted at that directory.
1340 These options are independent of @option{--dereference} and
1341 @option{--no-dereference} (@option{-h}), which control whether to modify
1342 a symlink or its referent.
1349 @cindex symbolic link to directory, traverse if on the command line
1350 If @option{--recursive} (@option{-R}) is specified and
1351 a command line argument is a symbolic link to a directory, traverse it.
1358 @cindex symbolic link to directory, traverse each that is encountered
1359 In a recursive traversal, traverse every symbolic link to a directory
1360 that is encountered.
1367 @cindex symbolic link to directory, never traverse
1368 Do not traverse any symbolic links.
1369 This is the default if none of @option{-H}, @option{-L},
1370 or @option{-P} is specified.
1377 @node Treating / specially
1378 @section Treating @file{/} specially
1380 Certain commands can operate destructively on entire hierarchies.
1381 For example, if a user with appropriate privileges mistakenly runs
1382 @samp{rm -rf / tmp/junk}, that may remove
1383 all files on the entire system. Since there are so few
1384 legitimate uses for such a command,
1385 @sc{gnu} @command{rm} normally declines to operate on any directory
1386 that resolves to @file{/}. If you really want to try to remove all
1387 the files on your system, you can use the @option{--no-preserve-root}
1388 option, but the default behavior, specified by the
1389 @option{--preserve-option}, is safer for most purposes.
1391 The commands @command{chgrp}, @command{chmod} and @command{chown}
1392 can also operate destructively on entire hierarchies, so they too
1393 support these options. Although, unlike @command{rm}, they don't
1394 actually unlink files, these commands are arguably more dangerous
1395 when operating recursively on @file{/}, since they often work much
1396 more quickly, and hence damage more files before an alert user can
1397 interrupt them. Tradition and @acronym{POSIX} require these commands
1398 to operate recursively on @file{/}, so they default to
1399 @option{--no-preserve-root}, but using the @option{--preserve-root}
1400 option makes them safer for most purposes. For convenience you can
1401 specify @option{--preserve-root} in an alias or in a shell function.
1403 Note that the @option{--preserve-root} option also ensures
1404 that @command{chgrp} and @command{chown} do not modify @file{/}
1405 even when dereferencing a symlink pointing to @file{/}.
1407 @node Special built-in utilities
1408 @section Special built-in utilities
1410 Some programs like @command{nice} can invoke other programs; for
1411 example, the command @samp{nice cat file} invokes the program
1412 @command{cat} by executing the command @samp{cat file}. However,
1413 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1414 this way. For example, the command @samp{nice exit} does not have a
1415 well-defined behavior: it may generate an error message instead of
1418 Here is a list of the special built-in utilities that are standardized
1419 by @acronym{POSIX} 1003.1-2004.
1422 @t{.@: : break continue eval exec exit export readonly
1423 return set shift times trap unset}
1426 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1427 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1428 pwd} do not work as you might expect.
1430 Many shells extend this list. For example, Bash has several extra
1431 special built-in utilities like @command{history}, and
1432 @command{suspend}, and with Bash the command @samp{nice suspend}
1433 generates an error message instead of suspending.
1435 @node Standards conformance
1436 @section Standards conformance
1438 @vindex POSIXLY_CORRECT
1439 In a few cases, the @sc{gnu} utilities' default behavior is
1440 incompatible with the @acronym{POSIX} standard. To suppress these
1441 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1442 variable. Unless you are checking for @acronym{POSIX} conformance, you
1443 probably do not need to define @env{POSIXLY_CORRECT}.
1445 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1446 versions. For example, older versions of @acronym{POSIX} required the
1447 command @samp{sort +1} to sort based on the second and succeeding
1448 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1449 the same command is required to sort the file named @file{+1}, and you
1450 must instead use the command @samp{sort -k 2} to get the field-based
1453 @vindex _POSIX2_VERSION
1454 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1455 that is standard for your system. To cause them to conform to a
1456 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1457 environment variable to a value of the form @var{yyyymm} specifying
1458 the year and month the standard was adopted. Three values are currently
1459 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1460 @acronym{POSIX} 1003.2-1992, @samp{200112} stands for @acronym{POSIX}
1461 1003.1-2001, and @samp{200809} stands for @acronym{POSIX} 1003.1-2008.
1462 For example, if you have a newer system but are running software
1463 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1464 or @samp{tail +10}, you can work around any compatibility problems by setting
1465 @samp{_POSIX2_VERSION=199209} in your environment.
1467 @node Output of entire files
1468 @chapter Output of entire files
1470 @cindex output of entire files
1471 @cindex entire files, output of
1473 These commands read and write entire files, possibly transforming them
1477 * cat invocation:: Concatenate and write files.
1478 * tac invocation:: Concatenate and write files in reverse.
1479 * nl invocation:: Number lines and write files.
1480 * od invocation:: Write files in octal or other formats.
1481 * base64 invocation:: Transform data into printable data.
1484 @node cat invocation
1485 @section @command{cat}: Concatenate and write files
1488 @cindex concatenate and write files
1489 @cindex copying files
1491 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1492 standard input if none are given, to standard output. Synopsis:
1495 cat [@var{option}] [@var{file}]@dots{}
1498 The program accepts the following options. Also see @ref{Common options}.
1506 Equivalent to @option{-vET}.
1509 @itemx --number-nonblank
1511 @opindex --number-nonblank
1512 Number all nonempty output lines, starting with 1.
1516 Equivalent to @option{-vE}.
1521 @opindex --show-ends
1522 Display a @samp{$} after the end of each line.
1528 Number all output lines, starting with 1. This option is ignored
1529 if @option{-b} is in effect.
1532 @itemx --squeeze-blank
1534 @opindex --squeeze-blank
1535 @cindex squeezing empty lines
1536 Suppress repeated adjacent empty lines; output just one empty line
1541 Equivalent to @option{-vT}.
1546 @opindex --show-tabs
1547 Display TAB characters as @samp{^I}.
1551 Ignored; for @acronym{POSIX} compatibility.
1554 @itemx --show-nonprinting
1556 @opindex --show-nonprinting
1557 Display control characters except for LFD and TAB using
1558 @samp{^} notation and precede characters that have the high bit set with
1563 On systems like MS-DOS that distinguish between text and binary files,
1564 @command{cat} normally reads and writes in binary mode. However,
1565 @command{cat} reads in text mode if one of the options
1566 @option{-bensAE} is used or if @command{cat} is reading from standard
1567 input and standard input is a terminal. Similarly, @command{cat}
1568 writes in text mode if one of the options @option{-bensAE} is used or
1569 if standard output is a terminal.
1576 # Output f's contents, then standard input, then g's contents.
1579 # Copy standard input to standard output.
1584 @node tac invocation
1585 @section @command{tac}: Concatenate and write files in reverse
1588 @cindex reversing files
1590 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1591 standard input if none are given, to standard output, reversing the
1592 records (lines by default) in each separately. Synopsis:
1595 tac [@var{option}]@dots{} [@var{file}]@dots{}
1598 @dfn{Records} are separated by instances of a string (newline by
1599 default). By default, this separator string is attached to the end of
1600 the record that it follows in the file.
1602 The program accepts the following options. Also see @ref{Common options}.
1610 The separator is attached to the beginning of the record that it
1611 precedes in the file.
1617 Treat the separator string as a regular expression. Users of @command{tac}
1618 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1619 binary mode, each line of a text file might end with a CR/LF pair
1620 instead of the Unix-style LF.
1622 @item -s @var{separator}
1623 @itemx --separator=@var{separator}
1625 @opindex --separator
1626 Use @var{separator} as the record separator, instead of newline.
1634 @section @command{nl}: Number lines and write files
1637 @cindex numbering lines
1638 @cindex line numbering
1640 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1641 standard input if none are given, to standard output, with line numbers
1642 added to some or all of the lines. Synopsis:
1645 nl [@var{option}]@dots{} [@var{file}]@dots{}
1648 @cindex logical pages, numbering on
1649 @command{nl} decomposes its input into (logical) pages; by default, the
1650 line number is reset to 1 at the top of each logical page. @command{nl}
1651 treats all of the input files as a single document; it does not reset
1652 line numbers or logical pages between files.
1654 @cindex headers, numbering
1655 @cindex body, numbering
1656 @cindex footers, numbering
1657 A logical page consists of three sections: header, body, and footer.
1658 Any of the sections can be empty. Each can be numbered in a different
1659 style from the others.
1661 The beginnings of the sections of logical pages are indicated in the
1662 input file by a line containing exactly one of these delimiter strings:
1673 The two characters from which these strings are made can be changed from
1674 @samp{\} and @samp{:} via options (see below), but the pattern and
1675 length of each string cannot be changed.
1677 A section delimiter is replaced by an empty line on output. Any text
1678 that comes before the first section delimiter string in the input file
1679 is considered to be part of a body section, so @command{nl} treats a
1680 file that contains no section delimiters as a single body section.
1682 The program accepts the following options. Also see @ref{Common options}.
1686 @item -b @var{style}
1687 @itemx --body-numbering=@var{style}
1689 @opindex --body-numbering
1690 Select the numbering style for lines in the body section of each
1691 logical page. When a line is not numbered, the current line number
1692 is not incremented, but the line number separator character is still
1693 prepended to the line. The styles are:
1699 number only nonempty lines (default for body),
1701 do not number lines (default for header and footer),
1703 number only lines that contain a match for the basic regular
1704 expression @var{bre}.
1705 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1709 @itemx --section-delimiter=@var{cd}
1711 @opindex --section-delimiter
1712 @cindex section delimiters of pages
1713 Set the section delimiter characters to @var{cd}; default is
1714 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1715 (Remember to protect @samp{\} or other metacharacters from shell
1716 expansion with quotes or extra backslashes.)
1718 @item -f @var{style}
1719 @itemx --footer-numbering=@var{style}
1721 @opindex --footer-numbering
1722 Analogous to @option{--body-numbering}.
1724 @item -h @var{style}
1725 @itemx --header-numbering=@var{style}
1727 @opindex --header-numbering
1728 Analogous to @option{--body-numbering}.
1730 @item -i @var{number}
1731 @itemx --line-increment=@var{number}
1733 @opindex --line-increment
1734 Increment line numbers by @var{number} (default 1).
1736 @item -l @var{number}
1737 @itemx --join-blank-lines=@var{number}
1739 @opindex --join-blank-lines
1740 @cindex empty lines, numbering
1741 @cindex blank lines, numbering
1742 Consider @var{number} (default 1) consecutive empty lines to be one
1743 logical line for numbering, and only number the last one. Where fewer
1744 than @var{number} consecutive empty lines occur, do not number them.
1745 An empty line is one that contains no characters, not even spaces
1748 @item -n @var{format}
1749 @itemx --number-format=@var{format}
1751 @opindex --number-format
1752 Select the line numbering format (default is @code{rn}):
1756 @opindex ln @r{format for @command{nl}}
1757 left justified, no leading zeros;
1759 @opindex rn @r{format for @command{nl}}
1760 right justified, no leading zeros;
1762 @opindex rz @r{format for @command{nl}}
1763 right justified, leading zeros.
1767 @itemx --no-renumber
1769 @opindex --no-renumber
1770 Do not reset the line number at the start of a logical page.
1772 @item -s @var{string}
1773 @itemx --number-separator=@var{string}
1775 @opindex --number-separator
1776 Separate the line number from the text line in the output with
1777 @var{string} (default is the TAB character).
1779 @item -v @var{number}
1780 @itemx --starting-line-number=@var{number}
1782 @opindex --starting-line-number
1783 Set the initial line number on each logical page to @var{number} (default 1).
1785 @item -w @var{number}
1786 @itemx --number-width=@var{number}
1788 @opindex --number-width
1789 Use @var{number} characters for line numbers (default 6).
1797 @section @command{od}: Write files in octal or other formats
1800 @cindex octal dump of files
1801 @cindex hex dump of files
1802 @cindex ASCII dump of files
1803 @cindex file contents, dumping unambiguously
1805 @command{od} writes an unambiguous representation of each @var{file}
1806 (@samp{-} means standard input), or standard input if none are given.
1810 od [@var{option}]@dots{} [@var{file}]@dots{}
1811 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1812 od [@var{option}]@dots{} --traditional [@var{file}]@c
1813 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1816 Each line of output consists of the offset in the input, followed by
1817 groups of data from the file. By default, @command{od} prints the offset in
1818 octal, and each group of file data is a C @code{short int}'s worth of input
1819 printed as a single octal number.
1821 If @var{offset} is given, it specifies how many input bytes to skip
1822 before formatting and writing. By default, it is interpreted as an
1823 octal number, but the optional trailing decimal point causes it to be
1824 interpreted as decimal. If no decimal is specified and the offset
1825 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1826 number. If there is a trailing @samp{b}, the number of bytes skipped
1827 will be @var{offset} multiplied by 512.
1829 If a command is of both the first and second forms, the second form is
1830 assumed if the last operand begins with @samp{+} or (if there are two
1831 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1832 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1835 The program accepts the following options. Also see @ref{Common options}.
1839 @item -A @var{radix}
1840 @itemx --address-radix=@var{radix}
1842 @opindex --address-radix
1843 @cindex radix for file offsets
1844 @cindex file offset radix
1845 Select the base in which file offsets are printed. @var{radix} can
1846 be one of the following:
1856 none (do not print offsets).
1859 The default is octal.
1861 @item -j @var{bytes}
1862 @itemx --skip-bytes=@var{bytes}
1864 @opindex --skip-bytes
1865 Skip @var{bytes} input bytes before formatting and writing. If
1866 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1867 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1869 @multiplierSuffixes{bytes}
1871 @item -N @var{bytes}
1872 @itemx --read-bytes=@var{bytes}
1874 @opindex --read-bytes
1875 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1876 @code{bytes} are interpreted as for the @option{-j} option.
1878 @item -S @var{bytes}
1879 @itemx --strings[=@var{bytes}]
1882 @cindex string constants, outputting
1883 Instead of the normal output, output only @dfn{string constants}: at
1884 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1885 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1886 Prefixes and suffixes on @var{bytes} are interpreted as for the
1889 If @var{n} is omitted with @option{--strings}, the default is 3.
1892 @itemx --format=@var{type}
1895 Select the format in which to output the file data. @var{type} is a
1896 string of one or more of the below type indicator characters. If you
1897 include more than one type indicator character in a single @var{type}
1898 string, or use this option more than once, @command{od} writes one copy
1899 of each output line using each of the data types that you specified,
1900 in the order that you specified.
1902 Adding a trailing ``z'' to any type specification appends a display
1903 of the @acronym{ASCII} character representation of the printable characters
1904 to the output line generated by the type specification.
1908 named character, ignoring high-order bit
1910 @acronym{ASCII} character or backslash escape,
1914 floating point (@pxref{Floating point})
1923 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1924 newline, and @samp{nul} for a zero byte. Only the least significant
1925 seven bits of each byte is used; the high-order bit is ignored.
1926 Type @code{c} outputs
1927 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1930 Except for types @samp{a} and @samp{c}, you can specify the number
1931 of bytes to use in interpreting each number in the given data type
1932 by following the type indicator character with a decimal integer.
1933 Alternately, you can specify the size of one of the C compiler's
1934 built-in data types by following the type indicator character with
1935 one of the following characters. For integers (@samp{d}, @samp{o},
1936 @samp{u}, @samp{x}):
1949 For floating point (@code{f}):
1961 @itemx --output-duplicates
1963 @opindex --output-duplicates
1964 Output consecutive lines that are identical. By default, when two or
1965 more consecutive output lines would be identical, @command{od} outputs only
1966 the first line, and puts just an asterisk on the following line to
1967 indicate the elision.
1970 @itemx --width[=@var{n}]
1973 Dump @code{n} input bytes per output line. This must be a multiple of
1974 the least common multiple of the sizes associated with the specified
1977 If this option is not given at all, the default is 16. If @var{n} is
1978 omitted, the default is 32.
1982 The next several options are shorthands for format specifications.
1983 @sc{gnu} @command{od} accepts any combination of shorthands and format
1984 specification options. These options accumulate.
1990 Output as named characters. Equivalent to @samp{-t a}.
1994 Output as octal bytes. Equivalent to @samp{-t o1}.
1998 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
2003 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
2007 Output as floats. Equivalent to @samp{-t fF}.
2011 Output as decimal ints. Equivalent to @samp{-t dI}.
2015 Output as decimal long ints. Equivalent to @samp{-t dL}.
2019 Output as octal two-byte units. Equivalent to @option{-t o2}.
2023 Output as decimal two-byte units. Equivalent to @option{-t d2}.
2027 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
2030 @opindex --traditional
2031 Recognize the non-option label argument that traditional @command{od}
2032 accepted. The following syntax:
2035 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2039 can be used to specify at most one file and optional arguments
2040 specifying an offset and a pseudo-start address, @var{label}.
2041 The @var{label} argument is interpreted
2042 just like @var{offset}, but it specifies an initial pseudo-address. The
2043 pseudo-addresses are displayed in parentheses following any normal
2050 @node base64 invocation
2051 @section @command{base64}: Transform data into printable data
2054 @cindex base64 encoding
2056 @command{base64} transforms data read from a file, or standard input,
2057 into (or from) base64 encoded form. The base64 encoded form uses
2058 printable @acronym{ASCII} characters to represent binary data.
2062 base64 [@var{option}]@dots{} [@var{file}]
2063 base64 --decode [@var{option}]@dots{} [@var{file}]
2066 The base64 encoding expands data to roughly 133% of the original.
2067 The format conforms to
2068 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2070 The program accepts the following options. Also see @ref{Common options}.
2075 @itemx --wrap=@var{cols}
2079 @cindex column to wrap data after
2080 During encoding, wrap lines after @var{cols} characters. This must be
2083 The default is to wrap after 76 characters. Use the value 0 to
2084 disable line wrapping altogether.
2090 @cindex Decode base64 data
2091 @cindex Base64 decoding
2092 Change the mode of operation, from the default of encoding data, to
2093 decoding data. Input is expected to be base64 encoded data, and the
2094 output will be the original data.
2097 @itemx --ignore-garbage
2099 @opindex --ignore-garbage
2100 @cindex Ignore garbage in base64 stream
2101 When decoding, newlines are always accepted.
2102 During decoding, ignore unrecognized bytes,
2103 to permit distorted data to be decoded.
2110 @node Formatting file contents
2111 @chapter Formatting file contents
2113 @cindex formatting file contents
2115 These commands reformat the contents of files.
2118 * fmt invocation:: Reformat paragraph text.
2119 * pr invocation:: Paginate or columnate files for printing.
2120 * fold invocation:: Wrap input lines to fit in specified width.
2124 @node fmt invocation
2125 @section @command{fmt}: Reformat paragraph text
2128 @cindex reformatting paragraph text
2129 @cindex paragraphs, reformatting
2130 @cindex text, reformatting
2132 @command{fmt} fills and joins lines to produce output lines of (at most)
2133 a given number of characters (75 by default). Synopsis:
2136 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2139 @command{fmt} reads from the specified @var{file} arguments (or standard
2140 input if none are given), and writes to standard output.
2142 By default, blank lines, spaces between words, and indentation are
2143 preserved in the output; successive input lines with different
2144 indentation are not joined; tabs are expanded on input and introduced on
2147 @cindex line-breaking
2148 @cindex sentences and line-breaking
2149 @cindex Knuth, Donald E.
2150 @cindex Plass, Michael F.
2151 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2152 avoid line breaks after the first word of a sentence or before the last
2153 word of a sentence. A @dfn{sentence break} is defined as either the end
2154 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2155 spaces or end of line, ignoring any intervening parentheses or quotes.
2156 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2157 breaks; the algorithm is a variant of that given by Donald E. Knuth
2158 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2159 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2162 The program accepts the following options. Also see @ref{Common options}.
2167 @itemx --crown-margin
2169 @opindex --crown-margin
2170 @cindex crown margin
2171 @dfn{Crown margin} mode: preserve the indentation of the first two
2172 lines within a paragraph, and align the left margin of each subsequent
2173 line with that of the second line.
2176 @itemx --tagged-paragraph
2178 @opindex --tagged-paragraph
2179 @cindex tagged paragraphs
2180 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2181 indentation of the first line of a paragraph is the same as the
2182 indentation of the second, the first line is treated as a one-line
2188 @opindex --split-only
2189 Split lines only. Do not join short lines to form longer ones. This
2190 prevents sample lines of code, and other such ``formatted'' text from
2191 being unduly combined.
2194 @itemx --uniform-spacing
2196 @opindex --uniform-spacing
2197 Uniform spacing. Reduce spacing between words to one space, and spacing
2198 between sentences to two spaces.
2201 @itemx -w @var{width}
2202 @itemx --width=@var{width}
2203 @opindex -@var{width}
2206 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2207 initially tries to make lines about 7% shorter than this, to give it
2208 room to balance line lengths.
2210 @item -p @var{prefix}
2211 @itemx --prefix=@var{prefix}
2212 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2213 are subject to formatting. The prefix and any preceding whitespace are
2214 stripped for the formatting and then re-attached to each formatted output
2215 line. One use is to format certain kinds of program comments, while
2216 leaving the code unchanged.
2224 @section @command{pr}: Paginate or columnate files for printing
2227 @cindex printing, preparing files for
2228 @cindex multicolumn output, generating
2229 @cindex merging files in parallel
2231 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2232 standard input if none are given, to standard output, paginating and
2233 optionally outputting in multicolumn format; optionally merges all
2234 @var{file}s, printing all in parallel, one per column. Synopsis:
2237 pr [@var{option}]@dots{} [@var{file}]@dots{}
2241 By default, a 5-line header is printed at each page: two blank lines;
2242 a line with the date, the file name, and the page count; and two more
2243 blank lines. A footer of five blank lines is also printed.
2244 The default @var{page_length} is 66
2245 lines. The default number of text lines is therefore 56.
2246 The text line of the header takes the form
2247 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2248 @var{string} so that the line takes up the full @var{page_width}. Here,
2249 @var{date} is the date (see the @option{-D} or @option{--date-format}
2250 option for details), @var{string} is the centered header string, and
2251 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2252 category affects the spelling of @var{page}; in the default C locale, it
2253 is @samp{Page @var{number}} where @var{number} is the decimal page
2256 Form feeds in the input cause page breaks in the output. Multiple form
2257 feeds produce empty pages.
2259 Columns are of equal width, separated by an optional string (default
2260 is @samp{space}). For multicolumn output, lines will always be truncated to
2261 @var{page_width} (default 72), unless you use the @option{-J} option.
2263 column output no line truncation occurs by default. Use @option{-W} option to
2264 truncate lines in that case.
2266 The following changes were made in version 1.22i and apply to later
2267 versions of @command{pr}:
2268 @c FIXME: this whole section here sounds very awkward to me. I
2269 @c made a few small changes, but really it all needs to be redone. - Brian
2270 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2275 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2276 redefined for better @acronym{POSIX} compliance. The output of some further
2277 cases has been adapted to other Unix systems. These changes are not
2278 compatible with earlier versions of the program.
2281 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2282 have been introduced to turn off unexpected interferences of small letter
2283 options. The @option{-N} option and the second argument @var{last_page}
2284 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2285 form feeds set in the input files requires the @option{-T} option.
2288 Capital letter options override small letter ones.
2291 Some of the option-arguments (compare @option{-s}, @option{-e},
2292 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2293 preceding option letter (already stated in the @acronym{POSIX} specification).
2296 The program accepts the following options. Also see @ref{Common options}.
2300 @item +@var{first_page}[:@var{last_page}]
2301 @itemx --pages=@var{first_page}[:@var{last_page}]
2302 @c The two following @opindex lines evoke warnings because they contain `:'
2303 @c The `info' spec does not permit that. If we use those lines, we end
2304 @c up with truncated index entries that don't work.
2305 @c @opindex +@var{first_page}[:@var{last_page}]
2306 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2307 @opindex +@var{page_range}
2308 @opindex --pages=@var{page_range}
2309 Begin printing with page @var{first_page} and stop with @var{last_page}.
2310 Missing @samp{:@var{last_page}} implies end of file. While estimating
2311 the number of skipped pages each form feed in the input file results
2312 in a new page. Page counting with and without @samp{+@var{first_page}}
2313 is identical. By default, counting starts with the first page of input
2314 file (not first page printed). Line numbering may be altered by @option{-N}
2318 @itemx --columns=@var{column}
2319 @opindex -@var{column}
2321 @cindex down columns
2322 With each single @var{file}, produce @var{column} columns of output
2323 (default is 1) and print columns down, unless @option{-a} is used. The
2324 column width is automatically decreased as @var{column} increases; unless
2325 you use the @option{-W/-w} option to increase @var{page_width} as well.
2326 This option might well cause some lines to be truncated. The number of
2327 lines in the columns on each page are balanced. The options @option{-e}
2328 and @option{-i} are on for multiple text-column output. Together with
2329 @option{-J} option column alignment and line truncation is turned off.
2330 Lines of full length are joined in a free field format and @option{-S}
2331 option may set field separators. @option{-@var{column}} may not be used
2332 with @option{-m} option.
2338 @cindex across columns
2339 With each single @var{file}, print columns across rather than down. The
2340 @option{-@var{column}} option must be given with @var{column} greater than one.
2341 If a line is too long to fit in a column, it is truncated.
2344 @itemx --show-control-chars
2346 @opindex --show-control-chars
2347 Print control characters using hat notation (e.g., @samp{^G}); print
2348 other nonprinting characters in octal backslash notation. By default,
2349 nonprinting characters are not changed.
2352 @itemx --double-space
2354 @opindex --double-space
2355 @cindex double spacing
2356 Double space the output.
2358 @item -D @var{format}
2359 @itemx --date-format=@var{format}
2360 @cindex time formats
2361 @cindex formatting times
2362 Format header dates using @var{format}, using the same conventions as
2363 for the command @samp{date +@var{format}}; @xref{date invocation}.
2364 Except for directives, which start with
2365 @samp{%}, characters in @var{format} are printed unchanged. You can use
2366 this option to specify an arbitrary string in place of the header date,
2367 e.g., @option{--date-format="Monday morning"}.
2369 @vindex POSIXLY_CORRECT
2371 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2372 @samp{2001-12-04 23:59});
2373 but if the @env{POSIXLY_CORRECT} environment variable is set
2374 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2375 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2376 @samp{Dec@ @ 4 23:59 2001}.
2379 Time stamps are listed according to the time zone rules specified by
2380 the @env{TZ} environment variable, or by the system default rules if
2381 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2382 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2384 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2385 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2387 @opindex --expand-tabs
2389 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2390 the input tab character (default is the TAB character). Second optional
2391 argument @var{in-tabwidth} is the input tab character's width (default
2399 @opindex --form-feed
2400 Use a form feed instead of newlines to separate output pages. This does
2401 not alter the default page length of 66 lines.
2403 @item -h @var{header}
2404 @itemx --header=@var{header}
2407 Replace the file name in the header with the centered string @var{header}.
2408 When using the shell, @var{header} should be quoted and should be
2409 separated from @option{-h} by a space.
2411 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2412 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2414 @opindex --output-tabs
2416 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2417 is the output tab character (default is the TAB character). Second optional
2418 argument @var{out-tabwidth} is the output tab character's width (default
2424 @opindex --join-lines
2425 Merge lines of full length. Used together with the column options
2426 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2427 @option{-W/-w} line truncation;
2428 no column alignment used; may be used with
2429 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2430 (together with @option{-W} and @option{--sep-string})
2431 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2432 @option{-s} along with the three column options.
2435 @item -l @var{page_length}
2436 @itemx --length=@var{page_length}
2439 Set the page length to @var{page_length} (default 66) lines, including
2440 the lines of the header [and the footer]. If @var{page_length} is less
2441 than or equal to 10, the header and footer are omitted, as if the
2442 @option{-t} option had been given.
2448 Merge and print all @var{file}s in parallel, one in each column. If a
2449 line is too long to fit in a column, it is truncated, unless the @option{-J}
2450 option is used. @option{--sep-string[=@var{string}]} may be used.
2452 some @var{file}s (form feeds set) produce empty columns, still marked
2453 by @var{string}. The result is a continuous line numbering and column
2454 marking throughout the whole merged file. Completely empty merged pages
2455 show no separators or line numbers. The default header becomes
2456 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2457 may be used with the @option{-h} or @option{--header} option to fill up
2458 the middle blank part.
2460 @item -n[@var{number-separator}[@var{digits}]]
2461 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2463 @opindex --number-lines
2464 Provide @var{digits} digit line numbering (default for @var{digits} is
2465 5). With multicolumn output the number occupies the first @var{digits}
2466 column positions of each text column or only each line of @option{-m}
2467 output. With single column output the number precedes each line just as
2468 @option{-m} does. Default counting of the line numbers starts with the
2469 first line of the input file (not the first line printed, compare the
2470 @option{--page} option and @option{-N} option).
2471 Optional argument @var{number-separator} is the character appended to
2472 the line number to separate it from the text followed. The default
2473 separator is the TAB character. In a strict sense a TAB is always
2474 printed with single column output only. The TAB width varies
2475 with the TAB position, e.g., with the left @var{margin} specified
2476 by @option{-o} option. With multicolumn output priority is given to
2477 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2478 The TAB width is fixed to the value of the first column and does
2479 not change with different values of left @var{margin}. That means a
2480 fixed number of spaces is always printed in the place of the
2481 @var{number-separator} TAB. The tabification depends upon the output
2484 @item -N @var{line_number}
2485 @itemx --first-line-number=@var{line_number}
2487 @opindex --first-line-number
2488 Start line counting with the number @var{line_number} at first line of
2489 first page printed (in most cases not the first line of the input file).
2491 @item -o @var{margin}
2492 @itemx --indent=@var{margin}
2495 @cindex indenting lines
2497 Indent each line with a margin @var{margin} spaces wide (default is zero).
2498 The total page width is the size of the margin plus the @var{page_width}
2499 set with the @option{-W/-w} option. A limited overflow may occur with
2500 numbered single column output (compare @option{-n} option).
2503 @itemx --no-file-warnings
2505 @opindex --no-file-warnings
2506 Do not print a warning message when an argument @var{file} cannot be
2507 opened. (The exit status will still be nonzero, however.)
2509 @item -s[@var{char}]
2510 @itemx --separator[=@var{char}]
2512 @opindex --separator
2513 Separate columns by a single character @var{char}. The default for
2514 @var{char} is the TAB character without @option{-w} and @samp{no
2515 character} with @option{-w}. Without @option{-s} the default separator
2516 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2517 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2518 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2521 @item -S@var{string}
2522 @itemx --sep-string[=@var{string}]
2524 @opindex --sep-string
2525 Use @var{string} to separate output columns. The @option{-S} option doesn't
2526 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2527 does not affect line truncation or column alignment.
2528 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2530 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2531 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2532 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2535 @itemx --omit-header
2537 @opindex --omit-header
2538 Do not print the usual header [and footer] on each page, and do not fill
2539 out the bottom of pages (with blank lines or a form feed). No page
2540 structure is produced, but form feeds set in the input files are retained.
2541 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2542 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2543 in the input file to 4 spaces but don't make any other changes. Use of
2544 @option{-t} overrides @option{-h}.
2547 @itemx --omit-pagination
2549 @opindex --omit-pagination
2550 Do not print header [and footer]. In addition eliminate all form feeds
2551 set in the input files.
2554 @itemx --show-nonprinting
2556 @opindex --show-nonprinting
2557 Print nonprinting characters in octal backslash notation.
2559 @item -w @var{page_width}
2560 @itemx --width=@var{page_width}
2563 Set page width to @var{page_width} characters for multiple text-column
2564 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2565 off the default page width and any line truncation and column alignment.
2566 Lines of full length are merged, regardless of the column options
2567 set. No @var{page_width} setting is possible with single column output.
2568 A @acronym{POSIX}-compliant formulation.
2570 @item -W @var{page_width}
2571 @itemx --page_width=@var{page_width}
2573 @opindex --page_width
2574 Set the page width to @var{page_width} characters. That's valid with and
2575 without a column option. Text lines are truncated, unless @option{-J}
2576 is used. Together with one of the three column options
2577 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2578 alignment is always used. The separator options @option{-S} or @option{-s}
2579 don't affect the @option{-W} option. Default is 72 characters. Without
2580 @option{-W @var{page_width}} and without any of the column options NO line
2581 truncation is used (defined to keep downward compatibility and to meet
2582 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2583 line is never truncated.
2590 @node fold invocation
2591 @section @command{fold}: Wrap input lines to fit in specified width
2594 @cindex wrapping long input lines
2595 @cindex folding long input lines
2597 @command{fold} writes each @var{file} (@option{-} means standard input), or
2598 standard input if none are given, to standard output, breaking long
2602 fold [@var{option}]@dots{} [@var{file}]@dots{}
2605 By default, @command{fold} breaks lines wider than 80 columns. The output
2606 is split into as many lines as necessary.
2608 @cindex screen columns
2609 @command{fold} counts screen columns by default; thus, a tab may count more
2610 than one column, backspace decreases the column count, and carriage
2611 return sets the column to zero.
2613 The program accepts the following options. Also see @ref{Common options}.
2621 Count bytes rather than columns, so that tabs, backspaces, and carriage
2622 returns are each counted as taking up one column, just like other
2629 Break at word boundaries: the line is broken after the last blank before
2630 the maximum line length. If the line contains no such blanks, the line
2631 is broken at the maximum line length as usual.
2633 @item -w @var{width}
2634 @itemx --width=@var{width}
2637 Use a maximum line length of @var{width} columns instead of 80.
2639 For compatibility @command{fold} supports an obsolete option syntax
2640 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2648 @node Output of parts of files
2649 @chapter Output of parts of files
2651 @cindex output of parts of files
2652 @cindex parts of files, output of
2654 These commands output pieces of the input.
2657 * head invocation:: Output the first part of files.
2658 * tail invocation:: Output the last part of files.
2659 * split invocation:: Split a file into pieces.
2660 * csplit invocation:: Split a file into context-determined pieces.
2663 @node head invocation
2664 @section @command{head}: Output the first part of files
2667 @cindex initial part of files, outputting
2668 @cindex first part of files, outputting
2670 @command{head} prints the first part (10 lines by default) of each
2671 @var{file}; it reads from standard input if no files are given or
2672 when given a @var{file} of @option{-}. Synopsis:
2675 head [@var{option}]@dots{} [@var{file}]@dots{}
2678 If more than one @var{file} is specified, @command{head} prints a
2679 one-line header consisting of:
2682 ==> @var{file name} <==
2686 before the output for each @var{file}.
2688 The program accepts the following options. Also see @ref{Common options}.
2693 @itemx --bytes=@var{k}
2696 Print the first @var{k} bytes, instead of initial lines.
2697 However, if @var{k} starts with a @samp{-},
2698 print all but the last @var{k} bytes of each file.
2699 @multiplierSuffixes{k}
2702 @itemx --lines=@var{k}
2705 Output the first @var{k} lines.
2706 However, if @var{k} starts with a @samp{-},
2707 print all but the last @var{k} lines of each file.
2708 Size multiplier suffixes are the same as with the @option{-c} option.
2716 Never print file name headers.
2722 Always print file name headers.
2726 For compatibility @command{head} also supports an obsolete option syntax
2727 @option{-@var{count}@var{options}}, which is recognized only if it is
2728 specified first. @var{count} is a decimal number optionally followed
2729 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2730 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2731 Scripts intended for standard hosts should use @option{-c @var{count}}
2732 or @option{-n @var{count}} instead. If your script must also run on
2733 hosts that support only the obsolete syntax, it is usually simpler to
2734 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2740 @node tail invocation
2741 @section @command{tail}: Output the last part of files
2744 @cindex last part of files, outputting
2746 @command{tail} prints the last part (10 lines by default) of each
2747 @var{file}; it reads from standard input if no files are given or
2748 when given a @var{file} of @samp{-}. Synopsis:
2751 tail [@var{option}]@dots{} [@var{file}]@dots{}
2754 If more than one @var{file} is specified, @command{tail} prints a
2755 one-line header consisting of:
2758 ==> @var{file name} <==
2762 before the output for each @var{file}.
2764 @cindex BSD @command{tail}
2765 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2766 @command{tail} cannot). It also has no @option{-r} option (print in
2767 reverse), since reversing a file is really a different job from printing
2768 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2769 only reverse files that are at most as large as its buffer, which is
2770 typically 32 KiB@. A more reliable and versatile way to reverse files is
2771 the @sc{gnu} @command{tac} command.
2773 The program accepts the following options. Also see @ref{Common options}.
2778 @itemx --bytes=@var{k}
2781 Output the last @var{k} bytes, instead of final lines.
2782 However, if @var{k} starts with a @samp{+}, start printing with the
2783 @var{k}th byte from the start of each file, instead of from the end.
2784 @multiplierSuffixes{k}
2787 @itemx --follow[=@var{how}]
2790 @cindex growing files
2791 @vindex name @r{follow option}
2792 @vindex descriptor @r{follow option}
2793 Loop forever trying to read more characters at the end of the file,
2794 presumably because the file is growing.
2795 If more than one file is given, @command{tail} prints a header whenever it
2796 gets output from a different file, to indicate which file that output is
2799 There are two ways to specify how you'd like to track files with this option,
2800 but that difference is noticeable only when a followed file is removed or
2802 If you'd like to continue to track the end of a growing file even after
2803 it has been unlinked, use @option{--follow=descriptor}. This is the default
2804 behavior, but it is not useful if you're tracking a log file that may be
2805 rotated (removed or renamed, then reopened). In that case, use
2806 @option{--follow=name} to track the named file, perhaps by reopening it
2807 periodically to see if it has been removed and recreated by some other program.
2808 Note that the inotify-based implementation handles this case without
2809 the need for any periodic reopening.
2811 No matter which method you use, if the tracked file is determined to have
2812 shrunk, @command{tail} prints a message saying the file has been truncated
2813 and resumes tracking the end of the file from the newly-determined endpoint.
2815 When a file is removed, @command{tail}'s behavior depends on whether it is
2816 following the name or the descriptor. When following by name, tail can
2817 detect that a file has been removed and gives a message to that effect,
2818 and if @option{--retry} has been specified it will continue checking
2819 periodically to see if the file reappears.
2820 When following a descriptor, tail does not detect that the file has
2821 been unlinked or renamed and issues no message; even though the file
2822 may no longer be accessible via its original name, it may still be
2825 The option values @samp{descriptor} and @samp{name} may be specified only
2826 with the long form of the option, not with @option{-f}.
2828 The @option{-f} option is ignored if
2829 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2830 Likewise, the @option{-f} option has no effect for any
2831 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2833 With kernel inotify support, output is triggered by file changes
2834 and is generally very prompt.
2835 Otherwise, @command{tail} sleeps for one second between checks---
2836 use @option{--sleep-interval=@var{n}} to change that default---which can
2837 make the output appear slightly less responsive or bursty.
2838 When using tail without inotify support, you can make it more responsive
2839 by using a sub-second sleep interval, e.g., via an alias like this:
2842 alias tail='tail -s.1'
2847 This option is the same as @option{--follow=name --retry}. That is, tail
2848 will attempt to reopen a file when it is removed. Should this fail, tail
2849 will keep trying until it becomes accessible again.
2853 This option is useful mainly when following by name (i.e., with
2854 @option{--follow=name}).
2855 Without this option, when tail encounters a file that doesn't
2856 exist or is otherwise inaccessible, it reports that fact and
2857 never checks it again.
2859 @itemx --sleep-interval=@var{number}
2860 @opindex --sleep-interval
2861 Change the number of seconds to wait between iterations (the default is 1.0).
2862 During one iteration, every specified file is checked to see if it has
2864 Historical implementations of @command{tail} have required that
2865 @var{number} be an integer. However, GNU @command{tail} accepts
2866 an arbitrary floating point number. @xref{Floating point}.
2867 When @command{tail} uses inotify, this polling-related option
2868 is usually ignored. However, if you also specify @option{--pid=@var{p}},
2869 @command{tail} checks whether process @var{p} is alive at least
2870 every @var{number} seconds.
2872 @itemx --pid=@var{pid}
2874 When following by name or by descriptor, you may specify the process ID,
2875 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2876 after that process terminates, tail will also terminate. This will
2877 work properly only if the writer and the tailing process are running on
2878 the same machine. For example, to save the output of a build in a file
2879 and to watch the file grow, if you invoke @command{make} and @command{tail}
2880 like this then the tail process will stop when your build completes.
2881 Without this option, you would have had to kill the @code{tail -f}
2885 $ make >& makerr & tail --pid=$! -f makerr
2888 If you specify a @var{pid} that is not in use or that does not correspond
2889 to the process that is writing to the tailed files, then @command{tail}
2890 may terminate long before any @var{file}s stop growing or it may not
2891 terminate until long after the real writer has terminated.
2892 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2893 will print a warning if this is the case.
2895 @itemx --max-unchanged-stats=@var{n}
2896 @opindex --max-unchanged-stats
2897 When tailing a file by name, if there have been @var{n} (default
2898 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2899 iterations for which the file has not changed, then
2900 @code{open}/@code{fstat} the file to determine if that file name is
2901 still associated with the same device/inode-number pair as before.
2902 When following a log file that is rotated, this is approximately the
2903 number of seconds between when tail prints the last pre-rotation lines
2904 and when it prints the lines that have accumulated in the new log file.
2905 This option is meaningful only when polling (i.e., without inotify)
2906 and when following by name.
2909 @itemx --lines=@var{k}
2912 Output the last @var{k} lines.
2913 However, if @var{k} starts with a @samp{+}, start printing with the
2914 @var{k}th line from the start of each file, instead of from the end.
2915 Size multiplier suffixes are the same as with the @option{-c} option.
2923 Never print file name headers.
2929 Always print file name headers.
2933 For compatibility @command{tail} also supports an obsolete usage
2934 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2935 only if it does not conflict with the usage described
2936 above. This obsolete form uses exactly one option and at most one
2937 file. In the option, @var{count} is an optional decimal number optionally
2938 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2939 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2940 which has the same meaning as @option{-f}.
2942 @vindex _POSIX2_VERSION
2943 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2944 the obsolete option syntax with the same meaning as in counts, and
2945 obsolete usage overrides normal usage when the two conflict.
2946 This obsolete behavior can be enabled or disabled with the
2947 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2950 Scripts intended for use on standard hosts should avoid obsolete
2951 syntax and should use @option{-c @var{count}[b]}, @option{-n
2952 @var{count}}, and/or @option{-f} instead. If your script must also
2953 run on hosts that support only the obsolete syntax, you can often
2954 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2955 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2956 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2957 then @dots{}} to decide which syntax to use.
2959 Even if your script assumes the standard behavior, you should still
2960 beware usages whose behaviors differ depending on the @acronym{POSIX}
2961 version. For example, avoid @samp{tail - main.c}, since it might be
2962 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2963 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2964 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2965 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2970 @node split invocation
2971 @section @command{split}: Split a file into pieces.
2974 @cindex splitting a file into pieces
2975 @cindex pieces, splitting a file into
2977 @command{split} creates output files containing consecutive or interleaved
2978 sections of @var{input} (standard input if none is given or @var{input}
2979 is @samp{-}). Synopsis:
2982 split [@var{option}] [@var{input} [@var{prefix}]]
2985 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2986 left over for the last section), into each output file.
2988 @cindex output file name prefix
2989 The output files' names consist of @var{prefix} (@samp{x} by default)
2990 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2991 default), such that concatenating the output files in traditional
2992 sorted order by file name produces the original input file (except
2993 @option{-r}). If the output file names are exhausted, @command{split}
2994 reports an error without deleting the output files that it did create.
2996 The program accepts the following options. Also see @ref{Common options}.
3000 @item -l @var{lines}
3001 @itemx --lines=@var{lines}
3004 Put @var{lines} lines of @var{input} into each output file.
3006 For compatibility @command{split} also supports an obsolete
3007 option syntax @option{-@var{lines}}. New scripts should use
3008 @option{-l @var{lines}} instead.
3011 @itemx --bytes=@var{size}
3014 Put @var{size} bytes of @var{input} into each output file.
3015 @multiplierSuffixes{size}
3018 @itemx --line-bytes=@var{size}
3020 @opindex --line-bytes
3021 Put into each output file as many complete lines of @var{input} as
3022 possible without exceeding @var{size} bytes. Individual lines longer than
3023 @var{size} bytes are broken into multiple files.
3024 @var{size} has the same format as for the @option{--bytes} option.
3026 @itemx --filter=@var{command}
3028 With this option, rather than simply writing to each output file,
3029 write through a pipe to the specified shell @var{command} for each output file.
3030 @var{command} should use the $FILE environment variable, which is set
3031 to a different output file name for each invocation of the command.
3032 For example, imagine that you have a 1TiB compressed file
3033 that, if uncompressed, would be too large to reside on disk,
3034 yet you must split it into individually-compressed pieces
3035 of a more manageable size.
3036 To do that, you might run this command:
3039 xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
3042 Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
3043 with names @file{big-xaa.xz}, @file{big-xab.xz}, @file{big-xac.xz}, etc.
3045 @item -n @var{chunks}
3046 @itemx --number=@var{chunks}
3050 Split @var{input} to @var{chunks} output files where @var{chunks} may be:
3053 @var{n} generate @var{n} files based on current size of @var{input}
3054 @var{k}/@var{n} only output @var{k}th of @var{n} to stdout
3055 l/@var{n} generate @var{n} files without splitting lines
3056 l/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3057 r/@var{n} like @samp{l} but use round robin distribution
3058 r/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3061 Any excess bytes remaining after dividing the @var{input}
3062 into @var{n} chunks, are assigned to the last chunk.
3063 Any excess bytes appearing after the initial calculation are discarded
3064 (except when using @samp{r} mode).
3066 All @var{n} files are created even if there are fewer than @var{n} lines,
3067 or the @var{input} is truncated.
3069 For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
3070 The @var{input} is partitioned into @var{n} equal sized portions, with
3071 the last assigned any excess. If a line @emph{starts} within a partition
3072 it is written completely to the corresponding file. Since lines
3073 are not split even if they overlap a partition, the files written
3074 can be larger or smaller than the partition size, and even empty
3075 if a line is so long as to completely overlap the partition.
3077 For @samp{r} mode, the size of @var{input} is irrelevant,
3078 and so can be a pipe for example.
3080 @item -a @var{length}
3081 @itemx --suffix-length=@var{length}
3083 @opindex --suffix-length
3084 Use suffixes of length @var{length}. The default @var{length} is 2.
3087 @itemx --numeric-suffixes
3089 @opindex --numeric-suffixes
3090 Use digits in suffixes rather than lower-case letters.
3093 @itemx --elide-empty-files
3095 @opindex --elide-empty-files
3096 Suppress the generation of zero-length output files. This can happen
3097 with the @option{--number} option if a file is (truncated to be) shorter
3098 than the number requested, or if a line is so long as to completely
3099 span a chunk. The output file sequence numbers, always run consecutively
3100 even when this option is specified.
3105 @opindex --unbuffered
3106 Immediately copy input to output in @option{--number r/...} mode,
3107 which is a much slower mode of operation.
3111 Write a diagnostic just before each output file is opened.
3117 Here are a few examples to illustrate how the
3118 @option{--number} (@option{-n}) option works:
3120 Notice how, by default, one line may be split onto two or more:
3123 $ seq -w 6 10 > k; split -n3 k; head xa?
3136 Use the "l/" modifier to suppress that:
3139 $ seq -w 6 10 > k; split -nl/3 k; head xa?
3152 Use the "r/" modifier to distribute lines in a round-robin fashion:
3155 $ seq -w 6 10 > k; split -nr/3 k; head xa?
3168 You can also extract just the Kth chunk.
3169 This extracts and prints just the 7th "chunk" of 33:
3172 $ seq 100 > k; split -nl/7/33 k
3179 @node csplit invocation
3180 @section @command{csplit}: Split a file into context-determined pieces
3183 @cindex context splitting
3184 @cindex splitting a file into pieces by context
3186 @command{csplit} creates zero or more output files containing sections of
3187 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3190 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3193 The contents of the output files are determined by the @var{pattern}
3194 arguments, as detailed below. An error occurs if a @var{pattern}
3195 argument refers to a nonexistent line of the input file (e.g., if no
3196 remaining line matches a given regular expression). After every
3197 @var{pattern} has been matched, any remaining input is copied into one
3200 By default, @command{csplit} prints the number of bytes written to each
3201 output file after it has been created.
3203 The types of pattern arguments are:
3208 Create an output file containing the input up to but not including line
3209 @var{n} (a positive integer). If followed by a repeat count, also
3210 create an output file containing the next @var{n} lines of the input
3211 file once for each repeat.
3213 @item /@var{regexp}/[@var{offset}]
3214 Create an output file containing the current line up to (but not
3215 including) the next line of the input file that contains a match for
3216 @var{regexp}. The optional @var{offset} is an integer.
3217 If it is given, the input up to (but not including) the
3218 matching line plus or minus @var{offset} is put into the output file,
3219 and the line after that begins the next section of input.
3221 @item %@var{regexp}%[@var{offset}]
3222 Like the previous type, except that it does not create an output
3223 file, so that section of the input file is effectively ignored.
3225 @item @{@var{repeat-count}@}
3226 Repeat the previous pattern @var{repeat-count} additional
3227 times. The @var{repeat-count} can either be a positive integer or an
3228 asterisk, meaning repeat as many times as necessary until the input is
3233 The output files' names consist of a prefix (@samp{xx} by default)
3234 followed by a suffix. By default, the suffix is an ascending sequence
3235 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3236 concatenating the output files in sorted order by file name produces the
3237 original input file.
3239 By default, if @command{csplit} encounters an error or receives a hangup,
3240 interrupt, quit, or terminate signal, it removes any output files
3241 that it has created so far before it exits.
3243 The program accepts the following options. Also see @ref{Common options}.
3247 @item -f @var{prefix}
3248 @itemx --prefix=@var{prefix}
3251 @cindex output file name prefix
3252 Use @var{prefix} as the output file name prefix.
3254 @item -b @var{suffix}
3255 @itemx --suffix=@var{suffix}
3258 @cindex output file name suffix
3259 Use @var{suffix} as the output file name suffix. When this option is
3260 specified, the suffix string must include exactly one
3261 @code{printf(3)}-style conversion specification, possibly including
3262 format specification flags, a field width, a precision specifications,
3263 or all of these kinds of modifiers. The format letter must convert a
3264 binary unsigned integer argument to readable form. The format letters
3265 @samp{d} and @samp{i} are aliases for @samp{u}, and the
3266 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3267 entire @var{suffix} is given (with the current output file number) to
3268 @code{sprintf(3)} to form the file name suffixes for each of the
3269 individual output files in turn. If this option is used, the
3270 @option{--digits} option is ignored.
3272 @item -n @var{digits}
3273 @itemx --digits=@var{digits}
3276 Use output file names containing numbers that are @var{digits} digits
3277 long instead of the default 2.
3282 @opindex --keep-files
3283 Do not remove output files when errors are encountered.
3286 @itemx --elide-empty-files
3288 @opindex --elide-empty-files
3289 Suppress the generation of zero-length output files. (In cases where
3290 the section delimiters of the input file are supposed to mark the first
3291 lines of each of the sections, the first output file will generally be a
3292 zero-length file unless you use this option.) The output file sequence
3293 numbers always run consecutively starting from 0, even when this option
3304 Do not print counts of output file sizes.
3310 Here is an example of its usage.
3311 First, create an empty directory for the exercise,
3318 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3321 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3327 Each number printed above is the size of an output
3328 file that csplit has just created.
3329 List the names of those output files:
3336 Use @command{head} to show their contents:
3361 @node Summarizing files
3362 @chapter Summarizing files
3364 @cindex summarizing files
3366 These commands generate just a few numbers representing entire
3370 * wc invocation:: Print newline, word, and byte counts.
3371 * sum invocation:: Print checksum and block counts.
3372 * cksum invocation:: Print CRC checksum and byte counts.
3373 * md5sum invocation:: Print or check MD5 digests.
3374 * sha1sum invocation:: Print or check SHA-1 digests.
3375 * sha2 utilities:: Print or check SHA-2 digests.
3380 @section @command{wc}: Print newline, word, and byte counts
3384 @cindex character count
3388 @command{wc} counts the number of bytes, characters, whitespace-separated
3389 words, and newlines in each given @var{file}, or standard input if none
3390 are given or for a @var{file} of @samp{-}. Synopsis:
3393 wc [@var{option}]@dots{} [@var{file}]@dots{}
3396 @cindex total counts
3397 @command{wc} prints one line of counts for each file, and if the file was
3398 given as an argument, it prints the file name following the counts. If
3399 more than one @var{file} is given, @command{wc} prints a final line
3400 containing the cumulative counts, with the file name @file{total}. The
3401 counts are printed in this order: newlines, words, characters, bytes,
3402 maximum line length.
3403 Each count is printed right-justified in a field with at least one
3404 space between fields so that the numbers and file names normally line
3405 up nicely in columns. The width of the count fields varies depending
3406 on the inputs, so you should not depend on a particular field width.
3407 However, as a @acronym{GNU} extension, if only one count is printed,
3408 it is guaranteed to be printed without leading spaces.
3410 By default, @command{wc} prints three counts: the newline, words, and byte
3411 counts. Options can specify that only certain counts be printed.
3412 Options do not undo others previously given, so
3419 prints both the byte counts and the word counts.
3421 With the @option{--max-line-length} option, @command{wc} prints the length
3422 of the longest line per file, and if there is more than one file it
3423 prints the maximum (not the sum) of those lengths. The line lengths here
3424 are measured in screen columns, according to the current locale and
3425 assuming tab positions in every 8th column.
3427 The program accepts the following options. Also see @ref{Common options}.
3435 Print only the byte counts.
3441 Print only the character counts.
3447 Print only the word counts.
3453 Print only the newline counts.
3456 @itemx --max-line-length
3458 @opindex --max-line-length
3459 Print only the maximum line lengths.
3461 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3462 @itemx --files0-from=@var{file}
3463 @opindex --files0-from=@var{file}
3464 @c This is commented out to avoid a texi2dvi failure.
3465 @c texi2dvi (GNU Texinfo 4.11) 1.104
3466 @c @cindex including files from @command{\cmd\}
3467 Disallow processing files named on the command line, and instead process
3468 those named in file @var{file}; each name being terminated by a zero byte
3469 (@acronym{ASCII} @sc{nul}).
3470 This is useful \withTotalOption\
3471 when the list of file names is so long that it may exceed a command line
3473 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3474 because it splits the list into pieces and makes @command{\cmd\} print
3475 \subListOutput\ for each sublist rather than for the entire list.
3476 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file
3477 names is with @sc{gnu}
3478 @command{find}, using its @option{-print0} predicate.
3479 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated
3480 file names are read from standard input.
3482 @filesZeroFromOption{wc,,a total}
3484 For example, to find the length of the longest line in any @file{.c} or
3485 @file{.h} file in the current hierarchy, do this:
3488 find . -name '*.[ch]' -print0 |
3489 wc -L --files0-from=- | tail -n1
3497 @node sum invocation
3498 @section @command{sum}: Print checksum and block counts
3501 @cindex 16-bit checksum
3502 @cindex checksum, 16-bit
3504 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3505 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3508 sum [@var{option}]@dots{} [@var{file}]@dots{}
3511 @command{sum} prints the checksum for each @var{file} followed by the
3512 number of blocks in the file (rounded up). If more than one @var{file}
3513 is given, file names are also printed (by default). (With the
3514 @option{--sysv} option, corresponding file names are printed when there is
3515 at least one file argument.)
3517 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3518 compatible with BSD @command{sum} and prints file sizes in units of
3521 The program accepts the following options. Also see @ref{Common options}.
3527 @cindex BSD @command{sum}
3528 Use the default (BSD compatible) algorithm. This option is included for
3529 compatibility with the System V @command{sum}. Unless @option{-s} was also
3530 given, it has no effect.
3536 @cindex System V @command{sum}
3537 Compute checksums using an algorithm compatible with System V
3538 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3542 @command{sum} is provided for compatibility; the @command{cksum} program (see
3543 next section) is preferable in new applications.
3548 @node cksum invocation
3549 @section @command{cksum}: Print CRC checksum and byte counts
3552 @cindex cyclic redundancy check
3553 @cindex CRC checksum
3555 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3556 given @var{file}, or standard input if none are given or for a
3557 @var{file} of @samp{-}. Synopsis:
3560 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3563 @command{cksum} prints the CRC checksum for each file along with the number
3564 of bytes in the file, and the file name unless no arguments were given.
3566 @command{cksum} is typically used to ensure that files
3567 transferred by unreliable means (e.g., netnews) have not been corrupted,
3568 by comparing the @command{cksum} output for the received files with the
3569 @command{cksum} output for the original files (typically given in the
3572 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3573 compatible with the BSD or System V @command{sum} algorithms (see the
3574 previous section); it is more robust.
3576 The only options are @option{--help} and @option{--version}. @xref{Common
3582 @node md5sum invocation
3583 @section @command{md5sum}: Print or check MD5 digests
3587 @cindex 128-bit checksum
3588 @cindex checksum, 128-bit
3589 @cindex fingerprint, 128-bit
3590 @cindex message-digest, 128-bit
3592 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3593 @dfn{message-digest}) for each specified @var{file}.
3595 Note: The MD5 digest is more reliable than a simple CRC (provided by
3596 the @command{cksum} command) for detecting accidental file corruption,
3597 as the chances of accidentally having two files with identical MD5
3598 are vanishingly small. However, it should not be considered secure
3599 against malicious tampering: although finding a file with a given MD5
3600 fingerprint is considered infeasible at the moment, it is known how
3601 to modify certain files, including digital certificates, so that they
3602 appear valid when signed with an MD5 digest.
3603 For more secure hashes, consider using SHA-2. @xref{sha2 utilities}.
3605 If a @var{file} is specified as @samp{-} or if no files are given
3606 @command{md5sum} computes the checksum for the standard input.
3607 @command{md5sum} can also determine whether a file and checksum are
3608 consistent. Synopsis:
3611 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3614 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3615 indicating a binary or text input file, and the file name.
3616 If @var{file} contains a backslash or newline, the
3617 line is started with a backslash, and each problematic character in
3618 the file name is escaped with a backslash, making the output
3619 unambiguous even in the presence of arbitrary file names.
3620 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3622 The program accepts the following options. Also see @ref{Common options}.
3630 @cindex binary input files
3631 Treat each input file as binary, by reading it in binary mode and
3632 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3633 On systems like @acronym{GNU} that do not distinguish between binary
3634 and text files, this option merely flags each input file as binary:
3635 the MD5 checksum is unaffected. This option is the default on systems
3636 like MS-DOS that distinguish between binary and text files, except
3637 for reading standard input when standard input is a terminal.
3641 Read file names and checksum information (not data) from each
3642 @var{file} (or from stdin if no @var{file} was specified) and report
3643 whether the checksums match the contents of the named files.
3644 The input to this mode of @command{md5sum} is usually the output of
3645 a prior, checksum-generating run of @samp{md5sum}.
3646 Each valid line of input consists of an MD5 checksum, a binary/text
3647 flag, and then a file name.
3648 Binary files are marked with @samp{*}, text with @samp{ }.
3649 For each such line, @command{md5sum} reads the named file and computes its
3650 MD5 checksum. Then, if the computed message digest does not match the
3651 one on the line with the file name, the file is noted as having
3652 failed the test. Otherwise, the file passes the test.
3653 By default, for each valid line, one line is written to standard
3654 output indicating whether the named file passed the test.
3655 After all checks have been performed, if there were any failures,
3656 a warning is issued to standard error.
3657 Use the @option{--status} option to inhibit that output.
3658 If any listed file cannot be opened or read, if any valid line has
3659 an MD5 checksum inconsistent with the associated file, or if no valid
3660 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3661 it exits successfully.
3665 @cindex verifying MD5 checksums
3666 This option is useful only when verifying checksums.
3667 When verifying checksums, don't generate an 'OK' message per successfully
3668 checked file. Files that fail the verification are reported in the
3669 default one-line-per-file format. If there is any checksum mismatch,
3670 print a warning summarizing the failures to standard error.
3674 @cindex verifying MD5 checksums
3675 This option is useful only when verifying checksums.
3676 When verifying checksums, don't generate the default one-line-per-file
3677 diagnostic and don't output the warning summarizing any failures.
3678 Failures to open or read a file still evoke individual diagnostics to
3680 If all listed files are readable and are consistent with the associated
3681 MD5 checksums, exit successfully. Otherwise exit with a status code
3682 indicating there was a failure.
3688 @cindex text input files
3689 Treat each input file as text, by reading it in text mode and
3690 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3691 This option is the default on systems like @acronym{GNU} that do not
3692 distinguish between binary and text files. On other systems, it is
3693 the default for reading standard input when standard input is a
3700 @cindex verifying MD5 checksums
3701 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3702 This option is useful only if all but a few lines in the checked input
3707 @cindex verifying MD5 checksums
3708 When verifying checksums,
3709 if one or more input line is invalid,
3710 exit nonzero after all warnings have been issued.
3717 @node sha1sum invocation
3718 @section @command{sha1sum}: Print or check SHA-1 digests
3722 @cindex 160-bit checksum
3723 @cindex checksum, 160-bit
3724 @cindex fingerprint, 160-bit
3725 @cindex message-digest, 160-bit
3727 @command{sha1sum} computes a 160-bit checksum for each specified
3728 @var{file}. The usage and options of this command are precisely the
3729 same as for @command{md5sum}. @xref{md5sum invocation}.
3731 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3732 it are known (different files having the same fingerprint). However,
3733 it is known that they can be produced with considerable, but not
3734 unreasonable, resources. For this reason, it is generally considered
3735 that SHA-1 should be gradually phased out in favor of the more secure
3736 SHA-2 hash algorithms. @xref{sha2 utilities}.
3739 @node sha2 utilities
3740 @section sha2 utilities: Print or check SHA-2 digests
3747 @cindex 224-bit checksum
3748 @cindex 256-bit checksum
3749 @cindex 384-bit checksum
3750 @cindex 512-bit checksum
3751 @cindex checksum, 224-bit
3752 @cindex checksum, 256-bit
3753 @cindex checksum, 384-bit
3754 @cindex checksum, 512-bit
3755 @cindex fingerprint, 224-bit
3756 @cindex fingerprint, 256-bit
3757 @cindex fingerprint, 384-bit
3758 @cindex fingerprint, 512-bit
3759 @cindex message-digest, 224-bit
3760 @cindex message-digest, 256-bit
3761 @cindex message-digest, 384-bit
3762 @cindex message-digest, 512-bit
3764 The commands @command{sha224sum}, @command{sha256sum},
3765 @command{sha384sum} and @command{sha512sum} compute checksums of
3766 various lengths (respectively 224, 256, 384 and 512 bits),
3767 collectively known as the SHA-2 hashes. The usage and options of
3768 these commands are precisely the same as for @command{md5sum}.
3769 @xref{md5sum invocation}.
3771 Note: The SHA384 and SHA512 digests are considerably slower to
3772 compute, especially on 32-bit computers, than SHA224 or SHA256.
3775 @node Operating on sorted files
3776 @chapter Operating on sorted files
3778 @cindex operating on sorted files
3779 @cindex sorted files, operations on
3781 These commands work with (or produce) sorted files.
3784 * sort invocation:: Sort text files.
3785 * shuf invocation:: Shuffle text files.
3786 * uniq invocation:: Uniquify files.
3787 * comm invocation:: Compare two sorted files line by line.
3788 * ptx invocation:: Produce a permuted index of file contents.
3789 * tsort invocation:: Topological sort.
3793 @node sort invocation
3794 @section @command{sort}: Sort text files
3797 @cindex sorting files
3799 @command{sort} sorts, merges, or compares all the lines from the given
3800 files, or standard input if none are given or for a @var{file} of
3801 @samp{-}. By default, @command{sort} writes the results to standard
3805 sort [@var{option}]@dots{} [@var{file}]@dots{}
3808 @command{sort} has three modes of operation: sort (the default), merge,
3809 and check for sortedness. The following options change the operation
3816 @itemx --check=diagnose-first
3819 @cindex checking for sortedness
3820 Check whether the given file is already sorted: if it is not all
3821 sorted, print a diagnostic containing the first out-of-order line and
3822 exit with a status of 1.
3823 Otherwise, exit successfully.
3824 At most one input file can be given.
3827 @itemx --check=quiet
3828 @itemx --check=silent
3831 @cindex checking for sortedness
3832 Exit successfully if the given file is already sorted, and
3833 exit with status 1 otherwise.
3834 At most one input file can be given.
3835 This is like @option{-c}, except it does not print a diagnostic.
3841 @cindex merging sorted files
3842 Merge the given files by sorting them as a group. Each input file must
3843 always be individually sorted. It always works to sort instead of
3844 merge; merging is provided because it is faster, in the case where it
3849 @cindex sort stability
3850 @cindex sort's last-resort comparison
3851 A pair of lines is compared as follows:
3852 @command{sort} compares each pair of fields, in the
3853 order specified on the command line, according to the associated
3854 ordering options, until a difference is found or no fields are left.
3855 If no key fields are specified, @command{sort} uses a default key of
3856 the entire line. Finally, as a last resort when all keys compare
3857 equal, @command{sort} compares entire lines as if no ordering options
3858 other than @option{--reverse} (@option{-r}) were specified. The
3859 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3860 comparison} so that lines in which all fields compare equal are left
3861 in their original relative order. The @option{--unique}
3862 (@option{-u}) option also disables the last-resort comparison.
3866 Unless otherwise specified, all comparisons use the character collating
3867 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3868 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3869 to @samp{en_US}), then @command{sort} may produce output that is sorted
3870 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3871 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3872 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3873 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3874 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3875 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3876 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3878 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3879 limit on input line length or restrictions on bytes allowed within lines.
3880 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3881 @command{sort} silently supplies one. A line's trailing newline is not
3882 part of the line for comparison purposes.
3884 @cindex exit status of @command{sort}
3888 0 if no error occurred
3889 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3890 2 if an error occurred
3894 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3895 value as the directory for temporary files instead of @file{/tmp}. The
3896 @option{--temporary-directory} (@option{-T}) option in turn overrides
3897 the environment variable.
3899 The following options affect the ordering of output lines. They may be
3900 specified globally or as part of a specific key field. If no key
3901 fields are specified, global options apply to comparison of entire
3902 lines; otherwise the global options are inherited by key fields that do
3903 not specify any special options of their own. In pre-@acronym{POSIX}
3904 versions of @command{sort}, global options affect only later key fields,
3905 so portable shell scripts should specify global options first.
3910 @itemx --ignore-leading-blanks
3912 @opindex --ignore-leading-blanks
3913 @cindex blanks, ignoring leading
3915 Ignore leading blanks when finding sort keys in each line.
3916 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3917 can change this. Note blanks may be ignored by your locale's collating
3918 rules, but without this option they will be significant for character
3919 positions specified in keys with the @option{-k} option.
3922 @itemx --dictionary-order
3924 @opindex --dictionary-order
3925 @cindex dictionary order
3926 @cindex phone directory order
3927 @cindex telephone directory order
3929 Sort in @dfn{phone directory} order: ignore all characters except
3930 letters, digits and blanks when sorting.
3931 By default letters and digits are those of @acronym{ASCII} and a blank
3932 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3935 @itemx --ignore-case
3937 @opindex --ignore-case
3938 @cindex ignoring case
3939 @cindex case folding
3941 Fold lowercase characters into the equivalent uppercase characters when
3942 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3943 The @env{LC_CTYPE} locale determines character types.
3944 When used with @option{--unique} those lower case equivalent lines are
3945 thrown away. (There is currently no way to throw away the upper case
3946 equivalent instead. (Any @option{--reverse} given would only affect
3947 the final result, after the throwing away.))
3950 @itemx --general-numeric-sort
3951 @itemx --sort=general-numeric
3953 @opindex --general-numeric-sort
3955 @cindex general numeric sort
3957 Sort numerically, converting a prefix of each line to a long
3958 double-precision floating point number. @xref{Floating point}.
3959 Do not report overflow, underflow, or conversion errors.
3960 Use the following collating sequence:
3964 Lines that do not start with numbers (all considered to be equal).
3966 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3967 in a consistent but machine-dependent order.
3971 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3976 Use this option only if there is no alternative; it is much slower than
3977 @option{--numeric-sort} (@option{-n}) and it can lose information when
3978 converting to floating point.
3981 @itemx --human-numeric-sort
3982 @itemx --sort=human-numeric
3984 @opindex --human-numeric-sort
3986 @cindex human numeric sort
3988 Sort numerically, first by numeric sign (negative, zero, or positive);
3989 then by @acronym{SI} suffix (either empty, or @samp{k} or @samp{K}, or
3990 one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
3991 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
3992 because @samp{M} (mega) precedes @samp{G} (giga) as an @acronym{SI}
3993 suffix. This option sorts values that are consistently scaled to the
3994 nearest suffix, regardless of whether suffixes denote powers of 1000
3995 or 1024, and it therefore sorts the output of any single invocation of
3996 the @command{df}, @command{du}, or @command{ls} commands that are
3997 invoked with their @option{--human-readable} or @option{--si} options.
3998 The syntax for numbers is the same as for the @option{--numeric-sort}
3999 option; the @acronym{SI} suffix must immediately follow the number.
4002 @itemx --ignore-nonprinting
4004 @opindex --ignore-nonprinting
4005 @cindex nonprinting characters, ignoring
4006 @cindex unprintable characters, ignoring
4008 Ignore nonprinting characters.
4009 The @env{LC_CTYPE} locale determines character types.
4010 This option has no effect if the stronger @option{--dictionary-order}
4011 (@option{-d}) option is also given.
4017 @opindex --month-sort
4019 @cindex months, sorting by
4021 An initial string, consisting of any amount of blanks, followed
4022 by a month name abbreviation, is folded to UPPER case and
4023 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
4024 Invalid names compare low to valid names. The @env{LC_TIME} locale
4025 category determines the month spellings.
4026 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4030 @itemx --numeric-sort
4031 @itemx --sort=numeric
4033 @opindex --numeric-sort
4035 @cindex numeric sort
4037 Sort numerically. The number begins each line and consists
4038 of optional blanks, an optional @samp{-} sign, and zero or more
4039 digits possibly separated by thousands separators, optionally followed
4040 by a decimal-point character and zero or more digits. An empty
4041 number is treated as @samp{0}. The @env{LC_NUMERIC}
4042 locale specifies the decimal-point character and thousands separator.
4043 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4046 Comparison is exact; there is no rounding error.
4048 Neither a leading @samp{+} nor exponential notation is recognized.
4049 To compare such strings numerically, use the
4050 @option{--general-numeric-sort} (@option{-g}) option.
4053 @itemx --version-sort
4055 @opindex --version-sort
4056 @cindex version number sort
4057 Sort by version name and number. It behaves like a standard sort,
4058 except that each sequence of decimal digits is treated numerically
4059 as an index/version number. (@xref{Details about version sort}.)
4065 @cindex reverse sorting
4066 Reverse the result of comparison, so that lines with greater key values
4067 appear earlier in the output instead of later.
4070 @itemx --random-sort
4071 @itemx --sort=random
4073 @opindex --random-sort
4076 Sort by hashing the input keys and then sorting the hash values.
4077 Choose the hash function at random, ensuring that it is free of
4078 collisions so that differing keys have differing hash values. This is
4079 like a random permutation of the inputs (@pxref{shuf invocation}),
4080 except that keys with the same value sort together.
4082 If multiple random sort fields are specified, the same random hash
4083 function is used for all fields. To use different random hash
4084 functions for different fields, you can invoke @command{sort} more
4087 The choice of hash function is affected by the
4088 @option{--random-source} option.
4096 @item --compress-program=@var{prog}
4097 Compress any temporary files with the program @var{prog}.
4099 With no arguments, @var{prog} must compress standard input to standard
4100 output, and when given the @option{-d} option it must decompress
4101 standard input to standard output.
4103 Terminate with an error if @var{prog} exits with nonzero status.
4105 White space and the backslash character should not appear in
4106 @var{prog}; they are reserved for future use.
4108 @filesZeroFromOption{sort,,sorted output}
4110 @item -k @var{pos1}[,@var{pos2}]
4111 @itemx --key=@var{pos1}[,@var{pos2}]
4115 Specify a sort field that consists of the part of the line between
4116 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
4117 omitted), @emph{inclusive}.
4119 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
4120 where @var{f} is the number of the field to use, and @var{c} is the number
4121 of the first character from the beginning of the field. Fields and character
4122 positions are numbered starting with 1; a character position of zero in
4123 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
4124 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
4125 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
4126 @var{opts} are ordering options, allowing individual keys to be sorted
4127 according to different rules; see below for details. Keys can span
4130 Example: To sort on the second field, use @option{--key=2,2}
4131 (@option{-k 2,2}). See below for more notes on keys and more examples.
4132 See also the @option{--debug} option to help determine the part
4133 of the line being used in the sort.
4136 Highlight the portion of each line used for sorting.
4137 Also issue warnings about questionable usage to stderr.
4139 @item --batch-size=@var{nmerge}
4140 @opindex --batch-size
4141 @cindex number of inputs to merge, nmerge
4142 Merge at most @var{nmerge} inputs at once.
4144 When @command{sort} has to merge more than @var{nmerge} inputs,
4145 it merges them in groups of @var{nmerge}, saving the result in
4146 a temporary file, which is then used as an input in a subsequent merge.
4148 A large value of @var{nmerge} may improve merge performance and decrease
4149 temporary storage utilization at the expense of increased memory usage
4150 and I/O. Conversely a small value of @var{nmerge} may reduce memory
4151 requirements and I/O at the expense of temporary storage consumption and
4154 The value of @var{nmerge} must be at least 2. The default value is
4155 currently 16, but this is implementation-dependent and may change in
4158 The value of @var{nmerge} may be bounded by a resource limit for open
4159 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
4160 OPEN_MAX} may display limits for your systems; these limits may be
4161 modified further if your program already has some files open, or if
4162 the operating system has other limits on the number of open files. If
4163 the value of @var{nmerge} exceeds the resource limit, @command{sort}
4164 silently uses a smaller value.
4166 @item -o @var{output-file}
4167 @itemx --output=@var{output-file}
4170 @cindex overwriting of input, allowed
4171 Write output to @var{output-file} instead of standard output.
4172 Normally, @command{sort} reads all input before opening
4173 @var{output-file}, so you can safely sort a file in place by using
4174 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
4175 However, @command{sort} with @option{--merge} (@option{-m}) can open
4176 the output file before reading all input, so a command like @code{cat
4177 F | sort -m -o F - G} is not safe as @command{sort} might start
4178 writing @file{F} before @command{cat} is done reading it.
4180 @vindex POSIXLY_CORRECT
4181 On newer systems, @option{-o} cannot appear after an input file if
4182 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
4183 scripts should specify @option{-o @var{output-file}} before any input
4186 @item --random-source=@var{file}
4187 @opindex --random-source
4188 @cindex random source for sorting
4189 Use @var{file} as a source of random data used to determine which
4190 random hash function to use with the @option{-R} option. @xref{Random
4197 @cindex sort stability
4198 @cindex sort's last-resort comparison
4200 Make @command{sort} stable by disabling its last-resort comparison.
4201 This option has no effect if no fields or global ordering options
4202 other than @option{--reverse} (@option{-r}) are specified.
4205 @itemx --buffer-size=@var{size}
4207 @opindex --buffer-size
4208 @cindex size for main memory sorting
4209 Use a main-memory sort buffer of the given @var{size}. By default,
4210 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4211 @var{size} to be interpreted as a percentage of physical memory.
4212 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4213 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4214 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4215 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4218 This option can improve the performance of @command{sort} by causing it
4219 to start with a larger or smaller sort buffer than the default.
4220 However, this option affects only the initial buffer size. The buffer
4221 grows beyond @var{size} if @command{sort} encounters input lines larger
4224 @item -t @var{separator}
4225 @itemx --field-separator=@var{separator}
4227 @opindex --field-separator
4228 @cindex field separator character
4229 Use character @var{separator} as the field separator when finding the
4230 sort keys in each line. By default, fields are separated by the empty
4231 string between a non-blank character and a blank character.
4232 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4235 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4236 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4237 not considered to be part of either the field preceding or the field
4238 following, so with @samp{sort @w{-t " "}} the same input line has
4239 three fields: an empty field, @samp{foo}, and @samp{bar}.
4240 However, fields that extend to the end of the line,
4241 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4242 retain the field separators present between the endpoints of the range.
4244 To specify @acronym{ASCII} @sc{nul} as the field separator,
4245 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4247 @item -T @var{tempdir}
4248 @itemx --temporary-directory=@var{tempdir}
4250 @opindex --temporary-directory
4251 @cindex temporary directory
4253 Use directory @var{tempdir} to store temporary files, overriding the
4254 @env{TMPDIR} environment variable. If this option is given more than
4255 once, temporary files are stored in all the directories given. If you
4256 have a large sort or merge that is I/O-bound, you can often improve
4257 performance by using this option to specify directories on different
4258 disks and controllers.
4260 @item --parallel=@var{n}
4262 @cindex multithreaded sort
4263 Set the number of sorts run in parallel to @var{n}. By default,
4264 @var{n} is set to the number of available processors, but limited
4265 to 8, as there are diminishing performance gains after that.
4266 Note also that using @var{n} threads increases the memory usage by
4267 a factor of log @var{n}. Also see @ref{nproc invocation}.
4273 @cindex uniquifying output
4275 Normally, output only the first of a sequence of lines that compare
4276 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4277 check that no pair of consecutive lines compares equal.
4279 This option also disables the default last-resort comparison.
4281 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4282 this equivalence does not extend to arbitrary @command{sort} options.
4283 For example, @code{sort -n -u} inspects only the value of the initial
4284 numeric string when checking for uniqueness, whereas @code{sort -n |
4285 uniq} inspects the entire line. @xref{uniq invocation}.
4287 @macro zeroTerminatedOption
4289 @itemx --zero-terminated
4291 @opindex --zero-terminated
4292 @cindex process zero-terminated items
4293 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4294 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4295 and terminate output items with @acronym{ASCII} @sc{nul}.
4296 This option can be useful in conjunction with @samp{perl -0} or
4297 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4298 reliably handle arbitrary file names (even those containing blanks
4299 or other special characters).
4301 @zeroTerminatedOption
4305 Historical (BSD and System V) implementations of @command{sort} have
4306 differed in their interpretation of some options, particularly
4307 @option{-b}, @option{-f}, and @option{-n}.
4308 @sc{gnu} sort follows the @acronym{POSIX}
4309 behavior, which is usually (but not always!) like the System V behavior.
4310 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4311 consistency, @option{-M} has been changed in the same way. This may
4312 affect the meaning of character positions in field specifications in
4313 obscure cases. The only fix is to add an explicit @option{-b}.
4315 A position in a sort field specified with @option{-k} may have any
4316 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4317 global ordering options are inherited by that particular field. The
4318 @option{-b} option may be independently attached to either or both of
4319 the start and end positions of a field specification, and if it is
4320 inherited from the global options it will be attached to both.
4321 If input lines can contain leading or adjacent blanks and @option{-t}
4322 is not used, then @option{-k} is typically combined with @option{-b} or
4323 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4324 the varying numbers of leading blanks in fields can cause confusing results.
4326 If the start position in a sort field specifier falls after the end of
4327 the line or after the end field, the field is empty. If the @option{-b}
4328 option was specified, the @samp{.@var{c}} part of a field specification
4329 is counted from the first nonblank character of the field.
4331 @vindex _POSIX2_VERSION
4332 @vindex POSIXLY_CORRECT
4333 On older systems, @command{sort} supports an obsolete origin-zero
4334 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4335 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4336 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4337 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4338 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4340 This obsolete behavior can be enabled or disabled with the
4341 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4342 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4343 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4345 Scripts intended for use on standard hosts should avoid obsolete
4346 syntax and should use @option{-k} instead. For example, avoid
4347 @samp{sort +2}, since it might be interpreted as either @samp{sort
4348 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4349 support only the obsolete syntax, it can use a test like @samp{if sort
4350 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4353 Here are some examples to illustrate various combinations of options.
4358 Sort in descending (reverse) numeric order.
4365 Run no more that 4 sorts concurrently, using a buffer size of 10M.
4368 sort --parallel=4 -S 10M
4372 Sort alphabetically, omitting the first and second fields
4373 and the blanks at the start of the third field.
4374 This uses a single key composed of the characters beginning
4375 at the start of the first nonblank character in field three
4376 and extending to the end of each line.
4383 Sort numerically on the second field and resolve ties by sorting
4384 alphabetically on the third and fourth characters of field five.
4385 Use @samp{:} as the field delimiter.
4388 sort -t : -k 2,2n -k 5.3,5.4
4391 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4392 @command{sort} would have used all characters beginning in the second field
4393 and extending to the end of the line as the primary @emph{numeric}
4394 key. For the large majority of applications, treating keys spanning
4395 more than one field as numeric will not do what you expect.
4397 Also note that the @samp{n} modifier was applied to the field-end
4398 specifier for the first key. It would have been equivalent to
4399 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4400 @samp{b} apply to the associated @emph{field}, regardless of whether
4401 the modifier character is attached to the field-start and/or the
4402 field-end part of the key specifier.
4405 Sort the password file on the fifth field and ignore any
4406 leading blanks. Sort lines with equal values in field five
4407 on the numeric user ID in field three. Fields are separated
4411 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4412 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4413 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4416 These three commands have equivalent effect. The first specifies that
4417 the first key's start position ignores leading blanks and the second
4418 key is sorted numerically. The other two commands rely on global
4419 options being inherited by sort keys that lack modifiers. The inheritance
4420 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4421 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4422 character position is not affected by whether initial blanks are
4426 Sort a set of log files, primarily by IPv4 address and secondarily by
4427 time stamp. If two lines' primary and secondary keys are identical,
4428 output the lines in the same order that they were input. The log
4429 files contain lines that look like this:
4432 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4433 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4436 Fields are separated by exactly one space. Sort IPv4 addresses
4437 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4438 because 61 is less than 129.
4441 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4442 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4445 This example cannot be done with a single @command{sort} invocation,
4446 since IPv4 address components are separated by @samp{.} while dates
4447 come just after a space. So it is broken down into two invocations of
4448 @command{sort}: the first sorts by time stamp and the second by IPv4
4449 address. The time stamp is sorted by year, then month, then day, and
4450 finally by hour-minute-second field, using @option{-k} to isolate each
4451 field. Except for hour-minute-second there's no need to specify the
4452 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4453 based on leading prefixes that cannot cross field boundaries. The
4454 IPv4 addresses are sorted lexicographically. The second sort uses
4455 @samp{-s} so that ties in the primary key are broken by the secondary
4456 key; the first sort uses @samp{-s} so that the combination of the two
4460 Generate a tags file in case-insensitive sorted order.
4463 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4466 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4467 that file names that contain blanks or other special characters are
4469 by the sort operation.
4471 @c This example is a bit contrived and needs more explanation.
4473 @c Sort records separated by an arbitrary string by using a pipe to convert
4474 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4475 @c and converting each @samp{\0} back to the original record delimiter.
4478 @c printf 'c\n\nb\n\na\n' |
4479 @c perl -0pe 's/\n\n/\n\0/g' |
4481 @c perl -0pe 's/\0/\n/g'
4485 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4486 sort lines according to their length.
4489 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4492 In general this technique can be used to sort data that the @command{sort}
4493 command does not support, or is inefficient at, sorting directly.
4496 Shuffle a list of directories, but preserve the order of files within
4497 each directory. For instance, one could use this to generate a music
4498 playlist in which albums are shuffled but the songs of each album are
4502 ls */* | sort -t / -k 1,1R -k 2,2
4508 @node shuf invocation
4509 @section @command{shuf}: Shuffling text
4512 @cindex shuffling files
4514 @command{shuf} shuffles its input by outputting a random permutation
4515 of its input lines. Each output permutation is equally likely.
4519 shuf [@var{option}]@dots{} [@var{file}]
4520 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4521 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4524 @command{shuf} has three modes of operation that affect where it
4525 obtains its input lines. By default, it reads lines from standard
4526 input. The following options change the operation mode:
4534 @cindex command-line operands to shuffle
4535 Treat each command-line operand as an input line.
4537 @item -i @var{lo}-@var{hi}
4538 @itemx --input-range=@var{lo}-@var{hi}
4540 @opindex --input-range
4541 @cindex input range to shuffle
4542 Act as if input came from a file containing the range of unsigned
4543 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4547 @command{shuf}'s other options can affect its behavior in all
4552 @item -n @var{lines}
4553 @itemx --head-count=@var{count}
4555 @opindex --head-count
4556 @cindex head of output
4557 Output at most @var{count} lines. By default, all input lines are
4560 @item -o @var{output-file}
4561 @itemx --output=@var{output-file}
4564 @cindex overwriting of input, allowed
4565 Write output to @var{output-file} instead of standard output.
4566 @command{shuf} reads all input before opening
4567 @var{output-file}, so you can safely shuffle a file in place by using
4568 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4570 @item --random-source=@var{file}
4571 @opindex --random-source
4572 @cindex random source for shuffling
4573 Use @var{file} as a source of random data used to determine which
4574 permutation to generate. @xref{Random sources}.
4576 @zeroTerminatedOption
4592 might produce the output
4602 Similarly, the command:
4605 shuf -e clubs hearts diamonds spades
4619 and the command @samp{shuf -i 1-4} might output:
4629 These examples all have four input lines, so @command{shuf} might
4630 produce any of the twenty-four possible permutations of the input. In
4631 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4632 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4633 output permutations.
4638 @node uniq invocation
4639 @section @command{uniq}: Uniquify files
4642 @cindex uniquify files
4644 @command{uniq} writes the unique lines in the given @file{input}, or
4645 standard input if nothing is given or for an @var{input} name of
4649 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4652 By default, @command{uniq} prints its input lines, except that
4653 it discards all but the first of adjacent repeated lines, so that
4654 no output lines are repeated. Optionally, it can instead discard
4655 lines that are not repeated, or all repeated lines.
4657 The input need not be sorted, but repeated input lines are detected
4658 only if they are adjacent. If you want to discard non-adjacent
4659 duplicate lines, perhaps you want to use @code{sort -u}.
4660 @xref{sort invocation}.
4663 Comparisons honor the rules specified by the @env{LC_COLLATE}
4666 If no @var{output} file is specified, @command{uniq} writes to standard
4669 The program accepts the following options. Also see @ref{Common options}.
4674 @itemx --skip-fields=@var{n}
4676 @opindex --skip-fields
4677 Skip @var{n} fields on each line before checking for uniqueness. Use
4678 a null string for comparison if a line has fewer than @var{n} fields. Fields
4679 are sequences of non-space non-tab characters that are separated from
4680 each other by at least one space or tab.
4682 For compatibility @command{uniq} supports an obsolete option syntax
4683 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4686 @itemx --skip-chars=@var{n}
4688 @opindex --skip-chars
4689 Skip @var{n} characters before checking for uniqueness. Use a null string
4690 for comparison if a line has fewer than @var{n} characters. If you use both
4691 the field and character skipping options, fields are skipped over first.
4693 @vindex _POSIX2_VERSION
4694 On older systems, @command{uniq} supports an obsolete option syntax
4696 This obsolete behavior can be enabled or disabled with the
4697 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4698 conformance}), but portable scripts should avoid commands whose
4699 behavior depends on this variable.
4700 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4701 the ambiguous @samp{uniq +10}.
4707 Print the number of times each line occurred along with the line.
4710 @itemx --ignore-case
4712 @opindex --ignore-case
4713 Ignore differences in case when comparing lines.
4719 @cindex repeated lines, outputting
4720 Discard lines that are not repeated. When used by itself, this option
4721 causes @command{uniq} to print the first copy of each repeated line,
4725 @itemx --all-repeated[=@var{delimit-method}]
4727 @opindex --all-repeated
4728 @cindex all repeated lines, outputting
4729 Do not discard the second and subsequent repeated input lines,
4730 but discard lines that are not repeated.
4731 This option is useful mainly in conjunction with other options e.g.,
4732 to ignore case or to compare only selected fields.
4733 The optional @var{delimit-method} tells how to delimit
4734 groups of repeated lines, and must be one of the following:
4739 Do not delimit groups of repeated lines.
4740 This is equivalent to @option{--all-repeated} (@option{-D}).
4743 Output a newline before each group of repeated lines.
4744 With @option{--zero-terminated} (@option{-z}), use a zero
4745 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4748 Separate groups of repeated lines with a single newline.
4749 With @option{--zero-terminated} (@option{-z}), use a zero
4750 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4751 This is the same as using @samp{prepend}, except that
4752 no delimiter is inserted before the first group, and hence
4753 may be better suited for output direct to users.
4756 Note that when groups are delimited and the input stream contains
4757 two or more consecutive blank lines, then the output is ambiguous.
4758 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4759 each sequence of consecutive newlines with a single newline.
4761 This is a @sc{gnu} extension.
4762 @c FIXME: give an example showing *how* it's useful
4768 @cindex unique lines, outputting
4769 Discard the first repeated line. When used by itself, this option
4770 causes @command{uniq} to print unique lines, and nothing else.
4773 @itemx --check-chars=@var{n}
4775 @opindex --check-chars
4776 Compare at most @var{n} characters on each line (after skipping any specified
4777 fields and characters). By default the entire rest of the lines are
4780 @zeroTerminatedOption
4787 @node comm invocation
4788 @section @command{comm}: Compare two sorted files line by line
4791 @cindex line-by-line comparison
4792 @cindex comparing sorted files
4794 @command{comm} writes to standard output lines that are common, and lines
4795 that are unique, to two input files; a file name of @samp{-} means
4796 standard input. Synopsis:
4799 comm [@var{option}]@dots{} @var{file1} @var{file2}
4803 Before @command{comm} can be used, the input files must be sorted using the
4804 collating sequence specified by the @env{LC_COLLATE} locale.
4805 If an input file ends in a non-newline
4806 character, a newline is silently appended. The @command{sort} command with
4807 no options always outputs a file that is suitable input to @command{comm}.
4809 @cindex differing lines
4810 @cindex common lines
4811 With no options, @command{comm} produces three-column output. Column one
4812 contains lines unique to @var{file1}, column two contains lines unique
4813 to @var{file2}, and column three contains lines common to both files.
4814 Columns are separated by a single TAB character.
4815 @c FIXME: when there's an option to supply an alternative separator
4816 @c string, append `by default' to the above sentence.
4821 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4822 the corresponding columns (and separators). Also see @ref{Common options}.
4824 Unlike some other comparison utilities, @command{comm} has an exit
4825 status that does not depend on the result of the comparison.
4826 Upon normal completion @command{comm} produces an exit code of zero.
4827 If there is an error it exits with nonzero status.
4829 @macro checkOrderOption{cmd}
4830 If the @option{--check-order} option is given, unsorted inputs will
4831 cause a fatal error message. If the option @option{--nocheck-order}
4832 is given, unsorted inputs will never cause an error message. If neither
4833 of these options is given, wrongly sorted inputs are diagnosed
4834 only if an input file is found to contain unpairable
4836 lines, and when both input files are non empty.
4838 @ifclear JOIN_COMMAND
4841 If an input file is diagnosed as being unsorted, the @command{\cmd\}
4842 command will exit with a nonzero status (and the output should not be used).
4844 Forcing @command{\cmd\} to process wrongly sorted input files
4845 containing unpairable lines by specifying @option{--nocheck-order} is
4846 not guaranteed to produce any particular output. The output will
4847 probably not correspond with whatever you hoped it would be.
4849 @checkOrderOption{comm}
4854 Fail with an error message if either input file is wrongly ordered.
4856 @item --nocheck-order
4857 Do not check that both input files are in sorted order.
4861 @item --output-delimiter=@var{str}
4862 Print @var{str} between adjacent output columns,
4863 rather than the default of a single TAB character.
4865 The delimiter @var{str} may not be empty.
4869 @node ptx invocation
4870 @section @command{ptx}: Produce permuted indexes
4874 @command{ptx} reads a text file and essentially produces a permuted index, with
4875 each keyword in its context. The calling sketch is either one of:
4878 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4879 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4882 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4883 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4884 limitations and changing several of the program's default option values.
4885 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4886 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4887 document. For the full list, see @xref{Compatibility in ptx}.
4889 Individual options are explained in the following sections.
4891 When @sc{gnu} extensions are enabled, there may be zero, one or several
4892 @var{file}s after the options. If there is no @var{file}, the program
4893 reads the standard input. If there is one or several @var{file}s, they
4894 give the name of input files which are all read in turn, as if all the
4895 input files were concatenated. However, there is a full contextual
4896 break between each file and, when automatic referencing is requested,
4897 file names and line numbers refer to individual text input files. In
4898 all cases, the program outputs the permuted index to the standard
4901 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4902 operates in traditional mode, there may be zero, one or two parameters
4903 besides the options. If there are no parameters, the program reads the
4904 standard input and outputs the permuted index to the standard output.
4905 If there is only one parameter, it names the text @var{input} to be read
4906 instead of the standard input. If two parameters are given, they give
4907 respectively the name of the @var{input} file to read and the name of
4908 the @var{output} file to produce. @emph{Be very careful} to note that,
4909 in this case, the contents of file given by the second parameter is
4910 destroyed. This behavior is dictated by System V @command{ptx}
4911 compatibility; @sc{gnu} Standards normally discourage output parameters not
4912 introduced by an option.
4914 Note that for @emph{any} file named as the value of an option or as an
4915 input text file, a single dash @kbd{-} may be used, in which case
4916 standard input is assumed. However, it would not make sense to use this
4917 convention more than once per program invocation.
4920 * General options in ptx:: Options which affect general program behavior.
4921 * Charset selection in ptx:: Underlying character set considerations.
4922 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4923 * Output formatting in ptx:: Types of output format, and sizing the fields.
4924 * Compatibility in ptx::
4928 @node General options in ptx
4929 @subsection General options
4934 @itemx --traditional
4935 As already explained, this option disables all @sc{gnu} extensions to
4936 @command{ptx} and switches to traditional mode.
4939 Print a short help on standard output, then exit without further
4943 Print the program version on standard output, then exit without further
4951 @node Charset selection in ptx
4952 @subsection Charset selection
4954 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4955 As it is set up now, the program assumes that the input file is coded
4956 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4957 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4958 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4959 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4960 of characters which are letters is different; this alters the behavior
4961 of regular expression matching. Thus, the default regular expression
4962 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4963 however, is still crude; it obeys the underlying character set ordering
4969 @itemx --ignore-case
4970 Fold lower case letters to upper case for sorting.
4975 @node Input processing in ptx
4976 @subsection Word selection and input processing
4981 @itemx --break-file=@var{file}
4983 This option provides an alternative (to @option{-W}) method of describing
4984 which characters make up words. It introduces the name of a
4985 file which contains a list of characters which can@emph{not} be part of
4986 one word; this file is called the @dfn{Break file}. Any character which
4987 is not part of the Break file is a word constituent. If both options
4988 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4989 @option{-b} is ignored.
4991 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4992 break character is to write all the break characters in the file with no
4993 newline at all, not even at the end of the file. When @sc{gnu} extensions
4994 are disabled, spaces, tabs and newlines are always considered as break
4995 characters even if not included in the Break file.
4998 @itemx --ignore-file=@var{file}
5000 The file associated with this option contains a list of words which will
5001 never be taken as keywords in concordance output. It is called the
5002 @dfn{Ignore file}. The file contains exactly one word in each line; the
5003 end of line separation of words is not subject to the value of the
5007 @itemx --only-file=@var{file}
5009 The file associated with this option contains a list of words which will
5010 be retained in concordance output; any word not mentioned in this file
5011 is ignored. The file is called the @dfn{Only file}. The file contains
5012 exactly one word in each line; the end of line separation of words is
5013 not subject to the value of the @option{-S} option.
5015 There is no default for the Only file. When both an Only file and an
5016 Ignore file are specified, a word is considered a keyword only
5017 if it is listed in the Only file and not in the Ignore file.
5022 On each input line, the leading sequence of non-white space characters will be
5023 taken to be a reference that has the purpose of identifying this input
5024 line in the resulting permuted index. For more information about reference
5025 production, see @xref{Output formatting in ptx}.
5026 Using this option changes the default value for option @option{-S}.
5028 Using this option, the program does not try very hard to remove
5029 references from contexts in output, but it succeeds in doing so
5030 @emph{when} the context ends exactly at the newline. If option
5031 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
5032 are disabled, this condition is always met and references are completely
5033 excluded from the output contexts.
5035 @item -S @var{regexp}
5036 @itemx --sentence-regexp=@var{regexp}
5038 This option selects which regular expression will describe the end of a
5039 line or the end of a sentence. In fact, this regular expression is not
5040 the only distinction between end of lines or end of sentences, and input
5041 line boundaries have no special significance outside this option. By
5042 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
5043 used, end of sentences are used. In this case, this @var{regex} is
5044 imported from @sc{gnu} Emacs:
5047 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
5050 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
5051 of lines are used; in this case, the default @var{regexp} is just:
5057 Using an empty @var{regexp} is equivalent to completely disabling end of
5058 line or end of sentence recognition. In this case, the whole file is
5059 considered to be a single big line or sentence. The user might want to
5060 disallow all truncation flag generation as well, through option @option{-F
5061 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5064 When the keywords happen to be near the beginning of the input line or
5065 sentence, this often creates an unused area at the beginning of the
5066 output context line; when the keywords happen to be near the end of the
5067 input line or sentence, this often creates an unused area at the end of
5068 the output context line. The program tries to fill those unused areas
5069 by wrapping around context in them; the tail of the input line or
5070 sentence is used to fill the unused area on the left of the output line;
5071 the head of the input line or sentence is used to fill the unused area
5072 on the right of the output line.
5074 As a matter of convenience to the user, many usual backslashed escape
5075 sequences from the C language are recognized and converted to the
5076 corresponding characters by @command{ptx} itself.
5078 @item -W @var{regexp}
5079 @itemx --word-regexp=@var{regexp}
5081 This option selects which regular expression will describe each keyword.
5082 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
5083 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
5084 disabled, a word is by default anything which ends with a space, a tab
5085 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
5087 An empty @var{regexp} is equivalent to not using this option.
5088 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5091 As a matter of convenience to the user, many usual backslashed escape
5092 sequences, as found in the C language, are recognized and converted to
5093 the corresponding characters by @command{ptx} itself.
5098 @node Output formatting in ptx
5099 @subsection Output formatting
5101 Output format is mainly controlled by the @option{-O} and @option{-T} options
5102 described in the table below. When neither @option{-O} nor @option{-T} are
5103 selected, and if @sc{gnu} extensions are enabled, the program chooses an
5104 output format suitable for a dumb terminal. Each keyword occurrence is
5105 output to the center of one line, surrounded by its left and right
5106 contexts. Each field is properly justified, so the concordance output
5107 can be readily observed. As a special feature, if automatic
5108 references are selected by option @option{-A} and are output before the
5109 left context, that is, if option @option{-R} is @emph{not} selected, then
5110 a colon is added after the reference; this nicely interfaces with @sc{gnu}
5111 Emacs @code{next-error} processing. In this default output format, each
5112 white space character, like newline and tab, is merely changed to
5113 exactly one space, with no special attempt to compress consecutive
5114 spaces. This might change in the future. Except for those white space
5115 characters, every other character of the underlying set of 256
5116 characters is transmitted verbatim.
5118 Output format is further controlled by the following options.
5122 @item -g @var{number}
5123 @itemx --gap-size=@var{number}
5125 Select the size of the minimum white space gap between the fields on the
5128 @item -w @var{number}
5129 @itemx --width=@var{number}
5131 Select the maximum output width of each final line. If references are
5132 used, they are included or excluded from the maximum output width
5133 depending on the value of option @option{-R}. If this option is not
5134 selected, that is, when references are output before the left context,
5135 the maximum output width takes into account the maximum length of all
5136 references. If this option is selected, that is, when references are
5137 output after the right context, the maximum output width does not take
5138 into account the space taken by references, nor the gap that precedes
5142 @itemx --auto-reference
5144 Select automatic references. Each input line will have an automatic
5145 reference made up of the file name and the line ordinal, with a single
5146 colon between them. However, the file name will be empty when standard
5147 input is being read. If both @option{-A} and @option{-r} are selected, then
5148 the input reference is still read and skipped, but the automatic
5149 reference is used at output time, overriding the input reference.
5152 @itemx --right-side-refs
5154 In the default output format, when option @option{-R} is not used, any
5155 references produced by the effect of options @option{-r} or @option{-A} are
5156 placed to the far right of output lines, after the right context. With
5157 default output format, when the @option{-R} option is specified, references
5158 are rather placed at the beginning of each output line, before the left
5159 context. For any other output format, option @option{-R} is
5160 ignored, with one exception: with @option{-R} the width of references
5161 is @emph{not} taken into account in total output width given by @option{-w}.
5163 This option is automatically selected whenever @sc{gnu} extensions are
5166 @item -F @var{string}
5167 @itemx --flac-truncation=@var{string}
5169 This option will request that any truncation in the output be reported
5170 using the string @var{string}. Most output fields theoretically extend
5171 towards the beginning or the end of the current line, or current
5172 sentence, as selected with option @option{-S}. But there is a maximum
5173 allowed output line width, changeable through option @option{-w}, which is
5174 further divided into space for various output fields. When a field has
5175 to be truncated because it cannot extend beyond the beginning or the end of
5176 the current line to fit in, then a truncation occurs. By default,
5177 the string used is a single slash, as in @option{-F /}.
5179 @var{string} may have more than one character, as in @option{-F ...}.
5180 Also, in the particular case when @var{string} is empty (@option{-F ""}),
5181 truncation flagging is disabled, and no truncation marks are appended in
5184 As a matter of convenience to the user, many usual backslashed escape
5185 sequences, as found in the C language, are recognized and converted to
5186 the corresponding characters by @command{ptx} itself.
5188 @item -M @var{string}
5189 @itemx --macro-name=@var{string}
5191 Select another @var{string} to be used instead of @samp{xx}, while
5192 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5195 @itemx --format=roff
5197 Choose an output format suitable for @command{nroff} or @command{troff}
5198 processing. Each output line will look like:
5201 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
5202 "@var{head}" "@var{ref}"
5205 so it will be possible to write a @samp{.xx} roff macro to take care of
5206 the output typesetting. This is the default output format when @sc{gnu}
5207 extensions are disabled. Option @option{-M} can be used to change
5208 @samp{xx} to another macro name.
5210 In this output format, each non-graphical character, like newline and
5211 tab, is merely changed to exactly one space, with no special attempt to
5212 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5213 so it will be correctly processed by @command{nroff} or @command{troff}.
5218 Choose an output format suitable for @TeX{} processing. Each output
5219 line will look like:
5222 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
5223 @{@var{after}@}@{@var{head}@}@{@var{ref}@}
5227 so it will be possible to write a @code{\xx} definition to take care of
5228 the output typesetting. Note that when references are not being
5229 produced, that is, neither option @option{-A} nor option @option{-r} is
5230 selected, the last parameter of each @code{\xx} call is inhibited.
5231 Option @option{-M} can be used to change @samp{xx} to another macro
5234 In this output format, some special characters, like @kbd{$}, @kbd{%},
5235 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5236 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5237 backslash and a pair of dollar signs (to force mathematical mode). The
5238 backslash itself produces the sequence @code{\backslash@{@}}.
5239 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5240 @code{~\@{ @}} respectively. Other diacriticized characters of the
5241 underlying character set produce an appropriate @TeX{} sequence as far
5242 as possible. The other non-graphical characters, like newline and tab,
5243 and all other characters which are not part of @acronym{ASCII}, are merely
5244 changed to exactly one space, with no special attempt to compress
5245 consecutive spaces. Let me know how to improve this special character
5246 processing for @TeX{}.
5251 @node Compatibility in ptx
5252 @subsection The @sc{gnu} extensions to @command{ptx}
5254 This version of @command{ptx} contains a few features which do not exist in
5255 System V @command{ptx}. These extra features are suppressed by using the
5256 @option{-G} command line option, unless overridden by other command line
5257 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5258 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5259 Here are the differences between this program and System V @command{ptx}.
5264 This program can read many input files at once, it always writes the
5265 resulting concordance on standard output. On the other hand, System V
5266 @command{ptx} reads only one file and sends the result to standard output
5267 or, if a second @var{file} parameter is given on the command, to that
5270 Having output parameters not introduced by options is a dangerous
5271 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5272 portably between @sc{gnu} and System V, you should always use it with a
5273 single input file, and always expect the result on standard output. You
5274 might also want to automatically configure in a @option{-G} option to
5275 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5276 that the installed @command{ptx} accepts @option{-G}.
5279 The only options available in System V @command{ptx} are options @option{-b},
5280 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5281 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5282 this enumeration. Moreover, some options have a slightly different
5283 meaning when @sc{gnu} extensions are enabled, as explained below.
5286 By default, concordance output is not formatted for @command{troff} or
5287 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5288 or @command{nroff} output may still be selected through option @option{-O}.
5291 Unless @option{-R} option is used, the maximum reference width is
5292 subtracted from the total output line width. With @sc{gnu} extensions
5293 disabled, width of references is not taken into account in the output
5294 line width computations.
5297 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5298 processed from input file with no adverse effect, even if @sc{gnu} extensions
5299 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5300 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5303 Input line length is only limited by available memory, even if @sc{gnu}
5304 extensions are disabled. However, System V @command{ptx} processes only
5305 the first 200 characters in each line.
5308 The break (non-word) characters default to be every character except all
5309 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5310 extensions are disabled, the break characters default to space, tab and
5314 The program makes better use of output line width. If @sc{gnu} extensions
5315 are disabled, the program rather tries to imitate System V @command{ptx},
5316 but still, there are some slight disposition glitches this program does
5317 not completely reproduce.
5320 The user can specify both an Ignore file and an Only file. This is not
5321 allowed with System V @command{ptx}.
5326 @node tsort invocation
5327 @section @command{tsort}: Topological sort
5330 @cindex topological sort
5332 @command{tsort} performs a topological sort on the given @var{file}, or
5333 standard input if no input file is given or for a @var{file} of
5334 @samp{-}. For more details and some history, see @ref{tsort background}.
5338 tsort [@var{option}] [@var{file}]
5341 @command{tsort} reads its input as pairs of strings, separated by blanks,
5342 indicating a partial ordering. The output is a total ordering that
5343 corresponds to the given partial ordering.
5357 will produce the output
5368 Consider a more realistic example.
5369 You have a large set of functions all in one file, and they may all be
5370 declared static except one. Currently that one (say @code{main}) is the
5371 first function defined in the file, and the ones it calls directly follow
5372 it, followed by those they call, etc. Let's say that you are determined
5373 to take advantage of prototypes, so you have to choose between declaring
5374 all of those functions (which means duplicating a lot of information from
5375 the definitions) and rearranging the functions so that as many as possible
5376 are defined before they are used. One way to automate the latter process
5377 is to get a list for each function of the functions it calls directly.
5378 Many programs can generate such lists. They describe a call graph.
5379 Consider the following list, in which a given line indicates that the
5380 function on the left calls the one on the right directly.
5386 tail_file pretty_name
5387 tail_file write_header
5389 tail_forever recheck
5390 tail_forever pretty_name
5391 tail_forever write_header
5392 tail_forever dump_remainder
5395 tail_lines start_lines
5396 tail_lines dump_remainder
5397 tail_lines file_lines
5398 tail_lines pipe_lines
5400 tail_bytes start_bytes
5401 tail_bytes dump_remainder
5402 tail_bytes pipe_bytes
5403 file_lines dump_remainder
5407 then you can use @command{tsort} to produce an ordering of those
5408 functions that satisfies your requirement.
5411 example$ tsort call-graph | tac
5431 @command{tsort} detects any cycles in the input and writes the first cycle
5432 encountered to standard error.
5434 Note that for a given partial ordering, generally there is no unique
5435 total ordering. In the context of the call graph above, the function
5436 @code{parse_options} may be placed anywhere in the list as long as it
5437 precedes @code{main}.
5439 The only options are @option{--help} and @option{--version}. @xref{Common
5445 * tsort background:: Where tsort came from.
5448 @node tsort background
5449 @subsection @command{tsort}: Background
5451 @command{tsort} exists because very early versions of the Unix linker processed
5452 an archive file exactly once, and in order. As @command{ld} read each object
5453 in the archive, it decided whether it was needed in the program based on
5454 whether it defined any symbols which were undefined at that point in
5457 This meant that dependencies within the archive had to be handled
5458 specially. For example, @code{scanf} probably calls @code{read}. That means
5459 that in a single pass through an archive, it was important for @code{scanf.o}
5460 to appear before read.o, because otherwise a program which calls
5461 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5462 reference to @code{read}.
5464 The way to address this problem was to first generate a set of
5465 dependencies of one object file on another. This was done by a shell
5466 script called @command{lorder}. The GNU tools don't provide a version of
5467 lorder, as far as I know, but you can still find it in BSD
5470 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5471 resulting sort to define the order in which you added objects to the archive.
5473 This whole procedure has been obsolete since about 1980, because
5474 Unix archives now contain a symbol table (traditionally built by
5475 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5476 linker uses the symbol table to effectively make multiple passes over
5479 Anyhow, that's where tsort came from. To solve an old problem with
5480 the way the linker handled archive files, which has since been solved
5484 @node Operating on fields
5485 @chapter Operating on fields
5488 * cut invocation:: Print selected parts of lines.
5489 * paste invocation:: Merge lines of files.
5490 * join invocation:: Join lines on a common field.
5494 @node cut invocation
5495 @section @command{cut}: Print selected parts of lines
5498 @command{cut} writes to standard output selected parts of each line of each
5499 input file, or standard input if no files are given or for a file name of
5503 cut @var{option}@dots{} [@var{file}]@dots{}
5506 In the table which follows, the @var{byte-list}, @var{character-list},
5507 and @var{field-list} are one or more numbers or ranges (two numbers
5508 separated by a dash) separated by commas. Bytes, characters, and
5509 fields are numbered starting at 1. Incomplete ranges may be
5510 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5511 @samp{@var{n}} through end of line or last field. The list elements
5512 can be repeated, can overlap, and can be specified in any order; but
5513 the selected input is written in the same order that it is read, and
5514 is written exactly once.
5516 The program accepts the following options. Also see @ref{Common
5521 @item -b @var{byte-list}
5522 @itemx --bytes=@var{byte-list}
5525 Select for printing only the bytes in positions listed in
5526 @var{byte-list}. Tabs and backspaces are treated like any other
5527 character; they take up 1 byte. If an output delimiter is specified,
5528 (see the description of @option{--output-delimiter}), then output that
5529 string between ranges of selected bytes.
5531 @item -c @var{character-list}
5532 @itemx --characters=@var{character-list}
5534 @opindex --characters
5535 Select for printing only the characters in positions listed in
5536 @var{character-list}. The same as @option{-b} for now, but
5537 internationalization will change that. Tabs and backspaces are
5538 treated like any other character; they take up 1 character. If an
5539 output delimiter is specified, (see the description of
5540 @option{--output-delimiter}), then output that string between ranges
5543 @item -f @var{field-list}
5544 @itemx --fields=@var{field-list}
5547 Select for printing only the fields listed in @var{field-list}.
5548 Fields are separated by a TAB character by default. Also print any
5549 line that contains no delimiter character, unless the
5550 @option{--only-delimited} (@option{-s}) option is specified.
5552 Note @command{awk} supports more sophisticated field processing,
5553 and by default will use (and discard) runs of blank characters to
5554 separate fields, and ignore leading and trailing blanks.
5557 awk '{print $2}' # print the second field
5558 awk '{print $NF-1}' # print the penultimate field
5559 awk '{print $2,$1}' # reorder the first two fields
5563 In the unlikely event that @command{awk} is unavailable,
5564 one can use the @command{join} command, to process blank
5565 characters as @command{awk} does above.
5568 join -a1 -o 1.2 - /dev/null # print the second field
5569 join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
5573 @item -d @var{input_delim_byte}
5574 @itemx --delimiter=@var{input_delim_byte}
5576 @opindex --delimiter
5577 With @option{-f}, use the first byte of @var{input_delim_byte} as
5578 the input fields separator (default is TAB).
5582 Do not split multi-byte characters (no-op for now).
5585 @itemx --only-delimited
5587 @opindex --only-delimited
5588 For @option{-f}, do not print lines that do not contain the field separator
5589 character. Normally, any line without a field separator is printed verbatim.
5591 @item --output-delimiter=@var{output_delim_string}
5592 @opindex --output-delimiter
5593 With @option{-f}, output fields are separated by @var{output_delim_string}.
5594 The default with @option{-f} is to use the input delimiter.
5595 When using @option{-b} or @option{-c} to select ranges of byte or
5596 character offsets (as opposed to ranges of fields),
5597 output @var{output_delim_string} between non-overlapping
5598 ranges of selected bytes.
5601 @opindex --complement
5602 This option is a @acronym{GNU} extension.
5603 Select for printing the complement of the bytes, characters or fields
5604 selected with the @option{-b}, @option{-c} or @option{-f} options.
5605 In other words, do @emph{not} print the bytes, characters or fields
5606 specified via those options. This option is useful when you have
5607 many fields and want to print all but a few of them.
5614 @node paste invocation
5615 @section @command{paste}: Merge lines of files
5618 @cindex merging files
5620 @command{paste} writes to standard output lines consisting of sequentially
5621 corresponding lines of each given file, separated by a TAB character.
5622 Standard input is used for a file name of @samp{-} or if no input files
5644 paste [@var{option}]@dots{} [@var{file}]@dots{}
5647 The program accepts the following options. Also see @ref{Common options}.
5655 Paste the lines of one file at a time rather than one line from each
5656 file. Using the above example data:
5659 $ paste -s num2 let3
5664 @item -d @var{delim-list}
5665 @itemx --delimiters=@var{delim-list}
5667 @opindex --delimiters
5668 Consecutively use the characters in @var{delim-list} instead of
5669 TAB to separate merged lines. When @var{delim-list} is
5670 exhausted, start again at its beginning. Using the above example data:
5673 $ paste -d '%_' num2 let3 num2
5684 @node join invocation
5685 @section @command{join}: Join lines on a common field
5688 @cindex common field, joining on
5690 @command{join} writes to standard output a line for each pair of input
5691 lines that have identical join fields. Synopsis:
5694 join [@var{option}]@dots{} @var{file1} @var{file2}
5697 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5698 meaning standard input. @var{file1} and @var{file2} should be
5699 sorted on the join fields.
5702 Normally, the sort order is that of the
5703 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5704 the @option{-t} option is given, the sort comparison ignores blanks at
5705 the start of the join field, as in @code{sort -b}. If the
5706 @option{--ignore-case} option is given, the sort comparison ignores
5707 the case of characters in the join field, as in @code{sort -f}.
5709 The @command{sort} and @command{join} commands should use consistent
5710 locales and options if the output of @command{sort} is fed to
5711 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5712 sort a file on its default join field, but if you select a non-default
5713 locale, join field, separator, or comparison options, then you should
5714 do so consistently between @command{join} and @command{sort}.
5715 If @samp{join -t ''} is specified then the whole line is considered which
5716 matches the default operation of sort.
5718 If the input has no unpairable lines, a @acronym{GNU} extension is
5719 available; the sort order can be any order that considers two fields
5720 to be equal if and only if the sort comparison described above
5721 considers them to be equal. For example:
5739 @checkOrderOption{join}
5744 @item the join field is the first field in each line;
5745 @item fields in the input are separated by one or more blanks, with leading
5746 blanks on the line ignored;
5747 @item fields in the output are separated by a space;
5748 @item each output line consists of the join field, the remaining
5749 fields from @var{file1}, then the remaining fields from @var{file2}.
5752 The program accepts the following options. Also see @ref{Common options}.
5756 @item -a @var{file-number}
5758 Print a line for each unpairable line in file @var{file-number} (either
5759 @samp{1} or @samp{2}), in addition to the normal output.
5762 Fail with an error message if either input file is wrongly ordered.
5764 @item --nocheck-order
5765 Do not check that both input files are in sorted order. This is the default.
5767 @item -e @var{string}
5769 Replace those output fields that are missing in the input with @var{string}.
5770 I.E. missing fields specified with the @option{-12jo} options.
5774 Treat the first line of each input file as a header line. The header lines will
5775 be joined and printed as the first output line. If @option{-o} is used to
5776 specify output format, the header line will be printed according to the
5777 specified format. The header lines will not be checked for ordering even if
5778 @option{--check-order} is specified. Also if the header lines from each file
5779 do not match, the heading fields from the first file will be used.
5782 @itemx --ignore-case
5784 @opindex --ignore-case
5785 Ignore differences in case when comparing keys.
5786 With this option, the lines of the input files must be ordered in the same way.
5787 Use @samp{sort -f} to produce this ordering.
5789 @item -1 @var{field}
5791 Join on field @var{field} (a positive integer) of file 1.
5793 @item -2 @var{field}
5795 Join on field @var{field} (a positive integer) of file 2.
5797 @item -j @var{field}
5798 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5800 @item -o @var{field-list}
5802 If the keyword @samp{auto} is specified, infer the output format from
5803 the first line in each file. This is the same as the default output format
5804 but also ensures the same number of fields are output for each line.
5805 Missing fields are replaced with the @option{-e} option and extra fields
5808 Otherwise, construct each output line according to the format in
5809 @var{field-list}. Each element in @var{field-list} is either the single
5810 character @samp{0} or has the form @var{m.n} where the file number, @var{m},
5811 is @samp{1} or @samp{2} and @var{n} is a positive field number.
5813 A field specification of @samp{0} denotes the join field.
5814 In most cases, the functionality of the @samp{0} field spec
5815 may be reproduced using the explicit @var{m.n} that corresponds
5816 to the join field. However, when printing unpairable lines
5817 (using either of the @option{-a} or @option{-v} options), there is no way
5818 to specify the join field using @var{m.n} in @var{field-list}
5819 if there are unpairable lines in both files.
5820 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5821 field specification notation.
5823 The elements in @var{field-list}
5824 are separated by commas or blanks.
5825 Blank separators typically need to be quoted for the shell. For
5826 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5827 2.2'} are equivalent.
5829 All output lines---including those printed because of any -a or -v
5830 option---are subject to the specified @var{field-list}.
5833 Use character @var{char} as the input and output field separator.
5834 Treat as significant each occurrence of @var{char} in the input file.
5835 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5836 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5837 the whole line is considered, matching the default operation of sort.
5838 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5839 character is used to delimit the fields.
5841 @item -v @var{file-number}
5842 Print a line for each unpairable line in file @var{file-number}
5843 (either @samp{1} or @samp{2}), instead of the normal output.
5850 @node Operating on characters
5851 @chapter Operating on characters
5853 @cindex operating on characters
5855 This commands operate on individual characters.
5858 * tr invocation:: Translate, squeeze, and/or delete characters.
5859 * expand invocation:: Convert tabs to spaces.
5860 * unexpand invocation:: Convert spaces to tabs.
5865 @section @command{tr}: Translate, squeeze, and/or delete characters
5872 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5875 @command{tr} copies standard input to standard output, performing
5876 one of the following operations:
5880 translate, and optionally squeeze repeated characters in the result,
5882 squeeze repeated characters,
5886 delete characters, then squeeze repeated characters from the result.
5889 The @var{set1} and (if given) @var{set2} arguments define ordered
5890 sets of characters, referred to below as @var{set1} and @var{set2}. These
5891 sets are the characters of the input that @command{tr} operates on.
5892 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5894 complement (all of the characters that are not in @var{set1}).
5896 Currently @command{tr} fully supports only single-byte characters.
5897 Eventually it will support multibyte characters; when it does, the
5898 @option{-C} option will cause it to complement the set of characters,
5899 whereas @option{-c} will cause it to complement the set of values.
5900 This distinction will matter only when some values are not characters,
5901 and this is possible only in locales using multibyte encodings when
5902 the input contains encoding errors.
5904 The program accepts the @option{--help} and @option{--version}
5905 options. @xref{Common options}. Options must precede operands.
5910 * Character sets:: Specifying sets of characters.
5911 * Translating:: Changing one set of characters to another.
5912 * Squeezing:: Squeezing repeats and deleting.
5916 @node Character sets
5917 @subsection Specifying sets of characters
5919 @cindex specifying sets of characters
5921 The format of the @var{set1} and @var{set2} arguments resembles
5922 the format of regular expressions; however, they are not regular
5923 expressions, only lists of characters. Most characters simply
5924 represent themselves in these strings, but the strings can contain
5925 the shorthands listed below, for convenience. Some of them can be
5926 used only in @var{set1} or @var{set2}, as noted below.
5930 @item Backslash escapes
5931 @cindex backslash escapes
5933 The following backslash escape sequences are recognized:
5951 The 8-bit character with the value given by @var{ooo}, which is 1 to 3
5952 octal digits. Note that @samp{\400} is interpreted as the two-byte
5953 sequence, @samp{\040} @samp{0}.
5958 While a backslash followed by a character not listed above is
5959 interpreted as that character, the backslash also effectively
5960 removes any special significance, so it is useful to escape
5961 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5966 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5967 from @var{m} through @var{n}, in ascending order. @var{m} should
5968 collate before @var{n}; if it doesn't, an error results. As an example,
5969 @samp{0-9} is the same as @samp{0123456789}.
5971 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5972 brackets to enclose ranges. Translations specified in that format
5973 sometimes work as expected, since the brackets are often transliterated
5974 to themselves. However, they should be avoided because they sometimes
5975 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5978 Many historically common and even accepted uses of ranges are not
5979 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5980 range will not do what most would expect because @samp{A} through @samp{Z}
5981 are not contiguous as they are in @acronym{ASCII}.
5982 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5983 the best way to work around this is to use character classes (see below).
5984 Otherwise, it is most portable (and most ugly) to enumerate the members
5987 @item Repeated characters
5988 @cindex repeated characters
5990 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5991 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5992 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5993 to as many copies of @var{c} as are needed to make @var{set2} as long as
5994 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5995 octal, otherwise in decimal.
5997 @item Character classes
5998 @cindex character classes
6000 The notation @samp{[:@var{class}:]} expands to all of the characters in
6001 the (predefined) class @var{class}. The characters expand in no
6002 particular order, except for the @code{upper} and @code{lower} classes,
6003 which expand in ascending order. When the @option{--delete} (@option{-d})
6004 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
6005 character class can be used in @var{set2}. Otherwise, only the
6006 character classes @code{lower} and @code{upper} are accepted in
6007 @var{set2}, and then only if the corresponding character class
6008 (@code{upper} and @code{lower}, respectively) is specified in the same
6009 relative position in @var{set1}. Doing this specifies case conversion.
6010 The class names are given below; an error results when an invalid class
6022 Horizontal whitespace.
6031 Printable characters, not including space.
6037 Printable characters, including space.
6040 Punctuation characters.
6043 Horizontal or vertical whitespace.
6052 @item Equivalence classes
6053 @cindex equivalence classes
6055 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
6056 equivalent to @var{c}, in no particular order. Equivalence classes are
6057 a relatively recent invention intended to support non-English alphabets.
6058 But there seems to be no standard way to define them or determine their
6059 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
6060 each character's equivalence class consists only of that character,
6061 which is of no particular use.
6067 @subsection Translating
6069 @cindex translating characters
6071 @command{tr} performs translation when @var{set1} and @var{set2} are
6072 both given and the @option{--delete} (@option{-d}) option is not given.
6073 @command{tr} translates each character of its input that is in @var{set1}
6074 to the corresponding character in @var{set2}. Characters not in
6075 @var{set1} are passed through unchanged. When a character appears more
6076 than once in @var{set1} and the corresponding characters in @var{set2}
6077 are not all the same, only the final one is used. For example, these
6078 two commands are equivalent:
6085 A common use of @command{tr} is to convert lowercase characters to
6086 uppercase. This can be done in many ways. Here are three of them:
6089 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
6091 tr '[:lower:]' '[:upper:]'
6095 But note that using ranges like @code{a-z} above is not portable.
6097 When @command{tr} is performing translation, @var{set1} and @var{set2}
6098 typically have the same length. If @var{set1} is shorter than
6099 @var{set2}, the extra characters at the end of @var{set2} are ignored.
6101 On the other hand, making @var{set1} longer than @var{set2} is not
6102 portable; @acronym{POSIX} says that the result is undefined. In this situation,
6103 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
6104 the last character of @var{set2} as many times as necessary. System V
6105 @command{tr} truncates @var{set1} to the length of @var{set2}.
6107 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
6108 When the @option{--truncate-set1} (@option{-t}) option is given,
6109 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
6110 instead. This option is ignored for operations other than translation.
6112 Acting like System V @command{tr} in this case breaks the relatively common
6116 tr -cs A-Za-z0-9 '\012'
6120 because it converts only zero bytes (the first element in the
6121 complement of @var{set1}), rather than all non-alphanumerics, to
6125 By the way, the above idiom is not portable because it uses ranges, and
6126 it assumes that the octal code for newline is 012.
6127 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better
6131 tr -cs '[:alnum:]' '[\n*]'
6136 @subsection Squeezing repeats and deleting
6138 @cindex squeezing repeat characters
6139 @cindex deleting characters
6141 When given just the @option{--delete} (@option{-d}) option, @command{tr}
6142 removes any input characters that are in @var{set1}.
6144 When given just the @option{--squeeze-repeats} (@option{-s}) option,
6145 @command{tr} replaces each input sequence of a repeated character that
6146 is in @var{set1} with a single occurrence of that character.
6148 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
6149 first performs any deletions using @var{set1}, then squeezes repeats
6150 from any remaining characters using @var{set2}.
6152 The @option{--squeeze-repeats} option may also be used when translating,
6153 in which case @command{tr} first performs translation, then squeezes
6154 repeats from any remaining characters using @var{set2}.
6156 Here are some examples to illustrate various combinations of options:
6161 Remove all zero bytes:
6168 Put all words on lines by themselves. This converts all
6169 non-alphanumeric characters to newlines, then squeezes each string
6170 of repeated newlines into a single newline:
6173 tr -cs '[:alnum:]' '[\n*]'
6177 Convert each sequence of repeated newlines to a single newline:
6184 Find doubled occurrences of words in a document.
6185 @c Separate the following two "the"s, so typo checkers don't complain.
6186 For example, people often write ``the @w{}the'' with the repeated words
6187 separated by a newline. The Bourne shell script below works first
6188 by converting each sequence of punctuation and blank characters to a
6189 single newline. That puts each ``word'' on a line by itself.
6190 Next it maps all uppercase characters to lower case, and finally it
6191 runs @command{uniq} with the @option{-d} option to print out only the words
6197 | tr -s '[:punct:][:blank:]' '[\n*]' \
6198 | tr '[:upper:]' '[:lower:]' \
6203 Deleting a small set of characters is usually straightforward. For example,
6204 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
6210 However, when @samp{-} is one of those characters, it can be tricky because
6211 @samp{-} has special meanings. Performing the same task as above but also
6212 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
6213 that would fail because @command{tr} would try to interpret @option{-a} as
6214 a command-line option. Alternatively, we could try putting the hyphen
6215 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
6216 it would make @command{tr} interpret @code{a-x} as the range of characters
6217 @samp{a}@dots{}@samp{x} rather than the three.
6218 One way to solve the problem is to put the hyphen at the end of the list
6225 Or you can use @samp{--} to terminate option processing:
6231 More generally, use the character class notation @code{[=c=]}
6232 with @samp{-} (or any other character) in place of the @samp{c}:
6238 Note how single quotes are used in the above example to protect the
6239 square brackets from interpretation by a shell.
6244 @node expand invocation
6245 @section @command{expand}: Convert tabs to spaces
6248 @cindex tabs to spaces, converting
6249 @cindex converting tabs to spaces
6251 @command{expand} writes the contents of each given @var{file}, or standard
6252 input if none are given or for a @var{file} of @samp{-}, to standard
6253 output, with tab characters converted to the appropriate number of
6257 expand [@var{option}]@dots{} [@var{file}]@dots{}
6260 By default, @command{expand} converts all tabs to spaces. It preserves
6261 backspace characters in the output; they decrement the column count for
6262 tab calculations. The default action is equivalent to @option{-t 8} (set
6263 tabs every 8 columns).
6265 The program accepts the following options. Also see @ref{Common options}.
6269 @item -t @var{tab1}[,@var{tab2}]@dots{}
6270 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6273 @cindex tab stops, setting
6274 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6275 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6276 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6277 last tab stop given with single spaces. Tab stops can be separated by
6278 blanks as well as by commas.
6280 For compatibility, GNU @command{expand} also accepts the obsolete
6281 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6282 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6288 @cindex initial tabs, converting
6289 Only convert initial tabs (those that precede all non-space or non-tab
6290 characters) on each line to spaces.
6297 @node unexpand invocation
6298 @section @command{unexpand}: Convert spaces to tabs
6302 @command{unexpand} writes the contents of each given @var{file}, or
6303 standard input if none are given or for a @var{file} of @samp{-}, to
6304 standard output, converting blanks at the beginning of each line into
6305 as many tab characters as needed. In the default @acronym{POSIX}
6306 locale, a @dfn{blank} is a space or a tab; other locales may specify
6307 additional blank characters. Synopsis:
6310 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6313 By default, @command{unexpand} converts only initial blanks (those
6314 that precede all non-blank characters) on each line. It
6315 preserves backspace characters in the output; they decrement the column
6316 count for tab calculations. By default, tabs are set at every 8th
6319 The program accepts the following options. Also see @ref{Common options}.
6323 @item -t @var{tab1}[,@var{tab2}]@dots{}
6324 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6327 If only one tab stop is given, set the tabs @var{tab1} columns apart
6328 instead of the default 8. Otherwise, set the tabs at columns
6329 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6330 beyond the tab stops given unchanged. Tab stops can be separated by
6331 blanks as well as by commas. This option implies the @option{-a} option.
6333 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6334 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6335 separated by commas. (Unlike @option{-t}, this obsolete option does
6336 not imply @option{-a}.) New scripts should use @option{--first-only -t
6337 @var{tab1}[,@var{tab2}]@dots{}} instead.
6343 Also convert all sequences of two or more blanks just before a tab stop,
6344 even if they occur after non-blank characters in a line.
6351 @node Directory listing
6352 @chapter Directory listing
6354 This chapter describes the @command{ls} command and its variants @command{dir}
6355 and @command{vdir}, which list information about files.
6358 * ls invocation:: List directory contents.
6359 * dir invocation:: Briefly ls.
6360 * vdir invocation:: Verbosely ls.
6361 * dircolors invocation:: Color setup for ls, etc.
6366 @section @command{ls}: List directory contents
6369 @cindex directory listing
6371 The @command{ls} program lists information about files (of any type,
6372 including directories). Options and file arguments can be intermixed
6373 arbitrarily, as usual.
6375 For non-option command-line arguments that are directories, by default
6376 @command{ls} lists the contents of directories, not recursively, and
6377 omitting files with names beginning with @samp{.}. For other non-option
6378 arguments, by default @command{ls} lists just the file name. If no
6379 non-option argument is specified, @command{ls} operates on the current
6380 directory, acting as if it had been invoked with a single argument of @samp{.}.
6383 By default, the output is sorted alphabetically, according to the locale
6384 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6385 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6386 produce output that is sorted differently than you're accustomed to.
6387 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6388 If standard output is
6389 a terminal, the output is in columns (sorted vertically) and control
6390 characters are output as question marks; otherwise, the output is listed
6391 one per line and control characters are output as-is.
6393 Because @command{ls} is such a fundamental program, it has accumulated many
6394 options over the years. They are described in the subsections below;
6395 within each section, options are listed alphabetically (ignoring case).
6396 The division of options into the subsections is not absolute, since some
6397 options affect more than one aspect of @command{ls}'s operation.
6399 @cindex exit status of @command{ls}
6404 1 minor problems (e.g., failure to access a file or directory not
6405 specified as a command line argument. This happens when listing a
6406 directory in which entries are actively being removed or renamed.)
6407 2 serious trouble (e.g., memory exhausted, invalid option, failure
6408 to access a file or directory specified as a command line argument
6409 or a directory loop)
6412 Also see @ref{Common options}.
6415 * Which files are listed::
6416 * What information is listed::
6417 * Sorting the output::
6418 * Details about version sort::
6419 * General output formatting::
6420 * Formatting file timestamps::
6421 * Formatting the file names::
6425 @node Which files are listed
6426 @subsection Which files are listed
6428 These options determine which files @command{ls} lists information for.
6429 By default, @command{ls} lists files and the contents of any
6430 directories on the command line, except that in directories it ignores
6431 files whose names start with @samp{.}.
6439 In directories, do not ignore file names that start with @samp{.}.
6444 @opindex --almost-all
6445 In directories, do not ignore all file names that start with @samp{.};
6446 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6447 option overrides this option.
6450 @itemx --ignore-backups
6452 @opindex --ignore-backups
6453 @cindex backup files, ignoring
6454 In directories, ignore files that end with @samp{~}. This option is
6455 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6460 @opindex --directory
6461 List just the names of directories, as with other types of files, rather
6462 than listing their contents.
6463 @c The following sentence is the same as the one for -F.
6464 Do not follow symbolic links listed on the
6465 command line unless the @option{--dereference-command-line} (@option{-H}),
6466 @option{--dereference} (@option{-L}), or
6467 @option{--dereference-command-line-symlink-to-dir} options are specified.
6470 @itemx --dereference-command-line
6472 @opindex --dereference-command-line
6473 @cindex symbolic links, dereferencing
6474 If a command line argument specifies a symbolic link, show information
6475 for the file the link references rather than for the link itself.
6477 @itemx --dereference-command-line-symlink-to-dir
6478 @opindex --dereference-command-line-symlink-to-dir
6479 @cindex symbolic links, dereferencing
6480 Do not dereference symbolic links, with one exception:
6481 if a command line argument specifies a symbolic link that refers to
6482 a directory, show information for that directory rather than for the
6484 This is the default behavior when no other dereferencing-related
6485 option has been specified (@option{--classify} (@option{-F}),
6486 @option{--directory} (@option{-d}),
6488 @option{--dereference} (@option{-L}), or
6489 @option{--dereference-command-line} (@option{-H})).
6491 @item --group-directories-first
6492 @opindex --group-directories-first
6493 Group all the directories before the files and then sort the
6494 directories and the files separately using the selected sort key
6495 (see --sort option).
6496 That is, this option specifies a primary sort key,
6497 and the --sort option specifies a secondary key.
6498 However, any use of @option{--sort=none}
6499 (@option{-U}) disables this option altogether.
6501 @item --hide=PATTERN
6502 @opindex --hide=@var{pattern}
6503 In directories, ignore files whose names match the shell pattern
6504 @var{pattern}, unless the @option{--all} (@option{-a}) or
6505 @option{--almost-all} (@option{-A}) is also given. This
6506 option acts like @option{--ignore=@var{pattern}} except that it has no
6507 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6508 (@option{-A}) is also given.
6510 This option can be useful in shell aliases. For example, if
6511 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6512 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6513 lists the file @file{README~} even though @samp{ly -A} would not.
6515 @item -I @var{pattern}
6516 @itemx --ignore=@var{pattern}
6518 @opindex --ignore=@var{pattern}
6519 In directories, ignore files whose names match the shell pattern
6520 (not regular expression) @var{pattern}. As
6521 in the shell, an initial @samp{.} in a file name does not match a
6522 wildcard at the start of @var{pattern}. Sometimes it is useful
6523 to give this option several times. For example,
6526 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6529 The first option ignores names of length 3 or more that start with @samp{.},
6530 the second ignores all two-character names that start with @samp{.}
6531 except @samp{..}, and the third ignores names that start with @samp{#}.
6534 @itemx --dereference
6536 @opindex --dereference
6537 @cindex symbolic links, dereferencing
6538 When showing file information for a symbolic link, show information
6539 for the file the link references rather than the link itself.
6540 However, even with this option, @command{ls} still prints the name
6541 of the link itself, not the name of the file that the link points to.
6546 @opindex --recursive
6547 @cindex recursive directory listing
6548 @cindex directory listing, recursive
6549 List the contents of all directories recursively.
6554 @node What information is listed
6555 @subsection What information is listed
6557 These options affect the information that @command{ls} displays. By
6558 default, only file names are shown.
6564 @cindex hurd, author, printing
6565 List each file's author when producing long format directory listings.
6566 In GNU/Hurd, file authors can differ from their owners, but in other
6567 operating systems the two are the same.
6573 @cindex dired Emacs mode support
6574 With the long listing (@option{-l}) format, print an additional line after
6578 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6582 The @var{begn} and @var{endn} are unsigned integers that record the
6583 byte position of the beginning and end of each file name in the output.
6584 This makes it easy for Emacs to find the names, even when they contain
6585 unusual characters such as space or newline, without fancy searching.
6587 If directories are being listed recursively (@option{-R}), output a similar
6588 line with offsets for each subdirectory name:
6591 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6594 Finally, output a line of the form:
6597 //DIRED-OPTIONS// --quoting-style=@var{word}
6601 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6603 Here is an actual example:
6606 $ mkdir -p a/sub/deeper a/sub2
6608 $ touch a/sub/deeper/file
6609 $ ls -gloRF --dired a
6612 -rw-r--r-- 1 0 Jun 10 12:27 f1
6613 -rw-r--r-- 1 0 Jun 10 12:27 f2
6614 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6615 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6619 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6623 -rw-r--r-- 1 0 Jun 10 12:27 file
6627 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6628 //SUBDIRED// 2 3 167 172 228 240 290 296
6629 //DIRED-OPTIONS// --quoting-style=literal
6632 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6633 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6635 The offsets on the @samp{//SUBDIRED//} line delimit the following
6636 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6638 Here is an example of how to extract the fifth entry name, @samp{deeper},
6639 corresponding to the pair of offsets, 222 and 228:
6642 $ ls -gloRF --dired a > out
6643 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6647 Note that although the listing above includes a trailing slash
6648 for the @samp{deeper} entry, the offsets select the name without
6649 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6650 along with an option like @option{--escape} (aka @option{-b}) and operate
6651 on a file whose name contains special characters, notice that the backslash
6656 $ ls -blog --dired 'a b'
6657 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6659 //DIRED-OPTIONS// --quoting-style=escape
6662 If you use a quoting style that adds quote marks
6663 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6664 So beware that the user may select the quoting style via the environment
6665 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6666 should either specify an explicit @option{--quoting-style=literal} option
6667 (aka @option{-N} or @option{--literal}) on the command line, or else be
6668 prepared to parse the escaped names.
6671 @opindex --full-time
6672 Produce long format directory listings, and list times in full. It is
6673 equivalent to using @option{--format=long} with
6674 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6678 Produce long format directory listings, but don't display owner information.
6684 Inhibit display of group information in a long format directory listing.
6685 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6686 provide this option for compatibility.)
6694 @cindex inode number, printing
6695 Print the inode number (also called the file serial number and index
6696 number) of each file to the left of the file name. (This number
6697 uniquely identifies each file within a particular file system.)
6700 @itemx --format=long
6701 @itemx --format=verbose
6704 @opindex long ls @r{format}
6705 @opindex verbose ls @r{format}
6706 In addition to the name of each file, print the file type, file mode bits,
6707 number of hard links, owner name, group name, size, and
6708 timestamp (@pxref{Formatting file timestamps}), normally
6709 the modification time. Print question marks for information that
6710 cannot be determined.
6712 Normally the size is printed as a byte count without punctuation, but
6713 this can be overridden (@pxref{Block size}). For example, @option{-h}
6714 prints an abbreviated, human-readable count, and
6715 @samp{--block-size="'1"} prints a byte count with the thousands
6716 separator of the current locale.
6718 For each directory that is listed, preface the files with a line
6719 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6720 for all files in that directory. The block size currently defaults to 1024
6721 bytes, but this can be overridden (@pxref{Block size}).
6722 The @var{blocks} computed counts each hard link separately;
6723 this is arguably a deficiency.
6725 The file type is one of the following characters:
6727 @c The commented-out entries are ones we're not sure about.
6735 character special file
6737 high performance (``contiguous data'') file
6741 door (Solaris 2.5 and up)
6743 @c semaphore, if this is a distinct file type
6747 @c multiplexed file (7th edition Unix; obsolete)
6749 off-line (``migrated'') file (Cray DMF)
6751 network special file (HP-UX)
6755 port (Solaris 10 and up)
6757 @c message queue, if this is a distinct file type
6761 @c shared memory object, if this is a distinct file type
6763 @c typed memory object, if this is a distinct file type
6765 @c whiteout (4.4BSD; not implemented)
6767 some other file type
6770 @cindex permissions, output by @command{ls}
6771 The file mode bits listed are similar to symbolic mode specifications
6772 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6773 third character of each set of permissions as follows:
6777 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6781 If the set-user-ID or set-group-ID bit is set but the corresponding
6782 executable bit is not set.
6785 If the restricted deletion flag or sticky bit, and the
6786 other-executable bit, are both set. The restricted deletion flag is
6787 another name for the sticky bit. @xref{Mode Structure}.
6790 If the restricted deletion flag or sticky bit is set but the
6791 other-executable bit is not set.
6794 If the executable bit is set and none of the above apply.
6800 Following the file mode bits is a single character that specifies
6801 whether an alternate access method such as an access control list
6802 applies to the file. When the character following the file mode bits is a
6803 space, there is no alternate access method. When it is a printing
6804 character, then there is such a method.
6806 GNU @command{ls} uses a @samp{.} character to indicate a file
6807 with an SELinux security context, but no other alternate access method.
6809 A file with any other combination of alternate access methods
6810 is marked with a @samp{+} character.
6813 @itemx --numeric-uid-gid
6815 @opindex --numeric-uid-gid
6816 @cindex numeric uid and gid
6817 @cindex numeric user and group IDs
6818 Produce long format directory listings, but
6819 display numeric user and group IDs instead of the owner and group names.
6823 Produce long format directory listings, but don't display group information.
6824 It is equivalent to using @option{--format=long} with @option{--no-group} .
6830 @cindex disk allocation
6831 @cindex size of files, reporting
6832 Print the disk allocation of each file to the left of the file name.
6833 This is the amount of disk space used by the file, which is usually a
6834 bit more than the file's size, but it can be less if the file has holes.
6836 Normally the disk allocation is printed in units of
6837 1024 bytes, but this can be overridden (@pxref{Block size}).
6839 @cindex NFS mounts from BSD to HP-UX
6840 For files that are NFS-mounted from an HP-UX system to a BSD system,
6841 this option reports sizes that are half the correct values. On HP-UX
6842 systems, it reports sizes that are twice the correct values for files
6843 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6844 it also affects the HP-UX @command{ls} program.
6853 @cindex security context
6854 Display the SELinux security context or @samp{?} if none is found.
6855 When used with the @option{-l} option, print the security context
6856 to the left of the size column.
6861 @node Sorting the output
6862 @subsection Sorting the output
6864 @cindex sorting @command{ls} output
6865 These options change the order in which @command{ls} sorts the information
6866 it outputs. By default, sorting is done by character code
6867 (e.g., @acronym{ASCII} order).
6873 @itemx --time=status
6876 @opindex ctime@r{, printing or sorting by}
6877 @opindex status time@r{, printing or sorting by}
6878 @opindex use time@r{, printing or sorting files by}
6879 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6880 print the status change time (the @samp{ctime} in the inode) instead of
6881 the modification time.
6882 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6883 or when not using a long listing format,
6884 sort according to the status change time.
6888 @cindex unsorted directory listing
6889 @cindex directory order, listing by
6890 Primarily, like @option{-U}---do not sort; list the files in whatever
6891 order they are stored in the directory. But also enable @option{-a} (list
6892 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6893 were specified before the @option{-f}).
6899 @cindex reverse sorting
6900 Reverse whatever the sorting method is---e.g., list files in reverse
6901 alphabetical order, youngest first, smallest first, or whatever.
6907 @opindex size of files@r{, sorting files by}
6908 Sort by file size, largest first.
6914 @opindex modification time@r{, sorting files by}
6915 Sort by modification time (the @samp{mtime} in the inode), newest first.
6919 @itemx --time=access
6923 @opindex use time@r{, printing or sorting files by}
6924 @opindex atime@r{, printing or sorting files by}
6925 @opindex access time@r{, printing or sorting files by}
6926 If the long listing format (e.g., @option{--format=long}) is being used,
6927 print the last access time (the @samp{atime} in the inode).
6928 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6929 or when not using a long listing format, sort according to the access time.
6935 @opindex none@r{, sorting option for @command{ls}}
6936 Do not sort; list the files in whatever order they are
6937 stored in the directory. (Do not do any of the other unrelated things
6938 that @option{-f} does.) This is especially useful when listing very large
6939 directories, since not doing any sorting can be noticeably faster.
6942 @itemx --sort=version
6945 @opindex version@r{, sorting option for @command{ls}}
6946 Sort by version name and number, lowest first. It behaves like a default
6947 sort, except that each sequence of decimal digits is treated numerically
6948 as an index/version number. (@xref{Details about version sort}.)
6951 @itemx --sort=extension
6954 @opindex extension@r{, sorting files by}
6955 Sort directory contents alphabetically by file extension (characters
6956 after the last @samp{.}); files with no extension are sorted first.
6961 @node Details about version sort
6962 @subsection Details about version sort
6964 Version sorting handles the fact that file names frequently include indices or
6965 version numbers. Standard sorting usually does not produce the order that one
6966 expects because comparisons are made on a character-by-character basis.
6967 Version sorting is especially useful when browsing directories that contain
6968 many files with indices/version numbers in their names:
6972 abc.zml-1.gz abc.zml-1.gz
6973 abc.zml-12.gz abc.zml-2.gz
6974 abc.zml-2.gz abc.zml-12.gz
6977 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6978 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6979 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6980 @var{ver1} < @var{ver2} implies that the name composed of
6981 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6982 ``@var{prefix} @var{ver2} @var{suffix}''.
6984 Note also that leading zeros of numeric parts are ignored:
6988 abc-1.007.tgz abc-1.01a.tgz
6989 abc-1.012b.tgz abc-1.007.tgz
6990 abc-1.01a.tgz abc-1.012b.tgz
6993 This functionality is implemented using gnulib's @code{filevercmp} function,
6994 which has some caveats worth noting.
6997 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6998 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6999 was set to @samp{C}.
7000 @item Some suffixes will not be matched by the regular
7001 expression mentioned above. Consequently these examples may
7002 not sort as you expect:
7010 abc-1.2.3.4.x86_64.rpm
7011 abc-1.2.3.x86_64.rpm
7015 @node General output formatting
7016 @subsection General output formatting
7018 These options affect the appearance of the overall output.
7023 @itemx --format=single-column
7026 @opindex single-column @r{output of files}
7027 List one file per line. This is the default for @command{ls} when standard
7028 output is not a terminal.
7031 @itemx --format=vertical
7034 @opindex vertical @r{sorted files in columns}
7035 List files in columns, sorted vertically. This is the default for
7036 @command{ls} if standard output is a terminal. It is always the default
7037 for the @command{dir} program.
7038 @sc{gnu} @command{ls} uses variable width columns to display as many files as
7039 possible in the fewest lines.
7041 @item --color [=@var{when}]
7043 @cindex color, distinguishing file types with
7044 Specify whether to use color for distinguishing file types. @var{when}
7045 may be omitted, or one of:
7048 @vindex none @r{color option}
7049 - Do not use color at all. This is the default.
7051 @vindex auto @r{color option}
7052 @cindex terminal, using color iff
7053 - Only use color if standard output is a terminal.
7055 @vindex always @r{color option}
7058 Specifying @option{--color} and no @var{when} is equivalent to
7059 @option{--color=always}.
7060 Piping a colorized listing through a pager like @command{more} or
7061 @command{less} usually produces unreadable results. However, using
7062 @code{more -f} does seem to work.
7065 @vindex SHELL @r{environment variable, and color}
7066 Note that using the @option{--color} option may incur a noticeable
7067 performance penalty when run in a directory with very many entries,
7068 because the default settings require that @command{ls} @code{stat} every
7069 single file it lists.
7070 However, if you would like most of the file-type coloring
7071 but can live without the other coloring options (e.g.,
7072 executable, orphan, sticky, other-writable, capability), use
7073 @command{dircolors} to set the @env{LS_COLORS} environment variable like this,
7075 eval $(dircolors -p | perl -pe \
7076 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
7078 and on a @code{dirent.d_type}-capable file system, @command{ls}
7079 will perform only one @code{stat} call per command line argument.
7083 @itemx --indicator-style=classify
7086 @opindex --indicator-style
7087 @cindex file type and executables, marking
7088 @cindex executables and file type, marking
7089 Append a character to each file name indicating the file type. Also,
7090 for regular files that are executable, append @samp{*}. The file type
7091 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
7092 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
7093 and nothing for regular files.
7094 @c The following sentence is the same as the one for -d.
7095 Do not follow symbolic links listed on the
7096 command line unless the @option{--dereference-command-line} (@option{-H}),
7097 @option{--dereference} (@option{-L}), or
7098 @option{--dereference-command-line-symlink-to-dir} options are specified.
7101 @itemx --indicator-style=file-type
7102 @opindex --file-type
7103 @opindex --indicator-style
7104 @cindex file type, marking
7105 Append a character to each file name indicating the file type. This is
7106 like @option{-F}, except that executables are not marked.
7108 @item --indicator-style=@var{word}
7109 @opindex --indicator-style
7110 Append a character indicator with style @var{word} to entry names,
7115 Do not append any character indicator; this is the default.
7117 Append @samp{/} for directories. This is the same as the @option{-p}
7120 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
7121 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
7122 the same as the @option{--file-type} option.
7124 Append @samp{*} for executable regular files, otherwise behave as for
7125 @samp{file-type}. This is the same as the @option{-F} or
7126 @option{--classify} option.
7131 Print file sizes in 1024-byte blocks, overriding the default block
7132 size (@pxref{Block size}).
7133 This option is equivalent to @option{--block-size=1K}.
7136 @itemx --format=commas
7139 @opindex commas@r{, outputting between files}
7140 List files horizontally, with as many as will fit on each line,
7141 separated by @samp{, } (a comma and a space).
7144 @itemx --indicator-style=slash
7146 @opindex --indicator-style
7147 @cindex file type, marking
7148 Append a @samp{/} to directory names.
7151 @itemx --format=across
7152 @itemx --format=horizontal
7155 @opindex across@r{, listing files}
7156 @opindex horizontal@r{, listing files}
7157 List the files in columns, sorted horizontally.
7160 @itemx --tabsize=@var{cols}
7163 Assume that each tab stop is @var{cols} columns wide. The default is 8.
7164 @command{ls} uses tabs where possible in the output, for efficiency. If
7165 @var{cols} is zero, do not use tabs at all.
7167 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
7168 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
7169 do not properly align columns to the right of a TAB following a
7170 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
7171 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
7172 @command{ls} to align using spaces, not tabs.
7175 @itemx --width=@var{cols}
7179 Assume the screen is @var{cols} columns wide. The default is taken
7180 from the terminal settings if possible; otherwise the environment
7181 variable @env{COLUMNS} is used if it is set; otherwise the default
7187 @node Formatting file timestamps
7188 @subsection Formatting file timestamps
7190 By default, file timestamps are listed in abbreviated form, using
7191 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
7192 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
7193 This format can change depending on the current locale as detailed below.
7195 A timestamp is considered to be @dfn{recent} if it is less than six
7196 months old, and is not dated in the future. If a timestamp dated
7197 today is not listed in recent form, the timestamp is in the future,
7198 which means you probably have clock skew problems which may break
7199 programs like @command{make} that rely on file timestamps.
7202 Time stamps are listed according to the time zone rules specified by
7203 the @env{TZ} environment variable, or by the system default rules if
7204 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
7205 with @env{TZ}, libc, The GNU C Library Reference Manual}.
7207 The following option changes how file timestamps are printed.
7210 @item --time-style=@var{style}
7211 @opindex --time-style
7213 List timestamps in style @var{style}. The @var{style} should
7214 be one of the following:
7219 List timestamps using @var{format}, where @var{format} is interpreted
7220 like the format argument of @command{date} (@pxref{date invocation}).
7221 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
7222 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
7223 with @command{date}, @var{format}'s interpretation is affected by the
7224 @env{LC_TIME} locale category.
7226 If @var{format} contains two format strings separated by a newline,
7227 the former is used for non-recent files and the latter for recent
7228 files; if you want output columns to line up, you may need to insert
7229 spaces in one of the two formats.
7232 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
7233 format with nanosecond precision, e.g., @samp{2002-03-30
7234 23:45:56.477817180 -0700}. This style is equivalent to
7235 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
7237 This is useful because the time output includes all the information that
7238 is available from the operating system. For example, this can help
7239 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
7240 uses the full timestamp to determine whether a file is out of date.
7243 List @acronym{ISO} 8601 date and time in minutes, e.g.,
7244 @samp{2002-03-30 23:45}. These timestamps are shorter than
7245 @samp{full-iso} timestamps, and are usually good enough for everyday
7246 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7249 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
7250 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
7251 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7252 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7253 nearly the same information in a smaller space and their brevity helps
7254 @command{ls} output fit within traditional 80-column output lines.
7255 The following two @command{ls} invocations are equivalent:
7260 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7261 ls -l --time-style="iso"
7266 List timestamps in a locale-dependent form. For example, a Finnish
7267 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7268 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7269 timestamps typically consume more space than @samp{iso} timestamps and
7270 are harder for programs to parse because locale conventions vary so
7271 widely, but they are easier for many people to read.
7273 The @env{LC_TIME} locale category specifies the timestamp format. The
7274 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7275 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7276 @command{ls} invocations are equivalent:
7281 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7282 ls -l --time-style="locale"
7285 Other locales behave differently. For example, in a German locale,
7286 @option{--time-style="locale"} might be equivalent to
7287 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7288 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7289 @samp{30. M@"ar 23:45}.
7291 @item posix-@var{style}
7293 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7294 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7295 example, the @samp{posix-long-iso} style lists
7296 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7297 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7302 You can specify the default value of the @option{--time-style} option
7303 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7304 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7305 later use the @option{--dired} option and therefore can parse any date
7306 format, but if you are using Emacs 21.1 or 21.2 and specify a
7307 non-@acronym{POSIX} locale you may need to set
7308 @samp{TIME_STYLE="posix-long-iso"}.
7310 To avoid certain denial-of-service attacks, timestamps that would be
7311 longer than 1000 bytes may be treated as errors.
7314 @node Formatting the file names
7315 @subsection Formatting the file names
7317 These options change how file names themselves are printed.
7323 @itemx --quoting-style=escape
7326 @opindex --quoting-style
7327 @cindex backslash sequences for file names
7328 Quote nongraphic characters in file names using alphabetic and octal
7329 backslash sequences like those used in C.
7333 @itemx --quoting-style=literal
7336 @opindex --quoting-style
7337 Do not quote file names. However, with @command{ls} nongraphic
7338 characters are still printed as question marks if the output is a
7339 terminal and you do not specify the @option{--show-control-chars}
7343 @itemx --hide-control-chars
7345 @opindex --hide-control-chars
7346 Print question marks instead of nongraphic characters in file names.
7347 This is the default if the output is a terminal and the program is
7352 @itemx --quoting-style=c
7354 @opindex --quote-name
7355 @opindex --quoting-style
7356 Enclose file names in double quotes and quote nongraphic characters as
7359 @item --quoting-style=@var{word}
7360 @opindex --quoting-style
7361 @cindex quoting style
7362 Use style @var{word} to quote file names and other strings that may
7363 contain arbitrary characters. The @var{word} should
7364 be one of the following:
7368 Output strings as-is; this is the same as the @option{-N} or
7369 @option{--literal} option.
7371 Quote strings for the shell if they contain shell metacharacters or would
7372 cause ambiguous output.
7373 The quoting is suitable for @acronym{POSIX}-compatible shells like
7374 @command{bash}, but it does not always work for incompatible shells
7377 Quote strings for the shell, even if they would normally not require quoting.
7379 Quote strings as for C character string literals, including the
7380 surrounding double-quote characters; this is the same as the
7381 @option{-Q} or @option{--quote-name} option.
7383 Quote strings as for C character string literals, except omit the
7384 surrounding double-quote
7385 characters; this is the same as the @option{-b} or @option{--escape} option.
7387 Quote strings as for C character string literals, except use
7388 surrounding quotation marks appropriate for the
7391 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7392 Quote strings as for C character string literals, except use
7393 surrounding quotation marks appropriate for the locale, and quote
7394 @t{`like this'} instead of @t{"like
7395 this"} in the default C locale. This looks nicer on many displays.
7398 You can specify the default value of the @option{--quoting-style} option
7399 with the environment variable @env{QUOTING_STYLE}. If that environment
7400 variable is not set, the default value is @samp{literal}, but this
7401 default may change to @samp{shell} in a future version of this package.
7403 @item --show-control-chars
7404 @opindex --show-control-chars
7405 Print nongraphic characters as-is in file names.
7406 This is the default unless the output is a terminal and the program is
7412 @node dir invocation
7413 @section @command{dir}: Briefly list directory contents
7416 @cindex directory listing, brief
7418 @command{dir} is equivalent to @code{ls -C
7419 -b}; that is, by default files are listed in columns, sorted vertically,
7420 and special characters are represented by backslash escape sequences.
7422 @xref{ls invocation, @command{ls}}.
7425 @node vdir invocation
7426 @section @command{vdir}: Verbosely list directory contents
7429 @cindex directory listing, verbose
7431 @command{vdir} is equivalent to @code{ls -l
7432 -b}; that is, by default files are listed in long format and special
7433 characters are represented by backslash escape sequences.
7435 @node dircolors invocation
7436 @section @command{dircolors}: Color setup for @command{ls}
7440 @cindex setup for color
7442 @command{dircolors} outputs a sequence of shell commands to set up the
7443 terminal for color output from @command{ls} (and @command{dir}, etc.).
7447 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7450 If @var{file} is specified, @command{dircolors} reads it to determine which
7451 colors to use for which file types and extensions. Otherwise, a
7452 precompiled database is used. For details on the format of these files,
7453 run @samp{dircolors --print-database}.
7455 To make @command{dircolors} read a @file{~/.dircolors} file if it
7456 exists, you can put the following lines in your @file{~/.bashrc} (or
7457 adapt them to your favorite shell):
7461 test -r $d && eval "$(dircolors $d)"
7465 @vindex SHELL @r{environment variable, and color}
7466 The output is a shell command to set the @env{LS_COLORS} environment
7467 variable. You can specify the shell syntax to use on the command line,
7468 or @command{dircolors} will guess it from the value of the @env{SHELL}
7469 environment variable.
7471 The program accepts the following options. Also see @ref{Common options}.
7476 @itemx --bourne-shell
7479 @opindex --bourne-shell
7480 @cindex Bourne shell syntax for color setup
7481 @cindex @command{sh} syntax for color setup
7482 Output Bourne shell commands. This is the default if the @env{SHELL}
7483 environment variable is set and does not end with @samp{csh} or
7492 @cindex C shell syntax for color setup
7493 @cindex @command{csh} syntax for color setup
7494 Output C shell commands. This is the default if @code{SHELL} ends with
7495 @command{csh} or @command{tcsh}.
7498 @itemx --print-database
7500 @opindex --print-database
7501 @cindex color database, printing
7502 @cindex database for color setup, printing
7503 @cindex printing color database
7504 Print the (compiled-in) default color configuration database. This
7505 output is itself a valid configuration file, and is fairly descriptive
7506 of the possibilities.
7513 @node Basic operations
7514 @chapter Basic operations
7516 @cindex manipulating files
7518 This chapter describes the commands for basic file manipulation:
7519 copying, moving (renaming), and deleting (removing).
7522 * cp invocation:: Copy files.
7523 * dd invocation:: Convert and copy a file.
7524 * install invocation:: Copy files and set attributes.
7525 * mv invocation:: Move (rename) files.
7526 * rm invocation:: Remove files or directories.
7527 * shred invocation:: Remove files more securely.
7532 @section @command{cp}: Copy files and directories
7535 @cindex copying files and directories
7536 @cindex files, copying
7537 @cindex directories, copying
7539 @command{cp} copies files (or, optionally, directories). The copy is
7540 completely independent of the original. You can either copy one file to
7541 another, or copy arbitrarily many files to a destination directory.
7545 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7546 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7547 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7552 If two file names are given, @command{cp} copies the first file to the
7556 If the @option{--target-directory} (@option{-t}) option is given, or
7557 failing that if the last file is a directory and the
7558 @option{--no-target-directory} (@option{-T}) option is not given,
7559 @command{cp} copies each @var{source} file to the specified directory,
7560 using the @var{source}s' names.
7563 Generally, files are written just as they are read. For exceptions,
7564 see the @option{--sparse} option below.
7566 By default, @command{cp} does not copy directories. However, the
7567 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7568 copy recursively by descending into source directories and copying files
7569 to corresponding destination directories.
7571 When copying from a symbolic link, @command{cp} normally follows the
7572 link only when not copying
7573 recursively. This default can be overridden with the
7574 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7575 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7576 @option{-H} options. If more than one of these options is specified,
7577 the last one silently overrides the others.
7579 When copying to a symbolic link, @command{cp} follows the
7580 link only when it refers to an existing regular file.
7581 However, when copying to a dangling symbolic link, @command{cp}
7582 refuses by default, and fails with a diagnostic, since the operation
7583 is inherently dangerous. This behavior is contrary to historical
7584 practice and to @acronym{POSIX}.
7585 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7586 the target of a dangling destination symlink, in spite of the possible risk.
7587 Also, when an option like
7588 @option{--backup} or @option{--link} acts to rename or remove the
7589 destination before copying, @command{cp} renames or removes the
7590 symbolic link rather than the file it points to.
7592 By default, @command{cp} copies the contents of special files only
7593 when not copying recursively. This default can be overridden with the
7594 @option{--copy-contents} option.
7596 @cindex self-backups
7597 @cindex backups, making only
7598 @command{cp} generally refuses to copy a file onto itself, with the
7599 following exception: if @option{--force --backup} is specified with
7600 @var{source} and @var{dest} identical, and referring to a regular file,
7601 @command{cp} will make a backup file, either regular or numbered, as
7602 specified in the usual ways (@pxref{Backup options}). This is useful when
7603 you simply want to make a backup of an existing file before changing it.
7605 The program accepts the following options. Also see @ref{Common options}.
7612 Preserve as much as possible of the structure and attributes of the
7613 original files in the copy (but do not attempt to preserve internal
7614 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7615 directory in a different order).
7616 Try to preserve SELinux security context and extended attributes (xattr),
7617 but ignore any failure to do that and print no corresponding diagnostic.
7618 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7620 @itemx --attributes-only
7621 @opindex --attributes-only
7622 Preserve the specified attributes of the original files in the copy,
7623 but do not copy any data. See the @option{--preserve} option for
7624 controlling which attributes to copy.
7627 @itemx @w{@kbd{--backup}[=@var{method}]}
7630 @vindex VERSION_CONTROL
7631 @cindex backups, making
7632 @xref{Backup options}.
7633 Make a backup of each file that would otherwise be overwritten or removed.
7634 As a special case, @command{cp} makes a backup of @var{source} when the force
7635 and backup options are given and @var{source} and @var{dest} are the same
7636 name for an existing, regular file. One useful application of this
7637 combination of options is this tiny Bourne shell script:
7641 # Usage: backup FILE...
7642 # Create a @sc{gnu}-style backup of each listed FILE.
7644 cp --backup --force -- "$i" "$i"
7648 @item --copy-contents
7649 @cindex directories, copying recursively
7650 @cindex copying directories recursively
7651 @cindex recursively copying directories
7652 @cindex non-directories, copying as special files
7653 If copying recursively, copy the contents of any special files (e.g.,
7654 FIFOs and device files) as if they were regular files. This means
7655 trying to read the data in each source file and writing it to the
7656 destination. It is usually a mistake to use this option, as it
7657 normally has undesirable effects on special files like FIFOs and the
7658 ones typically found in the @file{/dev} directory. In most cases,
7659 @code{cp -R --copy-contents} will hang indefinitely trying to read
7660 from FIFOs and special files like @file{/dev/console}, and it will
7661 fill up your destination disk if you use it to copy @file{/dev/zero}.
7662 This option has no effect unless copying recursively, and it does not
7663 affect the copying of symbolic links.
7667 @cindex symbolic links, copying
7668 @cindex hard links, preserving
7669 Copy symbolic links as symbolic links rather than copying the files that
7670 they point to, and preserve hard links between source files in the copies.
7671 Equivalent to @option{--no-dereference --preserve=links}.
7677 When copying without this option and an existing destination file cannot
7678 be opened for writing, the copy fails. However, with @option{--force}),
7679 when a destination file cannot be opened, @command{cp} then removes it and
7680 tries to open it again. Contrast this behavior with that enabled by
7681 @option{--link} and @option{--symbolic-link}, whereby the destination file
7682 is never opened but rather is removed unconditionally. Also see the
7683 description of @option{--remove-destination}.
7685 This option is independent of the @option{--interactive} or
7686 @option{-i} option: neither cancels the effect of the other.
7688 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7693 If a command line argument specifies a symbolic link, then copy the
7694 file it points to rather than the symbolic link itself. However,
7695 copy (preserving its nature) any symbolic link that is encountered
7696 via recursive traversal.
7699 @itemx --interactive
7701 @opindex --interactive
7702 When copying a file other than a directory, prompt whether to
7703 overwrite an existing destination file. The @option{-i} option overrides
7704 a previous @option{-n} option.
7710 Make hard links instead of copies of non-directories.
7713 @itemx --dereference
7715 @opindex --dereference
7716 Follow symbolic links when copying from them.
7717 With this option, @command{cp} cannot create a symbolic link.
7718 For example, a symlink (to regular file) in the source tree will be copied to
7719 a regular file in the destination tree.
7724 @opindex --no-clobber
7725 Do not overwrite an existing file. The @option{-n} option overrides a previous
7726 @option{-i} option. This option is mutually exclusive with @option{-b} or
7727 @option{--backup} option.
7730 @itemx --no-dereference
7732 @opindex --no-dereference
7733 @cindex symbolic links, copying
7734 Copy symbolic links as symbolic links rather than copying the files that
7735 they point to. This option affects only symbolic links in the source;
7736 symbolic links in the destination are always followed if possible.
7739 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7742 @cindex file information, preserving, extended attributes, xattr
7743 Preserve the specified attributes of the original files.
7744 If specified, the @var{attribute_list} must be a comma-separated list
7745 of one or more of the following strings:
7749 Preserve the file mode bits and access control lists.
7751 Preserve the owner and group. On most modern systems,
7752 only users with appropriate privileges may change the owner of a file,
7754 may preserve the group ownership of a file only if they happen to be
7755 a member of the desired group.
7757 Preserve the times of last access and last modification, when possible.
7758 On older systems, it is not possible to preserve these attributes
7759 when the affected file is a symbolic link.
7760 However, many systems now provide the @code{utimensat} function,
7761 which makes it possible even for symbolic links.
7763 Preserve in the destination files
7764 any links between corresponding source files.
7765 Note that with @option{-L} or @option{-H}, this option can convert
7766 symbolic links to hard links. For example,
7768 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7773 Note the inputs: @file{b} is a symlink to regular file @file{a},
7774 yet the files in destination directory, @file{c/}, are hard-linked.
7775 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7776 tells @command{cp} to dereference command line arguments, it sees two files
7777 with the same inode number, and preserves the perceived hard link.
7779 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7781 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7787 Preserve SELinux security context of the file, or fail with full diagnostics.
7789 Preserve extended attributes of the file, or fail with full diagnostics.
7790 If @command{cp} is built without xattr support, ignore this option.
7791 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7792 they are preserved by this option as well.
7794 Preserve all file attributes.
7795 Equivalent to specifying all of the above, but with the difference
7796 that failure to preserve SELinux security context or extended attributes
7797 does not change @command{cp}'s exit status. In contrast to @option{-a},
7798 all but @samp{Operation not supported} warnings are output.
7801 Using @option{--preserve} with no @var{attribute_list} is equivalent
7802 to @option{--preserve=mode,ownership,timestamps}.
7804 In the absence of this option, each destination file is created with the
7805 mode bits of the corresponding source file, minus the bits set in the
7806 umask and minus the set-user-ID and set-group-ID bits.
7807 @xref{File permissions}.
7809 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7810 @cindex file information, preserving
7811 Do not preserve the specified attributes. The @var{attribute_list}
7812 has the same form as for @option{--preserve}.
7816 @cindex parent directories and @command{cp}
7817 Form the name of each destination file by appending to the target
7818 directory a slash and the specified name of the source file. The last
7819 argument given to @command{cp} must be the name of an existing directory.
7820 For example, the command:
7823 cp --parents a/b/c existing_dir
7827 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7828 any missing intermediate directories.
7835 @opindex --recursive
7836 @cindex directories, copying recursively
7837 @cindex copying directories recursively
7838 @cindex recursively copying directories
7839 @cindex non-directories, copying as special files
7840 Copy directories recursively. By default, do not follow symbolic
7841 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7842 @option{--dereference} (@option{-L}), @option{--no-dereference}
7843 (@option{-P}), and @option{-H} options. Special files are copied by
7844 creating a destination file of the same type as the source; see the
7845 @option{--copy-contents} option. It is not portable to use
7846 @option{-r} to copy symbolic links or special files. On some
7847 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7848 @option{-L} and @option{--copy-contents} for historical reasons.
7849 Also, it is not portable to use @option{-R} to copy symbolic links
7850 unless you also specify @option{-P}, as @acronym{POSIX} allows
7851 implementations that dereference symbolic links by default.
7853 @item --reflink[=@var{when}]
7854 @opindex --reflink[=@var{when}]
7857 @cindex copy on write
7858 Perform a lightweight, copy-on-write (COW) copy, if supported by the
7859 file system. Once it has succeeded, beware that the source and destination
7860 files share the same disk data blocks as long as they remain unmodified.
7861 Thus, if a disk I/O error affects data blocks of one of the files,
7862 the other suffers the same fate.
7864 The @var{when} value can be one of the following:
7868 The default behavior: if the copy-on-write operation is not supported
7869 then report the failure for each file and exit with a failure status.
7872 If the copy-on-write operation is not supported then fall back
7873 to the standard copy behaviour.
7876 This option is overridden by the @option{--link}, @option{--symbolic-link}
7877 and @option{--attributes-only} options, thus allowing it to be used
7878 to configure the default data copying behavior for @command{cp}.
7879 For example, with the following alias, @command{cp} will use the
7880 minimum amount of space supported by the file system.
7883 alias cp='cp --reflink=auto --sparse=always'
7886 @item --remove-destination
7887 @opindex --remove-destination
7888 Remove each existing destination file before attempting to open it
7889 (contrast with @option{-f} above).
7891 @item --sparse=@var{when}
7892 @opindex --sparse=@var{when}
7893 @cindex sparse files, copying
7894 @cindex holes, copying files with
7895 @findex read @r{system call, and holes}
7896 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7897 does not occupy any physical disk blocks; the @samp{read} system call
7898 reads these as zeros. This can both save considerable disk space and
7899 increase speed, since many binary files contain lots of consecutive zero
7900 bytes. By default, @command{cp} detects holes in input source files via a crude
7901 heuristic and makes the corresponding output file sparse as well.
7902 Only regular files may be sparse.
7904 The @var{when} value can be one of the following:
7908 The default behavior: if the input file is sparse, attempt to make
7909 the output file sparse, too. However, if an output file exists but
7910 refers to a non-regular file, then do not attempt to make it sparse.
7913 For each sufficiently long sequence of zero bytes in the input file,
7914 attempt to create a corresponding hole in the output file, even if the
7915 input file does not appear to be sparse.
7916 This is useful when the input file resides on a file system
7917 that does not support sparse files
7918 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7919 but the output file is on a type of file system that does support them.
7920 Holes may be created only in regular files, so if the destination file
7921 is of some other type, @command{cp} does not even try to make it sparse.
7924 Never make the output file sparse.
7925 This is useful in creating a file for use with the @command{mkswap} command,
7926 since such a file must not have any holes.
7929 @optStripTrailingSlashes
7932 @itemx --symbolic-link
7934 @opindex --symbolic-link
7935 @cindex symbolic links, copying with
7936 Make symbolic links instead of copies of non-directories. All source
7937 file names must be absolute (starting with @samp{/}) unless the
7938 destination files are in the current directory. This option merely
7939 results in an error message on systems that do not support symbolic links.
7945 @optNoTargetDirectory
7951 @cindex newer files, copying only
7952 Do not copy a non-directory that has an existing destination with the
7953 same or newer modification time. If time stamps are being preserved,
7954 the comparison is to the source time stamp truncated to the
7955 resolutions of the destination file system and of the system calls
7956 used to update time stamps; this avoids duplicate work if several
7957 @samp{cp -pu} commands are executed with the same source and
7964 Print the name of each file before copying it.
7967 @itemx --one-file-system
7969 @opindex --one-file-system
7970 @cindex file systems, omitting copying to different
7971 Skip subdirectories that are on different file systems from the one that
7972 the copy started on.
7973 However, mount point directories @emph{are} copied.
7981 @section @command{dd}: Convert and copy a file
7984 @cindex converting while copying a file
7986 @command{dd} copies a file (from standard input to standard output, by
7987 default) with a changeable I/O block size, while optionally performing
7988 conversions on it. Synopses:
7991 dd [@var{operand}]@dots{}
7995 The only options are @option{--help} and @option{--version}.
7996 @xref{Common options}. @command{dd} accepts the following operands.
8002 Read from @var{file} instead of standard input.
8006 Write to @var{file} instead of standard output. Unless
8007 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
8008 bytes (or the size specified with @samp{seek=}).
8010 @item ibs=@var{bytes}
8012 @cindex block size of input
8013 @cindex input block size
8014 Set the input block size to @var{bytes}.
8015 This makes @command{dd} read @var{bytes} per block.
8016 The default is 512 bytes.
8018 @item obs=@var{bytes}
8020 @cindex block size of output
8021 @cindex output block size
8022 Set the output block size to @var{bytes}.
8023 This makes @command{dd} write @var{bytes} per block.
8024 The default is 512 bytes.
8026 @item bs=@var{bytes}
8029 Set both input and output block sizes to @var{bytes}.
8030 This makes @command{dd} read and write @var{bytes} per block,
8031 overriding any @samp{ibs} and @samp{obs} settings.
8032 In addition, if no data-transforming @option{conv} option is specified,
8033 input is copied to the output as soon as it's read,
8034 even if it is smaller than the block size.
8036 @item cbs=@var{bytes}
8038 @cindex block size of conversion
8039 @cindex conversion block size
8040 @cindex fixed-length records, converting to variable-length
8041 @cindex variable-length records, converting to fixed-length
8042 Set the conversion block size to @var{bytes}.
8043 When converting variable-length records to fixed-length ones
8044 (@option{conv=block}) or the reverse (@option{conv=unblock}),
8045 use @var{bytes} as the fixed record length.
8047 @item skip=@var{blocks}
8049 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
8051 @item seek=@var{blocks}
8053 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
8055 @item count=@var{blocks}
8057 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
8058 of everything until the end of the file.
8062 Do not print the overall transfer rate and volume statistics
8063 that normally make up the third status line when @command{dd} exits.
8065 @item conv=@var{conversion}[,@var{conversion}]@dots{}
8067 Convert the file as specified by the @var{conversion} argument(s).
8068 (No spaces around any comma(s).)
8075 @opindex ascii@r{, converting to}
8076 Convert @acronym{EBCDIC} to @acronym{ASCII},
8077 using the conversion table specified by @acronym{POSIX}.
8078 This provides a 1:1 translation for all 256 bytes.
8081 @opindex ebcdic@r{, converting to}
8082 Convert @acronym{ASCII} to @acronym{EBCDIC}.
8083 This is the inverse of the @samp{ascii} conversion.
8086 @opindex alternate ebcdic@r{, converting to}
8087 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
8088 using the alternate conversion table specified by @acronym{POSIX}.
8089 This is not a 1:1 translation, but reflects common historical practice
8090 for @samp{~}, @samp{[}, and @samp{]}.
8092 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
8096 @opindex block @r{(space-padding)}
8097 For each line in the input, output @samp{cbs} bytes, replacing the
8098 input newline with a space and padding with spaces as necessary.
8102 Remove any trailing spaces in each @samp{cbs}-sized input block,
8103 and append a newline.
8105 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
8108 @opindex lcase@r{, converting to}
8109 Change uppercase letters to lowercase.
8112 @opindex ucase@r{, converting to}
8113 Change lowercase letters to uppercase.
8115 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
8118 @opindex swab @r{(byte-swapping)}
8119 @cindex byte-swapping
8120 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
8121 when an odd number of bytes are read---the last byte is simply copied
8122 (since there is nothing to swap it with).
8125 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
8126 Pad every input block to size of @samp{ibs} with trailing zero bytes.
8127 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
8132 The following ``conversions'' are really file flags
8133 and don't affect internal processing:
8138 @cindex creating output file, requiring
8139 Fail if the output file already exists; @command{dd} must create the
8144 @cindex creating output file, avoiding
8145 Do not create the output file; the output file must already exist.
8147 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
8151 @cindex truncating output file, avoiding
8152 Do not truncate the output file.
8156 @cindex read errors, ignoring
8157 Continue after read errors.
8161 @cindex synchronized data writes, before finishing
8162 Synchronize output data just before finishing. This forces a physical
8163 write of output data.
8167 @cindex synchronized data and metadata writes, before finishing
8168 Synchronize output data and metadata just before finishing. This
8169 forces a physical write of output data and metadata.
8173 @item iflag=@var{flag}[,@var{flag}]@dots{}
8175 Access the input file using the flags specified by the @var{flag}
8176 argument(s). (No spaces around any comma(s).)
8178 @item oflag=@var{flag}[,@var{flag}]@dots{}
8180 Access the output file using the flags specified by the @var{flag}
8181 argument(s). (No spaces around any comma(s).)
8183 Here are the flags. Not every flag is supported on every operating
8190 @cindex appending to the output file
8191 Write in append mode, so that even if some other process is writing to
8192 this file, every @command{dd} write will append to the current
8193 contents of the file. This flag makes sense only for output.
8194 If you combine this flag with the @samp{of=@var{file}} operand,
8195 you should also specify @samp{conv=notrunc} unless you want the
8196 output file to be truncated before being appended to.
8200 @cindex concurrent I/O
8201 Use concurrent I/O mode for data. This mode performs direct I/O
8202 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
8203 A file cannot be opened in CIO mode and with a standard open at the
8209 Use direct I/O for data, avoiding the buffer cache.
8210 Note that the kernel may impose restrictions on read or write buffer sizes.
8211 For example, with an ext4 destination file system and a linux-based kernel,
8212 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
8213 output buffer size is not a multiple of 512.
8217 @cindex directory I/O
8219 Fail unless the file is a directory. Most operating systems do not
8220 allow I/O to a directory, so this flag has limited utility.
8224 @cindex synchronized data reads
8225 Use synchronized I/O for data. For the output file, this forces a
8226 physical write of output data on each write. For the input file,
8227 this flag can matter when reading from a remote file that has been
8228 written to synchronously by some other process. Metadata (e.g.,
8229 last-access and last-modified time) is not necessarily synchronized.
8233 @cindex synchronized data and metadata I/O
8234 Use synchronized I/O for both data and metadata.
8238 @cindex discarding file cache
8239 Discard the data cache for a file.
8240 When count=0 all cache is discarded,
8241 otherwise the cache is dropped for the processed
8242 portion of the file. Also when count=0
8243 failure to discard the cache is diagnosed
8244 and reflected in the exit status.
8245 Here as some usage examples:
8248 # Advise to drop cache for whole file
8249 dd if=ifile iflag=nocache count=0
8251 # Ensure drop cache for the whole file
8252 dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
8254 # Drop cache for part of file
8255 dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
8257 # Stream data using just the read-ahead cache
8258 dd if=ifile of=ofile iflag=nocache oflag=nocache
8263 @cindex nonblocking I/O
8264 Use non-blocking I/O.
8269 Do not update the file's access time.
8270 Some older file systems silently ignore this flag, so it is a good
8271 idea to test it on your files before relying on it.
8275 @cindex controlling terminal
8276 Do not assign the file to be a controlling terminal for @command{dd}.
8277 This has no effect when the file is not a terminal.
8278 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
8283 @cindex symbolic links, following
8284 Do not follow symbolic links.
8289 Fail if the file has multiple hard links.
8294 Use binary I/O. This option has an effect only on nonstandard
8295 platforms that distinguish binary from text I/O.
8300 Use text I/O. Like @samp{binary}, this option has no effect on
8305 Accumulate full blocks from input. The @code{read} system call
8306 may return early if a full block is not available.
8307 When that happens, continue calling @code{read} to fill the remainder
8309 This flag can be used only with @code{iflag}.
8313 These flags are not supported on all systems, and @samp{dd} rejects
8314 attempts to use them when they are not supported. When reading from
8315 standard input or writing to standard output, the @samp{nofollow} and
8316 @samp{noctty} flags should not be specified, and the other flags
8317 (e.g., @samp{nonblock}) can affect how other processes behave with the
8318 affected file descriptors, even after @command{dd} exits.
8322 @cindex multipliers after numbers
8323 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8324 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8325 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8326 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8328 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8329 should not be too large---values larger than a few megabytes
8330 are generally wasteful or (as in the gigabyte..exabyte case) downright
8331 counterproductive or error-inducing.
8333 Use different @command{dd} invocations to use different block sizes for
8334 skipping and I/O@. For example, the following shell commands copy data
8335 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8336 4 KiB label at the start of the disk:
8339 disk=/dev/rdsk/c0t1d0s2
8342 # Copy all but the label from disk to tape.
8343 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8345 # Copy from tape back to disk, but leave the disk label alone.
8346 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8349 Sending an @samp{INFO} signal to a running @command{dd}
8350 process makes it print I/O statistics to standard error
8351 and then resume copying. In the example below,
8352 @command{dd} is run in the background to copy 10 million blocks.
8353 The @command{kill} command makes it output intermediate I/O statistics,
8354 and when @command{dd} completes normally or is killed by the
8355 @code{SIGINT} signal, it outputs the final statistics.
8358 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8359 $ kill -s INFO $pid; wait $pid
8360 3385223+0 records in
8361 3385223+0 records out
8362 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8363 10000000+0 records in
8364 10000000+0 records out
8365 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8368 @vindex POSIXLY_CORRECT
8369 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8370 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8371 environment variable is set.
8376 @node install invocation
8377 @section @command{install}: Copy files and set attributes
8380 @cindex copying files and setting attributes
8382 @command{install} copies files while setting their file mode bits and, if
8383 possible, their owner and group. Synopses:
8386 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8387 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8388 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8389 install [@var{option}]@dots{} -d @var{directory}@dots{}
8394 If two file names are given, @command{install} copies the first file to the
8398 If the @option{--target-directory} (@option{-t}) option is given, or
8399 failing that if the last file is a directory and the
8400 @option{--no-target-directory} (@option{-T}) option is not given,
8401 @command{install} copies each @var{source} file to the specified
8402 directory, using the @var{source}s' names.
8405 If the @option{--directory} (@option{-d}) option is given,
8406 @command{install} creates each @var{directory} and any missing parent
8407 directories. Parent directories are created with mode
8408 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8409 current umask. @xref{Directory Setuid and Setgid}, for how the
8410 set-user-ID and set-group-ID bits of parent directories are inherited.
8413 @cindex Makefiles, installing programs in
8414 @command{install} is similar to @command{cp}, but allows you to control the
8415 attributes of destination files. It is typically used in Makefiles to
8416 copy programs into their destination directories. It refuses to copy
8417 files onto themselves.
8419 @cindex extended attributes, xattr
8420 @command{install} never preserves extended attributes (xattr).
8422 The program accepts the following options. Also see @ref{Common options}.
8432 Compare each pair of source and destination files, and if the destination has
8433 identical content and any specified owner, group, permissions, and possibly
8434 SELinux context, then do not modify the destination at all.
8438 Ignored; for compatibility with old Unix versions of @command{install}.
8442 Create any missing parent directories of @var{dest},
8443 then copy @var{source} to @var{dest}.
8444 This option is ignored if a destination directory is specified
8445 via @option{--target-directory=DIR}.
8450 @opindex --directory
8451 @cindex directories, creating with given attributes
8452 @cindex parent directories, creating missing
8453 @cindex leading directories, creating missing
8454 Create any missing parent directories, giving them the default
8455 attributes. Then create each given directory, setting their owner,
8456 group and mode as given on the command line or to the defaults.
8458 @item -g @var{group}
8459 @itemx --group=@var{group}
8462 @cindex group ownership of installed files, setting
8463 Set the group ownership of installed files or directories to
8464 @var{group}. The default is the process's current group. @var{group}
8465 may be either a group name or a numeric group ID.
8468 @itemx --mode=@var{mode}
8471 @cindex permissions of installed files, setting
8472 Set the file mode bits for the installed file or directory to @var{mode},
8473 which can be either an octal number, or a symbolic mode as in
8474 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8475 point of departure (@pxref{File permissions}).
8476 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8477 execute for the owner, read and execute for group and other, and with
8478 set-user-ID and set-group-ID disabled.
8479 This default is not quite the same as @samp{755}, since it disables
8480 instead of preserving set-user-ID and set-group-ID on directories.
8481 @xref{Directory Setuid and Setgid}.
8483 @item -o @var{owner}
8484 @itemx --owner=@var{owner}
8487 @cindex ownership of installed files, setting
8488 @cindex appropriate privileges
8489 @vindex root @r{as default owner}
8490 If @command{install} has appropriate privileges (is run as root), set the
8491 ownership of installed files or directories to @var{owner}. The default
8492 is @code{root}. @var{owner} may be either a user name or a numeric user
8495 @item --preserve-context
8496 @opindex --preserve-context
8498 @cindex security context
8499 Preserve the SELinux security context of files and directories.
8500 Failure to preserve the context in all of the files or directories
8501 will result in an exit status of 1. If SELinux is disabled then
8502 print a warning and ignore the option.
8505 @itemx --preserve-timestamps
8507 @opindex --preserve-timestamps
8508 @cindex timestamps of installed files, preserving
8509 Set the time of last access and the time of last modification of each
8510 installed file to match those of each corresponding original file.
8511 When a file is installed without this option, its last access and
8512 last modification times are both set to the time of installation.
8513 This option is useful if you want to use the last modification times
8514 of installed files to keep track of when they were last built as opposed
8515 to when they were last installed.
8521 @cindex symbol table information, stripping
8522 @cindex stripping symbol table information
8523 Strip the symbol tables from installed binary executables.
8525 @itemx --strip-program=@var{program}
8526 @opindex --strip-program
8527 @cindex symbol table information, stripping, program
8528 Program used to strip binaries.
8534 @optNoTargetDirectory
8540 Print the name of each file before copying it.
8542 @item -Z @var{context}
8543 @itemx --context=@var{context}
8547 @cindex security context
8548 Set the default SELinux security context to be used for any
8549 created files and directories. If SELinux is disabled then
8550 print a warning and ignore the option.
8558 @section @command{mv}: Move (rename) files
8562 @command{mv} moves or renames files (or directories). Synopses:
8565 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8566 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8567 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8572 If two file names are given, @command{mv} moves the first file to the
8576 If the @option{--target-directory} (@option{-t}) option is given, or
8577 failing that if the last file is a directory and the
8578 @option{--no-target-directory} (@option{-T}) option is not given,
8579 @command{mv} moves each @var{source} file to the specified
8580 directory, using the @var{source}s' names.
8583 @command{mv} can move any type of file from one file system to another.
8584 Prior to version @code{4.0} of the fileutils,
8585 @command{mv} could move only regular files between file systems.
8586 For example, now @command{mv} can move an entire directory hierarchy
8587 including special device files from one partition to another. It first
8588 uses some of the same code that's used by @code{cp -a} to copy the
8589 requested directories and files, then (assuming the copy succeeded)
8590 it removes the originals. If the copy fails, then the part that was
8591 copied to the destination partition is removed. If you were to copy
8592 three directories from one partition to another and the copy of the first
8593 directory succeeded, but the second didn't, the first would be left on
8594 the destination partition and the second and third would be left on the
8597 @cindex extended attributes, xattr
8598 @command{mv} always tries to copy extended attributes (xattr), which may
8599 include SELinux context, ACLs or Capabilities.
8600 Upon failure all but @samp{Operation not supported} warnings are output.
8602 @cindex prompting, and @command{mv}
8603 If a destination file exists but is normally unwritable, standard input
8604 is a terminal, and the @option{-f} or @option{--force} option is not given,
8605 @command{mv} prompts the user for whether to replace the file. (You might
8606 own the file, or have write permission on its directory.) If the
8607 response is not affirmative, the file is skipped.
8609 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8610 when it might be a symlink to a directory.
8611 Otherwise, @command{mv} may do something very surprising, since
8612 its behavior depends on the underlying rename system call.
8613 On a system with a modern Linux-based kernel, it fails with
8614 @code{errno=ENOTDIR}.
8615 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8616 renames not the symlink but rather the directory referenced by the symlink.
8617 @xref{Trailing slashes}.
8619 The program accepts the following options. Also see @ref{Common options}.
8629 @cindex prompts, omitting
8630 Do not prompt the user before removing a destination file.
8632 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8633 options, only the final one takes effect.
8638 @itemx --interactive
8640 @opindex --interactive
8641 @cindex prompts, forcing
8642 Prompt whether to overwrite each existing destination file, regardless
8644 If the response is not affirmative, the file is skipped.
8650 @opindex --no-clobber
8651 @cindex prompts, omitting
8652 Do not overwrite an existing file.
8654 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8660 @cindex newer files, moving only
8661 Do not move a non-directory that has an existing destination with the
8662 same or newer modification time.
8663 If the move is across file system boundaries, the comparison is to the
8664 source time stamp truncated to the resolutions of the destination file
8665 system and of the system calls used to update time stamps; this avoids
8666 duplicate work if several @samp{mv -u} commands are executed with the
8667 same source and destination.
8673 Print the name of each file before moving it.
8675 @optStripTrailingSlashes
8681 @optNoTargetDirectory
8689 @section @command{rm}: Remove files or directories
8692 @cindex removing files or directories
8694 @command{rm} removes each given @var{file}. By default, it does not remove
8695 directories. Synopsis:
8698 rm [@var{option}]@dots{} [@var{file}]@dots{}
8701 @cindex prompting, and @command{rm}
8702 If the @option{-I} or @option{--interactive=once} option is given,
8703 and there are more than three files or the @option{-r}, @option{-R},
8704 or @option{--recursive} are given, then @command{rm} prompts the user
8705 for whether to proceed with the entire operation. If the response is
8706 not affirmative, the entire command is aborted.
8708 Otherwise, if a file is unwritable, standard input is a terminal, and
8709 the @option{-f} or @option{--force} option is not given, or the
8710 @option{-i} or @option{--interactive=always} option @emph{is} given,
8711 @command{rm} prompts the user for whether to remove the file.
8712 If the response is not affirmative, the file is skipped.
8714 Any attempt to remove a file whose last file name component is
8715 @file{.} or @file{..} is rejected without any prompting.
8717 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8718 possible to recover the contents of that file. If you want more assurance
8719 that the contents are truly unrecoverable, consider using @command{shred}.
8721 The program accepts the following options. Also see @ref{Common options}.
8729 Ignore nonexistent files and never prompt the user.
8730 Ignore any previous @option{--interactive} (@option{-i}) option.
8734 Prompt whether to remove each file.
8735 If the response is not affirmative, the file is skipped.
8736 Ignore any previous @option{--force} (@option{-f}) option.
8737 Equivalent to @option{--interactive=always}.
8741 Prompt once whether to proceed with the command, if more than three
8742 files are named or if a recursive removal is requested. Ignore any
8743 previous @option{--force} (@option{-f}) option. Equivalent to
8744 @option{--interactive=once}.
8746 @itemx --interactive [=@var{when}]
8747 @opindex --interactive
8748 Specify when to issue an interactive prompt. @var{when} may be
8752 @vindex never @r{interactive option}
8753 - Do not prompt at all.
8755 @vindex once @r{interactive option}
8756 - Prompt once if more than three files are named or if a recursive
8757 removal is requested. Equivalent to @option{-I}.
8759 @vindex always @r{interactive option}
8760 - Prompt for every file being removed. Equivalent to @option{-i}.
8762 @option{--interactive} with no @var{when} is equivalent to
8763 @option{--interactive=always}.
8765 @itemx --one-file-system
8766 @opindex --one-file-system
8767 @cindex one file system, restricting @command{rm} to
8768 When removing a hierarchy recursively, skip any directory that is on a
8769 file system different from that of the corresponding command line argument.
8772 This option is useful when removing a build ``chroot'' hierarchy,
8773 which normally contains no valuable data. However, it is not uncommon
8774 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8775 use one's start-up file. The catch is that it's easy to forget to
8776 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8777 your normally throw-away chroot, that command will remove everything
8778 under @file{/home}, too.
8779 Use the @option{--one-file-system} option, and it will
8780 warn about and skip directories on other file systems.
8781 Of course, this will not save your @file{/home} if it and your
8782 chroot happen to be on the same file system.
8784 @itemx --preserve-root
8785 @opindex --preserve-root
8786 @cindex root directory, disallow recursive destruction
8787 Fail upon any attempt to remove the root directory, @file{/},
8788 when used with the @option{--recursive} option.
8789 This is the default behavior.
8790 @xref{Treating / specially}.
8792 @itemx --no-preserve-root
8793 @opindex --no-preserve-root
8794 @cindex root directory, allow recursive destruction
8795 Do not treat @file{/} specially when removing recursively.
8796 This option is not recommended unless you really want to
8797 remove all the files on your computer.
8798 @xref{Treating / specially}.
8805 @opindex --recursive
8806 @cindex directories, removing (recursively)
8807 Remove the listed directories and their contents recursively.
8813 Print the name of each file before removing it.
8817 @cindex files beginning with @samp{-}, removing
8818 @cindex @samp{-}, removing files beginning with
8819 One common question is how to remove files whose names begin with a
8820 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8821 function to parse its arguments, lets you use the @samp{--} option to
8822 indicate that all following arguments are non-options. To remove a file
8823 called @file{-f} in the current directory, you could type either:
8836 @opindex - @r{and Unix @command{rm}}
8837 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8838 predates the development of the getopt standard syntax.
8843 @node shred invocation
8844 @section @command{shred}: Remove files more securely
8847 @cindex data, erasing
8848 @cindex erasing data
8850 @command{shred} overwrites devices or files, to help prevent even
8851 very expensive hardware from recovering the data.
8853 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8854 not actually destroyed. Only the index listing where the file is
8855 stored is destroyed, and the storage is made available for reuse.
8856 There are undelete utilities that will attempt to reconstruct the index
8857 and can bring the file back if the parts were not reused.
8859 On a busy system with a nearly-full drive, space can get reused in a few
8860 seconds. But there is no way to know for sure. If you have sensitive
8861 data, you may want to be sure that recovery is not possible by actually
8862 overwriting the file with non-sensitive data.
8864 However, even after doing that, it is possible to take the disk back
8865 to a laboratory and use a lot of sensitive (and expensive) equipment
8866 to look for the faint ``echoes'' of the original data underneath the
8867 overwritten data. If the data has only been overwritten once, it's not
8870 The best way to remove something irretrievably is to destroy the media
8871 it's on with acid, melt it down, or the like. For cheap removable media
8872 like floppy disks, this is the preferred method. However, hard drives
8873 are expensive and hard to melt, so the @command{shred} utility tries
8874 to achieve a similar effect non-destructively.
8876 This uses many overwrite passes, with the data patterns chosen to
8877 maximize the damage they do to the old data. While this will work on
8878 floppies, the patterns are designed for best effect on hard drives.
8879 For more details, see the source code and Peter Gutmann's paper
8880 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8881 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8882 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8883 California, July 22--25, 1996).
8885 @strong{Please note} that @command{shred} relies on a very important assumption:
8886 that the file system overwrites data in place. This is the traditional
8887 way to do things, but many modern file system designs do not satisfy this
8888 assumption. Exceptions include:
8893 Log-structured or journaled file systems, such as those supplied with
8894 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8895 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8898 File systems that write redundant data and carry on even if some writes
8899 fail, such as RAID-based file systems.
8902 File systems that make snapshots, such as Network Appliance's NFS server.
8905 File systems that cache in temporary locations, such as NFS version 3
8909 Compressed file systems.
8912 In the particular case of ext3 file systems, the above disclaimer applies (and
8913 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8914 mode, which journals file data in addition to just metadata. In both
8915 the @code{data=ordered} (default) and @code{data=writeback} modes,
8916 @command{shred} works as usual. Ext3 journaling modes can be changed
8917 by adding the @code{data=something} option to the mount options for a
8918 particular file system in the @file{/etc/fstab} file, as documented in
8919 the mount man page (man mount).
8921 If you are not sure how your file system operates, then you should assume
8922 that it does not overwrite data in place, which means that shred cannot
8923 reliably operate on regular files in your file system.
8925 Generally speaking, it is more reliable to shred a device than a file,
8926 since this bypasses the problem of file system design mentioned above.
8927 However, even shredding devices is not always completely reliable. For
8928 example, most disks map out bad sectors invisibly to the application; if
8929 the bad sectors contain sensitive data, @command{shred} won't be able to
8932 @command{shred} makes no attempt to detect or report this problem, just as
8933 it makes no attempt to do anything about backups. However, since it is
8934 more reliable to shred devices than files, @command{shred} by default does
8935 not truncate or remove the output file. This default is more suitable
8936 for devices, which typically cannot be truncated and should not be
8939 Finally, consider the risk of backups and mirrors.
8940 File system backups and remote mirrors may contain copies of the
8941 file that cannot be removed, and that will allow a shredded file
8942 to be recovered later. So if you keep any data you may later want
8943 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8946 shred [@var{option}]@dots{} @var{file}[@dots{}]
8949 The program accepts the following options. Also see @ref{Common options}.
8957 @cindex force deletion
8958 Override file permissions if necessary to allow overwriting.
8961 @itemx -n @var{number}
8962 @itemx --iterations=@var{number}
8963 @opindex -n @var{number}
8964 @opindex --iterations=@var{number}
8965 @cindex iterations, selecting the number of
8966 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8967 overwrite. You can reduce this to save time, or increase it if you think it's
8968 appropriate. After 25 passes all of the internal overwrite patterns will have
8969 been used at least once.
8971 @item --random-source=@var{file}
8972 @opindex --random-source
8973 @cindex random source for shredding
8974 Use @var{file} as a source of random data used to overwrite and to
8975 choose pass ordering. @xref{Random sources}.
8977 @item -s @var{bytes}
8978 @itemx --size=@var{bytes}
8979 @opindex -s @var{bytes}
8980 @opindex --size=@var{bytes}
8981 @cindex size of file to shred
8982 Shred the first @var{bytes} bytes of the file. The default is to shred
8983 the whole file. @var{bytes} can be followed by a size specification like
8984 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8990 @cindex removing files after shredding
8991 After shredding a file, truncate it (if possible) and then remove it.
8992 If a file has multiple links, only the named links will be removed.
8998 Display to standard error all status updates as sterilization proceeds.
9004 By default, @command{shred} rounds the size of a regular file up to the next
9005 multiple of the file system block size to fully erase the last block
9007 Use @option{--exact} to suppress that behavior.
9008 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
9009 blocks, the resulting file will be 512 bytes long. With this option,
9010 shred does not increase the apparent size of the file.
9016 Normally, the last pass that @command{shred} writes is made up of
9017 random data. If this would be conspicuous on your hard drive (for
9018 example, because it looks like encrypted data), or you just think
9019 it's tidier, the @option{--zero} option adds an additional overwrite pass with
9020 all zero bits. This is in addition to the number of passes specified
9021 by the @option{--iterations} option.
9025 You might use the following command to erase all trace of the
9026 file system you'd created on the floppy disk in your first drive.
9027 That command takes about 20 minutes to erase a ``1.44MB'' (actually
9031 shred --verbose /dev/fd0
9034 Similarly, to erase all data on a selected partition of
9035 your hard disk, you could give a command like this:
9038 shred --verbose /dev/sda5
9041 On modern disks, a single pass should be adequate,
9042 and it will take one third the time of the default three-pass approach.
9045 # 1 pass, write pseudo-random data; 3x faster than the default
9046 shred --verbose -n1 /dev/sda5
9049 To be on the safe side, use at least one pass that overwrites using
9050 pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
9051 in case some disk controller optimizes the process of writing blocks
9052 of all zeros, and thereby does not clear all bytes in a block.
9053 Some SSDs may do just that.
9055 A @var{file} of @samp{-} denotes standard output.
9056 The intended use of this is to shred a removed temporary file.
9063 echo "Hello, world" >&3
9068 However, the command @samp{shred - >file} does not shred the contents
9069 of @var{file}, since the shell truncates @var{file} before invoking
9070 @command{shred}. Use the command @samp{shred file} or (if using a
9071 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
9076 @node Special file types
9077 @chapter Special file types
9079 @cindex special file types
9080 @cindex file types, special
9082 This chapter describes commands which create special types of files (and
9083 @command{rmdir}, which removes directories, one special file type).
9085 @cindex special file types
9087 Although Unix-like operating systems have markedly fewer special file
9088 types than others, not @emph{everything} can be treated only as the
9089 undifferentiated byte stream of @dfn{normal files}. For example, when a
9090 file is created or removed, the system must record this information,
9091 which it does in a @dfn{directory}---a special type of file. Although
9092 you can read directories as normal files, if you're curious, in order
9093 for the system to do its job it must impose a structure, a certain
9094 order, on the bytes of the file. Thus it is a ``special'' type of file.
9096 Besides directories, other special file types include named pipes
9097 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
9100 * link invocation:: Make a hard link via the link syscall
9101 * ln invocation:: Make links between files.
9102 * mkdir invocation:: Make directories.
9103 * mkfifo invocation:: Make FIFOs (named pipes).
9104 * mknod invocation:: Make block or character special files.
9105 * readlink invocation:: Print value of a symlink or canonical file name.
9106 * rmdir invocation:: Remove empty directories.
9107 * unlink invocation:: Remove files via the unlink syscall
9111 @node link invocation
9112 @section @command{link}: Make a hard link via the link syscall
9115 @cindex links, creating
9116 @cindex hard links, creating
9117 @cindex creating links (hard only)
9119 @command{link} creates a single hard link at a time.
9120 It is a minimalist interface to the system-provided
9121 @code{link} function. @xref{Hard Links, , , libc,
9122 The GNU C Library Reference Manual}.
9123 It avoids the bells and whistles of the more commonly-used
9124 @command{ln} command (@pxref{ln invocation}).
9128 link @var{filename} @var{linkname}
9131 @var{filename} must specify an existing file, and @var{linkname}
9132 must specify a nonexistent entry in an existing directory.
9133 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
9136 On a @acronym{GNU} system, this command acts like @samp{ln --directory
9137 --no-target-directory @var{filename} @var{linkname}}. However, the
9138 @option{--directory} and @option{--no-target-directory} options are
9139 not specified by @acronym{POSIX}, and the @command{link} command is
9140 more portable in practice.
9142 If @var{filename} is a symbolic link, it is unspecified whether
9143 @var{linkname} will be a hard link to the symbolic link or to the
9144 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
9145 to specify which behavior is desired.
9151 @section @command{ln}: Make links between files
9154 @cindex links, creating
9155 @cindex hard links, creating
9156 @cindex symbolic (soft) links, creating
9157 @cindex creating links (hard or soft)
9159 @cindex file systems and hard links
9160 @command{ln} makes links between files. By default, it makes hard links;
9161 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
9165 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
9166 ln [@var{option}]@dots{} @var{target}
9167 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
9168 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
9174 If two file names are given, @command{ln} creates a link to the first
9175 file from the second.
9178 If one @var{target} is given, @command{ln} creates a link to that file
9179 in the current directory.
9182 If the @option{--target-directory} (@option{-t}) option is given, or
9183 failing that if the last file is a directory and the
9184 @option{--no-target-directory} (@option{-T}) option is not given,
9185 @command{ln} creates a link to each @var{target} file in the specified
9186 directory, using the @var{target}s' names.
9190 Normally @command{ln} does not remove existing files. Use the
9191 @option{--force} (@option{-f}) option to remove them unconditionally,
9192 the @option{--interactive} (@option{-i}) option to remove them
9193 conditionally, and the @option{--backup} (@option{-b}) option to
9196 @cindex hard link, defined
9197 @cindex inode, and hard links
9198 A @dfn{hard link} is another name for an existing file; the link and the
9199 original are indistinguishable. Technically speaking, they share the
9200 same inode, and the inode contains all the information about a
9201 file---indeed, it is not incorrect to say that the inode @emph{is} the
9202 file. Most systems prohibit making a hard link to
9203 a directory; on those where it is allowed, only the super-user can do
9204 so (and with caution, since creating a cycle will cause problems to many
9205 other utilities). Hard links cannot cross file system boundaries. (These
9206 restrictions are not mandated by @acronym{POSIX}, however.)
9208 @cindex dereferencing symbolic links
9209 @cindex symbolic link, defined
9210 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
9211 a special file type (which not all kernels support: System V release 3
9212 (and older) systems lack symlinks) in which the link file actually
9213 refers to a different file, by name. When most operations (opening,
9214 reading, writing, and so on) are passed the symbolic link file, the
9215 kernel automatically @dfn{dereferences} the link and operates on the
9216 target of the link. But some operations (e.g., removing) work on the
9217 link file itself, rather than on its target. The owner and group of a
9218 symlink are not significant to file access performed through
9219 the link, but do have implications on deleting a symbolic link from a
9220 directory with the restricted deletion bit set. On the GNU system,
9221 the mode of a symlink has no significance and cannot be changed, but
9222 on some BSD systems, the mode can be changed and will affect whether
9223 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
9224 libc, The GNU C Library Reference Manual}.
9226 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
9227 occurs when the string in the symlink does not resolve to a file.
9228 There are no restrictions against creating dangling symbolic links.
9229 There are trade-offs to using absolute or relative symlinks. An
9230 absolute symlink always points to the same file, even if the directory
9231 containing the link is moved. However, if the symlink is visible from
9232 more than one machine (such as on a networked file system), the file
9233 pointed to might not always be the same. A relative symbolic link is
9234 resolved in relation to the directory that contains the link, and is
9235 often useful in referring to files on the same device without regards
9236 to what name that device is mounted on when accessed via networked
9239 When creating a relative symlink in a different location than the
9240 current directory, the resolution of the symlink will be different
9241 than the resolution of the same string from the current directory.
9242 Therefore, many users prefer to first change directories to the
9243 location where the relative symlink will be created, so that
9244 tab-completion or other file resolution will find the same target as
9245 what will be placed in the symlink.
9247 The program accepts the following options. Also see @ref{Common options}.
9258 @opindex --directory
9259 @cindex hard links to directories
9260 Allow users with appropriate privileges to attempt to make hard links
9262 However, note that this will probably fail due to
9263 system restrictions, even for the super-user.
9269 Remove existing destination files.
9272 @itemx --interactive
9274 @opindex --interactive
9275 @cindex prompting, and @command{ln}
9276 Prompt whether to remove existing destination files.
9282 If @option{-s} is not in effect, and the source file is a symbolic
9283 link, create the hard link to the file referred to by the symbolic
9284 link, rather than the symbolic link itself.
9287 @itemx --no-dereference
9289 @opindex --no-dereference
9290 Do not treat the last operand specially when it is a symbolic link to
9291 a directory. Instead, treat it as if it were a normal file.
9293 When the destination is an actual directory (not a symlink to one),
9294 there is no ambiguity. The link is created in that directory.
9295 But when the specified destination is a symlink to a directory,
9296 there are two ways to treat the user's request. @command{ln} can
9297 treat the destination just as it would a normal directory and create
9298 the link in it. On the other hand, the destination can be viewed as a
9299 non-directory---as the symlink itself. In that case, @command{ln}
9300 must delete or backup that symlink before creating the new link.
9301 The default is to treat a destination that is a symlink to a directory
9302 just like a directory.
9304 This option is weaker than the @option{--no-target-directory}
9305 (@option{-T}) option, so it has no effect if both options are given.
9311 If @option{-s} is not in effect, and the source file is a symbolic
9312 link, create the hard link to the symbolic link itself. On platforms
9313 where this is not supported by the kernel, this option creates a
9314 symbolic link with identical contents; since symbolic link contents
9315 cannot be edited, any file name resolution performed through either
9316 link will be the same as if a hard link had been created.
9322 Make symbolic links instead of hard links. This option merely produces
9323 an error message on systems that do not support symbolic links.
9329 @optNoTargetDirectory
9335 Print the name of each file after linking it successfully.
9339 @cindex hard links to symbolic links
9340 @cindex symbolic links and @command{ln}
9341 If @option{-L} and @option{-P} are both given, the last one takes
9342 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9343 are silently ignored. If neither option is given, then this
9344 implementation defaults to @option{-P} if the system @code{link} supports
9345 hard links to symbolic links (such as the GNU system), and @option{-L}
9346 if @code{link} follows symbolic links (such as on BSD).
9355 # Create link ../a pointing to a in that directory.
9356 # Not really useful because it points to itself.
9361 # Change to the target before creating symlinks to avoid being confused.
9367 # Hard coded file names don't move well.
9368 ln -s $(pwd)/a /some/dir/
9372 # Relative file names survive directory moves and also
9373 # work across networked file systems.
9374 ln -s afile anotherfile
9375 ln -s ../adir/afile yetanotherfile
9379 @node mkdir invocation
9380 @section @command{mkdir}: Make directories
9383 @cindex directories, creating
9384 @cindex creating directories
9386 @command{mkdir} creates directories with the specified names. Synopsis:
9389 mkdir [@var{option}]@dots{} @var{name}@dots{}
9392 @command{mkdir} creates each directory @var{name} in the order given.
9393 It reports an error if @var{name} already exists, unless the
9394 @option{-p} option is given and @var{name} is a directory.
9396 The program accepts the following options. Also see @ref{Common options}.
9401 @itemx --mode=@var{mode}
9404 @cindex modes of created directories, setting
9405 Set the file permission bits of created directories to @var{mode},
9406 which uses the same syntax as
9407 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9408 everyone) for the point of the departure. @xref{File permissions}.
9410 Normally the directory has the desired file mode bits at the moment it
9411 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9412 special mode bits, but in this case there may be a temporary window
9413 during which the directory exists but its special mode bits are
9414 incorrect. @xref{Directory Setuid and Setgid}, for how the
9415 set-user-ID and set-group-ID bits of directories are inherited unless
9416 overridden in this way.
9422 @cindex parent directories, creating
9423 Make any missing parent directories for each argument, setting their
9424 file permission bits to the umask modified by @samp{u+wx}. Ignore
9425 existing parent directories, and do not change their file permission
9428 To set the file permission bits of any newly-created parent
9429 directories to a value that includes @samp{u+wx}, you can set the
9430 umask before invoking @command{mkdir}. For example, if the shell
9431 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9432 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9433 To set a parent's special mode bits as well, you can invoke
9434 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9435 Setgid}, for how the set-user-ID and set-group-ID bits of
9436 newly-created parent directories are inherited.
9442 Print a message for each created directory. This is most useful with
9445 @item -Z @var{context}
9446 @itemx --context=@var{context}
9450 @cindex security context
9451 Set the default SELinux security context to be used for created directories.
9458 @node mkfifo invocation
9459 @section @command{mkfifo}: Make FIFOs (named pipes)
9462 @cindex FIFOs, creating
9463 @cindex named pipes, creating
9464 @cindex creating FIFOs (named pipes)
9466 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9467 specified names. Synopsis:
9470 mkfifo [@var{option}] @var{name}@dots{}
9473 A @dfn{FIFO} is a special file type that permits independent processes
9474 to communicate. One process opens the FIFO file for writing, and
9475 another for reading, after which data can flow as with the usual
9476 anonymous pipe in shells or elsewhere.
9478 The program accepts the following option. Also see @ref{Common options}.
9483 @itemx --mode=@var{mode}
9486 @cindex modes of created FIFOs, setting
9487 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9488 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9489 for the point of departure. @var{mode} should specify only file
9490 permission bits. @xref{File permissions}.
9492 @item -Z @var{context}
9493 @itemx --context=@var{context}
9497 @cindex security context
9498 Set the default SELinux security context to be used for created FIFOs.
9505 @node mknod invocation
9506 @section @command{mknod}: Make block or character special files
9509 @cindex block special files, creating
9510 @cindex character special files, creating
9512 @command{mknod} creates a FIFO, character special file, or block special
9513 file with the specified name. Synopsis:
9516 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9519 @cindex special files
9520 @cindex block special files
9521 @cindex character special files
9522 Unlike the phrase ``special file type'' above, the term @dfn{special
9523 file} has a technical meaning on Unix: something that can generate or
9524 receive data. Usually this corresponds to a physical piece of hardware,
9525 e.g., a printer or a disk. (These files are typically created at
9526 system-configuration time.) The @command{mknod} command is what creates
9527 files of this type. Such devices can be read either a character at a
9528 time or a ``block'' (many characters) at a time, hence we say there are
9529 @dfn{block special} files and @dfn{character special} files.
9531 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9532 @mayConflictWithShellBuiltIn{mknod}
9534 The arguments after @var{name} specify the type of file to make:
9539 @opindex p @r{for FIFO file}
9543 @opindex b @r{for block special file}
9544 for a block special file
9547 @c Don't document the `u' option -- it's just a synonym for `c'.
9548 @c Do *any* versions of mknod still use it?
9550 @opindex c @r{for character special file}
9551 @c @opindex u @r{for character special file}
9552 for a character special file
9556 When making a block or character special file, the major and minor
9557 device numbers must be given after the file type.
9558 If a major or minor device number begins with @samp{0x} or @samp{0X},
9559 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9560 as octal; otherwise, as decimal.
9562 The program accepts the following option. Also see @ref{Common options}.
9567 @itemx --mode=@var{mode}
9570 Set the mode of created files to @var{mode}, which is symbolic as in
9571 @command{chmod} and uses @samp{a=rw} as the point of departure.
9572 @var{mode} should specify only file permission bits.
9573 @xref{File permissions}.
9575 @item -Z @var{context}
9576 @itemx --context=@var{context}
9580 @cindex security context
9581 Set the default SELinux security context to be used for created files.
9588 @node readlink invocation
9589 @section @command{readlink}: Print value of a symlink or canonical file name
9592 @cindex displaying value of a symbolic link
9593 @cindex canonical file name
9594 @cindex canonicalize a file name
9598 @command{readlink} may work in one of two supported modes:
9604 @command{readlink} outputs the value of the given symbolic link.
9605 If @command{readlink} is invoked with an argument other than the name
9606 of a symbolic link, it produces no output and exits with a nonzero exit code.
9608 @item Canonicalize mode
9610 @command{readlink} outputs the absolute name of the given file which contains
9611 no @file{.}, @file{..} components nor any repeated separators
9612 (@file{/}) or symbolic links.
9617 readlink [@var{option}] @var{file}
9620 By default, @command{readlink} operates in readlink mode.
9622 The program accepts the following options. Also see @ref{Common options}.
9627 @itemx --canonicalize
9629 @opindex --canonicalize
9630 Activate canonicalize mode.
9631 If any component of the file name except the last one is missing or unavailable,
9632 @command{readlink} produces no output and exits with a nonzero exit
9633 code. A trailing slash is ignored.
9636 @itemx --canonicalize-existing
9638 @opindex --canonicalize-existing
9639 Activate canonicalize mode.
9640 If any component is missing or unavailable, @command{readlink} produces
9641 no output and exits with a nonzero exit code. A trailing slash
9642 requires that the name resolve to a directory.
9645 @itemx --canonicalize-missing
9647 @opindex --canonicalize-missing
9648 Activate canonicalize mode.
9649 If any component is missing or unavailable, @command{readlink} treats it
9655 @opindex --no-newline
9656 Do not output the trailing newline.
9666 Suppress most error messages.
9672 Report error messages.
9676 The @command{readlink} utility first appeared in OpenBSD 2.1.
9678 There is a @command{realpath} command on some systems
9679 which operates like @command{readlink} in canonicalize mode.
9684 @node rmdir invocation
9685 @section @command{rmdir}: Remove empty directories
9688 @cindex removing empty directories
9689 @cindex directories, removing empty
9691 @command{rmdir} removes empty directories. Synopsis:
9694 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9697 If any @var{directory} argument does not refer to an existing empty
9698 directory, it is an error.
9700 The program accepts the following options. Also see @ref{Common options}.
9704 @item --ignore-fail-on-non-empty
9705 @opindex --ignore-fail-on-non-empty
9706 @cindex directory deletion, ignoring failures
9707 Ignore each failure to remove a directory that is solely because
9708 the directory is non-empty.
9714 @cindex parent directories, removing
9715 Remove @var{directory}, then try to remove each component of @var{directory}.
9716 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9717 As such, it fails if any of those directories turns out not to be empty.
9718 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9719 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9720 exit unsuccessfully.
9726 @cindex directory deletion, reporting
9727 Give a diagnostic for each successful removal.
9728 @var{directory} is removed.
9732 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9737 @node unlink invocation
9738 @section @command{unlink}: Remove files via the unlink syscall
9741 @cindex removing files or directories (via the unlink syscall)
9743 @command{unlink} deletes a single specified file name.
9744 It is a minimalist interface to the system-provided
9745 @code{unlink} function. @xref{Deleting Files, , , libc,
9746 The GNU C Library Reference Manual}. Synopsis:
9747 It avoids the bells and whistles of the more commonly-used
9748 @command{rm} command (@pxref{rm invocation}).
9751 unlink @var{filename}
9754 On some systems @code{unlink} can be used to delete the name of a
9755 directory. On others, it can be used that way only by a privileged user.
9756 In the GNU system @code{unlink} can never delete the name of a directory.
9758 The @command{unlink} command honors the @option{--help} and
9759 @option{--version} options. To remove a file whose name begins with
9760 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9765 @node Changing file attributes
9766 @chapter Changing file attributes
9768 @cindex changing file attributes
9769 @cindex file attributes, changing
9770 @cindex attributes, file
9772 A file is not merely its contents, a name, and a file type
9773 (@pxref{Special file types}). A file also has an owner (a user ID), a
9774 group (a group ID), permissions (what the owner can do with the file,
9775 what people in the group can do, and what everyone else can do), various
9776 timestamps, and other information. Collectively, we call these a file's
9779 These commands change file attributes.
9782 * chgrp invocation:: Change file groups.
9783 * chmod invocation:: Change access permissions.
9784 * chown invocation:: Change file owners and groups.
9785 * touch invocation:: Change file timestamps.
9789 @node chown invocation
9790 @section @command{chown}: Change file owner and group
9793 @cindex file ownership, changing
9794 @cindex group ownership, changing
9795 @cindex changing file ownership
9796 @cindex changing group ownership
9798 @command{chown} changes the user and/or group ownership of each given @var{file}
9799 to @var{new-owner} or to the user and group of an existing reference file.
9803 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
9807 If used, @var{new-owner} specifies the new owner and/or group as follows
9808 (with no embedded white space):
9811 [@var{owner}] [ : [@var{group}] ]
9818 If only an @var{owner} (a user name or numeric user ID) is given, that
9819 user is made the owner of each given file, and the files' group is not
9822 @item owner@samp{:}group
9823 If the @var{owner} is followed by a colon and a @var{group} (a
9824 group name or numeric group ID), with no spaces between them, the group
9825 ownership of the files is changed as well (to @var{group}).
9828 If a colon but no group name follows @var{owner}, that user is
9829 made the owner of the files and the group of the files is changed to
9830 @var{owner}'s login group.
9833 If the colon and following @var{group} are given, but the owner
9834 is omitted, only the group of the files is changed; in this case,
9835 @command{chown} performs the same function as @command{chgrp}.
9838 If only a colon is given, or if @var{new-owner} is empty, neither the
9839 owner nor the group is changed.
9843 If @var{owner} or @var{group} is intended to represent a numeric user
9844 or group ID, then you may specify it with a leading @samp{+}.
9845 @xref{Disambiguating names and IDs}.
9847 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9848 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9849 require support for that, but for backward compatibility @acronym{GNU}
9850 @command{chown} supports @samp{.} so long as no ambiguity results.
9851 New scripts should avoid the use of @samp{.} because it is not
9852 portable, and because it has undesirable results if the entire
9853 @var{owner@samp{.}group} happens to identify a user whose name
9856 The @command{chown} command sometimes clears the set-user-ID or
9857 set-group-ID permission bits. This behavior depends on the policy and
9858 functionality of the underlying @code{chown} system call, which may
9859 make system-dependent file mode modifications outside the control of
9860 the @command{chown} command. For example, the @command{chown} command
9861 might not affect those bits when invoked by a user with appropriate
9862 privileges, or when the
9863 bits signify some function other than executable permission (e.g.,
9865 When in doubt, check the underlying system behavior.
9867 The program accepts the following options. Also see @ref{Common options}.
9875 @cindex changed owners, verbosely describing
9876 Verbosely describe the action for each @var{file} whose ownership
9885 @cindex error messages, omitting
9886 Do not print error messages about files whose ownership cannot be
9889 @itemx @w{@kbd{--from}=@var{old-owner}}
9891 @cindex symbolic links, changing owner
9892 Change a @var{file}'s ownership only if it has current attributes specified
9893 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9895 This option is useful primarily from a security standpoint in that
9896 it narrows considerably the window of potential abuse.
9897 For example, to reflect a user ID numbering change for one user's files
9898 without an option like this, @code{root} might run
9901 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9904 But that is dangerous because the interval between when the @command{find}
9905 tests the existing file's owner and when the @command{chown} is actually run
9907 One way to narrow the gap would be to invoke chown for each file
9911 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9914 But that is very slow if there are many affected files.
9915 With this option, it is safer (the gap is narrower still)
9916 though still not perfect:
9919 chown -h -R --from=OLDUSER NEWUSER /
9923 @opindex --dereference
9924 @cindex symbolic links, changing owner
9926 Do not act on symbolic links themselves but rather on what they point to.
9927 This is the default.
9930 @itemx --no-dereference
9932 @opindex --no-dereference
9933 @cindex symbolic links, changing owner
9935 Act on symbolic links themselves instead of what they point to.
9936 This mode relies on the @code{lchown} system call.
9937 On systems that do not provide the @code{lchown} system call,
9938 @command{chown} fails when a file specified on the command line
9940 By default, no diagnostic is issued for symbolic links encountered
9941 during a recursive traversal, but see @option{--verbose}.
9943 @itemx --preserve-root
9944 @opindex --preserve-root
9945 @cindex root directory, disallow recursive modification
9946 Fail upon any attempt to recursively change the root directory, @file{/}.
9947 Without @option{--recursive}, this option has no effect.
9948 @xref{Treating / specially}.
9950 @itemx --no-preserve-root
9951 @opindex --no-preserve-root
9952 @cindex root directory, allow recursive modification
9953 Cancel the effect of any preceding @option{--preserve-root} option.
9954 @xref{Treating / specially}.
9956 @item --reference=@var{ref_file}
9957 @opindex --reference
9958 Change the user and group of each @var{file} to be the same as those of
9959 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9960 user and group of the symbolic link, but rather those of the file it
9967 Output a diagnostic for every file processed.
9968 If a symbolic link is encountered during a recursive traversal
9969 on a system without the @code{lchown} system call, and @option{--no-dereference}
9970 is in effect, then issue a diagnostic saying neither the symbolic link nor
9971 its referent is being changed.
9976 @opindex --recursive
9977 @cindex recursively changing file ownership
9978 Recursively change ownership of directories and their contents.
9981 @xref{Traversing symlinks}.
9984 @xref{Traversing symlinks}.
9987 @xref{Traversing symlinks}.
9996 # Change the owner of /u to "root".
9999 # Likewise, but also change its group to "staff".
10000 chown root:staff /u
10002 # Change the owner of /u and subfiles to "root".
10007 @node chgrp invocation
10008 @section @command{chgrp}: Change group ownership
10011 @cindex group ownership, changing
10012 @cindex changing group ownership
10014 @command{chgrp} changes the group ownership of each given @var{file}
10015 to @var{group} (which can be either a group name or a numeric group ID)
10016 or to the group of an existing reference file. Synopsis:
10019 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
10023 If @var{group} is intended to represent a
10024 numeric group ID, then you may specify it with a leading @samp{+}.
10025 @xref{Disambiguating names and IDs}.
10027 The program accepts the following options. Also see @ref{Common options}.
10035 @cindex changed files, verbosely describing
10036 Verbosely describe the action for each @var{file} whose group actually
10045 @cindex error messages, omitting
10046 Do not print error messages about files whose group cannot be
10049 @item --dereference
10050 @opindex --dereference
10051 @cindex symbolic links, changing owner
10053 Do not act on symbolic links themselves but rather on what they point to.
10054 This is the default.
10057 @itemx --no-dereference
10059 @opindex --no-dereference
10060 @cindex symbolic links, changing group
10062 Act on symbolic links themselves instead of what they point to.
10063 This mode relies on the @code{lchown} system call.
10064 On systems that do not provide the @code{lchown} system call,
10065 @command{chgrp} fails when a file specified on the command line
10066 is a symbolic link.
10067 By default, no diagnostic is issued for symbolic links encountered
10068 during a recursive traversal, but see @option{--verbose}.
10070 @itemx --preserve-root
10071 @opindex --preserve-root
10072 @cindex root directory, disallow recursive modification
10073 Fail upon any attempt to recursively change the root directory, @file{/}.
10074 Without @option{--recursive}, this option has no effect.
10075 @xref{Treating / specially}.
10077 @itemx --no-preserve-root
10078 @opindex --no-preserve-root
10079 @cindex root directory, allow recursive modification
10080 Cancel the effect of any preceding @option{--preserve-root} option.
10081 @xref{Treating / specially}.
10083 @item --reference=@var{ref_file}
10084 @opindex --reference
10085 Change the group of each @var{file} to be the same as that of
10086 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10087 group of the symbolic link, but rather that of the file it refers to.
10093 Output a diagnostic for every file processed.
10094 If a symbolic link is encountered during a recursive traversal
10095 on a system without the @code{lchown} system call, and @option{--no-dereference}
10096 is in effect, then issue a diagnostic saying neither the symbolic link nor
10097 its referent is being changed.
10102 @opindex --recursive
10103 @cindex recursively changing group ownership
10104 Recursively change the group ownership of directories and their contents.
10107 @xref{Traversing symlinks}.
10110 @xref{Traversing symlinks}.
10113 @xref{Traversing symlinks}.
10122 # Change the group of /u to "staff".
10125 # Change the group of /u and subfiles to "staff".
10130 @node chmod invocation
10131 @section @command{chmod}: Change access permissions
10134 @cindex changing access permissions
10135 @cindex access permissions, changing
10136 @cindex permissions, changing access
10138 @command{chmod} changes the access permissions of the named files. Synopsis:
10141 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
10145 @cindex symbolic links, permissions of
10146 @command{chmod} never changes the permissions of symbolic links, since
10147 the @command{chmod} system call cannot change their permissions.
10148 This is not a problem since the permissions of symbolic links are
10149 never used. However, for each symbolic link listed on the command
10150 line, @command{chmod} changes the permissions of the pointed-to file.
10151 In contrast, @command{chmod} ignores symbolic links encountered during
10152 recursive directory traversals.
10154 A successful use of @command{chmod} clears the set-group-ID bit of a
10155 regular file if the file's group ID does not match the user's
10156 effective group ID or one of the user's supplementary group IDs,
10157 unless the user has appropriate privileges. Additional restrictions
10158 may cause the set-user-ID and set-group-ID bits of @var{mode} or
10159 @var{ref_file} to be ignored. This behavior depends on the policy and
10160 functionality of the underlying @code{chmod} system call. When in
10161 doubt, check the underlying system behavior.
10163 If used, @var{mode} specifies the new file mode bits.
10164 For details, see the section on @ref{File permissions}.
10165 If you really want @var{mode} to have a leading @samp{-}, you should
10166 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
10167 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
10168 file} (without the @option{--}) complains if it behaves differently
10169 from what @samp{chmod a-w file} would do.
10171 The program accepts the following options. Also see @ref{Common options}.
10179 Verbosely describe the action for each @var{file} whose permissions
10188 @cindex error messages, omitting
10189 Do not print error messages about files whose permissions cannot be
10192 @itemx --preserve-root
10193 @opindex --preserve-root
10194 @cindex root directory, disallow recursive modification
10195 Fail upon any attempt to recursively change the root directory, @file{/}.
10196 Without @option{--recursive}, this option has no effect.
10197 @xref{Treating / specially}.
10199 @itemx --no-preserve-root
10200 @opindex --no-preserve-root
10201 @cindex root directory, allow recursive modification
10202 Cancel the effect of any preceding @option{--preserve-root} option.
10203 @xref{Treating / specially}.
10209 Verbosely describe the action or non-action taken for every @var{file}.
10211 @item --reference=@var{ref_file}
10212 @opindex --reference
10213 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
10214 @xref{File permissions}.
10215 If @var{ref_file} is a symbolic link, do not use the mode
10216 of the symbolic link, but rather that of the file it refers to.
10221 @opindex --recursive
10222 @cindex recursively changing access permissions
10223 Recursively change permissions of directories and their contents.
10230 @node touch invocation
10231 @section @command{touch}: Change file timestamps
10234 @cindex changing file timestamps
10235 @cindex file timestamps, changing
10236 @cindex timestamps, changing file
10238 @command{touch} changes the access and/or modification times of the
10239 specified files. Synopsis:
10242 touch [@var{option}]@dots{} @var{file}@dots{}
10245 @cindex empty files, creating
10246 Any @var{file} argument that does not exist is created empty, unless
10247 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
10248 (@option{-h}) was in effect.
10250 A @var{file} argument string of @samp{-} is handled specially and
10251 causes @command{touch} to change the times of the file associated with
10254 @cindex permissions, for changing file timestamps
10255 If changing both the access and modification times to the current
10256 time, @command{touch} can change the timestamps for files that the user
10257 running it does not own but has write permission for. Otherwise, the
10258 user must own the files.
10260 Although @command{touch} provides options for changing two of the times---the
10261 times of last access and modification---of a file, there is actually
10262 a standard third one as well: the inode change time. This is often
10263 referred to as a file's @code{ctime}.
10264 The inode change time represents the time when the file's meta-information
10265 last changed. One common example of this is when the permissions of a
10266 file change. Changing the permissions doesn't access the file, so
10267 the atime doesn't change, nor does it modify the file, so the mtime
10268 doesn't change. Yet, something about the file itself has changed,
10269 and this must be noted somewhere. This is the job of the ctime field.
10270 This is necessary, so that, for example, a backup program can make a
10271 fresh copy of the file, including the new permissions value.
10272 Another operation that modifies a file's ctime without affecting
10273 the others is renaming. In any case, it is not possible, in normal
10274 operations, for a user to change the ctime field to a user-specified value.
10275 Some operating systems and file systems support a fourth time: the
10276 birth time, when the file was first created; by definition, this
10277 timestamp never changes.
10280 Time stamps assume the time zone rules specified by the @env{TZ}
10281 environment variable, or by the system default rules if @env{TZ} is
10282 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
10283 libc, The GNU C Library Reference Manual}.
10284 You can avoid ambiguities during
10285 daylight saving transitions by using @sc{utc} time stamps.
10287 The program accepts the following options. Also see @ref{Common options}.
10292 @itemx --time=atime
10293 @itemx --time=access
10297 @opindex atime@r{, changing}
10298 @opindex access @r{time, changing}
10299 @opindex use @r{time, changing}
10300 Change the access time only.
10305 @opindex --no-create
10306 Do not warn about or create files that do not exist.
10309 @itemx --date=@var{time}
10313 Use @var{time} instead of the current time. It can contain month names,
10314 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10315 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10316 specifies the instant of time that is 489,392,193 nanoseconds after
10317 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10318 minutes east of @acronym{UTC}. @xref{Date input formats}.
10319 File systems that do not support high-resolution time stamps
10320 silently ignore any excess precision here.
10324 @cindex BSD @command{touch} compatibility
10325 Ignored; for compatibility with BSD versions of @command{touch}.
10328 @itemx --no-dereference
10330 @opindex --no-dereference
10331 @cindex symbolic links, changing time
10333 Attempt to change the timestamps of a symbolic link, rather than what
10334 the link refers to. When using this option, empty files are not
10335 created, but option @option{-c} must also be used to avoid warning
10336 about files that do not exist. Not all systems support changing the
10337 timestamps of symlinks, since underlying system support for this
10338 action was not required until @acronym{POSIX} 2008. Also, on some
10339 systems, the mere act of examining a symbolic link changes the access
10340 time, such that only changes to the modification time will persist
10341 long enough to be observable. When coupled with option @option{-r}, a
10342 reference timestamp is taken from a symbolic link rather than the file
10346 @itemx --time=mtime
10347 @itemx --time=modify
10350 @opindex mtime@r{, changing}
10351 @opindex modify @r{time, changing}
10352 Change the modification time only.
10354 @item -r @var{file}
10355 @itemx --reference=@var{file}
10357 @opindex --reference
10358 Use the times of the reference @var{file} instead of the current time.
10359 If this option is combined with the @option{--date=@var{time}}
10360 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10361 the origin for any relative @var{time}s given, but is otherwise ignored.
10362 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10363 equal to five seconds before the corresponding time stamp for @file{foo}.
10364 If @var{file} is a symbolic link, the reference timestamp is taken
10365 from the target of the symlink, unless @option{-h} was also in effect.
10367 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10368 Use the argument (optional four-digit or two-digit years, months,
10369 days, hours, minutes, optional seconds) instead of the current time.
10370 If the year is specified with only two digits, then @var{cc}
10371 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10372 69 @dots{} 99. If no digits of the year are specified,
10373 the argument is interpreted as a date in the current year.
10374 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10378 @vindex _POSIX2_VERSION
10379 On older systems, @command{touch} supports an obsolete syntax, as follows.
10380 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10381 @option{-t} options, and if there are two or more @var{file}s and the
10382 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10383 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10384 any, were moved to the front), and if the represented year
10385 is in the range 1969--1999, that argument is interpreted as the time
10386 for the other files instead of as a file name.
10387 This obsolete behavior can be enabled or disabled with the
10388 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10389 conformance}), but portable scripts should avoid commands whose
10390 behavior depends on this variable.
10391 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10392 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10398 @chapter Disk usage
10402 No disk can hold an infinite amount of data. These commands report
10403 how much disk storage is in use or available, report other file and
10404 file status information, and write buffers to disk.
10407 * df invocation:: Report file system disk space usage.
10408 * du invocation:: Estimate file space usage.
10409 * stat invocation:: Report file or file system status.
10410 * sync invocation:: Synchronize memory and disk.
10411 * truncate invocation:: Shrink or extend the size of a file.
10415 @node df invocation
10416 @section @command{df}: Report file system disk space usage
10419 @cindex file system disk usage
10420 @cindex disk usage by file system
10422 @command{df} reports the amount of disk space used and available on
10423 file systems. Synopsis:
10426 df [@var{option}]@dots{} [@var{file}]@dots{}
10429 With no arguments, @command{df} reports the space used and available on all
10430 currently mounted file systems (of all types). Otherwise, @command{df}
10431 reports on the file system containing each argument @var{file}.
10433 Normally the disk space is printed in units of
10434 1024 bytes, but this can be overridden (@pxref{Block size}).
10435 Non-integer quantities are rounded up to the next higher unit.
10437 @cindex disk device file
10438 @cindex device file, disk
10439 If an argument @var{file} is a disk device file containing a mounted
10440 file system, @command{df} shows the space available on that file system
10441 rather than on the file system containing the device node (i.e., the root
10442 file system). @sc{gnu} @command{df} does not attempt to determine the
10444 on unmounted file systems, because on most kinds of systems doing so
10445 requires extremely nonportable intimate knowledge of file system
10448 The program accepts the following options. Also see @ref{Common options}.
10456 @cindex automounter file systems
10457 @cindex ignore file systems
10458 Include in the listing dummy file systems, which
10459 are omitted by default. Such file systems are typically special-purpose
10460 pseudo-file-systems, such as automounter entries.
10462 @item -B @var{size}
10463 @itemx --block-size=@var{size}
10465 @opindex --block-size
10466 @cindex file system sizes
10467 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10468 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10472 @cindex grand total of disk size, usage and available space
10473 Print a grand total of all arguments after all arguments have
10474 been processed. This can be used to find out the total disk size, usage
10475 and available space of all listed devices.
10481 Equivalent to @option{--si}.
10487 @cindex inode usage
10488 List inode usage information instead of block usage. An inode (short
10489 for index node) contains information about a file such as its owner,
10490 permissions, timestamps, and location on the disk.
10494 @cindex kibibytes for file system sizes
10495 Print sizes in 1024-byte blocks, overriding the default block size
10496 (@pxref{Block size}).
10497 This option is equivalent to @option{--block-size=1K}.
10503 @cindex file system types, limiting output to certain
10504 Limit the listing to local file systems. By default, remote file systems
10509 @cindex file system space, retrieving old data more quickly
10510 Do not invoke the @code{sync} system call before getting any usage data.
10511 This may make @command{df} run significantly faster on systems with many
10512 disks, but on some systems (notably SunOS) the results may be slightly
10513 out of date. This is the default.
10516 @itemx --portability
10518 @opindex --portability
10519 @cindex one-line output format
10520 @cindex @acronym{POSIX} output format
10521 @cindex portable output format
10522 @cindex output format, portable
10523 Use the @acronym{POSIX} output format. This is like the default format except
10528 The information about each file system is always printed on exactly
10529 one line; a mount device is never put on a line by itself. This means
10530 that if the mount device name is more than 20 characters long (e.g., for
10531 some network mounts), the columns are misaligned.
10534 The labels in the header output line are changed to conform to @acronym{POSIX}.
10537 The default block size and output format are unaffected by the
10538 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10539 variables. However, the default block size is still affected by
10540 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10541 otherwise. @xref{Block size}.
10548 @cindex file system space, retrieving current data more slowly
10549 Invoke the @code{sync} system call before getting any usage data. On
10550 some systems (notably SunOS), doing this yields more up to date results,
10551 but in general this option makes @command{df} much slower, especially when
10552 there are many or very busy file systems.
10554 @item -t @var{fstype}
10555 @itemx --type=@var{fstype}
10558 @cindex file system types, limiting output to certain
10559 Limit the listing to file systems of type @var{fstype}. Multiple
10560 file system types can be specified by giving multiple @option{-t} options.
10561 By default, nothing is omitted.
10564 @itemx --print-type
10566 @opindex --print-type
10567 @cindex file system types, printing
10568 Print each file system's type. The types printed here are the same ones
10569 you can include or exclude with @option{-t} and @option{-x}. The particular
10570 types printed are whatever is supported by the system. Here are some of
10571 the common names (this list is certainly not exhaustive):
10576 @cindex @acronym{NFS} file system type
10577 An @acronym{NFS} file system, i.e., one mounted over a network from another
10578 machine. This is the one type name which seems to be used uniformly by
10581 @item 4.2@r{, }ufs@r{, }efs@dots{}
10582 @cindex Linux file system types
10583 @cindex local file system types
10584 @opindex 4.2 @r{file system type}
10585 @opindex ufs @r{file system type}
10586 @opindex efs @r{file system type}
10587 A file system on a locally-mounted hard disk. (The system might even
10588 support more than one type here; Linux does.)
10590 @item hsfs@r{, }cdfs
10591 @cindex CD-ROM file system type
10592 @cindex High Sierra file system
10593 @opindex hsfs @r{file system type}
10594 @opindex cdfs @r{file system type}
10595 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10596 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10599 @cindex PC file system
10600 @cindex DOS file system
10601 @cindex MS-DOS file system
10602 @cindex diskette file system
10604 An MS-DOS file system, usually on a diskette.
10608 @item -x @var{fstype}
10609 @itemx --exclude-type=@var{fstype}
10611 @opindex --exclude-type
10612 Limit the listing to file systems not of type @var{fstype}.
10613 Multiple file system types can be eliminated by giving multiple
10614 @option{-x} options. By default, no file system types are omitted.
10617 Ignored; for compatibility with System V versions of @command{df}.
10622 Failure includes the case where no output is generated, so you can
10623 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10624 @var{dir}} to test whether @var{dir} is on a file system of type
10625 @samp{ext3} or @samp{reiserfs}.
10628 @node du invocation
10629 @section @command{du}: Estimate file space usage
10632 @cindex file space usage
10633 @cindex disk usage for files
10635 @command{du} reports the amount of disk space used by the specified files
10636 and for each subdirectory (of directory arguments). Synopsis:
10639 du [@var{option}]@dots{} [@var{file}]@dots{}
10642 With no arguments, @command{du} reports the disk space for the current
10643 directory. Normally the disk space is printed in units of
10644 1024 bytes, but this can be overridden (@pxref{Block size}).
10645 Non-integer quantities are rounded up to the next higher unit.
10647 If two or more hard links point to the same file, only one of the hard
10648 links is counted. The @var{file} argument order affects which links
10649 are counted, and changing the argument order may change the numbers
10650 that @command{du} outputs.
10652 The program accepts the following options. Also see @ref{Common options}.
10660 Show counts for all files, not just directories.
10662 @itemx --apparent-size
10663 @opindex --apparent-size
10664 Print apparent sizes, rather than disk usage. The apparent size of a
10665 file is the number of bytes reported by @code{wc -c} on regular files,
10666 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10667 For example, a file containing the word @samp{zoo} with no newline would,
10668 of course, have an apparent size of 3. Such a small file may require
10669 anywhere from 0 to 16 KiB or more of disk space, depending on
10670 the type and configuration of the file system on which the file resides.
10671 However, a sparse file created with this command:
10674 dd bs=1 seek=2GiB if=/dev/null of=big
10678 has an apparent size of 2 GiB, yet on most modern
10679 systems, it actually uses almost no disk space.
10685 Equivalent to @code{--apparent-size --block-size=1}.
10687 @item -B @var{size}
10688 @itemx --block-size=@var{size}
10690 @opindex --block-size
10692 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10693 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10699 @cindex grand total of disk space
10700 Print a grand total of all arguments after all arguments have
10701 been processed. This can be used to find out the total disk usage of
10702 a given set of files or directories.
10705 @itemx --dereference-args
10707 @opindex --dereference-args
10708 Dereference symbolic links that are command line arguments.
10709 Does not affect other symbolic links. This is helpful for finding
10710 out the disk usage of directories, such as @file{/usr/tmp}, which
10711 are often symbolic links.
10713 @c --files0-from=FILE
10714 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10720 Equivalent to @option{--dereference-args} (@option{-D}).
10724 @cindex kibibytes for file sizes
10725 Print sizes in 1024-byte blocks, overriding the default block size
10726 (@pxref{Block size}).
10727 This option is equivalent to @option{--block-size=1K}.
10730 @itemx --count-links
10732 @opindex --count-links
10733 @cindex hard links, counting in @command{du}
10734 Count the size of all files, even if they have appeared already (as a
10738 @itemx --dereference
10740 @opindex --dereference
10741 @cindex symbolic links, dereferencing in @command{du}
10742 Dereference symbolic links (show the disk space used by the file
10743 or directory that the link points to instead of the space used by
10748 @cindex mebibytes for file sizes
10749 Print sizes in 1,048,576-byte blocks, overriding the default block size
10750 (@pxref{Block size}).
10751 This option is equivalent to @option{--block-size=1M}.
10754 @itemx --no-dereference
10756 @opindex --no-dereference
10757 @cindex symbolic links, dereferencing in @command{du}
10758 For each symbolic links encountered by @command{du},
10759 consider the disk space used by the symbolic link.
10761 @item -d @var{depth}
10762 @item --max-depth=@var{depth}
10763 @opindex -d @var{depth}
10764 @opindex --max-depth=@var{depth}
10765 @cindex limiting output of @command{du}
10766 Show the total for each directory (and file if --all) that is at
10767 most MAX_DEPTH levels down from the root of the hierarchy. The root
10768 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10777 @opindex --summarize
10778 Display only a total for each argument.
10781 @itemx --separate-dirs
10783 @opindex --separate-dirs
10784 Normally, in the output of @command{du} (when not using @option{--summarize}),
10785 the size listed next to a directory name, @var{d}, represents the sum
10786 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10787 With @option{--separate-dirs}, the size reported for a directory name,
10788 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10793 @cindex last modified dates, displaying in @command{du}
10794 Show time of the most recent modification of any file in the directory,
10795 or any of its subdirectories.
10797 @itemx --time=ctime
10798 @itemx --time=status
10801 @opindex ctime@r{, show the most recent}
10802 @opindex status time@r{, show the most recent}
10803 @opindex use time@r{, show the most recent}
10804 Show the most recent status change time (the @samp{ctime} in the inode) of
10805 any file in the directory, instead of the modification time.
10807 @itemx --time=atime
10808 @itemx --time=access
10810 @opindex atime@r{, show the most recent}
10811 @opindex access time@r{, show the most recent}
10812 Show the most recent access time (the @samp{atime} in the inode) of
10813 any file in the directory, instead of the modification time.
10815 @item --time-style=@var{style}
10816 @opindex --time-style
10818 List timestamps in style @var{style}. This option has an effect only if
10819 the @option{--time} option is also specified. The @var{style} should
10820 be one of the following:
10823 @item +@var{format}
10825 List timestamps using @var{format}, where @var{format} is interpreted
10826 like the format argument of @command{date} (@pxref{date invocation}).
10827 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10828 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10829 with @command{date}, @var{format}'s interpretation is affected by the
10830 @env{LC_TIME} locale category.
10833 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10834 format with nanosecond precision, e.g., @samp{2002-03-30
10835 23:45:56.477817180 -0700}. This style is equivalent to
10836 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10839 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10840 @samp{2002-03-30 23:45}. These timestamps are shorter than
10841 @samp{full-iso} timestamps, and are usually good enough for everyday
10842 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10845 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10846 This style is equivalent to @samp{+%Y-%m-%d}.
10850 You can specify the default value of the @option{--time-style} option
10851 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10852 the default style is @samp{long-iso}. For compatibility with @command{ls},
10853 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10854 the newline and any later characters are ignored; if @env{TIME_STYLE}
10855 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10856 @env{TIME_STYLE} is @samp{locale} it is ignored.
10859 @itemx --one-file-system
10861 @opindex --one-file-system
10862 @cindex one file system, restricting @command{du} to
10863 Skip directories that are on different file systems from the one that
10864 the argument being processed is on.
10866 @item --exclude=@var{pattern}
10867 @opindex --exclude=@var{pattern}
10868 @cindex excluding files from @command{du}
10869 When recursing, skip subdirectories or files matching @var{pattern}.
10870 For example, @code{du --exclude='*.o'} excludes files whose names
10873 @item -X @var{file}
10874 @itemx --exclude-from=@var{file}
10875 @opindex -X @var{file}
10876 @opindex --exclude-from=@var{file}
10877 @cindex excluding files from @command{du}
10878 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10879 one per line. If @var{file} is @samp{-}, take the patterns from standard
10884 @cindex NFS mounts from BSD to HP-UX
10885 On BSD systems, @command{du} reports sizes that are half the correct
10886 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10887 systems, it reports sizes that are twice the correct values for
10888 files that are NFS-mounted from BSD systems. This is due to a flaw
10889 in HP-UX; it also affects the HP-UX @command{du} program.
10894 @node stat invocation
10895 @section @command{stat}: Report file or file system status
10898 @cindex file status
10899 @cindex file system status
10901 @command{stat} displays information about the specified file(s). Synopsis:
10904 stat [@var{option}]@dots{} [@var{file}]@dots{}
10907 With no option, @command{stat} reports all information about the given files.
10908 But it also can be used to report the information of the file systems the
10909 given files are located on. If the files are links, @command{stat} can
10910 also give information about the files the links point to.
10912 @mayConflictWithShellBuiltIn{stat}
10917 @itemx --dereference
10919 @opindex --dereference
10920 @cindex symbolic links, dereferencing in @command{stat}
10921 Change how @command{stat} treats symbolic links.
10922 With this option, @command{stat} acts on the file referenced
10923 by each symbolic link argument.
10924 Without it, @command{stat} acts on any symbolic link argument directly.
10927 @itemx --file-system
10929 @opindex --file-system
10930 @cindex file systems
10931 Report information about the file systems where the given files are located
10932 instead of information about the files themselves.
10933 This option implies the @option{-L} option.
10936 @itemx --format=@var{format}
10938 @opindex --format=@var{format}
10939 @cindex output format
10940 Use @var{format} rather than the default format.
10941 @var{format} is automatically newline-terminated, so
10942 running a command like the following with two or more @var{file}
10943 operands produces a line of output for each operand:
10945 $ stat --format=%d:%i / /usr
10950 @itemx --printf=@var{format}
10951 @opindex --printf=@var{format}
10952 @cindex output format
10953 Use @var{format} rather than the default format.
10954 Like @option{--format}, but interpret backslash escapes,
10955 and do not output a mandatory trailing newline.
10956 If you want a newline, include @samp{\n} in the @var{format}.
10957 Here's how you would use @option{--printf} to print the device
10958 and inode numbers of @file{/} and @file{/usr}:
10960 $ stat --printf='%d:%i\n' / /usr
10969 @cindex terse output
10970 Print the information in terse form, suitable for parsing by other programs.
10974 The valid @var{format} directives for files with @option{--format} and
10975 @option{--printf} are:
10978 @item %a - Access rights in octal
10979 @item %A - Access rights in human readable form
10980 @item %b - Number of blocks allocated (see @samp{%B})
10981 @item %B - The size in bytes of each block reported by @samp{%b}
10982 @item %C - The SELinux security context of a file, if available
10983 @item %d - Device number in decimal
10984 @item %D - Device number in hex
10985 @item %f - Raw mode in hex
10986 @item %F - File type
10987 @item %g - Group ID of owner
10988 @item %G - Group name of owner
10989 @item %h - Number of hard links
10990 @item %i - Inode number
10991 @item %m - Mount point (See note below)
10992 @item %n - File name
10993 @item %N - Quoted file name with dereference if symbolic link
10994 @item %o - I/O block size
10995 @item %s - Total size, in bytes
10996 @item %t - Major device type in hex
10997 @item %T - Minor device type in hex
10998 @item %u - User ID of owner
10999 @item %U - User name of owner
11000 @item %w - Time of file birth, or @samp{-} if unknown
11001 @item %W - Time of file birth as seconds since Epoch, or @samp{0}
11002 @item %x - Time of last access
11003 @item %X - Time of last access as seconds since Epoch
11004 @item %y - Time of last modification
11005 @item %Y - Time of last modification as seconds since Epoch
11006 @item %z - Time of last change
11007 @item %Z - Time of last change as seconds since Epoch
11010 The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
11011 precision preceded by a period to specify the number of digits to
11012 print after the decimal point. For example, @samp{%.3X} outputs the
11013 last access time to millisecond precision. If a period is given but no
11014 precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
11015 @samp{%.9X}. When discarding excess precision, time stamps are truncated
11016 toward minus infinity.
11020 $ stat -c '[%015Y]' /usr
11023 $ stat -c '[%15Y]' /usr
11025 $ stat -c '[%-15Y]' /usr
11028 $ stat -c '[%.3Y]' /usr
11030 $ stat -c '[%.Y]' /usr
11031 [1288929712.114951834]
11034 The mount point printed by @samp{%m} is similar to that output
11035 by @command{df}, except that:
11038 stat does not dereference symlinks by default
11039 (unless @option{-L} is specified)
11041 stat does not search for specified device nodes in the
11042 file system list, instead operating on them directly
11045 stat outputs the alias for a bind mounted file, rather than
11046 the initial mount point of its backing device.
11047 One can recursively call stat until there is no change in output,
11048 to get the current base mount point
11051 When listing file system information (@option{--file-system} (@option{-f})),
11052 you must use a different set of @var{format} directives:
11055 @item %a - Free blocks available to non-super-user
11056 @item %b - Total data blocks in file system
11057 @item %c - Total file nodes in file system
11058 @item %d - Free file nodes in file system
11059 @item %f - Free blocks in file system
11060 @item %i - File System ID in hex
11061 @item %l - Maximum length of file names
11062 @item %n - File name
11063 @item %s - Block size (for faster transfers)
11064 @item %S - Fundamental block size (for block counts)
11065 @item %t - Type in hex
11066 @item %T - Type in human readable form
11070 Time stamps are listed according to the time zone rules specified by
11071 the @env{TZ} environment variable, or by the system default rules if
11072 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11073 with @env{TZ}, libc, The GNU C Library Reference Manual}.
11078 @node sync invocation
11079 @section @command{sync}: Synchronize data on disk with memory
11082 @cindex synchronize disk and memory
11084 @cindex superblock, writing
11085 @cindex inodes, written buffered
11086 @command{sync} writes any data buffered in memory out to disk. This can
11087 include (but is not limited to) modified superblocks, modified inodes,
11088 and delayed reads and writes. This must be implemented by the kernel;
11089 The @command{sync} program does nothing but exercise the @code{sync} system
11092 @cindex crashes and corruption
11093 The kernel keeps data in memory to avoid doing (relatively slow) disk
11094 reads and writes. This improves performance, but if the computer
11095 crashes, data may be lost or the file system corrupted as a
11096 result. The @command{sync} command ensures everything in memory
11097 is written to disk.
11099 Any arguments are ignored, except for a lone @option{--help} or
11100 @option{--version} (@pxref{Common options}).
11105 @node truncate invocation
11106 @section @command{truncate}: Shrink or extend the size of a file
11109 @cindex truncating, file sizes
11111 @command{truncate} shrinks or extends the size of each @var{file} to the
11112 specified size. Synopsis:
11115 truncate @var{option}@dots{} @var{file}@dots{}
11118 @cindex files, creating
11119 Any @var{file} that does not exist is created.
11121 @cindex sparse files, creating
11122 @cindex holes, creating files with
11123 If a @var{file} is larger than the specified size, the extra data is lost.
11124 If a @var{file} is shorter, it is extended and the extended part (or hole)
11125 reads as zero bytes.
11127 The program accepts the following options. Also see @ref{Common options}.
11134 @opindex --no-create
11135 Do not create files that do not exist.
11140 @opindex --io-blocks
11141 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
11143 @item -r @var{rfile}
11144 @itemx --reference=@var{rfile}
11146 @opindex --reference
11147 Base the size of each @var{file} on the size of @var{rfile}.
11149 @item -s @var{size}
11150 @itemx --size=@var{size}
11153 Set or adjust the size of each @var{file} according to @var{size}.
11154 @multiplierSuffixesNoBlocks{size}
11156 @var{size} may also be prefixed by one of the following to adjust
11157 the size of each @var{file} based on their current size:
11159 @samp{+} => extend by
11160 @samp{-} => reduce by
11161 @samp{<} => at most
11162 @samp{>} => at least
11163 @samp{/} => round down to multiple of
11164 @samp{%} => round up to multiple of
11172 @node Printing text
11173 @chapter Printing text
11175 @cindex printing text, commands for
11176 @cindex commands for printing text
11178 This section describes commands that display text strings.
11181 * echo invocation:: Print a line of text.
11182 * printf invocation:: Format and print data.
11183 * yes invocation:: Print a string until interrupted.
11187 @node echo invocation
11188 @section @command{echo}: Print a line of text
11191 @cindex displaying text
11192 @cindex printing text
11193 @cindex text, displaying
11194 @cindex arbitrary text, displaying
11196 @command{echo} writes each given @var{string} to standard output, with a
11197 space between each and a newline after the last one. Synopsis:
11200 echo [@var{option}]@dots{} [@var{string}]@dots{}
11203 @mayConflictWithShellBuiltIn{echo}
11205 The program accepts the following options. Also see @ref{Common options}.
11206 Options must precede operands, and the normally-special argument
11207 @samp{--} has no special meaning and is treated like any other
11213 Do not output the trailing newline.
11217 @cindex backslash escapes
11218 Enable interpretation of the following backslash-escaped characters in
11227 produce no further output
11243 the eight-bit value that is the octal number @var{nnn}
11244 (zero to three octal digits), if @var{nnn} is
11245 a nine-bit value, the ninth bit is ignored
11247 the eight-bit value that is the octal number @var{nnn}
11248 (one to three octal digits), if @var{nnn} is
11249 a nine-bit value, the ninth bit is ignored
11251 the eight-bit value that is the hexadecimal number @var{hh}
11252 (one or two hexadecimal digits)
11257 @cindex backslash escapes
11258 Disable interpretation of backslash escapes in each @var{string}.
11259 This is the default. If @option{-e} and @option{-E} are both
11260 specified, the last one given takes effect.
11264 @vindex POSIXLY_CORRECT
11265 If the @env{POSIXLY_CORRECT} environment variable is set, then when
11266 @command{echo}'s first argument is not @option{-n} it outputs
11267 option-like arguments instead of treating them as options. For
11268 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
11269 plain @samp{hello}.
11271 @acronym{POSIX} does not require support for any options, and says
11272 that the behavior of @command{echo} is implementation-defined if any
11273 @var{string} contains a backslash or if the first argument is
11274 @option{-n}. Portable programs can use the @command{printf} command
11275 if they need to omit trailing newlines or output control characters or
11276 backslashes. @xref{printf invocation}.
11281 @node printf invocation
11282 @section @command{printf}: Format and print data
11285 @command{printf} does formatted printing of text. Synopsis:
11288 printf @var{format} [@var{argument}]@dots{}
11291 @command{printf} prints the @var{format} string, interpreting @samp{%}
11292 directives and @samp{\} escapes to format numeric and string arguments
11293 in a way that is mostly similar to the C @samp{printf} function.
11294 @xref{Output Conversion Syntax,, @command{printf} format directives,
11295 libc, The GNU C Library Reference Manual}, for details.
11296 The differences are listed below.
11298 @mayConflictWithShellBuiltIn{printf}
11303 The @var{format} argument is reused as necessary to convert all the
11304 given @var{argument}s. For example, the command @samp{printf %s a b}
11308 Missing @var{argument}s are treated as null strings or as zeros,
11309 depending on whether the context expects a string or a number. For
11310 example, the command @samp{printf %sx%d} prints @samp{x0}.
11314 An additional escape, @samp{\c}, causes @command{printf} to produce no
11315 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
11316 E} prints @samp{ABC}.
11319 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
11320 digits, as opposed to C where it can have an unlimited number of
11321 digits. For example, the command @samp{printf '\x07e'} prints two
11322 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
11327 @command{printf} has an additional directive, @samp{%b}, which prints its
11328 argument string with @samp{\} escapes interpreted in the same way as in
11329 the @var{format} string, except that octal escapes are of the form
11330 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If
11331 @samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
11332 If a precision is also given, it limits the number of bytes printed
11333 from the converted string.
11336 Numeric arguments must be single C constants, possibly with leading
11337 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
11341 @vindex POSIXLY_CORRECT
11342 If the leading character of a numeric argument is @samp{"} or @samp{'}
11343 then its value is the numeric value of the immediately following
11344 character. Any remaining characters are silently ignored if the
11345 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
11346 warning is printed. For example, @samp{printf "%d" "'a"} outputs
11347 @samp{97} on hosts that use the @acronym{ASCII} character set, since
11348 @samp{a} has the numeric value 97 in @acronym{ASCII}.
11353 A floating-point argument must use a period before any fractional
11354 digits, but is printed according to the @env{LC_NUMERIC} category of the
11355 current locale. For example, in a locale whose radix character is a
11356 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11357 the command @samp{printf %g 3,14} is an error.
11358 @xref{Floating point}.
11362 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11363 (if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
11364 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11365 digits) specifying a character to print.
11366 Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
11367 @command{printf} ignores the ninth bit.
11368 For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.
11373 @cindex ISO/IEC 10646
11375 @command{printf} interprets two character syntaxes introduced in
11376 @acronym{ISO} C 99:
11377 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
11378 characters, specified as
11379 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11380 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11381 @command{printf} outputs the Unicode characters
11382 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11383 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11384 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11386 The processing of @samp{\u} and @samp{\U} requires a full-featured
11387 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11388 or when @code{libiconv} is installed prior to this package. Otherwise
11389 @samp{\u} and @samp{\U} will print as-is.
11391 The only options are a lone @option{--help} or
11392 @option{--version}. @xref{Common options}.
11393 Options must precede operands.
11395 The Unicode character syntaxes are useful for writing strings in a locale
11396 independent way. For example, a string containing the Euro currency symbol
11399 $ env printf '\u20AC 14.95'
11403 will be output correctly in all locales supporting the Euro symbol
11404 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11407 $ env printf '\u4e2d\u6587'
11411 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11413 Note that in these examples, the @command{printf} command has been
11414 invoked via @command{env} to ensure that we run the program found via
11415 your shell's search path, and not a shell alias or a built-in function.
11417 For larger strings, you don't need to look up the hexadecimal code
11418 values of each character one by one. @acronym{ASCII} characters mixed with \u
11419 escape sequences is also known as the JAVA source file encoding. You can
11420 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11421 is how to convert a piece of text into a shell script which will output
11422 this text in a locale-independent way:
11425 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11426 '\u4e2d\u6587\n' > sample.txt
11427 $ recode BIG5..JAVA < sample.txt \
11428 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11435 @node yes invocation
11436 @section @command{yes}: Print a string until interrupted
11439 @cindex repeated output of a string
11441 @command{yes} prints the command line arguments, separated by spaces and
11442 followed by a newline, forever until it is killed. If no arguments are
11443 given, it prints @samp{y} followed by a newline forever until killed.
11445 Upon a write error, @command{yes} exits with status @samp{1}.
11447 The only options are a lone @option{--help} or @option{--version}.
11448 To output an argument that begins with
11449 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11450 @xref{Common options}.
11454 @chapter Conditions
11457 @cindex commands for exit status
11458 @cindex exit status commands
11460 This section describes commands that are primarily useful for their exit
11461 status, rather than their output. Thus, they are often used as the
11462 condition of shell @code{if} statements, or as the last command in a
11466 * false invocation:: Do nothing, unsuccessfully.
11467 * true invocation:: Do nothing, successfully.
11468 * test invocation:: Check file types and compare values.
11469 * expr invocation:: Evaluate expressions.
11473 @node false invocation
11474 @section @command{false}: Do nothing, unsuccessfully
11477 @cindex do nothing, unsuccessfully
11478 @cindex failure exit status
11479 @cindex exit status of @command{false}
11481 @command{false} does nothing except return an exit status of 1, meaning
11482 @dfn{failure}. It can be used as a place holder in shell scripts
11483 where an unsuccessful command is needed.
11484 In most modern shells, @command{false} is a built-in command, so when
11485 you use @samp{false} in a script, you're probably using the built-in
11486 command, not the one documented here.
11488 @command{false} honors the @option{--help} and @option{--version} options.
11490 This version of @command{false} is implemented as a C program, and is thus
11491 more secure and faster than a shell script implementation, and may safely
11492 be used as a dummy shell for the purpose of disabling accounts.
11494 Note that @command{false} (unlike all other programs documented herein)
11495 exits unsuccessfully, even when invoked with
11496 @option{--help} or @option{--version}.
11498 Portable programs should not assume that the exit status of
11499 @command{false} is 1, as it is greater than 1 on some
11500 non-@acronym{GNU} hosts.
11503 @node true invocation
11504 @section @command{true}: Do nothing, successfully
11507 @cindex do nothing, successfully
11509 @cindex successful exit
11510 @cindex exit status of @command{true}
11512 @command{true} does nothing except return an exit status of 0, meaning
11513 @dfn{success}. It can be used as a place holder in shell scripts
11514 where a successful command is needed, although the shell built-in
11515 command @code{:} (colon) may do the same thing faster.
11516 In most modern shells, @command{true} is a built-in command, so when
11517 you use @samp{true} in a script, you're probably using the built-in
11518 command, not the one documented here.
11520 @command{true} honors the @option{--help} and @option{--version} options.
11522 Note, however, that it is possible to cause @command{true}
11523 to exit with nonzero status: with the @option{--help} or @option{--version}
11524 option, and with standard
11525 output already closed or redirected to a file that evokes an I/O error.
11526 For example, using a Bourne-compatible shell:
11529 $ ./true --version >&-
11530 ./true: write error: Bad file number
11531 $ ./true --version > /dev/full
11532 ./true: write error: No space left on device
11535 This version of @command{true} is implemented as a C program, and is thus
11536 more secure and faster than a shell script implementation, and may safely
11537 be used as a dummy shell for the purpose of disabling accounts.
11539 @node test invocation
11540 @section @command{test}: Check file types and compare values
11543 @cindex check file types
11544 @cindex compare values
11545 @cindex expression evaluation
11547 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11548 evaluation of the conditional expression @var{expr}. Each part of the
11549 expression must be a separate argument.
11551 @command{test} has file status checks, string operators, and numeric
11552 comparison operators.
11554 @command{test} has an alternate form that uses opening and closing
11555 square brackets instead a leading @samp{test}. For example, instead
11556 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11557 brackets must be separate arguments; for example, @samp{[-d /]} does
11558 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11559 @var{expr} ]} have the same meaning, only the former form is discussed
11565 test @var{expression}
11567 [ @var{expression} ]
11572 @mayConflictWithShellBuiltIn{test}
11574 If @var{expression} is omitted, @command{test} returns false.
11575 If @var{expression} is a single argument,
11576 @command{test} returns false if the argument is null and true
11577 otherwise. The argument
11578 can be any string, including strings like @samp{-d}, @samp{-1},
11579 @samp{--}, @samp{--help}, and @samp{--version} that most other
11580 programs would treat as options. To get help and version information,
11581 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11582 the usual closing brackets. @xref{Common options}.
11584 @cindex exit status of @command{test}
11588 0 if the expression is true,
11589 1 if the expression is false,
11590 2 if an error occurred.
11594 * File type tests:: -[bcdfhLpSt]
11595 * Access permission tests:: -[gkruwxOG]
11596 * File characteristic tests:: -e -s -nt -ot -ef
11597 * String tests:: -z -n = == !=
11598 * Numeric tests:: -eq -ne -lt -le -gt -ge
11599 * Connectives for test:: ! -a -o
11603 @node File type tests
11604 @subsection File type tests
11606 @cindex file type tests
11608 These options test for particular types of files. (Everything's a file,
11609 but not all files are the same!)
11613 @item -b @var{file}
11615 @cindex block special check
11616 True if @var{file} exists and is a block special device.
11618 @item -c @var{file}
11620 @cindex character special check
11621 True if @var{file} exists and is a character special device.
11623 @item -d @var{file}
11625 @cindex directory check
11626 True if @var{file} exists and is a directory.
11628 @item -f @var{file}
11630 @cindex regular file check
11631 True if @var{file} exists and is a regular file.
11633 @item -h @var{file}
11634 @itemx -L @var{file}
11637 @cindex symbolic link check
11638 True if @var{file} exists and is a symbolic link.
11639 Unlike all other file-related tests, this test does not dereference
11640 @var{file} if it is a symbolic link.
11642 @item -p @var{file}
11644 @cindex named pipe check
11645 True if @var{file} exists and is a named pipe.
11647 @item -S @var{file}
11649 @cindex socket check
11650 True if @var{file} exists and is a socket.
11654 @cindex terminal check
11655 True if @var{fd} is a file descriptor that is associated with a
11661 @node Access permission tests
11662 @subsection Access permission tests
11664 @cindex access permission tests
11665 @cindex permission tests
11667 These options test for particular access permissions.
11671 @item -g @var{file}
11673 @cindex set-group-ID check
11674 True if @var{file} exists and has its set-group-ID bit set.
11676 @item -k @var{file}
11678 @cindex sticky bit check
11679 True if @var{file} exists and has its @dfn{sticky} bit set.
11681 @item -r @var{file}
11683 @cindex readable file check
11684 True if @var{file} exists and read permission is granted.
11686 @item -u @var{file}
11688 @cindex set-user-ID check
11689 True if @var{file} exists and has its set-user-ID bit set.
11691 @item -w @var{file}
11693 @cindex writable file check
11694 True if @var{file} exists and write permission is granted.
11696 @item -x @var{file}
11698 @cindex executable file check
11699 True if @var{file} exists and execute permission is granted
11700 (or search permission, if it is a directory).
11702 @item -O @var{file}
11704 @cindex owned by effective user ID check
11705 True if @var{file} exists and is owned by the current effective user ID.
11707 @item -G @var{file}
11709 @cindex owned by effective group ID check
11710 True if @var{file} exists and is owned by the current effective group ID.
11714 @node File characteristic tests
11715 @subsection File characteristic tests
11717 @cindex file characteristic tests
11719 These options test other file characteristics.
11723 @item -e @var{file}
11725 @cindex existence-of-file check
11726 True if @var{file} exists.
11728 @item -s @var{file}
11730 @cindex nonempty file check
11731 True if @var{file} exists and has a size greater than zero.
11733 @item @var{file1} -nt @var{file2}
11735 @cindex newer-than file check
11736 True if @var{file1} is newer (according to modification date) than
11737 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11739 @item @var{file1} -ot @var{file2}
11741 @cindex older-than file check
11742 True if @var{file1} is older (according to modification date) than
11743 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11745 @item @var{file1} -ef @var{file2}
11747 @cindex same file check
11748 @cindex hard link check
11749 True if @var{file1} and @var{file2} have the same device and inode
11750 numbers, i.e., if they are hard links to each other.
11756 @subsection String tests
11758 @cindex string tests
11760 These options test string characteristics. You may need to quote
11761 @var{string} arguments for the shell. For example:
11767 The quotes here prevent the wrong arguments from being passed to
11768 @command{test} if @samp{$V} is empty or contains special characters.
11772 @item -z @var{string}
11774 @cindex zero-length string check
11775 True if the length of @var{string} is zero.
11777 @item -n @var{string}
11778 @itemx @var{string}
11780 @cindex nonzero-length string check
11781 True if the length of @var{string} is nonzero.
11783 @item @var{string1} = @var{string2}
11785 @cindex equal string check
11786 True if the strings are equal.
11788 @item @var{string1} == @var{string2}
11790 @cindex equal string check
11791 True if the strings are equal (synonym for =).
11793 @item @var{string1} != @var{string2}
11795 @cindex not-equal string check
11796 True if the strings are not equal.
11801 @node Numeric tests
11802 @subsection Numeric tests
11804 @cindex numeric tests
11805 @cindex arithmetic tests
11807 Numeric relational operators. The arguments must be entirely numeric
11808 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11809 which evaluates to the length of @var{string}.
11813 @item @var{arg1} -eq @var{arg2}
11814 @itemx @var{arg1} -ne @var{arg2}
11815 @itemx @var{arg1} -lt @var{arg2}
11816 @itemx @var{arg1} -le @var{arg2}
11817 @itemx @var{arg1} -gt @var{arg2}
11818 @itemx @var{arg1} -ge @var{arg2}
11825 These arithmetic binary operators return true if @var{arg1} is equal,
11826 not-equal, less-than, less-than-or-equal, greater-than, or
11827 greater-than-or-equal than @var{arg2}, respectively.
11834 test -1 -gt -2 && echo yes
11836 test -l abc -gt 1 && echo yes
11839 @error{} test: integer expression expected before -eq
11843 @node Connectives for test
11844 @subsection Connectives for @command{test}
11846 @cindex logical connectives
11847 @cindex connectives, logical
11849 The usual logical connectives.
11855 True if @var{expr} is false.
11857 @item @var{expr1} -a @var{expr2}
11859 @cindex logical and operator
11860 @cindex and operator
11861 True if both @var{expr1} and @var{expr2} are true.
11863 @item @var{expr1} -o @var{expr2}
11865 @cindex logical or operator
11866 @cindex or operator
11867 True if either @var{expr1} or @var{expr2} is true.
11872 @node expr invocation
11873 @section @command{expr}: Evaluate expressions
11876 @cindex expression evaluation
11877 @cindex evaluation of expressions
11879 @command{expr} evaluates an expression and writes the result on standard
11880 output. Each token of the expression must be a separate argument.
11882 Operands are either integers or strings. Integers consist of one or
11883 more decimal digits, with an optional leading @samp{-}.
11884 @command{expr} converts
11885 anything appearing in an operand position to an integer or a string
11886 depending on the operation being applied to it.
11888 Strings are not quoted for @command{expr} itself, though you may need to
11889 quote them to protect characters with special meaning to the shell,
11890 e.g., spaces. However, regardless of whether it is quoted, a string
11891 operand should not be a parenthesis or any of @command{expr}'s
11892 operators like @code{+}, so you cannot safely pass an arbitrary string
11893 @code{$str} to expr merely by quoting it to the shell. One way to
11894 work around this is to use the @sc{gnu} extension @code{+},
11895 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11896 @code{@w{" $str"}} and to adjust the rest of the expression to take
11897 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11899 You should not pass a negative integer or a string with leading
11900 @samp{-} as @command{expr}'s first argument, as it might be
11901 misinterpreted as an option; this can be avoided by parenthesization.
11902 Also, portable scripts should not use a string operand that happens to
11903 take the form of an integer; this can be worked around by inserting
11904 leading spaces as mentioned above.
11906 @cindex parentheses for grouping
11907 Operators may be given as infix symbols or prefix keywords. Parentheses
11908 may be used for grouping in the usual manner. You must quote
11909 parentheses and many operators to avoid the shell evaluating them,
11912 When built with support for the GNU MP library, @command{expr} uses
11913 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11914 types and may fail due to arithmetic overflow.
11916 The only options are @option{--help} and @option{--version}. @xref{Common
11917 options}. Options must precede operands.
11919 @cindex exit status of @command{expr}
11923 0 if the expression is neither null nor 0,
11924 1 if the expression is null or 0,
11925 2 if the expression is invalid,
11926 3 if an internal error occurred (e.g., arithmetic overflow).
11930 * String expressions:: + : match substr index length
11931 * Numeric expressions:: + - * / %
11932 * Relations for expr:: | & < <= = == != >= >
11933 * Examples of expr:: Examples.
11937 @node String expressions
11938 @subsection String expressions
11940 @cindex string expressions
11941 @cindex expressions, string
11943 @command{expr} supports pattern matching and other string operators. These
11944 have higher precedence than both the numeric and relational operators (in
11945 the next sections).
11949 @item @var{string} : @var{regex}
11950 @cindex pattern matching
11951 @cindex regular expression matching
11952 @cindex matching patterns
11953 Perform pattern matching. The arguments are converted to strings and the
11954 second is considered to be a (basic, a la GNU @code{grep}) regular
11955 expression, with a @code{^} implicitly prepended. The first argument is
11956 then matched against this regular expression.
11958 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11959 @code{:} expression returns the part of @var{string} that matched the
11960 subexpression; otherwise, it returns the number of characters matched.
11962 If the match fails, the @code{:} operator returns the null string if
11963 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11965 @kindex \( @r{regexp operator}
11966 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11967 value; additional pairs are meaningful only for grouping the regular
11968 expression operators.
11970 @kindex \+ @r{regexp operator}
11971 @kindex \? @r{regexp operator}
11972 @kindex \| @r{regexp operator}
11973 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11974 operators which respectively match one or more, zero or one, or separate
11975 alternatives. SunOS and other @command{expr}'s treat these as regular
11976 characters. (@acronym{POSIX} allows either behavior.)
11977 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11978 regular expression syntax. Some examples are in @ref{Examples of expr}.
11980 @item match @var{string} @var{regex}
11982 An alternative way to do pattern matching. This is the same as
11983 @w{@samp{@var{string} : @var{regex}}}.
11985 @item substr @var{string} @var{position} @var{length}
11987 Returns the substring of @var{string} beginning at @var{position}
11988 with length at most @var{length}. If either @var{position} or
11989 @var{length} is negative, zero, or non-numeric, returns the null string.
11991 @item index @var{string} @var{charset}
11993 Returns the first position in @var{string} where the first character in
11994 @var{charset} was found. If no character in @var{charset} is found in
11995 @var{string}, return 0.
11997 @item length @var{string}
11999 Returns the length of @var{string}.
12001 @item + @var{token}
12003 Interpret @var{token} as a string, even if it is a keyword like @var{match}
12004 or an operator like @code{/}.
12005 This makes it possible to test @code{expr length + "$x"} or
12006 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
12007 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
12008 This operator is a @acronym{GNU} extension. Portable shell scripts should use
12009 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
12013 To make @command{expr} interpret keywords as strings, you must use the
12014 @code{quote} operator.
12017 @node Numeric expressions
12018 @subsection Numeric expressions
12020 @cindex numeric expressions
12021 @cindex expressions, numeric
12023 @command{expr} supports the usual numeric operators, in order of increasing
12024 precedence. These numeric operators have lower precedence than the
12025 string operators described in the previous section, and higher precedence
12026 than the connectives (next section).
12034 @cindex subtraction
12035 Addition and subtraction. Both arguments are converted to integers;
12036 an error occurs if this cannot be done.
12042 @cindex multiplication
12045 Multiplication, division, remainder. Both arguments are converted to
12046 integers; an error occurs if this cannot be done.
12051 @node Relations for expr
12052 @subsection Relations for @command{expr}
12054 @cindex connectives, logical
12055 @cindex logical connectives
12056 @cindex relations, numeric or string
12058 @command{expr} supports the usual logical connectives and relations. These
12059 have lower precedence than the string and numeric operators
12060 (previous sections). Here is the list, lowest-precedence operator first.
12066 @cindex logical or operator
12067 @cindex or operator
12068 Returns its first argument if that is neither null nor zero, otherwise
12069 its second argument if it is neither null nor zero, otherwise 0. It
12070 does not evaluate its second argument if its first argument is neither
12075 @cindex logical and operator
12076 @cindex and operator
12077 Return its first argument if neither argument is null or zero, otherwise
12078 0. It does not evaluate its second argument if its first argument is
12081 @item < <= = == != >= >
12088 @cindex comparison operators
12090 Compare the arguments and return 1 if the relation is true, 0 otherwise.
12091 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
12092 both arguments to integers and do a numeric comparison; if either
12093 conversion fails, it does a lexicographic comparison using the character
12094 collating sequence specified by the @env{LC_COLLATE} locale.
12099 @node Examples of expr
12100 @subsection Examples of using @command{expr}
12102 @cindex examples of @command{expr}
12103 Here are a few examples, including quoting for shell metacharacters.
12105 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
12108 foo=`expr $foo + 1`
12111 To print the non-directory part of the file name stored in
12112 @code{$fname}, which need not contain a @code{/}:
12115 expr $fname : '.*/\(.*\)' '|' $fname
12118 An example showing that @code{\+} is an operator:
12126 expr abc : 'a\(.\)c'
12128 expr index abcdef cz
12131 @error{} expr: syntax error
12132 expr index + index a
12138 @chapter Redirection
12140 @cindex redirection
12141 @cindex commands for redirection
12143 Unix shells commonly provide several forms of @dfn{redirection}---ways
12144 to change the input source or output destination of a command. But one
12145 useful redirection is performed by a separate command, not by the shell;
12146 it's described here.
12149 * tee invocation:: Redirect output to multiple files or processes.
12153 @node tee invocation
12154 @section @command{tee}: Redirect output to multiple files or processes
12157 @cindex pipe fitting
12158 @cindex destinations, multiple output
12159 @cindex read from stdin and write to stdout and files
12161 The @command{tee} command copies standard input to standard output and also
12162 to any files given as arguments. This is useful when you want not only
12163 to send some data down a pipe, but also to save a copy. Synopsis:
12166 tee [@var{option}]@dots{} [@var{file}]@dots{}
12169 If a file being written to does not already exist, it is created. If a
12170 file being written to already exists, the data it previously contained
12171 is overwritten unless the @option{-a} option is used.
12173 A @var{file} of @samp{-} causes @command{tee} to send another copy of
12174 input to standard output, but this is typically not that useful as the
12175 copies are interleaved.
12177 The program accepts the following options. Also see @ref{Common options}.
12184 Append standard input to the given files rather than overwriting
12188 @itemx --ignore-interrupts
12190 @opindex --ignore-interrupts
12191 Ignore interrupt signals.
12195 The @command{tee} command is useful when you happen to be transferring a large
12196 amount of data and also want to summarize that data without reading
12197 it a second time. For example, when you are downloading a DVD image,
12198 you often want to verify its signature or checksum right away.
12199 The inefficient way to do it is simply:
12202 wget http://example.com/some.iso && sha1sum some.iso
12205 One problem with the above is that it makes you wait for the
12206 download to complete before starting the time-consuming SHA1 computation.
12207 Perhaps even more importantly, the above requires reading
12208 the DVD image a second time (the first was from the network).
12210 The efficient way to do it is to interleave the download
12211 and SHA1 computation. Then, you'll get the checksum for
12212 free, because the entire process parallelizes so well:
12215 # slightly contrived, to demonstrate process substitution
12216 wget -O - http://example.com/dvd.iso \
12217 | tee >(sha1sum > dvd.sha1) > dvd.iso
12220 That makes @command{tee} write not just to the expected output file,
12221 but also to a pipe running @command{sha1sum} and saving the final
12222 checksum in a file named @file{dvd.sha1}.
12224 Note, however, that this example relies on a feature of modern shells
12225 called @dfn{process substitution}
12226 (the @samp{>(command)} syntax, above;
12227 @xref{Process Substitution,,Process Substitution, bashref,
12228 The Bash Reference Manual}.),
12229 so it works with @command{zsh}, @command{bash}, and @command{ksh},
12230 but not with @command{/bin/sh}. So if you write code like this
12231 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
12233 Since the above example writes to one file and one process,
12234 a more conventional and portable use of @command{tee} is even better:
12237 wget -O - http://example.com/dvd.iso \
12238 | tee dvd.iso | sha1sum > dvd.sha1
12241 You can extend this example to make @command{tee} write to two processes,
12242 computing MD5 and SHA1 checksums in parallel. In this case,
12243 process substitution is required:
12246 wget -O - http://example.com/dvd.iso \
12247 | tee >(sha1sum > dvd.sha1) \
12248 >(md5sum > dvd.md5) \
12252 This technique is also useful when you want to make a @emph{compressed}
12253 copy of the contents of a pipe.
12254 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
12255 For a large hierarchy, @samp{du -ak} can run for a long time,
12256 and can easily produce terabytes of data, so you won't want to
12257 rerun the command unnecessarily. Nor will you want to save
12258 the uncompressed output.
12260 Doing it the inefficient way, you can't even start the GUI
12261 until after you've compressed all of the @command{du} output:
12264 du -ak | gzip -9 > /tmp/du.gz
12265 gzip -d /tmp/du.gz | xdiskusage -a
12268 With @command{tee} and process substitution, you start the GUI
12269 right away and eliminate the decompression completely:
12272 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
12275 Finally, if you regularly create more than one type of
12276 compressed tarball at once, for example when @code{make dist} creates
12277 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
12278 there may be a better way.
12279 Typical @command{automake}-generated @file{Makefile} rules create
12280 the two compressed tar archives with commands in sequence, like this
12281 (slightly simplified):
12284 tardir=your-pkg-M.N
12285 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
12286 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12289 However, if the hierarchy you are archiving and compressing is larger
12290 than a couple megabytes, and especially if you are using a multi-processor
12291 system with plenty of memory, then you can do much better by reading the
12292 directory contents only once and running the compression programs in parallel:
12295 tardir=your-pkg-M.N
12296 tar chof - "$tardir" \
12297 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
12298 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12304 @node File name manipulation
12305 @chapter File name manipulation
12307 @cindex file name manipulation
12308 @cindex manipulation of file names
12309 @cindex commands for file name manipulation
12311 This section describes commands that manipulate file names.
12314 * basename invocation:: Strip directory and suffix from a file name.
12315 * dirname invocation:: Strip last file name component.
12316 * pathchk invocation:: Check file name validity and portability.
12317 * mktemp invocation:: Create temporary file or directory.
12321 @node basename invocation
12322 @section @command{basename}: Strip directory and suffix from a file name
12325 @cindex strip directory and suffix from file names
12326 @cindex directory, stripping from file names
12327 @cindex suffix, stripping from file names
12328 @cindex file names, stripping directory and suffix
12329 @cindex leading directory components, stripping
12331 @command{basename} removes any leading directory components from
12332 @var{name}. Synopsis:
12335 basename @var{name} [@var{suffix}]
12338 If @var{suffix} is specified and is identical to the end of @var{name},
12339 it is removed from @var{name} as well. Note that since trailing slashes
12340 are removed prior to suffix matching, @var{suffix} will do nothing if it
12341 contains slashes. @command{basename} prints the result on standard
12344 @c This test is used both here and in the section on dirname.
12345 @macro basenameAndDirname
12346 Together, @command{basename} and @command{dirname} are designed such
12347 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
12348 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
12349 for everything except file names containing a trailing newline.
12351 @basenameAndDirname
12353 @acronym{POSIX} allows the implementation to define the results if
12354 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
12355 @command{basename} returns the empty string. In the latter case, the
12356 result is @samp{//} on platforms where @var{//} is distinct from
12357 @var{/}, and @samp{/} on platforms where there is no difference.
12359 The only options are @option{--help} and @option{--version}. @xref{Common
12360 options}. Options must precede operands.
12368 basename /usr/bin/sort
12371 basename include/stdio.h .h
12375 @node dirname invocation
12376 @section @command{dirname}: Strip last file name component
12379 @cindex directory components, printing
12380 @cindex stripping non-directory suffix
12381 @cindex non-directory suffix, stripping
12383 @command{dirname} prints all but the final slash-delimited component of
12384 @var{name}. Slashes on either side of the final component are also
12385 removed. If the string contains no slash, @command{dirname} prints
12386 @samp{.} (meaning the current directory). Synopsis:
12392 @var{name} need not be a file name, but if it is, this operation
12393 effectively lists the directory that contains the final component,
12394 including the case when the final component is itself a directory.
12396 @basenameAndDirname
12398 @acronym{POSIX} allows the implementation to define the results if
12399 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12400 result is @samp{//} on platforms where @var{//} is distinct from
12401 @var{/}, and @samp{/} on platforms where there is no difference.
12403 The only options are @option{--help} and @option{--version}. @xref{Common
12411 # Output "/usr/bin".
12412 dirname /usr/bin/sort
12413 dirname /usr/bin//.//
12420 @node pathchk invocation
12421 @section @command{pathchk}: Check file name validity and portability
12424 @cindex file names, checking validity and portability
12425 @cindex valid file names, checking for
12426 @cindex portable file names, checking for
12428 @command{pathchk} checks validity and portability of file names. Synopsis:
12431 pathchk [@var{option}]@dots{} @var{name}@dots{}
12434 For each @var{name}, @command{pathchk} prints an error message if any of
12435 these conditions is true:
12439 One of the existing directories in @var{name} does not have search
12440 (execute) permission,
12442 The length of @var{name} is larger than the maximum supported by the
12445 The length of one component of @var{name} is longer than
12446 its file system's maximum.
12449 A nonexistent @var{name} is not an error, so long a file with that
12450 name could be created under the above conditions.
12452 The program accepts the following options. Also see @ref{Common options}.
12453 Options must precede operands.
12459 Instead of performing checks based on the underlying file system,
12460 print an error message if any of these conditions is true:
12464 A file name is empty.
12467 A file name contains a character outside the @acronym{POSIX} portable file
12468 name character set, namely, the ASCII letters and digits, @samp{.},
12469 @samp{_}, @samp{-}, and @samp{/}.
12472 The length of a file name or one of its components exceeds the
12473 @acronym{POSIX} minimum limits for portability.
12478 Print an error message if a file name is empty, or if it contains a component
12479 that begins with @samp{-}.
12481 @item --portability
12482 @opindex --portability
12483 Print an error message if a file name is not portable to all @acronym{POSIX}
12484 hosts. This option is equivalent to @samp{-p -P}.
12488 @cindex exit status of @command{pathchk}
12492 0 if all specified file names passed all checks,
12496 @node mktemp invocation
12497 @section @command{mktemp}: Create temporary file or directory
12500 @cindex file names, creating temporary
12501 @cindex directory, creating temporary
12502 @cindex temporary files and directories
12504 @command{mktemp} manages the creation of temporary files and
12505 directories. Synopsis:
12508 mktemp [@var{option}]@dots{} [@var{template}]
12511 Safely create a temporary file or directory based on @var{template},
12512 and print its name. If given, @var{template} must include at least
12513 three consecutive @samp{X}s in the last component. If omitted, the template
12514 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12515 implied. The final run of @samp{X}s in the @var{template} will be replaced
12516 by alpha-numeric characters; thus, on a case-sensitive file system,
12517 and with a @var{template} including a run of @var{n} instances of @samp{X},
12518 there are @samp{62**@var{n}} potential file names.
12520 Older scripts used to create temporary files by simply joining the
12521 name of the program with the process id (@samp{$$}) as a suffix.
12522 However, that naming scheme is easily predictable, and suffers from a
12523 race condition where the attacker can create an appropriately named
12524 symbolic link, such that when the script then opens a handle to what
12525 it thought was an unused file, it is instead modifying an existing
12526 file. Using the same scheme to create a directory is slightly safer,
12527 since the @command{mkdir} will fail if the target already exists, but
12528 it is still inferior because it allows for denial of service attacks.
12529 Therefore, modern scripts should use the @command{mktemp} command to
12530 guarantee that the generated name will be unpredictable, and that
12531 knowledge of the temporary file name implies that the file was created
12532 by the current script and cannot be modified by other users.
12534 When creating a file, the resulting file has read and write
12535 permissions for the current user, but no permissions for the group or
12536 others; these permissions are reduced if the current umask is more
12539 Here are some examples (although note that if you repeat them, you
12540 will most likely get different file names):
12545 Create a temporary file in the current directory.
12552 Create a temporary file with a known suffix.
12554 $ mktemp --suffix=.txt file-XXXX
12556 $ mktemp file-XXXX-XXXX.txt
12561 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12562 but falling back to the current directory rather than @file{/tmp}.
12563 Note that @command{mktemp} does not create fifos, but can create a
12564 secure directory in which the fifo can live. Exit the shell if the
12565 directory or fifo could not be created.
12567 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12569 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12573 Create and use a temporary file if possible, but ignore failure. The
12574 file will reside in the directory named by @env{TMPDIR}, if specified,
12575 or else in @file{/tmp}.
12577 $ file=$(mktemp -q) && @{
12578 > # Safe to use $file only within this block. Use quotes,
12579 > # since $TMPDIR, and thus $file, may contain whitespace.
12580 > echo ... > "$file"
12586 Act as a semi-random character generator (it is not fully random,
12587 since it is impacted by the contents of the current directory). To
12588 avoid security holes, do not use the resulting names to create a file.
12598 The program accepts the following options. Also see @ref{Common options}.
12605 @opindex --directory
12606 Create a directory rather than a file. The directory will have read,
12607 write, and search permissions for the current user, but no permissions
12608 for the group or others; these permissions are reduced if the current
12609 umask is more restrictive.
12615 Suppress diagnostics about failure to create a file or directory. The
12616 exit status will still reflect whether a file was created.
12622 Generate a temporary name that does not name an existing file, without
12623 changing the file system contents. Using the output of this command
12624 to create a new file is inherently unsafe, as there is a window of
12625 time between generating the name and using it where another process
12626 can create an object by the same name.
12629 @itemx --tmpdir[=@var{dir}]
12632 Treat @var{template} relative to the directory @var{dir}. If
12633 @var{dir} is not specified (only possible with the long option
12634 @option{--tmpdir}) or is the empty string, use the value of
12635 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12636 specified, @var{template} must not be absolute. However,
12637 @var{template} can still contain slashes, although intermediate
12638 directories must already exist.
12640 @item --suffix=@var{suffix}
12642 Append @var{suffix} to the @var{template}. @var{suffix} must not
12643 contain slash. If @option{--suffix} is specified, @var{template} must
12644 end in @samp{X}; if it is not specified, then an appropriate
12645 @option{--suffix} is inferred by finding the last @samp{X} in
12646 @var{template}. This option exists for use with the default
12647 @var{template} and for the creation of a @var{suffix} that starts with
12652 Treat @var{template} as a single file relative to the value of
12653 @env{TMPDIR} if available, or to the directory specified by
12654 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12655 contain slashes. This option is deprecated; the use of @option{-p}
12656 without @option{-t} offers better defaults (by favoring the command
12657 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12662 @cindex exit status of @command{mktemp}
12666 0 if the file was created,
12671 @node Working context
12672 @chapter Working context
12674 @cindex working context
12675 @cindex commands for printing the working context
12677 This section describes commands that display or alter the context in
12678 which you are working: the current directory, the terminal settings, and
12679 so forth. See also the user-related commands in the next section.
12682 * pwd invocation:: Print working directory.
12683 * stty invocation:: Print or change terminal characteristics.
12684 * printenv invocation:: Print environment variables.
12685 * tty invocation:: Print file name of terminal on standard input.
12689 @node pwd invocation
12690 @section @command{pwd}: Print working directory
12693 @cindex print name of current directory
12694 @cindex current working directory, printing
12695 @cindex working directory, printing
12698 @command{pwd} prints the name of the current directory. Synopsis:
12701 pwd [@var{option}]@dots{}
12704 The program accepts the following options. Also see @ref{Common options}.
12711 If the contents of the environment variable @env{PWD} provide an
12712 absolute name of the current directory with no @samp{.} or @samp{..}
12713 components, but possibly with symbolic links, then output those
12714 contents. Otherwise, fall back to default @option{-P} handling.
12719 @opindex --physical
12720 Print a fully resolved name for the current directory. That is, all
12721 components of the printed name will be actual directory names---none
12722 will be symbolic links.
12725 @cindex symbolic links and @command{pwd}
12726 If @option{-L} and @option{-P} are both given, the last one takes
12727 precedence. If neither option is given, then this implementation uses
12728 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12729 environment variable is set.
12731 @mayConflictWithShellBuiltIn{pwd}
12736 @node stty invocation
12737 @section @command{stty}: Print or change terminal characteristics
12740 @cindex change or print terminal settings
12741 @cindex terminal settings
12742 @cindex line settings of terminal
12744 @command{stty} prints or changes terminal characteristics, such as baud rate.
12748 stty [@var{option}] [@var{setting}]@dots{}
12749 stty [@var{option}]
12752 If given no line settings, @command{stty} prints the baud rate, line
12753 discipline number (on systems that support it), and line settings
12754 that have been changed from the values set by @samp{stty sane}.
12755 By default, mode reading and setting are performed on the tty line
12756 connected to standard input, although this can be modified by the
12757 @option{--file} option.
12759 @command{stty} accepts many non-option arguments that change aspects of
12760 the terminal line operation, as described below.
12762 The program accepts the following options. Also see @ref{Common options}.
12769 Print all current settings in human-readable form. This option may not
12770 be used in combination with any line settings.
12772 @item -F @var{device}
12773 @itemx --file=@var{device}
12776 Set the line opened by the file name specified in @var{device} instead of
12777 the tty line connected to standard input. This option is necessary
12778 because opening a @acronym{POSIX} tty requires use of the
12779 @code{O_NONDELAY} flag to prevent a @acronym{POSIX} tty from blocking
12780 until the carrier detect line is high if
12781 the @code{clocal} flag is not set. Hence, it is not always possible
12782 to allow the shell to open the device in the traditional manner.
12788 @cindex machine-readable @command{stty} output
12789 Print all current settings in a form that can be used as an argument to
12790 another @command{stty} command to restore the current settings. This option
12791 may not be used in combination with any line settings.
12795 Many settings can be turned off by preceding them with a @samp{-}.
12796 Such arguments are marked below with ``May be negated'' in their
12797 description. The descriptions themselves refer to the positive
12798 case, that is, when @emph{not} negated (unless stated otherwise,
12801 Some settings are not available on all @acronym{POSIX} systems, since they use
12802 extensions. Such arguments are marked below with
12803 ``Non-@acronym{POSIX}'' in their description. On non-@acronym{POSIX}
12804 systems, those or other settings also may not
12805 be available, but it's not feasible to document all the variations: just
12811 * Control:: Control settings
12812 * Input:: Input settings
12813 * Output:: Output settings
12814 * Local:: Local settings
12815 * Combination:: Combination settings
12816 * Characters:: Special characters
12817 * Special:: Special settings
12822 @subsection Control settings
12824 @cindex control settings
12830 @cindex two-way parity
12831 Generate parity bit in output and expect parity bit in input.
12837 @cindex even parity
12838 Set odd parity (even if negated). May be negated.
12845 @cindex character size
12846 @cindex eight-bit characters
12847 Set character size to 5, 6, 7, or 8 bits.
12852 Send a hangup signal when the last process closes the tty. May be
12858 Use two stop bits per character (one if negated). May be negated.
12862 Allow input to be received. May be negated.
12866 @cindex modem control
12867 Disable modem control signals. May be negated.
12871 @cindex hardware flow control
12872 @cindex flow control, hardware
12873 @cindex RTS/CTS flow control
12874 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12879 @subsection Input settings
12881 @cindex input settings
12882 These settings control operations on data received from the terminal.
12887 @cindex breaks, ignoring
12888 Ignore break characters. May be negated.
12892 @cindex breaks, cause interrupts
12893 Make breaks cause an interrupt signal. May be negated.
12897 @cindex parity, ignoring
12898 Ignore characters with parity errors. May be negated.
12902 @cindex parity errors, marking
12903 Mark parity errors (with a 255-0-character sequence). May be negated.
12907 Enable input parity checking. May be negated.
12911 @cindex eight-bit input
12912 Clear high (8th) bit of input characters. May be negated.
12916 @cindex newline, translating to return
12917 Translate newline to carriage return. May be negated.
12921 @cindex return, ignoring
12922 Ignore carriage return. May be negated.
12926 @cindex return, translating to newline
12927 Translate carriage return to newline. May be negated.
12931 @cindex input encoding, UTF-8
12932 Assume input characters are UTF-8 encoded. May be negated.
12936 @kindex C-s/C-q flow control
12937 @cindex XON/XOFF flow control
12938 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12945 @cindex software flow control
12946 @cindex flow control, software
12947 Enable sending of @code{stop} character when the system input buffer
12948 is almost full, and @code{start} character when it becomes almost
12949 empty again. May be negated.
12953 @cindex uppercase, translating to lowercase
12954 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12955 negated. Note ilcuc is not implemented, as one would not be able to issue
12956 almost any (lowercase) Unix command, after invoking it.
12960 Allow any character to restart output (only the start character
12961 if negated). Non-@acronym{POSIX}. May be negated.
12965 @cindex beeping at input buffer full
12966 Enable beeping and not flushing input buffer if a character arrives
12967 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12972 @subsection Output settings
12974 @cindex output settings
12975 These settings control operations on data sent to the terminal.
12980 Postprocess output. May be negated.
12984 @cindex lowercase, translating to output
12985 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12986 negated. (Note ouclc is not currently implemented.)
12990 @cindex return, translating to newline
12991 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12995 @cindex newline, translating to crlf
12996 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
13001 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
13006 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
13010 @cindex pad instead of timing for delaying
13011 Use fill (padding) characters instead of timing for delays.
13012 Non-@acronym{POSIX}.
13017 @cindex pad character
13018 Use @acronym{ASCII} @sc{del} characters for fill instead of
13019 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
13025 Newline delay style. Non-@acronym{POSIX}.
13032 Carriage return delay style. Non-@acronym{POSIX}.
13038 @opindex tab@var{n}
13039 Horizontal tab delay style. Non-@acronym{POSIX}.
13044 Backspace delay style. Non-@acronym{POSIX}.
13049 Vertical tab delay style. Non-@acronym{POSIX}.
13054 Form feed delay style. Non-@acronym{POSIX}.
13059 @subsection Local settings
13061 @cindex local settings
13066 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
13067 characters. May be negated.
13071 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
13072 special characters. May be negated.
13076 Enable non-@acronym{POSIX} special characters. May be negated.
13080 Echo input characters. May be negated.
13086 Echo @code{erase} characters as backspace-space-backspace. May be
13091 @cindex newline echoing after @code{kill}
13092 Echo a newline after a @code{kill} character. May be negated.
13096 @cindex newline, echoing
13097 Echo newline even if not echoing other characters. May be negated.
13101 @cindex flushing, disabling
13102 Disable flushing after @code{interrupt} and @code{quit} special
13103 characters. May be negated.
13107 @cindex case translation
13108 Enable input and output of uppercase characters by preceding their
13109 lowercase equivalents with @samp{\}, when @code{icanon} is set.
13110 Non-@acronym{POSIX}. May be negated.
13114 @cindex background jobs, stopping at terminal write
13115 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
13122 Echo erased characters backward, between @samp{\} and @samp{/}.
13123 Non-@acronym{POSIX}. May be negated.
13129 @cindex control characters, using @samp{^@var{c}}
13130 @cindex hat notation for control characters
13131 Echo control characters in hat notation (@samp{^@var{c}}) instead
13132 of literally. Non-@acronym{POSIX}. May be negated.
13138 Echo the @code{kill} special character by erasing each character on
13139 the line as indicated by the @code{echoprt} and @code{echoe} settings,
13140 instead of by the @code{echoctl} and @code{echok} settings.
13141 Non-@acronym{POSIX}.
13147 @subsection Combination settings
13149 @cindex combination settings
13150 Combination settings:
13157 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
13158 as @code{-parenb cs8}.
13162 Same as @code{parenb parodd cs7}. May be negated. If negated, same
13163 as @code{-parenb cs8}.
13167 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
13168 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
13172 Reset the @code{erase} and @code{kill} special characters to their default
13179 @c This is too long to write inline.
13181 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
13182 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
13183 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
13184 ff0 isig icanon iexten echo echoe echok -echonl
13185 -noflsh -xcase -tostop -echoprt echoctl echoke
13189 and also sets all special characters to their default values.
13193 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
13194 sets the @code{eof} and @code{eol} characters to their default values
13195 if they are the same as the @code{min} and @code{time} characters.
13196 May be negated. If negated, same as @code{raw}.
13203 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
13204 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
13205 -imaxbel -opost -isig -icanon -xcase min 1 time 0
13209 May be negated. If negated, same as @code{cooked}.
13213 Same as @option{-icanon}. May be negated. If negated, same as
13218 @cindex eight-bit characters
13219 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
13220 same as @code{parenb istrip cs7}.
13224 Same as @option{-parenb -istrip -opost cs8}. May be negated.
13225 If negated, same as @code{parenb istrip opost cs7}.
13229 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
13233 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
13240 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
13241 (Used for terminals with uppercase characters only.)
13245 Same as @code{echoe echoctl echoke}.
13249 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
13254 @subsection Special characters
13256 @cindex special characters
13257 @cindex characters, special
13259 The special characters' default values vary from system to system.
13260 They are set with the syntax @samp{name value}, where the names are
13261 listed below and the value can be given either literally, in hat
13262 notation (@samp{^@var{c}}), or as an integer which may start with
13263 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
13264 any other digit to indicate decimal.
13266 @cindex disabling special characters
13267 @kindex u@r{, and disabling special characters}
13268 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
13269 special character. (This is incompatible with Ultrix @command{stty},
13270 which uses a value of @samp{u} to disable a special character. GNU
13271 @command{stty} treats a value @samp{u} like any other, namely to set that
13272 special character to @key{U}.)
13278 Send an interrupt signal.
13282 Send a quit signal.
13286 Erase the last character typed.
13290 Erase the current line.
13294 Send an end of file (terminate the input).
13302 Alternate character to end the line. Non-@acronym{POSIX}.
13306 Switch to a different shell layer. Non-@acronym{POSIX}.
13310 Restart the output after stopping it.
13318 Send a terminal stop signal.
13322 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
13326 Redraw the current line. Non-@acronym{POSIX}.
13330 Erase the last word typed. Non-@acronym{POSIX}.
13334 Enter the next character typed literally, even if it is a special
13335 character. Non-@acronym{POSIX}.
13340 @subsection Special settings
13342 @cindex special settings
13347 Set the minimum number of characters that will satisfy a read until
13348 the time value has expired, when @option{-icanon} is set.
13352 Set the number of tenths of a second before reads time out if the minimum
13353 number of characters have not been read, when @option{-icanon} is set.
13355 @item ispeed @var{n}
13357 Set the input speed to @var{n}.
13359 @item ospeed @var{n}
13361 Set the output speed to @var{n}.
13365 Tell the tty kernel driver that the terminal has @var{n} rows.
13366 Non-@acronym{POSIX}.
13369 @itemx columns @var{n}
13372 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
13378 Print the number of rows and columns that the kernel thinks the
13379 terminal has. (Systems that don't support rows and columns in the kernel
13380 typically use the environment variables @env{LINES} and @env{COLUMNS}
13381 instead; however, GNU @command{stty} does not know anything about them.)
13382 Non-@acronym{POSIX}.
13386 Use line discipline @var{n}. Non-@acronym{POSIX}.
13390 Print the terminal speed.
13393 @cindex baud rate, setting
13394 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13395 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13396 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13397 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13398 support higher speeds. The @command{stty} command includes support
13415 4000000 where the system supports these.
13416 0 hangs up the line if @option{-clocal} is set.
13420 @node printenv invocation
13421 @section @command{printenv}: Print all or some environment variables
13424 @cindex printing all or some environment variables
13425 @cindex environment variables, printing
13427 @command{printenv} prints environment variable values. Synopsis:
13430 printenv [@var{option}] [@var{variable}]@dots{}
13433 If no @var{variable}s are specified, @command{printenv} prints the value of
13434 every environment variable. Otherwise, it prints the value of each
13435 @var{variable} that is set, and nothing for those that are not set.
13437 The program accepts the following option. Also see @ref{Common options}.
13445 @cindex exit status of @command{printenv}
13449 0 if all variables specified were found
13450 1 if at least one specified variable was not found
13451 2 if a write error occurred
13455 @node tty invocation
13456 @section @command{tty}: Print file name of terminal on standard input
13459 @cindex print terminal file name
13460 @cindex terminal file name, printing
13462 @command{tty} prints the file name of the terminal connected to its standard
13463 input. It prints @samp{not a tty} if standard input is not a terminal.
13467 tty [@var{option}]@dots{}
13470 The program accepts the following option. Also see @ref{Common options}.
13480 Print nothing; only return an exit status.
13484 @cindex exit status of @command{tty}
13488 0 if standard input is a terminal
13489 1 if standard input is not a terminal
13490 2 if given incorrect arguments
13491 3 if a write error occurs
13495 @node User information
13496 @chapter User information
13498 @cindex user information, commands for
13499 @cindex commands for printing user information
13501 This section describes commands that print user-related information:
13502 logins, groups, and so forth.
13505 * id invocation:: Print user identity.
13506 * logname invocation:: Print current login name.
13507 * whoami invocation:: Print effective user ID.
13508 * groups invocation:: Print group names a user is in.
13509 * users invocation:: Print login names of users currently logged in.
13510 * who invocation:: Print who is currently logged in.
13514 @node id invocation
13515 @section @command{id}: Print user identity
13518 @cindex real user and group IDs, printing
13519 @cindex effective user and group IDs, printing
13520 @cindex printing real and effective user and group IDs
13522 @command{id} prints information about the given user, or the process
13523 running it if no user is specified. Synopsis:
13526 id [@var{option}]@dots{} [@var{username}]
13529 @vindex POSIXLY_CORRECT
13530 By default, it prints the real user ID, real group ID, effective user ID
13531 if different from the real user ID, effective group ID if different from
13532 the real group ID, and supplemental group IDs.
13533 In addition, if SELinux
13534 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13535 then print @samp{context=@var{c}}, where @var{c} is the security context.
13537 Each of these numeric values is preceded by an identifying string and
13538 followed by the corresponding user or group name in parentheses.
13540 The options cause @command{id} to print only part of the above information.
13541 Also see @ref{Common options}.
13548 Print only the group ID.
13554 Print only the group ID and the supplementary groups.
13560 Print the user or group name instead of the ID number. Requires
13561 @option{-u}, @option{-g}, or @option{-G}.
13567 Print the real, instead of effective, user or group ID. Requires
13568 @option{-u}, @option{-g}, or @option{-G}.
13574 Print only the user ID.
13581 @cindex security context
13582 Print only the security context of the current user.
13583 If SELinux is disabled then print a warning and
13584 set the exit status to 1.
13590 @macro primaryAndSupplementaryGroups{cmd,arg}
13591 Primary and supplementary groups for a process are normally inherited
13592 from its parent and are usually unchanged since login. This means
13593 that if you change the group database after logging in, @command{\cmd\}
13594 will not reflect your changes within your existing login session.
13595 Running @command{\cmd\} with a \arg\ causes the user and group
13596 database to be consulted afresh, and so will give a different result.
13598 @primaryAndSupplementaryGroups{id,user argument}
13600 @node logname invocation
13601 @section @command{logname}: Print current login name
13604 @cindex printing user's login name
13605 @cindex login name, printing
13606 @cindex user name, printing
13609 @command{logname} prints the calling user's name, as found in a
13610 system-maintained file (often @file{/var/run/utmp} or
13611 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13612 for the calling process, @command{logname} prints
13613 an error message and exits with a status of 1.
13615 The only options are @option{--help} and @option{--version}. @xref{Common
13621 @node whoami invocation
13622 @section @command{whoami}: Print effective user ID
13625 @cindex effective user ID, printing
13626 @cindex printing the effective user ID
13628 @command{whoami} prints the user name associated with the current
13629 effective user ID. It is equivalent to the command @samp{id -un}.
13631 The only options are @option{--help} and @option{--version}. @xref{Common
13637 @node groups invocation
13638 @section @command{groups}: Print group names a user is in
13641 @cindex printing groups a user is in
13642 @cindex supplementary groups, printing
13644 @command{groups} prints the names of the primary and any supplementary
13645 groups for each given @var{username}, or the current process if no names
13646 are given. If more than one name is given, the name of each user is
13648 the list of that user's groups and the user name is separated from the
13649 group list by a colon. Synopsis:
13652 groups [@var{username}]@dots{}
13655 The group lists are equivalent to the output of the command @samp{id -Gn}.
13657 @primaryAndSupplementaryGroups{groups,list of users}
13659 The only options are @option{--help} and @option{--version}. @xref{Common
13665 @node users invocation
13666 @section @command{users}: Print login names of users currently logged in
13669 @cindex printing current usernames
13670 @cindex usernames, printing current
13672 @cindex login sessions, printing users with
13673 @command{users} prints on a single line a blank-separated list of user
13674 names of users currently logged in to the current host. Each user name
13675 corresponds to a login session, so if a user has more than one login
13676 session, that user's name will appear the same number of times in the
13685 With no @var{file} argument, @command{users} extracts its information from
13686 a system-maintained file (often @file{/var/run/utmp} or
13687 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13688 that file instead. A common choice is @file{/var/log/wtmp}.
13690 The only options are @option{--help} and @option{--version}. @xref{Common
13696 @node who invocation
13697 @section @command{who}: Print who is currently logged in
13700 @cindex printing current user information
13701 @cindex information, about current users
13703 @command{who} prints information about users who are currently logged on.
13707 @command{who} [@var{option}] [@var{file}] [am i]
13710 @cindex terminal lines, currently used
13712 @cindex remote hostname
13713 If given no non-option arguments, @command{who} prints the following
13714 information for each user currently logged on: login name, terminal
13715 line, login time, and remote hostname or X display.
13719 If given one non-option argument, @command{who} uses that instead of
13720 a default system-maintained file (often @file{/var/run/utmp} or
13721 @file{/etc/utmp}) as the name of the file containing the record of
13722 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13723 to @command{who} to look at who has previously logged on.
13727 If given two non-option arguments, @command{who} prints only the entry
13728 for the user running it (determined from its standard input), preceded
13729 by the hostname. Traditionally, the two arguments given are @samp{am
13730 i}, as in @samp{who am i}.
13733 Time stamps are listed according to the time zone rules specified by
13734 the @env{TZ} environment variable, or by the system default rules if
13735 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13736 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13738 The program accepts the following options. Also see @ref{Common options}.
13746 Same as @samp{-b -d --login -p -r -t -T -u}.
13752 Print the date and time of last system boot.
13758 Print information corresponding to dead processes.
13764 Print a line of column headings.
13770 List only the entries that correspond to processes via which the
13771 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13775 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13776 is not the default because it can cause significant delays on systems with
13777 automatic dial-up internet access.
13781 Same as @samp{who am i}.
13787 List active processes spawned by init.
13793 Print only the login names and the number of users logged on.
13794 Overrides all other options.
13799 @opindex --runlevel
13800 Print the current (and maybe previous) run-level of the init process.
13804 Ignored; for compatibility with other versions of @command{who}.
13810 Print last system clock change.
13815 After the login time, print the number of hours and minutes that the
13816 user has been idle. @samp{.} means the user was active in the last minute.
13817 @samp{old} means the user has been idle for more than 24 hours.
13828 @opindex --writable
13829 @cindex message status
13830 @pindex write@r{, allowed}
13831 After each login name print a character indicating the user's message status:
13834 @samp{+} allowing @code{write} messages
13835 @samp{-} disallowing @code{write} messages
13836 @samp{?} cannot find terminal device
13844 @node System context
13845 @chapter System context
13847 @cindex system context
13848 @cindex context, system
13849 @cindex commands for system context
13851 This section describes commands that print or change system-wide
13855 * date invocation:: Print or set system date and time.
13856 * arch invocation:: Print machine hardware name.
13857 * nproc invocation:: Print the number of processors.
13858 * uname invocation:: Print system information.
13859 * hostname invocation:: Print or set system name.
13860 * hostid invocation:: Print numeric host identifier.
13861 * uptime invocation:: Print system uptime and load.
13864 @node date invocation
13865 @section @command{date}: Print or set system date and time
13868 @cindex time, printing or setting
13869 @cindex printing the current time
13874 date [@var{option}]@dots{} [+@var{format}]
13875 date [-u|--utc|--universal] @c this avoids a newline in the output
13876 [ MMDDhhmm[[CC]YY][.ss] ]
13880 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13881 it with a default format that depends on the @env{LC_TIME} locale category.
13882 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13883 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13886 Normally, @command{date} uses the time zone rules indicated by the
13887 @env{TZ} environment variable, or the system default rules if @env{TZ}
13888 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13889 @env{TZ}, libc, The GNU C Library Reference Manual}.
13891 @findex strftime @r{and @command{date}}
13892 @cindex time formats
13893 @cindex formatting times
13894 If given an argument that starts with a @samp{+}, @command{date} prints the
13895 current date and time (or the date and time specified by the
13896 @option{--date} option, see below) in the format defined by that argument,
13897 which is similar to that of the @code{strftime} function. Except for
13898 conversion specifiers, which start with @samp{%}, characters in the
13899 format string are printed unchanged. The conversion specifiers are
13905 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13906 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13907 * Literal conversion specifiers:: %[%nt]
13908 * Padding and other flags:: Pad with zeros, spaces, etc.
13909 * Setting the time:: Changing the system clock.
13910 * Options for date:: Instead of the current time.
13912 * Date input formats:: Specifying date strings.
13914 * Examples of date:: Examples.
13917 @node Time conversion specifiers
13918 @subsection Time conversion specifiers
13920 @cindex time conversion specifiers
13921 @cindex conversion specifiers, time
13923 @command{date} conversion specifiers related to times.
13927 hour (@samp{00}@dots{}@samp{23})
13929 hour (@samp{01}@dots{}@samp{12})
13931 hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}.
13932 This is a @acronym{GNU} extension.
13934 hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}.
13935 This is a @acronym{GNU} extension.
13937 minute (@samp{00}@dots{}@samp{59})
13939 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13940 This is a @acronym{GNU} extension.
13942 locale's equivalent of either @samp{AM} or @samp{PM};
13943 blank in many locales.
13944 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13946 like @samp{%p}, except lower case.
13947 This is a @acronym{GNU} extension.
13949 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13951 24-hour hour and minute. Same as @samp{%H:%M}.
13952 This is a @acronym{GNU} extension.
13954 @cindex epoch, seconds since
13955 @cindex seconds since the epoch
13956 @cindex beginning of time
13957 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13958 Leap seconds are not counted unless leap second support is available.
13959 @xref{%s-examples}, for examples.
13960 This is a @acronym{GNU} extension.
13962 second (@samp{00}@dots{}@samp{60}).
13963 This may be @samp{60} if leap seconds are supported.
13965 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13967 locale's time representation (e.g., @samp{23:13:48})
13969 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13970 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13971 time zone is determinable. This value reflects the numeric time zone
13972 appropriate for the current time, using the time zone rules specified
13973 by the @env{TZ} environment variable.
13974 The time (and optionally, the time zone rules) can be overridden
13975 by the @option{--date} option.
13976 This is a @acronym{GNU} extension.
13978 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13979 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13980 zone is determinable.
13981 This is a @acronym{GNU} extension.
13983 Numeric time zone to the nearest second with @samp{:} (e.g.,
13984 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13986 This is a @acronym{GNU} extension.
13988 Numeric time zone with @samp{:} using the minimum necessary precision
13989 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13990 no time zone is determinable.
13991 This is a @acronym{GNU} extension.
13993 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13994 time zone is determinable. See @samp{%z} for how it is determined.
13998 @node Date conversion specifiers
13999 @subsection Date conversion specifiers
14001 @cindex date conversion specifiers
14002 @cindex conversion specifiers, date
14004 @command{date} conversion specifiers related to dates.
14008 locale's abbreviated weekday name (e.g., @samp{Sun})
14010 locale's full weekday name, variable length (e.g., @samp{Sunday})
14012 locale's abbreviated month name (e.g., @samp{Jan})
14014 locale's full month name, variable length (e.g., @samp{January})
14016 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
14018 century. This is like @samp{%Y}, except the last two digits are omitted.
14019 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
14020 and is @samp{-0} if @samp{%Y} is @samp{-001}.
14021 It is normally at least two characters, but it may be more.
14023 day of month (e.g., @samp{01})
14025 date; same as @samp{%m/%d/%y}
14027 day of month, space padded; same as @samp{%_d}
14029 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
14030 This is a good choice for a date format, as it is standard and
14031 is easy to sort in the usual case where years are in the range
14033 This is a @acronym{GNU} extension.
14035 year corresponding to the @acronym{ISO} week number, but without the century
14036 (range @samp{00} through @samp{99}). This has the same format and value
14037 as @samp{%y}, except that if the @acronym{ISO} week number (see
14039 to the previous or next year, that year is used instead.
14040 This is a @acronym{GNU} extension.
14042 year corresponding to the @acronym{ISO} week number. This has the
14043 same format and value as @samp{%Y}, except that if the @acronym{ISO}
14045 @samp{%V}) belongs to the previous or next year, that year is used
14047 It is normally useful only if @samp{%V} is also used;
14048 for example, the format @samp{%G-%m-%d} is probably a mistake,
14049 since it combines the ISO week number year with the conventional month and day.
14050 This is a @acronym{GNU} extension.
14054 day of year (@samp{001}@dots{}@samp{366})
14056 month (@samp{01}@dots{}@samp{12})
14058 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
14060 week number of year, with Sunday as the first day of the week
14061 (@samp{00}@dots{}@samp{53}).
14062 Days in a new year preceding the first Sunday are in week zero.
14064 @acronym{ISO} week number, that is, the
14065 week number of year, with Monday as the first day of the week
14066 (@samp{01}@dots{}@samp{53}).
14067 If the week containing January 1 has four or more days in
14068 the new year, then it is considered week 1; otherwise, it is week 53 of
14069 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
14072 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
14074 week number of year, with Monday as first day of week
14075 (@samp{00}@dots{}@samp{53}).
14076 Days in a new year preceding the first Monday are in week zero.
14078 locale's date representation (e.g., @samp{12/31/99})
14080 last two digits of year (@samp{00}@dots{}@samp{99})
14082 year. This is normally at least four characters, but it may be more.
14083 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
14084 precedes year @samp{0000}.
14088 @node Literal conversion specifiers
14089 @subsection Literal conversion specifiers
14091 @cindex literal conversion specifiers
14092 @cindex conversion specifiers, literal
14094 @command{date} conversion specifiers that produce literal strings.
14106 @node Padding and other flags
14107 @subsection Padding and other flags
14109 @cindex numeric field padding
14110 @cindex padding of numeric fields
14111 @cindex fields, padding numeric
14113 Unless otherwise specified, @command{date} normally pads numeric fields
14114 with zeros, so that, for
14115 example, numeric months are always output as two digits.
14116 Seconds since the epoch are not padded, though,
14117 since there is no natural width for them.
14119 As a @acronym{GNU} extension, @command{date} recognizes any of the
14120 following optional flags after the @samp{%}:
14124 (hyphen) Do not pad the field; useful if the output is intended for
14127 (underscore) Pad with spaces; useful if you need a fixed
14128 number of characters in the output, but zeros are too distracting.
14130 (zero) Pad with zeros even if the conversion specifier
14131 would normally pad with spaces.
14133 Use upper case characters if possible.
14135 Use opposite case characters if possible.
14136 A field that is normally upper case becomes lower case, and vice versa.
14140 Here are some examples of padding:
14143 date +%d/%m -d "Feb 1"
14145 date +%-d/%-m -d "Feb 1"
14147 date +%_d/%_m -d "Feb 1"
14151 As a @acronym{GNU} extension, you can specify the field width
14152 (after any flag, if present) as a decimal number. If the natural size of the
14153 output of the field has less than the specified number of characters,
14154 the result is written right adjusted and padded to the given
14155 size. For example, @samp{%9B} prints the right adjusted month name in
14156 a field of width 9.
14158 An optional modifier can follow the optional flag and width
14159 specification. The modifiers are:
14163 Use the locale's alternate representation for date and time. This
14164 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
14165 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
14166 example, @samp{%Ex} might yield a date format based on the Japanese
14170 Use the locale's alternate numeric symbols for numbers. This modifier
14171 applies only to numeric conversion specifiers.
14174 If the format supports the modifier but no alternate representation
14175 is available, it is ignored.
14178 @node Setting the time
14179 @subsection Setting the time
14181 @cindex setting the time
14182 @cindex time setting
14183 @cindex appropriate privileges
14185 If given an argument that does not start with @samp{+}, @command{date} sets
14186 the system clock to the date and time specified by that argument (as
14187 described below). You must have appropriate privileges to set the
14188 system clock. The @option{--date} and @option{--set} options may not be
14189 used with such an argument. The @option{--universal} option may be used
14190 with such an argument to indicate that the specified date and time are
14191 relative to Coordinated Universal Time rather than to the local time
14194 The argument must consist entirely of digits, which have the following
14207 first two digits of year (optional)
14209 last two digits of year (optional)
14214 The @option{--set} option also sets the system clock; see the next section.
14217 @node Options for date
14218 @subsection Options for @command{date}
14220 @cindex @command{date} options
14221 @cindex options for @command{date}
14223 The program accepts the following options. Also see @ref{Common options}.
14227 @item -d @var{datestr}
14228 @itemx --date=@var{datestr}
14231 @cindex parsing date strings
14232 @cindex date strings, parsing
14233 @cindex arbitrary date strings, parsing
14236 @opindex next @var{day}
14237 @opindex last @var{day}
14238 Display the date and time specified in @var{datestr} instead of the
14239 current date and time. @var{datestr} can be in almost any common
14240 format. It can contain month names, time zones, @samp{am} and @samp{pm},
14241 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
14242 14:19:13.489392193 +0530"} specifies the instant of time that is
14243 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
14244 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
14245 Note: input currently must be in locale independent format. E.g., the
14246 LC_TIME=C below is needed to print back the correct date in many locales:
14248 date -d "$(LC_TIME=C date)"
14250 @xref{Date input formats}.
14252 @item -f @var{datefile}
14253 @itemx --file=@var{datefile}
14256 Parse each line in @var{datefile} as with @option{-d} and display the
14257 resulting date and time. If @var{datefile} is @samp{-}, use standard
14258 input. This is useful when you have many dates to process, because the
14259 system overhead of starting up the @command{date} executable many times can
14262 @item -r @var{file}
14263 @itemx --reference=@var{file}
14265 @opindex --reference
14266 Display the date and time of the last modification of @var{file},
14267 instead of the current date and time.
14274 @opindex --rfc-2822
14275 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
14276 %z}, evaluated in the C locale so abbreviations are always in English.
14280 Fri, 09 Sep 2005 13:51:39 -0700
14283 This format conforms to
14284 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
14285 @acronym{RFCs} 2822} and
14286 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
14287 current and previous standards for Internet email.
14289 @item --rfc-3339=@var{timespec}
14290 @opindex --rfc-3339=@var{timespec}
14291 Display the date using a format specified by
14292 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
14293 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
14294 format, except that it also permits applications to use a space rather
14295 than a @samp{T} to separate dates from times. Unlike the other
14296 standard formats, @acronym{RFC} 3339 format is always suitable as
14297 input for the @option{--date} (@option{-d}) and @option{--file}
14298 (@option{-f}) options, regardless of the current locale.
14300 The argument @var{timespec} specifies how much of the time to include.
14301 It can be one of the following:
14305 Print just the full-date, e.g., @samp{2005-09-14}.
14306 This is equivalent to the format @samp{%Y-%m-%d}.
14309 Print the full-date and full-time separated by a space, e.g.,
14310 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
14311 time-offset; here the @samp{+05:30} means that local time is five
14312 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
14313 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
14316 Like @samp{seconds}, but also print nanoseconds, e.g.,
14317 @samp{2005-09-14 00:56:06.998458565+05:30}.
14318 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
14322 @item -s @var{datestr}
14323 @itemx --set=@var{datestr}
14326 Set the date and time to @var{datestr}. See @option{-d} above.
14333 @opindex --universal
14334 @cindex Coordinated Universal Time
14336 @cindex Greenwich Mean Time
14339 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
14340 @env{TZ} environment variable were set to the string @samp{UTC0}.
14342 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
14343 historical reasons.
14347 @node Examples of date
14348 @subsection Examples of @command{date}
14350 @cindex examples of @command{date}
14352 Here are a few examples. Also see the documentation for the @option{-d}
14353 option in the previous section.
14358 To print the date of the day before yesterday:
14361 date --date='2 days ago'
14365 To print the date of the day three months and one day hence:
14368 date --date='3 months 1 day'
14372 To print the day of year of Christmas in the current year:
14375 date --date='25 Dec' +%j
14379 To print the current full month name and the day of the month:
14385 But this may not be what you want because for the first nine days of
14386 the month, the @samp{%d} expands to a zero-padded two-digit field,
14387 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14390 To print a date without the leading zero for one-digit days
14391 of the month, you can use the (@acronym{GNU} extension)
14392 @samp{-} flag to suppress
14393 the padding altogether:
14396 date -d 1may '+%B %-d
14400 To print the current date and time in the format required by many
14401 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14404 date +%m%d%H%M%Y.%S
14408 To set the system clock forward by two minutes:
14411 date --set='+2 minutes'
14415 To print the date in @acronym{RFC} 2822 format,
14416 use @samp{date --rfc-2822}. Here is some example output:
14419 Fri, 09 Sep 2005 13:51:39 -0700
14422 @anchor{%s-examples}
14424 To convert a date string to the number of seconds since the epoch
14425 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14426 the @samp{%s} format. That can be useful in sorting and/or graphing
14427 and/or comparing data by date. The following command outputs the
14428 number of the seconds since the epoch for the time two minutes after the
14432 date --date='1970-01-01 00:02:00 +0000' +%s
14436 If you do not specify time zone information in the date string,
14437 @command{date} uses your computer's idea of the time zone when
14438 interpreting the string. For example, if your computer's time zone is
14439 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14440 seconds) behind UTC:
14443 # local time zone used
14444 date --date='1970-01-01 00:02:00' +%s
14449 If you're sorting or graphing dated data, your raw date values may be
14450 represented as seconds since the epoch. But few people can look at
14451 the date @samp{946684800} and casually note ``Oh, that's the first second
14452 of the year 2000 in Greenwich, England.''
14455 date --date='2000-01-01 UTC' +%s
14459 An alternative is to use the @option{--utc} (@option{-u}) option.
14460 Then you may omit @samp{UTC} from the date string. Although this
14461 produces the same result for @samp{%s} and many other format sequences,
14462 with a time zone offset different from zero, it would give a different
14463 result for zone-dependent formats like @samp{%z}.
14466 date -u --date=2000-01-01 +%s
14470 To convert such an unwieldy number of seconds back to
14471 a more readable form, use a command like this:
14474 # local time zone used
14475 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14476 1999-12-31 19:00:00 -0500
14479 Or if you do not mind depending on the @samp{@@} feature present since
14480 coreutils 5.3.0, you could shorten this to:
14483 date -d @@946684800 +"%F %T %z"
14484 1999-12-31 19:00:00 -0500
14487 Often it is better to output UTC-relative date and time:
14490 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14491 2000-01-01 00:00:00 +0000
14497 @node arch invocation
14498 @section @command{arch}: Print machine hardware name
14501 @cindex print machine hardware name
14502 @cindex system information, printing
14504 @command{arch} prints the machine hardware name,
14505 and is equivalent to @samp{uname -m}.
14509 arch [@var{option}]
14512 The program accepts the @ref{Common options} only.
14517 @node nproc invocation
14518 @section @command{nproc}: Print the number of available processors
14521 @cindex Print the number of processors
14522 @cindex system information, printing
14524 Print the number of processing units available to the current process,
14525 which may be less than the number of online processors.
14526 If this information is not accessible, then print the number of
14527 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14528 set, then it will determine the returned value. The result is guaranteed to be
14529 greater than zero. Synopsis:
14532 nproc [@var{option}]
14535 The program accepts the following options. Also see @ref{Common options}.
14541 Print the number of installed processors on the system, which may
14542 be greater than the number online or available to the current process.
14543 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14545 @item --ignore=@var{number}
14547 If possible, exclude this @var{number} of processing units.
14554 @node uname invocation
14555 @section @command{uname}: Print system information
14558 @cindex print system information
14559 @cindex system information, printing
14561 @command{uname} prints information about the machine and operating system
14562 it is run on. If no options are given, @command{uname} acts as if the
14563 @option{-s} option were given. Synopsis:
14566 uname [@var{option}]@dots{}
14569 If multiple options or @option{-a} are given, the selected information is
14570 printed in this order:
14573 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14574 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14577 The information may contain internal spaces, so such output cannot be
14578 parsed reliably. In the following example, @var{release} is
14579 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14583 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
14584 unknown unknown GNU/Linux
14588 The program accepts the following options. Also see @ref{Common options}.
14596 Print all of the below information, except omit the processor type
14597 and the hardware platform name if they are unknown.
14600 @itemx --hardware-platform
14602 @opindex --hardware-platform
14603 @cindex implementation, hardware
14604 @cindex hardware platform
14605 @cindex platform, hardware
14606 Print the hardware platform name
14607 (sometimes called the hardware implementation).
14608 Print @samp{unknown} if the kernel does not make this information
14609 easily available, as is the case with Linux kernels.
14615 @cindex machine type
14616 @cindex hardware class
14617 @cindex hardware type
14618 Print the machine hardware name (sometimes called the hardware class
14624 @opindex --nodename
14627 @cindex network node name
14628 Print the network node hostname.
14633 @opindex --processor
14634 @cindex host processor type
14635 Print the processor type (sometimes called the instruction set
14636 architecture or ISA).
14637 Print @samp{unknown} if the kernel does not make this information
14638 easily available, as is the case with Linux kernels.
14641 @itemx --operating-system
14643 @opindex --operating-system
14644 @cindex operating system name
14645 Print the name of the operating system.
14648 @itemx --kernel-release
14650 @opindex --kernel-release
14651 @cindex kernel release
14652 @cindex release of kernel
14653 Print the kernel release.
14656 @itemx --kernel-name
14658 @opindex --kernel-name
14659 @cindex kernel name
14660 @cindex name of kernel
14661 Print the kernel name.
14662 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14663 ``the implementation of the operating system'', because the
14664 @acronym{POSIX} specification itself has no notion of ``kernel''.
14665 The kernel name might be the same as the operating system name printed
14666 by the @option{-o} or @option{--operating-system} option, but it might
14667 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14668 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14672 @itemx --kernel-version
14674 @opindex --kernel-version
14675 @cindex kernel version
14676 @cindex version of kernel
14677 Print the kernel version.
14684 @node hostname invocation
14685 @section @command{hostname}: Print or set system name
14688 @cindex setting the hostname
14689 @cindex printing the hostname
14690 @cindex system name, printing
14691 @cindex appropriate privileges
14693 With no arguments, @command{hostname} prints the name of the current host
14694 system. With one argument, it sets the current host name to the
14695 specified string. You must have appropriate privileges to set the host
14699 hostname [@var{name}]
14702 The only options are @option{--help} and @option{--version}. @xref{Common
14708 @node hostid invocation
14709 @section @command{hostid}: Print numeric host identifier
14712 @cindex printing the host identifier
14714 @command{hostid} prints the numeric identifier of the current host
14715 in hexadecimal. This command accepts no arguments.
14716 The only options are @option{--help} and @option{--version}.
14717 @xref{Common options}.
14719 For example, here's what it prints on one system I use:
14726 On that system, the 32-bit quantity happens to be closely
14727 related to the system's Internet address, but that isn't always
14732 @node uptime invocation
14733 @section @command{uptime}: Print system uptime and load
14736 @cindex printing the system uptime and load
14738 @command{uptime} prints the current time, the system's uptime, the
14739 number of logged-in users and the current load average.
14741 If an argument is specified, it is used as the file to be read
14742 to discover how many users are logged in. If no argument is
14743 specified, a system default is used (@command{uptime --help} indicates
14744 the default setting).
14746 The only options are @option{--help} and @option{--version}.
14747 @xref{Common options}.
14749 For example, here's what it prints right now on one system I use:
14753 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14756 The precise method of calculation of load average varies somewhat
14757 between systems. Some systems calculate it as the average number of
14758 runnable processes over the last 1, 5 and 15 minutes, but some systems
14759 also include processes in the uninterruptible sleep state (that is,
14760 those processes which are waiting for disk I/O). The Linux kernel
14761 includes uninterruptible processes.
14763 @node SELinux context
14764 @chapter SELinux context
14766 @cindex SELinux context
14767 @cindex SELinux, context
14768 @cindex commands for SELinux context
14770 This section describes commands for operations with SELinux
14774 * chcon invocation:: Change SELinux context of file
14775 * runcon invocation:: Run a command in specified SELinux context
14778 @node chcon invocation
14779 @section @command{chcon}: Change SELinux context of file
14782 @cindex changing security context
14783 @cindex change SELinux context
14785 @command{chcon} changes the SELinux security context of the selected files.
14789 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14790 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
14791 [-t @var{type}] @var{file}@dots{}
14792 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14795 Change the SELinux security context of each @var{file} to @var{context}.
14796 With @option{--reference}, change the security context of each @var{file}
14797 to that of @var{rfile}.
14799 The program accepts the following options. Also see @ref{Common options}.
14804 @itemx --no-dereference
14806 @opindex --no-dereference
14807 @cindex no dereference
14808 Affect symbolic links instead of any referenced file.
14810 @item --reference=@var{rfile}
14811 @opindex --reference
14812 @cindex reference file
14813 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14818 @opindex --recursive
14819 Operate on files and directories recursively.
14822 @xref{Traversing symlinks}.
14825 @xref{Traversing symlinks}.
14828 @xref{Traversing symlinks}.
14835 Output a diagnostic for every file processed.
14837 @item -u @var{user}
14838 @itemx --user=@var{user}
14841 Set user @var{user} in the target security context.
14843 @item -r @var{role}
14844 @itemx --role=@var{role}
14847 Set role @var{role} in the target security context.
14849 @item -t @var{type}
14850 @itemx --type=@var{type}
14853 Set type @var{type} in the target security context.
14855 @item -l @var{range}
14856 @itemx --range=@var{range}
14859 Set range @var{range} in the target security context.
14865 @node runcon invocation
14866 @section @command{runcon}: Run a command in specified SELinux context
14869 @cindex run with security context
14872 @command{runcon} runs file in specified SELinux security context.
14876 runcon @var{context} @var{command} [@var{args}]
14877 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
14878 [-l @var{range}] @var{command} [@var{args}]
14881 Run @var{command} with completely-specified @var{context}, or with
14882 current or transitioned security context modified by one or more of @var{level},
14883 @var{role}, @var{type} and @var{user}.
14885 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14886 is specified, the first argument is used as the complete context.
14887 Any additional arguments after @var{command}
14888 are interpreted as arguments to the command.
14890 With neither @var{context} nor @var{command}, print the current
14893 The program accepts the following options. Also see @ref{Common options}.
14901 Compute process transition context before modifying.
14903 @item -u @var{user}
14904 @itemx --user=@var{user}
14907 Set user @var{user} in the target security context.
14909 @item -r @var{role}
14910 @itemx --role=@var{role}
14913 Set role @var{role} in the target security context.
14915 @item -t @var{type}
14916 @itemx --type=@var{type}
14919 Set type @var{type} in the target security context.
14921 @item -l @var{range}
14922 @itemx --range=@var{range}
14925 Set range @var{range} in the target security context.
14929 @cindex exit status of @command{runcon}
14933 126 if @var{command} is found but cannot be invoked
14934 127 if @command{runcon} itself fails or if @var{command} cannot be found
14935 the exit status of @var{command} otherwise
14938 @node Modified command invocation
14939 @chapter Modified command invocation
14941 @cindex modified command invocation
14942 @cindex invocation of commands, modified
14943 @cindex commands for invoking other commands
14945 This section describes commands that run other commands in some context
14946 different than the current one: a modified environment, as a different
14950 * chroot invocation:: Modify the root directory.
14951 * env invocation:: Modify environment variables.
14952 * nice invocation:: Modify niceness.
14953 * nohup invocation:: Immunize to hangups.
14954 * stdbuf invocation:: Modify buffering of standard streams.
14955 * su invocation:: Modify user and group ID.
14956 * timeout invocation:: Run with time limit.
14960 @node chroot invocation
14961 @section @command{chroot}: Run a command with a different root directory
14964 @cindex running a program in a specified root directory
14965 @cindex root directory, running a program in a specified
14967 @command{chroot} runs a command with a specified root directory.
14968 On many systems, only the super-user can do this.@footnote{However,
14969 some systems (e.g., FreeBSD) can be configured to allow certain regular
14970 users to use the @code{chroot} system call, and hence to run this program.
14971 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14972 underlying function is non-privileged due to lack of support in MS-Windows.}
14976 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14977 chroot @var{option}
14980 Ordinarily, file names are looked up starting at the root of the
14981 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14982 the directory @var{newroot} (which must exist) and then runs
14983 @var{command} with optional @var{args}. If @var{command} is not
14984 specified, the default is the value of the @env{SHELL} environment
14985 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14986 @var{command} must not be a special built-in utility
14987 (@pxref{Special built-in utilities}).
14989 The program accepts the following options. Also see @ref{Common options}.
14990 Options must precede operands.
14994 @itemx --userspec=@var{user}[:@var{group}]
14995 @opindex --userspec
14996 By default, @var{command} is run with the same credentials
14997 as the invoking process.
14998 Use this option to run it as a different @var{user} and/or with a
14999 different primary @var{group}.
15001 @itemx --groups=@var{groups}
15003 Use this option to specify the supplementary @var{groups} to be
15004 used by the new process.
15005 The items in the list (names or numeric IDs) must be separated by commas.
15009 Here are a few tips to help avoid common problems in using chroot.
15010 To start with a simple example, make @var{command} refer to a statically
15011 linked binary. If you were to use a dynamically linked executable, then
15012 you'd have to arrange to have the shared libraries in the right place under
15013 your new root directory.
15015 For example, if you create a statically linked @command{ls} executable,
15016 and put it in @file{/tmp/empty}, you can run this command as root:
15019 $ chroot /tmp/empty /ls -Rl /
15022 Then you'll see output like this:
15027 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
15030 If you want to use a dynamically linked executable, say @command{bash},
15031 then first run @samp{ldd bash} to see what shared objects it needs.
15032 Then, in addition to copying the actual binary, also copy the listed
15033 files to the required positions under your intended new root directory.
15034 Finally, if the executable requires any other files (e.g., data, state,
15035 device files), copy them into place, too.
15037 @cindex exit status of @command{chroot}
15041 125 if @command{chroot} itself fails
15042 126 if @var{command} is found but cannot be invoked
15043 127 if @var{command} cannot be found
15044 the exit status of @var{command} otherwise
15048 @node env invocation
15049 @section @command{env}: Run a command in a modified environment
15052 @cindex environment, running a program in a modified
15053 @cindex modified environment, running a program in a
15054 @cindex running a program in a modified environment
15056 @command{env} runs a command with a modified environment. Synopses:
15059 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
15060 [@var{command} [@var{args}]@dots{}]
15064 Operands of the form @samp{@var{variable}=@var{value}} set
15065 the environment variable @var{variable} to value @var{value}.
15066 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
15067 to an empty value is different from unsetting it.
15068 These operands are evaluated left-to-right, so if two operands
15069 mention the same variable the earlier is ignored.
15071 Environment variable names can be empty, and can contain any
15072 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
15073 However, it is wise to limit yourself to names that
15074 consist solely of underscores, digits, and @acronym{ASCII} letters,
15075 and that begin with a non-digit, as applications like the shell do not
15076 work well with other names.
15079 The first operand that does not contain the character @samp{=}
15080 specifies the program to invoke; it is
15081 searched for according to the @env{PATH} environment variable. Any
15082 remaining arguments are passed as arguments to that program.
15083 The program should not be a special built-in utility
15084 (@pxref{Special built-in utilities}).
15086 Modifications to @env{PATH} take effect prior to searching for
15087 @var{command}. Use caution when reducing @env{PATH}; behavior is
15088 not portable when @env{PATH} is undefined or omits key directories
15089 such as @file{/bin}.
15091 In the rare case that a utility contains a @samp{=} in the name, the
15092 only way to disambiguate it from a variable assignment is to use an
15093 intermediate command for @var{command}, and pass the problematic
15094 program name via @var{args}. For example, if @file{./prog=} is an
15095 executable in the current @env{PATH}:
15098 env prog= true # runs 'true', with prog= in environment
15099 env ./prog= true # runs 'true', with ./prog= in environment
15100 env -- prog= true # runs 'true', with prog= in environment
15101 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
15102 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
15105 @cindex environment, printing
15107 If no command name is specified following the environment
15108 specifications, the resulting environment is printed. This is like
15109 specifying the @command{printenv} program.
15111 For some examples, suppose the environment passed to @command{env}
15112 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
15113 @samp{PATH=.:/gnubin:/hacks}:
15118 Output the current environment.
15120 $ env | LC_ALL=C sort
15123 PATH=.:/gnubin:/hacks
15127 Run @command{foo} with a reduced environment, preserving only the
15128 original @env{PATH} to avoid problems in locating @command{foo}.
15130 env - PATH="$PATH" foo
15134 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
15135 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
15136 that @command{foo} was found in the file system rather than as a shell
15143 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
15144 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
15145 @samp{DISPLAY=gnu:0}.
15147 env DISPLAY=gnu:0 LOGNAME=foo nemacs
15151 Attempt to run the program @command{/energy/--} (as that is the only
15152 possible path search result); if the command exists, the environment
15153 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
15154 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
15156 env -u EDITOR PATH=/energy -- e=mc2 bar baz
15162 The program accepts the following options. Also see @ref{Common options}.
15163 Options must precede operands.
15169 @item -u @var{name}
15170 @itemx --unset=@var{name}
15173 Remove variable @var{name} from the environment, if it was in the
15178 @itemx --ignore-environment
15181 @opindex --ignore-environment
15182 Start with an empty environment, ignoring the inherited environment.
15186 @cindex exit status of @command{env}
15190 0 if no @var{command} is specified and the environment is output
15191 125 if @command{env} itself fails
15192 126 if @var{command} is found but cannot be invoked
15193 127 if @var{command} cannot be found
15194 the exit status of @var{command} otherwise
15198 @node nice invocation
15199 @section @command{nice}: Run a command with modified niceness
15203 @cindex scheduling, affecting
15204 @cindex appropriate privileges
15206 @command{nice} prints or modifies a process's @dfn{niceness},
15207 a parameter that affects whether the process is scheduled favorably.
15211 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
15214 If no arguments are given, @command{nice} prints the current niceness.
15215 Otherwise, @command{nice} runs the given @var{command} with its
15216 niceness adjusted. By default, its niceness is incremented by 10.
15218 Niceness values range at least from @minus{}20 (process has high priority
15219 and gets more resources, thus slowing down other processes) through 19
15220 (process has lower priority and runs slowly itself, but has less impact
15221 on the speed of other running processes). Some systems
15222 may have a wider range of nicenesses; conversely, other systems may
15223 enforce more restrictive limits. An attempt to set the niceness
15224 outside the supported range is treated as an attempt to use the
15225 minimum or maximum supported value.
15227 A niceness should not be confused with a scheduling priority, which
15228 lets applications determine the order in which threads are scheduled
15229 to run. Unlike a priority, a niceness is merely advice to the
15230 scheduler, which the scheduler is free to ignore. Also, as a point of
15231 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
15232 terms of a @dfn{nice value}, which is the nonnegative difference
15233 between a niceness and the minimum niceness. Though @command{nice}
15234 conforms to @acronym{POSIX}, its documentation and diagnostics use the
15235 term ``niceness'' for compatibility with historical practice.
15237 @var{command} must not be a special built-in utility (@pxref{Special
15238 built-in utilities}).
15240 @mayConflictWithShellBuiltIn{nice}
15242 The program accepts the following option. Also see @ref{Common options}.
15243 Options must precede operands.
15246 @item -n @var{adjustment}
15247 @itemx --adjustment=@var{adjustment}
15249 @opindex --adjustment
15250 Add @var{adjustment} instead of 10 to the command's niceness. If
15251 @var{adjustment} is negative and you lack appropriate privileges,
15252 @command{nice} issues a warning but otherwise acts as if you specified
15255 For compatibility @command{nice} also supports an obsolete
15256 option syntax @option{-@var{adjustment}}. New scripts should use
15257 @option{-n @var{adjustment}} instead.
15261 @cindex exit status of @command{nice}
15265 0 if no @var{command} is specified and the niceness is output
15266 125 if @command{nice} itself fails
15267 126 if @var{command} is found but cannot be invoked
15268 127 if @var{command} cannot be found
15269 the exit status of @var{command} otherwise
15272 It is sometimes useful to run a non-interactive program with reduced niceness.
15275 $ nice factor 4611686018427387903
15278 Since @command{nice} prints the current niceness,
15279 you can invoke it through itself to demonstrate how it works.
15281 The default behavior is to increase the niceness by @samp{10}:
15292 The @var{adjustment} is relative to the current niceness. In the
15293 next example, the first @command{nice} invocation runs the second one
15294 with niceness 10, and it in turn runs the final one with a niceness
15298 $ nice nice -n 3 nice
15302 Specifying a niceness larger than the supported range
15303 is the same as specifying the maximum supported value:
15306 $ nice -n 10000000000 nice
15310 Only a privileged user may run a process with lower niceness:
15314 nice: cannot set niceness: Permission denied
15316 $ sudo nice -n -1 nice
15321 @node nohup invocation
15322 @section @command{nohup}: Run a command immune to hangups
15325 @cindex hangups, immunity to
15326 @cindex immunity to hangups
15327 @cindex logging out and continuing to run
15330 @command{nohup} runs the given @var{command} with hangup signals ignored,
15331 so that the command can continue running in the background after you log
15335 nohup @var{command} [@var{arg}]@dots{}
15338 If standard input is a terminal, it is redirected from
15339 @file{/dev/null} so that terminal sessions do not mistakenly consider
15340 the terminal to be used by the command. This is a @acronym{GNU}
15341 extension; programs intended to be portable to non-@acronym{GNU} hosts
15342 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
15346 If standard output is a terminal, the command's standard output is appended
15347 to the file @file{nohup.out}; if that cannot be written to, it is appended
15348 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
15349 command is not run.
15350 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
15351 @command{nohup} is made readable and writable only to the user,
15352 regardless of the current umask settings.
15354 If standard error is a terminal, it is normally redirected to the same file
15355 descriptor as the (possibly-redirected) standard output.
15356 However, if standard output is closed, standard error terminal output
15357 is instead appended to the file @file{nohup.out} or
15358 @file{$HOME/nohup.out} as above.
15360 To capture the command's output to a file other than @file{nohup.out}
15361 you can redirect it. For example, to capture the output of
15365 nohup make > make.log
15368 @command{nohup} does not automatically put the command it runs in the
15369 background; you must do that explicitly, by ending the command line
15370 with an @samp{&}. Also, @command{nohup} does not alter the
15371 niceness of @var{command}; use @command{nice} for that,
15372 e.g., @samp{nohup nice @var{command}}.
15374 @var{command} must not be a special built-in utility (@pxref{Special
15375 built-in utilities}).
15377 The only options are @option{--help} and @option{--version}. @xref{Common
15378 options}. Options must precede operands.
15380 @cindex exit status of @command{nohup}
15384 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15385 126 if @var{command} is found but cannot be invoked
15386 127 if @var{command} cannot be found
15387 the exit status of @var{command} otherwise
15390 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15394 @node stdbuf invocation
15395 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15398 @cindex standard streams, buffering
15399 @cindex line buffered
15401 @command{stdbuf} allows one to modify the buffering operations of the
15402 three standard I/O streams associated with a program. Synopsis:
15405 stdbuf @var{option}@dots{} @var{command}
15408 @var{command} must start with the name of a program that
15411 uses the ISO C @code{FILE} streams for input/output (note the
15412 programs @command{dd} and @command{cat} don't do that),
15415 does not adjust the buffering of its standard streams (note the
15416 program @command{tee} is not in this category).
15419 Any additional @var{arg}s are passed as additional arguments to the
15422 The program accepts the following options. Also see @ref{Common options}.
15426 @item -i @var{mode}
15427 @itemx --input=@var{mode}
15430 Adjust the standard input stream buffering.
15432 @item -o @var{mode}
15433 @itemx --output=@var{mode}
15436 Adjust the standard output stream buffering.
15438 @item -e @var{mode}
15439 @itemx --error=@var{mode}
15442 Adjust the standard error stream buffering.
15446 The @var{mode} can be specified as follows:
15451 Set the stream to line buffered mode.
15452 In this mode data is coalesced until a newline is output or
15453 input is read from any stream attached to a terminal device.
15454 This option is invalid with standard input.
15457 Disable buffering of the selected stream.
15458 In this mode, data is output immediately and only the
15459 amount of data requested is read from input.
15460 Note the difference in function for input and output.
15461 Disabling buffering for input will not influence the responsiveness
15462 or blocking behavior of the stream input functions.
15463 For example @code{fread} will still block until @code{EOF} or error,
15464 even if the underlying @code{read} returns less data than requested.
15467 Specify the size of the buffer to use in fully buffered mode.
15468 @multiplierSuffixesNoBlocks{size}
15472 @cindex exit status of @command{stdbuf}
15476 125 if @command{stdbuf} itself fails
15477 126 if @var{command} is found but cannot be invoked
15478 127 if @var{command} cannot be found
15479 the exit status of @var{command} otherwise
15483 @node su invocation
15484 @section @command{su}: Run a command with substitute user and group ID
15487 @cindex substitute user and group IDs
15488 @cindex user ID, switching
15489 @cindex super-user, becoming
15490 @cindex root, becoming
15492 @command{su} allows one user to temporarily become another user. It runs a
15493 command (often an interactive shell) with the real and effective user
15494 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15497 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15500 @cindex passwd entry, and @command{su} shell
15502 @flindex /etc/passwd
15503 If no @var{user} is given, the default is @code{root}, the super-user.
15504 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15505 @file{/bin/sh} if none is specified there. If @var{user} has a
15506 password, @command{su} prompts for the password unless run by a user with
15507 effective user ID of zero (the super-user).
15513 @cindex login shell
15514 By default, @command{su} does not change the current directory.
15515 It sets the environment variables @env{HOME} and @env{SHELL}
15516 from the password entry for @var{user}, and if @var{user} is not
15517 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15518 By default, the shell is not a login shell.
15520 Any additional @var{arg}s are passed as additional arguments to the
15523 @cindex @option{-su}
15524 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15525 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15526 to certain shells, etc.).
15529 @command{su} can optionally be compiled to use @code{syslog} to report
15530 failed, and optionally successful, @command{su} attempts. (If the system
15531 supports @code{syslog}.) However, GNU @command{su} does not check if the
15532 user is a member of the @code{wheel} group; see below.
15534 The program accepts the following options. Also see @ref{Common options}.
15537 @item -c @var{command}
15538 @itemx --command=@var{command}
15541 Pass @var{command}, a single command line to run, to the shell with
15542 a @option{-c} option instead of starting an interactive shell.
15549 @cindex file name pattern expansion, disabled
15550 @cindex globbing, disabled
15551 Pass the @option{-f} option to the shell. This probably only makes sense
15552 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15553 option prevents reading the startup file (@file{.cshrc}). With
15554 Bourne-like shells, the @option{-f} option disables file name pattern
15555 expansion (globbing), which is not likely to be useful.
15563 @c other variables already indexed above
15566 @cindex login shell, creating
15567 Make the shell a login shell. This means the following. Unset all
15568 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15569 (which are set as described above), and @env{USER} and @env{LOGNAME}
15570 (which are set, even for the super-user, as described above), and set
15571 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15572 directory. Prepend @samp{-} to the shell's name, intended to make it
15573 read its login startup file(s).
15577 @itemx --preserve-environment
15580 @opindex --preserve-environment
15581 @cindex environment, preserving
15582 @flindex /etc/shells
15583 @cindex restricted shell
15584 Do not change the environment variables @env{HOME}, @env{USER},
15585 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15586 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15587 entry, unless the user running @command{su} is not the super-user and
15588 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15589 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15590 if that file does not exist. Parts of what this option does can be
15591 overridden by @option{--login} and @option{--shell}.
15593 @item -s @var{shell}
15594 @itemx --shell=@var{shell}
15597 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15598 unless the user running @command{su} is not the super-user and @var{user}'s
15599 shell is restricted (see @option{-m} just above).
15603 @cindex exit status of @command{su}
15607 125 if @command{su} itself fails
15608 126 if subshell is found but cannot be invoked
15609 127 if subshell cannot be found
15610 the exit status of the subshell otherwise
15613 @cindex wheel group, not supported
15614 @cindex group wheel, not supported
15616 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15618 (This section is by Richard Stallman.)
15622 Sometimes a few of the users try to hold total power over all the
15623 rest. For example, in 1984, a few users at the MIT AI lab decided to
15624 seize power by changing the operator password on the Twenex system and
15625 keeping it secret from everyone else. (I was able to thwart this coup
15626 and give power back to the users by patching the kernel, but I
15627 wouldn't know how to do that in Unix.)
15629 However, occasionally the rulers do tell someone. Under the usual
15630 @command{su} mechanism, once someone learns the root password who
15631 sympathizes with the ordinary users, he or she can tell the rest. The
15632 ``wheel group'' feature would make this impossible, and thus cement the
15633 power of the rulers.
15635 I'm on the side of the masses, not that of the rulers. If you are
15636 used to supporting the bosses and sysadmins in whatever they do, you
15637 might find this idea strange at first.
15640 @node timeout invocation
15641 @section @command{timeout}: Run a command with a time limit
15645 @cindex run commands with bounded time
15647 @command{timeout} runs the given @var{command} and kills it if it is
15648 still running after the specified time interval. Synopsis:
15651 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15654 @var{command} must not be a special built-in utility (@pxref{Special
15655 built-in utilities}).
15657 The program accepts the following options. Also see @ref{Common options}.
15658 Options must precede operands.
15661 @itemx --foreground
15662 @opindex --foreground
15663 Don't create a separate background program group, so that
15664 the managed @var{command} can use the foreground TTY normally.
15665 This is needed to support timing out commands not started
15666 directly from an interactive shell, in two situations.
15669 @var{command} is interactive and needs to read from the terminal for example
15671 the user wants to support sending signals directly to @var{command}
15672 from the terminal (like Ctrl-C for example)
15675 Note in this mode of operation, any children of @var{command}
15676 will not be timed out.
15678 @item -k @var{duration}
15679 @itemx --kill-after=@var{duration}
15681 @opindex --kill-after
15682 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15683 signal, after the specified @var{duration}. Without this option, if the
15684 selected signal proves not to be fatal, @command{timeout} does not kill
15687 @item -s @var{signal}
15688 @itemx --signal=@var{signal}
15691 Send this @var{signal} to @var{command} on timeout, rather than the
15692 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15693 or a number. Also see @xref{Signal specifications}.
15697 @var{duration} is an integer followed by an optional unit:
15699 @samp{s} for seconds (the default)
15700 @samp{m} for minutes
15704 A duration of 0 disables the associated timeout.
15706 @cindex exit status of @command{timeout}
15710 124 if @var{command} times out
15711 125 if @command{timeout} itself fails
15712 126 if @var{command} is found but cannot be invoked
15713 127 if @var{command} cannot be found
15714 the exit status of @var{command} otherwise
15718 @node Process control
15719 @chapter Process control
15721 @cindex processes, commands for controlling
15722 @cindex commands for controlling processes
15725 * kill invocation:: Sending a signal to processes.
15729 @node kill invocation
15730 @section @command{kill}: Send a signal to processes
15733 @cindex send a signal to processes
15735 The @command{kill} command sends a signal to processes, causing them
15736 to terminate or otherwise act upon receiving the signal in some way.
15737 Alternatively, it lists information about signals. Synopses:
15740 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15741 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15744 @mayConflictWithShellBuiltIn{kill}
15746 The first form of the @command{kill} command sends a signal to all
15747 @var{pid} arguments. The default signal to send if none is specified
15748 is @samp{TERM}. The special signal number @samp{0} does not denote a
15749 valid signal, but can be used to test whether the @var{pid} arguments
15750 specify processes to which a signal could be sent.
15752 If @var{pid} is positive, the signal is sent to the process with the
15753 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15754 processes in the process group of the current process. If @var{pid}
15755 is @minus{}1, the signal is sent to all processes for which the user has
15756 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15757 is sent to all processes in the process group that equals the absolute
15758 value of @var{pid}.
15760 If @var{pid} is not positive, a system-dependent set of system
15761 processes is excluded from the list of processes to which the signal
15764 If a negative @var{pid} argument is desired as the first one, it
15765 should be preceded by @option{--}. However, as a common extension to
15766 @acronym{POSIX}, @option{--} is not required with @samp{kill
15767 -@var{signal} -@var{pid}}. The following commands are equivalent:
15776 The first form of the @command{kill} command succeeds if every @var{pid}
15777 argument specifies at least one process that the signal was sent to.
15779 The second form of the @command{kill} command lists signal information.
15780 Either the @option{-l} or @option{--list} option, or the @option{-t}
15781 or @option{--table} option must be specified. Without any
15782 @var{signal} argument, all supported signals are listed. The output
15783 of @option{-l} or @option{--list} is a list of the signal names, one
15784 per line; if @var{signal} is already a name, the signal number is
15785 printed instead. The output of @option{-t} or @option{--table} is a
15786 table of signal numbers, names, and descriptions. This form of the
15787 @command{kill} command succeeds if all @var{signal} arguments are valid
15788 and if there is no output error.
15790 The @command{kill} command also supports the @option{--help} and
15791 @option{--version} options. @xref{Common options}.
15793 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15794 number like @samp{1}, or an exit status of a process terminated by the
15795 signal. A signal name can be given in canonical form or prefixed by
15796 @samp{SIG}. The case of the letters is ignored, except for the
15797 @option{-@var{signal}} option which must use upper case to avoid
15798 ambiguity with lower case option letters. For a list of supported
15799 signal names and numbers see @xref{Signal specifications}.
15804 @cindex delaying commands
15805 @cindex commands for delaying
15807 @c Perhaps @command{wait} or other commands should be described here also?
15810 * sleep invocation:: Delay for a specified time.
15814 @node sleep invocation
15815 @section @command{sleep}: Delay for a specified time
15818 @cindex delay for a specified time
15820 @command{sleep} pauses for an amount of time specified by the sum of
15821 the values of the command line arguments.
15825 sleep @var{number}[smhd]@dots{}
15829 Each argument is a number followed by an optional unit; the default
15830 is seconds. The units are:
15843 Historical implementations of @command{sleep} have required that
15844 @var{number} be an integer, and only accepted a single argument
15845 without a suffix. However, GNU @command{sleep} accepts
15846 arbitrary floating point numbers. @xref{Floating point}.
15848 The only options are @option{--help} and @option{--version}. @xref{Common
15851 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15852 @mayConflictWithShellBuiltIn{sleep}
15857 @node Numeric operations
15858 @chapter Numeric operations
15860 @cindex numeric operations
15861 These programs do numerically-related operations.
15864 * factor invocation:: Show factors of numbers.
15865 * seq invocation:: Print sequences of numbers.
15869 @node factor invocation
15870 @section @command{factor}: Print prime factors
15873 @cindex prime factors
15875 @command{factor} prints prime factors. Synopses:
15878 factor [@var{number}]@dots{}
15879 factor @var{option}
15882 If no @var{number} is specified on the command line, @command{factor} reads
15883 numbers from standard input, delimited by newlines, tabs, or spaces.
15885 The @command{factor} command supports only a small number of options:
15889 Print a short help on standard output, then exit without further
15893 Print the program version on standard output, then exit without further
15897 Factoring the product of the eighth and ninth Mersenne primes
15898 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15901 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15902 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15903 4951760154835678088235319297: 2147483647 2305843009213693951
15907 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15908 about 20 seconds on the same machine.
15910 Factoring large numbers is, in general, hard. The Pollard Rho
15911 algorithm used by @command{factor} is particularly effective for
15912 numbers with relatively small factors. If you wish to factor large
15913 numbers which do not have small factors (for example, numbers which
15914 are the product of two large primes), other methods are far better.
15916 If @command{factor} is built without using GNU MP, only
15917 single-precision arithmetic is available, and so large numbers
15918 (typically @math{2^{64}} and above) will not be supported. The single-precision
15919 code uses an algorithm which is designed for factoring smaller
15925 @node seq invocation
15926 @section @command{seq}: Print numeric sequences
15929 @cindex numeric sequences
15930 @cindex sequence of numbers
15932 @command{seq} prints a sequence of numbers to standard output. Synopses:
15935 seq [@var{option}]@dots{} @var{last}
15936 seq [@var{option}]@dots{} @var{first} @var{last}
15937 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15940 @command{seq} prints the numbers from @var{first} to @var{last} by
15941 @var{increment}. By default, each number is printed on a separate line.
15942 When @var{increment} is not specified, it defaults to @samp{1},
15943 even when @var{first} is larger than @var{last}.
15944 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15945 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15946 Floating-point numbers may be specified. @xref{Floating point}.
15948 The program accepts the following options. Also see @ref{Common options}.
15949 Options must precede operands.
15952 @item -f @var{format}
15953 @itemx --format=@var{format}
15954 @opindex -f @var{format}
15955 @opindex --format=@var{format}
15956 @cindex formatting of numbers in @command{seq}
15957 Print all numbers using @var{format}.
15958 @var{format} must contain exactly one of the @samp{printf}-style
15959 floating point conversion specifications @samp{%a}, @samp{%e},
15960 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15961 The @samp{%} may be followed by zero or more flags taken from the set
15962 @samp{-+#0 '}, then an optional width containing one or more digits,
15963 then an optional precision consisting of a @samp{.} followed by zero
15964 or more digits. @var{format} may also contain any number of @samp{%%}
15965 conversion specifications. All conversion specifications have the
15966 same meaning as with @samp{printf}.
15968 The default format is derived from @var{first}, @var{step}, and
15969 @var{last}. If these all use a fixed point decimal representation,
15970 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15971 precision that can represent the output numbers exactly. Otherwise,
15972 the default format is @samp{%g}.
15974 @item -s @var{string}
15975 @itemx --separator=@var{string}
15976 @cindex separator for numbers in @command{seq}
15977 Separate numbers with @var{string}; default is a newline.
15978 The output always terminates with a newline.
15981 @itemx --equal-width
15982 Print all numbers with the same width, by padding with leading zeros.
15983 @var{first}, @var{step}, and @var{last} should all use a fixed point
15984 decimal representation.
15985 (To have other kinds of padding, use @option{--format}).
15989 You can get finer-grained control over output with @option{-f}:
15992 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15998 If you want hexadecimal integer output, you can use @command{printf}
15999 to perform the conversion:
16002 $ printf '%x\n' `seq 1048575 1024 1050623`
16008 For very long lists of numbers, use xargs to avoid
16009 system limitations on the length of an argument list:
16012 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
16018 To generate octal output, use the printf @code{%o} format instead
16021 On most systems, seq can produce whole-number output for values up to
16022 at least @math{2^{53}}. Larger integers are approximated. The details
16023 differ depending on your floating-point implementation.
16024 @xref{Floating point}. A common
16025 case is that @command{seq} works with integers through @math{2^{64}},
16026 and larger integers may not be numerically correct:
16029 $ seq 18446744073709551616 1 18446744073709551618
16030 18446744073709551616
16031 18446744073709551616
16032 18446744073709551618
16035 Be careful when using @command{seq} with outlandish values: otherwise
16036 you may see surprising results, as @command{seq} uses floating point
16037 internally. For example, on the x86 platform, where the internal
16038 representation uses a 64-bit fraction, the command:
16041 seq 1 0.0000000000000000001 1.0000000000000000009
16044 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
16049 @node File permissions
16050 @chapter File permissions
16053 @include parse-datetime.texi
16057 @node Opening the software toolbox
16058 @chapter Opening the Software Toolbox
16060 An earlier version of this chapter appeared in
16061 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
16062 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
16063 It was written by Arnold Robbins.
16066 * Toolbox introduction:: Toolbox introduction
16067 * I/O redirection:: I/O redirection
16068 * The who command:: The @command{who} command
16069 * The cut command:: The @command{cut} command
16070 * The sort command:: The @command{sort} command
16071 * The uniq command:: The @command{uniq} command
16072 * Putting the tools together:: Putting the tools together
16076 @node Toolbox introduction
16077 @unnumberedsec Toolbox Introduction
16079 This month's column is only peripherally related to the GNU Project, in
16080 that it describes a number of the GNU tools on your GNU/Linux system
16082 might be used. What it's really about is the ``Software Tools'' philosophy
16083 of program development and usage.
16085 The software tools philosophy was an important and integral concept
16086 in the initial design and development of Unix (of which Linux and GNU are
16087 essentially clones). Unfortunately, in the modern day press of
16088 Internetworking and flashy GUIs, it seems to have fallen by the
16089 wayside. This is a shame, since it provides a powerful mental model
16090 for solving many kinds of problems.
16092 Many people carry a Swiss Army knife around in their pants pockets (or
16093 purse). A Swiss Army knife is a handy tool to have: it has several knife
16094 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
16095 a number of other things on it. For the everyday, small miscellaneous jobs
16096 where you need a simple, general purpose tool, it's just the thing.
16098 On the other hand, an experienced carpenter doesn't build a house using
16099 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
16100 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
16101 exactly when and where to use each tool; you won't catch him hammering nails
16102 with the handle of his screwdriver.
16104 The Unix developers at Bell Labs were all professional programmers and trained
16105 computer scientists. They had found that while a one-size-fits-all program
16106 might appeal to a user because there's only one program to use, in practice
16111 difficult to write,
16114 difficult to maintain and
16118 difficult to extend to meet new situations.
16121 Instead, they felt that programs should be specialized tools. In short, each
16122 program ``should do one thing well.'' No more and no less. Such programs are
16123 simpler to design, write, and get right---they only do one thing.
16125 Furthermore, they found that with the right machinery for hooking programs
16126 together, that the whole was greater than the sum of the parts. By combining
16127 several special purpose programs, you could accomplish a specific task
16128 that none of the programs was designed for, and accomplish it much more
16129 quickly and easily than if you had to write a special purpose program.
16130 We will see some (classic) examples of this further on in the column.
16131 (An important additional point was that, if necessary, take a detour
16132 and build any software tools you may need first, if you don't already
16133 have something appropriate in the toolbox.)
16135 @node I/O redirection
16136 @unnumberedsec I/O Redirection
16138 Hopefully, you are familiar with the basics of I/O redirection in the
16139 shell, in particular the concepts of ``standard input,'' ``standard output,''
16140 and ``standard error''. Briefly, ``standard input'' is a data source, where
16141 data comes from. A program should not need to either know or care if the
16142 data source is a disk file, a keyboard, a magnetic tape, or even a punched
16143 card reader. Similarly, ``standard output'' is a data sink, where data goes
16144 to. The program should neither know nor care where this might be.
16145 Programs that only read their standard input, do something to the data,
16146 and then send it on, are called @dfn{filters}, by analogy to filters in a
16149 With the Unix shell, it's very easy to set up data pipelines:
16152 program_to_create_data | filter1 | ... | filterN > final.pretty.data
16155 We start out by creating the raw data; each filter applies some successive
16156 transformation to the data, until by the time it comes out of the pipeline,
16157 it is in the desired form.
16159 This is fine and good for standard input and standard output. Where does the
16160 standard error come in to play? Well, think about @command{filter1} in
16161 the pipeline above. What happens if it encounters an error in the data it
16162 sees? If it writes an error message to standard output, it will just
16163 disappear down the pipeline into @command{filter2}'s input, and the
16164 user will probably never see it. So programs need a place where they can send
16165 error messages so that the user will notice them. This is standard error,
16166 and it is usually connected to your console or window, even if you have
16167 redirected standard output of your program away from your screen.
16169 For filter programs to work together, the format of the data has to be
16170 agreed upon. The most straightforward and easiest format to use is simply
16171 lines of text. Unix data files are generally just streams of bytes, with
16172 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
16173 conventionally called a ``newline'' in the Unix literature. (This is
16174 @code{'\n'} if you're a C programmer.) This is the format used by all
16175 the traditional filtering programs. (Many earlier operating systems
16176 had elaborate facilities and special purpose programs for managing
16177 binary data. Unix has always shied away from such things, under the
16178 philosophy that it's easiest to simply be able to view and edit your
16179 data with a text editor.)
16181 OK, enough introduction. Let's take a look at some of the tools, and then
16182 we'll see how to hook them together in interesting ways. In the following
16183 discussion, we will only present those command line options that interest
16184 us. As you should always do, double check your system documentation
16185 for the full story.
16187 @node The who command
16188 @unnumberedsec The @command{who} Command
16190 The first program is the @command{who} command. By itself, it generates a
16191 list of the users who are currently logged in. Although I'm writing
16192 this on a single-user system, we'll pretend that several people are
16197 @print{} arnold console Jan 22 19:57
16198 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
16199 @print{} bill ttyp1 Jan 21 09:32(:0.0)
16200 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
16203 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
16204 There are three people logged in, and I am logged in twice. On traditional
16205 Unix systems, user names are never more than eight characters long. This
16206 little bit of trivia will be useful later. The output of @command{who} is nice,
16207 but the data is not all that exciting.
16209 @node The cut command
16210 @unnumberedsec The @command{cut} Command
16212 The next program we'll look at is the @command{cut} command. This program
16213 cuts out columns or fields of input data. For example, we can tell it
16214 to print just the login name and full name from the @file{/etc/passwd}
16215 file. The @file{/etc/passwd} file has seven fields, separated by
16219 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
16222 To get the first and fifth fields, we would use @command{cut} like this:
16225 $ cut -d: -f1,5 /etc/passwd
16226 @print{} root:Operator
16228 @print{} arnold:Arnold D. Robbins
16229 @print{} miriam:Miriam A. Robbins
16233 With the @option{-c} option, @command{cut} will cut out specific characters
16234 (i.e., columns) in the input lines. This is useful for input data
16235 that has fixed width fields, and does not have a field separator. For
16236 example, list the Monday dates for the current month:
16238 @c Is using cal ok? Looked at gcal, but I don't like it.
16249 @node The sort command
16250 @unnumberedsec The @command{sort} Command
16252 Next we'll look at the @command{sort} command. This is one of the most
16253 powerful commands on a Unix-style system; one that you will often find
16254 yourself using when setting up fancy data plumbing.
16257 command reads and sorts each file named on the command line. It then
16258 merges the sorted data and writes it to standard output. It will read
16259 standard input if no files are given on the command line (thus
16260 making it into a filter). The sort is based on the character collating
16261 sequence or based on user-supplied ordering criteria.
16264 @node The uniq command
16265 @unnumberedsec The @command{uniq} Command
16267 Finally (at least for now), we'll look at the @command{uniq} program. When
16268 sorting data, you will often end up with duplicate lines, lines that
16269 are identical. Usually, all you need is one instance of each line.
16270 This is where @command{uniq} comes in. The @command{uniq} program reads its
16271 standard input. It prints only one
16272 copy of each repeated line. It does have several options. Later on,
16273 we'll use the @option{-c} option, which prints each unique line, preceded
16274 by a count of the number of times that line occurred in the input.
16277 @node Putting the tools together
16278 @unnumberedsec Putting the Tools Together
16280 Now, let's suppose this is a large ISP server system with dozens of users
16281 logged in. The management wants the system administrator to write a
16283 generate a sorted list of logged in users. Furthermore, even if a user
16284 is logged in multiple times, his or her name should only show up in the
16287 The administrator could sit down with the system documentation and write a C
16288 program that did this. It would take perhaps a couple of hundred lines
16289 of code and about two hours to write it, test it, and debug it.
16290 However, knowing the software toolbox, the administrator can instead start out
16291 by generating just a list of logged on users:
16301 Next, sort the list:
16304 $ who | cut -c1-8 | sort
16311 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
16314 $ who | cut -c1-8 | sort | uniq
16320 The @command{sort} command actually has a @option{-u} option that does what
16321 @command{uniq} does. However, @command{uniq} has other uses for which one
16322 cannot substitute @samp{sort -u}.
16324 The administrator puts this pipeline into a shell script, and makes it
16326 all the users on the system (@samp{#} is the system administrator,
16327 or @code{root}, prompt):
16330 # cat > /usr/local/bin/listusers
16331 who | cut -c1-8 | sort | uniq
16333 # chmod +x /usr/local/bin/listusers
16336 There are four major points to note here. First, with just four
16337 programs, on one command line, the administrator was able to save about two
16338 hours worth of work. Furthermore, the shell pipeline is just about as
16339 efficient as the C program would be, and it is much more efficient in
16340 terms of programmer time. People time is much more expensive than
16341 computer time, and in our modern ``there's never enough time to do
16342 everything'' society, saving two hours of programmer time is no mean
16345 Second, it is also important to emphasize that with the
16346 @emph{combination} of the tools, it is possible to do a special
16347 purpose job never imagined by the authors of the individual programs.
16349 Third, it is also valuable to build up your pipeline in stages, as we did here.
16350 This allows you to view the data at each stage in the pipeline, which helps
16351 you acquire the confidence that you are indeed using these tools correctly.
16353 Finally, by bundling the pipeline in a shell script, other users can use
16354 your command, without having to remember the fancy plumbing you set up for
16355 them. In terms of how you run them, shell scripts and compiled programs are
16358 After the previous warm-up exercise, we'll look at two additional, more
16359 complicated pipelines. For them, we need to introduce two more tools.
16361 The first is the @command{tr} command, which stands for ``transliterate.''
16362 The @command{tr} command works on a character-by-character basis, changing
16363 characters. Normally it is used for things like mapping upper case to
16367 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
16368 @print{} this example has mixed case!
16371 There are several options of interest:
16375 work on the complement of the listed characters, i.e.,
16376 operations apply to characters not in the given set
16379 delete characters in the first set from the output
16382 squeeze repeated characters in the output into just one character.
16385 We will be using all three options in a moment.
16387 The other command we'll look at is @command{comm}. The @command{comm}
16388 command takes two sorted input files as input data, and prints out the
16389 files' lines in three columns. The output columns are the data lines
16390 unique to the first file, the data lines unique to the second file, and
16391 the data lines that are common to both. The @option{-1}, @option{-2}, and
16392 @option{-3} command line options @emph{omit} the respective columns. (This is
16393 non-intuitive and takes a little getting used to.) For example:
16415 The file name @file{-} tells @command{comm} to read standard input
16416 instead of a regular file.
16418 Now we're ready to build a fancy pipeline. The first application is a word
16419 frequency counter. This helps an author determine if he or she is over-using
16422 The first step is to change the case of all the letters in our input file
16423 to one case. ``The'' and ``the'' are the same word when doing counting.
16426 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16429 The next step is to get rid of punctuation. Quoted words and unquoted words
16430 should be treated identically; it's easiest to just get the punctuation out of
16434 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16437 The second @command{tr} command operates on the complement of the listed
16438 characters, which are all the letters, the digits, the underscore, and
16439 the blank. The @samp{\n} represents the newline character; it has to
16440 be left alone. (The @acronym{ASCII} tab character should also be included for
16441 good measure in a production script.)
16443 At this point, we have data consisting of words separated by blank space.
16444 The words only contain alphanumeric characters (and the underscore). The
16445 next step is break the data apart so that we have one word per line. This
16446 makes the counting operation much easier, as we will see shortly.
16449 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16450 > tr -s ' ' '\n' | ...
16453 This command turns blanks into newlines. The @option{-s} option squeezes
16454 multiple newline characters in the output into just one. This helps us
16455 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16456 This is what the shell prints when it notices you haven't finished
16457 typing in all of a command.)
16459 We now have data consisting of one word per line, no punctuation, all one
16460 case. We're ready to count each word:
16463 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16464 > tr -s ' ' '\n' | sort | uniq -c | ...
16467 At this point, the data might look something like this:
16480 The output is sorted by word, not by count! What we want is the most
16481 frequently used words first. Fortunately, this is easy to accomplish,
16482 with the help of two more @command{sort} options:
16486 do a numeric sort, not a textual one
16489 reverse the order of the sort
16492 The final pipeline looks like this:
16495 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16496 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16505 Whew! That's a lot to digest. Yet, the same principles apply. With six
16506 commands, on two lines (really one long one split for convenience), we've
16507 created a program that does something interesting and useful, in much
16508 less time than we could have written a C program to do the same thing.
16510 A minor modification to the above pipeline can give us a simple spelling
16511 checker! To determine if you've spelled a word correctly, all you have to
16512 do is look it up in a dictionary. If it is not there, then chances are
16513 that your spelling is incorrect. So, we need a dictionary.
16514 The conventional location for a dictionary is @file{/usr/dict/words}.
16515 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16516 revision of this article.}
16517 this is a sorted, 45,402 word dictionary.
16519 Now, how to compare our file with the dictionary? As before, we generate
16520 a sorted list of words, one per line:
16523 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16524 > tr -s ' ' '\n' | sort -u | ...
16527 Now, all we need is a list of words that are @emph{not} in the
16528 dictionary. Here is where the @command{comm} command comes in.
16531 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16532 > tr -s ' ' '\n' | sort -u |
16533 > comm -23 - /usr/dict/words
16536 The @option{-2} and @option{-3} options eliminate lines that are only in the
16537 dictionary (the second file), and lines that are in both files. Lines
16538 only in the first file (standard input, our stream of words), are
16539 words that are not in the dictionary. These are likely candidates for
16540 spelling errors. This pipeline was the first cut at a production
16541 spelling checker on Unix.
16543 There are some other tools that deserve brief mention.
16547 search files for text that matches a regular expression
16550 count lines, words, characters
16553 a T-fitting for data pipes, copies data to files and to standard output
16556 the stream editor, an advanced tool
16559 a data manipulation language, another advanced tool
16562 The software tools philosophy also espoused the following bit of
16563 advice: ``Let someone else do the hard part.'' This means, take
16564 something that gives you most of what you need, and then massage it the
16565 rest of the way until it's in the form that you want.
16571 Each program should do one thing well. No more, no less.
16574 Combining programs with appropriate plumbing leads to results where
16575 the whole is greater than the sum of the parts. It also leads to novel
16576 uses of programs that the authors might never have imagined.
16579 Programs should never print extraneous header or trailer data, since these
16580 could get sent on down a pipeline. (A point we didn't mention earlier.)
16583 Let someone else do the hard part.
16586 Know your toolbox! Use each program appropriately. If you don't have an
16587 appropriate tool, build one.
16590 As of this writing, all the programs we've discussed are available via
16591 anonymous @command{ftp} from: @*
16592 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16593 be more recent versions available now.)
16595 None of what I have presented in this column is new. The Software Tools
16596 philosophy was first introduced in the book @cite{Software Tools}, by
16597 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16598 This book showed how to write and use software tools. It was written in
16599 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16600 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16601 was. The last chapter presented a @command{ratfor} to FORTRAN
16602 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16603 lot like C; if you know C, you won't have any problem following the
16606 In 1981, the book was updated and made available as @cite{Software Tools
16607 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16608 still in print and are well worth
16609 reading if you're a programmer. They certainly made a major change in
16610 how I view programming.
16612 The programs in both books are available from
16613 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16614 For a number of years, there was an active
16615 Software Tools Users Group, whose members had ported the original
16616 @command{ratfor} programs to essentially every computer system with a
16617 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16618 as Unix began to spread beyond universities.
16620 With the current proliferation of GNU code and other clones of Unix programs,
16621 these programs now receive little attention; modern C versions are
16622 much more efficient and do more than these programs do. Nevertheless, as
16623 exposition of good programming style, and evangelism for a still-valuable
16624 philosophy, these books are unparalleled, and I recommend them highly.
16626 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16627 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16629 @node GNU Free Documentation License
16630 @appendix GNU Free Documentation License
16634 @node Concept index
16641 @c Local variables:
16642 @c texinfo-column-for-description: 32