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.
34 @c * mktemp: (coreutils)mktemp invocation. FIXME.
36 @dircategory Individual utilities
38 * arch: (coreutils)arch invocation. Print machine hardware name.
39 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
40 * basename: (coreutils)basename invocation. Strip directory and suffix.
41 * cat: (coreutils)cat invocation. Concatenate and write files.
42 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
43 * chgrp: (coreutils)chgrp invocation. Change file groups.
44 * chmod: (coreutils)chmod invocation. Change file permissions.
45 * chown: (coreutils)chown invocation. Change file owners/groups.
46 * chroot: (coreutils)chroot invocation. Specify the root directory.
47 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
48 * comm: (coreutils)comm invocation. Compare sorted files by line.
49 * cp: (coreutils)cp invocation. Copy files.
50 * csplit: (coreutils)csplit invocation. Split by context.
51 * cut: (coreutils)cut invocation. Print selected parts of lines.
52 * date: (coreutils)date invocation. Print/set system date and time.
53 * dd: (coreutils)dd invocation. Copy and convert a file.
54 * df: (coreutils)df invocation. Report file system disk usage.
55 * dir: (coreutils)dir invocation. List directories briefly.
56 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
57 * dirname: (coreutils)dirname invocation. Strip non-directory suffix.
58 * du: (coreutils)du invocation. Report on disk usage.
59 * echo: (coreutils)echo invocation. Print a line of text.
60 * env: (coreutils)env invocation. Modify the environment.
61 * expand: (coreutils)expand invocation. Convert tabs to spaces.
62 * expr: (coreutils)expr invocation. Evaluate expressions.
63 * factor: (coreutils)factor invocation. Print prime factors
64 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
65 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
66 * fold: (coreutils)fold invocation. Wrap long input lines.
67 * groups: (coreutils)groups invocation. Print group names a user is in.
68 * head: (coreutils)head invocation. Output the first part of files.
69 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
70 * hostname: (coreutils)hostname invocation. Print or set system name.
71 * id: (coreutils)id invocation. Print user identity.
72 * install: (coreutils)install invocation. Copy and change attributes.
73 * join: (coreutils)join invocation. Join lines on a common field.
74 * kill: (coreutils)kill invocation. Send a signal to processes.
75 * link: (coreutils)link invocation. Make hard links between files.
76 * ln: (coreutils)ln invocation. Make links between files.
77 * logname: (coreutils)logname invocation. Print current login name.
78 * ls: (coreutils)ls invocation. List directory contents.
79 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
80 * mkdir: (coreutils)mkdir invocation. Create directories.
81 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
82 * mknod: (coreutils)mknod invocation. Create special 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 * od: (coreutils)od invocation. Dump files in octal, etc.
88 * paste: (coreutils)paste invocation. Merge lines of files.
89 * pathchk: (coreutils)pathchk invocation. Check file name portability.
90 * pr: (coreutils)pr invocation. Paginate or columnate files.
91 * printenv: (coreutils)printenv invocation. Print environment variables.
92 * printf: (coreutils)printf invocation. Format and print data.
93 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
94 * pwd: (coreutils)pwd invocation. Print working directory.
95 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
96 * rm: (coreutils)rm invocation. Remove files.
97 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
98 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
99 * seq: (coreutils)seq invocation. Print numeric sequences
100 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
101 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
102 * shred: (coreutils)shred invocation. Remove files more securely.
103 * shuf: (coreutils)shuf invocation. Shuffling text files.
104 * sleep: (coreutils)sleep invocation. Delay for a specified time.
105 * sort: (coreutils)sort invocation. Sort text files.
106 * split: (coreutils)split invocation. Split into fixed-size pieces.
107 * stat: (coreutils)stat invocation. Report file(system) status.
108 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
109 * stty: (coreutils)stty invocation. Print/change terminal settings.
110 * su: (coreutils)su invocation. Modify user and group ID.
111 * sum: (coreutils)sum invocation. Print traditional checksum.
112 * sync: (coreutils)sync invocation. Synchronize memory and disk.
113 * tac: (coreutils)tac invocation. Reverse files.
114 * tail: (coreutils)tail invocation. Output the last part of files.
115 * tee: (coreutils)tee invocation. Redirect to multiple files.
116 * test: (coreutils)test invocation. File/string tests.
117 * timeout: (coreutils)timeout invocation. Run with time limit.
118 * touch: (coreutils)touch invocation. Change file timestamps.
119 * tr: (coreutils)tr invocation. Translate characters.
120 * true: (coreutils)true invocation. Do nothing, successfully.
121 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
122 * tsort: (coreutils)tsort invocation. Topological sort.
123 * tty: (coreutils)tty invocation. Print terminal name.
124 * uname: (coreutils)uname invocation. Print system information.
125 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
126 * uniq: (coreutils)uniq invocation. Uniquify files.
127 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
128 * uptime: (coreutils)uptime invocation. Print uptime and load.
129 * users: (coreutils)users invocation. Print current user names.
130 * vdir: (coreutils)vdir invocation. List directories verbosely.
131 * wc: (coreutils)wc invocation. Line, word, and byte counts.
132 * who: (coreutils)who invocation. Print who is logged in.
133 * whoami: (coreutils)whoami invocation. Print effective user ID.
134 * yes: (coreutils)yes invocation. Print a string indefinitely.
138 This manual documents version @value{VERSION} of the @sc{gnu} core
139 utilities, including the standard programs for text and file manipulation.
141 Copyright @copyright{} 1994-1996, 2000-2009 Free Software Foundation, Inc.
144 Permission is granted to copy, distribute and/or modify this document
145 under the terms of the GNU Free Documentation License, Version 1.3 or
146 any later version published by the Free Software Foundation; with no
147 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
148 Texts. A copy of the license is included in the section entitled ``GNU
149 Free Documentation License''.
154 @title @sc{gnu} @code{Coreutils}
155 @subtitle Core GNU utilities
156 @subtitle for version @value{VERSION}, @value{UPDATED}
157 @author David MacKenzie et al.
160 @vskip 0pt plus 1filll
173 @cindex core utilities
174 @cindex text utilities
175 @cindex shell utilities
176 @cindex file utilities
179 * Introduction:: Caveats, overview, and authors.
180 * Common options:: Common options.
181 * Output of entire files:: cat tac nl od
182 * Formatting file contents:: fmt pr fold
183 * Output of parts of files:: head tail split csplit
184 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
185 * Operating on sorted files:: sort shuf uniq comm ptx tsort
186 * Operating on fields within a line:: cut paste join
187 * Operating on characters:: tr expand unexpand
188 * Directory listing:: ls dir vdir dircolors
189 * Basic operations:: cp dd install mv rm shred
190 * Special file types:: ln mkdir rmdir mkfifo mknod
191 * Changing file attributes:: chgrp chmod chown touch
192 * Disk usage:: df du stat sync truncate
193 * Printing text:: echo printf yes
194 * Conditions:: false true test expr
196 * File name manipulation:: dirname basename pathchk
197 * Working context:: pwd stty printenv tty
198 * User information:: id logname whoami groups users who
199 * System context:: date uname hostname hostid uptime
200 * SELinux context:: chcon runcon
201 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
202 * Process control:: kill
204 * Numeric operations:: factor seq
205 * File permissions:: Access modes.
206 * Date input formats:: Specifying date strings.
207 * Opening the software toolbox:: The software tools philosophy.
208 * GNU Free Documentation License:: Copying and sharing this manual.
209 * Concept index:: General index.
212 --- The Detailed Node Listing ---
216 * Exit status:: Indicating program success or failure.
217 * Backup options:: Backup options
218 * Block size:: Block size
219 * Signal specifications:: Specifying signals
220 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
221 * Random sources:: Sources of random data
222 * Target directory:: Target directory
223 * Trailing slashes:: Trailing slashes
224 * Traversing symlinks:: Traversing symlinks to directories
225 * Treating / specially:: Treating / specially
226 * Standards conformance:: Standards conformance
228 Output of entire files
230 * cat invocation:: Concatenate and write files.
231 * tac invocation:: Concatenate and write files in reverse.
232 * nl invocation:: Number lines and write files.
233 * od invocation:: Write files in octal or other formats.
234 * base64 invocation:: Transform data into printable data.
236 Formatting file contents
238 * fmt invocation:: Reformat paragraph text.
239 * pr invocation:: Paginate or columnate files for printing.
240 * fold invocation:: Wrap input lines to fit in specified width.
242 Output of parts of files
244 * head invocation:: Output the first part of files.
245 * tail invocation:: Output the last part of files.
246 * split invocation:: Split a file into fixed-size pieces.
247 * csplit invocation:: Split a file into context-determined pieces.
251 * wc invocation:: Print newline, word, and byte counts.
252 * sum invocation:: Print checksum and block counts.
253 * cksum invocation:: Print CRC checksum and byte counts.
254 * md5sum invocation:: Print or check MD5 digests.
255 * sha1sum invocation:: Print or check SHA-1 digests.
256 * sha2 utilities:: Print or check SHA-2 digests.
258 Operating on sorted files
260 * sort invocation:: Sort text files.
261 * shuf invocation:: Shuffle text files.
262 * uniq invocation:: Uniquify files.
263 * comm invocation:: Compare two sorted files line by line.
264 * ptx invocation:: Produce a permuted index of file contents.
265 * tsort invocation:: Topological sort.
267 @command{ptx}: Produce permuted indexes
269 * General options in ptx:: Options which affect general program behavior.
270 * Charset selection in ptx:: Underlying character set considerations.
271 * Input processing in ptx:: Input fields, contexts, and keyword selection.
272 * Output formatting in ptx:: Types of output format, and sizing the fields.
273 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
275 Operating on fields within a line
277 * cut invocation:: Print selected parts of lines.
278 * paste invocation:: Merge lines of files.
279 * join invocation:: Join lines on a common field.
281 Operating on characters
283 * tr invocation:: Translate, squeeze, and/or delete characters.
284 * expand invocation:: Convert tabs to spaces.
285 * unexpand invocation:: Convert spaces to tabs.
287 @command{tr}: Translate, squeeze, and/or delete characters
289 * Character sets:: Specifying sets of characters.
290 * Translating:: Changing one set of characters to another.
291 * Squeezing:: Squeezing repeats and deleting.
295 * ls invocation:: List directory contents
296 * dir invocation:: Briefly list directory contents
297 * vdir invocation:: Verbosely list directory contents
298 * dircolors invocation:: Color setup for @command{ls}
300 @command{ls}: List directory contents
302 * Which files are listed:: Which files are listed
303 * What information is listed:: What information is listed
304 * Sorting the output:: Sorting the output
305 * More details about version sort:: More details about version sort
306 * General output formatting:: General output formatting
307 * Formatting the file names:: Formatting the file names
311 * cp invocation:: Copy files and directories
312 * dd invocation:: Convert and copy a file
313 * install invocation:: Copy files and set attributes
314 * mv invocation:: Move (rename) files
315 * rm invocation:: Remove files or directories
316 * shred invocation:: Remove files more securely
320 * link invocation:: Make a hard link via the link syscall
321 * ln invocation:: Make links between files
322 * mkdir invocation:: Make directories
323 * mkfifo invocation:: Make FIFOs (named pipes)
324 * mknod invocation:: Make block or character special files
325 * readlink invocation:: Print value of a symlink or canonical file name
326 * rmdir invocation:: Remove empty directories
327 * unlink invocation:: Remove files via unlink syscall
329 Changing file attributes
331 * chown invocation:: Change file owner and group
332 * chgrp invocation:: Change group ownership
333 * chmod invocation:: Change access permissions
334 * touch invocation:: Change file timestamps
338 * df invocation:: Report file system disk space usage
339 * du invocation:: Estimate file space usage
340 * stat invocation:: Report file or file system status
341 * sync invocation:: Synchronize data on disk with memory
342 * truncate invocation:: Shrink or extend the size of a file
346 * echo invocation:: Print a line of text
347 * printf invocation:: Format and print data
348 * yes invocation:: Print a string until interrupted
352 * false invocation:: Do nothing, unsuccessfully
353 * true invocation:: Do nothing, successfully
354 * test invocation:: Check file types and compare values
355 * expr invocation:: Evaluate expressions
357 @command{test}: Check file types and compare values
359 * File type tests:: File type tests
360 * Access permission tests:: Access permission tests
361 * File characteristic tests:: File characteristic tests
362 * String tests:: String tests
363 * Numeric tests:: Numeric tests
365 @command{expr}: Evaluate expression
367 * String expressions:: + : match substr index length
368 * Numeric expressions:: + - * / %
369 * Relations for expr:: | & < <= = == != >= >
370 * Examples of expr:: Examples of using @command{expr}
374 * tee invocation:: Redirect output to multiple files or processes
376 File name manipulation
378 * basename invocation:: Strip directory and suffix from a file name
379 * dirname invocation:: Strip non-directory suffix from a file name
380 * pathchk invocation:: Check file name validity and portability
384 * pwd invocation:: Print working directory
385 * stty invocation:: Print or change terminal characteristics
386 * printenv invocation:: Print all or some environment variables
387 * tty invocation:: Print file name of terminal on standard input
389 @command{stty}: Print or change terminal characteristics
391 * Control:: Control settings
392 * Input:: Input settings
393 * Output:: Output settings
394 * Local:: Local settings
395 * Combination:: Combination settings
396 * Characters:: Special characters
397 * Special:: Special settings
401 * id invocation:: Print user identity
402 * logname invocation:: Print current login name
403 * whoami invocation:: Print effective user ID
404 * groups invocation:: Print group names a user is in
405 * users invocation:: Print login names of users currently logged in
406 * who invocation:: Print who is currently logged in
410 * arch invocation:: Print machine hardware name
411 * date invocation:: Print or set system date and time
412 * uname invocation:: Print system information
413 * hostname invocation:: Print or set system name
414 * hostid invocation:: Print numeric host identifier
415 * uptime invocation:: Print system uptime and load
417 @command{date}: Print or set system date and time
419 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
420 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
421 * Literal conversion specifiers:: %[%nt]
422 * Padding and other flags:: Pad with zeros, spaces, etc.
423 * Setting the time:: Changing the system clock.
424 * Options for date:: Instead of the current time.
425 * Date input formats:: Specifying date strings.
426 * Examples of date:: Examples.
430 * chcon invocation:: Change SELinux context of file
431 * runcon invocation:: Run a command in specified SELinux context
433 Modified command invocation
435 * chroot invocation:: Run a command with a different root directory
436 * env invocation:: Run a command in a modified environment
437 * nice invocation:: Run a command with modified niceness
438 * nohup invocation:: Run a command immune to hangups
439 * stdbuf invocation:: Run a command with modified I/O buffering
440 * su invocation:: Run a command with substitute user and group ID
441 * timeout invocation:: Run a command with a time limit
445 * kill invocation:: Sending a signal to processes.
449 * sleep invocation:: Delay for a specified time
453 * factor invocation:: Print prime factors
454 * seq invocation:: Print numeric sequences
458 * Mode Structure:: Structure of file mode bits.
459 * Symbolic Modes:: Mnemonic representation of file mode bits.
460 * Numeric Modes:: File mode bits as octal numbers.
461 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.
465 * General date syntax:: Common rules.
466 * Calendar date items:: 19 Dec 1994.
467 * Time of day items:: 9:20pm.
468 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
469 * Day of week items:: Monday and others.
470 * Relative items in date strings:: next tuesday, 2 years ago.
471 * Pure numbers in date strings:: 19931219, 1440.
472 * Seconds since the Epoch:: @@1078100502.
473 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
474 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
476 Opening the software toolbox
478 * Toolbox introduction:: Toolbox introduction
479 * I/O redirection:: I/O redirection
480 * The who command:: The @command{who} command
481 * The cut command:: The @command{cut} command
482 * The sort command:: The @command{sort} command
483 * The uniq command:: The @command{uniq} command
484 * Putting the tools together:: Putting the tools together
488 * GNU Free Documentation License:: Copying and sharing this manual.
495 @chapter Introduction
497 This manual is a work in progress: many sections make no attempt to explain
498 basic concepts in a way suitable for novices. Thus, if you are interested,
499 please get involved in improving this manual. The entire @sc{gnu} community
502 @cindex @acronym{POSIX}
503 The @sc{gnu} utilities documented here are mostly compatible with the
504 @acronym{POSIX} standard.
505 @cindex bugs, reporting
506 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
507 to include the version number, machine architecture, input files, and
508 any other information needed to reproduce the bug: your input, what you
509 expected, what you got, and why it is wrong. Diffs are welcome, but
510 please include a description of the problem as well, since this is
511 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
517 @cindex MacKenzie, D.
520 This manual was originally derived from the Unix man pages in the
521 distributions, which were written by David MacKenzie and updated by Jim
522 Meyering. What you are reading now is the authoritative documentation
523 for these utilities; the man pages are no longer being maintained. The
524 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
525 Pinard did the initial conversion to Texinfo format. Karl Berry did the
526 indexing, some reorganization, and editing of the results. Brian
527 Youmans of the Free Software Foundation office staff combined the
528 manuals for textutils, fileutils, and sh-utils to produce the present
529 omnibus manual. Richard Stallman contributed his usual invaluable
530 insights to the overall process.
533 @chapter Common options
537 @itemx @w{@kbd{--backup}[=@var{method}]}
540 @vindex VERSION_CONTROL
541 @cindex backups, making
542 @xref{Backup options}.
543 Make a backup of each file that would otherwise be overwritten or removed.
546 @macro optBackupSuffix
547 @item -S @var{suffix}
548 @itemx --suffix=@var{suffix}
551 Append @var{suffix} to each backup file made with @option{-b}.
552 @xref{Backup options}.
555 @macro optTargetDirectory
556 @item -t @var{directory}
557 @itemx @w{@kbd{--target-directory}=@var{directory}}
559 @opindex --target-directory
560 @cindex target directory
561 @cindex destination directory
562 Specify the destination @var{directory}.
563 @xref{Target directory}.
566 @macro optNoTargetDirectory
568 @itemx --no-target-directory
570 @opindex --no-target-directory
571 @cindex target directory
572 @cindex destination directory
573 Do not treat the last operand specially when it is a directory or a
574 symbolic link to a directory. @xref{Target directory}.
581 Append an SI-style abbreviation to each size, such as @samp{M} for
582 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
583 1,000,000 bytes. This option is equivalent to
584 @option{--block-size=si}. Use the @option{-h} or
585 @option{--human-readable} option if
586 you prefer powers of 1024.
589 @macro optHumanReadable
591 @itemx --human-readable
593 @opindex --human-readable
594 @cindex human-readable output
595 Append a size letter to each size, such as @samp{M} for mebibytes.
596 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
597 This option is equivalent to @option{--block-size=human-readable}.
598 Use the @option{--si} option if you prefer powers of 1000.
601 @macro optStripTrailingSlashes
602 @itemx @w{@kbd{--strip-trailing-slashes}}
603 @opindex --strip-trailing-slashes
604 @cindex stripping trailing slashes
605 Remove any trailing slashes from each @var{source} argument.
606 @xref{Trailing slashes}.
609 @macro mayConflictWithShellBuiltIn{cmd}
610 @cindex conflicts with shell built-ins
611 @cindex built-in shell commands, conflicts with
612 Due to shell aliases and built-in @command{\cmd\} command, using an
613 unadorned @command{\cmd\} interactively or in a script may get you
614 different functionality than that described here. Invoke it via
615 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
620 @macro multiplierSuffixes{varName}
622 Appending @samp{b} multiplies @var{\varName\} by 512,
623 @samp{kB} by 1000, @samp{K} by 1024,
624 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
625 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
626 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
628 @var{\varName\} is a number which may have one of the following
629 multiplicative suffixes:
631 @samp{b} => 512 ("blocks")
632 @samp{KB} => 1000 (KiloBytes)
633 @samp{K} => 1024 (KibiBytes)
634 @samp{MB} => 1000*1000 (MegaBytes)
635 @samp{M} => 1024*1024 (MebiBytes)
636 @samp{GB} => 1000*1000*1000 (GigaBytes)
637 @samp{G} => 1024*1024*1024 (GibiBytes)
639 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
642 @c FIXME: same as above, but no ``blocks'' line.
643 @macro multiplierSuffixesNoBlocks{varName}
644 @var{\varName\} is a number which may have one of the following
645 multiplicative suffixes:
647 @samp{KB} => 1000 (KiloBytes)
648 @samp{K} => 1024 (KibiBytes)
649 @samp{MB} => 1000*1000 (MegaBytes)
650 @samp{M} => 1024*1024 (MebiBytes)
651 @samp{GB} => 1000*1000*1000 (GigaBytes)
652 @samp{G} => 1024*1024*1024 (GibiBytes)
654 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
657 @cindex common options
659 Certain options are available in all of these programs. Rather than
660 writing identical descriptions for each of the programs, they are
661 described here. (In fact, every @sc{gnu} program accepts (or should accept)
664 @vindex POSIXLY_CORRECT
665 Normally options and operands can appear in any order, and programs act
666 as if all the options appear before any operands. For example,
667 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
668 @samp{:} is an option-argument of @option{-t}. However, if the
669 @env{POSIXLY_CORRECT} environment variable is set, options must appear
670 before operands, unless otherwise specified for a particular command.
672 A few programs can usefully have trailing operands with leading
673 @samp{-}. With such a program, options must precede operands even if
674 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
675 program description. For example, the @command{env} command's options
676 must appear before its operands, since in some cases the operands
677 specify a command that itself contains options.
679 Most programs that accept long options recognize unambiguous
680 abbreviations of those options. For example, @samp{rmdir
681 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
682 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
683 @samp{ls --h}, are identified as such.
685 Some of these programs recognize the @option{--help} and @option{--version}
686 options only when one of them is the sole command line argument. For
687 these programs, abbreviations of the long options are not always recognized.
694 Print a usage message listing all available options, then exit successfully.
698 @cindex version number, finding
699 Print the version number, then exit successfully.
703 @cindex option delimiter
704 Delimit the option list. Later arguments, if any, are treated as
705 operands even if they begin with @samp{-}. For example, @samp{sort --
706 -r} reads from the file named @file{-r}.
710 @cindex standard input
711 @cindex standard output
712 A single @samp{-} operand is not really an option, though it looks like one. It
713 stands for standard input, or for standard output if that is clear from
714 the context. For example, @samp{sort -} reads from standard input,
715 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
716 extra copy of its input to standard output. Unless otherwise
717 specified, @samp{-} can appear as any operand that requires a file
721 * Exit status:: Indicating program success or failure.
722 * Backup options:: -b -S, in some programs.
723 * Block size:: BLOCK_SIZE and --block-size, in some programs.
724 * Signal specifications:: Specifying signals using the --signal option.
725 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
726 * Random sources:: --random-source, in some programs.
727 * Target directory:: Specifying a target directory, in some programs.
728 * Trailing slashes:: --strip-trailing-slashes, in some programs.
729 * Traversing symlinks:: -H, -L, or -P, in some programs.
730 * Treating / specially:: --preserve-root and --no-preserve-root.
731 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
732 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
740 An exit status of zero indicates success,
741 and a nonzero value indicates failure.
744 Nearly every command invocation yields an integral @dfn{exit status}
745 that can be used to change how other commands work.
746 For the vast majority of commands, an exit status of zero indicates
747 success. Failure is indicated by a nonzero value---typically
748 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
749 requires only that it be nonzero.
751 However, some of the programs documented here do produce
752 other exit status values and a few associate different
753 meanings with the values @samp{0} and @samp{1}.
754 Here are some of the exceptions:
755 @command{chroot}, @command{env}, @command{expr},
756 @command{nice}, @command{nohup}, @command{printenv}, @command{sort},
757 @command{su}, @command{test}, @command{timeout}, @command{tty}.
761 @section Backup options
763 @cindex backup options
765 Some @sc{gnu} programs (at least @command{cp}, @command{install},
766 @command{ln}, and @command{mv}) optionally make backups of files
767 before writing new versions.
768 These options control the details of these backups. The options are also
769 briefly mentioned in the descriptions of the particular programs.
774 @itemx @w{@kbd{--backup}[=@var{method}]}
777 @vindex VERSION_CONTROL
778 @cindex backups, making
779 Make a backup of each file that would otherwise be overwritten or removed.
780 Without this option, the original versions are destroyed.
781 Use @var{method} to determine the type of backups to make.
782 When this option is used but @var{method} is not specified,
783 then the value of the @env{VERSION_CONTROL}
784 environment variable is used. And if @env{VERSION_CONTROL} is not set,
785 the default backup type is @samp{existing}.
787 Note that the short form of this option, @option{-b} does not accept any
788 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
790 @vindex version-control @r{Emacs variable}
791 This option corresponds to the Emacs variable @samp{version-control};
792 the values for @var{method} are the same as those used in Emacs.
793 This option also accepts more descriptive names.
794 The valid @var{method}s are (unique abbreviations are accepted):
799 @opindex none @r{backup method}
804 @opindex numbered @r{backup method}
805 Always make numbered backups.
809 @opindex existing @r{backup method}
810 Make numbered backups of files that already have them, simple backups
815 @opindex simple @r{backup method}
816 Always make simple backups. Please note @samp{never} is not to be
817 confused with @samp{none}.
821 @item -S @var{suffix}
822 @itemx --suffix=@var{suffix}
825 @cindex backup suffix
826 @vindex SIMPLE_BACKUP_SUFFIX
827 Append @var{suffix} to each backup file made with @option{-b}. If this
828 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
829 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
830 set, the default is @samp{~}, just as in Emacs.
839 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
840 @command{ls}) display sizes in ``blocks''. You can adjust the block size
841 and method of display to make sizes easier to read. The block size
842 used for display is independent of any file system block size.
843 Fractional block counts are rounded up to the nearest integer.
845 @opindex --block-size=@var{size}
848 @vindex DF_BLOCK_SIZE
849 @vindex DU_BLOCK_SIZE
850 @vindex LS_BLOCK_SIZE
851 @vindex POSIXLY_CORRECT@r{, and block size}
853 The default block size is chosen by examining the following environment
854 variables in turn; the first one that is set determines the block size.
859 This specifies the default block size for the @command{df} command.
860 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
861 @env{LS_BLOCK_SIZE} for @command{ls}.
864 This specifies the default block size for all three commands, if the
865 above command-specific environment variables are not set.
868 This specifies the default block size for all values that are normally
869 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
870 command-specific environment variables are set. Unlike the other
871 environment variables, @env{BLOCKSIZE} does not affect values that are
872 normally printed as byte counts, e.g., the file sizes contained in
875 @item POSIXLY_CORRECT
876 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
877 @env{BLOCKSIZE} is set, but this variable is set, the block size
882 If none of the above environment variables are set, the block size
883 currently defaults to 1024 bytes in most contexts, but this number may
884 change in the future. For @command{ls} file sizes, the block size
887 @cindex human-readable output
890 A block size specification can be a positive integer specifying the number
891 of bytes per block, or it can be @code{human-readable} or @code{si} to
892 select a human-readable format. Integers may be followed by suffixes
893 that are upward compatible with the
894 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
895 for decimal multiples and with the
896 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
897 prefixes for binary multiples}.
899 With human-readable formats, output sizes are followed by a size letter
900 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
901 powers of 1024; @samp{M} stands for 1,048,576 bytes.
902 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
903 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
906 A block size specification preceded by @samp{'} causes output sizes to
907 be displayed with thousands separators. The @env{LC_NUMERIC} locale
908 specifies the thousands separator and grouping. For example, in an
909 American English locale, @samp{--block-size="'1kB"} would cause a size
910 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
911 locale, there is no thousands separator so a leading @samp{'} has no
914 An integer block size can be followed by a suffix to specify a
915 multiple of that size. A bare size letter,
916 or one followed by @samp{iB}, specifies
917 a multiple using powers of 1024. A size letter followed by @samp{B}
918 specifies powers of 1000 instead. For example, @samp{1M} and
919 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
920 equivalent to @samp{1000000}.
922 A plain suffix without a preceding integer acts as if @samp{1} were
923 prepended, except that it causes a size indication to be appended to
924 the output. For example, @samp{--block-size="kB"} displays 3000 as
927 The following suffixes are defined. Large sizes like @code{1Y}
928 may be rejected by your computer due to limitations of its arithmetic.
932 @cindex kilobyte, definition of
933 kilobyte: @math{10^3 = 1000}.
937 @cindex kibibyte, definition of
938 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
939 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
940 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
942 @cindex megabyte, definition of
943 megabyte: @math{10^6 = 1,000,000}.
946 @cindex mebibyte, definition of
947 mebibyte: @math{2^{20} = 1,048,576}.
949 @cindex gigabyte, definition of
950 gigabyte: @math{10^9 = 1,000,000,000}.
953 @cindex gibibyte, definition of
954 gibibyte: @math{2^{30} = 1,073,741,824}.
956 @cindex terabyte, definition of
957 terabyte: @math{10^{12} = 1,000,000,000,000}.
960 @cindex tebibyte, definition of
961 tebibyte: @math{2^{40} = 1,099,511,627,776}.
963 @cindex petabyte, definition of
964 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
967 @cindex pebibyte, definition of
968 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
970 @cindex exabyte, definition of
971 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
974 @cindex exbibyte, definition of
975 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
977 @cindex zettabyte, definition of
978 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
981 @math{2^{70} = 1,180,591,620,717,411,303,424}.
982 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
984 @cindex yottabyte, definition of
985 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
988 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
989 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
994 @opindex --block-size
995 @opindex --human-readable
998 Block size defaults can be overridden by an explicit
999 @option{--block-size=@var{size}} option. The @option{-k}
1000 option is equivalent to @option{--block-size=1K}, which
1001 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1002 set. The @option{-h} or @option{--human-readable} option is equivalent to
1003 @option{--block-size=human-readable}. The @option{--si} option is
1004 equivalent to @option{--block-size=si}.
1006 @node Signal specifications
1007 @section Signal specifications
1008 @cindex signals, specifying
1010 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1011 number like @samp{1}, or an exit status of a process terminated by the
1012 signal. A signal name can be given in canonical form or prefixed by
1013 @samp{SIG}. The case of the letters is ignored. The following signal names
1014 and numbers are supported on all @acronym{POSIX} compliant systems:
1020 2. Terminal interrupt.
1026 9. Kill (cannot be caught or ignored).
1034 Other supported signal names have system-dependent corresponding
1035 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1036 support the following signals:
1040 Access to an undefined portion of a memory object.
1042 Child process terminated, stopped, or continued.
1044 Continue executing, if stopped.
1046 Erroneous arithmetic operation.
1048 Illegal Instruction.
1050 Write on a pipe with no one to read it.
1052 Invalid memory reference.
1054 Stop executing (cannot be caught or ignored).
1058 Background process attempting read.
1060 Background process attempting write.
1062 High bandwidth data is available at a socket.
1064 User-defined signal 1.
1066 User-defined signal 2.
1070 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1071 also support the following signals:
1077 Profiling timer expired.
1081 Trace/breakpoint trap.
1083 Virtual timer expired.
1085 CPU time limit exceeded.
1087 File size limit exceeded.
1091 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1092 also support at least eight real-time signals called @samp{RTMIN},
1093 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1095 @node Disambiguating names and IDs
1096 @section chown and chgrp: Disambiguating user names and IDs
1097 @cindex user names, disambiguating
1098 @cindex user IDs, disambiguating
1099 @cindex group names, disambiguating
1100 @cindex group IDs, disambiguating
1101 @cindex disambiguating group names and IDs
1103 Since the @var{owner} and @var{group} arguments to @command{chown} and
1104 @command{chgrp} may be specified as names or numeric IDs, there is an
1106 What if a user or group @emph{name} is a string of digits?
1107 @footnote{Using a number as a user name is common in some environments.}
1108 Should the command interpret it as a user name or as an ID?
1109 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1110 first attempt to resolve the specified string as a name, and
1111 only once that fails, then try to interpret it as an ID.
1112 This is troublesome when you want to specify a numeric ID, say 42,
1113 and it must work even in a pathological situation where
1114 @samp{42} is a user name that maps to some other user ID, say 1000.
1115 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1116 1000---not what you intended.
1118 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1119 that at the same time may result in a significant performance improvement
1120 by eliminating a database look-up.
1121 Simply precede each numeric user ID and/or group ID with a @samp{+},
1122 in order to force its interpretation as an integer:
1126 chgrp +$numeric_group_id another-file
1130 GNU @command{chown} and @command{chgrp}
1131 skip the name look-up process for each @samp{+}-prefixed string,
1132 because a string containing @samp{+} is never a valid user or group name.
1133 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1135 @node Random sources
1136 @section Sources of random data
1138 @cindex random sources
1140 The @command{shuf}, @command{shred}, and @command{sort} commands
1141 sometimes need random data to do their work. For example, @samp{sort
1142 -R} must choose a hash function at random, and it needs random data to
1143 make this selection.
1145 By default these commands use an internal pseudorandom generator
1146 initialized by a small amount of entropy, but can be directed to use
1147 an external source with the @option{--random-source=@var{file}} option.
1148 An error is reported if @var{file} does not contain enough bytes.
1150 For example, the device file @file{/dev/urandom} could be used as the
1151 source of random data. Typically, this device gathers environmental
1152 noise from device drivers and other sources into an entropy pool, and
1153 uses the pool to generate random bits. If the pool is short of data,
1154 the device reuses the internal pool to produce more bits, using a
1155 cryptographically secure pseudorandom number generator. But be aware
1156 that this device is not designed for bulk random data generation
1157 and is relatively slow.
1159 @file{/dev/urandom} suffices for most practical uses, but applications
1160 requiring high-value or long-term protection of private data may
1161 require an alternate data source like @file{/dev/random} or
1162 @file{/dev/arandom}. The set of available sources depends on your
1165 To reproduce the results of an earlier invocation of a command, you
1166 can save some random data into a file and then use that file as the
1167 random source in earlier and later invocations of the command.
1169 @node Target directory
1170 @section Target directory
1172 @cindex target directory
1174 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1175 commands normally treat the last operand specially when it is a
1176 directory or a symbolic link to a directory. For example, @samp{cp
1177 source dest} is equivalent to @samp{cp source dest/source} if
1178 @file{dest} is a directory. Sometimes this behavior is not exactly
1179 what is wanted, so these commands support the following options to
1180 allow more fine-grained control:
1185 @itemx --no-target-directory
1186 @opindex --no-target-directory
1187 @cindex target directory
1188 @cindex destination directory
1189 Do not treat the last operand specially when it is a directory or a
1190 symbolic link to a directory. This can help avoid race conditions in
1191 programs that operate in a shared area. For example, when the command
1192 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1193 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1194 renamed to @file{/tmp/dest/source} instead, if some other process
1195 created @file{/tmp/dest} as a directory. However, if @file{mv
1196 -T /tmp/source /tmp/dest} succeeds, there is no
1197 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1199 In the opposite situation, where you want the last operand to be
1200 treated as a directory and want a diagnostic otherwise, you can use
1201 the @option{--target-directory} (@option{-t}) option.
1203 @item -t @var{directory}
1204 @itemx @w{@kbd{--target-directory}=@var{directory}}
1205 @opindex --target-directory
1206 @cindex target directory
1207 @cindex destination directory
1208 Use @var{directory} as the directory component of each destination
1211 The interface for most programs is that after processing options and a
1212 finite (possibly zero) number of fixed-position arguments, the remaining
1213 argument list is either expected to be empty, or is a list of items
1214 (usually files) that will all be handled identically. The @command{xargs}
1215 program is designed to work well with this convention.
1217 The commands in the @command{mv}-family are unusual in that they take
1218 a variable number of arguments with a special case at the @emph{end}
1219 (namely, the target directory). This makes it nontrivial to perform some
1220 operations, e.g., ``move all files from here to ../d/'', because
1221 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1222 doesn't have a clean way to specify an extra final argument for each
1223 invocation of the subject command. (It can be done by going through a
1224 shell command, but that requires more human labor and brain power than
1227 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1228 @command{install}, @command{ln}, and @command{mv} programs to be used
1229 conveniently with @command{xargs}. For example, you can move the files
1230 from the current directory to a sibling directory, @code{d} like this:
1233 ls | xargs mv -t ../d --
1236 However, this doesn't move files whose names begin with @samp{.}.
1237 If you use the @sc{gnu} @command{find} program, you can move those
1238 files too, with this command:
1241 find . -mindepth 1 -maxdepth 1 \
1245 But both of the above approaches fail if there are no files in the
1246 current directory, or if any file has a name containing a blank or
1247 some other special characters.
1248 The following example removes those limitations and requires both
1249 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1252 find . -mindepth 1 -maxdepth 1 -print0 \
1253 | xargs --null --no-run-if-empty \
1260 The @option{--target-directory} (@option{-t}) and
1261 @option{--no-target-directory} (@option{-T})
1262 options cannot be combined.
1264 @node Trailing slashes
1265 @section Trailing slashes
1267 @cindex trailing slashes
1269 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1270 remove any trailing slashes from each @var{source} argument before
1271 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1274 This is useful when a @var{source} argument may have a trailing slash and
1275 @c FIXME: mv's behavior in this case is system-dependent
1276 specify a symbolic link to a directory. This scenario is in fact rather
1277 common because some shells can automatically append a trailing slash when
1278 performing file name completion on such symbolic links. Without this
1279 option, @command{mv}, for example, (via the system's rename function) must
1280 interpret a trailing slash as a request to dereference the symbolic link
1281 and so must rename the indirectly referenced @emph{directory} and not
1282 the symbolic link. Although it may seem surprising that such behavior
1283 be the default, it is required by @acronym{POSIX} and is consistent with
1284 other parts of that standard.
1286 @node Traversing symlinks
1287 @section Traversing symlinks
1289 @cindex symbolic link to directory, controlling traversal of
1291 The following options modify how @command{chown} and @command{chgrp}
1292 @c FIXME: note that `du' has these options, too, but they have slightly
1293 @c different meaning.
1294 traverse a hierarchy when the @option{--recursive} (@option{-R})
1295 option is also specified.
1296 If more than one of the following options is specified, only the final
1298 These options specify whether processing a symbolic link to a directory
1299 entails operating on just the symbolic link or on all files in the
1300 hierarchy rooted at that directory.
1302 These options are independent of @option{--dereference} and
1303 @option{--no-dereference} (@option{-h}), which control whether to modify
1304 a symlink or its referent.
1311 @cindex symbolic link to directory, traverse each that is specified on the command line
1312 If @option{--recursive} (@option{-R}) is specified and
1313 a command line argument is a symbolic link to a directory, traverse it.
1320 @cindex symbolic link to directory, traverse each that is encountered
1321 In a recursive traversal, traverse every symbolic link to a directory
1322 that is encountered.
1329 @cindex symbolic link to directory, never traverse
1330 Do not traverse any symbolic links.
1331 This is the default if none of @option{-H}, @option{-L},
1332 or @option{-P} is specified.
1339 @node Treating / specially
1340 @section Treating @file{/} specially
1342 Certain commands can operate destructively on entire hierarchies.
1343 For example, if a user with appropriate privileges mistakenly runs
1344 @samp{rm -rf / tmp/junk}, that may remove
1345 all files on the entire system. Since there are so few
1346 legitimate uses for such a command,
1347 @sc{gnu} @command{rm} normally declines to operate on any directory
1348 that resolves to @file{/}. If you really want to try to remove all
1349 the files on your system, you can use the @option{--no-preserve-root}
1350 option, but the default behavior, specified by the
1351 @option{--preserve-option}, is safer for most purposes.
1353 The commands @command{chgrp}, @command{chmod} and @command{chown}
1354 can also operate destructively on entire hierarchies, so they too
1355 support these options. Although, unlike @command{rm}, they don't
1356 actually unlink files, these commands are arguably more dangerous
1357 when operating recursively on @file{/}, since they often work much
1358 more quickly, and hence damage more files before an alert user can
1359 interrupt them. Tradition and @acronym{POSIX} require these commands
1360 to operate recursively on @file{/}, so they default to
1361 @option{--no-preserve-root}, but using the @option{--preserve-root}
1362 option makes them safer for most purposes. For convenience you can
1363 specify @option{--preserve-root} in an alias or in a shell function.
1365 Note that the @option{--preserve-root} option also ensures
1366 that @command{chgrp} and @command{chown} do not modify @file{/}
1367 even when dereferencing a symlink pointing to @file{/}.
1369 @node Special built-in utilities
1370 @section Special built-in utilities
1372 Some programs like @command{nice} can invoke other programs; for
1373 example, the command @samp{nice cat file} invokes the program
1374 @command{cat} by executing the command @samp{cat file}. However,
1375 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1376 this way. For example, the command @samp{nice exit} does not have a
1377 well-defined behavior: it may generate an error message instead of
1380 Here is a list of the special built-in utilities that are standardized
1381 by @acronym{POSIX} 1003.1-2004.
1384 @t{.@: : break continue eval exec exit export readonly
1385 return set shift times trap unset}
1388 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1389 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1390 pwd} do not work as you might expect.
1392 Many shells extend this list. For example, Bash has several extra
1393 special built-in utilities like @command{history}, and
1394 @command{suspend}, and with Bash the command @samp{nice suspend}
1395 generates an error message instead of suspending.
1397 @node Standards conformance
1398 @section Standards conformance
1400 @vindex POSIXLY_CORRECT
1401 In a few cases, the @sc{gnu} utilities' default behavior is
1402 incompatible with the @acronym{POSIX} standard. To suppress these
1403 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1404 variable. Unless you are checking for @acronym{POSIX} conformance, you
1405 probably do not need to define @env{POSIXLY_CORRECT}.
1407 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1408 versions. For example, older versions of @acronym{POSIX} required the
1409 command @samp{sort +1} to sort based on the second and succeeding
1410 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1411 the same command is required to sort the file named @file{+1}, and you
1412 must instead use the command @samp{sort -k 2} to get the field-based
1415 @vindex _POSIX2_VERSION
1416 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1417 that is standard for your system. To cause them to conform to a
1418 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1419 environment variable to a value of the form @var{yyyymm} specifying
1420 the year and month the standard was adopted. Two values are currently
1421 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1422 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1423 1003.1-2001. For example, if you have a newer system but are running software
1424 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1425 or @samp{tail +10}, you can work around any compatibility problems by setting
1426 @samp{_POSIX2_VERSION=199209} in your environment.
1428 @node Output of entire files
1429 @chapter Output of entire files
1431 @cindex output of entire files
1432 @cindex entire files, output of
1434 These commands read and write entire files, possibly transforming them
1438 * cat invocation:: Concatenate and write files.
1439 * tac invocation:: Concatenate and write files in reverse.
1440 * nl invocation:: Number lines and write files.
1441 * od invocation:: Write files in octal or other formats.
1442 * base64 invocation:: Transform data into printable data.
1445 @node cat invocation
1446 @section @command{cat}: Concatenate and write files
1449 @cindex concatenate and write files
1450 @cindex copying files
1452 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1453 standard input if none are given, to standard output. Synopsis:
1456 cat [@var{option}] [@var{file}]@dots{}
1459 The program accepts the following options. Also see @ref{Common options}.
1467 Equivalent to @option{-vET}.
1470 @itemx --number-nonblank
1472 @opindex --number-nonblank
1473 Number all nonempty output lines, starting with 1.
1477 Equivalent to @option{-vE}.
1482 @opindex --show-ends
1483 Display a @samp{$} after the end of each line.
1489 Number all output lines, starting with 1.
1492 @itemx --squeeze-blank
1494 @opindex --squeeze-blank
1495 @cindex squeezing empty lines
1496 Suppress repeated adjacent empty lines; output just one empty line
1501 Equivalent to @option{-vT}.
1506 @opindex --show-tabs
1507 Display TAB characters as @samp{^I}.
1511 Ignored; for @acronym{POSIX} compatibility.
1514 @itemx --show-nonprinting
1516 @opindex --show-nonprinting
1517 Display control characters except for LFD and TAB using
1518 @samp{^} notation and precede characters that have the high bit set with
1523 On systems like MS-DOS that distinguish between text and binary files,
1524 @command{cat} normally reads and writes in binary mode. However,
1525 @command{cat} reads in text mode if one of the options
1526 @option{-bensAE} is used or if @command{cat} is reading from standard
1527 input and standard input is a terminal. Similarly, @command{cat}
1528 writes in text mode if one of the options @option{-bensAE} is used or
1529 if standard output is a terminal.
1536 # Output f's contents, then standard input, then g's contents.
1539 # Copy standard input to standard output.
1544 @node tac invocation
1545 @section @command{tac}: Concatenate and write files in reverse
1548 @cindex reversing files
1550 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1551 standard input if none are given, to standard output, reversing the
1552 records (lines by default) in each separately. Synopsis:
1555 tac [@var{option}]@dots{} [@var{file}]@dots{}
1558 @dfn{Records} are separated by instances of a string (newline by
1559 default). By default, this separator string is attached to the end of
1560 the record that it follows in the file.
1562 The program accepts the following options. Also see @ref{Common options}.
1570 The separator is attached to the beginning of the record that it
1571 precedes in the file.
1577 Treat the separator string as a regular expression. Users of @command{tac}
1578 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1579 binary mode, each line of a text file might end with a CR/LF pair
1580 instead of the Unix-style LF.
1582 @item -s @var{separator}
1583 @itemx --separator=@var{separator}
1585 @opindex --separator
1586 Use @var{separator} as the record separator, instead of newline.
1594 @section @command{nl}: Number lines and write files
1597 @cindex numbering lines
1598 @cindex line numbering
1600 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1601 standard input if none are given, to standard output, with line numbers
1602 added to some or all of the lines. Synopsis:
1605 nl [@var{option}]@dots{} [@var{file}]@dots{}
1608 @cindex logical pages, numbering on
1609 @command{nl} decomposes its input into (logical) pages; by default, the
1610 line number is reset to 1 at the top of each logical page. @command{nl}
1611 treats all of the input files as a single document; it does not reset
1612 line numbers or logical pages between files.
1614 @cindex headers, numbering
1615 @cindex body, numbering
1616 @cindex footers, numbering
1617 A logical page consists of three sections: header, body, and footer.
1618 Any of the sections can be empty. Each can be numbered in a different
1619 style from the others.
1621 The beginnings of the sections of logical pages are indicated in the
1622 input file by a line containing exactly one of these delimiter strings:
1633 The two characters from which these strings are made can be changed from
1634 @samp{\} and @samp{:} via options (see below), but the pattern and
1635 length of each string cannot be changed.
1637 A section delimiter is replaced by an empty line on output. Any text
1638 that comes before the first section delimiter string in the input file
1639 is considered to be part of a body section, so @command{nl} treats a
1640 file that contains no section delimiters as a single body section.
1642 The program accepts the following options. Also see @ref{Common options}.
1646 @item -b @var{style}
1647 @itemx --body-numbering=@var{style}
1649 @opindex --body-numbering
1650 Select the numbering style for lines in the body section of each
1651 logical page. When a line is not numbered, the current line number
1652 is not incremented, but the line number separator character is still
1653 prepended to the line. The styles are:
1659 number only nonempty lines (default for body),
1661 do not number lines (default for header and footer),
1663 number only lines that contain a match for the basic regular
1664 expression @var{bre}.
1665 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1669 @itemx --section-delimiter=@var{cd}
1671 @opindex --section-delimiter
1672 @cindex section delimiters of pages
1673 Set the section delimiter characters to @var{cd}; default is
1674 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1675 (Remember to protect @samp{\} or other metacharacters from shell
1676 expansion with quotes or extra backslashes.)
1678 @item -f @var{style}
1679 @itemx --footer-numbering=@var{style}
1681 @opindex --footer-numbering
1682 Analogous to @option{--body-numbering}.
1684 @item -h @var{style}
1685 @itemx --header-numbering=@var{style}
1687 @opindex --header-numbering
1688 Analogous to @option{--body-numbering}.
1690 @item -i @var{number}
1691 @itemx --page-increment=@var{number}
1693 @opindex --page-increment
1694 Increment line numbers by @var{number} (default 1).
1696 @item -l @var{number}
1697 @itemx --join-blank-lines=@var{number}
1699 @opindex --join-blank-lines
1700 @cindex empty lines, numbering
1701 @cindex blank lines, numbering
1702 Consider @var{number} (default 1) consecutive empty lines to be one
1703 logical line for numbering, and only number the last one. Where fewer
1704 than @var{number} consecutive empty lines occur, do not number them.
1705 An empty line is one that contains no characters, not even spaces
1708 @item -n @var{format}
1709 @itemx --number-format=@var{format}
1711 @opindex --number-format
1712 Select the line numbering format (default is @code{rn}):
1716 @opindex ln @r{format for @command{nl}}
1717 left justified, no leading zeros;
1719 @opindex rn @r{format for @command{nl}}
1720 right justified, no leading zeros;
1722 @opindex rz @r{format for @command{nl}}
1723 right justified, leading zeros.
1727 @itemx --no-renumber
1729 @opindex --no-renumber
1730 Do not reset the line number at the start of a logical page.
1732 @item -s @var{string}
1733 @itemx --number-separator=@var{string}
1735 @opindex --number-separator
1736 Separate the line number from the text line in the output with
1737 @var{string} (default is the TAB character).
1739 @item -v @var{number}
1740 @itemx --starting-line-number=@var{number}
1742 @opindex --starting-line-number
1743 Set the initial line number on each logical page to @var{number} (default 1).
1745 @item -w @var{number}
1746 @itemx --number-width=@var{number}
1748 @opindex --number-width
1749 Use @var{number} characters for line numbers (default 6).
1757 @section @command{od}: Write files in octal or other formats
1760 @cindex octal dump of files
1761 @cindex hex dump of files
1762 @cindex ASCII dump of files
1763 @cindex file contents, dumping unambiguously
1765 @command{od} writes an unambiguous representation of each @var{file}
1766 (@samp{-} means standard input), or standard input if none are given.
1770 od [@var{option}]@dots{} [@var{file}]@dots{}
1771 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1772 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1775 Each line of output consists of the offset in the input, followed by
1776 groups of data from the file. By default, @command{od} prints the offset in
1777 octal, and each group of file data is a C @code{short int}'s worth of input
1778 printed as a single octal number.
1780 If @var{offset} is given, it specifies how many input bytes to skip
1781 before formatting and writing. By default, it is interpreted as an
1782 octal number, but the optional trailing decimal point causes it to be
1783 interpreted as decimal. If no decimal is specified and the offset
1784 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1785 number. If there is a trailing @samp{b}, the number of bytes skipped
1786 will be @var{offset} multiplied by 512.
1788 If a command is of both the first and second forms, the second form is
1789 assumed if the last operand begins with @samp{+} or (if there are two
1790 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1791 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1794 The program accepts the following options. Also see @ref{Common options}.
1798 @item -A @var{radix}
1799 @itemx --address-radix=@var{radix}
1801 @opindex --address-radix
1802 @cindex radix for file offsets
1803 @cindex file offset radix
1804 Select the base in which file offsets are printed. @var{radix} can
1805 be one of the following:
1815 none (do not print offsets).
1818 The default is octal.
1820 @item -j @var{bytes}
1821 @itemx --skip-bytes=@var{bytes}
1823 @opindex --skip-bytes
1824 Skip @var{bytes} input bytes before formatting and writing. If
1825 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1826 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1828 @multiplierSuffixes{bytes}
1830 @item -N @var{bytes}
1831 @itemx --read-bytes=@var{bytes}
1833 @opindex --read-bytes
1834 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1835 @code{bytes} are interpreted as for the @option{-j} option.
1837 @item -S @var{bytes}
1838 @itemx --strings[=@var{bytes}]
1841 @cindex string constants, outputting
1842 Instead of the normal output, output only @dfn{string constants}: at
1843 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1844 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1845 Prefixes and suffixes on @code{bytes} are interpreted as for the
1848 If @var{n} is omitted with @option{--strings}, the default is 3.
1851 @itemx --format=@var{type}
1854 Select the format in which to output the file data. @var{type} is a
1855 string of one or more of the below type indicator characters. If you
1856 include more than one type indicator character in a single @var{type}
1857 string, or use this option more than once, @command{od} writes one copy
1858 of each output line using each of the data types that you specified,
1859 in the order that you specified.
1861 Adding a trailing ``z'' to any type specification appends a display
1862 of the @acronym{ASCII} character representation of the printable characters
1863 to the output line generated by the type specification.
1867 named character, ignoring high-order bit
1869 @acronym{ASCII} character or backslash escape,
1882 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1883 newline, and @samp{nul} for a zero byte. Only the least significant
1884 seven bits of each byte is used; the high-order bit is ignored.
1885 Type @code{c} outputs
1886 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1889 Except for types @samp{a} and @samp{c}, you can specify the number
1890 of bytes to use in interpreting each number in the given data type
1891 by following the type indicator character with a decimal integer.
1892 Alternately, you can specify the size of one of the C compiler's
1893 built-in data types by following the type indicator character with
1894 one of the following characters. For integers (@samp{d}, @samp{o},
1895 @samp{u}, @samp{x}):
1908 For floating point (@code{f}):
1920 @itemx --output-duplicates
1922 @opindex --output-duplicates
1923 Output consecutive lines that are identical. By default, when two or
1924 more consecutive output lines would be identical, @command{od} outputs only
1925 the first line, and puts just an asterisk on the following line to
1926 indicate the elision.
1929 @itemx --width[=@var{n}]
1932 Dump @code{n} input bytes per output line. This must be a multiple of
1933 the least common multiple of the sizes associated with the specified
1936 If this option is not given at all, the default is 16. If @var{n} is
1937 omitted, the default is 32.
1941 The next several options are shorthands for format specifications.
1942 @sc{gnu} @command{od} accepts any combination of shorthands and format
1943 specification options. These options accumulate.
1949 Output as named characters. Equivalent to @samp{-t a}.
1953 Output as octal bytes. Equivalent to @samp{-t o1}.
1957 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1962 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1966 Output as floats. Equivalent to @samp{-t fF}.
1970 Output as decimal ints. Equivalent to @samp{-t dI}.
1974 Output as decimal long ints. Equivalent to @samp{-t dL}.
1978 Output as octal two-byte units. Equivalent to @option{-t o2}.
1982 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1986 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1989 @opindex --traditional
1990 Recognize the non-option label argument that traditional @command{od}
1991 accepted. The following syntax:
1994 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1998 can be used to specify at most one file and optional arguments
1999 specifying an offset and a pseudo-start address, @var{label}.
2000 The @var{label} argument is interpreted
2001 just like @var{offset}, but it specifies an initial pseudo-address. The
2002 pseudo-addresses are displayed in parentheses following any normal
2009 @node base64 invocation
2010 @section @command{base64}: Transform data into printable data
2013 @cindex base64 encoding
2015 @command{base64} transforms data read from a file, or standard input,
2016 into (or from) base64 encoded form. The base64 encoded form uses
2017 printable @acronym{ASCII} characters to represent binary data.
2021 base64 [@var{option}]@dots{} [@var{file}]
2022 base64 --decode [@var{option}]@dots{} [@var{file}]
2025 The base64 encoding expands data to roughly 133% of the original.
2026 The format conforms to
2027 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2029 The program accepts the following options. Also see @ref{Common options}.
2034 @itemx --wrap=@var{cols}
2038 @cindex column to wrap data after
2039 During encoding, wrap lines after @var{cols} characters. This must be
2042 The default is to wrap after 76 characters. Use the value 0 to
2043 disable line wrapping altogether.
2049 @cindex Decode base64 data
2050 @cindex Base64 decoding
2051 Change the mode of operation, from the default of encoding data, to
2052 decoding data. Input is expected to be base64 encoded data, and the
2053 output will be the original data.
2056 @itemx --ignore-garbage
2058 @opindex --ignore-garbage
2059 @cindex Ignore garbage in base64 stream
2060 When decoding, newlines are always accepted.
2061 During decoding, ignore unrecognized bytes,
2062 to permit distorted data to be decoded.
2069 @node Formatting file contents
2070 @chapter Formatting file contents
2072 @cindex formatting file contents
2074 These commands reformat the contents of files.
2077 * fmt invocation:: Reformat paragraph text.
2078 * pr invocation:: Paginate or columnate files for printing.
2079 * fold invocation:: Wrap input lines to fit in specified width.
2083 @node fmt invocation
2084 @section @command{fmt}: Reformat paragraph text
2087 @cindex reformatting paragraph text
2088 @cindex paragraphs, reformatting
2089 @cindex text, reformatting
2091 @command{fmt} fills and joins lines to produce output lines of (at most)
2092 a given number of characters (75 by default). Synopsis:
2095 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2098 @command{fmt} reads from the specified @var{file} arguments (or standard
2099 input if none are given), and writes to standard output.
2101 By default, blank lines, spaces between words, and indentation are
2102 preserved in the output; successive input lines with different
2103 indentation are not joined; tabs are expanded on input and introduced on
2106 @cindex line-breaking
2107 @cindex sentences and line-breaking
2108 @cindex Knuth, Donald E.
2109 @cindex Plass, Michael F.
2110 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2111 avoid line breaks after the first word of a sentence or before the last
2112 word of a sentence. A @dfn{sentence break} is defined as either the end
2113 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2114 spaces or end of line, ignoring any intervening parentheses or quotes.
2115 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2116 breaks; the algorithm is a variant of that given by Donald E. Knuth
2117 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2118 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2121 The program accepts the following options. Also see @ref{Common options}.
2129 Compare each pair of source and destination files, and if the destination has
2130 identical content and any specified owner, group, permissions, and possibly
2131 SELinux context, then do not modify the destination at all.
2134 @itemx --crown-margin
2136 @opindex --crown-margin
2137 @cindex crown margin
2138 @dfn{Crown margin} mode: preserve the indentation of the first two
2139 lines within a paragraph, and align the left margin of each subsequent
2140 line with that of the second line.
2143 @itemx --tagged-paragraph
2145 @opindex --tagged-paragraph
2146 @cindex tagged paragraphs
2147 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2148 indentation of the first line of a paragraph is the same as the
2149 indentation of the second, the first line is treated as a one-line
2155 @opindex --split-only
2156 Split lines only. Do not join short lines to form longer ones. This
2157 prevents sample lines of code, and other such ``formatted'' text from
2158 being unduly combined.
2161 @itemx --uniform-spacing
2163 @opindex --uniform-spacing
2164 Uniform spacing. Reduce spacing between words to one space, and spacing
2165 between sentences to two spaces.
2168 @itemx -w @var{width}
2169 @itemx --width=@var{width}
2170 @opindex -@var{width}
2173 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2174 initially tries to make lines about 7% shorter than this, to give it
2175 room to balance line lengths.
2177 @item -p @var{prefix}
2178 @itemx --prefix=@var{prefix}
2179 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2180 are subject to formatting. The prefix and any preceding whitespace are
2181 stripped for the formatting and then re-attached to each formatted output
2182 line. One use is to format certain kinds of program comments, while
2183 leaving the code unchanged.
2191 @section @command{pr}: Paginate or columnate files for printing
2194 @cindex printing, preparing files for
2195 @cindex multicolumn output, generating
2196 @cindex merging files in parallel
2198 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2199 standard input if none are given, to standard output, paginating and
2200 optionally outputting in multicolumn format; optionally merges all
2201 @var{file}s, printing all in parallel, one per column. Synopsis:
2204 pr [@var{option}]@dots{} [@var{file}]@dots{}
2208 By default, a 5-line header is printed at each page: two blank lines;
2209 a line with the date, the file name, and the page count; and two more
2210 blank lines. A footer of five blank lines is also printed.
2211 The default @var{page_length} is 66
2212 lines. The default number of text lines is therefore 56.
2213 The text line of the header takes the form
2214 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2215 @var{string} so that the line takes up the full @var{page_width}. Here,
2216 @var{date} is the date (see the @option{-D} or @option{--date-format}
2217 option for details), @var{string} is the centered header string, and
2218 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2219 category affects the spelling of @var{page}; in the default C locale, it
2220 is @samp{Page @var{number}} where @var{number} is the decimal page
2223 Form feeds in the input cause page breaks in the output. Multiple form
2224 feeds produce empty pages.
2226 Columns are of equal width, separated by an optional string (default
2227 is @samp{space}). For multicolumn output, lines will always be truncated to
2228 @var{page_width} (default 72), unless you use the @option{-J} option.
2230 column output no line truncation occurs by default. Use @option{-W} option to
2231 truncate lines in that case.
2233 The following changes were made in version 1.22i and apply to later
2234 versions of @command{pr}:
2235 @c FIXME: this whole section here sounds very awkward to me. I
2236 @c made a few small changes, but really it all needs to be redone. - Brian
2237 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2242 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2243 redefined for better @acronym{POSIX} compliance. The output of some further
2244 cases has been adapted to other Unix systems. These changes are not
2245 compatible with earlier versions of the program.
2248 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2249 have been introduced to turn off unexpected interferences of small letter
2250 options. The @option{-N} option and the second argument @var{last_page}
2251 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2252 form feeds set in the input files requires the @option{-T} option.
2255 Capital letter options override small letter ones.
2258 Some of the option-arguments (compare @option{-s}, @option{-e},
2259 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2260 preceding option letter (already stated in the @acronym{POSIX} specification).
2263 The program accepts the following options. Also see @ref{Common options}.
2267 @item +@var{first_page}[:@var{last_page}]
2268 @itemx --pages=@var{first_page}[:@var{last_page}]
2269 @c The two following @opindex lines evoke warnings because they contain `:'
2270 @c The `info' spec does not permit that. If we use those lines, we end
2271 @c up with truncated index entries that don't work.
2272 @c @opindex +@var{first_page}[:@var{last_page}]
2273 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2274 @opindex +@var{page_range}
2275 @opindex --pages=@var{page_range}
2276 Begin printing with page @var{first_page} and stop with @var{last_page}.
2277 Missing @samp{:@var{last_page}} implies end of file. While estimating
2278 the number of skipped pages each form feed in the input file results
2279 in a new page. Page counting with and without @samp{+@var{first_page}}
2280 is identical. By default, counting starts with the first page of input
2281 file (not first page printed). Line numbering may be altered by @option{-N}
2285 @itemx --columns=@var{column}
2286 @opindex -@var{column}
2288 @cindex down columns
2289 With each single @var{file}, produce @var{column} columns of output
2290 (default is 1) and print columns down, unless @option{-a} is used. The
2291 column width is automatically decreased as @var{column} increases; unless
2292 you use the @option{-W/-w} option to increase @var{page_width} as well.
2293 This option might well cause some lines to be truncated. The number of
2294 lines in the columns on each page are balanced. The options @option{-e}
2295 and @option{-i} are on for multiple text-column output. Together with
2296 @option{-J} option column alignment and line truncation is turned off.
2297 Lines of full length are joined in a free field format and @option{-S}
2298 option may set field separators. @option{-@var{column}} may not be used
2299 with @option{-m} option.
2305 @cindex across columns
2306 With each single @var{file}, print columns across rather than down. The
2307 @option{-@var{column}} option must be given with @var{column} greater than one.
2308 If a line is too long to fit in a column, it is truncated.
2311 @itemx --show-control-chars
2313 @opindex --show-control-chars
2314 Print control characters using hat notation (e.g., @samp{^G}); print
2315 other nonprinting characters in octal backslash notation. By default,
2316 nonprinting characters are not changed.
2319 @itemx --double-space
2321 @opindex --double-space
2322 @cindex double spacing
2323 Double space the output.
2325 @item -D @var{format}
2326 @itemx --date-format=@var{format}
2327 @cindex time formats
2328 @cindex formatting times
2329 Format header dates using @var{format}, using the same conventions as
2330 for the command @samp{date +@var{format}}; @xref{date invocation}.
2331 Except for directives, which start with
2332 @samp{%}, characters in @var{format} are printed unchanged. You can use
2333 this option to specify an arbitrary string in place of the header date,
2334 e.g., @option{--date-format="Monday morning"}.
2336 @vindex POSIXLY_CORRECT
2338 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2339 @samp{2001-12-04 23:59});
2340 but if the @env{POSIXLY_CORRECT} environment variable is set
2341 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2342 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2343 @samp{Dec@ @ 4 23:59 2001}.
2346 Time stamps are listed according to the time zone rules specified by
2347 the @env{TZ} environment variable, or by the system default rules if
2348 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2349 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2351 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2352 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2354 @opindex --expand-tabs
2356 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2357 the input tab character (default is the TAB character). Second optional
2358 argument @var{in-tabwidth} is the input tab character's width (default
2366 @opindex --form-feed
2367 Use a form feed instead of newlines to separate output pages. This does
2368 not alter the default page length of 66 lines.
2370 @item -h @var{header}
2371 @itemx --header=@var{header}
2374 Replace the file name in the header with the centered string @var{header}.
2375 When using the shell, @var{header} should be quoted and should be
2376 separated from @option{-h} by a space.
2378 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2379 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2381 @opindex --output-tabs
2383 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2384 is the output tab character (default is the TAB character). Second optional
2385 argument @var{out-tabwidth} is the output tab character's width (default
2391 @opindex --join-lines
2392 Merge lines of full length. Used together with the column options
2393 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2394 @option{-W/-w} line truncation;
2395 no column alignment used; may be used with
2396 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2397 (together with @option{-W} and @option{--sep-string})
2398 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2399 @option{-s} along with the three column options.
2402 @item -l @var{page_length}
2403 @itemx --length=@var{page_length}
2406 Set the page length to @var{page_length} (default 66) lines, including
2407 the lines of the header [and the footer]. If @var{page_length} is less
2408 than or equal to 10, the header and footer are omitted, as if the
2409 @option{-t} option had been given.
2415 Merge and print all @var{file}s in parallel, one in each column. If a
2416 line is too long to fit in a column, it is truncated, unless the @option{-J}
2417 option is used. @option{--sep-string[=@var{string}]} may be used.
2419 some @var{file}s (form feeds set) produce empty columns, still marked
2420 by @var{string}. The result is a continuous line numbering and column
2421 marking throughout the whole merged file. Completely empty merged pages
2422 show no separators or line numbers. The default header becomes
2423 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2424 may be used with the @option{-h} or @option{--header} option to fill up
2425 the middle blank part.
2427 @item -n[@var{number-separator}[@var{digits}]]
2428 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2430 @opindex --number-lines
2431 Provide @var{digits} digit line numbering (default for @var{digits} is
2432 5). With multicolumn output the number occupies the first @var{digits}
2433 column positions of each text column or only each line of @option{-m}
2434 output. With single column output the number precedes each line just as
2435 @option{-m} does. Default counting of the line numbers starts with the
2436 first line of the input file (not the first line printed, compare the
2437 @option{--page} option and @option{-N} option).
2438 Optional argument @var{number-separator} is the character appended to
2439 the line number to separate it from the text followed. The default
2440 separator is the TAB character. In a strict sense a TAB is always
2441 printed with single column output only. The TAB width varies
2442 with the TAB position, e.g., with the left @var{margin} specified
2443 by @option{-o} option. With multicolumn output priority is given to
2444 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2445 The TAB width is fixed to the value of the first column and does
2446 not change with different values of left @var{margin}. That means a
2447 fixed number of spaces is always printed in the place of the
2448 @var{number-separator} TAB. The tabification depends upon the output
2451 @item -N @var{line_number}
2452 @itemx --first-line-number=@var{line_number}
2454 @opindex --first-line-number
2455 Start line counting with the number @var{line_number} at first line of
2456 first page printed (in most cases not the first line of the input file).
2458 @item -o @var{margin}
2459 @itemx --indent=@var{margin}
2462 @cindex indenting lines
2464 Indent each line with a margin @var{margin} spaces wide (default is zero).
2465 The total page width is the size of the margin plus the @var{page_width}
2466 set with the @option{-W/-w} option. A limited overflow may occur with
2467 numbered single column output (compare @option{-n} option).
2470 @itemx --no-file-warnings
2472 @opindex --no-file-warnings
2473 Do not print a warning message when an argument @var{file} cannot be
2474 opened. (The exit status will still be nonzero, however.)
2476 @item -s[@var{char}]
2477 @itemx --separator[=@var{char}]
2479 @opindex --separator
2480 Separate columns by a single character @var{char}. The default for
2481 @var{char} is the TAB character without @option{-w} and @samp{no
2482 character} with @option{-w}. Without @option{-s} the default separator
2483 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2484 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2485 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2488 @item -S@var{string}
2489 @itemx --sep-string[=@var{string}]
2491 @opindex --sep-string
2492 Use @var{string} to separate output columns. The @option{-S} option doesn't
2493 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2494 does not affect line truncation or column alignment.
2495 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2497 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2498 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2499 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2502 @itemx --omit-header
2504 @opindex --omit-header
2505 Do not print the usual header [and footer] on each page, and do not fill
2506 out the bottom of pages (with blank lines or a form feed). No page
2507 structure is produced, but form feeds set in the input files are retained.
2508 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2509 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2510 in the input file to 4 spaces but don't make any other changes. Use of
2511 @option{-t} overrides @option{-h}.
2514 @itemx --omit-pagination
2516 @opindex --omit-pagination
2517 Do not print header [and footer]. In addition eliminate all form feeds
2518 set in the input files.
2521 @itemx --show-nonprinting
2523 @opindex --show-nonprinting
2524 Print nonprinting characters in octal backslash notation.
2526 @item -w @var{page_width}
2527 @itemx --width=@var{page_width}
2530 Set page width to @var{page_width} characters for multiple text-column
2531 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2532 off the default page width and any line truncation and column alignment.
2533 Lines of full length are merged, regardless of the column options
2534 set. No @var{page_width} setting is possible with single column output.
2535 A @acronym{POSIX}-compliant formulation.
2537 @item -W @var{page_width}
2538 @itemx --page_width=@var{page_width}
2540 @opindex --page_width
2541 Set the page width to @var{page_width} characters. That's valid with and
2542 without a column option. Text lines are truncated, unless @option{-J}
2543 is used. Together with one of the three column options
2544 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2545 alignment is always used. The separator options @option{-S} or @option{-s}
2546 don't affect the @option{-W} option. Default is 72 characters. Without
2547 @option{-W @var{page_width}} and without any of the column options NO line
2548 truncation is used (defined to keep downward compatibility and to meet
2549 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2550 line is never truncated.
2557 @node fold invocation
2558 @section @command{fold}: Wrap input lines to fit in specified width
2561 @cindex wrapping long input lines
2562 @cindex folding long input lines
2564 @command{fold} writes each @var{file} (@option{-} means standard input), or
2565 standard input if none are given, to standard output, breaking long
2569 fold [@var{option}]@dots{} [@var{file}]@dots{}
2572 By default, @command{fold} breaks lines wider than 80 columns. The output
2573 is split into as many lines as necessary.
2575 @cindex screen columns
2576 @command{fold} counts screen columns by default; thus, a tab may count more
2577 than one column, backspace decreases the column count, and carriage
2578 return sets the column to zero.
2580 The program accepts the following options. Also see @ref{Common options}.
2588 Count bytes rather than columns, so that tabs, backspaces, and carriage
2589 returns are each counted as taking up one column, just like other
2596 Break at word boundaries: the line is broken after the last blank before
2597 the maximum line length. If the line contains no such blanks, the line
2598 is broken at the maximum line length as usual.
2600 @item -w @var{width}
2601 @itemx --width=@var{width}
2604 Use a maximum line length of @var{width} columns instead of 80.
2606 For compatibility @command{fold} supports an obsolete option syntax
2607 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2615 @node Output of parts of files
2616 @chapter Output of parts of files
2618 @cindex output of parts of files
2619 @cindex parts of files, output of
2621 These commands output pieces of the input.
2624 * head invocation:: Output the first part of files.
2625 * tail invocation:: Output the last part of files.
2626 * split invocation:: Split a file into fixed-size pieces.
2627 * csplit invocation:: Split a file into context-determined pieces.
2630 @node head invocation
2631 @section @command{head}: Output the first part of files
2634 @cindex initial part of files, outputting
2635 @cindex first part of files, outputting
2637 @command{head} prints the first part (10 lines by default) of each
2638 @var{file}; it reads from standard input if no files are given or
2639 when given a @var{file} of @option{-}. Synopsis:
2642 head [@var{option}]@dots{} [@var{file}]@dots{}
2645 If more than one @var{file} is specified, @command{head} prints a
2646 one-line header consisting of:
2649 ==> @var{file name} <==
2653 before the output for each @var{file}.
2655 The program accepts the following options. Also see @ref{Common options}.
2660 @itemx --bytes=@var{k}
2663 Print the first @var{k} bytes, instead of initial lines.
2664 However, if @var{k} starts with a @samp{-},
2665 print all but the last @var{k} bytes of each file.
2666 @multiplierSuffixes{k}
2669 @itemx --lines=@var{k}
2672 Output the first @var{k} lines.
2673 However, if @var{k} starts with a @samp{-},
2674 print all but the last @var{k} lines of each file.
2675 Size multiplier suffixes are the same as with the @option{-c} option.
2683 Never print file name headers.
2689 Always print file name headers.
2693 For compatibility @command{head} also supports an obsolete option syntax
2694 @option{-@var{count}@var{options}}, which is recognized only if it is
2695 specified first. @var{count} is a decimal number optionally followed
2696 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2697 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2698 Scripts intended for standard hosts should use @option{-c @var{count}}
2699 or @option{-n @var{count}} instead. If your script must also run on
2700 hosts that support only the obsolete syntax, it is usually simpler to
2701 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2707 @node tail invocation
2708 @section @command{tail}: Output the last part of files
2711 @cindex last part of files, outputting
2713 @command{tail} prints the last part (10 lines by default) of each
2714 @var{file}; it reads from standard input if no files are given or
2715 when given a @var{file} of @samp{-}. Synopsis:
2718 tail [@var{option}]@dots{} [@var{file}]@dots{}
2721 If more than one @var{file} is specified, @command{tail} prints a
2722 one-line header consisting of:
2725 ==> @var{file name} <==
2729 before the output for each @var{file}.
2731 @cindex BSD @command{tail}
2732 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2733 @command{tail} cannot). It also has no @option{-r} option (print in
2734 reverse), since reversing a file is really a different job from printing
2735 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2736 only reverse files that are at most as large as its buffer, which is
2737 typically 32 KiB@. A more reliable and versatile way to reverse files is
2738 the @sc{gnu} @command{tac} command.
2740 The program accepts the following options. Also see @ref{Common options}.
2745 @itemx --bytes=@var{k}
2748 Output the last @var{k} bytes, instead of final lines.
2749 However, if @var{k} starts with a @samp{+}, start printing with the
2750 @var{k}th byte from the start of each file, instead of from the end.
2751 @multiplierSuffixes{k}
2754 @itemx --follow[=@var{how}]
2757 @cindex growing files
2758 @vindex name @r{follow option}
2759 @vindex descriptor @r{follow option}
2760 Loop forever trying to read more characters at the end of the file,
2761 presumably because the file is growing.
2762 If more than one file is given, @command{tail} prints a header whenever it
2763 gets output from a different file, to indicate which file that output is
2766 There are two ways to specify how you'd like to track files with this option,
2767 but that difference is noticeable only when a followed file is removed or
2769 If you'd like to continue to track the end of a growing file even after
2770 it has been unlinked, use @option{--follow=descriptor}. This is the default
2771 behavior, but it is not useful if you're tracking a log file that may be
2772 rotated (removed or renamed, then reopened). In that case, use
2773 @option{--follow=name} to track the named file by reopening it periodically
2774 to see if it has been removed and recreated by some other program.
2776 No matter which method you use, if the tracked file is determined to have
2777 shrunk, @command{tail} prints a message saying the file has been truncated
2778 and resumes tracking the end of the file from the newly-determined endpoint.
2780 When a file is removed, @command{tail}'s behavior depends on whether it is
2781 following the name or the descriptor. When following by name, tail can
2782 detect that a file has been removed and gives a message to that effect,
2783 and if @option{--retry} has been specified it will continue checking
2784 periodically to see if the file reappears.
2785 When following a descriptor, tail does not detect that the file has
2786 been unlinked or renamed and issues no message; even though the file
2787 may no longer be accessible via its original name, it may still be
2790 The option values @samp{descriptor} and @samp{name} may be specified only
2791 with the long form of the option, not with @option{-f}.
2793 @vindex POSIXLY_CORRECT
2794 If @env{POSIXLY_CORRECT} is set, the @option{-f} option is ignored if
2795 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2799 This option is the same as @option{--follow=name --retry}. That is, tail
2800 will attempt to reopen a file when it is removed. Should this fail, tail
2801 will keep trying until it becomes accessible again.
2805 This option is useful mainly when following by name (i.e., with
2806 @option{--follow=name}).
2807 Without this option, when tail encounters a file that doesn't
2808 exist or is otherwise inaccessible, it reports that fact and
2809 never checks it again.
2811 @itemx --sleep-interval=@var{number}
2812 @opindex --sleep-interval
2813 Change the number of seconds to wait between iterations (the default is 1.0).
2814 During one iteration, every specified file is checked to see if it has
2816 Historical implementations of @command{tail} have required that
2817 @var{number} be an integer. However, GNU @command{tail} accepts
2818 an arbitrary floating point number (using a period before any
2821 @itemx --pid=@var{pid}
2823 When following by name or by descriptor, you may specify the process ID,
2824 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2825 after that process terminates, tail will also terminate. This will
2826 work properly only if the writer and the tailing process are running on
2827 the same machine. For example, to save the output of a build in a file
2828 and to watch the file grow, if you invoke @command{make} and @command{tail}
2829 like this then the tail process will stop when your build completes.
2830 Without this option, you would have had to kill the @code{tail -f}
2834 $ make >& makerr & tail --pid=$! -f makerr
2837 If you specify a @var{pid} that is not in use or that does not correspond
2838 to the process that is writing to the tailed files, then @command{tail}
2839 may terminate long before any @var{file}s stop growing or it may not
2840 terminate until long after the real writer has terminated.
2841 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2842 will print a warning if this is the case.
2844 @itemx --max-unchanged-stats=@var{n}
2845 @opindex --max-unchanged-stats
2846 When tailing a file by name, if there have been @var{n} (default
2847 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2848 iterations for which the file has not changed, then
2849 @code{open}/@code{fstat} the file to determine if that file name is
2850 still associated with the same device/inode-number pair as before.
2851 When following a log file that is rotated, this is approximately the
2852 number of seconds between when tail prints the last pre-rotation lines
2853 and when it prints the lines that have accumulated in the new log file.
2854 This option is meaningful only when following by name.
2857 @itemx --lines=@var{k}
2860 Output the last @var{k} lines.
2861 However, if @var{k} starts with a @samp{+}, start printing with the
2862 @var{k}th line from the start of each file, instead of from the end.
2863 Size multiplier suffixes are the same as with the @option{-c} option.
2871 Never print file name headers.
2877 Always print file name headers.
2881 For compatibility @command{tail} also supports an obsolete usage
2882 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2883 only if it does not conflict with the usage described
2884 above. This obsolete form uses exactly one option and at most one
2885 file. In the option, @var{count} is an optional decimal number optionally
2886 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2887 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2888 which has the same meaning as @option{-f}.
2890 @vindex _POSIX2_VERSION
2891 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2892 the obsolete option syntax with the same meaning as in counts, and
2893 obsolete usage overrides normal usage when the two conflict.
2894 This obsolete behavior can be enabled or disabled with the
2895 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2898 Scripts intended for use on standard hosts should avoid obsolete
2899 syntax and should use @option{-c @var{count}[b]}, @option{-n
2900 @var{count}}, and/or @option{-f} instead. If your script must also
2901 run on hosts that support only the obsolete syntax, you can often
2902 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2903 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2904 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2905 then @dots{}} to decide which syntax to use.
2907 Even if your script assumes the standard behavior, you should still
2908 beware usages whose behaviors differ depending on the @acronym{POSIX}
2909 version. For example, avoid @samp{tail - main.c}, since it might be
2910 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2911 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2912 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2913 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2918 @node split invocation
2919 @section @command{split}: Split a file into fixed-size pieces
2922 @cindex splitting a file into pieces
2923 @cindex pieces, splitting a file into
2925 @command{split} creates output files containing consecutive sections of
2926 @var{input} (standard input if none is given or @var{input} is
2927 @samp{-}). Synopsis:
2930 split [@var{option}] [@var{input} [@var{prefix}]]
2933 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2934 left over for the last section), into each output file.
2936 @cindex output file name prefix
2937 The output files' names consist of @var{prefix} (@samp{x} by default)
2938 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2939 default), such that concatenating the output files in traditional
2940 sorted order by file name produces
2941 the original input file. If the output file names are exhausted,
2942 @command{split} reports an error without deleting the output files
2945 The program accepts the following options. Also see @ref{Common options}.
2949 @item -l @var{lines}
2950 @itemx --lines=@var{lines}
2953 Put @var{lines} lines of @var{input} into each output file.
2955 For compatibility @command{split} also supports an obsolete
2956 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2957 @var{lines}} instead.
2960 @itemx --bytes=@var{size}
2963 Put @var{size} bytes of @var{input} into each output file.
2964 @multiplierSuffixes{size}
2967 @itemx --line-bytes=@var{size}
2969 @opindex --line-bytes
2970 Put into each output file as many complete lines of @var{input} as
2971 possible without exceeding @var{size} bytes. Individual lines longer than
2972 @var{size} bytes are broken into multiple files.
2973 @var{size} has the same format as for the @option{--bytes} option.
2975 @item -a @var{length}
2976 @itemx --suffix-length=@var{length}
2978 @opindex --suffix-length
2979 Use suffixes of length @var{length}. The default @var{length} is 2.
2982 @itemx --numeric-suffixes
2984 @opindex --numeric-suffixes
2985 Use digits in suffixes rather than lower-case letters.
2989 Write a diagnostic just before each output file is opened.
2996 @node csplit invocation
2997 @section @command{csplit}: Split a file into context-determined pieces
3000 @cindex context splitting
3001 @cindex splitting a file into pieces by context
3003 @command{csplit} creates zero or more output files containing sections of
3004 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3007 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3010 The contents of the output files are determined by the @var{pattern}
3011 arguments, as detailed below. An error occurs if a @var{pattern}
3012 argument refers to a nonexistent line of the input file (e.g., if no
3013 remaining line matches a given regular expression). After every
3014 @var{pattern} has been matched, any remaining input is copied into one
3017 By default, @command{csplit} prints the number of bytes written to each
3018 output file after it has been created.
3020 The types of pattern arguments are:
3025 Create an output file containing the input up to but not including line
3026 @var{n} (a positive integer). If followed by a repeat count, also
3027 create an output file containing the next @var{n} lines of the input
3028 file once for each repeat.
3030 @item /@var{regexp}/[@var{offset}]
3031 Create an output file containing the current line up to (but not
3032 including) the next line of the input file that contains a match for
3033 @var{regexp}. The optional @var{offset} is an integer.
3034 If it is given, the input up to (but not including) the
3035 matching line plus or minus @var{offset} is put into the output file,
3036 and the line after that begins the next section of input.
3038 @item %@var{regexp}%[@var{offset}]
3039 Like the previous type, except that it does not create an output
3040 file, so that section of the input file is effectively ignored.
3042 @item @{@var{repeat-count}@}
3043 Repeat the previous pattern @var{repeat-count} additional
3044 times. The @var{repeat-count} can either be a positive integer or an
3045 asterisk, meaning repeat as many times as necessary until the input is
3050 The output files' names consist of a prefix (@samp{xx} by default)
3051 followed by a suffix. By default, the suffix is an ascending sequence
3052 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3053 concatenating the output files in sorted order by file name produces the
3054 original input file.
3056 By default, if @command{csplit} encounters an error or receives a hangup,
3057 interrupt, quit, or terminate signal, it removes any output files
3058 that it has created so far before it exits.
3060 The program accepts the following options. Also see @ref{Common options}.
3064 @item -f @var{prefix}
3065 @itemx --prefix=@var{prefix}
3068 @cindex output file name prefix
3069 Use @var{prefix} as the output file name prefix.
3071 @item -b @var{suffix}
3072 @itemx --suffix=@var{suffix}
3075 @cindex output file name suffix
3076 Use @var{suffix} as the output file name suffix. When this option is
3077 specified, the suffix string must include exactly one
3078 @code{printf(3)}-style conversion specification, possibly including
3079 format specification flags, a field width, a precision specifications,
3080 or all of these kinds of modifiers. The format letter must convert a
3081 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3082 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3083 entire @var{suffix} is given (with the current output file number) to
3084 @code{sprintf(3)} to form the file name suffixes for each of the
3085 individual output files in turn. If this option is used, the
3086 @option{--digits} option is ignored.
3088 @item -n @var{digits}
3089 @itemx --digits=@var{digits}
3092 Use output file names containing numbers that are @var{digits} digits
3093 long instead of the default 2.
3098 @opindex --keep-files
3099 Do not remove output files when errors are encountered.
3102 @itemx --elide-empty-files
3104 @opindex --elide-empty-files
3105 Suppress the generation of zero-length output files. (In cases where
3106 the section delimiters of the input file are supposed to mark the first
3107 lines of each of the sections, the first output file will generally be a
3108 zero-length file unless you use this option.) The output file sequence
3109 numbers always run consecutively starting from 0, even when this option
3120 Do not print counts of output file sizes.
3126 Here is an example of its usage.
3127 First, create an empty directory for the exercise,
3134 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3137 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3143 Each number printed above is the size of an output
3144 file that csplit has just created.
3145 List the names of those output files:
3152 Use @command{head} to show their contents:
3177 @node Summarizing files
3178 @chapter Summarizing files
3180 @cindex summarizing files
3182 These commands generate just a few numbers representing entire
3186 * wc invocation:: Print newline, word, and byte counts.
3187 * sum invocation:: Print checksum and block counts.
3188 * cksum invocation:: Print CRC checksum and byte counts.
3189 * md5sum invocation:: Print or check MD5 digests.
3190 * sha1sum invocation:: Print or check SHA-1 digests.
3191 * sha2 utilities:: Print or check SHA-2 digests.
3196 @section @command{wc}: Print newline, word, and byte counts
3200 @cindex character count
3204 @command{wc} counts the number of bytes, characters, whitespace-separated
3205 words, and newlines in each given @var{file}, or standard input if none
3206 are given or for a @var{file} of @samp{-}. Synopsis:
3209 wc [@var{option}]@dots{} [@var{file}]@dots{}
3212 @cindex total counts
3213 @command{wc} prints one line of counts for each file, and if the file was
3214 given as an argument, it prints the file name following the counts. If
3215 more than one @var{file} is given, @command{wc} prints a final line
3216 containing the cumulative counts, with the file name @file{total}. The
3217 counts are printed in this order: newlines, words, characters, bytes,
3218 maximum line length.
3219 Each count is printed right-justified in a field with at least one
3220 space between fields so that the numbers and file names normally line
3221 up nicely in columns. The width of the count fields varies depending
3222 on the inputs, so you should not depend on a particular field width.
3223 However, as a @acronym{GNU} extension, if only one count is printed,
3224 it is guaranteed to be printed without leading spaces.
3226 By default, @command{wc} prints three counts: the newline, words, and byte
3227 counts. Options can specify that only certain counts be printed.
3228 Options do not undo others previously given, so
3235 prints both the byte counts and the word counts.
3237 With the @option{--max-line-length} option, @command{wc} prints the length
3238 of the longest line per file, and if there is more than one file it
3239 prints the maximum (not the sum) of those lengths. The line lengths here
3240 are measured in screen columns, according to the current locale and
3241 assuming tab positions in every 8th column.
3243 The program accepts the following options. Also see @ref{Common options}.
3251 Print only the byte counts.
3257 Print only the character counts.
3263 Print only the word counts.
3269 Print only the newline counts.
3272 @itemx --max-line-length
3274 @opindex --max-line-length
3275 Print only the maximum line lengths.
3277 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3278 @itemx --files0-from=@var{file}
3279 @opindex --files0-from=@var{file}
3280 @c This is commented out to avoid a texi2dvi failure.
3281 @c texi2dvi (GNU Texinfo 4.11) 1.104
3282 @c @cindex including files from @command{\cmd\}
3283 Disallow processing files named on the command line, and instead process
3284 those named in file @var{file}; each name being terminated by a zero byte
3285 (@acronym{ASCII} @sc{nul}).
3286 This is useful \withTotalOption\
3287 when the list of file names is so long that it may exceed a command line
3289 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3290 because it splits the list into pieces and makes @command{\cmd\} print
3291 \subListOutput\ for each sublist rather than for the entire list.
3292 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3293 @command{find}, using its @option{-print0} predicate.
3294 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3295 are read from standard input.
3297 @filesZeroFromOption{wc,,a total}
3299 For example, to find the length of the longest line in any @file{.c} or
3300 @file{.h} file in the current hierarchy, do this:
3303 find . -name '*.[ch]' -print0 |
3304 wc -L --files0-from=- | tail -n1
3312 @node sum invocation
3313 @section @command{sum}: Print checksum and block counts
3316 @cindex 16-bit checksum
3317 @cindex checksum, 16-bit
3319 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3320 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3323 sum [@var{option}]@dots{} [@var{file}]@dots{}
3326 @command{sum} prints the checksum for each @var{file} followed by the
3327 number of blocks in the file (rounded up). If more than one @var{file}
3328 is given, file names are also printed (by default). (With the
3329 @option{--sysv} option, corresponding file names are printed when there is
3330 at least one file argument.)
3332 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3333 compatible with BSD @command{sum} and prints file sizes in units of
3336 The program accepts the following options. Also see @ref{Common options}.
3342 @cindex BSD @command{sum}
3343 Use the default (BSD compatible) algorithm. This option is included for
3344 compatibility with the System V @command{sum}. Unless @option{-s} was also
3345 given, it has no effect.
3351 @cindex System V @command{sum}
3352 Compute checksums using an algorithm compatible with System V
3353 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3357 @command{sum} is provided for compatibility; the @command{cksum} program (see
3358 next section) is preferable in new applications.
3363 @node cksum invocation
3364 @section @command{cksum}: Print CRC checksum and byte counts
3367 @cindex cyclic redundancy check
3368 @cindex CRC checksum
3370 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3371 given @var{file}, or standard input if none are given or for a
3372 @var{file} of @samp{-}. Synopsis:
3375 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3378 @command{cksum} prints the CRC checksum for each file along with the number
3379 of bytes in the file, and the file name unless no arguments were given.
3381 @command{cksum} is typically used to ensure that files
3382 transferred by unreliable means (e.g., netnews) have not been corrupted,
3383 by comparing the @command{cksum} output for the received files with the
3384 @command{cksum} output for the original files (typically given in the
3387 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3388 compatible with the BSD or System V @command{sum} algorithms (see the
3389 previous section); it is more robust.
3391 The only options are @option{--help} and @option{--version}. @xref{Common
3397 @node md5sum invocation
3398 @section @command{md5sum}: Print or check MD5 digests
3402 @cindex 128-bit checksum
3403 @cindex checksum, 128-bit
3404 @cindex fingerprint, 128-bit
3405 @cindex message-digest, 128-bit
3407 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3408 @dfn{message-digest}) for each specified @var{file}.
3410 Note: The MD5 digest is more reliable than a simple CRC (provided by
3411 the @command{cksum} command) for detecting accidental file corruption,
3412 as the chances of accidentally having two files with identical MD5
3413 are vanishingly small. However, it should not be considered truly
3414 secure against malicious tampering: although finding a file with a
3415 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3416 considered infeasible at the moment, it is known how to produce
3417 different files with identical MD5 (a ``collision''), something which
3418 can be a security issue in certain contexts. For more secure hashes,
3419 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3420 @ref{sha2 utilities}.
3422 If a @var{file} is specified as @samp{-} or if no files are given
3423 @command{md5sum} computes the checksum for the standard input.
3424 @command{md5sum} can also determine whether a file and checksum are
3425 consistent. Synopsis:
3428 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3431 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3432 indicating a binary or text input file, and the file name.
3433 If @var{file} contains a backslash or newline, the
3434 line is started with a backslash, and each problematic character in
3435 the file name is escaped with a backslash, making the output
3436 unambiguous even in the presence of arbitrary file names.
3437 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3439 The program accepts the following options. Also see @ref{Common options}.
3447 @cindex binary input files
3448 Treat each input file as binary, by reading it in binary mode and
3449 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3450 On systems like @acronym{GNU} that do not distinguish between binary
3451 and text files, this option merely flags each input file as binary:
3452 the MD5 checksum is unaffected. This option is the default on systems
3453 like MS-DOS that distinguish between binary and text files, except
3454 for reading standard input when standard input is a terminal.
3458 Read file names and checksum information (not data) from each
3459 @var{file} (or from stdin if no @var{file} was specified) and report
3460 whether the checksums match the contents of the named files.
3461 The input to this mode of @command{md5sum} is usually the output of
3462 a prior, checksum-generating run of @samp{md5sum}.
3463 Each valid line of input consists of an MD5 checksum, a binary/text
3464 flag, and then a file name.
3465 Binary files are marked with @samp{*}, text with @samp{ }.
3466 For each such line, @command{md5sum} reads the named file and computes its
3467 MD5 checksum. Then, if the computed message digest does not match the
3468 one on the line with the file name, the file is noted as having
3469 failed the test. Otherwise, the file passes the test.
3470 By default, for each valid line, one line is written to standard
3471 output indicating whether the named file passed the test.
3472 After all checks have been performed, if there were any failures,
3473 a warning is issued to standard error.
3474 Use the @option{--status} option to inhibit that output.
3475 If any listed file cannot be opened or read, if any valid line has
3476 an MD5 checksum inconsistent with the associated file, or if no valid
3477 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3478 it exits successfully.
3482 @cindex verifying MD5 checksums
3483 This option is useful only when verifying checksums.
3484 When verifying checksums, don't generate an 'OK' message per successfully
3485 checked file. Files that fail the verification are reported in the
3486 default one-line-per-file format. If there is any checksum mismatch,
3487 print a warning summarizing the failures to standard error.
3491 @cindex verifying MD5 checksums
3492 This option is useful only when verifying checksums.
3493 When verifying checksums, don't generate the default one-line-per-file
3494 diagnostic and don't output the warning summarizing any failures.
3495 Failures to open or read a file still evoke individual diagnostics to
3497 If all listed files are readable and are consistent with the associated
3498 MD5 checksums, exit successfully. Otherwise exit with a status code
3499 indicating there was a failure.
3505 @cindex text input files
3506 Treat each input file as text, by reading it in text mode and
3507 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3508 This option is the default on systems like @acronym{GNU} that do not
3509 distinguish between binary and text files. On other systems, it is
3510 the default for reading standard input when standard input is a
3517 @cindex verifying MD5 checksums
3518 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3519 This option is useful only if all but a few lines in the checked input
3527 @node sha1sum invocation
3528 @section @command{sha1sum}: Print or check SHA-1 digests
3532 @cindex 160-bit checksum
3533 @cindex checksum, 160-bit
3534 @cindex fingerprint, 160-bit
3535 @cindex message-digest, 160-bit
3537 @command{sha1sum} computes a 160-bit checksum for each specified
3538 @var{file}. The usage and options of this command are precisely the
3539 same as for @command{md5sum}. @xref{md5sum invocation}.
3541 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3542 it are known (different files having the same fingerprint). However,
3543 it is known that they can be produced with considerable, but not
3544 unreasonable, resources. For this reason, it is generally considered
3545 that SHA-1 should be gradually phased out in favor of the more secure
3546 SHA-2 hash algorithms. @xref{sha2 utilities}.
3549 @node sha2 utilities
3550 @section sha2 utilities: Print or check SHA-2 digests
3557 @cindex 224-bit checksum
3558 @cindex 256-bit checksum
3559 @cindex 384-bit checksum
3560 @cindex 512-bit checksum
3561 @cindex checksum, 224-bit
3562 @cindex checksum, 256-bit
3563 @cindex checksum, 384-bit
3564 @cindex checksum, 512-bit
3565 @cindex fingerprint, 224-bit
3566 @cindex fingerprint, 256-bit
3567 @cindex fingerprint, 384-bit
3568 @cindex fingerprint, 512-bit
3569 @cindex message-digest, 224-bit
3570 @cindex message-digest, 256-bit
3571 @cindex message-digest, 384-bit
3572 @cindex message-digest, 512-bit
3574 The commands @command{sha224sum}, @command{sha256sum},
3575 @command{sha384sum} and @command{sha512sum} compute checksums of
3576 various lengths (respectively 224, 256, 384 and 512 bits),
3577 collectively known as the SHA-2 hashes. The usage and options of
3578 these commands are precisely the same as for @command{md5sum}.
3579 @xref{md5sum invocation}.
3581 Note: The SHA384 and SHA512 digests are considerably slower to
3582 compute, especially on 32-bit computers, than SHA224 or SHA256.
3585 @node Operating on sorted files
3586 @chapter Operating on sorted files
3588 @cindex operating on sorted files
3589 @cindex sorted files, operations on
3591 These commands work with (or produce) sorted files.
3594 * sort invocation:: Sort text files.
3595 * shuf invocation:: Shuffle text files.
3596 * uniq invocation:: Uniquify files.
3597 * comm invocation:: Compare two sorted files line by line.
3598 * ptx invocation:: Produce a permuted index of file contents.
3599 * tsort invocation:: Topological sort.
3603 @node sort invocation
3604 @section @command{sort}: Sort text files
3607 @cindex sorting files
3609 @command{sort} sorts, merges, or compares all the lines from the given
3610 files, or standard input if none are given or for a @var{file} of
3611 @samp{-}. By default, @command{sort} writes the results to standard
3615 sort [@var{option}]@dots{} [@var{file}]@dots{}
3618 @command{sort} has three modes of operation: sort (the default), merge,
3619 and check for sortedness. The following options change the operation
3626 @itemx --check=diagnose-first
3629 @cindex checking for sortedness
3630 Check whether the given file is already sorted: if it is not all
3631 sorted, print a diagnostic containing the first out-of-order line and
3632 exit with a status of 1.
3633 Otherwise, exit successfully.
3634 At most one input file can be given.
3637 @itemx --check=quiet
3638 @itemx --check=silent
3641 @cindex checking for sortedness
3642 Exit successfully if the given file is already sorted, and
3643 exit with status 1 otherwise.
3644 At most one input file can be given.
3645 This is like @option{-c}, except it does not print a diagnostic.
3651 @cindex merging sorted files
3652 Merge the given files by sorting them as a group. Each input file must
3653 always be individually sorted. It always works to sort instead of
3654 merge; merging is provided because it is faster, in the case where it
3659 @cindex sort stability
3660 @cindex sort's last-resort comparison
3661 A pair of lines is compared as follows:
3662 @command{sort} compares each pair of fields, in the
3663 order specified on the command line, according to the associated
3664 ordering options, until a difference is found or no fields are left.
3665 If no key fields are specified, @command{sort} uses a default key of
3666 the entire line. Finally, as a last resort when all keys compare
3667 equal, @command{sort} compares entire lines as if no ordering options
3668 other than @option{--reverse} (@option{-r}) were specified. The
3669 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3670 comparison} so that lines in which all fields compare equal are left
3671 in their original relative order. The @option{--unique}
3672 (@option{-u}) option also disables the last-resort comparison.
3676 Unless otherwise specified, all comparisons use the character collating
3677 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3678 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3679 to @samp{en_US}), then @command{sort} may produce output that is sorted
3680 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3681 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3682 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3683 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3684 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3685 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3686 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3688 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3689 limit on input line length or restrictions on bytes allowed within lines.
3690 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3691 @command{sort} silently supplies one. A line's trailing newline is not
3692 part of the line for comparison purposes.
3694 @cindex exit status of @command{sort}
3698 0 if no error occurred
3699 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3700 2 if an error occurred
3704 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3705 value as the directory for temporary files instead of @file{/tmp}. The
3706 @option{--temporary-directory} (@option{-T}) option in turn overrides
3707 the environment variable.
3709 The following options affect the ordering of output lines. They may be
3710 specified globally or as part of a specific key field. If no key
3711 fields are specified, global options apply to comparison of entire
3712 lines; otherwise the global options are inherited by key fields that do
3713 not specify any special options of their own. In pre-@acronym{POSIX}
3714 versions of @command{sort}, global options affect only later key fields,
3715 so portable shell scripts should specify global options first.
3720 @itemx --ignore-leading-blanks
3722 @opindex --ignore-leading-blanks
3723 @cindex blanks, ignoring leading
3725 Ignore leading blanks when finding sort keys in each line.
3726 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3727 can change this. Note blanks may be ignored by your locale's collating
3728 rules, but without this option they will be significant for character
3729 positions specified in keys with the @option{-k} option.
3732 @itemx --dictionary-order
3734 @opindex --dictionary-order
3735 @cindex dictionary order
3736 @cindex phone directory order
3737 @cindex telephone directory order
3739 Sort in @dfn{phone directory} order: ignore all characters except
3740 letters, digits and blanks when sorting.
3741 By default letters and digits are those of @acronym{ASCII} and a blank
3742 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3745 @itemx --ignore-case
3747 @opindex --ignore-case
3748 @cindex ignoring case
3749 @cindex case folding
3751 Fold lowercase characters into the equivalent uppercase characters when
3752 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3753 The @env{LC_CTYPE} locale determines character types.
3754 When used with @option{--unique} those lower case equivalent lines are
3755 thrown away. (There is currently no way to throw away the upper case
3756 equivalent instead. (Any @option{--reverse} given would only affect
3757 the final result, after the throwing away.))
3760 @itemx --general-numeric-sort
3761 @itemx --sort=general-numeric
3763 @opindex --general-numeric-sort
3765 @cindex general numeric sort
3767 Sort numerically, using the standard C function @code{strtod} to convert
3768 a prefix of each line to a double-precision floating point number.
3769 This allows floating point numbers to be specified in scientific notation,
3770 like @code{1.0e-34} and @code{10e100}.
3771 The @env{LC_NUMERIC} locale determines the decimal-point character.
3772 Do not report overflow, underflow, or conversion errors.
3773 Use the following collating sequence:
3777 Lines that do not start with numbers (all considered to be equal).
3779 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3780 in a consistent but machine-dependent order.
3784 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3789 Use this option only if there is no alternative; it is much slower than
3790 @option{--numeric-sort} (@option{-n}) and it can lose information when
3791 converting to floating point.
3794 @itemx --human-numeric-sort
3795 @itemx --sort=human-numeric
3797 @opindex --human-numeric-sort
3799 @cindex human numeric sort
3801 Sort numerically, as per the @option{--numeric-sort} option below, and in
3802 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3803 Note a mixture of IEC and SI suffixes is not supported and will
3804 be flagged as an error. Also the numbers must be abbreviated uniformly.
3805 I.E. values with different precisions like 6000K and 5M will be sorted
3809 @itemx --ignore-nonprinting
3811 @opindex --ignore-nonprinting
3812 @cindex nonprinting characters, ignoring
3813 @cindex unprintable characters, ignoring
3815 Ignore nonprinting characters.
3816 The @env{LC_CTYPE} locale determines character types.
3817 This option has no effect if the stronger @option{--dictionary-order}
3818 (@option{-d}) option is also given.
3824 @opindex --month-sort
3826 @cindex months, sorting by
3828 An initial string, consisting of any amount of blanks, followed
3829 by a month name abbreviation, is folded to UPPER case and
3830 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3831 Invalid names compare low to valid names. The @env{LC_TIME} locale
3832 category determines the month spellings.
3833 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3837 @itemx --numeric-sort
3838 @itemx --sort=numeric
3840 @opindex --numeric-sort
3842 @cindex numeric sort
3844 Sort numerically. The number begins each line and consists
3845 of optional blanks, an optional @samp{-} sign, and zero or more
3846 digits possibly separated by thousands separators, optionally followed
3847 by a decimal-point character and zero or more digits. An empty
3848 number is treated as @samp{0}. The @env{LC_NUMERIC}
3849 locale specifies the decimal-point character and thousands separator.
3850 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3853 Comparison is exact; there is no rounding error.
3855 Neither a leading @samp{+} nor exponential notation is recognized.
3856 To compare such strings numerically, use the
3857 @option{--general-numeric-sort} (@option{-g}) option.
3860 @itemx --version-sort
3862 @opindex --version-sort
3863 @cindex version number sort
3865 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3866 that embedded decimal numbers are sorted by numeric value
3867 (see @option{--numeric-sort} above).
3873 @cindex reverse sorting
3874 Reverse the result of comparison, so that lines with greater key values
3875 appear earlier in the output instead of later.
3878 @itemx --random-sort
3879 @itemx --sort=random
3881 @opindex --random-sort
3884 Sort by hashing the input keys and then sorting the hash values.
3885 Choose the hash function at random, ensuring that it is free of
3886 collisions so that differing keys have differing hash values. This is
3887 like a random permutation of the inputs (@pxref{shuf invocation}),
3888 except that keys with the same value sort together.
3890 If multiple random sort fields are specified, the same random hash
3891 function is used for all fields. To use different random hash
3892 functions for different fields, you can invoke @command{sort} more
3895 The choice of hash function is affected by the
3896 @option{--random-source} option.
3904 @item --compress-program=@var{prog}
3905 Compress any temporary files with the program @var{prog}.
3907 With no arguments, @var{prog} must compress standard input to standard
3908 output, and when given the @option{-d} option it must decompress
3909 standard input to standard output.
3911 Terminate with an error if @var{prog} exits with nonzero status.
3913 White space and the backslash character should not appear in
3914 @var{prog}; they are reserved for future use.
3916 @filesZeroFromOption{sort,,sorted output}
3918 @item -k @var{pos1}[,@var{pos2}]
3919 @itemx --key=@var{pos1}[,@var{pos2}]
3923 Specify a sort field that consists of the part of the line between
3924 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3925 omitted), @emph{inclusive}.
3927 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3928 where @var{f} is the number of the field to use, and @var{c} is the number
3929 of the first character from the beginning of the field. Fields and character
3930 positions are numbered starting with 1; a character position of zero in
3931 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3932 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3933 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3934 @var{opts} are ordering options, allowing individual keys to be sorted
3935 according to different rules; see below for details. Keys can span
3938 Example: To sort on the second field, use @option{--key=2,2}
3939 (@option{-k 2,2}). See below for more notes on keys and more examples.
3941 @item --batch-size=@var{nmerge}
3942 @opindex --batch-size
3943 @cindex number of inputs to merge, nmerge
3944 Merge at most @var{nmerge} inputs at once.
3946 When @command{sort} has to merge more than @var{nmerge} inputs,
3947 it merges them in groups of @var{nmerge}, saving the result in
3948 a temporary file, which is then used as an input in a subsequent merge.
3950 A large value of @var{nmerge} may improve merge performance and decrease
3951 temporary storage utilization at the expense of increased memory usage
3952 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3953 requirements and I/0 at the expense of temporary storage consumption and
3956 The value of @var{nmerge} must be at least 2. The default value is
3957 currently 16, but this is implementation-dependent and may change in
3960 The value of @var{nmerge} may be bounded by a resource limit for open
3961 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3962 OPEN_MAX} may display limits for your systems; these limits may be
3963 modified further if your program already has some files open, or if
3964 the operating system has other limits on the number of open files. If
3965 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3966 silently uses a smaller value.
3968 @item -o @var{output-file}
3969 @itemx --output=@var{output-file}
3972 @cindex overwriting of input, allowed
3973 Write output to @var{output-file} instead of standard output.
3974 Normally, @command{sort} reads all input before opening
3975 @var{output-file}, so you can safely sort a file in place by using
3976 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3977 However, @command{sort} with @option{--merge} (@option{-m}) can open
3978 the output file before reading all input, so a command like @code{cat
3979 F | sort -m -o F - G} is not safe as @command{sort} might start
3980 writing @file{F} before @command{cat} is done reading it.
3982 @vindex POSIXLY_CORRECT
3983 On newer systems, @option{-o} cannot appear after an input file if
3984 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3985 scripts should specify @option{-o @var{output-file}} before any input
3988 @item --random-source=@var{file}
3989 @opindex --random-source
3990 @cindex random source for sorting
3991 Use @var{file} as a source of random data used to determine which
3992 random hash function to use with the @option{-R} option. @xref{Random
3999 @cindex sort stability
4000 @cindex sort's last-resort comparison
4002 Make @command{sort} stable by disabling its last-resort comparison.
4003 This option has no effect if no fields or global ordering options
4004 other than @option{--reverse} (@option{-r}) are specified.
4007 @itemx --buffer-size=@var{size}
4009 @opindex --buffer-size
4010 @cindex size for main memory sorting
4011 Use a main-memory sort buffer of the given @var{size}. By default,
4012 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4013 @var{size} to be interpreted as a percentage of physical memory.
4014 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4015 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4016 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4017 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4020 This option can improve the performance of @command{sort} by causing it
4021 to start with a larger or smaller sort buffer than the default.
4022 However, this option affects only the initial buffer size. The buffer
4023 grows beyond @var{size} if @command{sort} encounters input lines larger
4026 @item -t @var{separator}
4027 @itemx --field-separator=@var{separator}
4029 @opindex --field-separator
4030 @cindex field separator character
4031 Use character @var{separator} as the field separator when finding the
4032 sort keys in each line. By default, fields are separated by the empty
4033 string between a non-blank character and a blank character.
4034 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4037 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4038 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4039 not considered to be part of either the field preceding or the field
4040 following, so with @samp{sort @w{-t " "}} the same input line has
4041 three fields: an empty field, @samp{foo}, and @samp{bar}.
4042 However, fields that extend to the end of the line,
4043 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4044 retain the field separators present between the endpoints of the range.
4046 To specify @acronym{ASCII} @sc{nul} as the field separator,
4047 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4049 @item -T @var{tempdir}
4050 @itemx --temporary-directory=@var{tempdir}
4052 @opindex --temporary-directory
4053 @cindex temporary directory
4055 Use directory @var{tempdir} to store temporary files, overriding the
4056 @env{TMPDIR} environment variable. If this option is given more than
4057 once, temporary files are stored in all the directories given. If you
4058 have a large sort or merge that is I/O-bound, you can often improve
4059 performance by using this option to specify directories on different
4060 disks and controllers.
4066 @cindex uniquifying output
4068 Normally, output only the first of a sequence of lines that compare
4069 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4070 check that no pair of consecutive lines compares equal.
4072 This option also disables the default last-resort comparison.
4074 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4075 this equivalence does not extend to arbitrary @command{sort} options.
4076 For example, @code{sort -n -u} inspects only the value of the initial
4077 numeric string when checking for uniqueness, whereas @code{sort -n |
4078 uniq} inspects the entire line. @xref{uniq invocation}.
4080 @macro zeroTerminatedOption
4082 @itemx --zero-terminated
4084 @opindex --zero-terminated
4085 @cindex process zero-terminated items
4086 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4087 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4088 and terminate output items with @acronym{ASCII} @sc{nul}.
4089 This option can be useful in conjunction with @samp{perl -0} or
4090 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4091 reliably handle arbitrary file names (even those containing blanks
4092 or other special characters).
4094 @zeroTerminatedOption
4098 Historical (BSD and System V) implementations of @command{sort} have
4099 differed in their interpretation of some options, particularly
4100 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4101 behavior, which is usually (but not always!) like the System V behavior.
4102 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4103 consistency, @option{-M} has been changed in the same way. This may
4104 affect the meaning of character positions in field specifications in
4105 obscure cases. The only fix is to add an explicit @option{-b}.
4107 A position in a sort field specified with @option{-k} may have any
4108 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4109 global ordering options are inherited by that particular field. The
4110 @option{-b} option may be independently attached to either or both of
4111 the start and end positions of a field specification, and if it is
4112 inherited from the global options it will be attached to both.
4113 If input lines can contain leading or adjacent blanks and @option{-t}
4114 is not used, then @option{-k} is typically combined with @option{-b} or
4115 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4116 the varying numbers of leading blanks in fields can cause confusing results.
4118 If the start position in a sort field specifier falls after the end of
4119 the line or after the end field, the field is empty. If the @option{-b}
4120 option was specified, the @samp{.@var{c}} part of a field specification
4121 is counted from the first nonblank character of the field.
4123 @vindex _POSIX2_VERSION
4124 @vindex POSIXLY_CORRECT
4125 On older systems, @command{sort} supports an obsolete origin-zero
4126 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4127 This obsolete behavior can be enabled or disabled with the
4128 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4129 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4130 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4132 Scripts intended for use on standard hosts should avoid obsolete
4133 syntax and should use @option{-k} instead. For example, avoid
4134 @samp{sort +2}, since it might be interpreted as either @samp{sort
4135 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4136 support only the obsolete syntax, it can use a test like @samp{if sort
4137 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4140 Here are some examples to illustrate various combinations of options.
4145 Sort in descending (reverse) numeric order.
4152 Sort alphabetically, omitting the first and second fields
4153 and the blanks at the start of the third field.
4154 This uses a single key composed of the characters beginning
4155 at the start of the first nonblank character in field three
4156 and extending to the end of each line.
4163 Sort numerically on the second field and resolve ties by sorting
4164 alphabetically on the third and fourth characters of field five.
4165 Use @samp{:} as the field delimiter.
4168 sort -t : -k 2,2n -k 5.3,5.4
4171 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4172 @command{sort} would have used all characters beginning in the second field
4173 and extending to the end of the line as the primary @emph{numeric}
4174 key. For the large majority of applications, treating keys spanning
4175 more than one field as numeric will not do what you expect.
4177 Also note that the @samp{n} modifier was applied to the field-end
4178 specifier for the first key. It would have been equivalent to
4179 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4180 @samp{b} apply to the associated @emph{field}, regardless of whether
4181 the modifier character is attached to the field-start and/or the
4182 field-end part of the key specifier.
4185 Sort the password file on the fifth field and ignore any
4186 leading blanks. Sort lines with equal values in field five
4187 on the numeric user ID in field three. Fields are separated
4191 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4192 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4193 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4196 These three commands have equivalent effect. The first specifies that
4197 the first key's start position ignores leading blanks and the second
4198 key is sorted numerically. The other two commands rely on global
4199 options being inherited by sort keys that lack modifiers. The inheritance
4200 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4201 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4202 character position is not affected by whether initial blanks are
4206 Sort a set of log files, primarily by IPv4 address and secondarily by
4207 time stamp. If two lines' primary and secondary keys are identical,
4208 output the lines in the same order that they were input. The log
4209 files contain lines that look like this:
4212 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4213 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4216 Fields are separated by exactly one space. Sort IPv4 addresses
4217 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4218 because 61 is less than 129.
4221 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4222 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4225 This example cannot be done with a single @command{sort} invocation,
4226 since IPv4 address components are separated by @samp{.} while dates
4227 come just after a space. So it is broken down into two invocations of
4228 @command{sort}: the first sorts by time stamp and the second by IPv4
4229 address. The time stamp is sorted by year, then month, then day, and
4230 finally by hour-minute-second field, using @option{-k} to isolate each
4231 field. Except for hour-minute-second there's no need to specify the
4232 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4233 based on leading prefixes that cannot cross field boundaries. The
4234 IPv4 addresses are sorted lexicographically. The second sort uses
4235 @samp{-s} so that ties in the primary key are broken by the secondary
4236 key; the first sort uses @samp{-s} so that the combination of the two
4240 Generate a tags file in case-insensitive sorted order.
4243 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4246 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4247 that file names that contain blanks or other special characters are
4249 by the sort operation.
4251 @c This example is a bit contrived and needs more explanation.
4253 @c Sort records separated by an arbitrary string by using a pipe to convert
4254 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4255 @c and converting each @samp{\0} back to the original record delimiter.
4258 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4262 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4263 sort lines according to their length.
4266 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4269 In general this technique can be used to sort data that the @command{sort}
4270 command does not support, or is inefficient at, sorting directly.
4273 Shuffle a list of directories, but preserve the order of files within
4274 each directory. For instance, one could use this to generate a music
4275 playlist in which albums are shuffled but the songs of each album are
4279 ls */* | sort -t / -k 1,1R -k 2,2
4285 @node shuf invocation
4286 @section @command{shuf}: Shuffling text
4289 @cindex shuffling files
4291 @command{shuf} shuffles its input by outputting a random permutation
4292 of its input lines. Each output permutation is equally likely.
4296 shuf [@var{option}]@dots{} [@var{file}]
4297 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4298 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4301 @command{shuf} has three modes of operation that affect where it
4302 obtains its input lines. By default, it reads lines from standard
4303 input. The following options change the operation mode:
4311 @cindex command-line operands to shuffle
4312 Treat each command-line operand as an input line.
4314 @item -i @var{lo}-@var{hi}
4315 @itemx --input-range=@var{lo}-@var{hi}
4317 @opindex --input-range
4318 @cindex input range to shuffle
4319 Act as if input came from a file containing the range of unsigned
4320 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4324 @command{shuf}'s other options can affect its behavior in all
4329 @item -n @var{lines}
4330 @itemx --head-count=@var{count}
4332 @opindex --head-count
4333 @cindex head of output
4334 Output at most @var{count} lines. By default, all input lines are
4337 @item -o @var{output-file}
4338 @itemx --output=@var{output-file}
4341 @cindex overwriting of input, allowed
4342 Write output to @var{output-file} instead of standard output.
4343 @command{shuf} reads all input before opening
4344 @var{output-file}, so you can safely shuffle a file in place by using
4345 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4347 @item --random-source=@var{file}
4348 @opindex --random-source
4349 @cindex random source for shuffling
4350 Use @var{file} as a source of random data used to determine which
4351 permutation to generate. @xref{Random sources}.
4353 @zeroTerminatedOption
4369 might produce the output
4379 Similarly, the command:
4382 shuf -e clubs hearts diamonds spades
4396 and the command @samp{shuf -i 1-4} might output:
4406 These examples all have four input lines, so @command{shuf} might
4407 produce any of the twenty-four possible permutations of the input. In
4408 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4409 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4410 output permutations.
4415 @node uniq invocation
4416 @section @command{uniq}: Uniquify files
4419 @cindex uniquify files
4421 @command{uniq} writes the unique lines in the given @file{input}, or
4422 standard input if nothing is given or for an @var{input} name of
4426 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4429 By default, @command{uniq} prints its input lines, except that
4430 it discards all but the first of adjacent repeated lines, so that
4431 no output lines are repeated. Optionally, it can instead discard
4432 lines that are not repeated, or all repeated lines.
4434 The input need not be sorted, but repeated input lines are detected
4435 only if they are adjacent. If you want to discard non-adjacent
4436 duplicate lines, perhaps you want to use @code{sort -u}.
4437 @xref{sort invocation}.
4440 Comparisons honor the rules specified by the @env{LC_COLLATE}
4443 If no @var{output} file is specified, @command{uniq} writes to standard
4446 The program accepts the following options. Also see @ref{Common options}.
4451 @itemx --skip-fields=@var{n}
4453 @opindex --skip-fields
4454 Skip @var{n} fields on each line before checking for uniqueness. Use
4455 a null string for comparison if a line has fewer than @var{n} fields. Fields
4456 are sequences of non-space non-tab characters that are separated from
4457 each other by at least one space or tab.
4459 For compatibility @command{uniq} supports an obsolete option syntax
4460 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4463 @itemx --skip-chars=@var{n}
4465 @opindex --skip-chars
4466 Skip @var{n} characters before checking for uniqueness. Use a null string
4467 for comparison if a line has fewer than @var{n} characters. If you use both
4468 the field and character skipping options, fields are skipped over first.
4470 @vindex _POSIX2_VERSION
4471 On older systems, @command{uniq} supports an obsolete option syntax
4473 This obsolete behavior can be enabled or disabled with the
4474 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4475 conformance}), but portable scripts should avoid commands whose
4476 behavior depends on this variable.
4477 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4478 the ambiguous @samp{uniq +10}.
4484 Print the number of times each line occurred along with the line.
4487 @itemx --ignore-case
4489 @opindex --ignore-case
4490 Ignore differences in case when comparing lines.
4496 @cindex repeated lines, outputting
4497 Discard lines that are not repeated. When used by itself, this option
4498 causes @command{uniq} to print the first copy of each repeated line,
4502 @itemx --all-repeated[=@var{delimit-method}]
4504 @opindex --all-repeated
4505 @cindex all repeated lines, outputting
4506 Do not discard the second and subsequent repeated input lines,
4507 but discard lines that are not repeated.
4508 This option is useful mainly in conjunction with other options e.g.,
4509 to ignore case or to compare only selected fields.
4510 The optional @var{delimit-method} tells how to delimit
4511 groups of repeated lines, and must be one of the following:
4516 Do not delimit groups of repeated lines.
4517 This is equivalent to @option{--all-repeated} (@option{-D}).
4520 Output a newline before each group of repeated lines.
4521 With @option{--zero-terminated} (@option{-z}), use a zero
4522 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4525 Separate groups of repeated lines with a single newline.
4526 With @option{--zero-terminated} (@option{-z}), use a zero
4527 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4528 This is the same as using @samp{prepend}, except that
4529 no delimiter is inserted before the first group, and hence
4530 may be better suited for output direct to users.
4533 Note that when groups are delimited and the input stream contains
4534 two or more consecutive blank lines, then the output is ambiguous.
4535 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4536 each sequence of consecutive newlines with a single newline.
4538 This is a @sc{gnu} extension.
4539 @c FIXME: give an example showing *how* it's useful
4545 @cindex unique lines, outputting
4546 Discard the first repeated line. When used by itself, this option
4547 causes @command{uniq} to print unique lines, and nothing else.
4550 @itemx --check-chars=@var{n}
4552 @opindex --check-chars
4553 Compare at most @var{n} characters on each line (after skipping any specified
4554 fields and characters). By default the entire rest of the lines are
4557 @zeroTerminatedOption
4564 @node comm invocation
4565 @section @command{comm}: Compare two sorted files line by line
4568 @cindex line-by-line comparison
4569 @cindex comparing sorted files
4571 @command{comm} writes to standard output lines that are common, and lines
4572 that are unique, to two input files; a file name of @samp{-} means
4573 standard input. Synopsis:
4576 comm [@var{option}]@dots{} @var{file1} @var{file2}
4580 Before @command{comm} can be used, the input files must be sorted using the
4581 collating sequence specified by the @env{LC_COLLATE} locale.
4582 If an input file ends in a non-newline
4583 character, a newline is silently appended. The @command{sort} command with
4584 no options always outputs a file that is suitable input to @command{comm}.
4586 @cindex differing lines
4587 @cindex common lines
4588 With no options, @command{comm} produces three-column output. Column one
4589 contains lines unique to @var{file1}, column two contains lines unique
4590 to @var{file2}, and column three contains lines common to both files.
4591 Columns are separated by a single TAB character.
4592 @c FIXME: when there's an option to supply an alternative separator
4593 @c string, append `by default' to the above sentence.
4598 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4599 the corresponding columns (and separators). Also see @ref{Common options}.
4601 Unlike some other comparison utilities, @command{comm} has an exit
4602 status that does not depend on the result of the comparison.
4603 Upon normal completion @command{comm} produces an exit code of zero.
4604 If there is an error it exits with nonzero status.
4606 @macro checkOrderOption{cmd}
4607 If the @option{--check-order} option is given, unsorted inputs will
4608 cause a fatal error message. If the option @option{--nocheck-order}
4609 is given, unsorted inputs will never cause an error message. If
4610 neither of these options is given, wrongly sorted inputs are diagnosed
4611 only if an input file is found to contain unpairable lines. If an
4612 input file is diagnosed as being unsorted, the @command{\cmd\} command
4613 will exit with a nonzero status (and the output should not be used).
4615 Forcing @command{\cmd\} to process wrongly sorted input files
4616 containing unpairable lines by specifying @option{--nocheck-order} is
4617 not guaranteed to produce any particular output. The output will
4618 probably not correspond with whatever you hoped it would be.
4620 @checkOrderOption{comm}
4625 Fail with an error message if either input file is wrongly ordered.
4627 @item --nocheck-order
4628 Do not check that both input files are in sorted order.
4632 @item --output-delimiter=@var{str}
4633 Print @var{str} between adjacent output columns,
4634 rather than the default of a single TAB character.
4636 The delimiter @var{str} may not be empty.
4640 @node ptx invocation
4641 @section @command{ptx}: Produce permuted indexes
4645 @command{ptx} reads a text file and essentially produces a permuted index, with
4646 each keyword in its context. The calling sketch is either one of:
4649 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4650 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4653 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4654 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4655 limitations and changing several of the program's default option values.
4656 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4657 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4658 document. For the full list, see @xref{Compatibility in ptx}.
4660 Individual options are explained in the following sections.
4662 When @sc{gnu} extensions are enabled, there may be zero, one or several
4663 @var{file}s after the options. If there is no @var{file}, the program
4664 reads the standard input. If there is one or several @var{file}s, they
4665 give the name of input files which are all read in turn, as if all the
4666 input files were concatenated. However, there is a full contextual
4667 break between each file and, when automatic referencing is requested,
4668 file names and line numbers refer to individual text input files. In
4669 all cases, the program outputs the permuted index to the standard
4672 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4673 operates in traditional mode, there may be zero, one or two parameters
4674 besides the options. If there are no parameters, the program reads the
4675 standard input and outputs the permuted index to the standard output.
4676 If there is only one parameter, it names the text @var{input} to be read
4677 instead of the standard input. If two parameters are given, they give
4678 respectively the name of the @var{input} file to read and the name of
4679 the @var{output} file to produce. @emph{Be very careful} to note that,
4680 in this case, the contents of file given by the second parameter is
4681 destroyed. This behavior is dictated by System V @command{ptx}
4682 compatibility; @sc{gnu} Standards normally discourage output parameters not
4683 introduced by an option.
4685 Note that for @emph{any} file named as the value of an option or as an
4686 input text file, a single dash @kbd{-} may be used, in which case
4687 standard input is assumed. However, it would not make sense to use this
4688 convention more than once per program invocation.
4691 * General options in ptx:: Options which affect general program behavior.
4692 * Charset selection in ptx:: Underlying character set considerations.
4693 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4694 * Output formatting in ptx:: Types of output format, and sizing the fields.
4695 * Compatibility in ptx::
4699 @node General options in ptx
4700 @subsection General options
4705 @itemx --traditional
4706 As already explained, this option disables all @sc{gnu} extensions to
4707 @command{ptx} and switches to traditional mode.
4710 Print a short help on standard output, then exit without further
4714 Print the program version on standard output, then exit without further
4722 @node Charset selection in ptx
4723 @subsection Charset selection
4725 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4726 As it is set up now, the program assumes that the input file is coded
4727 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4728 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4729 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4730 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4731 of characters which are letters is different; this alters the behavior
4732 of regular expression matching. Thus, the default regular expression
4733 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4734 however, is still crude; it obeys the underlying character set ordering
4740 @itemx --ignore-case
4741 Fold lower case letters to upper case for sorting.
4746 @node Input processing in ptx
4747 @subsection Word selection and input processing
4752 @itemx --break-file=@var{file}
4754 This option provides an alternative (to @option{-W}) method of describing
4755 which characters make up words. It introduces the name of a
4756 file which contains a list of characters which can@emph{not} be part of
4757 one word; this file is called the @dfn{Break file}. Any character which
4758 is not part of the Break file is a word constituent. If both options
4759 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4760 @option{-b} is ignored.
4762 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4763 break character is to write all the break characters in the file with no
4764 newline at all, not even at the end of the file. When @sc{gnu} extensions
4765 are disabled, spaces, tabs and newlines are always considered as break
4766 characters even if not included in the Break file.
4769 @itemx --ignore-file=@var{file}
4771 The file associated with this option contains a list of words which will
4772 never be taken as keywords in concordance output. It is called the
4773 @dfn{Ignore file}. The file contains exactly one word in each line; the
4774 end of line separation of words is not subject to the value of the
4778 @itemx --only-file=@var{file}
4780 The file associated with this option contains a list of words which will
4781 be retained in concordance output; any word not mentioned in this file
4782 is ignored. The file is called the @dfn{Only file}. The file contains
4783 exactly one word in each line; the end of line separation of words is
4784 not subject to the value of the @option{-S} option.
4786 There is no default for the Only file. When both an Only file and an
4787 Ignore file are specified, a word is considered a keyword only
4788 if it is listed in the Only file and not in the Ignore file.
4793 On each input line, the leading sequence of non-white space characters will be
4794 taken to be a reference that has the purpose of identifying this input
4795 line in the resulting permuted index. For more information about reference
4796 production, see @xref{Output formatting in ptx}.
4797 Using this option changes the default value for option @option{-S}.
4799 Using this option, the program does not try very hard to remove
4800 references from contexts in output, but it succeeds in doing so
4801 @emph{when} the context ends exactly at the newline. If option
4802 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4803 are disabled, this condition is always met and references are completely
4804 excluded from the output contexts.
4806 @item -S @var{regexp}
4807 @itemx --sentence-regexp=@var{regexp}
4809 This option selects which regular expression will describe the end of a
4810 line or the end of a sentence. In fact, this regular expression is not
4811 the only distinction between end of lines or end of sentences, and input
4812 line boundaries have no special significance outside this option. By
4813 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4814 used, end of sentences are used. In this case, this @var{regex} is
4815 imported from @sc{gnu} Emacs:
4818 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4821 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4822 of lines are used; in this case, the default @var{regexp} is just:
4828 Using an empty @var{regexp} is equivalent to completely disabling end of
4829 line or end of sentence recognition. In this case, the whole file is
4830 considered to be a single big line or sentence. The user might want to
4831 disallow all truncation flag generation as well, through option @option{-F
4832 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4835 When the keywords happen to be near the beginning of the input line or
4836 sentence, this often creates an unused area at the beginning of the
4837 output context line; when the keywords happen to be near the end of the
4838 input line or sentence, this often creates an unused area at the end of
4839 the output context line. The program tries to fill those unused areas
4840 by wrapping around context in them; the tail of the input line or
4841 sentence is used to fill the unused area on the left of the output line;
4842 the head of the input line or sentence is used to fill the unused area
4843 on the right of the output line.
4845 As a matter of convenience to the user, many usual backslashed escape
4846 sequences from the C language are recognized and converted to the
4847 corresponding characters by @command{ptx} itself.
4849 @item -W @var{regexp}
4850 @itemx --word-regexp=@var{regexp}
4852 This option selects which regular expression will describe each keyword.
4853 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4854 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4855 disabled, a word is by default anything which ends with a space, a tab
4856 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4858 An empty @var{regexp} is equivalent to not using this option.
4859 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4862 As a matter of convenience to the user, many usual backslashed escape
4863 sequences, as found in the C language, are recognized and converted to
4864 the corresponding characters by @command{ptx} itself.
4869 @node Output formatting in ptx
4870 @subsection Output formatting
4872 Output format is mainly controlled by the @option{-O} and @option{-T} options
4873 described in the table below. When neither @option{-O} nor @option{-T} are
4874 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4875 output format suitable for a dumb terminal. Each keyword occurrence is
4876 output to the center of one line, surrounded by its left and right
4877 contexts. Each field is properly justified, so the concordance output
4878 can be readily observed. As a special feature, if automatic
4879 references are selected by option @option{-A} and are output before the
4880 left context, that is, if option @option{-R} is @emph{not} selected, then
4881 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4882 Emacs @code{next-error} processing. In this default output format, each
4883 white space character, like newline and tab, is merely changed to
4884 exactly one space, with no special attempt to compress consecutive
4885 spaces. This might change in the future. Except for those white space
4886 characters, every other character of the underlying set of 256
4887 characters is transmitted verbatim.
4889 Output format is further controlled by the following options.
4893 @item -g @var{number}
4894 @itemx --gap-size=@var{number}
4896 Select the size of the minimum white space gap between the fields on the
4899 @item -w @var{number}
4900 @itemx --width=@var{number}
4902 Select the maximum output width of each final line. If references are
4903 used, they are included or excluded from the maximum output width
4904 depending on the value of option @option{-R}. If this option is not
4905 selected, that is, when references are output before the left context,
4906 the maximum output width takes into account the maximum length of all
4907 references. If this option is selected, that is, when references are
4908 output after the right context, the maximum output width does not take
4909 into account the space taken by references, nor the gap that precedes
4913 @itemx --auto-reference
4915 Select automatic references. Each input line will have an automatic
4916 reference made up of the file name and the line ordinal, with a single
4917 colon between them. However, the file name will be empty when standard
4918 input is being read. If both @option{-A} and @option{-r} are selected, then
4919 the input reference is still read and skipped, but the automatic
4920 reference is used at output time, overriding the input reference.
4923 @itemx --right-side-refs
4925 In the default output format, when option @option{-R} is not used, any
4926 references produced by the effect of options @option{-r} or @option{-A} are
4927 placed to the far right of output lines, after the right context. With
4928 default output format, when the @option{-R} option is specified, references
4929 are rather placed at the beginning of each output line, before the left
4930 context. For any other output format, option @option{-R} is
4931 ignored, with one exception: with @option{-R} the width of references
4932 is @emph{not} taken into account in total output width given by @option{-w}.
4934 This option is automatically selected whenever @sc{gnu} extensions are
4937 @item -F @var{string}
4938 @itemx --flac-truncation=@var{string}
4940 This option will request that any truncation in the output be reported
4941 using the string @var{string}. Most output fields theoretically extend
4942 towards the beginning or the end of the current line, or current
4943 sentence, as selected with option @option{-S}. But there is a maximum
4944 allowed output line width, changeable through option @option{-w}, which is
4945 further divided into space for various output fields. When a field has
4946 to be truncated because it cannot extend beyond the beginning or the end of
4947 the current line to fit in, then a truncation occurs. By default,
4948 the string used is a single slash, as in @option{-F /}.
4950 @var{string} may have more than one character, as in @option{-F ...}.
4951 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4952 truncation flagging is disabled, and no truncation marks are appended in
4955 As a matter of convenience to the user, many usual backslashed escape
4956 sequences, as found in the C language, are recognized and converted to
4957 the corresponding characters by @command{ptx} itself.
4959 @item -M @var{string}
4960 @itemx --macro-name=@var{string}
4962 Select another @var{string} to be used instead of @samp{xx}, while
4963 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4966 @itemx --format=roff
4968 Choose an output format suitable for @command{nroff} or @command{troff}
4969 processing. Each output line will look like:
4972 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4975 so it will be possible to write a @samp{.xx} roff macro to take care of
4976 the output typesetting. This is the default output format when @sc{gnu}
4977 extensions are disabled. Option @option{-M} can be used to change
4978 @samp{xx} to another macro name.
4980 In this output format, each non-graphical character, like newline and
4981 tab, is merely changed to exactly one space, with no special attempt to
4982 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4983 so it will be correctly processed by @command{nroff} or @command{troff}.
4988 Choose an output format suitable for @TeX{} processing. Each output
4989 line will look like:
4992 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4996 so it will be possible to write a @code{\xx} definition to take care of
4997 the output typesetting. Note that when references are not being
4998 produced, that is, neither option @option{-A} nor option @option{-r} is
4999 selected, the last parameter of each @code{\xx} call is inhibited.
5000 Option @option{-M} can be used to change @samp{xx} to another macro
5003 In this output format, some special characters, like @kbd{$}, @kbd{%},
5004 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5005 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5006 backslash and a pair of dollar signs (to force mathematical mode). The
5007 backslash itself produces the sequence @code{\backslash@{@}}.
5008 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5009 @code{~\@{ @}} respectively. Other diacriticized characters of the
5010 underlying character set produce an appropriate @TeX{} sequence as far
5011 as possible. The other non-graphical characters, like newline and tab,
5012 and all other characters which are not part of @acronym{ASCII}, are merely
5013 changed to exactly one space, with no special attempt to compress
5014 consecutive spaces. Let me know how to improve this special character
5015 processing for @TeX{}.
5020 @node Compatibility in ptx
5021 @subsection The @sc{gnu} extensions to @command{ptx}
5023 This version of @command{ptx} contains a few features which do not exist in
5024 System V @command{ptx}. These extra features are suppressed by using the
5025 @option{-G} command line option, unless overridden by other command line
5026 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5027 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5028 Here are the differences between this program and System V @command{ptx}.
5033 This program can read many input files at once, it always writes the
5034 resulting concordance on standard output. On the other hand, System V
5035 @command{ptx} reads only one file and sends the result to standard output
5036 or, if a second @var{file} parameter is given on the command, to that
5039 Having output parameters not introduced by options is a dangerous
5040 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5041 portably between @sc{gnu} and System V, you should always use it with a
5042 single input file, and always expect the result on standard output. You
5043 might also want to automatically configure in a @option{-G} option to
5044 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5045 that the installed @command{ptx} accepts @option{-G}.
5048 The only options available in System V @command{ptx} are options @option{-b},
5049 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5050 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5051 this enumeration. Moreover, some options have a slightly different
5052 meaning when @sc{gnu} extensions are enabled, as explained below.
5055 By default, concordance output is not formatted for @command{troff} or
5056 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5057 or @command{nroff} output may still be selected through option @option{-O}.
5060 Unless @option{-R} option is used, the maximum reference width is
5061 subtracted from the total output line width. With @sc{gnu} extensions
5062 disabled, width of references is not taken into account in the output
5063 line width computations.
5066 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5067 processed from input file with no adverse effect, even if @sc{gnu} extensions
5068 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5069 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5072 Input line length is only limited by available memory, even if @sc{gnu}
5073 extensions are disabled. However, System V @command{ptx} processes only
5074 the first 200 characters in each line.
5077 The break (non-word) characters default to be every character except all
5078 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5079 extensions are disabled, the break characters default to space, tab and
5083 The program makes better use of output line width. If @sc{gnu} extensions
5084 are disabled, the program rather tries to imitate System V @command{ptx},
5085 but still, there are some slight disposition glitches this program does
5086 not completely reproduce.
5089 The user can specify both an Ignore file and an Only file. This is not
5090 allowed with System V @command{ptx}.
5095 @node tsort invocation
5096 @section @command{tsort}: Topological sort
5099 @cindex topological sort
5101 @command{tsort} performs a topological sort on the given @var{file}, or
5102 standard input if no input file is given or for a @var{file} of
5103 @samp{-}. For more details and some history, see @ref{tsort background}.
5107 tsort [@var{option}] [@var{file}]
5110 @command{tsort} reads its input as pairs of strings, separated by blanks,
5111 indicating a partial ordering. The output is a total ordering that
5112 corresponds to the given partial ordering.
5126 will produce the output
5137 Consider a more realistic example.
5138 You have a large set of functions all in one file, and they may all be
5139 declared static except one. Currently that one (say @code{main}) is the
5140 first function defined in the file, and the ones it calls directly follow
5141 it, followed by those they call, etc. Let's say that you are determined
5142 to take advantage of prototypes, so you have to choose between declaring
5143 all of those functions (which means duplicating a lot of information from
5144 the definitions) and rearranging the functions so that as many as possible
5145 are defined before they are used. One way to automate the latter process
5146 is to get a list for each function of the functions it calls directly.
5147 Many programs can generate such lists. They describe a call graph.
5148 Consider the following list, in which a given line indicates that the
5149 function on the left calls the one on the right directly.
5155 tail_file pretty_name
5156 tail_file write_header
5158 tail_forever recheck
5159 tail_forever pretty_name
5160 tail_forever write_header
5161 tail_forever dump_remainder
5164 tail_lines start_lines
5165 tail_lines dump_remainder
5166 tail_lines file_lines
5167 tail_lines pipe_lines
5169 tail_bytes start_bytes
5170 tail_bytes dump_remainder
5171 tail_bytes pipe_bytes
5172 file_lines dump_remainder
5176 then you can use @command{tsort} to produce an ordering of those
5177 functions that satisfies your requirement.
5180 example$ tsort call-graph | tac
5200 @command{tsort} detects any cycles in the input and writes the first cycle
5201 encountered to standard error.
5203 Note that for a given partial ordering, generally there is no unique
5204 total ordering. In the context of the call graph above, the function
5205 @code{parse_options} may be placed anywhere in the list as long as it
5206 precedes @code{main}.
5208 The only options are @option{--help} and @option{--version}. @xref{Common
5214 * tsort background:: Where tsort came from.
5217 @node tsort background
5218 @subsection @command{tsort}: Background
5220 @command{tsort} exists because very early versions of the Unix linker processed
5221 an archive file exactly once, and in order. As @command{ld} read each object
5222 in the archive, it decided whether it was needed in the program based on
5223 whether it defined any symbols which were undefined at that point in
5226 This meant that dependencies within the archive had to be handled
5227 specially. For example, @code{scanf} probably calls @code{read}. That means
5228 that in a single pass through an archive, it was important for @code{scanf.o}
5229 to appear before read.o, because otherwise a program which calls
5230 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5231 reference to @code{read}.
5233 The way to address this problem was to first generate a set of
5234 dependencies of one object file on another. This was done by a shell
5235 script called @command{lorder}. The GNU tools don't provide a version of
5236 lorder, as far as I know, but you can still find it in BSD
5239 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5240 resulting sort to define the order in which you added objects to the archive.
5242 This whole procedure has been obsolete since about 1980, because
5243 Unix archives now contain a symbol table (traditionally built by
5244 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5245 linker uses the symbol table to effectively make multiple passes over
5248 Anyhow, that's where tsort came from. To solve an old problem with
5249 the way the linker handled archive files, which has since been solved
5253 @node Operating on fields within a line
5254 @chapter Operating on fields within a line
5257 * cut invocation:: Print selected parts of lines.
5258 * paste invocation:: Merge lines of files.
5259 * join invocation:: Join lines on a common field.
5263 @node cut invocation
5264 @section @command{cut}: Print selected parts of lines
5267 @command{cut} writes to standard output selected parts of each line of each
5268 input file, or standard input if no files are given or for a file name of
5272 cut @var{option}@dots{} [@var{file}]@dots{}
5275 In the table which follows, the @var{byte-list}, @var{character-list},
5276 and @var{field-list} are one or more numbers or ranges (two numbers
5277 separated by a dash) separated by commas. Bytes, characters, and
5278 fields are numbered starting at 1. Incomplete ranges may be
5279 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5280 @samp{@var{n}} through end of line or last field. The list elements
5281 can be repeated, can overlap, and can be specified in any order; but
5282 the selected input is written in the same order that it is read, and
5283 is written exactly once.
5285 The program accepts the following options. Also see @ref{Common
5290 @item -b @var{byte-list}
5291 @itemx --bytes=@var{byte-list}
5294 Select for printing only the bytes in positions listed in
5295 @var{byte-list}. Tabs and backspaces are treated like any other
5296 character; they take up 1 byte. If an output delimiter is specified,
5297 (see the description of @option{--output-delimiter}), then output that
5298 string between ranges of selected bytes.
5300 @item -c @var{character-list}
5301 @itemx --characters=@var{character-list}
5303 @opindex --characters
5304 Select for printing only the characters in positions listed in
5305 @var{character-list}. The same as @option{-b} for now, but
5306 internationalization will change that. Tabs and backspaces are
5307 treated like any other character; they take up 1 character. If an
5308 output delimiter is specified, (see the description of
5309 @option{--output-delimiter}), then output that string between ranges
5312 @item -f @var{field-list}
5313 @itemx --fields=@var{field-list}
5316 Select for printing only the fields listed in @var{field-list}.
5317 Fields are separated by a TAB character by default. Also print any
5318 line that contains no delimiter character, unless the
5319 @option{--only-delimited} (@option{-s}) option is specified
5321 @item -d @var{input_delim_byte}
5322 @itemx --delimiter=@var{input_delim_byte}
5324 @opindex --delimiter
5325 With @option{-f}, use the first byte of @var{input_delim_byte} as
5326 the input fields separator (default is TAB).
5330 Do not split multi-byte characters (no-op for now).
5333 @itemx --only-delimited
5335 @opindex --only-delimited
5336 For @option{-f}, do not print lines that do not contain the field separator
5337 character. Normally, any line without a field separator is printed verbatim.
5339 @item --output-delimiter=@var{output_delim_string}
5340 @opindex --output-delimiter
5341 With @option{-f}, output fields are separated by @var{output_delim_string}.
5342 The default with @option{-f} is to use the input delimiter.
5343 When using @option{-b} or @option{-c} to select ranges of byte or
5344 character offsets (as opposed to ranges of fields),
5345 output @var{output_delim_string} between non-overlapping
5346 ranges of selected bytes.
5349 @opindex --complement
5350 This option is a @acronym{GNU} extension.
5351 Select for printing the complement of the bytes, characters or fields
5352 selected with the @option{-b}, @option{-c} or @option{-f} options.
5353 In other words, do @emph{not} print the bytes, characters or fields
5354 specified via those options. This option is useful when you have
5355 many fields and want to print all but a few of them.
5362 @node paste invocation
5363 @section @command{paste}: Merge lines of files
5366 @cindex merging files
5368 @command{paste} writes to standard output lines consisting of sequentially
5369 corresponding lines of each given file, separated by a TAB character.
5370 Standard input is used for a file name of @samp{-} or if no input files
5392 paste [@var{option}]@dots{} [@var{file}]@dots{}
5395 The program accepts the following options. Also see @ref{Common options}.
5403 Paste the lines of one file at a time rather than one line from each
5404 file. Using the above example data:
5407 $ paste -s num2 let3
5412 @item -d @var{delim-list}
5413 @itemx --delimiters=@var{delim-list}
5415 @opindex --delimiters
5416 Consecutively use the characters in @var{delim-list} instead of
5417 TAB to separate merged lines. When @var{delim-list} is
5418 exhausted, start again at its beginning. Using the above example data:
5421 $ paste -d '%_' num2 let3 num2
5432 @node join invocation
5433 @section @command{join}: Join lines on a common field
5436 @cindex common field, joining on
5438 @command{join} writes to standard output a line for each pair of input
5439 lines that have identical join fields. Synopsis:
5442 join [@var{option}]@dots{} @var{file1} @var{file2}
5445 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5446 meaning standard input. @var{file1} and @var{file2} should be
5447 sorted on the join fields.
5450 Normally, the sort order is that of the
5451 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5452 the @option{-t} option is given, the sort comparison ignores blanks at
5453 the start of the join field, as in @code{sort -b}. If the
5454 @option{--ignore-case} option is given, the sort comparison ignores
5455 the case of characters in the join field, as in @code{sort -f}.
5457 The @command{sort} and @command{join} commands should use consistent
5458 locales and options if the output of @command{sort} is fed to
5459 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5460 sort a file on its default join field, but if you select a non-default
5461 locale, join field, separator, or comparison options, then you should
5462 do so consistently between @command{join} and @command{sort}.
5464 If the input has no unpairable lines, a @acronym{GNU} extension is
5465 available; the sort order can be any order that considers two fields
5466 to be equal if and only if the sort comparison described above
5467 considers them to be equal. For example:
5484 @checkOrderOption{join}
5488 @item the join field is the first field in each line;
5489 @item fields in the input are separated by one or more blanks, with leading
5490 blanks on the line ignored;
5491 @item fields in the output are separated by a space;
5492 @item each output line consists of the join field, the remaining
5493 fields from @var{file1}, then the remaining fields from @var{file2}.
5496 The program accepts the following options. Also see @ref{Common options}.
5500 @item -a @var{file-number}
5502 Print a line for each unpairable line in file @var{file-number} (either
5503 @samp{1} or @samp{2}), in addition to the normal output.
5506 Fail with an error message if either input file is wrongly ordered.
5508 @item --nocheck-order
5509 Do not check that both input files are in sorted order. This is the default.
5511 @item -e @var{string}
5513 Replace those output fields that are missing in the input with
5517 @itemx --ignore-case
5519 @opindex --ignore-case
5520 Ignore differences in case when comparing keys.
5521 With this option, the lines of the input files must be ordered in the same way.
5522 Use @samp{sort -f} to produce this ordering.
5524 @item -1 @var{field}
5526 Join on field @var{field} (a positive integer) of file 1.
5528 @item -2 @var{field}
5530 Join on field @var{field} (a positive integer) of file 2.
5532 @item -j @var{field}
5533 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5535 @item -o @var{field-list}
5536 Construct each output line according to the format in @var{field-list}.
5537 Each element in @var{field-list} is either the single character @samp{0} or
5538 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5539 @samp{2} and @var{n} is a positive field number.
5541 A field specification of @samp{0} denotes the join field.
5542 In most cases, the functionality of the @samp{0} field spec
5543 may be reproduced using the explicit @var{m.n} that corresponds
5544 to the join field. However, when printing unpairable lines
5545 (using either of the @option{-a} or @option{-v} options), there is no way
5546 to specify the join field using @var{m.n} in @var{field-list}
5547 if there are unpairable lines in both files.
5548 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5549 field specification notation.
5551 The elements in @var{field-list}
5552 are separated by commas or blanks.
5553 Blank separators typically need to be quoted for the shell. For
5554 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5555 2.2'} are equivalent.
5557 All output lines---including those printed because of any -a or -v
5558 option---are subject to the specified @var{field-list}.
5561 Use character @var{char} as the input and output field separator.
5562 Treat as significant each occurrence of @var{char} in the input file.
5563 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5564 @samp{sort}, to produce this ordering.
5566 @item -v @var{file-number}
5567 Print a line for each unpairable line in file @var{file-number}
5568 (either @samp{1} or @samp{2}), instead of the normal output.
5575 @node Operating on characters
5576 @chapter Operating on characters
5578 @cindex operating on characters
5580 This commands operate on individual characters.
5583 * tr invocation:: Translate, squeeze, and/or delete characters.
5584 * expand invocation:: Convert tabs to spaces.
5585 * unexpand invocation:: Convert spaces to tabs.
5590 @section @command{tr}: Translate, squeeze, and/or delete characters
5597 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5600 @command{tr} copies standard input to standard output, performing
5601 one of the following operations:
5605 translate, and optionally squeeze repeated characters in the result,
5607 squeeze repeated characters,
5611 delete characters, then squeeze repeated characters from the result.
5614 The @var{set1} and (if given) @var{set2} arguments define ordered
5615 sets of characters, referred to below as @var{set1} and @var{set2}. These
5616 sets are the characters of the input that @command{tr} operates on.
5617 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5619 complement (all of the characters that are not in @var{set1}).
5621 Currently @command{tr} fully supports only single-byte characters.
5622 Eventually it will support multibyte characters; when it does, the
5623 @option{-C} option will cause it to complement the set of characters,
5624 whereas @option{-c} will cause it to complement the set of values.
5625 This distinction will matter only when some values are not characters,
5626 and this is possible only in locales using multibyte encodings when
5627 the input contains encoding errors.
5629 The program accepts the @option{--help} and @option{--version}
5630 options. @xref{Common options}. Options must precede operands.
5635 * Character sets:: Specifying sets of characters.
5636 * Translating:: Changing one set of characters to another.
5637 * Squeezing:: Squeezing repeats and deleting.
5641 @node Character sets
5642 @subsection Specifying sets of characters
5644 @cindex specifying sets of characters
5646 The format of the @var{set1} and @var{set2} arguments resembles
5647 the format of regular expressions; however, they are not regular
5648 expressions, only lists of characters. Most characters simply
5649 represent themselves in these strings, but the strings can contain
5650 the shorthands listed below, for convenience. Some of them can be
5651 used only in @var{set1} or @var{set2}, as noted below.
5655 @item Backslash escapes
5656 @cindex backslash escapes
5658 The following backslash escape sequences are recognized:
5676 The character with the value given by @var{ooo}, which is 1 to 3
5682 While a backslash followed by a character not listed above is
5683 interpreted as that character, the backslash also effectively
5684 removes any special significance, so it is useful to escape
5685 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5690 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5691 from @var{m} through @var{n}, in ascending order. @var{m} should
5692 collate before @var{n}; if it doesn't, an error results. As an example,
5693 @samp{0-9} is the same as @samp{0123456789}.
5695 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5696 brackets to enclose ranges. Translations specified in that format
5697 sometimes work as expected, since the brackets are often transliterated
5698 to themselves. However, they should be avoided because they sometimes
5699 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5702 Many historically common and even accepted uses of ranges are not
5703 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5704 range will not do what most would expect because @samp{A} through @samp{Z}
5705 are not contiguous as they are in @acronym{ASCII}.
5706 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5707 the best way to work around this is to use character classes (see below).
5708 Otherwise, it is most portable (and most ugly) to enumerate the members
5711 @item Repeated characters
5712 @cindex repeated characters
5714 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5715 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5716 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5717 to as many copies of @var{c} as are needed to make @var{set2} as long as
5718 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5719 octal, otherwise in decimal.
5721 @item Character classes
5722 @cindex character classes
5724 The notation @samp{[:@var{class}:]} expands to all of the characters in
5725 the (predefined) class @var{class}. The characters expand in no
5726 particular order, except for the @code{upper} and @code{lower} classes,
5727 which expand in ascending order. When the @option{--delete} (@option{-d})
5728 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5729 character class can be used in @var{set2}. Otherwise, only the
5730 character classes @code{lower} and @code{upper} are accepted in
5731 @var{set2}, and then only if the corresponding character class
5732 (@code{upper} and @code{lower}, respectively) is specified in the same
5733 relative position in @var{set1}. Doing this specifies case conversion.
5734 The class names are given below; an error results when an invalid class
5746 Horizontal whitespace.
5755 Printable characters, not including space.
5761 Printable characters, including space.
5764 Punctuation characters.
5767 Horizontal or vertical whitespace.
5776 @item Equivalence classes
5777 @cindex equivalence classes
5779 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5780 equivalent to @var{c}, in no particular order. Equivalence classes are
5781 a relatively recent invention intended to support non-English alphabets.
5782 But there seems to be no standard way to define them or determine their
5783 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5784 each character's equivalence class consists only of that character,
5785 which is of no particular use.
5791 @subsection Translating
5793 @cindex translating characters
5795 @command{tr} performs translation when @var{set1} and @var{set2} are
5796 both given and the @option{--delete} (@option{-d}) option is not given.
5797 @command{tr} translates each character of its input that is in @var{set1}
5798 to the corresponding character in @var{set2}. Characters not in
5799 @var{set1} are passed through unchanged. When a character appears more
5800 than once in @var{set1} and the corresponding characters in @var{set2}
5801 are not all the same, only the final one is used. For example, these
5802 two commands are equivalent:
5809 A common use of @command{tr} is to convert lowercase characters to
5810 uppercase. This can be done in many ways. Here are three of them:
5813 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5815 tr '[:lower:]' '[:upper:]'
5819 But note that using ranges like @code{a-z} above is not portable.
5821 When @command{tr} is performing translation, @var{set1} and @var{set2}
5822 typically have the same length. If @var{set1} is shorter than
5823 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5825 On the other hand, making @var{set1} longer than @var{set2} is not
5826 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5827 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5828 the last character of @var{set2} as many times as necessary. System V
5829 @command{tr} truncates @var{set1} to the length of @var{set2}.
5831 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5832 When the @option{--truncate-set1} (@option{-t}) option is given,
5833 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5834 instead. This option is ignored for operations other than translation.
5836 Acting like System V @command{tr} in this case breaks the relatively common
5840 tr -cs A-Za-z0-9 '\012'
5844 because it converts only zero bytes (the first element in the
5845 complement of @var{set1}), rather than all non-alphanumerics, to
5849 By the way, the above idiom is not portable because it uses ranges, and
5850 it assumes that the octal code for newline is 012.
5851 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5854 tr -cs '[:alnum:]' '[\n*]'
5859 @subsection Squeezing repeats and deleting
5861 @cindex squeezing repeat characters
5862 @cindex deleting characters
5864 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5865 removes any input characters that are in @var{set1}.
5867 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5868 @command{tr} replaces each input sequence of a repeated character that
5869 is in @var{set1} with a single occurrence of that character.
5871 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5872 first performs any deletions using @var{set1}, then squeezes repeats
5873 from any remaining characters using @var{set2}.
5875 The @option{--squeeze-repeats} option may also be used when translating,
5876 in which case @command{tr} first performs translation, then squeezes
5877 repeats from any remaining characters using @var{set2}.
5879 Here are some examples to illustrate various combinations of options:
5884 Remove all zero bytes:
5891 Put all words on lines by themselves. This converts all
5892 non-alphanumeric characters to newlines, then squeezes each string
5893 of repeated newlines into a single newline:
5896 tr -cs '[:alnum:]' '[\n*]'
5900 Convert each sequence of repeated newlines to a single newline:
5907 Find doubled occurrences of words in a document.
5908 @c Separate the following two "the"s, so typo checkers don't complain.
5909 For example, people often write ``the @w{}the'' with the repeated words
5910 separated by a newline. The Bourne shell script below works first
5911 by converting each sequence of punctuation and blank characters to a
5912 single newline. That puts each ``word'' on a line by itself.
5913 Next it maps all uppercase characters to lower case, and finally it
5914 runs @command{uniq} with the @option{-d} option to print out only the words
5920 | tr -s '[:punct:][:blank:]' '[\n*]' \
5921 | tr '[:upper:]' '[:lower:]' \
5926 Deleting a small set of characters is usually straightforward. For example,
5927 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5933 However, when @samp{-} is one of those characters, it can be tricky because
5934 @samp{-} has special meanings. Performing the same task as above but also
5935 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5936 that would fail because @command{tr} would try to interpret @option{-a} as
5937 a command-line option. Alternatively, we could try putting the hyphen
5938 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5939 it would make @command{tr} interpret @code{a-x} as the range of characters
5940 @samp{a}@dots{}@samp{x} rather than the three.
5941 One way to solve the problem is to put the hyphen at the end of the list
5948 Or you can use @samp{--} to terminate option processing:
5954 More generally, use the character class notation @code{[=c=]}
5955 with @samp{-} (or any other character) in place of the @samp{c}:
5961 Note how single quotes are used in the above example to protect the
5962 square brackets from interpretation by a shell.
5967 @node expand invocation
5968 @section @command{expand}: Convert tabs to spaces
5971 @cindex tabs to spaces, converting
5972 @cindex converting tabs to spaces
5974 @command{expand} writes the contents of each given @var{file}, or standard
5975 input if none are given or for a @var{file} of @samp{-}, to standard
5976 output, with tab characters converted to the appropriate number of
5980 expand [@var{option}]@dots{} [@var{file}]@dots{}
5983 By default, @command{expand} converts all tabs to spaces. It preserves
5984 backspace characters in the output; they decrement the column count for
5985 tab calculations. The default action is equivalent to @option{-t 8} (set
5986 tabs every 8 columns).
5988 The program accepts the following options. Also see @ref{Common options}.
5992 @item -t @var{tab1}[,@var{tab2}]@dots{}
5993 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5996 @cindex tab stops, setting
5997 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5998 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5999 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6000 last tab stop given with single spaces. Tab stops can be separated by
6001 blanks as well as by commas.
6003 For compatibility, GNU @command{expand} also accepts the obsolete
6004 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6005 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6011 @cindex initial tabs, converting
6012 Only convert initial tabs (those that precede all non-space or non-tab
6013 characters) on each line to spaces.
6020 @node unexpand invocation
6021 @section @command{unexpand}: Convert spaces to tabs
6025 @command{unexpand} writes the contents of each given @var{file}, or
6026 standard input if none are given or for a @var{file} of @samp{-}, to
6027 standard output, converting blanks at the beginning of each line into
6028 as many tab characters as needed. In the default @acronym{POSIX}
6029 locale, a @dfn{blank} is a space or a tab; other locales may specify
6030 additional blank characters. Synopsis:
6033 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6036 By default, @command{unexpand} converts only initial blanks (those
6037 that precede all non-blank characters) on each line. It
6038 preserves backspace characters in the output; they decrement the column
6039 count for tab calculations. By default, tabs are set at every 8th
6042 The program accepts the following options. Also see @ref{Common options}.
6046 @item -t @var{tab1}[,@var{tab2}]@dots{}
6047 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6050 If only one tab stop is given, set the tabs @var{tab1} columns apart
6051 instead of the default 8. Otherwise, set the tabs at columns
6052 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6053 beyond the tab stops given unchanged. Tab stops can be separated by
6054 blanks as well as by commas. This option implies the @option{-a} option.
6056 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6057 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6058 separated by commas. (Unlike @option{-t}, this obsolete option does
6059 not imply @option{-a}.) New scripts should use @option{--first-only -t
6060 @var{tab1}[,@var{tab2}]@dots{}} instead.
6066 Also convert all sequences of two or more blanks just before a tab stop,
6067 even if they occur after non-blank characters in a line.
6074 @node Directory listing
6075 @chapter Directory listing
6077 This chapter describes the @command{ls} command and its variants @command{dir}
6078 and @command{vdir}, which list information about files.
6081 * ls invocation:: List directory contents.
6082 * dir invocation:: Briefly ls.
6083 * vdir invocation:: Verbosely ls.
6084 * dircolors invocation:: Color setup for ls, etc.
6089 @section @command{ls}: List directory contents
6092 @cindex directory listing
6094 The @command{ls} program lists information about files (of any type,
6095 including directories). Options and file arguments can be intermixed
6096 arbitrarily, as usual.
6098 For non-option command-line arguments that are directories, by default
6099 @command{ls} lists the contents of directories, not recursively, and
6100 omitting files with names beginning with @samp{.}. For other non-option
6101 arguments, by default @command{ls} lists just the file name. If no
6102 non-option argument is specified, @command{ls} operates on the current
6103 directory, acting as if it had been invoked with a single argument of @samp{.}.
6106 By default, the output is sorted alphabetically, according to the locale
6107 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6108 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6109 produce output that is sorted differently than you're accustomed to.
6110 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6111 If standard output is
6112 a terminal, the output is in columns (sorted vertically) and control
6113 characters are output as question marks; otherwise, the output is listed
6114 one per line and control characters are output as-is.
6116 Because @command{ls} is such a fundamental program, it has accumulated many
6117 options over the years. They are described in the subsections below;
6118 within each section, options are listed alphabetically (ignoring case).
6119 The division of options into the subsections is not absolute, since some
6120 options affect more than one aspect of @command{ls}'s operation.
6122 @cindex exit status of @command{ls}
6127 1 minor problems (e.g., failure to access a file or directory not
6128 specified as a command line argument. This happens when listing a
6129 directory in which entries are actively being removed or renamed.)
6130 2 serious trouble (e.g., memory exhausted, invalid option or failure
6131 to access file or directory specified as a command line argument)
6134 Also see @ref{Common options}.
6137 * Which files are listed::
6138 * What information is listed::
6139 * Sorting the output::
6140 * More details about version sort::
6141 * General output formatting::
6142 * Formatting file timestamps::
6143 * Formatting the file names::
6147 @node Which files are listed
6148 @subsection Which files are listed
6150 These options determine which files @command{ls} lists information for.
6151 By default, @command{ls} lists files and the contents of any
6152 directories on the command line, except that in directories it ignores
6153 files whose names start with @samp{.}.
6161 In directories, do not ignore file names that start with @samp{.}.
6166 @opindex --almost-all
6167 In directories, do not ignore all file names that start with @samp{.};
6168 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6169 option overrides this option.
6172 @itemx --ignore-backups
6174 @opindex --ignore-backups
6175 @cindex backup files, ignoring
6176 In directories, ignore files that end with @samp{~}. This option is
6177 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6182 @opindex --directory
6183 List just the names of directories, as with other types of files, rather
6184 than listing their contents.
6185 @c The following sentence is the same as the one for -F.
6186 Do not follow symbolic links listed on the
6187 command line unless the @option{--dereference-command-line} (@option{-H}),
6188 @option{--dereference} (@option{-L}), or
6189 @option{--dereference-command-line-symlink-to-dir} options are specified.
6192 @itemx --dereference-command-line
6194 @opindex --dereference-command-line
6195 @cindex symbolic links, dereferencing
6196 If a command line argument specifies a symbolic link, show information
6197 for the file the link references rather than for the link itself.
6199 @itemx --dereference-command-line-symlink-to-dir
6200 @opindex --dereference-command-line-symlink-to-dir
6201 @cindex symbolic links, dereferencing
6202 Do not dereference symbolic links, with one exception:
6203 if a command line argument specifies a symbolic link that refers to
6204 a directory, show information for that directory rather than for the
6206 This is the default behavior when no other dereferencing-related
6207 option has been specified (@option{--classify} (@option{-F}),
6208 @option{--directory} (@option{-d}),
6210 @option{--dereference} (@option{-L}), or
6211 @option{--dereference-command-line} (@option{-H})).
6213 @item --group-directories-first
6214 @opindex --group-directories-first
6215 Group all the directories before the files and then sort the
6216 directories and the files separately using the selected sort key
6217 (see --sort option).
6218 That is, this option specifies a primary sort key,
6219 and the --sort option specifies a secondary key.
6220 However, any use of @option{--sort=none}
6221 (@option{-U}) disables this option altogether.
6223 @item --hide=PATTERN
6224 @opindex --hide=@var{pattern}
6225 In directories, ignore files whose names match the shell pattern
6226 @var{pattern}, unless the @option{--all} (@option{-a}) or
6227 @option{--almost-all} (@option{-A}) is also given. This
6228 option acts like @option{--ignore=@var{pattern}} except that it has no
6229 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6230 (@option{-A}) is also given.
6232 This option can be useful in shell aliases. For example, if
6233 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6234 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6235 lists the file @file{README~} even though @samp{ly -A} would not.
6237 @item -I @var{pattern}
6238 @itemx --ignore=@var{pattern}
6240 @opindex --ignore=@var{pattern}
6241 In directories, ignore files whose names match the shell pattern
6242 (not regular expression) @var{pattern}. As
6243 in the shell, an initial @samp{.} in a file name does not match a
6244 wildcard at the start of @var{pattern}. Sometimes it is useful
6245 to give this option several times. For example,
6248 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6251 The first option ignores names of length 3 or more that start with @samp{.},
6252 the second ignores all two-character names that start with @samp{.}
6253 except @samp{..}, and the third ignores names that start with @samp{#}.
6256 @itemx --dereference
6258 @opindex --dereference
6259 @cindex symbolic links, dereferencing
6260 When showing file information for a symbolic link, show information
6261 for the file the link references rather than the link itself.
6262 However, even with this option, @command{ls} still prints the name
6263 of the link itself, not the name of the file that the link points to.
6268 @opindex --recursive
6269 @cindex recursive directory listing
6270 @cindex directory listing, recursive
6271 List the contents of all directories recursively.
6276 @node What information is listed
6277 @subsection What information is listed
6279 These options affect the information that @command{ls} displays. By
6280 default, only file names are shown.
6286 @cindex hurd, author, printing
6287 List each file's author when producing long format directory listings.
6288 In GNU/Hurd, file authors can differ from their owners, but in other
6289 operating systems the two are the same.
6295 @cindex dired Emacs mode support
6296 With the long listing (@option{-l}) format, print an additional line after
6300 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6304 The @var{begn} and @var{endn} are unsigned integers that record the
6305 byte position of the beginning and end of each file name in the output.
6306 This makes it easy for Emacs to find the names, even when they contain
6307 unusual characters such as space or newline, without fancy searching.
6309 If directories are being listed recursively (@option{-R}), output a similar
6310 line with offsets for each subdirectory name:
6313 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6316 Finally, output a line of the form:
6319 //DIRED-OPTIONS// --quoting-style=@var{word}
6323 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6325 Here is an actual example:
6328 $ mkdir -p a/sub/deeper a/sub2
6330 $ touch a/sub/deeper/file
6331 $ ls -gloRF --dired a
6334 -rw-r--r-- 1 0 Jun 10 12:27 f1
6335 -rw-r--r-- 1 0 Jun 10 12:27 f2
6336 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6337 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6341 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6345 -rw-r--r-- 1 0 Jun 10 12:27 file
6349 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6350 //SUBDIRED// 2 3 167 172 228 240 290 296
6351 //DIRED-OPTIONS// --quoting-style=literal
6354 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6355 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6357 The offsets on the @samp{//SUBDIRED//} line delimit the following
6358 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6360 Here is an example of how to extract the fifth entry name, @samp{deeper},
6361 corresponding to the pair of offsets, 222 and 228:
6364 $ ls -gloRF --dired a > out
6365 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6369 Note that although the listing above includes a trailing slash
6370 for the @samp{deeper} entry, the offsets select the name without
6371 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6372 along with an option like @option{--escape} (aka @option{-b}) and operate
6373 on a file whose name contains special characters, notice that the backslash
6378 $ ls -blog --dired 'a b'
6379 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6381 //DIRED-OPTIONS// --quoting-style=escape
6384 If you use a quoting style that adds quote marks
6385 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6386 So beware that the user may select the quoting style via the environment
6387 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6388 should either specify an explicit @option{--quoting-style=literal} option
6389 (aka @option{-N} or @option{--literal}) on the command line, or else be
6390 prepared to parse the escaped names.
6393 @opindex --full-time
6394 Produce long format directory listings, and list times in full. It is
6395 equivalent to using @option{--format=long} with
6396 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6400 Produce long format directory listings, but don't display owner information.
6406 Inhibit display of group information in a long format directory listing.
6407 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6408 provide this option for compatibility.)
6416 @cindex inode number, printing
6417 Print the inode number (also called the file serial number and index
6418 number) of each file to the left of the file name. (This number
6419 uniquely identifies each file within a particular file system.)
6422 @itemx --format=long
6423 @itemx --format=verbose
6426 @opindex long ls @r{format}
6427 @opindex verbose ls @r{format}
6428 In addition to the name of each file, print the file type, file mode bits,
6429 number of hard links, owner name, group name, size, and
6430 timestamp (@pxref{Formatting file timestamps}), normally
6431 the modification time. Print question marks for information that
6432 cannot be determined.
6434 Normally the size is printed as a byte count without punctuation, but
6435 this can be overridden (@pxref{Block size}). For example, @option{-h}
6436 prints an abbreviated, human-readable count, and
6437 @samp{--block-size="'1"} prints a byte count with the thousands
6438 separator of the current locale.
6440 For each directory that is listed, preface the files with a line
6441 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6442 for all files in that directory. The block size currently defaults to 1024
6443 bytes, but this can be overridden (@pxref{Block size}).
6444 The @var{blocks} computed counts each hard link separately;
6445 this is arguably a deficiency.
6447 The file type is one of the following characters:
6449 @c The commented-out entries are ones we're not sure about.
6457 character special file
6459 high performance (``contiguous data'') file
6463 door (Solaris 2.5 and up)
6465 @c semaphore, if this is a distinct file type
6469 @c multiplexed file (7th edition Unix; obsolete)
6471 off-line (``migrated'') file (Cray DMF)
6473 network special file (HP-UX)
6477 port (Solaris 10 and up)
6479 @c message queue, if this is a distinct file type
6483 @c shared memory object, if this is a distinct file type
6485 @c typed memory object, if this is a distinct file type
6487 @c whiteout (4.4BSD; not implemented)
6489 some other file type
6492 @cindex permissions, output by @command{ls}
6493 The file mode bits listed are similar to symbolic mode specifications
6494 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6495 third character of each set of permissions as follows:
6499 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6503 If the set-user-ID or set-group-ID bit is set but the corresponding
6504 executable bit is not set.
6507 If the restricted deletion flag or sticky bit, and the
6508 other-executable bit, are both set. The restricted deletion flag is
6509 another name for the sticky bit. @xref{Mode Structure}.
6512 If the restricted deletion flag or sticky bit is set but the
6513 other-executable bit is not set.
6516 If the executable bit is set and none of the above apply.
6522 Following the file mode bits is a single character that specifies
6523 whether an alternate access method such as an access control list
6524 applies to the file. When the character following the file mode bits is a
6525 space, there is no alternate access method. When it is a printing
6526 character, then there is such a method.
6528 GNU @command{ls} uses a @samp{.} character to indicate a file
6529 with an SELinux security context, but no other alternate access method.
6531 A file with any other combination of alternate access methods
6532 is marked with a @samp{+} character.
6535 @itemx --numeric-uid-gid
6537 @opindex --numeric-uid-gid
6538 @cindex numeric uid and gid
6539 @cindex numeric user and group IDs
6540 Produce long format directory listings, but
6541 display numeric user and group IDs instead of the owner and group names.
6545 Produce long format directory listings, but don't display group information.
6546 It is equivalent to using @option{--format=long} with @option{--no-group} .
6552 @cindex disk allocation
6553 @cindex size of files, reporting
6554 Print the disk allocation of each file to the left of the file name.
6555 This is the amount of disk space used by the file, which is usually a
6556 bit more than the file's size, but it can be less if the file has holes.
6558 Normally the disk allocation is printed in units of
6559 1024 bytes, but this can be overridden (@pxref{Block size}).
6561 @cindex NFS mounts from BSD to HP-UX
6562 For files that are NFS-mounted from an HP-UX system to a BSD system,
6563 this option reports sizes that are half the correct values. On HP-UX
6564 systems, it reports sizes that are twice the correct values for files
6565 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6566 it also affects the HP-UX @command{ls} program.
6575 @cindex security context
6576 Display the SELinux security context or @samp{?} if none is found.
6577 When used with the @option{-l} option, print the security context
6578 to the left of the size column.
6583 @node Sorting the output
6584 @subsection Sorting the output
6586 @cindex sorting @command{ls} output
6587 These options change the order in which @command{ls} sorts the information
6588 it outputs. By default, sorting is done by character code
6589 (e.g., @acronym{ASCII} order).
6595 @itemx --time=status
6598 @opindex ctime@r{, printing or sorting by}
6599 @opindex status time@r{, printing or sorting by}
6600 @opindex use time@r{, printing or sorting files by}
6601 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6602 print the status change time (the @samp{ctime} in the inode) instead of
6603 the modification time.
6604 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6605 or when not using a long listing format,
6606 sort according to the status change time.
6610 @cindex unsorted directory listing
6611 @cindex directory order, listing by
6612 Primarily, like @option{-U}---do not sort; list the files in whatever
6613 order they are stored in the directory. But also enable @option{-a} (list
6614 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6615 were specified before the @option{-f}).
6621 @cindex reverse sorting
6622 Reverse whatever the sorting method is---e.g., list files in reverse
6623 alphabetical order, youngest first, smallest first, or whatever.
6629 @opindex size of files@r{, sorting files by}
6630 Sort by file size, largest first.
6636 @opindex modification time@r{, sorting files by}
6637 Sort by modification time (the @samp{mtime} in the inode), newest first.
6641 @itemx --time=access
6645 @opindex use time@r{, printing or sorting files by}
6646 @opindex atime@r{, printing or sorting files by}
6647 @opindex access time@r{, printing or sorting files by}
6648 If the long listing format (e.g., @option{--format=long}) is being used,
6649 print the last access time (the @samp{atime} in the inode).
6650 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6651 or when not using a long listing format, sort according to the access time.
6657 @opindex none@r{, sorting option for @command{ls}}
6658 Do not sort; list the files in whatever order they are
6659 stored in the directory. (Do not do any of the other unrelated things
6660 that @option{-f} does.) This is especially useful when listing very large
6661 directories, since not doing any sorting can be noticeably faster.
6664 @itemx --sort=version
6667 @opindex version@r{, sorting option for @command{ls}}
6668 Sort by version name and number, lowest first. It behaves like a default
6669 sort, except that each sequence of decimal digits is treated numerically
6670 as an index/version number. (@xref{More details about version sort}.)
6673 @itemx --sort=extension
6676 @opindex extension@r{, sorting files by}
6677 Sort directory contents alphabetically by file extension (characters
6678 after the last @samp{.}); files with no extension are sorted first.
6683 @node More details about version sort
6684 @subsection More details about version sort
6686 The version sort takes into account the fact that file names frequently include
6687 indices or version numbers. Standard sorting functions usually do not produce
6688 the ordering that people expect because comparisons are made on a
6689 character-by-character basis. The version
6690 sort addresses this problem, and is especially useful when browsing
6691 directories that contain many files with indices/version numbers in their
6696 foo.zml-1.gz foo.zml-1.gz
6697 foo.zml-100.gz foo.zml-2.gz
6698 foo.zml-12.gz foo.zml-6.gz
6699 foo.zml-13.gz foo.zml-12.gz
6700 foo.zml-2.gz foo.zml-13.gz
6701 foo.zml-25.gz foo.zml-25.gz
6702 foo.zml-6.gz foo.zml-100.gz
6705 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6706 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6707 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6708 @var{ver1} < @var{ver2} implies that the name composed of
6709 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6710 ``@var{prefix} @var{ver2} @var{suffix}''.
6712 Note also that leading zeros of numeric parts are ignored:
6716 abc-1.007.tgz abc-1.01a.tgz
6717 abc-1.012b.tgz abc-1.007.tgz
6718 abc-1.01a.tgz abc-1.012b.tgz
6721 This functionality is implemented using gnulib's @code{filevercmp} function.
6722 One result of that implementation decision is that @samp{ls -v}
6723 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6724 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6727 @node General output formatting
6728 @subsection General output formatting
6730 These options affect the appearance of the overall output.
6735 @itemx --format=single-column
6738 @opindex single-column @r{output of files}
6739 List one file per line. This is the default for @command{ls} when standard
6740 output is not a terminal.
6743 @itemx --format=vertical
6746 @opindex vertical @r{sorted files in columns}
6747 List files in columns, sorted vertically. This is the default for
6748 @command{ls} if standard output is a terminal. It is always the default
6749 for the @command{dir} program.
6750 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6751 possible in the fewest lines.
6753 @item --color [=@var{when}]
6755 @cindex color, distinguishing file types with
6756 Specify whether to use color for distinguishing file types. @var{when}
6757 may be omitted, or one of:
6760 @vindex none @r{color option}
6761 - Do not use color at all. This is the default.
6763 @vindex auto @r{color option}
6764 @cindex terminal, using color iff
6765 - Only use color if standard output is a terminal.
6767 @vindex always @r{color option}
6770 Specifying @option{--color} and no @var{when} is equivalent to
6771 @option{--color=always}.
6772 Piping a colorized listing through a pager like @command{more} or
6773 @command{less} usually produces unreadable results. However, using
6774 @code{more -f} does seem to work.
6778 @itemx --indicator-style=classify
6781 @opindex --indicator-style
6782 @cindex file type and executables, marking
6783 @cindex executables and file type, marking
6784 Append a character to each file name indicating the file type. Also,
6785 for regular files that are executable, append @samp{*}. The file type
6786 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6787 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6788 and nothing for regular files.
6789 @c The following sentence is the same as the one for -d.
6790 Do not follow symbolic links listed on the
6791 command line unless the @option{--dereference-command-line} (@option{-H}),
6792 @option{--dereference} (@option{-L}), or
6793 @option{--dereference-command-line-symlink-to-dir} options are specified.
6796 @itemx --indicator-style=file-type
6797 @opindex --file-type
6798 @opindex --indicator-style
6799 @cindex file type, marking
6800 Append a character to each file name indicating the file type. This is
6801 like @option{-F}, except that executables are not marked.
6803 @item --indicator-style=@var{word}
6804 @opindex --indicator-style
6805 Append a character indicator with style @var{word} to entry names,
6810 Do not append any character indicator; this is the default.
6812 Append @samp{/} for directories. This is the same as the @option{-p}
6815 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6816 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6817 the same as the @option{--file-type} option.
6819 Append @samp{*} for executable regular files, otherwise behave as for
6820 @samp{file-type}. This is the same as the @option{-F} or
6821 @option{--classify} option.
6826 Print file sizes in 1024-byte blocks, overriding the default block
6827 size (@pxref{Block size}).
6828 This option is equivalent to @option{--block-size=1K}.
6831 @itemx --format=commas
6834 @opindex commas@r{, outputting between files}
6835 List files horizontally, with as many as will fit on each line,
6836 separated by @samp{, } (a comma and a space).
6839 @itemx --indicator-style=slash
6841 @opindex --indicator-style
6842 @cindex file type, marking
6843 Append a @samp{/} to directory names.
6846 @itemx --format=across
6847 @itemx --format=horizontal
6850 @opindex across@r{, listing files}
6851 @opindex horizontal@r{, listing files}
6852 List the files in columns, sorted horizontally.
6855 @itemx --tabsize=@var{cols}
6858 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6859 @command{ls} uses tabs where possible in the output, for efficiency. If
6860 @var{cols} is zero, do not use tabs at all.
6862 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6863 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6864 do not properly align columns to the right of a TAB following a
6865 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6866 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6867 @command{ls} to align using spaces, not tabs.
6870 @itemx --width=@var{cols}
6874 Assume the screen is @var{cols} columns wide. The default is taken
6875 from the terminal settings if possible; otherwise the environment
6876 variable @env{COLUMNS} is used if it is set; otherwise the default
6882 @node Formatting file timestamps
6883 @subsection Formatting file timestamps
6885 By default, file timestamps are listed in abbreviated form. Most
6886 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6887 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6888 for non-recent timestamps, and a date-without-year and time like
6889 @samp{Mar 30 23:45} for recent timestamps.
6891 A timestamp is considered to be @dfn{recent} if it is less than six
6892 months old, and is not dated in the future. If a timestamp dated
6893 today is not listed in recent form, the timestamp is in the future,
6894 which means you probably have clock skew problems which may break
6895 programs like @command{make} that rely on file timestamps.
6898 Time stamps are listed according to the time zone rules specified by
6899 the @env{TZ} environment variable, or by the system default rules if
6900 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6901 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6903 The following option changes how file timestamps are printed.
6906 @item --time-style=@var{style}
6907 @opindex --time-style
6909 List timestamps in style @var{style}. The @var{style} should
6910 be one of the following:
6915 List timestamps using @var{format}, where @var{format} is interpreted
6916 like the format argument of @command{date} (@pxref{date invocation}).
6917 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6918 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6919 with @command{date}, @var{format}'s interpretation is affected by the
6920 @env{LC_TIME} locale category.
6922 If @var{format} contains two format strings separated by a newline,
6923 the former is used for non-recent files and the latter for recent
6924 files; if you want output columns to line up, you may need to insert
6925 spaces in one of the two formats.
6928 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6929 format with nanosecond precision, e.g., @samp{2002-03-30
6930 23:45:56.477817180 -0700}. This style is equivalent to
6931 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6933 This is useful because the time output includes all the information that
6934 is available from the operating system. For example, this can help
6935 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6936 uses the full timestamp to determine whether a file is out of date.
6939 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6940 @samp{2002-03-30 23:45}. These timestamps are shorter than
6941 @samp{full-iso} timestamps, and are usually good enough for everyday
6942 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6945 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6946 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6947 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6948 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6949 nearly the same information in a smaller space and their brevity helps
6950 @command{ls} output fit within traditional 80-column output lines.
6951 The following two @command{ls} invocations are equivalent:
6956 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6957 ls -l --time-style="iso"
6962 List timestamps in a locale-dependent form. For example, a Finnish
6963 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6964 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6965 timestamps typically consume more space than @samp{iso} timestamps and
6966 are harder for programs to parse because locale conventions vary so
6967 widely, but they are easier for many people to read.
6969 The @env{LC_TIME} locale category specifies the timestamp format. The
6970 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6971 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6972 @command{ls} invocations are equivalent:
6977 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6978 ls -l --time-style="locale"
6981 Other locales behave differently. For example, in a German locale,
6982 @option{--time-style="locale"} might be equivalent to
6983 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6984 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6985 @samp{30. M@"ar 23:45}.
6987 @item posix-@var{style}
6989 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6990 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6991 example, the @samp{posix-long-iso} style lists
6992 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6993 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6998 You can specify the default value of the @option{--time-style} option
6999 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7000 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7001 later use the @option{--dired} option and therefore can parse any date
7002 format, but if you are using Emacs 21.1 or 21.2 and specify a
7003 non-@acronym{POSIX} locale you may need to set
7004 @samp{TIME_STYLE="posix-long-iso"}.
7006 To avoid certain denial-of-service attacks, timestamps that would be
7007 longer than 1000 bytes may be treated as errors.
7010 @node Formatting the file names
7011 @subsection Formatting the file names
7013 These options change how file names themselves are printed.
7019 @itemx --quoting-style=escape
7022 @opindex --quoting-style
7023 @cindex backslash sequences for file names
7024 Quote nongraphic characters in file names using alphabetic and octal
7025 backslash sequences like those used in C.
7029 @itemx --quoting-style=literal
7032 @opindex --quoting-style
7033 Do not quote file names. However, with @command{ls} nongraphic
7034 characters are still printed as question marks if the output is a
7035 terminal and you do not specify the @option{--show-control-chars}
7039 @itemx --hide-control-chars
7041 @opindex --hide-control-chars
7042 Print question marks instead of nongraphic characters in file names.
7043 This is the default if the output is a terminal and the program is
7048 @itemx --quoting-style=c
7050 @opindex --quote-name
7051 @opindex --quoting-style
7052 Enclose file names in double quotes and quote nongraphic characters as
7055 @item --quoting-style=@var{word}
7056 @opindex --quoting-style
7057 @cindex quoting style
7058 Use style @var{word} to quote file names and other strings that may
7059 contain arbitrary characters. The @var{word} should
7060 be one of the following:
7064 Output strings as-is; this is the same as the @option{-N} or
7065 @option{--literal} option.
7067 Quote strings for the shell if they contain shell metacharacters or would
7068 cause ambiguous output.
7069 The quoting is suitable for @acronym{POSIX}-compatible shells like
7070 @command{bash}, but it does not always work for incompatible shells
7073 Quote strings for the shell, even if they would normally not require quoting.
7075 Quote strings as for C character string literals, including the
7076 surrounding double-quote characters; this is the same as the
7077 @option{-Q} or @option{--quote-name} option.
7079 Quote strings as for C character string literals, except omit the
7080 surrounding double-quote
7081 characters; this is the same as the @option{-b} or @option{--escape} option.
7083 Quote strings as for C character string literals, except use
7084 surrounding quotation marks appropriate for the
7087 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7088 Quote strings as for C character string literals, except use
7089 surrounding quotation marks appropriate for the locale, and quote
7090 @t{`like this'} instead of @t{"like
7091 this"} in the default C locale. This looks nicer on many displays.
7094 You can specify the default value of the @option{--quoting-style} option
7095 with the environment variable @env{QUOTING_STYLE}. If that environment
7096 variable is not set, the default value is @samp{literal}, but this
7097 default may change to @samp{shell} in a future version of this package.
7099 @item --show-control-chars
7100 @opindex --show-control-chars
7101 Print nongraphic characters as-is in file names.
7102 This is the default unless the output is a terminal and the program is
7108 @node dir invocation
7109 @section @command{dir}: Briefly list directory contents
7112 @cindex directory listing, brief
7114 @command{dir} is equivalent to @code{ls -C
7115 -b}; that is, by default files are listed in columns, sorted vertically,
7116 and special characters are represented by backslash escape sequences.
7118 @xref{ls invocation, @command{ls}}.
7121 @node vdir invocation
7122 @section @command{vdir}: Verbosely list directory contents
7125 @cindex directory listing, verbose
7127 @command{vdir} is equivalent to @code{ls -l
7128 -b}; that is, by default files are listed in long format and special
7129 characters are represented by backslash escape sequences.
7131 @node dircolors invocation
7132 @section @command{dircolors}: Color setup for @command{ls}
7136 @cindex setup for color
7138 @command{dircolors} outputs a sequence of shell commands to set up the
7139 terminal for color output from @command{ls} (and @command{dir}, etc.).
7143 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7146 If @var{file} is specified, @command{dircolors} reads it to determine which
7147 colors to use for which file types and extensions. Otherwise, a
7148 precompiled database is used. For details on the format of these files,
7149 run @samp{dircolors --print-database}.
7151 To make @command{dircolors} read a @file{~/.dircolors} file if it
7152 exists, you can put the following lines in your @file{~/.bashrc} (or
7153 adapt them to your favorite shell):
7157 test -r $d && eval "$(dircolors $d)"
7161 @vindex SHELL @r{environment variable, and color}
7162 The output is a shell command to set the @env{LS_COLORS} environment
7163 variable. You can specify the shell syntax to use on the command line,
7164 or @command{dircolors} will guess it from the value of the @env{SHELL}
7165 environment variable.
7167 The program accepts the following options. Also see @ref{Common options}.
7172 @itemx --bourne-shell
7175 @opindex --bourne-shell
7176 @cindex Bourne shell syntax for color setup
7177 @cindex @command{sh} syntax for color setup
7178 Output Bourne shell commands. This is the default if the @env{SHELL}
7179 environment variable is set and does not end with @samp{csh} or
7188 @cindex C shell syntax for color setup
7189 @cindex @command{csh} syntax for color setup
7190 Output C shell commands. This is the default if @code{SHELL} ends with
7191 @command{csh} or @command{tcsh}.
7194 @itemx --print-database
7196 @opindex --print-database
7197 @cindex color database, printing
7198 @cindex database for color setup, printing
7199 @cindex printing color database
7200 Print the (compiled-in) default color configuration database. This
7201 output is itself a valid configuration file, and is fairly descriptive
7202 of the possibilities.
7209 @node Basic operations
7210 @chapter Basic operations
7212 @cindex manipulating files
7214 This chapter describes the commands for basic file manipulation:
7215 copying, moving (renaming), and deleting (removing).
7218 * cp invocation:: Copy files.
7219 * dd invocation:: Convert and copy a file.
7220 * install invocation:: Copy files and set attributes.
7221 * mv invocation:: Move (rename) files.
7222 * rm invocation:: Remove files or directories.
7223 * shred invocation:: Remove files more securely.
7228 @section @command{cp}: Copy files and directories
7231 @cindex copying files and directories
7232 @cindex files, copying
7233 @cindex directories, copying
7235 @command{cp} copies files (or, optionally, directories). The copy is
7236 completely independent of the original. You can either copy one file to
7237 another, or copy arbitrarily many files to a destination directory.
7241 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7242 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7243 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7248 If two file names are given, @command{cp} copies the first file to the
7252 If the @option{--target-directory} (@option{-t}) option is given, or
7253 failing that if the last file is a directory and the
7254 @option{--no-target-directory} (@option{-T}) option is not given,
7255 @command{cp} copies each @var{source} file to the specified directory,
7256 using the @var{source}s' names.
7259 Generally, files are written just as they are read. For exceptions,
7260 see the @option{--sparse} option below.
7262 By default, @command{cp} does not copy directories. However, the
7263 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7264 copy recursively by descending into source directories and copying files
7265 to corresponding destination directories.
7267 When copying from a symbolic link, @command{cp} normally follows the
7268 link only when not copying
7269 recursively. This default can be overridden with the
7270 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7271 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7272 @option{-H} options. If more than one of these options is specified,
7273 the last one silently overrides the others.
7275 When copying to a symbolic link, @command{cp} follows the
7276 link only when it refers to an existing regular file.
7277 However, when copying to a dangling symbolic link, @command{cp}
7278 refuses by default, and fails with a diagnostic, since the operation
7279 is inherently dangerous. This behavior is contrary to historical
7280 practice and to @acronym{POSIX}.
7281 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7282 the target of a dangling destination symlink, in spite of the possible risk.
7283 Also, when an option like
7284 @option{--backup} or @option{--link} acts to rename or remove the
7285 destination before copying, @command{cp} renames or removes the
7286 symbolic link rather than the file it points to.
7288 By default, @command{cp} copies the contents of special files only
7289 when not copying recursively. This default can be overridden with the
7290 @option{--copy-contents} option.
7292 @cindex self-backups
7293 @cindex backups, making only
7294 @command{cp} generally refuses to copy a file onto itself, with the
7295 following exception: if @option{--force --backup} is specified with
7296 @var{source} and @var{dest} identical, and referring to a regular file,
7297 @command{cp} will make a backup file, either regular or numbered, as
7298 specified in the usual ways (@pxref{Backup options}). This is useful when
7299 you simply want to make a backup of an existing file before changing it.
7301 The program accepts the following options. Also see @ref{Common options}.
7308 Preserve as much as possible of the structure and attributes of the
7309 original files in the copy (but do not attempt to preserve internal
7310 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7311 directory in a different order).
7312 Try to preserve SELinux security context and extended attributes (xattr),
7313 but ignore any failure to do that and print no corresponding diagnostic.
7314 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7317 @itemx @w{@kbd{--backup}[=@var{method}]}
7320 @vindex VERSION_CONTROL
7321 @cindex backups, making
7322 @xref{Backup options}.
7323 Make a backup of each file that would otherwise be overwritten or removed.
7324 As a special case, @command{cp} makes a backup of @var{source} when the force
7325 and backup options are given and @var{source} and @var{dest} are the same
7326 name for an existing, regular file. One useful application of this
7327 combination of options is this tiny Bourne shell script:
7331 # Usage: backup FILE...
7332 # Create a @sc{gnu}-style backup of each listed FILE.
7334 cp --backup --force -- "$i" "$i"
7338 @item --copy-contents
7339 @cindex directories, copying recursively
7340 @cindex copying directories recursively
7341 @cindex recursively copying directories
7342 @cindex non-directories, copying as special files
7343 If copying recursively, copy the contents of any special files (e.g.,
7344 FIFOs and device files) as if they were regular files. This means
7345 trying to read the data in each source file and writing it to the
7346 destination. It is usually a mistake to use this option, as it
7347 normally has undesirable effects on special files like FIFOs and the
7348 ones typically found in the @file{/dev} directory. In most cases,
7349 @code{cp -R --copy-contents} will hang indefinitely trying to read
7350 from FIFOs and special files like @file{/dev/console}, and it will
7351 fill up your destination disk if you use it to copy @file{/dev/zero}.
7352 This option has no effect unless copying recursively, and it does not
7353 affect the copying of symbolic links.
7357 @cindex symbolic links, copying
7358 @cindex hard links, preserving
7359 Copy symbolic links as symbolic links rather than copying the files that
7360 they point to, and preserve hard links between source files in the copies.
7361 Equivalent to @option{--no-dereference --preserve=links}.
7367 When copying without this option and an existing destination file cannot
7368 be opened for writing, the copy fails. However, with @option{--force}),
7369 when a destination file cannot be opened, @command{cp} then removes it and
7370 tries to open it again. Contrast this behavior with that enabled by
7371 @option{--link} and @option{--symbolic-link}, whereby the destination file
7372 is never opened but rather is removed unconditionally. Also see the
7373 description of @option{--remove-destination}.
7375 This option is independent of the @option{--interactive} or
7376 @option{-i} option: neither cancels the effect of the other.
7378 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7383 If a command line argument specifies a symbolic link, then copy the
7384 file it points to rather than the symbolic link itself. However,
7385 copy (preserving its nature) any symbolic link that is encountered
7386 via recursive traversal.
7389 @itemx --interactive
7391 @opindex --interactive
7392 When copying a file other than a directory, prompt whether to
7393 overwrite an existing destination file. The @option{-i} option overrides
7394 a previous @option{-n} option.
7400 Make hard links instead of copies of non-directories.
7403 @itemx --dereference
7405 @opindex --dereference
7406 Follow symbolic links when copying from them.
7407 With this option, @command{cp} cannot create a symbolic link.
7408 For example, a symlink (to regular file) in the source tree will be copied to
7409 a regular file in the destination tree.
7414 @opindex --no-clobber
7415 Do not overwrite an existing file. The @option{-n} option overrides a previous
7416 @option{-i} option. This option is mutually exclusive with @option{-b} or
7417 @option{--backup} option.
7420 @itemx --no-dereference
7422 @opindex --no-dereference
7423 @cindex symbolic links, copying
7424 Copy symbolic links as symbolic links rather than copying the files that
7425 they point to. This option affects only symbolic links in the source;
7426 symbolic links in the destination are always followed if possible.
7429 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7432 @cindex file information, preserving, extended attributes, xattr
7433 Preserve the specified attributes of the original files.
7434 If specified, the @var{attribute_list} must be a comma-separated list
7435 of one or more of the following strings:
7439 Preserve the file mode bits and access control lists.
7441 Preserve the owner and group. On most modern systems,
7442 only users with appropriate privileges may change the owner of a file,
7444 may preserve the group ownership of a file only if they happen to be
7445 a member of the desired group.
7447 Preserve the times of last access and last modification, when possible.
7448 In general, it is not possible to preserve these attributes
7449 when the affected file is a symbolic link.
7450 However, FreeBSD now provides the @code{lutimes} function, which makes
7451 it possible even for symbolic links. However, this implementation does
7452 not yet take advantage of that.
7453 @c FIXME: once we provide lutimes support, update the above.
7455 Preserve in the destination files
7456 any links between corresponding source files.
7457 Note that with @option{-L} or @option{-H}, this option can convert
7458 symbolic links to hard links. For example,
7460 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7465 Note the inputs: @file{b} is a symlink to regular file @file{a},
7466 yet the files in destination directory, @file{c/}, are hard-linked.
7467 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7468 tells @command{cp} to dereference command line arguments, it sees two files
7469 with the same inode number, and preserves the perceived hard link.
7471 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7473 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7479 Preserve SELinux security context of the file. @command{cp} will fail
7480 if the preserving of SELinux security context is not succesful.
7482 Preserve extended attributes if @command{cp} is built with xattr support,
7483 and xattrs are supported and enabled on your file system.
7484 If SELinux context and/or ACLs are implemented using xattrs,
7485 they are preserved by this option as well.
7487 Preserve all file attributes.
7488 Equivalent to specifying all of the above, but with the difference
7489 that failure to preserve SELinux security context or extended attributes
7490 does not change @command{cp}'s exit status.
7491 @command{cp} does diagnose such failures.
7494 Using @option{--preserve} with no @var{attribute_list} is equivalent
7495 to @option{--preserve=mode,ownership,timestamps}.
7497 In the absence of this option, each destination file is created with the
7498 mode bits of the corresponding source file, minus the bits set in the
7499 umask and minus the set-user-ID and set-group-ID bits.
7500 @xref{File permissions}.
7502 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7503 @cindex file information, preserving
7504 Do not preserve the specified attributes. The @var{attribute_list}
7505 has the same form as for @option{--preserve}.
7509 @cindex parent directories and @command{cp}
7510 Form the name of each destination file by appending to the target
7511 directory a slash and the specified name of the source file. The last
7512 argument given to @command{cp} must be the name of an existing directory.
7513 For example, the command:
7516 cp --parents a/b/c existing_dir
7520 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7521 any missing intermediate directories.
7528 @opindex --recursive
7529 @cindex directories, copying recursively
7530 @cindex copying directories recursively
7531 @cindex recursively copying directories
7532 @cindex non-directories, copying as special files
7533 Copy directories recursively. By default, do not follow symbolic
7534 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7535 @option{--dereference} (@option{-L}), @option{--no-dereference}
7536 (@option{-P}), and @option{-H} options. Special files are copied by
7537 creating a destination file of the same type as the source; see the
7538 @option{--copy-contents} option. It is not portable to use
7539 @option{-r} to copy symbolic links or special files. On some
7540 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7541 @option{-L} and @option{--copy-contents} for historical reasons.
7542 Also, it is not portable to use @option{-R} to copy symbolic links
7543 unless you also specify @option{-P}, as @acronym{POSIX} allows
7544 implementations that dereference symbolic links by default.
7546 @item --remove-destination
7547 @opindex --remove-destination
7548 Remove each existing destination file before attempting to open it
7549 (contrast with @option{-f} above).
7551 @item --sparse=@var{when}
7552 @opindex --sparse=@var{when}
7553 @cindex sparse files, copying
7554 @cindex holes, copying files with
7555 @findex read @r{system call, and holes}
7556 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7557 does not occupy any physical disk blocks; the @samp{read} system call
7558 reads these as zeros. This can both save considerable disk space and
7559 increase speed, since many binary files contain lots of consecutive zero
7560 bytes. By default, @command{cp} detects holes in input source files via a crude
7561 heuristic and makes the corresponding output file sparse as well.
7562 Only regular files may be sparse.
7564 The @var{when} value can be one of the following:
7568 The default behavior: if the input file is sparse, attempt to make
7569 the output file sparse, too. However, if an output file exists but
7570 refers to a non-regular file, then do not attempt to make it sparse.
7573 For each sufficiently long sequence of zero bytes in the input file,
7574 attempt to create a corresponding hole in the output file, even if the
7575 input file does not appear to be sparse.
7576 This is useful when the input file resides on a file system
7577 that does not support sparse files
7578 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7579 but the output file is on a type of file system that does support them.
7580 Holes may be created only in regular files, so if the destination file
7581 is of some other type, @command{cp} does not even try to make it sparse.
7584 Never make the output file sparse.
7585 This is useful in creating a file for use with the @command{mkswap} command,
7586 since such a file must not have any holes.
7589 @optStripTrailingSlashes
7592 @itemx --symbolic-link
7594 @opindex --symbolic-link
7595 @cindex symbolic links, copying with
7596 Make symbolic links instead of copies of non-directories. All source
7597 file names must be absolute (starting with @samp{/}) unless the
7598 destination files are in the current directory. This option merely
7599 results in an error message on systems that do not support symbolic links.
7605 @optNoTargetDirectory
7611 @cindex newer files, copying only
7612 Do not copy a non-directory that has an existing destination with the
7613 same or newer modification time. If time stamps are being preserved,
7614 the comparison is to the source time stamp truncated to the
7615 resolutions of the destination file system and of the system calls
7616 used to update time stamps; this avoids duplicate work if several
7617 @samp{cp -pu} commands are executed with the same source and
7624 Print the name of each file before copying it.
7627 @itemx --one-file-system
7629 @opindex --one-file-system
7630 @cindex file systems, omitting copying to different
7631 Skip subdirectories that are on different file systems from the one that
7632 the copy started on.
7633 However, mount point directories @emph{are} copied.
7641 @section @command{dd}: Convert and copy a file
7644 @cindex converting while copying a file
7646 @command{dd} copies a file (from standard input to standard output, by
7647 default) with a changeable I/O block size, while optionally performing
7648 conversions on it. Synopses:
7651 dd [@var{operand}]@dots{}
7655 The only options are @option{--help} and @option{--version}.
7656 @xref{Common options}. @command{dd} accepts the following operands.
7662 Read from @var{file} instead of standard input.
7666 Write to @var{file} instead of standard output. Unless
7667 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7668 bytes (or the size specified with @samp{seek=}).
7670 @item ibs=@var{bytes}
7672 @cindex block size of input
7673 @cindex input block size
7674 Set the input block size to @var{bytes}.
7675 This makes @command{dd} read @var{bytes} per block.
7676 The default is 512 bytes.
7678 @item obs=@var{bytes}
7680 @cindex block size of output
7681 @cindex output block size
7682 Set the output block size to @var{bytes}.
7683 This makes @command{dd} write @var{bytes} per block.
7684 The default is 512 bytes.
7686 @item bs=@var{bytes}
7689 Set both input and output block sizes to @var{bytes}.
7690 This makes @command{dd} read and write @var{bytes} per block,
7691 overriding any @samp{ibs} and @samp{obs} settings.
7692 In addition, if no data-transforming @option{conv} option is specified,
7693 each input block is copied to the output as a single block,
7694 without aggregating short reads.
7696 @item cbs=@var{bytes}
7698 @cindex block size of conversion
7699 @cindex conversion block size
7700 @cindex fixed-length records, converting to variable-length
7701 @cindex variable-length records, converting to fixed-length
7702 Set the conversion block size to @var{bytes}.
7703 When converting variable-length records to fixed-length ones
7704 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7705 use @var{bytes} as the fixed record length.
7707 @item skip=@var{blocks}
7709 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7711 @item seek=@var{blocks}
7713 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7715 @item count=@var{blocks}
7717 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7718 of everything until the end of the file.
7722 Do not print the overall transfer rate and volume statistics
7723 that normally make up the third status line when @command{dd} exits.
7725 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7727 Convert the file as specified by the @var{conversion} argument(s).
7728 (No spaces around any comma(s).)
7735 @opindex ascii@r{, converting to}
7736 Convert @acronym{EBCDIC} to @acronym{ASCII},
7737 using the conversion table specified by @acronym{POSIX}.
7738 This provides a 1:1 translation for all 256 bytes.
7741 @opindex ebcdic@r{, converting to}
7742 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7743 This is the inverse of the @samp{ascii} conversion.
7746 @opindex alternate ebcdic@r{, converting to}
7747 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7748 using the alternate conversion table specified by @acronym{POSIX}.
7749 This is not a 1:1 translation, but reflects common historical practice
7750 for @samp{~}, @samp{[}, and @samp{]}.
7752 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7756 @opindex block @r{(space-padding)}
7757 For each line in the input, output @samp{cbs} bytes, replacing the
7758 input newline with a space and padding with spaces as necessary.
7762 Replace trailing spaces in each @samp{cbs}-sized input block with a
7765 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7768 @opindex lcase@r{, converting to}
7769 Change uppercase letters to lowercase.
7772 @opindex ucase@r{, converting to}
7773 Change lowercase letters to uppercase.
7775 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7778 @opindex swab @r{(byte-swapping)}
7779 @cindex byte-swapping
7780 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7781 when an odd number of bytes are read---the last byte is simply copied
7782 (since there is nothing to swap it with).
7786 @cindex read errors, ignoring
7787 Continue after read errors.
7791 @cindex creating output file, avoiding
7792 Do not create the output file; the output file must already exist.
7796 @cindex creating output file, requiring
7797 Fail if the output file already exists; @command{dd} must create the
7800 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7804 @cindex truncating output file, avoiding
7805 Do not truncate the output file.
7808 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7809 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7810 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7815 @cindex synchronized data writes, before finishing
7816 Synchronize output data just before finishing. This forces a physical
7817 write of output data.
7821 @cindex synchronized data and metadata writes, before finishing
7822 Synchronize output data and metadata just before finishing. This
7823 forces a physical write of output data and metadata.
7827 @item iflag=@var{flag}[,@var{flag}]@dots{}
7829 Access the input file using the flags specified by the @var{flag}
7830 argument(s). (No spaces around any comma(s).)
7832 @item oflag=@var{flag}[,@var{flag}]@dots{}
7834 Access the output file using the flags specified by the @var{flag}
7835 argument(s). (No spaces around any comma(s).)
7837 Here are the flags. Not every flag is supported on every operating
7844 @cindex appending to the output file
7845 Write in append mode, so that even if some other process is writing to
7846 this file, every @command{dd} write will append to the current
7847 contents of the file. This flag makes sense only for output.
7848 If you combine this flag with the @samp{of=@var{file}} operand,
7849 you should also specify @samp{conv=notrunc} unless you want the
7850 output file to be truncated before being appended to.
7854 @cindex concurrent I/O
7855 Use concurrent I/O mode for data. This mode performs direct I/O
7856 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7857 A file cannot be opened in CIO mode and with a standard open at the
7863 Use direct I/O for data, avoiding the buffer cache.
7864 Note that the kernel may impose restrictions on read or write buffer sizes.
7865 For example, with an ext4 destination file system and a linux-based kernel,
7866 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7867 output buffer size is not a multiple of 512.
7871 @cindex directory I/O
7873 Fail unless the file is a directory. Most operating systems do not
7874 allow I/O to a directory, so this flag has limited utility.
7878 @cindex synchronized data reads
7879 Use synchronized I/O for data. For the output file, this forces a
7880 physical write of output data on each write. For the input file,
7881 this flag can matter when reading from a remote file that has been
7882 written to synchronously by some other process. Metadata (e.g.,
7883 last-access and last-modified time) is not necessarily synchronized.
7887 @cindex synchronized data and metadata I/O
7888 Use synchronized I/O for both data and metadata.
7892 @cindex nonblocking I/O
7893 Use non-blocking I/O.
7898 Do not update the file's access time.
7899 Some older file systems silently ignore this flag, so it is a good
7900 idea to test it on your files before relying on it.
7904 @cindex controlling terminal
7905 Do not assign the file to be a controlling terminal for @command{dd}.
7906 This has no effect when the file is not a terminal.
7907 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7912 @cindex symbolic links, following
7913 Do not follow symbolic links.
7918 Fail if the file has multiple hard links.
7923 Use binary I/O. This option has an effect only on nonstandard
7924 platforms that distinguish binary from text I/O.
7929 Use text I/O. Like @samp{binary}, this option has no effect on
7934 Accumulate full blocks from input. The @code{read} system call
7935 may return early if a full block is not available.
7936 When that happens, continue calling @code{read} to fill the remainder
7938 This flag can be used only with @code{iflag}.
7942 These flags are not supported on all systems, and @samp{dd} rejects
7943 attempts to use them when they are not supported. When reading from
7944 standard input or writing to standard output, the @samp{nofollow} and
7945 @samp{noctty} flags should not be specified, and the other flags
7946 (e.g., @samp{nonblock}) can affect how other processes behave with the
7947 affected file descriptors, even after @command{dd} exits.
7951 @cindex multipliers after numbers
7952 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7953 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7954 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7955 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7957 Use different @command{dd} invocations to use different block sizes for
7958 skipping and I/O@. For example, the following shell commands copy data
7959 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7960 4 KiB label at the start of the disk:
7963 disk=/dev/rdsk/c0t1d0s2
7966 # Copy all but the label from disk to tape.
7967 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7969 # Copy from tape back to disk, but leave the disk label alone.
7970 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7973 Sending an @samp{INFO} signal to a running @command{dd}
7974 process makes it print I/O statistics to standard error
7975 and then resume copying. In the example below,
7976 @command{dd} is run in the background to copy 10 million blocks.
7977 The @command{kill} command makes it output intermediate I/O statistics,
7978 and when @command{dd} completes normally or is killed by the
7979 @code{SIGINT} signal, it outputs the final statistics.
7982 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7983 $ kill -s INFO $pid; wait $pid
7984 3385223+0 records in
7985 3385223+0 records out
7986 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7987 10000000+0 records in
7988 10000000+0 records out
7989 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
7992 @vindex POSIXLY_CORRECT
7993 On systems lacking the @samp{INFO} signal @command{dd} responds to the
7994 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
7995 environment variable is set.
8000 @node install invocation
8001 @section @command{install}: Copy files and set attributes
8004 @cindex copying files and setting attributes
8006 @command{install} copies files while setting their file mode bits and, if
8007 possible, their owner and group. Synopses:
8010 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8011 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8012 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8013 install [@var{option}]@dots{} -d @var{directory}@dots{}
8018 If two file names are given, @command{install} copies the first file to the
8022 If the @option{--target-directory} (@option{-t}) option is given, or
8023 failing that if the last file is a directory and the
8024 @option{--no-target-directory} (@option{-T}) option is not given,
8025 @command{install} copies each @var{source} file to the specified
8026 directory, using the @var{source}s' names.
8029 If the @option{--directory} (@option{-d}) option is given,
8030 @command{install} creates each @var{directory} and any missing parent
8031 directories. Parent directories are created with mode
8032 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8033 current umask. @xref{Directory Setuid and Setgid}, for how the
8034 set-user-ID and set-group-ID bits of parent directories are inherited.
8037 @cindex Makefiles, installing programs in
8038 @command{install} is similar to @command{cp}, but allows you to control the
8039 attributes of destination files. It is typically used in Makefiles to
8040 copy programs into their destination directories. It refuses to copy
8041 files onto themselves.
8043 @cindex extended attributes, xattr
8044 @command{install} never preserves extended attributes (xattr).
8046 The program accepts the following options. Also see @ref{Common options}.
8054 Ignored; for compatibility with old Unix versions of @command{install}.
8058 Create any missing parent directories of @var{dest},
8059 then copy @var{source} to @var{dest}.
8060 This option is ignored if a destination directory is specified
8061 via @option{--target-directory=DIR}.
8066 @opindex --directory
8067 @cindex directories, creating with given attributes
8068 @cindex parent directories, creating missing
8069 @cindex leading directories, creating missing
8070 Create any missing parent directories, giving them the default
8071 attributes. Then create each given directory, setting their owner,
8072 group and mode as given on the command line or to the defaults.
8074 @item -g @var{group}
8075 @itemx --group=@var{group}
8078 @cindex group ownership of installed files, setting
8079 Set the group ownership of installed files or directories to
8080 @var{group}. The default is the process's current group. @var{group}
8081 may be either a group name or a numeric group ID.
8084 @itemx --mode=@var{mode}
8087 @cindex permissions of installed files, setting
8088 Set the file mode bits for the installed file or directory to @var{mode},
8089 which can be either an octal number, or a symbolic mode as in
8090 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8091 point of departure (@pxref{File permissions}).
8092 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8093 execute for the owner, read and execute for group and other, and with
8094 set-user-ID and set-group-ID disabled.
8095 This default is not quite the same as @samp{755}, since it disables
8096 instead of preserving set-user-ID and set-group-ID on directories.
8097 @xref{Directory Setuid and Setgid}.
8099 @item -o @var{owner}
8100 @itemx --owner=@var{owner}
8103 @cindex ownership of installed files, setting
8104 @cindex appropriate privileges
8105 @vindex root @r{as default owner}
8106 If @command{install} has appropriate privileges (is run as root), set the
8107 ownership of installed files or directories to @var{owner}. The default
8108 is @code{root}. @var{owner} may be either a user name or a numeric user
8111 @item --preserve-context
8112 @opindex --preserve-context
8114 @cindex security context
8115 Preserve the SELinux security context of files and directories.
8116 Failure to preserve the context in all of the files or directories
8117 will result in an exit status of 1. If SELinux is disabled then
8118 print a warning and ignore the option.
8121 @itemx --preserve-timestamps
8123 @opindex --preserve-timestamps
8124 @cindex timestamps of installed files, preserving
8125 Set the time of last access and the time of last modification of each
8126 installed file to match those of each corresponding original file.
8127 When a file is installed without this option, its last access and
8128 last modification times are both set to the time of installation.
8129 This option is useful if you want to use the last modification times
8130 of installed files to keep track of when they were last built as opposed
8131 to when they were last installed.
8137 @cindex symbol table information, stripping
8138 @cindex stripping symbol table information
8139 Strip the symbol tables from installed binary executables.
8141 @itemx --strip-program=@var{program}
8142 @opindex --strip-program
8143 @cindex symbol table information, stripping, program
8144 Program used to strip binaries.
8150 @optNoTargetDirectory
8156 Print the name of each file before copying it.
8158 @item -Z @var{context}
8159 @itemx --context=@var{context}
8163 @cindex security context
8164 Set the default SELinux security context to be used for any
8165 created files and directories. If SELinux is disabled then
8166 print a warning and ignore the option.
8174 @section @command{mv}: Move (rename) files
8178 @command{mv} moves or renames files (or directories). Synopses:
8181 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8182 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8183 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8188 If two file names are given, @command{mv} moves the first file to the
8192 If the @option{--target-directory} (@option{-t}) option is given, or
8193 failing that if the last file is a directory and the
8194 @option{--no-target-directory} (@option{-T}) option is not given,
8195 @command{mv} moves each @var{source} file to the specified
8196 directory, using the @var{source}s' names.
8199 @command{mv} can move any type of file from one file system to another.
8200 Prior to version @code{4.0} of the fileutils,
8201 @command{mv} could move only regular files between file systems.
8202 For example, now @command{mv} can move an entire directory hierarchy
8203 including special device files from one partition to another. It first
8204 uses some of the same code that's used by @code{cp -a} to copy the
8205 requested directories and files, then (assuming the copy succeeded)
8206 it removes the originals. If the copy fails, then the part that was
8207 copied to the destination partition is removed. If you were to copy
8208 three directories from one partition to another and the copy of the first
8209 directory succeeded, but the second didn't, the first would be left on
8210 the destination partition and the second and third would be left on the
8213 @cindex extended attributes, xattr
8214 @command{mv} always tries to copy extended attributes (xattr).
8216 @cindex prompting, and @command{mv}
8217 If a destination file exists but is normally unwritable, standard input
8218 is a terminal, and the @option{-f} or @option{--force} option is not given,
8219 @command{mv} prompts the user for whether to replace the file. (You might
8220 own the file, or have write permission on its directory.) If the
8221 response is not affirmative, the file is skipped.
8223 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8224 when it might be a symlink to a directory.
8225 Otherwise, @command{mv} may do something very surprising, since
8226 its behavior depends on the underlying rename system call.
8227 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8228 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8229 renames not the symlink but rather the directory referenced by the symlink.
8230 @xref{Trailing slashes}.
8232 The program accepts the following options. Also see @ref{Common options}.
8242 @cindex prompts, omitting
8243 Do not prompt the user before removing a destination file.
8245 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8246 options, only the final one takes effect.
8251 @itemx --interactive
8253 @opindex --interactive
8254 @cindex prompts, forcing
8255 Prompt whether to overwrite each existing destination file, regardless
8257 If the response is not affirmative, the file is skipped.
8263 @opindex --no-clobber
8264 @cindex prompts, omitting
8265 Do not overwrite an existing file.
8267 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8273 @cindex newer files, moving only
8274 Do not move a non-directory that has an existing destination with the
8275 same or newer modification time.
8276 If the move is across file system boundaries, the comparison is to the
8277 source time stamp truncated to the resolutions of the destination file
8278 system and of the system calls used to update time stamps; this avoids
8279 duplicate work if several @samp{mv -u} commands are executed with the
8280 same source and destination.
8286 Print the name of each file before moving it.
8288 @optStripTrailingSlashes
8294 @optNoTargetDirectory
8302 @section @command{rm}: Remove files or directories
8305 @cindex removing files or directories
8307 @command{rm} removes each given @var{file}. By default, it does not remove
8308 directories. Synopsis:
8311 rm [@var{option}]@dots{} [@var{file}]@dots{}
8314 @cindex prompting, and @command{rm}
8315 If the @option{-I} or @option{--interactive=once} option is given,
8316 and there are more than three files or the @option{-r}, @option{-R},
8317 or @option{--recursive} are given, then @command{rm} prompts the user
8318 for whether to proceed with the entire operation. If the response is
8319 not affirmative, the entire command is aborted.
8321 Otherwise, if a file is unwritable, standard input is a terminal, and
8322 the @option{-f} or @option{--force} option is not given, or the
8323 @option{-i} or @option{--interactive=always} option @emph{is} given,
8324 @command{rm} prompts the user for whether to remove the file.
8325 If the response is not affirmative, the file is skipped.
8327 Any attempt to remove a file whose last file name component is
8328 @file{.} or @file{..} is rejected without any prompting.
8330 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8331 possible to recover the contents of that file. If you want more assurance
8332 that the contents are truly unrecoverable, consider using @command{shred}.
8334 The program accepts the following options. Also see @ref{Common options}.
8342 Ignore nonexistent files and never prompt the user.
8343 Ignore any previous @option{--interactive} (@option{-i}) option.
8347 Prompt whether to remove each file.
8348 If the response is not affirmative, the file is skipped.
8349 Ignore any previous @option{--force} (@option{-f}) option.
8350 Equivalent to @option{--interactive=always}.
8354 Prompt once whether to proceed with the command, if more than three
8355 files are named or if a recursive removal is requested. Ignore any
8356 previous @option{--force} (@option{-f}) option. Equivalent to
8357 @option{--interactive=once}.
8359 @itemx --interactive [=@var{when}]
8360 @opindex --interactive
8361 Specify when to issue an interactive prompt. @var{when} may be
8365 @vindex never @r{interactive option}
8366 - Do not prompt at all.
8368 @vindex once @r{interactive option}
8369 - Prompt once if more than three files are named or if a recursive
8370 removal is requested. Equivalent to @option{-I}.
8372 @vindex always @r{interactive option}
8373 - Prompt for every file being removed. Equivalent to @option{-i}.
8375 @option{--interactive} with no @var{when} is equivalent to
8376 @option{--interactive=always}.
8378 @itemx --one-file-system
8379 @opindex --one-file-system
8380 @cindex one file system, restricting @command{rm} to
8381 When removing a hierarchy recursively, skip any directory that is on a
8382 file system different from that of the corresponding command line argument.
8384 This option is useful when removing a build ``chroot'' hierarchy,
8385 which normally contains no valuable data. However, it is not uncommon
8386 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8387 use one's start-up file. The catch is that it's easy to forget to
8388 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8389 your normally throw-away chroot, that command will remove everything
8390 under @file{/home}, too.
8391 Use the @option{--one-file-system} option, and it will
8392 warn about and skip directories on other file systems.
8393 Of course, this will not save your @file{/home} if it and your
8394 chroot happen to be on the same file system.
8396 @itemx --preserve-root
8397 @opindex --preserve-root
8398 @cindex root directory, disallow recursive destruction
8399 Fail upon any attempt to remove the root directory, @file{/},
8400 when used with the @option{--recursive} option.
8401 This is the default behavior.
8402 @xref{Treating / specially}.
8404 @itemx --no-preserve-root
8405 @opindex --no-preserve-root
8406 @cindex root directory, allow recursive destruction
8407 Do not treat @file{/} specially when removing recursively.
8408 This option is not recommended unless you really want to
8409 remove all the files on your computer.
8410 @xref{Treating / specially}.
8417 @opindex --recursive
8418 @cindex directories, removing (recursively)
8419 Remove the listed directories and their contents recursively.
8425 Print the name of each file before removing it.
8429 @cindex files beginning with @samp{-}, removing
8430 @cindex @samp{-}, removing files beginning with
8431 One common question is how to remove files whose names begin with a
8432 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8433 function to parse its arguments, lets you use the @samp{--} option to
8434 indicate that all following arguments are non-options. To remove a file
8435 called @file{-f} in the current directory, you could type either:
8448 @opindex - @r{and Unix @command{rm}}
8449 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8450 predates the development of the getopt standard syntax.
8455 @node shred invocation
8456 @section @command{shred}: Remove files more securely
8459 @cindex data, erasing
8460 @cindex erasing data
8462 @command{shred} overwrites devices or files, to help prevent even
8463 very expensive hardware from recovering the data.
8465 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8466 not actually destroyed. Only the index listing where the file is
8467 stored is destroyed, and the storage is made available for reuse.
8468 There are undelete utilities that will attempt to reconstruct the index
8469 and can bring the file back if the parts were not reused.
8471 On a busy system with a nearly-full drive, space can get reused in a few
8472 seconds. But there is no way to know for sure. If you have sensitive
8473 data, you may want to be sure that recovery is not possible by actually
8474 overwriting the file with non-sensitive data.
8476 However, even after doing that, it is possible to take the disk back
8477 to a laboratory and use a lot of sensitive (and expensive) equipment
8478 to look for the faint ``echoes'' of the original data underneath the
8479 overwritten data. If the data has only been overwritten once, it's not
8482 The best way to remove something irretrievably is to destroy the media
8483 it's on with acid, melt it down, or the like. For cheap removable media
8484 like floppy disks, this is the preferred method. However, hard drives
8485 are expensive and hard to melt, so the @command{shred} utility tries
8486 to achieve a similar effect non-destructively.
8488 This uses many overwrite passes, with the data patterns chosen to
8489 maximize the damage they do to the old data. While this will work on
8490 floppies, the patterns are designed for best effect on hard drives.
8491 For more details, see the source code and Peter Gutmann's paper
8492 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8493 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8494 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8495 California, July 22--25, 1996).
8497 @strong{Please note} that @command{shred} relies on a very important assumption:
8498 that the file system overwrites data in place. This is the traditional
8499 way to do things, but many modern file system designs do not satisfy this
8500 assumption. Exceptions include:
8505 Log-structured or journaled file systems, such as those supplied with
8506 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8507 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8510 File systems that write redundant data and carry on even if some writes
8511 fail, such as RAID-based file systems.
8514 File systems that make snapshots, such as Network Appliance's NFS server.
8517 File systems that cache in temporary locations, such as NFS version 3
8521 Compressed file systems.
8524 In the particular case of ext3 file systems, the above disclaimer applies (and
8525 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8526 mode, which journals file data in addition to just metadata. In both
8527 the @code{data=ordered} (default) and @code{data=writeback} modes,
8528 @command{shred} works as usual. Ext3 journaling modes can be changed
8529 by adding the @code{data=something} option to the mount options for a
8530 particular file system in the @file{/etc/fstab} file, as documented in
8531 the mount man page (man mount).
8533 If you are not sure how your file system operates, then you should assume
8534 that it does not overwrite data in place, which means that shred cannot
8535 reliably operate on regular files in your file system.
8537 Generally speaking, it is more reliable to shred a device than a file,
8538 since this bypasses the problem of file system design mentioned above.
8539 However, even shredding devices is not always completely reliable. For
8540 example, most disks map out bad sectors invisibly to the application; if
8541 the bad sectors contain sensitive data, @command{shred} won't be able to
8544 @command{shred} makes no attempt to detect or report this problem, just as
8545 it makes no attempt to do anything about backups. However, since it is
8546 more reliable to shred devices than files, @command{shred} by default does
8547 not truncate or remove the output file. This default is more suitable
8548 for devices, which typically cannot be truncated and should not be
8551 Finally, consider the risk of backups and mirrors.
8552 File system backups and remote mirrors may contain copies of the
8553 file that cannot be removed, and that will allow a shredded file
8554 to be recovered later. So if you keep any data you may later want
8555 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8558 shred [@var{option}]@dots{} @var{file}[@dots{}]
8561 The program accepts the following options. Also see @ref{Common options}.
8569 @cindex force deletion
8570 Override file permissions if necessary to allow overwriting.
8573 @itemx -n @var{number}
8574 @itemx --iterations=@var{number}
8575 @opindex -n @var{number}
8576 @opindex --iterations=@var{number}
8577 @cindex iterations, selecting the number of
8578 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8579 overwrite. You can reduce this to save time, or increase it if you think it's
8580 appropriate. After 25 passes all of the internal overwrite patterns will have
8581 been used at least once.
8583 @item --random-source=@var{file}
8584 @opindex --random-source
8585 @cindex random source for shredding
8586 Use @var{file} as a source of random data used to overwrite and to
8587 choose pass ordering. @xref{Random sources}.
8589 @item -s @var{bytes}
8590 @itemx --size=@var{bytes}
8591 @opindex -s @var{bytes}
8592 @opindex --size=@var{bytes}
8593 @cindex size of file to shred
8594 Shred the first @var{bytes} bytes of the file. The default is to shred
8595 the whole file. @var{bytes} can be followed by a size specification like
8596 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8602 @cindex removing files after shredding
8603 After shredding a file, truncate it (if possible) and then remove it.
8604 If a file has multiple links, only the named links will be removed.
8610 Display to standard error all status updates as sterilization proceeds.
8616 By default, @command{shred} rounds the size of a regular file up to the next
8617 multiple of the file system block size to fully erase the last block of the file.
8618 Use @option{--exact} to suppress that behavior.
8619 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8620 blocks, the resulting file will be 512 bytes long. With this option,
8621 shred does not increase the apparent size of the file.
8627 Normally, the last pass that @command{shred} writes is made up of
8628 random data. If this would be conspicuous on your hard drive (for
8629 example, because it looks like encrypted data), or you just think
8630 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8631 all zero bits. This is in addition to the number of passes specified
8632 by the @option{--iterations} option.
8636 You might use the following command to erase all trace of the
8637 file system you'd created on the floppy disk in your first drive.
8638 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8642 shred --verbose /dev/fd0
8645 Similarly, to erase all data on a selected partition of
8646 your hard disk, you could give a command like this:
8649 shred --verbose /dev/sda5
8652 A @var{file} of @samp{-} denotes standard output.
8653 The intended use of this is to shred a removed temporary file.
8657 i=`tempfile -m 0600`
8660 echo "Hello, world" >&3
8665 However, the command @samp{shred - >file} does not shred the contents
8666 of @var{file}, since the shell truncates @var{file} before invoking
8667 @command{shred}. Use the command @samp{shred file} or (if using a
8668 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8673 @node Special file types
8674 @chapter Special file types
8676 @cindex special file types
8677 @cindex file types, special
8679 This chapter describes commands which create special types of files (and
8680 @command{rmdir}, which removes directories, one special file type).
8682 @cindex special file types
8684 Although Unix-like operating systems have markedly fewer special file
8685 types than others, not @emph{everything} can be treated only as the
8686 undifferentiated byte stream of @dfn{normal files}. For example, when a
8687 file is created or removed, the system must record this information,
8688 which it does in a @dfn{directory}---a special type of file. Although
8689 you can read directories as normal files, if you're curious, in order
8690 for the system to do its job it must impose a structure, a certain
8691 order, on the bytes of the file. Thus it is a ``special'' type of file.
8693 Besides directories, other special file types include named pipes
8694 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8697 * link invocation:: Make a hard link via the link syscall
8698 * ln invocation:: Make links between files.
8699 * mkdir invocation:: Make directories.
8700 * mkfifo invocation:: Make FIFOs (named pipes).
8701 * mknod invocation:: Make block or character special files.
8702 * readlink invocation:: Print value of a symlink or canonical file name.
8703 * rmdir invocation:: Remove empty directories.
8704 * unlink invocation:: Remove files via the unlink syscall
8708 @node link invocation
8709 @section @command{link}: Make a hard link via the link syscall
8712 @cindex links, creating
8713 @cindex hard links, creating
8714 @cindex creating links (hard only)
8716 @command{link} creates a single hard link at a time.
8717 It is a minimalist interface to the system-provided
8718 @code{link} function. @xref{Hard Links, , , libc,
8719 The GNU C Library Reference Manual}.
8720 It avoids the bells and whistles of the more commonly-used
8721 @command{ln} command (@pxref{ln invocation}).
8725 link @var{filename} @var{linkname}
8728 @var{filename} must specify an existing file, and @var{linkname}
8729 must specify a nonexistent entry in an existing directory.
8730 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8733 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8734 --no-target-directory @var{filename} @var{linkname}}. However, the
8735 @option{--directory} and @option{--no-target-directory} options are
8736 not specified by @acronym{POSIX}, and the @command{link} command is
8737 more portable in practice.
8743 @section @command{ln}: Make links between files
8746 @cindex links, creating
8747 @cindex hard links, creating
8748 @cindex symbolic (soft) links, creating
8749 @cindex creating links (hard or soft)
8751 @cindex file systems and hard links
8752 @command{ln} makes links between files. By default, it makes hard links;
8753 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8757 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8758 ln [@var{option}]@dots{} @var{target}
8759 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8760 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8766 If two file names are given, @command{ln} creates a link to the first
8767 file from the second.
8770 If one @var{target} is given, @command{ln} creates a link to that file
8771 in the current directory.
8774 If the @option{--target-directory} (@option{-t}) option is given, or
8775 failing that if the last file is a directory and the
8776 @option{--no-target-directory} (@option{-T}) option is not given,
8777 @command{ln} creates a link to each @var{target} file in the specified
8778 directory, using the @var{target}s' names.
8782 Normally @command{ln} does not remove existing files. Use the
8783 @option{--force} (@option{-f}) option to remove them unconditionally,
8784 the @option{--interactive} (@option{-i}) option to remove them
8785 conditionally, and the @option{--backup} (@option{-b}) option to
8788 @cindex hard link, defined
8789 @cindex inode, and hard links
8790 A @dfn{hard link} is another name for an existing file; the link and the
8791 original are indistinguishable. Technically speaking, they share the
8792 same inode, and the inode contains all the information about a
8793 file---indeed, it is not incorrect to say that the inode @emph{is} the
8794 file. On all existing implementations, you cannot make a hard link to
8795 a directory, and hard links cannot cross file system boundaries. (These
8796 restrictions are not mandated by @acronym{POSIX}, however.)
8798 @cindex dereferencing symbolic links
8799 @cindex symbolic link, defined
8800 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8801 a special file type (which not all kernels support: System V release 3
8802 (and older) systems lack symlinks) in which the link file actually
8803 refers to a different file, by name. When most operations (opening,
8804 reading, writing, and so on) are passed the symbolic link file, the
8805 kernel automatically @dfn{dereferences} the link and operates on the
8806 target of the link. But some operations (e.g., removing) work on the
8807 link file itself, rather than on its target. The owner, group, and
8808 mode of a symlink are not significant to file access performed through
8809 the link. @xref{Symbolic Links,,,
8810 libc, The GNU C Library Reference Manual}.
8812 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8813 occurs when the string in the symlink does not resolve to a file.
8814 There are no restrictions against creating dangling symbolic links.
8815 There are trade-offs to using absolute or relative symlinks. An
8816 absolute symlink always points to the same file, even if the directory
8817 containing the link is moved. However, if the symlink is visible from
8818 more than one machine (such as on a networked file system), the file
8819 pointed to might not always be the same. A relative symbolic link is
8820 resolved in relation to the directory that contains the link, and is
8821 often useful in referring to files on the same device without regards
8822 to what name that device is mounted on when accessed via networked
8825 When creating a relative symlink in a different location than the
8826 current directory, the resolution of the symlink will be different
8827 than the resolution of the same string from the current directory.
8828 Therefore, many users prefer to first change directories to the
8829 location where the relative symlink will be created, so that
8830 tab-completion or other file resolution will find the same target as
8831 what will be placed in the symlink.
8833 The program accepts the following options. Also see @ref{Common options}.
8844 @opindex --directory
8845 @cindex hard links to directories
8846 Allow users with appropriate privileges to attempt to make hard links
8848 However, note that this will probably fail due to
8849 system restrictions, even for the super-user.
8855 Remove existing destination files.
8858 @itemx --interactive
8860 @opindex --interactive
8861 @cindex prompting, and @command{ln}
8862 Prompt whether to remove existing destination files.
8865 @itemx --no-dereference
8867 @opindex --no-dereference
8868 Do not treat the last operand specially when it is a symbolic link to
8869 a directory. Instead, treat it as if it were a normal file.
8871 When the destination is an actual directory (not a symlink to one),
8872 there is no ambiguity. The link is created in that directory.
8873 But when the specified destination is a symlink to a directory,
8874 there are two ways to treat the user's request. @command{ln} can
8875 treat the destination just as it would a normal directory and create
8876 the link in it. On the other hand, the destination can be viewed as a
8877 non-directory---as the symlink itself. In that case, @command{ln}
8878 must delete or backup that symlink before creating the new link.
8879 The default is to treat a destination that is a symlink to a directory
8880 just like a directory.
8882 This option is weaker than the @option{--no-target-directory}
8883 (@option{-T}) option, so it has no effect if both options are given.
8889 Make symbolic links instead of hard links. This option merely produces
8890 an error message on systems that do not support symbolic links.
8896 @optNoTargetDirectory
8902 Print the name of each file after linking it successfully.
8913 # Create link ../a pointing to a in that directory.
8914 # Not really useful because it points to itself.
8919 # Change to the target before creating symlinks to avoid being confused.
8925 # Hard coded file names don't move well.
8926 ln -s $(pwd)/a /some/dir/
8930 # Relative file names survive directory moves and also
8931 # work across networked file systems.
8932 ln -s afile anotherfile
8933 ln -s ../adir/afile yetanotherfile
8937 @node mkdir invocation
8938 @section @command{mkdir}: Make directories
8941 @cindex directories, creating
8942 @cindex creating directories
8944 @command{mkdir} creates directories with the specified names. Synopsis:
8947 mkdir [@var{option}]@dots{} @var{name}@dots{}
8950 @command{mkdir} creates each directory @var{name} in the order given.
8951 It reports an error if @var{name} already exists, unless the
8952 @option{-p} option is given and @var{name} is a directory.
8954 The program accepts the following options. Also see @ref{Common options}.
8959 @itemx --mode=@var{mode}
8962 @cindex modes of created directories, setting
8963 Set the file permission bits of created directories to @var{mode},
8964 which uses the same syntax as
8965 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8966 everyone) for the point of the departure. @xref{File permissions}.
8968 Normally the directory has the desired file mode bits at the moment it
8969 is created. As a @acronym{GNU} extension, @var{mode} may also mention
8970 special mode bits, but in this case there may be a temporary window
8971 during which the directory exists but its special mode bits are
8972 incorrect. @xref{Directory Setuid and Setgid}, for how the
8973 set-user-ID and set-group-ID bits of directories are inherited unless
8974 overridden in this way.
8980 @cindex parent directories, creating
8981 Make any missing parent directories for each argument, setting their
8982 file permission bits to the umask modified by @samp{u+wx}. Ignore
8983 existing parent directories, and do not change their file permission
8986 To set the file permission bits of any newly-created parent
8987 directories to a value that includes @samp{u+wx}, you can set the
8988 umask before invoking @command{mkdir}. For example, if the shell
8989 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
8990 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
8991 To set a parent's special mode bits as well, you can invoke
8992 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
8993 Setgid}, for how the set-user-ID and set-group-ID bits of
8994 newly-created parent directories are inherited.
9000 Print a message for each created directory. This is most useful with
9003 @item -Z @var{context}
9004 @itemx --context=@var{context}
9008 @cindex security context
9009 Set the default SELinux security context to be used for created directories.
9016 @node mkfifo invocation
9017 @section @command{mkfifo}: Make FIFOs (named pipes)
9020 @cindex FIFOs, creating
9021 @cindex named pipes, creating
9022 @cindex creating FIFOs (named pipes)
9024 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9025 specified names. Synopsis:
9028 mkfifo [@var{option}] @var{name}@dots{}
9031 A @dfn{FIFO} is a special file type that permits independent processes
9032 to communicate. One process opens the FIFO file for writing, and
9033 another for reading, after which data can flow as with the usual
9034 anonymous pipe in shells or elsewhere.
9036 The program accepts the following option. Also see @ref{Common options}.
9041 @itemx --mode=@var{mode}
9044 @cindex modes of created FIFOs, setting
9045 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9046 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9047 for the point of departure. @var{mode} should specify only file
9048 permission bits. @xref{File permissions}.
9050 @item -Z @var{context}
9051 @itemx --context=@var{context}
9055 @cindex security context
9056 Set the default SELinux security context to be used for created FIFOs.
9063 @node mknod invocation
9064 @section @command{mknod}: Make block or character special files
9067 @cindex block special files, creating
9068 @cindex character special files, creating
9070 @command{mknod} creates a FIFO, character special file, or block special
9071 file with the specified name. Synopsis:
9074 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9077 @cindex special files
9078 @cindex block special files
9079 @cindex character special files
9080 Unlike the phrase ``special file type'' above, the term @dfn{special
9081 file} has a technical meaning on Unix: something that can generate or
9082 receive data. Usually this corresponds to a physical piece of hardware,
9083 e.g., a printer or a disk. (These files are typically created at
9084 system-configuration time.) The @command{mknod} command is what creates
9085 files of this type. Such devices can be read either a character at a
9086 time or a ``block'' (many characters) at a time, hence we say there are
9087 @dfn{block special} files and @dfn{character special} files.
9089 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9090 @mayConflictWithShellBuiltIn{mknod}
9092 The arguments after @var{name} specify the type of file to make:
9097 @opindex p @r{for FIFO file}
9101 @opindex b @r{for block special file}
9102 for a block special file
9105 @c Don't document the `u' option -- it's just a synonym for `c'.
9106 @c Do *any* versions of mknod still use it?
9108 @opindex c @r{for character special file}
9109 @c @opindex u @r{for character special file}
9110 for a character special file
9114 When making a block or character special file, the major and minor
9115 device numbers must be given after the file type.
9116 If a major or minor device number begins with @samp{0x} or @samp{0X},
9117 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9118 as octal; otherwise, as decimal.
9120 The program accepts the following option. Also see @ref{Common options}.
9125 @itemx --mode=@var{mode}
9128 Set the mode of created files to @var{mode}, which is symbolic as in
9129 @command{chmod} and uses @samp{a=rw} as the point of departure.
9130 @var{mode} should specify only file permission bits.
9131 @xref{File permissions}.
9133 @item -Z @var{context}
9134 @itemx --context=@var{context}
9138 @cindex security context
9139 Set the default SELinux security context to be used for created files.
9146 @node readlink invocation
9147 @section @command{readlink}: Print value of a symlink or canonical file name
9150 @cindex displaying value of a symbolic link
9151 @cindex canonical file name
9152 @cindex canonicalize a file name
9156 @command{readlink} may work in one of two supported modes:
9162 @command{readlink} outputs the value of the given symbolic link.
9163 If @command{readlink} is invoked with an argument other than the name
9164 of a symbolic link, it produces no output and exits with a nonzero exit code.
9166 @item Canonicalize mode
9168 @command{readlink} outputs the absolute name of the given file which contains
9169 no @file{.}, @file{..} components nor any repeated separators
9170 (@file{/}) or symbolic links.
9175 readlink [@var{option}] @var{file}
9178 By default, @command{readlink} operates in readlink mode.
9180 The program accepts the following options. Also see @ref{Common options}.
9185 @itemx --canonicalize
9187 @opindex --canonicalize
9188 Activate canonicalize mode.
9189 If any component of the file name except the last one is missing or unavailable,
9190 @command{readlink} produces no output and exits with a nonzero exit code.
9193 @itemx --canonicalize-existing
9195 @opindex --canonicalize-existing
9196 Activate canonicalize mode.
9197 If any component is missing or unavailable, @command{readlink} produces
9198 no output and exits with a nonzero exit code.
9201 @itemx --canonicalize-missing
9203 @opindex --canonicalize-missing
9204 Activate canonicalize mode.
9205 If any component is missing or unavailable, @command{readlink} treats it
9211 @opindex --no-newline
9212 Do not output the trailing newline.
9222 Suppress most error messages.
9228 Report error messages.
9232 The @command{readlink} utility first appeared in OpenBSD 2.1.
9234 There is a @command{realpath} command on some systems
9235 which operates like @command{readlink} in canonicalize mode.
9240 @node rmdir invocation
9241 @section @command{rmdir}: Remove empty directories
9244 @cindex removing empty directories
9245 @cindex directories, removing empty
9247 @command{rmdir} removes empty directories. Synopsis:
9250 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9253 If any @var{directory} argument does not refer to an existing empty
9254 directory, it is an error.
9256 The program accepts the following options. Also see @ref{Common options}.
9260 @item --ignore-fail-on-non-empty
9261 @opindex --ignore-fail-on-non-empty
9262 @cindex directory deletion, ignoring failures
9263 Ignore each failure to remove a directory that is solely because
9264 the directory is non-empty.
9270 @cindex parent directories, removing
9271 Remove @var{directory}, then try to remove each component of @var{directory}.
9272 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9273 As such, it fails if any of those directories turns out not to be empty.
9274 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9275 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9276 exit unsuccessfully.
9282 @cindex directory deletion, reporting
9283 Give a diagnostic for each successful removal.
9284 @var{directory} is removed.
9288 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9293 @node unlink invocation
9294 @section @command{unlink}: Remove files via the unlink syscall
9297 @cindex removing files or directories (via the unlink syscall)
9299 @command{unlink} deletes a single specified file name.
9300 It is a minimalist interface to the system-provided
9301 @code{unlink} function. @xref{Deleting Files, , , libc,
9302 The GNU C Library Reference Manual}. Synopsis:
9303 It avoids the bells and whistles of the more commonly-used
9304 @command{rm} command (@pxref{rm invocation}).
9307 unlink @var{filename}
9310 On some systems @code{unlink} can be used to delete the name of a
9311 directory. On others, it can be used that way only by a privileged user.
9312 In the GNU system @code{unlink} can never delete the name of a directory.
9314 The @command{unlink} command honors the @option{--help} and
9315 @option{--version} options. To remove a file whose name begins with
9316 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9321 @node Changing file attributes
9322 @chapter Changing file attributes
9324 @cindex changing file attributes
9325 @cindex file attributes, changing
9326 @cindex attributes, file
9328 A file is not merely its contents, a name, and a file type
9329 (@pxref{Special file types}). A file also has an owner (a user ID), a
9330 group (a group ID), permissions (what the owner can do with the file,
9331 what people in the group can do, and what everyone else can do), various
9332 timestamps, and other information. Collectively, we call these a file's
9335 These commands change file attributes.
9338 * chgrp invocation:: Change file groups.
9339 * chmod invocation:: Change access permissions.
9340 * chown invocation:: Change file owners and groups.
9341 * touch invocation:: Change file timestamps.
9345 @node chown invocation
9346 @section @command{chown}: Change file owner and group
9349 @cindex file ownership, changing
9350 @cindex group ownership, changing
9351 @cindex changing file ownership
9352 @cindex changing group ownership
9354 @command{chown} changes the user and/or group ownership of each given @var{file}
9355 to @var{new-owner} or to the user and group of an existing reference file.
9359 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9362 If used, @var{new-owner} specifies the new owner and/or group as follows
9363 (with no embedded white space):
9366 [@var{owner}] [ : [@var{group}] ]
9373 If only an @var{owner} (a user name or numeric user ID) is given, that
9374 user is made the owner of each given file, and the files' group is not
9377 @item owner@samp{:}group
9378 If the @var{owner} is followed by a colon and a @var{group} (a
9379 group name or numeric group ID), with no spaces between them, the group
9380 ownership of the files is changed as well (to @var{group}).
9383 If a colon but no group name follows @var{owner}, that user is
9384 made the owner of the files and the group of the files is changed to
9385 @var{owner}'s login group.
9388 If the colon and following @var{group} are given, but the owner
9389 is omitted, only the group of the files is changed; in this case,
9390 @command{chown} performs the same function as @command{chgrp}.
9393 If only a colon is given, or if @var{new-owner} is empty, neither the
9394 owner nor the group is changed.
9398 If @var{owner} or @var{group} is intended to represent a numeric user
9399 or group ID, then you may specify it with a leading @samp{+}.
9400 @xref{Disambiguating names and IDs}.
9402 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9403 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9404 require support for that, but for backward compatibility @acronym{GNU}
9405 @command{chown} supports @samp{.} so long as no ambiguity results.
9406 New scripts should avoid the use of @samp{.} because it is not
9407 portable, and because it has undesirable results if the entire
9408 @var{owner@samp{.}group} happens to identify a user whose name
9411 The @command{chown} command sometimes clears the set-user-ID or
9412 set-group-ID permission bits. This behavior depends on the policy and
9413 functionality of the underlying @code{chown} system call, which may
9414 make system-dependent file mode modifications outside the control of
9415 the @command{chown} command. For example, the @command{chown} command
9416 might not affect those bits when invoked by a user with appropriate
9417 privileges, or when the
9418 bits signify some function other than executable permission (e.g.,
9420 When in doubt, check the underlying system behavior.
9422 The program accepts the following options. Also see @ref{Common options}.
9430 @cindex changed owners, verbosely describing
9431 Verbosely describe the action for each @var{file} whose ownership
9440 @cindex error messages, omitting
9441 Do not print error messages about files whose ownership cannot be
9444 @itemx @w{@kbd{--from}=@var{old-owner}}
9446 @cindex symbolic links, changing owner
9447 Change a @var{file}'s ownership only if it has current attributes specified
9448 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9450 This option is useful primarily from a security standpoint in that
9451 it narrows considerably the window of potential abuse.
9452 For example, to reflect a user ID numbering change for one user's files
9453 without an option like this, @code{root} might run
9456 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9459 But that is dangerous because the interval between when the @command{find}
9460 tests the existing file's owner and when the @command{chown} is actually run
9462 One way to narrow the gap would be to invoke chown for each file
9466 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9469 But that is very slow if there are many affected files.
9470 With this option, it is safer (the gap is narrower still)
9471 though still not perfect:
9474 chown -h -R --from=OLDUSER NEWUSER /
9478 @opindex --dereference
9479 @cindex symbolic links, changing owner
9481 Do not act on symbolic links themselves but rather on what they point to.
9482 This is the default.
9485 @itemx --no-dereference
9487 @opindex --no-dereference
9488 @cindex symbolic links, changing owner
9490 Act on symbolic links themselves instead of what they point to.
9491 This mode relies on the @code{lchown} system call.
9492 On systems that do not provide the @code{lchown} system call,
9493 @command{chown} fails when a file specified on the command line
9495 By default, no diagnostic is issued for symbolic links encountered
9496 during a recursive traversal, but see @option{--verbose}.
9498 @itemx --preserve-root
9499 @opindex --preserve-root
9500 @cindex root directory, disallow recursive modification
9501 Fail upon any attempt to recursively change the root directory, @file{/}.
9502 Without @option{--recursive}, this option has no effect.
9503 @xref{Treating / specially}.
9505 @itemx --no-preserve-root
9506 @opindex --no-preserve-root
9507 @cindex root directory, allow recursive modification
9508 Cancel the effect of any preceding @option{--preserve-root} option.
9509 @xref{Treating / specially}.
9511 @item --reference=@var{ref_file}
9512 @opindex --reference
9513 Change the user and group of each @var{file} to be the same as those of
9514 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9515 user and group of the symbolic link, but rather those of the file it
9522 Output a diagnostic for every file processed.
9523 If a symbolic link is encountered during a recursive traversal
9524 on a system without the @code{lchown} system call, and @option{--no-dereference}
9525 is in effect, then issue a diagnostic saying neither the symbolic link nor
9526 its referent is being changed.
9531 @opindex --recursive
9532 @cindex recursively changing file ownership
9533 Recursively change ownership of directories and their contents.
9536 @xref{Traversing symlinks}.
9539 @xref{Traversing symlinks}.
9542 @xref{Traversing symlinks}.
9551 # Change the owner of /u to "root".
9554 # Likewise, but also change its group to "staff".
9557 # Change the owner of /u and subfiles to "root".
9562 @node chgrp invocation
9563 @section @command{chgrp}: Change group ownership
9566 @cindex group ownership, changing
9567 @cindex changing group ownership
9569 @command{chgrp} changes the group ownership of each given @var{file}
9570 to @var{group} (which can be either a group name or a numeric group ID)
9571 or to the group of an existing reference file. Synopsis:
9574 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9577 If @var{group} is intended to represent a
9578 numeric group ID, then you may specify it with a leading @samp{+}.
9579 @xref{Disambiguating names and IDs}.
9581 The program accepts the following options. Also see @ref{Common options}.
9589 @cindex changed files, verbosely describing
9590 Verbosely describe the action for each @var{file} whose group actually
9599 @cindex error messages, omitting
9600 Do not print error messages about files whose group cannot be
9604 @opindex --dereference
9605 @cindex symbolic links, changing owner
9607 Do not act on symbolic links themselves but rather on what they point to.
9608 This is the default.
9611 @itemx --no-dereference
9613 @opindex --no-dereference
9614 @cindex symbolic links, changing group
9616 Act on symbolic links themselves instead of what they point to.
9617 This mode relies on the @code{lchown} system call.
9618 On systems that do not provide the @code{lchown} system call,
9619 @command{chgrp} fails when a file specified on the command line
9621 By default, no diagnostic is issued for symbolic links encountered
9622 during a recursive traversal, but see @option{--verbose}.
9624 @itemx --preserve-root
9625 @opindex --preserve-root
9626 @cindex root directory, disallow recursive modification
9627 Fail upon any attempt to recursively change the root directory, @file{/}.
9628 Without @option{--recursive}, this option has no effect.
9629 @xref{Treating / specially}.
9631 @itemx --no-preserve-root
9632 @opindex --no-preserve-root
9633 @cindex root directory, allow recursive modification
9634 Cancel the effect of any preceding @option{--preserve-root} option.
9635 @xref{Treating / specially}.
9637 @item --reference=@var{ref_file}
9638 @opindex --reference
9639 Change the group of each @var{file} to be the same as that of
9640 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9641 group of the symbolic link, but rather that of the file it refers to.
9647 Output a diagnostic for every file processed.
9648 If a symbolic link is encountered during a recursive traversal
9649 on a system without the @code{lchown} system call, and @option{--no-dereference}
9650 is in effect, then issue a diagnostic saying neither the symbolic link nor
9651 its referent is being changed.
9656 @opindex --recursive
9657 @cindex recursively changing group ownership
9658 Recursively change the group ownership of directories and their contents.
9661 @xref{Traversing symlinks}.
9664 @xref{Traversing symlinks}.
9667 @xref{Traversing symlinks}.
9676 # Change the group of /u to "staff".
9679 # Change the group of /u and subfiles to "staff".
9684 @node chmod invocation
9685 @section @command{chmod}: Change access permissions
9688 @cindex changing access permissions
9689 @cindex access permissions, changing
9690 @cindex permissions, changing access
9692 @command{chmod} changes the access permissions of the named files. Synopsis:
9695 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9698 @cindex symbolic links, permissions of
9699 @command{chmod} never changes the permissions of symbolic links, since
9700 the @command{chmod} system call cannot change their permissions.
9701 This is not a problem since the permissions of symbolic links are
9702 never used. However, for each symbolic link listed on the command
9703 line, @command{chmod} changes the permissions of the pointed-to file.
9704 In contrast, @command{chmod} ignores symbolic links encountered during
9705 recursive directory traversals.
9707 A successful use of @command{chmod} clears the set-group-ID bit of a
9708 regular file if the file's group ID does not match the user's
9709 effective group ID or one of the user's supplementary group IDs,
9710 unless the user has appropriate privileges. Additional restrictions
9711 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9712 @var{ref_file} to be ignored. This behavior depends on the policy and
9713 functionality of the underlying @code{chmod} system call. When in
9714 doubt, check the underlying system behavior.
9716 If used, @var{mode} specifies the new file mode bits.
9717 For details, see the section on @ref{File permissions}.
9718 If you really want @var{mode} to have a leading @samp{-}, you should
9719 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9720 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9721 file} (without the @option{--}) complains if it behaves differently
9722 from what @samp{chmod a-w file} would do.
9724 The program accepts the following options. Also see @ref{Common options}.
9732 Verbosely describe the action for each @var{file} whose permissions
9741 @cindex error messages, omitting
9742 Do not print error messages about files whose permissions cannot be
9745 @itemx --preserve-root
9746 @opindex --preserve-root
9747 @cindex root directory, disallow recursive modification
9748 Fail upon any attempt to recursively change the root directory, @file{/}.
9749 Without @option{--recursive}, this option has no effect.
9750 @xref{Treating / specially}.
9752 @itemx --no-preserve-root
9753 @opindex --no-preserve-root
9754 @cindex root directory, allow recursive modification
9755 Cancel the effect of any preceding @option{--preserve-root} option.
9756 @xref{Treating / specially}.
9762 Verbosely describe the action or non-action taken for every @var{file}.
9764 @item --reference=@var{ref_file}
9765 @opindex --reference
9766 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9767 @xref{File permissions}.
9768 If @var{ref_file} is a symbolic link, do not use the mode
9769 of the symbolic link, but rather that of the file it refers to.
9774 @opindex --recursive
9775 @cindex recursively changing access permissions
9776 Recursively change permissions of directories and their contents.
9783 @node touch invocation
9784 @section @command{touch}: Change file timestamps
9787 @cindex changing file timestamps
9788 @cindex file timestamps, changing
9789 @cindex timestamps, changing file
9791 @command{touch} changes the access and/or modification times of the
9792 specified files. Synopsis:
9795 touch [@var{option}]@dots{} @var{file}@dots{}
9798 @cindex empty files, creating
9799 Any @var{file} argument that does not exist is created empty.
9801 A @var{file} argument string of @samp{-} is handled specially and
9802 causes @command{touch} to change the times of the file associated with
9805 @cindex permissions, for changing file timestamps
9806 If changing both the access and modification times to the current
9807 time, @command{touch} can change the timestamps for files that the user
9808 running it does not own but has write permission for. Otherwise, the
9809 user must own the files.
9811 Although @command{touch} provides options for changing two of the times---the
9812 times of last access and modification---of a file, there is actually
9813 a third one as well: the inode change time. This is often referred to
9814 as a file's @code{ctime}.
9815 The inode change time represents the time when the file's meta-information
9816 last changed. One common example of this is when the permissions of a
9817 file change. Changing the permissions doesn't access the file, so
9818 the atime doesn't change, nor does it modify the file, so the mtime
9819 doesn't change. Yet, something about the file itself has changed,
9820 and this must be noted somewhere. This is the job of the ctime field.
9821 This is necessary, so that, for example, a backup program can make a
9822 fresh copy of the file, including the new permissions value.
9823 Another operation that modifies a file's ctime without affecting
9824 the others is renaming. In any case, it is not possible, in normal
9825 operations, for a user to change the ctime field to a user-specified value.
9828 Time stamps assume the time zone rules specified by the @env{TZ}
9829 environment variable, or by the system default rules if @env{TZ} is
9830 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9831 libc, The GNU C Library Reference Manual}.
9832 You can avoid ambiguities during
9833 daylight saving transitions by using @sc{utc} time stamps.
9835 The program accepts the following options. Also see @ref{Common options}.
9841 @itemx --time=access
9845 @opindex atime@r{, changing}
9846 @opindex access @r{time, changing}
9847 @opindex use @r{time, changing}
9848 Change the access time only.
9853 @opindex --no-create
9854 Do not create files that do not exist.
9857 @itemx --date=@var{time}
9861 Use @var{time} instead of the current time. It can contain month names,
9862 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9863 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9864 specifies the instant of time that is 489,392,193 nanoseconds after
9865 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9866 minutes east of @acronym{UTC}. @xref{Date input formats}.
9867 File systems that do not support high-resolution time stamps
9868 silently ignore any excess precision here.
9872 @cindex BSD @command{touch} compatibility
9873 Ignored; for compatibility with BSD versions of @command{touch}.
9877 @itemx --time=modify
9880 @opindex mtime@r{, changing}
9881 @opindex modify @r{time, changing}
9882 Change the modification time only.
9885 @itemx --reference=@var{file}
9887 @opindex --reference
9888 Use the times of the reference @var{file} instead of the current time.
9889 If this option is combined with the @option{--date=@var{time}}
9890 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9891 the origin for any relative @var{time}s given, but is otherwise ignored.
9892 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9893 equal to five seconds before the corresponding time stamp for @file{foo}.
9895 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9896 Use the argument (optional four-digit or two-digit years, months,
9897 days, hours, minutes, optional seconds) instead of the current time.
9898 If the year is specified with only two digits, then @var{cc}
9899 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9900 69 @dots{} 99. If no digits of the year are specified,
9901 the argument is interpreted as a date in the current year.
9905 @vindex _POSIX2_VERSION
9906 On older systems, @command{touch} supports an obsolete syntax, as follows.
9907 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9908 @option{-t} options, and if there are two or more @var{file}s and the
9909 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
9910 would be a valid argument to the @option{-t} option (if the @var{yy}, if
9911 any, were moved to the front), and if the represented year
9912 is in the range 1969--1999, that argument is interpreted as the time
9913 for the other files instead of as a file name.
9914 This obsolete behavior can be enabled or disabled with the
9915 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
9916 conformance}), but portable scripts should avoid commands whose
9917 behavior depends on this variable.
9918 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
9919 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
9929 No disk can hold an infinite amount of data. These commands report
9930 how much disk storage is in use or available, report other file and
9931 file status information, and write buffers to disk.
9934 * df invocation:: Report file system disk space usage.
9935 * du invocation:: Estimate file space usage.
9936 * stat invocation:: Report file or file system status.
9937 * sync invocation:: Synchronize memory and disk.
9938 * truncate invocation:: Shrink or extend the size of a file.
9943 @section @command{df}: Report file system disk space usage
9946 @cindex file system disk usage
9947 @cindex disk usage by file system
9949 @command{df} reports the amount of disk space used and available on
9950 file systems. Synopsis:
9953 df [@var{option}]@dots{} [@var{file}]@dots{}
9956 With no arguments, @command{df} reports the space used and available on all
9957 currently mounted file systems (of all types). Otherwise, @command{df}
9958 reports on the file system containing each argument @var{file}.
9960 Normally the disk space is printed in units of
9961 1024 bytes, but this can be overridden (@pxref{Block size}).
9962 Non-integer quantities are rounded up to the next higher unit.
9964 @cindex disk device file
9965 @cindex device file, disk
9966 If an argument @var{file} is a disk device file containing a mounted
9967 file system, @command{df} shows the space available on that file system
9968 rather than on the file system containing the device node (i.e., the root
9969 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
9970 on unmounted file systems, because on most kinds of systems doing so
9971 requires extremely nonportable intimate knowledge of file system
9974 The program accepts the following options. Also see @ref{Common options}.
9982 @cindex automounter file systems
9983 @cindex ignore file systems
9984 Include in the listing dummy file systems, which
9985 are omitted by default. Such file systems are typically special-purpose
9986 pseudo-file-systems, such as automounter entries.
9989 @itemx --block-size=@var{size}
9991 @opindex --block-size
9992 @cindex file system sizes
9993 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9994 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9998 @cindex grand total of disk size, usage and available space
9999 Print a grand total of all arguments after all arguments have
10000 been processed. This can be used to find out the total disk size, usage
10001 and available space of all listed devices.
10007 Equivalent to @option{--si}.
10013 @cindex inode usage
10014 List inode usage information instead of block usage. An inode (short
10015 for index node) contains information about a file such as its owner,
10016 permissions, timestamps, and location on the disk.
10020 @cindex kibibytes for file system sizes
10021 Print sizes in 1024-byte blocks, overriding the default block size
10022 (@pxref{Block size}).
10023 This option is equivalent to @option{--block-size=1K}.
10029 @cindex file system types, limiting output to certain
10030 Limit the listing to local file systems. By default, remote file systems
10035 @cindex file system space, retrieving old data more quickly
10036 Do not invoke the @code{sync} system call before getting any usage data.
10037 This may make @command{df} run significantly faster on systems with many
10038 disks, but on some systems (notably SunOS) the results may be slightly
10039 out of date. This is the default.
10042 @itemx --portability
10044 @opindex --portability
10045 @cindex one-line output format
10046 @cindex @acronym{POSIX} output format
10047 @cindex portable output format
10048 @cindex output format, portable
10049 Use the @acronym{POSIX} output format. This is like the default format except
10054 The information about each file system is always printed on exactly
10055 one line; a mount device is never put on a line by itself. This means
10056 that if the mount device name is more than 20 characters long (e.g., for
10057 some network mounts), the columns are misaligned.
10060 The labels in the header output line are changed to conform to @acronym{POSIX}.
10063 The default block size and output format are unaffected by the
10064 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10065 variables. However, the default block size is still affected by
10066 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10067 otherwise. @xref{Block size}.
10074 @cindex file system space, retrieving current data more slowly
10075 Invoke the @code{sync} system call before getting any usage data. On
10076 some systems (notably SunOS), doing this yields more up to date results,
10077 but in general this option makes @command{df} much slower, especially when
10078 there are many or very busy file systems.
10080 @item -t @var{fstype}
10081 @itemx --type=@var{fstype}
10084 @cindex file system types, limiting output to certain
10085 Limit the listing to file systems of type @var{fstype}. Multiple
10086 file system types can be specified by giving multiple @option{-t} options.
10087 By default, nothing is omitted.
10090 @itemx --print-type
10092 @opindex --print-type
10093 @cindex file system types, printing
10094 Print each file system's type. The types printed here are the same ones
10095 you can include or exclude with @option{-t} and @option{-x}. The particular
10096 types printed are whatever is supported by the system. Here are some of
10097 the common names (this list is certainly not exhaustive):
10102 @cindex @acronym{NFS} file system type
10103 An @acronym{NFS} file system, i.e., one mounted over a network from another
10104 machine. This is the one type name which seems to be used uniformly by
10107 @item 4.2@r{, }ufs@r{, }efs@dots{}
10108 @cindex Linux file system types
10109 @cindex local file system types
10110 @opindex 4.2 @r{file system type}
10111 @opindex ufs @r{file system type}
10112 @opindex efs @r{file system type}
10113 A file system on a locally-mounted hard disk. (The system might even
10114 support more than one type here; Linux does.)
10116 @item hsfs@r{, }cdfs
10117 @cindex CD-ROM file system type
10118 @cindex High Sierra file system
10119 @opindex hsfs @r{file system type}
10120 @opindex cdfs @r{file system type}
10121 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10122 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10125 @cindex PC file system
10126 @cindex DOS file system
10127 @cindex MS-DOS file system
10128 @cindex diskette file system
10130 An MS-DOS file system, usually on a diskette.
10134 @item -x @var{fstype}
10135 @itemx --exclude-type=@var{fstype}
10137 @opindex --exclude-type
10138 Limit the listing to file systems not of type @var{fstype}.
10139 Multiple file system types can be eliminated by giving multiple
10140 @option{-x} options. By default, no file system types are omitted.
10143 Ignored; for compatibility with System V versions of @command{df}.
10148 Failure includes the case where no output is generated, so you can
10149 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10150 @var{dir}} to test whether @var{dir} is on a file system of type
10151 @samp{ext3} or @samp{reiserfs}.
10154 @node du invocation
10155 @section @command{du}: Estimate file space usage
10158 @cindex file space usage
10159 @cindex disk usage for files
10161 @command{du} reports the amount of disk space used by the specified files
10162 and for each subdirectory (of directory arguments). Synopsis:
10165 du [@var{option}]@dots{} [@var{file}]@dots{}
10168 With no arguments, @command{du} reports the disk space for the current
10169 directory. Normally the disk space is printed in units of
10170 1024 bytes, but this can be overridden (@pxref{Block size}).
10171 Non-integer quantities are rounded up to the next higher unit.
10173 If two or more hard links point to the same file, only one of the hard
10174 links is counted. The @var{file} argument order affects which links
10175 are counted, and changing the argument order may change the numbers
10176 that @command{du} outputs.
10178 The program accepts the following options. Also see @ref{Common options}.
10186 Show counts for all files, not just directories.
10188 @itemx --apparent-size
10189 @opindex --apparent-size
10190 Print apparent sizes, rather than disk usage. The apparent size of a
10191 file is the number of bytes reported by @code{wc -c} on regular files,
10192 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10193 For example, a file containing the word @samp{zoo} with no newline would,
10194 of course, have an apparent size of 3. Such a small file may require
10195 anywhere from 0 to 16 KiB or more of disk space, depending on
10196 the type and configuration of the file system on which the file resides.
10197 However, a sparse file created with this command:
10200 dd bs=1 seek=2GiB if=/dev/null of=big
10204 has an apparent size of 2 GiB, yet on most modern
10205 systems, it actually uses almost no disk space.
10211 Equivalent to @code{--apparent-size --block-size=1}.
10213 @item -B @var{size}
10214 @itemx --block-size=@var{size}
10216 @opindex --block-size
10218 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10219 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10225 @cindex grand total of disk space
10226 Print a grand total of all arguments after all arguments have
10227 been processed. This can be used to find out the total disk usage of
10228 a given set of files or directories.
10231 @itemx --dereference-args
10233 @opindex --dereference-args
10234 Dereference symbolic links that are command line arguments.
10235 Does not affect other symbolic links. This is helpful for finding
10236 out the disk usage of directories, such as @file{/usr/tmp}, which
10237 are often symbolic links.
10239 @c --files0-from=FILE
10240 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10246 Equivalent to @option{--dereference-args} (@option{-D}).
10250 @cindex kibibytes for file sizes
10251 Print sizes in 1024-byte blocks, overriding the default block size
10252 (@pxref{Block size}).
10253 This option is equivalent to @option{--block-size=1K}.
10256 @itemx --count-links
10258 @opindex --count-links
10259 @cindex hard links, counting in @command{du}
10260 Count the size of all files, even if they have appeared already (as a
10264 @itemx --dereference
10266 @opindex --dereference
10267 @cindex symbolic links, dereferencing in @command{du}
10268 Dereference symbolic links (show the disk space used by the file
10269 or directory that the link points to instead of the space used by
10274 @cindex mebibytes for file sizes
10275 Print sizes in 1,048,576-byte blocks, overriding the default block size
10276 (@pxref{Block size}).
10277 This option is equivalent to @option{--block-size=1M}.
10280 @itemx --no-dereference
10282 @opindex --no-dereference
10283 @cindex symbolic links, dereferencing in @command{du}
10284 For each symbolic links encountered by @command{du},
10285 consider the disk space used by the symbolic link.
10287 @item --max-depth=@var{depth}
10288 @opindex --max-depth=@var{depth}
10289 @cindex limiting output of @command{du}
10290 Show the total for each directory (and file if --all) that is at
10291 most MAX_DEPTH levels down from the root of the hierarchy. The root
10292 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10298 @cindex output null-byte-terminated lines
10299 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
10300 rather than a newline. This option enables other programs to parse the
10301 output of @command{du} even when that output would contain file names
10302 with embedded newlines.
10309 @opindex --summarize
10310 Display only a total for each argument.
10313 @itemx --separate-dirs
10315 @opindex --separate-dirs
10316 Normally, in the output of @command{du} (when not using @option{--summarize}),
10317 the size listed next to a directory name, @var{d}, represents the sum
10318 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10319 With @option{--separate-dirs}, the size reported for a directory name,
10320 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10325 @cindex last modified dates, displaying in @command{du}
10326 Show time of the most recent modification of any file in the directory,
10327 or any of its subdirectories.
10329 @itemx --time=ctime
10330 @itemx --time=status
10333 @opindex ctime@r{, show the most recent}
10334 @opindex status time@r{, show the most recent}
10335 @opindex use time@r{, show the most recent}
10336 Show the most recent status change time (the @samp{ctime} in the inode) of
10337 any file in the directory, instead of the modification time.
10339 @itemx --time=atime
10340 @itemx --time=access
10342 @opindex atime@r{, show the most recent}
10343 @opindex access time@r{, show the most recent}
10344 Show the most recent access time (the @samp{atime} in the inode) of
10345 any file in the directory, instead of the modification time.
10347 @item --time-style=@var{style}
10348 @opindex --time-style
10350 List timestamps in style @var{style}. This option has an effect only if
10351 the @option{--time} option is also specified. The @var{style} should
10352 be one of the following:
10355 @item +@var{format}
10357 List timestamps using @var{format}, where @var{format} is interpreted
10358 like the format argument of @command{date} (@pxref{date invocation}).
10359 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10360 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10361 with @command{date}, @var{format}'s interpretation is affected by the
10362 @env{LC_TIME} locale category.
10365 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10366 format with nanosecond precision, e.g., @samp{2002-03-30
10367 23:45:56.477817180 -0700}. This style is equivalent to
10368 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10371 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10372 @samp{2002-03-30 23:45}. These timestamps are shorter than
10373 @samp{full-iso} timestamps, and are usually good enough for everyday
10374 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10377 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10378 This style is equivalent to @samp{+%Y-%m-%d}.
10382 You can specify the default value of the @option{--time-style} option
10383 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10384 the default style is @samp{long-iso}. For compatibility with @command{ls},
10385 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10386 the newline and any later characters are ignored; if @env{TIME_STYLE}
10387 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10388 @env{TIME_STYLE} is @samp{locale} it is ignored.
10391 @itemx --one-file-system
10393 @opindex --one-file-system
10394 @cindex one file system, restricting @command{du} to
10395 Skip directories that are on different file systems from the one that
10396 the argument being processed is on.
10398 @item --exclude=@var{pattern}
10399 @opindex --exclude=@var{pattern}
10400 @cindex excluding files from @command{du}
10401 When recursing, skip subdirectories or files matching @var{pattern}.
10402 For example, @code{du --exclude='*.o'} excludes files whose names
10405 @item -X @var{file}
10406 @itemx --exclude-from=@var{file}
10407 @opindex -X @var{file}
10408 @opindex --exclude-from=@var{file}
10409 @cindex excluding files from @command{du}
10410 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10411 one per line. If @var{file} is @samp{-}, take the patterns from standard
10416 @cindex NFS mounts from BSD to HP-UX
10417 On BSD systems, @command{du} reports sizes that are half the correct
10418 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10419 systems, it reports sizes that are twice the correct values for
10420 files that are NFS-mounted from BSD systems. This is due to a flaw
10421 in HP-UX; it also affects the HP-UX @command{du} program.
10426 @node stat invocation
10427 @section @command{stat}: Report file or file system status
10430 @cindex file status
10431 @cindex file system status
10433 @command{stat} displays information about the specified file(s). Synopsis:
10436 stat [@var{option}]@dots{} [@var{file}]@dots{}
10439 With no option, @command{stat} reports all information about the given files.
10440 But it also can be used to report the information of the file systems the
10441 given files are located on. If the files are links, @command{stat} can
10442 also give information about the files the links point to.
10444 @mayConflictWithShellBuiltIn{stat}
10449 @itemx --dereference
10451 @opindex --dereference
10452 @cindex symbolic links, dereferencing in @command{stat}
10453 Change how @command{stat} treats symbolic links.
10454 With this option, @command{stat} acts on the file referenced
10455 by each symbolic link argument.
10456 Without it, @command{stat} acts on any symbolic link argument directly.
10459 @itemx --file-system
10461 @opindex --file-system
10462 @cindex file systems
10463 Report information about the file systems where the given files are located
10464 instead of information about the files themselves.
10467 @itemx --format=@var{format}
10469 @opindex --format=@var{format}
10470 @cindex output format
10471 Use @var{format} rather than the default format.
10472 @var{format} is automatically newline-terminated, so
10473 running a command like the following with two or more @var{file}
10474 operands produces a line of output for each operand:
10476 $ stat --format=%d:%i / /usr
10481 @itemx --printf=@var{format}
10482 @opindex --printf=@var{format}
10483 @cindex output format
10484 Use @var{format} rather than the default format.
10485 Like @option{--format}, but interpret backslash escapes,
10486 and do not output a mandatory trailing newline.
10487 If you want a newline, include @samp{\n} in the @var{format}.
10488 Here's how you would use @option{--printf} to print the device
10489 and inode numbers of @file{/} and @file{/usr}:
10491 $ stat --printf='%d:%i\n' / /usr
10500 @cindex terse output
10501 Print the information in terse form, suitable for parsing by other programs.
10505 The valid @var{format} directives for files with @option{--format} and
10506 @option{--printf} are:
10509 @item %a - Access rights in octal
10510 @item %A - Access rights in human readable form
10511 @item %b - Number of blocks allocated (see @samp{%B})
10512 @item %B - The size in bytes of each block reported by @samp{%b}
10513 @item %d - Device number in decimal
10514 @item %D - Device number in hex
10515 @item %f - Raw mode in hex
10516 @item %F - File type
10517 @item %g - Group ID of owner
10518 @item %G - Group name of owner
10519 @item %h - Number of hard links
10520 @item %i - Inode number
10521 @item %n - File name
10522 @item %N - Quoted file name with dereference if symbolic link
10523 @item %o - I/O block size
10524 @item %s - Total size, in bytes
10525 @item %t - Major device type in hex
10526 @item %T - Minor device type in hex
10527 @item %u - User ID of owner
10528 @item %U - User name of owner
10529 @item %x - Time of last access
10530 @item %X - Time of last access as seconds since Epoch
10531 @item %y - Time of last modification
10532 @item %Y - Time of last modification as seconds since Epoch
10533 @item %z - Time of last change
10534 @item %Z - Time of last change as seconds since Epoch
10537 When listing file system information (@option{--file-system} (@option{-f})),
10538 you must use a different set of @var{format} directives:
10541 @item %a - Free blocks available to non-super-user
10542 @item %b - Total data blocks in file system
10543 @item %c - Total file nodes in file system
10544 @item %d - Free file nodes in file system
10545 @item %f - Free blocks in file system
10546 @item %i - File System ID in hex
10547 @item %l - Maximum length of file names
10548 @item %n - File name
10549 @item %s - Block size (for faster transfers)
10550 @item %S - Fundamental block size (for block counts)
10551 @item %t - Type in hex
10552 @item %T - Type in human readable form
10556 Time stamps are listed according to the time zone rules specified by
10557 the @env{TZ} environment variable, or by the system default rules if
10558 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10559 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10564 @node sync invocation
10565 @section @command{sync}: Synchronize data on disk with memory
10568 @cindex synchronize disk and memory
10570 @cindex superblock, writing
10571 @cindex inodes, written buffered
10572 @command{sync} writes any data buffered in memory out to disk. This can
10573 include (but is not limited to) modified superblocks, modified inodes,
10574 and delayed reads and writes. This must be implemented by the kernel;
10575 The @command{sync} program does nothing but exercise the @code{sync} system
10578 @cindex crashes and corruption
10579 The kernel keeps data in memory to avoid doing (relatively slow) disk
10580 reads and writes. This improves performance, but if the computer
10581 crashes, data may be lost or the file system corrupted as a
10582 result. The @command{sync} command ensures everything in memory
10583 is written to disk.
10585 Any arguments are ignored, except for a lone @option{--help} or
10586 @option{--version} (@pxref{Common options}).
10591 @node truncate invocation
10592 @section @command{truncate}: Shrink or extend the size of a file
10595 @cindex truncating, file sizes
10597 @command{truncate} shrinks or extends the size of each @var{file} to the
10598 specified size. Synopsis:
10601 truncate @var{option}@dots{} @var{file}@dots{}
10604 @cindex files, creating
10605 Any @var{file} that does not exist is created.
10607 @cindex sparse files, creating
10608 @cindex holes, creating files with
10609 If a @var{file} is larger than the specified size, the extra data is lost.
10610 If a @var{file} is shorter, it is extended and the extended part (or hole)
10611 reads as zero bytes.
10613 The program accepts the following options. Also see @ref{Common options}.
10620 @opindex --no-create
10621 Do not create files that do not exist.
10626 @opindex --io-blocks
10627 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10629 @item -r @var{rfile}
10630 @itemx --reference=@var{rfile}
10632 @opindex --reference
10633 Set the size of each @var{file} to the same size as @var{rfile}.
10635 @item -s @var{size}
10636 @itemx --size=@var{size}
10639 Set the size of each @var{file} to this @var{size}.
10640 @multiplierSuffixesNoBlocks{size}
10642 @var{size} may also be prefixed by one of the following to adjust
10643 the size of each @var{file} based on their current size:
10645 @samp{+} => extend by
10646 @samp{-} => reduce by
10647 @samp{<} => at most
10648 @samp{>} => at least
10649 @samp{/} => round down to multiple of
10650 @samp{%} => round up to multiple of
10658 @node Printing text
10659 @chapter Printing text
10661 @cindex printing text, commands for
10662 @cindex commands for printing text
10664 This section describes commands that display text strings.
10667 * echo invocation:: Print a line of text.
10668 * printf invocation:: Format and print data.
10669 * yes invocation:: Print a string until interrupted.
10673 @node echo invocation
10674 @section @command{echo}: Print a line of text
10677 @cindex displaying text
10678 @cindex printing text
10679 @cindex text, displaying
10680 @cindex arbitrary text, displaying
10682 @command{echo} writes each given @var{string} to standard output, with a
10683 space between each and a newline after the last one. Synopsis:
10686 echo [@var{option}]@dots{} [@var{string}]@dots{}
10689 @mayConflictWithShellBuiltIn{echo}
10691 The program accepts the following options. Also see @ref{Common options}.
10692 Options must precede operands, and the normally-special argument
10693 @samp{--} has no special meaning and is treated like any other
10699 Do not output the trailing newline.
10703 @cindex backslash escapes
10704 Enable interpretation of the following backslash-escaped characters in
10713 produce no further output
10727 the eight-bit value that is the octal number @var{nnn}
10728 (zero to three octal digits)
10730 the eight-bit value that is the octal number @var{nnn}
10731 (one to three octal digits)
10733 the eight-bit value that is the hexadecimal number @var{hh}
10734 (one or two hexadecimal digits)
10739 @cindex backslash escapes
10740 Disable interpretation of backslash escapes in each @var{string}.
10741 This is the default. If @option{-e} and @option{-E} are both
10742 specified, the last one given takes effect.
10746 @vindex POSIXLY_CORRECT
10747 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10748 @command{echo}'s first argument is not @option{-n} it outputs
10749 option-like arguments instead of treating them as options. For
10750 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10751 plain @samp{hello}.
10753 @acronym{POSIX} does not require support for any options, and says
10754 that the behavior of @command{echo} is implementation-defined if any
10755 @var{string} contains a backslash or if the first argument is
10756 @option{-n}. Portable programs can use the @command{printf} command
10757 if they need to omit trailing newlines or output control characters or
10758 backslashes. @xref{printf invocation}.
10763 @node printf invocation
10764 @section @command{printf}: Format and print data
10767 @command{printf} does formatted printing of text. Synopsis:
10770 printf @var{format} [@var{argument}]@dots{}
10773 @command{printf} prints the @var{format} string, interpreting @samp{%}
10774 directives and @samp{\} escapes to format numeric and string arguments
10775 in a way that is mostly similar to the C @samp{printf} function.
10776 @xref{Output Conversion Syntax,, @command{printf} format directives,
10777 libc, The GNU C Library Reference Manual}, for details.
10778 The differences are listed below.
10780 @mayConflictWithShellBuiltIn{printf}
10785 The @var{format} argument is reused as necessary to convert all the
10786 given @var{argument}s. For example, the command @samp{printf %s a b}
10790 Missing @var{argument}s are treated as null strings or as zeros,
10791 depending on whether the context expects a string or a number. For
10792 example, the command @samp{printf %sx%d} prints @samp{x0}.
10796 An additional escape, @samp{\c}, causes @command{printf} to produce no
10797 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10798 E} prints @samp{ABC}.
10801 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10802 digits, as opposed to C where it can have an unlimited number of
10803 digits. For example, the command @samp{printf '\x07e'} prints two
10804 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10809 @command{printf} has an additional directive, @samp{%b}, which prints its
10810 argument string with @samp{\} escapes interpreted in the same way as in
10811 the @var{format} string, except that octal escapes are of the form
10812 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10813 If a precision is also given, it limits the number of bytes printed
10814 from the converted string.
10817 Numeric arguments must be single C constants, possibly with leading
10818 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10822 @vindex POSIXLY_CORRECT
10823 If the leading character of a numeric argument is @samp{"} or @samp{'}
10824 then its value is the numeric value of the immediately following
10825 character. Any remaining characters are silently ignored if the
10826 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10827 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10828 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10829 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10834 A floating-point argument must use a period before any fractional
10835 digits, but is printed according to the @env{LC_NUMERIC} category of the
10836 current locale. For example, in a locale whose radix character is a
10837 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10838 the command @samp{printf %g 3,14} is an error.
10842 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10843 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10844 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10845 digits) specifying a character to print.
10850 @cindex ISO/IEC 10646
10852 @command{printf} interprets two character syntaxes introduced in
10853 @acronym{ISO} C 99:
10854 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10855 characters, specified as
10856 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10857 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10858 @command{printf} outputs the Unicode characters
10859 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10860 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10861 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10863 The processing of @samp{\u} and @samp{\U} requires a full-featured
10864 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10865 or when @code{libiconv} is installed prior to this package. Otherwise
10866 @samp{\u} and @samp{\U} will print as-is.
10868 The only options are a lone @option{--help} or
10869 @option{--version}. @xref{Common options}.
10870 Options must precede operands.
10872 The Unicode character syntaxes are useful for writing strings in a locale
10873 independent way. For example, a string containing the Euro currency symbol
10876 $ env printf '\u20AC 14.95'
10880 will be output correctly in all locales supporting the Euro symbol
10881 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10884 $ env printf '\u4e2d\u6587'
10888 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10890 Note that in these examples, the @command{printf} command has been
10891 invoked via @command{env} to ensure that we run the program found via
10892 your shell's search path, and not a shell alias or a built-in function.
10894 For larger strings, you don't need to look up the hexadecimal code
10895 values of each character one by one. @acronym{ASCII} characters mixed with \u
10896 escape sequences is also known as the JAVA source file encoding. You can
10897 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10898 is how to convert a piece of text into a shell script which will output
10899 this text in a locale-independent way:
10902 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10903 '\u4e2d\u6587\n' > sample.txt
10904 $ recode BIG5..JAVA < sample.txt \
10905 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10912 @node yes invocation
10913 @section @command{yes}: Print a string until interrupted
10916 @cindex repeated output of a string
10918 @command{yes} prints the command line arguments, separated by spaces and
10919 followed by a newline, forever until it is killed. If no arguments are
10920 given, it prints @samp{y} followed by a newline forever until killed.
10922 Upon a write error, @command{yes} exits with status @samp{1}.
10924 The only options are a lone @option{--help} or @option{--version}.
10925 To output an argument that begins with
10926 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
10927 @xref{Common options}.
10931 @chapter Conditions
10934 @cindex commands for exit status
10935 @cindex exit status commands
10937 This section describes commands that are primarily useful for their exit
10938 status, rather than their output. Thus, they are often used as the
10939 condition of shell @code{if} statements, or as the last command in a
10943 * false invocation:: Do nothing, unsuccessfully.
10944 * true invocation:: Do nothing, successfully.
10945 * test invocation:: Check file types and compare values.
10946 * expr invocation:: Evaluate expressions.
10950 @node false invocation
10951 @section @command{false}: Do nothing, unsuccessfully
10954 @cindex do nothing, unsuccessfully
10955 @cindex failure exit status
10956 @cindex exit status of @command{false}
10958 @command{false} does nothing except return an exit status of 1, meaning
10959 @dfn{failure}. It can be used as a place holder in shell scripts
10960 where an unsuccessful command is needed.
10961 In most modern shells, @command{false} is a built-in command, so when
10962 you use @samp{false} in a script, you're probably using the built-in
10963 command, not the one documented here.
10965 @command{false} honors the @option{--help} and @option{--version} options.
10967 This version of @command{false} is implemented as a C program, and is thus
10968 more secure and faster than a shell script implementation, and may safely
10969 be used as a dummy shell for the purpose of disabling accounts.
10971 Note that @command{false} (unlike all other programs documented herein)
10972 exits unsuccessfully, even when invoked with
10973 @option{--help} or @option{--version}.
10975 Portable programs should not assume that the exit status of
10976 @command{false} is 1, as it is greater than 1 on some
10977 non-@acronym{GNU} hosts.
10980 @node true invocation
10981 @section @command{true}: Do nothing, successfully
10984 @cindex do nothing, successfully
10986 @cindex successful exit
10987 @cindex exit status of @command{true}
10989 @command{true} does nothing except return an exit status of 0, meaning
10990 @dfn{success}. It can be used as a place holder in shell scripts
10991 where a successful command is needed, although the shell built-in
10992 command @code{:} (colon) may do the same thing faster.
10993 In most modern shells, @command{true} is a built-in command, so when
10994 you use @samp{true} in a script, you're probably using the built-in
10995 command, not the one documented here.
10997 @command{true} honors the @option{--help} and @option{--version} options.
10999 Note, however, that it is possible to cause @command{true}
11000 to exit with nonzero status: with the @option{--help} or @option{--version}
11001 option, and with standard
11002 output already closed or redirected to a file that evokes an I/O error.
11003 For example, using a Bourne-compatible shell:
11006 $ ./true --version >&-
11007 ./true: write error: Bad file number
11008 $ ./true --version > /dev/full
11009 ./true: write error: No space left on device
11012 This version of @command{true} is implemented as a C program, and is thus
11013 more secure and faster than a shell script implementation, and may safely
11014 be used as a dummy shell for the purpose of disabling accounts.
11016 @node test invocation
11017 @section @command{test}: Check file types and compare values
11020 @cindex check file types
11021 @cindex compare values
11022 @cindex expression evaluation
11024 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11025 evaluation of the conditional expression @var{expr}. Each part of the
11026 expression must be a separate argument.
11028 @command{test} has file status checks, string operators, and numeric
11029 comparison operators.
11031 @command{test} has an alternate form that uses opening and closing
11032 square brackets instead a leading @samp{test}. For example, instead
11033 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11034 brackets must be separate arguments; for example, @samp{[-d /]} does
11035 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11036 @var{expr} ]} have the same meaning, only the former form is discussed
11042 test @var{expression}
11044 [ @var{expression} ]
11049 @mayConflictWithShellBuiltIn{test}
11051 If @var{expression} is omitted, @command{test} returns false.
11052 If @var{expression} is a single argument,
11053 @command{test} returns false if the argument is null and true otherwise. The argument
11054 can be any string, including strings like @samp{-d}, @samp{-1},
11055 @samp{--}, @samp{--help}, and @samp{--version} that most other
11056 programs would treat as options. To get help and version information,
11057 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11058 the usual closing brackets. @xref{Common options}.
11060 @cindex exit status of @command{test}
11064 0 if the expression is true,
11065 1 if the expression is false,
11066 2 if an error occurred.
11070 * File type tests:: -[bcdfhLpSt]
11071 * Access permission tests:: -[gkruwxOG]
11072 * File characteristic tests:: -e -s -nt -ot -ef
11073 * String tests:: -z -n = !=
11074 * Numeric tests:: -eq -ne -lt -le -gt -ge
11075 * Connectives for test:: ! -a -o
11079 @node File type tests
11080 @subsection File type tests
11082 @cindex file type tests
11084 These options test for particular types of files. (Everything's a file,
11085 but not all files are the same!)
11089 @item -b @var{file}
11091 @cindex block special check
11092 True if @var{file} exists and is a block special device.
11094 @item -c @var{file}
11096 @cindex character special check
11097 True if @var{file} exists and is a character special device.
11099 @item -d @var{file}
11101 @cindex directory check
11102 True if @var{file} exists and is a directory.
11104 @item -f @var{file}
11106 @cindex regular file check
11107 True if @var{file} exists and is a regular file.
11109 @item -h @var{file}
11110 @itemx -L @var{file}
11113 @cindex symbolic link check
11114 True if @var{file} exists and is a symbolic link.
11115 Unlike all other file-related tests, this test does not dereference
11116 @var{file} if it is a symbolic link.
11118 @item -p @var{file}
11120 @cindex named pipe check
11121 True if @var{file} exists and is a named pipe.
11123 @item -S @var{file}
11125 @cindex socket check
11126 True if @var{file} exists and is a socket.
11130 @cindex terminal check
11131 True if @var{fd} is a file descriptor that is associated with a
11137 @node Access permission tests
11138 @subsection Access permission tests
11140 @cindex access permission tests
11141 @cindex permission tests
11143 These options test for particular access permissions.
11147 @item -g @var{file}
11149 @cindex set-group-ID check
11150 True if @var{file} exists and has its set-group-ID bit set.
11152 @item -k @var{file}
11154 @cindex sticky bit check
11155 True if @var{file} exists and has its @dfn{sticky} bit set.
11157 @item -r @var{file}
11159 @cindex readable file check
11160 True if @var{file} exists and read permission is granted.
11162 @item -u @var{file}
11164 @cindex set-user-ID check
11165 True if @var{file} exists and has its set-user-ID bit set.
11167 @item -w @var{file}
11169 @cindex writable file check
11170 True if @var{file} exists and write permission is granted.
11172 @item -x @var{file}
11174 @cindex executable file check
11175 True if @var{file} exists and execute permission is granted
11176 (or search permission, if it is a directory).
11178 @item -O @var{file}
11180 @cindex owned by effective user ID check
11181 True if @var{file} exists and is owned by the current effective user ID.
11183 @item -G @var{file}
11185 @cindex owned by effective group ID check
11186 True if @var{file} exists and is owned by the current effective group ID.
11190 @node File characteristic tests
11191 @subsection File characteristic tests
11193 @cindex file characteristic tests
11195 These options test other file characteristics.
11199 @item -e @var{file}
11201 @cindex existence-of-file check
11202 True if @var{file} exists.
11204 @item -s @var{file}
11206 @cindex nonempty file check
11207 True if @var{file} exists and has a size greater than zero.
11209 @item @var{file1} -nt @var{file2}
11211 @cindex newer-than file check
11212 True if @var{file1} is newer (according to modification date) than
11213 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11215 @item @var{file1} -ot @var{file2}
11217 @cindex older-than file check
11218 True if @var{file1} is older (according to modification date) than
11219 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11221 @item @var{file1} -ef @var{file2}
11223 @cindex same file check
11224 @cindex hard link check
11225 True if @var{file1} and @var{file2} have the same device and inode
11226 numbers, i.e., if they are hard links to each other.
11232 @subsection String tests
11234 @cindex string tests
11236 These options test string characteristics. You may need to quote
11237 @var{string} arguments for the shell. For example:
11243 The quotes here prevent the wrong arguments from being passed to
11244 @command{test} if @samp{$V} is empty or contains special characters.
11248 @item -z @var{string}
11250 @cindex zero-length string check
11251 True if the length of @var{string} is zero.
11253 @item -n @var{string}
11254 @itemx @var{string}
11256 @cindex nonzero-length string check
11257 True if the length of @var{string} is nonzero.
11259 @item @var{string1} = @var{string2}
11261 @cindex equal string check
11262 True if the strings are equal.
11264 @item @var{string1} != @var{string2}
11266 @cindex not-equal string check
11267 True if the strings are not equal.
11272 @node Numeric tests
11273 @subsection Numeric tests
11275 @cindex numeric tests
11276 @cindex arithmetic tests
11278 Numeric relational operators. The arguments must be entirely numeric
11279 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11280 which evaluates to the length of @var{string}.
11284 @item @var{arg1} -eq @var{arg2}
11285 @itemx @var{arg1} -ne @var{arg2}
11286 @itemx @var{arg1} -lt @var{arg2}
11287 @itemx @var{arg1} -le @var{arg2}
11288 @itemx @var{arg1} -gt @var{arg2}
11289 @itemx @var{arg1} -ge @var{arg2}
11296 These arithmetic binary operators return true if @var{arg1} is equal,
11297 not-equal, less-than, less-than-or-equal, greater-than, or
11298 greater-than-or-equal than @var{arg2}, respectively.
11305 test -1 -gt -2 && echo yes
11307 test -l abc -gt 1 && echo yes
11310 @error{} test: integer expression expected before -eq
11314 @node Connectives for test
11315 @subsection Connectives for @command{test}
11317 @cindex logical connectives
11318 @cindex connectives, logical
11320 The usual logical connectives.
11326 True if @var{expr} is false.
11328 @item @var{expr1} -a @var{expr2}
11330 @cindex logical and operator
11331 @cindex and operator
11332 True if both @var{expr1} and @var{expr2} are true.
11334 @item @var{expr1} -o @var{expr2}
11336 @cindex logical or operator
11337 @cindex or operator
11338 True if either @var{expr1} or @var{expr2} is true.
11343 @node expr invocation
11344 @section @command{expr}: Evaluate expressions
11347 @cindex expression evaluation
11348 @cindex evaluation of expressions
11350 @command{expr} evaluates an expression and writes the result on standard
11351 output. Each token of the expression must be a separate argument.
11353 Operands are either integers or strings. Integers consist of one or
11354 more decimal digits, with an optional leading @samp{-}.
11355 @command{expr} converts
11356 anything appearing in an operand position to an integer or a string
11357 depending on the operation being applied to it.
11359 Strings are not quoted for @command{expr} itself, though you may need to
11360 quote them to protect characters with special meaning to the shell,
11361 e.g., spaces. However, regardless of whether it is quoted, a string
11362 operand should not be a parenthesis or any of @command{expr}'s
11363 operators like @code{+}, so you cannot safely pass an arbitrary string
11364 @code{$str} to expr merely by quoting it to the shell. One way to
11365 work around this is to use the @sc{gnu} extension @code{+},
11366 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11367 @code{@w{" $str"}} and to adjust the rest of the expression to take
11368 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11370 You should not pass a negative integer or a string with leading
11371 @samp{-} as @command{expr}'s first argument, as it might be
11372 misinterpreted as an option; this can be avoided by parenthesization.
11373 Also, portable scripts should not use a string operand that happens to
11374 take the form of an integer; this can be worked around by inserting
11375 leading spaces as mentioned above.
11377 @cindex parentheses for grouping
11378 Operators may be given as infix symbols or prefix keywords. Parentheses
11379 may be used for grouping in the usual manner. You must quote
11380 parentheses and many operators to avoid the shell evaluating them,
11383 When built with support for the GNU MP library, @command{expr} uses
11384 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11385 types and may fail due to arithmetic overflow.
11387 The only options are @option{--help} and @option{--version}. @xref{Common
11388 options}. Options must precede operands.
11390 @cindex exit status of @command{expr}
11394 0 if the expression is neither null nor 0,
11395 1 if the expression is null or 0,
11396 2 if the expression is invalid,
11397 3 if an internal error occurred (e.g., arithmetic overflow).
11401 * String expressions:: + : match substr index length
11402 * Numeric expressions:: + - * / %
11403 * Relations for expr:: | & < <= = == != >= >
11404 * Examples of expr:: Examples.
11408 @node String expressions
11409 @subsection String expressions
11411 @cindex string expressions
11412 @cindex expressions, string
11414 @command{expr} supports pattern matching and other string operators. These
11415 have higher precedence than both the numeric and relational operators (in
11416 the next sections).
11420 @item @var{string} : @var{regex}
11421 @cindex pattern matching
11422 @cindex regular expression matching
11423 @cindex matching patterns
11424 Perform pattern matching. The arguments are converted to strings and the
11425 second is considered to be a (basic, a la GNU @code{grep}) regular
11426 expression, with a @code{^} implicitly prepended. The first argument is
11427 then matched against this regular expression.
11429 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11430 @code{:} expression returns the part of @var{string} that matched the
11431 subexpression; otherwise, it returns the number of characters matched.
11433 If the match fails, the @code{:} operator returns the null string if
11434 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11436 @kindex \( @r{regexp operator}
11437 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11438 value; additional pairs are meaningful only for grouping the regular
11439 expression operators.
11441 @kindex \+ @r{regexp operator}
11442 @kindex \? @r{regexp operator}
11443 @kindex \| @r{regexp operator}
11444 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11445 operators which respectively match one or more, zero or one, or separate
11446 alternatives. SunOS and other @command{expr}'s treat these as regular
11447 characters. (@acronym{POSIX} allows either behavior.)
11448 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11449 regular expression syntax. Some examples are in @ref{Examples of expr}.
11451 @item match @var{string} @var{regex}
11453 An alternative way to do pattern matching. This is the same as
11454 @w{@samp{@var{string} : @var{regex}}}.
11456 @item substr @var{string} @var{position} @var{length}
11458 Returns the substring of @var{string} beginning at @var{position}
11459 with length at most @var{length}. If either @var{position} or
11460 @var{length} is negative, zero, or non-numeric, returns the null string.
11462 @item index @var{string} @var{charset}
11464 Returns the first position in @var{string} where the first character in
11465 @var{charset} was found. If no character in @var{charset} is found in
11466 @var{string}, return 0.
11468 @item length @var{string}
11470 Returns the length of @var{string}.
11472 @item + @var{token}
11474 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11475 or an operator like @code{/}.
11476 This makes it possible to test @code{expr length + "$x"} or
11477 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11478 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11479 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11480 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11484 To make @command{expr} interpret keywords as strings, you must use the
11485 @code{quote} operator.
11488 @node Numeric expressions
11489 @subsection Numeric expressions
11491 @cindex numeric expressions
11492 @cindex expressions, numeric
11494 @command{expr} supports the usual numeric operators, in order of increasing
11495 precedence. These numeric operators have lower precedence than the
11496 string operators described in the previous section, and higher precedence
11497 than the connectives (next section).
11505 @cindex subtraction
11506 Addition and subtraction. Both arguments are converted to integers;
11507 an error occurs if this cannot be done.
11513 @cindex multiplication
11516 Multiplication, division, remainder. Both arguments are converted to
11517 integers; an error occurs if this cannot be done.
11522 @node Relations for expr
11523 @subsection Relations for @command{expr}
11525 @cindex connectives, logical
11526 @cindex logical connectives
11527 @cindex relations, numeric or string
11529 @command{expr} supports the usual logical connectives and relations. These
11530 have lower precedence than the string and numeric operators
11531 (previous sections). Here is the list, lowest-precedence operator first.
11537 @cindex logical or operator
11538 @cindex or operator
11539 Returns its first argument if that is neither null nor zero, otherwise
11540 its second argument if it is neither null nor zero, otherwise 0. It
11541 does not evaluate its second argument if its first argument is neither
11546 @cindex logical and operator
11547 @cindex and operator
11548 Return its first argument if neither argument is null or zero, otherwise
11549 0. It does not evaluate its second argument if its first argument is
11552 @item < <= = == != >= >
11559 @cindex comparison operators
11561 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11562 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11563 both arguments to integers and do a numeric comparison; if either
11564 conversion fails, it does a lexicographic comparison using the character
11565 collating sequence specified by the @env{LC_COLLATE} locale.
11570 @node Examples of expr
11571 @subsection Examples of using @command{expr}
11573 @cindex examples of @command{expr}
11574 Here are a few examples, including quoting for shell metacharacters.
11576 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11579 foo=`expr $foo + 1`
11582 To print the non-directory part of the file name stored in
11583 @code{$fname}, which need not contain a @code{/}:
11586 expr $fname : '.*/\(.*\)' '|' $fname
11589 An example showing that @code{\+} is an operator:
11597 expr abc : 'a\(.\)c'
11599 expr index abcdef cz
11602 @error{} expr: syntax error
11603 expr index + index a
11609 @chapter Redirection
11611 @cindex redirection
11612 @cindex commands for redirection
11614 Unix shells commonly provide several forms of @dfn{redirection}---ways
11615 to change the input source or output destination of a command. But one
11616 useful redirection is performed by a separate command, not by the shell;
11617 it's described here.
11620 * tee invocation:: Redirect output to multiple files or processes.
11624 @node tee invocation
11625 @section @command{tee}: Redirect output to multiple files or processes
11628 @cindex pipe fitting
11629 @cindex destinations, multiple output
11630 @cindex read from stdin and write to stdout and files
11632 The @command{tee} command copies standard input to standard output and also
11633 to any files given as arguments. This is useful when you want not only
11634 to send some data down a pipe, but also to save a copy. Synopsis:
11637 tee [@var{option}]@dots{} [@var{file}]@dots{}
11640 If a file being written to does not already exist, it is created. If a
11641 file being written to already exists, the data it previously contained
11642 is overwritten unless the @option{-a} option is used.
11644 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11645 input to standard output, but this is typically not that useful as the
11646 copies are interleaved.
11648 The program accepts the following options. Also see @ref{Common options}.
11655 Append standard input to the given files rather than overwriting
11659 @itemx --ignore-interrupts
11661 @opindex --ignore-interrupts
11662 Ignore interrupt signals.
11666 The @command{tee} command is useful when you happen to be transferring a large
11667 amount of data and also want to summarize that data without reading
11668 it a second time. For example, when you are downloading a DVD image,
11669 you often want to verify its signature or checksum right away.
11670 The inefficient way to do it is simply:
11673 wget http://example.com/some.iso && sha1sum some.iso
11676 One problem with the above is that it makes you wait for the
11677 download to complete before starting the time-consuming SHA1 computation.
11678 Perhaps even more importantly, the above requires reading
11679 the DVD image a second time (the first was from the network).
11681 The efficient way to do it is to interleave the download
11682 and SHA1 computation. Then, you'll get the checksum for
11683 free, because the entire process parallelizes so well:
11686 # slightly contrived, to demonstrate process substitution
11687 wget -O - http://example.com/dvd.iso \
11688 | tee >(sha1sum > dvd.sha1) > dvd.iso
11691 That makes @command{tee} write not just to the expected output file,
11692 but also to a pipe running @command{sha1sum} and saving the final
11693 checksum in a file named @file{dvd.sha1}.
11695 Note, however, that this example relies on a feature of modern shells
11696 called @dfn{process substitution}
11697 (the @samp{>(command)} syntax, above;
11698 @xref{Process Substitution,,Process Substitution, bashref,
11699 The Bash Reference Manual}.),
11700 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11701 but not with @command{/bin/sh}. So if you write code like this
11702 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11704 Since the above example writes to one file and one process,
11705 a more conventional and portable use of @command{tee} is even better:
11708 wget -O - http://example.com/dvd.iso \
11709 | tee dvd.iso | sha1sum > dvd.sha1
11712 You can extend this example to make @command{tee} write to two processes,
11713 computing MD5 and SHA1 checksums in parallel. In this case,
11714 process substitution is required:
11717 wget -O - http://example.com/dvd.iso \
11718 | tee >(sha1sum > dvd.sha1) \
11719 >(md5sum > dvd.md5) \
11723 This technique is also useful when you want to make a @emph{compressed}
11724 copy of the contents of a pipe.
11725 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11726 For a large hierarchy, @samp{du -ak} can run for a long time,
11727 and can easily produce terabytes of data, so you won't want to
11728 rerun the command unnecessarily. Nor will you want to save
11729 the uncompressed output.
11731 Doing it the inefficient way, you can't even start the GUI
11732 until after you've compressed all of the @command{du} output:
11735 du -ak | gzip -9 > /tmp/du.gz
11736 gzip -d /tmp/du.gz | xdiskusage -a
11739 With @command{tee} and process substitution, you start the GUI
11740 right away and eliminate the decompression completely:
11743 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11746 Finally, if you regularly create more than one type of
11747 compressed tarball at once, for example when @code{make dist} creates
11748 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11749 there may be a better way.
11750 Typical @command{automake}-generated @file{Makefile} rules create
11751 the two compressed tar archives with commands in sequence, like this
11752 (slightly simplified):
11755 tardir=your-pkg-M.N
11756 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11757 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11760 However, if the hierarchy you are archiving and compressing is larger
11761 than a couple megabytes, and especially if you are using a multi-processor
11762 system with plenty of memory, then you can do much better by reading the
11763 directory contents only once and running the compression programs in parallel:
11766 tardir=your-pkg-M.N
11767 tar chof - "$tardir" \
11768 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11769 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11775 @node File name manipulation
11776 @chapter File name manipulation
11778 @cindex file name manipulation
11779 @cindex manipulation of file names
11780 @cindex commands for file name manipulation
11782 This section describes commands that manipulate file names.
11785 * basename invocation:: Strip directory and suffix from a file name.
11786 * dirname invocation:: Strip non-directory suffix from a file name.
11787 * pathchk invocation:: Check file name validity and portability.
11791 @node basename invocation
11792 @section @command{basename}: Strip directory and suffix from a file name
11795 @cindex strip directory and suffix from file names
11796 @cindex directory, stripping from file names
11797 @cindex suffix, stripping from file names
11798 @cindex file names, stripping directory and suffix
11799 @cindex leading directory components, stripping
11801 @command{basename} removes any leading directory components from
11802 @var{name}. Synopsis:
11805 basename @var{name} [@var{suffix}]
11808 If @var{suffix} is specified and is identical to the end of @var{name},
11809 it is removed from @var{name} as well. Note that since trailing slashes
11810 are removed prior to suffix matching, @var{suffix} will do nothing if it
11811 contains slashes. @command{basename} prints the result on standard
11814 @c This test is used both here and in the section on dirname.
11815 @macro basenameAndDirname
11816 Together, @command{basename} and @command{dirname} are designed such
11817 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11818 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11819 for everything except file names containing a trailing newline.
11821 @basenameAndDirname
11823 @acronym{POSIX} allows the implementation to define the results if
11824 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11825 @command{basename} returns the empty string. In the latter case, the
11826 result is @samp{//} on platforms where @var{//} is distinct from
11827 @var{/}, and @samp{/} on platforms where there is no difference.
11829 The only options are @option{--help} and @option{--version}. @xref{Common
11830 options}. Options must precede operands.
11838 basename /usr/bin/sort
11841 basename include/stdio.h .h
11845 @node dirname invocation
11846 @section @command{dirname}: Strip non-directory suffix from a file name
11849 @cindex directory components, printing
11850 @cindex stripping non-directory suffix
11851 @cindex non-directory suffix, stripping
11853 @command{dirname} prints all but the final slash-delimited component of
11854 a string (presumably a file name). Synopsis:
11860 If @var{name} is a single component, @command{dirname} prints @samp{.}
11861 (meaning the current directory).
11863 @basenameAndDirname
11865 @acronym{POSIX} allows the implementation to define the results if
11866 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11867 result is @samp{//} on platforms where @var{//} is distinct from
11868 @var{/}, and @samp{/} on platforms where there is no difference.
11870 The only options are @option{--help} and @option{--version}. @xref{Common
11878 # Output "/usr/bin".
11879 dirname /usr/bin/sort
11886 @node pathchk invocation
11887 @section @command{pathchk}: Check file name validity and portability
11890 @cindex file names, checking validity and portability
11891 @cindex valid file names, checking for
11892 @cindex portable file names, checking for
11894 @command{pathchk} checks validity and portability of file names. Synopsis:
11897 pathchk [@var{option}]@dots{} @var{name}@dots{}
11900 For each @var{name}, @command{pathchk} prints an error message if any of
11901 these conditions is true:
11905 One of the existing directories in @var{name} does not have search
11906 (execute) permission,
11908 The length of @var{name} is larger than the maximum supported by the
11911 The length of one component of @var{name} is longer than
11912 its file system's maximum.
11915 A nonexistent @var{name} is not an error, so long a file with that
11916 name could be created under the above conditions.
11918 The program accepts the following options. Also see @ref{Common options}.
11919 Options must precede operands.
11925 Instead of performing checks based on the underlying file system,
11926 print an error message if any of these conditions is true:
11930 A file name is empty.
11933 A file name contains a character outside the @acronym{POSIX} portable file
11934 name character set, namely, the ASCII letters and digits, @samp{.},
11935 @samp{_}, @samp{-}, and @samp{/}.
11938 The length of a file name or one of its components exceeds the
11939 @acronym{POSIX} minimum limits for portability.
11944 Print an error message if a file name is empty, or if it contains a component
11945 that begins with @samp{-}.
11947 @item --portability
11948 @opindex --portability
11949 Print an error message if a file name is not portable to all @acronym{POSIX}
11950 hosts. This option is equivalent to @samp{-p -P}.
11954 @cindex exit status of @command{pathchk}
11958 0 if all specified file names passed all checks,
11963 @node Working context
11964 @chapter Working context
11966 @cindex working context
11967 @cindex commands for printing the working context
11969 This section describes commands that display or alter the context in
11970 which you are working: the current directory, the terminal settings, and
11971 so forth. See also the user-related commands in the next section.
11974 * pwd invocation:: Print working directory.
11975 * stty invocation:: Print or change terminal characteristics.
11976 * printenv invocation:: Print environment variables.
11977 * tty invocation:: Print file name of terminal on standard input.
11981 @node pwd invocation
11982 @section @command{pwd}: Print working directory
11985 @cindex print name of current directory
11986 @cindex current working directory, printing
11987 @cindex working directory, printing
11990 @command{pwd} prints the name of the current directory. Synopsis:
11993 pwd [@var{option}]@dots{}
11996 The program accepts the following options. Also see @ref{Common options}.
12003 If the contents of the environment variable @env{PWD} provide an
12004 absolute name of the current directory with no @samp{.} or @samp{..}
12005 components, but possibly with symbolic links, then output those
12006 contents. Otherwise, fall back to default @option{-P} handling.
12011 @opindex --physical
12012 Print a fully resolved name for the current directory. That is, all
12013 components of the printed name will be actual directory names---none
12014 will be symbolic links.
12017 @cindex symbolic links and @command{pwd}
12018 If @option{-L} and @option{-P} are both given, the last one takes
12019 precedence. If neither option is given, then this implementation uses
12020 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12021 environment variable is set.
12023 @mayConflictWithShellBuiltIn{pwd}
12028 @node stty invocation
12029 @section @command{stty}: Print or change terminal characteristics
12032 @cindex change or print terminal settings
12033 @cindex terminal settings
12034 @cindex line settings of terminal
12036 @command{stty} prints or changes terminal characteristics, such as baud rate.
12040 stty [@var{option}] [@var{setting}]@dots{}
12041 stty [@var{option}]
12044 If given no line settings, @command{stty} prints the baud rate, line
12045 discipline number (on systems that support it), and line settings
12046 that have been changed from the values set by @samp{stty sane}.
12047 By default, mode reading and setting are performed on the tty line
12048 connected to standard input, although this can be modified by the
12049 @option{--file} option.
12051 @command{stty} accepts many non-option arguments that change aspects of
12052 the terminal line operation, as described below.
12054 The program accepts the following options. Also see @ref{Common options}.
12061 Print all current settings in human-readable form. This option may not
12062 be used in combination with any line settings.
12064 @item -F @var{device}
12065 @itemx --file=@var{device}
12068 Set the line opened by the file name specified in @var{device} instead of
12069 the tty line connected to standard input. This option is necessary
12070 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12071 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12072 the @code{clocal} flag is not set. Hence, it is not always possible
12073 to allow the shell to open the device in the traditional manner.
12079 @cindex machine-readable @command{stty} output
12080 Print all current settings in a form that can be used as an argument to
12081 another @command{stty} command to restore the current settings. This option
12082 may not be used in combination with any line settings.
12086 Many settings can be turned off by preceding them with a @samp{-}.
12087 Such arguments are marked below with ``May be negated'' in their
12088 description. The descriptions themselves refer to the positive
12089 case, that is, when @emph{not} negated (unless stated otherwise,
12092 Some settings are not available on all @acronym{POSIX} systems, since they use
12093 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12094 description. On non-@acronym{POSIX} systems, those or other settings also may not
12095 be available, but it's not feasible to document all the variations: just
12101 * Control:: Control settings
12102 * Input:: Input settings
12103 * Output:: Output settings
12104 * Local:: Local settings
12105 * Combination:: Combination settings
12106 * Characters:: Special characters
12107 * Special:: Special settings
12112 @subsection Control settings
12114 @cindex control settings
12120 @cindex two-way parity
12121 Generate parity bit in output and expect parity bit in input.
12127 @cindex even parity
12128 Set odd parity (even if negated). May be negated.
12135 @cindex character size
12136 @cindex eight-bit characters
12137 Set character size to 5, 6, 7, or 8 bits.
12142 Send a hangup signal when the last process closes the tty. May be
12148 Use two stop bits per character (one if negated). May be negated.
12152 Allow input to be received. May be negated.
12156 @cindex modem control
12157 Disable modem control signals. May be negated.
12161 @cindex hardware flow control
12162 @cindex flow control, hardware
12163 @cindex RTS/CTS flow control
12164 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12169 @subsection Input settings
12171 @cindex input settings
12172 These settings control operations on data received from the terminal.
12177 @cindex breaks, ignoring
12178 Ignore break characters. May be negated.
12182 @cindex breaks, cause interrupts
12183 Make breaks cause an interrupt signal. May be negated.
12187 @cindex parity, ignoring
12188 Ignore characters with parity errors. May be negated.
12192 @cindex parity errors, marking
12193 Mark parity errors (with a 255-0-character sequence). May be negated.
12197 Enable input parity checking. May be negated.
12201 @cindex eight-bit input
12202 Clear high (8th) bit of input characters. May be negated.
12206 @cindex newline, translating to return
12207 Translate newline to carriage return. May be negated.
12211 @cindex return, ignoring
12212 Ignore carriage return. May be negated.
12216 @cindex return, translating to newline
12217 Translate carriage return to newline. May be negated.
12221 @cindex input encoding, UTF-8
12222 Assume input characters are UTF-8 encoded. May be negated.
12226 @kindex C-s/C-q flow control
12227 @cindex XON/XOFF flow control
12228 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12235 @cindex software flow control
12236 @cindex flow control, software
12237 Enable sending of @code{stop} character when the system input buffer
12238 is almost full, and @code{start} character when it becomes almost
12239 empty again. May be negated.
12243 @cindex uppercase, translating to lowercase
12244 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12245 negated. Note ilcuc is not implemented, as one would not be able to issue
12246 almost any (lowercase) Unix command, after invoking it.
12250 Allow any character to restart output (only the start character
12251 if negated). Non-@acronym{POSIX}. May be negated.
12255 @cindex beeping at input buffer full
12256 Enable beeping and not flushing input buffer if a character arrives
12257 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12262 @subsection Output settings
12264 @cindex output settings
12265 These settings control operations on data sent to the terminal.
12270 Postprocess output. May be negated.
12274 @cindex lowercase, translating to output
12275 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12276 negated. (Note ouclc is not currently implemented.)
12280 @cindex return, translating to newline
12281 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12285 @cindex newline, translating to crlf
12286 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12291 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12296 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12300 @cindex pad instead of timing for delaying
12301 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12306 @cindex pad character
12307 Use @acronym{ASCII} @sc{del} characters for fill instead of
12308 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12314 Newline delay style. Non-@acronym{POSIX}.
12321 Carriage return delay style. Non-@acronym{POSIX}.
12327 @opindex tab@var{n}
12328 Horizontal tab delay style. Non-@acronym{POSIX}.
12333 Backspace delay style. Non-@acronym{POSIX}.
12338 Vertical tab delay style. Non-@acronym{POSIX}.
12343 Form feed delay style. Non-@acronym{POSIX}.
12348 @subsection Local settings
12350 @cindex local settings
12355 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12356 characters. May be negated.
12360 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12361 special characters. May be negated.
12365 Enable non-@acronym{POSIX} special characters. May be negated.
12369 Echo input characters. May be negated.
12375 Echo @code{erase} characters as backspace-space-backspace. May be
12380 @cindex newline echoing after @code{kill}
12381 Echo a newline after a @code{kill} character. May be negated.
12385 @cindex newline, echoing
12386 Echo newline even if not echoing other characters. May be negated.
12390 @cindex flushing, disabling
12391 Disable flushing after @code{interrupt} and @code{quit} special
12392 characters. May be negated.
12396 @cindex case translation
12397 Enable input and output of uppercase characters by preceding their
12398 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12399 Non-@acronym{POSIX}. May be negated.
12403 @cindex background jobs, stopping at terminal write
12404 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12411 Echo erased characters backward, between @samp{\} and @samp{/}.
12412 Non-@acronym{POSIX}. May be negated.
12418 @cindex control characters, using @samp{^@var{c}}
12419 @cindex hat notation for control characters
12420 Echo control characters in hat notation (@samp{^@var{c}}) instead
12421 of literally. Non-@acronym{POSIX}. May be negated.
12427 Echo the @code{kill} special character by erasing each character on
12428 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12429 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12435 @subsection Combination settings
12437 @cindex combination settings
12438 Combination settings:
12445 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12446 as @code{-parenb cs8}.
12450 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12451 as @code{-parenb cs8}.
12455 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12456 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12460 Reset the @code{erase} and @code{kill} special characters to their default
12467 @c This is too long to write inline.
12469 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12470 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12471 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12472 ff0 isig icanon iexten echo echoe echok -echonl
12473 -noflsh -xcase -tostop -echoprt echoctl echoke
12477 and also sets all special characters to their default values.
12481 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12482 sets the @code{eof} and @code{eol} characters to their default values
12483 if they are the same as the @code{min} and @code{time} characters.
12484 May be negated. If negated, same as @code{raw}.
12491 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12492 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12493 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12497 May be negated. If negated, same as @code{cooked}.
12501 Same as @option{-icanon}. May be negated. If negated, same as
12506 @cindex eight-bit characters
12507 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12508 same as @code{parenb istrip cs7}.
12512 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12513 If negated, same as @code{parenb istrip opost cs7}.
12517 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12521 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12528 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12529 (Used for terminals with uppercase characters only.)
12533 Same as @code{echoe echoctl echoke}.
12537 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12542 @subsection Special characters
12544 @cindex special characters
12545 @cindex characters, special
12547 The special characters' default values vary from system to system.
12548 They are set with the syntax @samp{name value}, where the names are
12549 listed below and the value can be given either literally, in hat
12550 notation (@samp{^@var{c}}), or as an integer which may start with
12551 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12552 any other digit to indicate decimal.
12554 @cindex disabling special characters
12555 @kindex u@r{, and disabling special characters}
12556 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12557 special character. (This is incompatible with Ultrix @command{stty},
12558 which uses a value of @samp{u} to disable a special character. GNU
12559 @command{stty} treats a value @samp{u} like any other, namely to set that
12560 special character to @key{U}.)
12566 Send an interrupt signal.
12570 Send a quit signal.
12574 Erase the last character typed.
12578 Erase the current line.
12582 Send an end of file (terminate the input).
12590 Alternate character to end the line. Non-@acronym{POSIX}.
12594 Switch to a different shell layer. Non-@acronym{POSIX}.
12598 Restart the output after stopping it.
12606 Send a terminal stop signal.
12610 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12614 Redraw the current line. Non-@acronym{POSIX}.
12618 Erase the last word typed. Non-@acronym{POSIX}.
12622 Enter the next character typed literally, even if it is a special
12623 character. Non-@acronym{POSIX}.
12628 @subsection Special settings
12630 @cindex special settings
12635 Set the minimum number of characters that will satisfy a read until
12636 the time value has expired, when @option{-icanon} is set.
12640 Set the number of tenths of a second before reads time out if the minimum
12641 number of characters have not been read, when @option{-icanon} is set.
12643 @item ispeed @var{n}
12645 Set the input speed to @var{n}.
12647 @item ospeed @var{n}
12649 Set the output speed to @var{n}.
12653 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12656 @itemx columns @var{n}
12659 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12665 Print the number of rows and columns that the kernel thinks the
12666 terminal has. (Systems that don't support rows and columns in the kernel
12667 typically use the environment variables @env{LINES} and @env{COLUMNS}
12668 instead; however, GNU @command{stty} does not know anything about them.)
12669 Non-@acronym{POSIX}.
12673 Use line discipline @var{n}. Non-@acronym{POSIX}.
12677 Print the terminal speed.
12680 @cindex baud rate, setting
12681 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12682 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12683 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12684 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12685 support higher speeds. The @command{stty} command includes support
12702 4000000 where the system supports these.
12703 0 hangs up the line if @option{-clocal} is set.
12707 @node printenv invocation
12708 @section @command{printenv}: Print all or some environment variables
12711 @cindex printing all or some environment variables
12712 @cindex environment variables, printing
12714 @command{printenv} prints environment variable values. Synopsis:
12717 printenv [@var{option}] [@var{variable}]@dots{}
12720 If no @var{variable}s are specified, @command{printenv} prints the value of
12721 every environment variable. Otherwise, it prints the value of each
12722 @var{variable} that is set, and nothing for those that are not set.
12724 The only options are a lone @option{--help} or @option{--version}.
12725 @xref{Common options}.
12727 @cindex exit status of @command{printenv}
12731 0 if all variables specified were found
12732 1 if at least one specified variable was not found
12733 2 if a write error occurred
12737 @node tty invocation
12738 @section @command{tty}: Print file name of terminal on standard input
12741 @cindex print terminal file name
12742 @cindex terminal file name, printing
12744 @command{tty} prints the file name of the terminal connected to its standard
12745 input. It prints @samp{not a tty} if standard input is not a terminal.
12749 tty [@var{option}]@dots{}
12752 The program accepts the following option. Also see @ref{Common options}.
12762 Print nothing; only return an exit status.
12766 @cindex exit status of @command{tty}
12770 0 if standard input is a terminal
12771 1 if standard input is not a terminal
12772 2 if given incorrect arguments
12773 3 if a write error occurs
12777 @node User information
12778 @chapter User information
12780 @cindex user information, commands for
12781 @cindex commands for printing user information
12783 This section describes commands that print user-related information:
12784 logins, groups, and so forth.
12787 * id invocation:: Print user identity.
12788 * logname invocation:: Print current login name.
12789 * whoami invocation:: Print effective user ID.
12790 * groups invocation:: Print group names a user is in.
12791 * users invocation:: Print login names of users currently logged in.
12792 * who invocation:: Print who is currently logged in.
12796 @node id invocation
12797 @section @command{id}: Print user identity
12800 @cindex real user and group IDs, printing
12801 @cindex effective user and group IDs, printing
12802 @cindex printing real and effective user and group IDs
12804 @command{id} prints information about the given user, or the process
12805 running it if no user is specified. Synopsis:
12808 id [@var{option}]@dots{} [@var{username}]
12811 By default, it prints the real user ID, real group ID, effective user ID
12812 if different from the real user ID, effective group ID if different from
12813 the real group ID, and supplemental group IDs.
12815 Each of these numeric values is preceded by an identifying string and
12816 followed by the corresponding user or group name in parentheses.
12818 The options cause @command{id} to print only part of the above information.
12819 Also see @ref{Common options}.
12826 Print only the group ID.
12832 Print only the group ID and the supplementary groups.
12838 Print the user or group name instead of the ID number. Requires
12839 @option{-u}, @option{-g}, or @option{-G}.
12845 Print the real, instead of effective, user or group ID. Requires
12846 @option{-u}, @option{-g}, or @option{-G}.
12852 Print only the user ID.
12859 @cindex security context
12860 Print only the security context of the current user.
12861 If SELinux is disabled then print a warning and
12862 set the exit status to 1.
12868 @macro primaryAndSupplementaryGroups{cmd,arg}
12869 Primary and supplementary groups for a process are normally inherited
12870 from its parent and are usually unchanged since login. This means
12871 that if you change the group database after logging in, @command{\cmd\}
12872 will not reflect your changes within your existing login session.
12873 Running @command{\cmd\} with a \arg\ causes the user and group
12874 database to be consulted afresh, and so will give a different result.
12876 @primaryAndSupplementaryGroups{id,user argument}
12878 @node logname invocation
12879 @section @command{logname}: Print current login name
12882 @cindex printing user's login name
12883 @cindex login name, printing
12884 @cindex user name, printing
12887 @command{logname} prints the calling user's name, as found in a
12888 system-maintained file (often @file{/var/run/utmp} or
12889 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12890 for the calling process, @command{logname} prints
12891 an error message and exits with a status of 1.
12893 The only options are @option{--help} and @option{--version}. @xref{Common
12899 @node whoami invocation
12900 @section @command{whoami}: Print effective user ID
12903 @cindex effective user ID, printing
12904 @cindex printing the effective user ID
12906 @command{whoami} prints the user name associated with the current
12907 effective user ID. It is equivalent to the command @samp{id -un}.
12909 The only options are @option{--help} and @option{--version}. @xref{Common
12915 @node groups invocation
12916 @section @command{groups}: Print group names a user is in
12919 @cindex printing groups a user is in
12920 @cindex supplementary groups, printing
12922 @command{groups} prints the names of the primary and any supplementary
12923 groups for each given @var{username}, or the current process if no names
12924 are given. If more than one name is given, the name of each user is
12926 the list of that user's groups and the user name is separated from the
12927 group list by a colon. Synopsis:
12930 groups [@var{username}]@dots{}
12933 The group lists are equivalent to the output of the command @samp{id -Gn}.
12935 @primaryAndSupplementaryGroups{groups,list of users}
12937 The only options are @option{--help} and @option{--version}. @xref{Common
12943 @node users invocation
12944 @section @command{users}: Print login names of users currently logged in
12947 @cindex printing current usernames
12948 @cindex usernames, printing current
12950 @cindex login sessions, printing users with
12951 @command{users} prints on a single line a blank-separated list of user
12952 names of users currently logged in to the current host. Each user name
12953 corresponds to a login session, so if a user has more than one login
12954 session, that user's name will appear the same number of times in the
12963 With no @var{file} argument, @command{users} extracts its information from
12964 a system-maintained file (often @file{/var/run/utmp} or
12965 @file{/etc/utmp}). If a file argument is given, @command{users} uses
12966 that file instead. A common choice is @file{/var/log/wtmp}.
12968 The only options are @option{--help} and @option{--version}. @xref{Common
12974 @node who invocation
12975 @section @command{who}: Print who is currently logged in
12978 @cindex printing current user information
12979 @cindex information, about current users
12981 @command{who} prints information about users who are currently logged on.
12985 @command{who} [@var{option}] [@var{file}] [am i]
12988 @cindex terminal lines, currently used
12990 @cindex remote hostname
12991 If given no non-option arguments, @command{who} prints the following
12992 information for each user currently logged on: login name, terminal
12993 line, login time, and remote hostname or X display.
12997 If given one non-option argument, @command{who} uses that instead of
12998 a default system-maintained file (often @file{/var/run/utmp} or
12999 @file{/etc/utmp}) as the name of the file containing the record of
13000 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13001 to @command{who} to look at who has previously logged on.
13005 If given two non-option arguments, @command{who} prints only the entry
13006 for the user running it (determined from its standard input), preceded
13007 by the hostname. Traditionally, the two arguments given are @samp{am
13008 i}, as in @samp{who am i}.
13011 Time stamps are listed according to the time zone rules specified by
13012 the @env{TZ} environment variable, or by the system default rules if
13013 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13014 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13016 The program accepts the following options. Also see @ref{Common options}.
13024 Same as @samp{-b -d --login -p -r -t -T -u}.
13030 Print the date and time of last system boot.
13036 Print information corresponding to dead processes.
13042 Print a line of column headings.
13048 List only the entries that correspond to processes via which the
13049 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13053 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13054 is not the default because it can cause significant delays on systems with
13055 automatic dial-up internet access.
13059 Same as @samp{who am i}.
13065 List active processes spawned by init.
13071 Print only the login names and the number of users logged on.
13072 Overrides all other options.
13077 @opindex --runlevel
13078 Print the current (and maybe previous) run-level of the init process.
13082 Ignored; for compatibility with other versions of @command{who}.
13088 Print last system clock change.
13093 After the login time, print the number of hours and minutes that the
13094 user has been idle. @samp{.} means the user was active in the last minute.
13095 @samp{old} means the user has been idle for more than 24 hours.
13106 @opindex --writable
13107 @cindex message status
13108 @pindex write@r{, allowed}
13109 After each login name print a character indicating the user's message status:
13112 @samp{+} allowing @code{write} messages
13113 @samp{-} disallowing @code{write} messages
13114 @samp{?} cannot find terminal device
13122 @node System context
13123 @chapter System context
13125 @cindex system context
13126 @cindex context, system
13127 @cindex commands for system context
13129 This section describes commands that print or change system-wide
13133 * date invocation:: Print or set system date and time.
13134 * arch invocation:: Print machine hardware name.
13135 * uname invocation:: Print system information.
13136 * hostname invocation:: Print or set system name.
13137 * hostid invocation:: Print numeric host identifier.
13138 * uptime invocation:: Print system uptime and load.
13141 @node date invocation
13142 @section @command{date}: Print or set system date and time
13145 @cindex time, printing or setting
13146 @cindex printing the current time
13151 date [@var{option}]@dots{} [+@var{format}]
13152 date [-u|--utc|--universal] @c this avoids a newline in the output
13153 [ MMDDhhmm[[CC]YY][.ss] ]
13157 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13158 it with a default format that depends on the @env{LC_TIME} locale category.
13159 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13160 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13163 Normally, @command{date} uses the time zone rules indicated by the
13164 @env{TZ} environment variable, or the system default rules if @env{TZ}
13165 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13166 @env{TZ}, libc, The GNU C Library Reference Manual}.
13168 @findex strftime @r{and @command{date}}
13169 @cindex time formats
13170 @cindex formatting times
13171 If given an argument that starts with a @samp{+}, @command{date} prints the
13172 current date and time (or the date and time specified by the
13173 @option{--date} option, see below) in the format defined by that argument,
13174 which is similar to that of the @code{strftime} function. Except for
13175 conversion specifiers, which start with @samp{%}, characters in the
13176 format string are printed unchanged. The conversion specifiers are
13182 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13183 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13184 * Literal conversion specifiers:: %[%nt]
13185 * Padding and other flags:: Pad with zeros, spaces, etc.
13186 * Setting the time:: Changing the system clock.
13187 * Options for date:: Instead of the current time.
13189 * Date input formats:: Specifying date strings.
13191 * Examples of date:: Examples.
13194 @node Time conversion specifiers
13195 @subsection Time conversion specifiers
13197 @cindex time conversion specifiers
13198 @cindex conversion specifiers, time
13200 @command{date} conversion specifiers related to times.
13204 hour (@samp{00}@dots{}@samp{23})
13206 hour (@samp{01}@dots{}@samp{12})
13208 hour (@samp{ 0}@dots{}@samp{23}).
13209 This is a @acronym{GNU} extension.
13211 hour (@samp{ 1}@dots{}@samp{12}).
13212 This is a @acronym{GNU} extension.
13214 minute (@samp{00}@dots{}@samp{59})
13216 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13217 This is a @acronym{GNU} extension.
13219 locale's equivalent of either @samp{AM} or @samp{PM};
13220 blank in many locales.
13221 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13223 like @samp{%p}, except lower case.
13224 This is a @acronym{GNU} extension.
13226 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13228 24-hour hour and minute. Same as @samp{%H:%M}.
13229 This is a @acronym{GNU} extension.
13231 @cindex epoch, seconds since
13232 @cindex seconds since the epoch
13233 @cindex beginning of time
13234 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13235 Leap seconds are not counted unless leap second support is available.
13236 @xref{%s-examples}, for examples.
13237 This is a @acronym{GNU} extension.
13239 second (@samp{00}@dots{}@samp{60}).
13240 This may be @samp{60} if leap seconds are supported.
13242 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13244 locale's time representation (e.g., @samp{23:13:48})
13246 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13247 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13248 time zone is determinable. This value reflects the numeric time zone
13249 appropriate for the current time, using the time zone rules specified
13250 by the @env{TZ} environment variable.
13251 The time (and optionally, the time zone rules) can be overridden
13252 by the @option{--date} option.
13253 This is a @acronym{GNU} extension.
13255 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13256 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13257 zone is determinable.
13258 This is a @acronym{GNU} extension.
13260 Numeric time zone to the nearest second with @samp{:} (e.g.,
13261 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13263 This is a @acronym{GNU} extension.
13265 Numeric time zone with @samp{:} using the minimum necessary precision
13266 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13267 no time zone is determinable.
13268 This is a @acronym{GNU} extension.
13270 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13271 time zone is determinable. See @samp{%z} for how it is determined.
13275 @node Date conversion specifiers
13276 @subsection Date conversion specifiers
13278 @cindex date conversion specifiers
13279 @cindex conversion specifiers, date
13281 @command{date} conversion specifiers related to dates.
13285 locale's abbreviated weekday name (e.g., @samp{Sun})
13287 locale's full weekday name, variable length (e.g., @samp{Sunday})
13289 locale's abbreviated month name (e.g., @samp{Jan})
13291 locale's full month name, variable length (e.g., @samp{January})
13293 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13295 century. This is like @samp{%Y}, except the last two digits are omitted.
13296 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13297 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13298 It is normally at least two characters, but it may be more.
13300 day of month (e.g., @samp{01})
13302 date; same as @samp{%m/%d/%y}
13304 day of month, space padded; same as @samp{%_d}
13306 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13307 This is a good choice for a date format, as it is standard and
13308 is easy to sort in the usual case where years are in the range
13310 This is a @acronym{GNU} extension.
13312 year corresponding to the @acronym{ISO} week number, but without the century
13313 (range @samp{00} through @samp{99}). This has the same format and value
13314 as @samp{%y}, except that if the @acronym{ISO} week number (see
13316 to the previous or next year, that year is used instead.
13317 This is a @acronym{GNU} extension.
13319 year corresponding to the @acronym{ISO} week number. This has the
13320 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13322 @samp{%V}) belongs to the previous or next year, that year is used
13324 It is normally useful only if @samp{%V} is also used;
13325 for example, the format @samp{%G-%m-%d} is probably a mistake,
13326 since it combines the ISO week number year with the conventional month and day.
13327 This is a @acronym{GNU} extension.
13331 day of year (@samp{001}@dots{}@samp{366})
13333 month (@samp{01}@dots{}@samp{12})
13335 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13337 week number of year, with Sunday as the first day of the week
13338 (@samp{00}@dots{}@samp{53}).
13339 Days in a new year preceding the first Sunday are in week zero.
13341 @acronym{ISO} week number, that is, the
13342 week number of year, with Monday as the first day of the week
13343 (@samp{01}@dots{}@samp{53}).
13344 If the week containing January 1 has four or more days in
13345 the new year, then it is considered week 1; otherwise, it is week 53 of
13346 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13349 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13351 week number of year, with Monday as first day of week
13352 (@samp{00}@dots{}@samp{53}).
13353 Days in a new year preceding the first Monday are in week zero.
13355 locale's date representation (e.g., @samp{12/31/99})
13357 last two digits of year (@samp{00}@dots{}@samp{99})
13359 year. This is normally at least four characters, but it may be more.
13360 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13361 precedes year @samp{0000}.
13365 @node Literal conversion specifiers
13366 @subsection Literal conversion specifiers
13368 @cindex literal conversion specifiers
13369 @cindex conversion specifiers, literal
13371 @command{date} conversion specifiers that produce literal strings.
13383 @node Padding and other flags
13384 @subsection Padding and other flags
13386 @cindex numeric field padding
13387 @cindex padding of numeric fields
13388 @cindex fields, padding numeric
13390 Unless otherwise specified, @command{date} normally pads numeric fields
13391 with zeros, so that, for
13392 example, numeric months are always output as two digits.
13393 Seconds since the epoch are not padded, though,
13394 since there is no natural width for them.
13396 As a @acronym{GNU} extension, @command{date} recognizes any of the
13397 following optional flags after the @samp{%}:
13401 (hyphen) Do not pad the field; useful if the output is intended for
13404 (underscore) Pad with spaces; useful if you need a fixed
13405 number of characters in the output, but zeros are too distracting.
13407 (zero) Pad with zeros even if the conversion specifier
13408 would normally pad with spaces.
13410 Use upper case characters if possible.
13412 Use opposite case characters if possible.
13413 A field that is normally upper case becomes lower case, and vice versa.
13417 Here are some examples of padding:
13420 date +%d/%m -d "Feb 1"
13422 date +%-d/%-m -d "Feb 1"
13424 date +%_d/%_m -d "Feb 1"
13428 As a @acronym{GNU} extension, you can specify the field width
13429 (after any flag, if present) as a decimal number. If the natural size of the
13430 output of the field has less than the specified number of characters,
13431 the result is written right adjusted and padded to the given
13432 size. For example, @samp{%9B} prints the right adjusted month name in
13433 a field of width 9.
13435 An optional modifier can follow the optional flag and width
13436 specification. The modifiers are:
13440 Use the locale's alternate representation for date and time. This
13441 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13442 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13443 example, @samp{%Ex} might yield a date format based on the Japanese
13447 Use the locale's alternate numeric symbols for numbers. This modifier
13448 applies only to numeric conversion specifiers.
13451 If the format supports the modifier but no alternate representation
13452 is available, it is ignored.
13455 @node Setting the time
13456 @subsection Setting the time
13458 @cindex setting the time
13459 @cindex time setting
13460 @cindex appropriate privileges
13462 If given an argument that does not start with @samp{+}, @command{date} sets
13463 the system clock to the date and time specified by that argument (as
13464 described below). You must have appropriate privileges to set the
13465 system clock. The @option{--date} and @option{--set} options may not be
13466 used with such an argument. The @option{--universal} option may be used
13467 with such an argument to indicate that the specified date and time are
13468 relative to Coordinated Universal Time rather than to the local time
13471 The argument must consist entirely of digits, which have the following
13484 first two digits of year (optional)
13486 last two digits of year (optional)
13491 The @option{--set} option also sets the system clock; see the next section.
13494 @node Options for date
13495 @subsection Options for @command{date}
13497 @cindex @command{date} options
13498 @cindex options for @command{date}
13500 The program accepts the following options. Also see @ref{Common options}.
13504 @item -d @var{datestr}
13505 @itemx --date=@var{datestr}
13508 @cindex parsing date strings
13509 @cindex date strings, parsing
13510 @cindex arbitrary date strings, parsing
13513 @opindex next @var{day}
13514 @opindex last @var{day}
13515 Display the date and time specified in @var{datestr} instead of the
13516 current date and time. @var{datestr} can be in almost any common
13517 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13518 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13519 14:19:13.489392193 +0530"} specifies the instant of time that is
13520 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13521 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13522 Note: input currently must be in locale independent format. E.g., the
13523 LC_TIME=C below is needed to print back the correct date in many locales:
13525 date -d "$(LC_TIME=C date)"
13527 @xref{Date input formats}.
13529 @item -f @var{datefile}
13530 @itemx --file=@var{datefile}
13533 Parse each line in @var{datefile} as with @option{-d} and display the
13534 resulting date and time. If @var{datefile} is @samp{-}, use standard
13535 input. This is useful when you have many dates to process, because the
13536 system overhead of starting up the @command{date} executable many times can
13539 @item -r @var{file}
13540 @itemx --reference=@var{file}
13542 @opindex --reference
13543 Display the date and time of the last modification of @var{file},
13544 instead of the current date and time.
13551 @opindex --rfc-2822
13552 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13553 %z}, evaluated in the C locale so abbreviations are always in English.
13557 Fri, 09 Sep 2005 13:51:39 -0700
13560 This format conforms to
13561 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13562 @acronym{RFCs} 2822} and
13563 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13564 current and previous standards for Internet email.
13566 @item --rfc-3339=@var{timespec}
13567 @opindex --rfc-3339=@var{timespec}
13568 Display the date using a format specified by
13569 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13570 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13571 format, except that it also permits applications to use a space rather
13572 than a @samp{T} to separate dates from times. Unlike the other
13573 standard formats, @acronym{RFC} 3339 format is always suitable as
13574 input for the @option{--date} (@option{-d}) and @option{--file}
13575 (@option{-f}) options, regardless of the current locale.
13577 The argument @var{timespec} specifies how much of the time to include.
13578 It can be one of the following:
13582 Print just the full-date, e.g., @samp{2005-09-14}.
13583 This is equivalent to the format @samp{%Y-%m-%d}.
13586 Print the full-date and full-time separated by a space, e.g.,
13587 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13588 time-offset; here the @samp{+05:30} means that local time is five
13589 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13590 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13593 Like @samp{seconds}, but also print nanoseconds, e.g.,
13594 @samp{2005-09-14 00:56:06.998458565+05:30}.
13595 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13599 @item -s @var{datestr}
13600 @itemx --set=@var{datestr}
13603 Set the date and time to @var{datestr}. See @option{-d} above.
13610 @opindex --universal
13611 @cindex Coordinated Universal Time
13613 @cindex Greenwich Mean Time
13616 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13617 @env{TZ} environment variable were set to the string @samp{UTC0}.
13619 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13620 historical reasons.
13624 @node Examples of date
13625 @subsection Examples of @command{date}
13627 @cindex examples of @command{date}
13629 Here are a few examples. Also see the documentation for the @option{-d}
13630 option in the previous section.
13635 To print the date of the day before yesterday:
13638 date --date='2 days ago'
13642 To print the date of the day three months and one day hence:
13645 date --date='3 months 1 day'
13649 To print the day of year of Christmas in the current year:
13652 date --date='25 Dec' +%j
13656 To print the current full month name and the day of the month:
13662 But this may not be what you want because for the first nine days of
13663 the month, the @samp{%d} expands to a zero-padded two-digit field,
13664 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13667 To print a date without the leading zero for one-digit days
13668 of the month, you can use the (@acronym{GNU} extension)
13669 @samp{-} flag to suppress
13670 the padding altogether:
13673 date -d 1may '+%B %-d
13677 To print the current date and time in the format required by many
13678 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13681 date +%m%d%H%M%Y.%S
13685 To set the system clock forward by two minutes:
13688 date --set='+2 minutes'
13692 To print the date in @acronym{RFC} 2822 format,
13693 use @samp{date --rfc-2822}. Here is some example output:
13696 Fri, 09 Sep 2005 13:51:39 -0700
13699 @anchor{%s-examples}
13701 To convert a date string to the number of seconds since the epoch
13702 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13703 the @samp{%s} format. That can be useful in sorting and/or graphing
13704 and/or comparing data by date. The following command outputs the
13705 number of the seconds since the epoch for the time two minutes after the
13709 date --date='1970-01-01 00:02:00 +0000' +%s
13713 If you do not specify time zone information in the date string,
13714 @command{date} uses your computer's idea of the time zone when
13715 interpreting the string. For example, if your computer's time zone is
13716 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13717 seconds) behind UTC:
13720 # local time zone used
13721 date --date='1970-01-01 00:02:00' +%s
13726 If you're sorting or graphing dated data, your raw date values may be
13727 represented as seconds since the epoch. But few people can look at
13728 the date @samp{946684800} and casually note ``Oh, that's the first second
13729 of the year 2000 in Greenwich, England.''
13732 date --date='2000-01-01 UTC' +%s
13736 An alternative is to use the @option{--utc} (@option{-u}) option.
13737 Then you may omit @samp{UTC} from the date string. Although this
13738 produces the same result for @samp{%s} and many other format sequences,
13739 with a time zone offset different from zero, it would give a different
13740 result for zone-dependent formats like @samp{%z}.
13743 date -u --date=2000-01-01 +%s
13747 To convert such an unwieldy number of seconds back to
13748 a more readable form, use a command like this:
13751 # local time zone used
13752 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13753 1999-12-31 19:00:00 -0500
13756 Or if you do not mind depending on the @samp{@@} feature present since
13757 coreutils 5.3.0, you could shorten this to:
13760 date -d @@946684800 +"%F %T %z"
13761 1999-12-31 19:00:00 -0500
13764 Often it is better to output UTC-relative date and time:
13767 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13768 2000-01-01 00:00:00 +0000
13774 @node arch invocation
13775 @section @command{arch}: Print machine hardware name
13778 @cindex print machine hardware name
13779 @cindex system information, printing
13781 @command{arch} prints the machine hardware name,
13782 and is equivalent to @samp{uname -m}.
13786 arch [@var{option}]
13789 The program accepts the @ref{Common options} only.
13794 @node uname invocation
13795 @section @command{uname}: Print system information
13798 @cindex print system information
13799 @cindex system information, printing
13801 @command{uname} prints information about the machine and operating system
13802 it is run on. If no options are given, @command{uname} acts as if the
13803 @option{-s} option were given. Synopsis:
13806 uname [@var{option}]@dots{}
13809 If multiple options or @option{-a} are given, the selected information is
13810 printed in this order:
13813 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13814 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13817 The information may contain internal spaces, so such output cannot be
13818 parsed reliably. In the following example, @var{release} is
13819 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13823 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13827 The program accepts the following options. Also see @ref{Common options}.
13835 Print all of the below information, except omit the processor type
13836 and the hardware platform name if they are unknown.
13839 @itemx --hardware-platform
13841 @opindex --hardware-platform
13842 @cindex implementation, hardware
13843 @cindex hardware platform
13844 @cindex platform, hardware
13845 Print the hardware platform name
13846 (sometimes called the hardware implementation).
13847 Print @samp{unknown} if the kernel does not make this information
13848 easily available, as is the case with Linux kernels.
13854 @cindex machine type
13855 @cindex hardware class
13856 @cindex hardware type
13857 Print the machine hardware name (sometimes called the hardware class
13863 @opindex --nodename
13866 @cindex network node name
13867 Print the network node hostname.
13872 @opindex --processor
13873 @cindex host processor type
13874 Print the processor type (sometimes called the instruction set
13875 architecture or ISA).
13876 Print @samp{unknown} if the kernel does not make this information
13877 easily available, as is the case with Linux kernels.
13880 @itemx --operating-system
13882 @opindex --operating-system
13883 @cindex operating system name
13884 Print the name of the operating system.
13887 @itemx --kernel-release
13889 @opindex --kernel-release
13890 @cindex kernel release
13891 @cindex release of kernel
13892 Print the kernel release.
13895 @itemx --kernel-name
13897 @opindex --kernel-name
13898 @cindex kernel name
13899 @cindex name of kernel
13900 Print the kernel name.
13901 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
13902 ``the implementation of the operating system'', because the
13903 @acronym{POSIX} specification itself has no notion of ``kernel''.
13904 The kernel name might be the same as the operating system name printed
13905 by the @option{-o} or @option{--operating-system} option, but it might
13906 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
13907 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
13911 @itemx --kernel-version
13913 @opindex --kernel-version
13914 @cindex kernel version
13915 @cindex version of kernel
13916 Print the kernel version.
13923 @node hostname invocation
13924 @section @command{hostname}: Print or set system name
13927 @cindex setting the hostname
13928 @cindex printing the hostname
13929 @cindex system name, printing
13930 @cindex appropriate privileges
13932 With no arguments, @command{hostname} prints the name of the current host
13933 system. With one argument, it sets the current host name to the
13934 specified string. You must have appropriate privileges to set the host
13938 hostname [@var{name}]
13941 The only options are @option{--help} and @option{--version}. @xref{Common
13947 @node hostid invocation
13948 @section @command{hostid}: Print numeric host identifier
13951 @cindex printing the host identifier
13953 @command{hostid} prints the numeric identifier of the current host
13954 in hexadecimal. This command accepts no arguments.
13955 The only options are @option{--help} and @option{--version}.
13956 @xref{Common options}.
13958 For example, here's what it prints on one system I use:
13965 On that system, the 32-bit quantity happens to be closely
13966 related to the system's Internet address, but that isn't always
13971 @node uptime invocation
13972 @section @command{uptime}: Print system uptime and load
13975 @cindex printing the system uptime and load
13977 @command{uptime} prints the current time, the system's uptime, the
13978 number of logged-in users and the current load average.
13980 If an argument is specified, it is used as the file to be read
13981 to discover how many users are logged in. If no argument is
13982 specified, a system default is used (@command{uptime --help} indicates
13983 the default setting).
13985 The only options are @option{--help} and @option{--version}.
13986 @xref{Common options}.
13988 For example, here's what it prints right now on one system I use:
13992 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
13995 The precise method of calculation of load average varies somewhat
13996 between systems. Some systems calculate it as the average number of
13997 runnable processes over the last 1, 5 and 15 minutes, but some systems
13998 also include processes in the uninterruptible sleep state (that is,
13999 those processes which are waiting for disk I/O). The Linux kernel
14000 includes uninterruptible processes.
14002 @node SELinux context
14003 @chapter SELinux context
14005 @cindex SELinux context
14006 @cindex SELinux, context
14007 @cindex commands for SELinux context
14009 This section describes commands for operations with SELinux
14013 * chcon invocation:: Change SELinux context of file
14014 * runcon invocation:: Run a command in specified SELinux context
14017 @node chcon invocation
14018 @section @command{chcon}: Change SELinux context of file
14021 @cindex changing security context
14022 @cindex change SELinux context
14024 @command{chcon} changes the SELinux security context of the selected files.
14028 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14029 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14030 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14033 Change the SELinux security context of each @var{file} to @var{context}.
14034 With @option{--reference}, change the security context of each @var{file}
14035 to that of @var{rfile}.
14037 The program accepts the following options. Also see @ref{Common options}.
14042 @itemx --no-dereference
14044 @opindex --no-dereference
14045 @cindex no dereference
14046 Affect symbolic links instead of any referenced file.
14048 @item --reference=@var{rfile}
14049 @opindex --reference
14050 @cindex reference file
14051 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14056 @opindex --recursive
14057 Operate on files and directories recursively.
14060 @xref{Traversing symlinks}.
14063 @xref{Traversing symlinks}.
14066 @xref{Traversing symlinks}.
14073 Output a diagnostic for every file processed.
14075 @item -u @var{user}
14076 @itemx --user=@var{user}
14079 Set user @var{user} in the target security context.
14081 @item -r @var{role}
14082 @itemx --role=@var{role}
14085 Set role @var{role} in the target security context.
14087 @item -t @var{type}
14088 @itemx --type=@var{type}
14091 Set type @var{type} in the target security context.
14093 @item -l @var{range}
14094 @itemx --range=@var{range}
14097 Set range @var{range} in the target security context.
14103 @node runcon invocation
14104 @section @command{runcon}: Run a command in specified SELinux context
14107 @cindex run with security context
14110 @command{runcon} runs file in specified SELinux security context.
14114 runcon @var{context} @var{command} [@var{args}]
14115 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14118 Run @var{command} with completely-specified @var{context}, or with
14119 current or transitioned security context modified by one or more of @var{level},
14120 @var{role}, @var{type} and @var{user}.
14122 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14123 is specified, the first argument is used as the complete context.
14124 Any additional arguments after @var{command}
14125 are interpreted as arguments to the command.
14127 With neither @var{context} nor @var{command}, print the current security context.
14129 The program accepts the following options. Also see @ref{Common options}.
14137 Compute process transition context before modifying.
14139 @item -u @var{user}
14140 @itemx --user=@var{user}
14143 Set user @var{user} in the target security context.
14145 @item -r @var{role}
14146 @itemx --role=@var{role}
14149 Set role @var{role} in the target security context.
14151 @item -t @var{type}
14152 @itemx --type=@var{type}
14155 Set type @var{type} in the target security context.
14157 @item -l @var{range}
14158 @itemx --range=@var{range}
14161 Set range @var{range} in the target security context.
14165 @cindex exit status of @command{runcon}
14169 126 if @var{command} is found but cannot be invoked
14170 127 if @command{runcon} itself fails or if @var{command} cannot be found
14171 the exit status of @var{command} otherwise
14174 @node Modified command invocation
14175 @chapter Modified command invocation
14177 @cindex modified command invocation
14178 @cindex invocation of commands, modified
14179 @cindex commands for invoking other commands
14181 This section describes commands that run other commands in some context
14182 different than the current one: a modified environment, as a different
14186 * chroot invocation:: Modify the root directory.
14187 * env invocation:: Modify environment variables.
14188 * nice invocation:: Modify niceness.
14189 * nohup invocation:: Immunize to hangups.
14190 * stdbuf invocation:: Modify buffering of standard streams.
14191 * su invocation:: Modify user and group ID.
14192 * timeout invocation:: Run with time limit.
14196 @node chroot invocation
14197 @section @command{chroot}: Run a command with a different root directory
14200 @cindex running a program in a specified root directory
14201 @cindex root directory, running a program in a specified
14203 @command{chroot} runs a command with a specified root directory.
14204 On many systems, only the super-user can do this.@footnote{However,
14205 some systems (e.g., FreeBSD) can be configured to allow certain regular
14206 users to use the @code{chroot} system call, and hence to run this program.
14207 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14208 underlying function is non-privileged due to lack of support in MS-Windows.}
14212 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14213 chroot @var{option}
14216 Ordinarily, file names are looked up starting at the root of the
14217 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14218 the directory @var{newroot} (which must exist) and then runs
14219 @var{command} with optional @var{args}. If @var{command} is not
14220 specified, the default is the value of the @env{SHELL} environment
14221 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14222 @var{command} must not be a special built-in utility
14223 (@pxref{Special built-in utilities}).
14225 The program accepts the following options. Also see @ref{Common options}.
14226 Options must precede operands.
14230 @itemx --userspec=@var{user}[:@var{group}]
14231 @opindex --userspec
14232 By default, @var{command} is run with the same credentials
14233 as the invoking process.
14234 Use this option to run it as a different @var{user} and/or with a
14235 different primary @var{group}.
14237 @itemx --groups=@var{groups}
14239 Use this option to specify the supplementary @var{groups} to be
14240 used by the new process.
14241 The items in the list (names or numeric IDs) must be separated by commas.
14245 Here are a few tips to help avoid common problems in using chroot.
14246 To start with a simple example, make @var{command} refer to a statically
14247 linked binary. If you were to use a dynamically linked executable, then
14248 you'd have to arrange to have the shared libraries in the right place under
14249 your new root directory.
14251 For example, if you create a statically linked @command{ls} executable,
14252 and put it in @file{/tmp/empty}, you can run this command as root:
14255 $ chroot /tmp/empty /ls -Rl /
14258 Then you'll see output like this:
14263 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14266 If you want to use a dynamically linked executable, say @command{bash},
14267 then first run @samp{ldd bash} to see what shared objects it needs.
14268 Then, in addition to copying the actual binary, also copy the listed
14269 files to the required positions under your intended new root directory.
14270 Finally, if the executable requires any other files (e.g., data, state,
14271 device files), copy them into place, too.
14273 @cindex exit status of @command{chroot}
14277 1 if @command{chroot} itself fails
14278 126 if @var{command} is found but cannot be invoked
14279 127 if @var{command} cannot be found
14280 the exit status of @var{command} otherwise
14284 @node env invocation
14285 @section @command{env}: Run a command in a modified environment
14288 @cindex environment, running a program in a modified
14289 @cindex modified environment, running a program in a
14290 @cindex running a program in a modified environment
14292 @command{env} runs a command with a modified environment. Synopses:
14295 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14296 [@var{command} [@var{args}]@dots{}]
14300 Operands of the form @samp{@var{variable}=@var{value}} set
14301 the environment variable @var{variable} to value @var{value}.
14302 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14303 to an empty value is different from unsetting it.
14304 These operands are evaluated left-to-right, so if two operands
14305 mention the same variable the earlier is ignored.
14307 Environment variable names can be empty, and can contain any
14308 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14309 However, it is wise to limit yourself to names that
14310 consist solely of underscores, digits, and @acronym{ASCII} letters,
14311 and that begin with a non-digit, as applications like the shell do not
14312 work well with other names.
14315 The first operand that does not contain the character @samp{=}
14316 specifies the program to invoke; it is
14317 searched for according to the @env{PATH} environment variable. Any
14318 remaining arguments are passed as arguments to that program.
14319 The program should not be a special built-in utility
14320 (@pxref{Special built-in utilities}).
14322 @cindex environment, printing
14324 If no command name is specified following the environment
14325 specifications, the resulting environment is printed. This is like
14326 specifying the @command{printenv} program.
14328 The program accepts the following options. Also see @ref{Common options}.
14329 Options must precede operands.
14333 @item -u @var{name}
14334 @itemx --unset=@var{name}
14337 Remove variable @var{name} from the environment, if it was in the
14342 @itemx --ignore-environment
14345 @opindex --ignore-environment
14346 Start with an empty environment, ignoring the inherited environment.
14350 @cindex exit status of @command{env}
14354 0 if no @var{command} is specified and the environment is output
14355 1 if @command{env} itself fails
14356 126 if @var{command} is found but cannot be invoked
14357 127 if @var{command} cannot be found
14358 the exit status of @var{command} otherwise
14362 @node nice invocation
14363 @section @command{nice}: Run a command with modified niceness
14367 @cindex scheduling, affecting
14368 @cindex appropriate privileges
14370 @command{nice} prints or modifies a process's @dfn{niceness},
14371 a parameter that affects whether the process is scheduled favorably.
14375 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14378 If no arguments are given, @command{nice} prints the current niceness.
14379 Otherwise, @command{nice} runs the given @var{command} with its
14380 niceness adjusted. By default, its niceness is incremented by 10.
14382 Niceness values range at least from @minus{}20 (process has high priority
14383 and gets more resources, thus slowing down other processes) through 19
14384 (process has lower priority and runs slowly itself, but has less impact
14385 on the speed of other running processes). Some systems
14386 may have a wider range of nicenesses; conversely, other systems may
14387 enforce more restrictive limits. An attempt to set the niceness
14388 outside the supported range is treated as an attempt to use the
14389 minimum or maximum supported value.
14391 A niceness should not be confused with a scheduling priority, which
14392 lets applications determine the order in which threads are scheduled
14393 to run. Unlike a priority, a niceness is merely advice to the
14394 scheduler, which the scheduler is free to ignore. Also, as a point of
14395 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14396 terms of a @dfn{nice value}, which is the nonnegative difference
14397 between a niceness and the minimum niceness. Though @command{nice}
14398 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14399 term ``niceness'' for compatibility with historical practice.
14401 @var{command} must not be a special built-in utility (@pxref{Special
14402 built-in utilities}).
14404 @mayConflictWithShellBuiltIn{nice}
14406 The program accepts the following option. Also see @ref{Common options}.
14407 Options must precede operands.
14410 @item -n @var{adjustment}
14411 @itemx --adjustment=@var{adjustment}
14413 @opindex --adjustment
14414 Add @var{adjustment} instead of 10 to the command's niceness. If
14415 @var{adjustment} is negative and you lack appropriate privileges,
14416 @command{nice} issues a warning but otherwise acts as if you specified
14419 For compatibility @command{nice} also supports an obsolete
14420 option syntax @option{-@var{adjustment}}. New scripts should use
14421 @option{-n @var{adjustment}} instead.
14425 @cindex exit status of @command{nice}
14429 0 if no @var{command} is specified and the niceness is output
14430 1 if @command{nice} itself fails
14431 126 if @var{command} is found but cannot be invoked
14432 127 if @var{command} cannot be found
14433 the exit status of @var{command} otherwise
14436 It is sometimes useful to run a non-interactive program with reduced niceness.
14439 $ nice factor 4611686018427387903
14442 Since @command{nice} prints the current niceness,
14443 you can invoke it through itself to demonstrate how it works.
14445 The default behavior is to increase the niceness by @samp{10}:
14456 The @var{adjustment} is relative to the current niceness. In the
14457 next example, the first @command{nice} invocation runs the second one
14458 with niceness 10, and it in turn runs the final one with a niceness
14462 $ nice nice -n 3 nice
14466 Specifying a niceness larger than the supported range
14467 is the same as specifying the maximum supported value:
14470 $ nice -n 10000000000 nice
14474 Only a privileged user may run a process with lower niceness:
14478 nice: cannot set niceness: Permission denied
14480 $ sudo nice -n -1 nice
14485 @node nohup invocation
14486 @section @command{nohup}: Run a command immune to hangups
14489 @cindex hangups, immunity to
14490 @cindex immunity to hangups
14491 @cindex logging out and continuing to run
14494 @command{nohup} runs the given @var{command} with hangup signals ignored,
14495 so that the command can continue running in the background after you log
14499 nohup @var{command} [@var{arg}]@dots{}
14502 If standard input is a terminal, it is redirected from
14503 @file{/dev/null} so that terminal sessions do not mistakenly consider
14504 the terminal to be used by the command. This is a @acronym{GNU}
14505 extension; programs intended to be portable to non-@acronym{GNU} hosts
14506 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14510 If standard output is a terminal, the command's standard output is appended
14511 to the file @file{nohup.out}; if that cannot be written to, it is appended
14512 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14513 command is not run.
14514 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14515 @command{nohup} is made readable and writable only to the user,
14516 regardless of the current umask settings.
14518 If standard error is a terminal, it is normally redirected to the same file
14519 descriptor as the (possibly-redirected) standard output.
14520 However, if standard output is closed, standard error terminal output
14521 is instead appended to the file @file{nohup.out} or
14522 @file{$HOME/nohup.out} as above.
14524 To capture the command's output to a file other than @file{nohup.out}
14525 you can redirect it. For example, to capture the output of
14529 nohup make > make.log
14532 @command{nohup} does not automatically put the command it runs in the
14533 background; you must do that explicitly, by ending the command line
14534 with an @samp{&}. Also, @command{nohup} does not alter the
14535 niceness of @var{command}; use @command{nice} for that,
14536 e.g., @samp{nohup nice @var{command}}.
14538 @var{command} must not be a special built-in utility (@pxref{Special
14539 built-in utilities}).
14541 The only options are @option{--help} and @option{--version}. @xref{Common
14542 options}. Options must precede operands.
14544 @cindex exit status of @command{nohup}
14548 126 if @var{command} is found but cannot be invoked
14549 127 if @command{nohup} itself fails or if @var{command} cannot be found
14550 the exit status of @var{command} otherwise
14554 @node stdbuf invocation
14555 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14558 @cindex standard streams, buffering
14559 @cindex line buffered
14561 @command{stdbuf} allows one to modify the buffering operations of the
14562 three standard I/O streams associated with a program. Synopsis:
14565 stdbuf @var{option}@dots{} @var{command}
14568 Any additional @var{arg}s are passed as additional arguments to the
14571 The program accepts the following options. Also see @ref{Common options}.
14575 @item -i @var{mode}
14576 @itemx --input=@var{mode}
14579 Adjust the standard input stream buffering.
14581 @item -o @var{mode}
14582 @itemx --output=@var{mode}
14585 Adjust the standard output stream buffering.
14587 @item -e @var{mode}
14588 @itemx --error=@var{mode}
14591 Adjust the standard error stream buffering.
14595 The @var{mode} can be specified as follows:
14600 Set the stream to line buffered mode.
14601 In this mode data is coalesced until a newline is output or
14602 input is read from any stream attached to a terminal device.
14603 This option is invalid with standard input.
14606 Disable buffering of the selected stream.
14607 In this mode data is output immediately and only the
14608 amount of data requested is read from input.
14611 Specify the size of the buffer to use in fully buffered mode.
14612 @multiplierSuffixesNoBlocks{size}
14616 NOTE: If @var{command} adjusts the buffering of its standard streams
14617 (@command{tee} does for e.g.) then that will override corresponding settings
14618 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14619 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14620 by @command{stdbuf} settings.
14622 @cindex exit status of @command{stdbuf}
14626 125 if @command{stdbuf} itself fails
14627 126 if @var{command} is found but cannot be invoked
14628 127 if @var{command} cannot be found
14629 the exit status of @var{command} otherwise
14633 @node su invocation
14634 @section @command{su}: Run a command with substitute user and group ID
14637 @cindex substitute user and group IDs
14638 @cindex user ID, switching
14639 @cindex super-user, becoming
14640 @cindex root, becoming
14642 @command{su} allows one user to temporarily become another user. It runs a
14643 command (often an interactive shell) with the real and effective user
14644 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14647 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14650 @cindex passwd entry, and @command{su} shell
14652 @flindex /etc/passwd
14653 If no @var{user} is given, the default is @code{root}, the super-user.
14654 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14655 @file{/bin/sh} if none is specified there. If @var{user} has a
14656 password, @command{su} prompts for the password unless run by a user with
14657 effective user ID of zero (the super-user).
14663 @cindex login shell
14664 By default, @command{su} does not change the current directory.
14665 It sets the environment variables @env{HOME} and @env{SHELL}
14666 from the password entry for @var{user}, and if @var{user} is not
14667 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14668 By default, the shell is not a login shell.
14670 Any additional @var{arg}s are passed as additional arguments to the
14673 @cindex @option{-su}
14674 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14675 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14676 to certain shells, etc.).
14679 @command{su} can optionally be compiled to use @code{syslog} to report
14680 failed, and optionally successful, @command{su} attempts. (If the system
14681 supports @code{syslog}.) However, GNU @command{su} does not check if the
14682 user is a member of the @code{wheel} group; see below.
14684 The program accepts the following options. Also see @ref{Common options}.
14687 @item -c @var{command}
14688 @itemx --command=@var{command}
14691 Pass @var{command}, a single command line to run, to the shell with
14692 a @option{-c} option instead of starting an interactive shell.
14699 @cindex file name pattern expansion, disabled
14700 @cindex globbing, disabled
14701 Pass the @option{-f} option to the shell. This probably only makes sense
14702 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14703 option prevents reading the startup file (@file{.cshrc}). With
14704 Bourne-like shells, the @option{-f} option disables file name pattern
14705 expansion (globbing), which is not likely to be useful.
14713 @c other variables already indexed above
14716 @cindex login shell, creating
14717 Make the shell a login shell. This means the following. Unset all
14718 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14719 (which are set as described above), and @env{USER} and @env{LOGNAME}
14720 (which are set, even for the super-user, as described above), and set
14721 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14722 directory. Prepend @samp{-} to the shell's name, intended to make it
14723 read its login startup file(s).
14727 @itemx --preserve-environment
14730 @opindex --preserve-environment
14731 @cindex environment, preserving
14732 @flindex /etc/shells
14733 @cindex restricted shell
14734 Do not change the environment variables @env{HOME}, @env{USER},
14735 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14736 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14737 entry, unless the user running @command{su} is not the super-user and
14738 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14739 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14740 if that file does not exist. Parts of what this option does can be
14741 overridden by @option{--login} and @option{--shell}.
14743 @item -s @var{shell}
14744 @itemx --shell=@var{shell}
14747 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14748 unless the user running @command{su} is not the super-user and @var{user}'s
14749 shell is restricted (see @option{-m} just above).
14753 @cindex exit status of @command{su}
14757 1 if @command{su} itself fails
14758 126 if subshell is found but cannot be invoked
14759 127 if subshell cannot be found
14760 the exit status of the subshell otherwise
14763 @cindex wheel group, not supported
14764 @cindex group wheel, not supported
14766 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14768 (This section is by Richard Stallman.)
14772 Sometimes a few of the users try to hold total power over all the
14773 rest. For example, in 1984, a few users at the MIT AI lab decided to
14774 seize power by changing the operator password on the Twenex system and
14775 keeping it secret from everyone else. (I was able to thwart this coup
14776 and give power back to the users by patching the kernel, but I
14777 wouldn't know how to do that in Unix.)
14779 However, occasionally the rulers do tell someone. Under the usual
14780 @command{su} mechanism, once someone learns the root password who
14781 sympathizes with the ordinary users, he or she can tell the rest. The
14782 ``wheel group'' feature would make this impossible, and thus cement the
14783 power of the rulers.
14785 I'm on the side of the masses, not that of the rulers. If you are
14786 used to supporting the bosses and sysadmins in whatever they do, you
14787 might find this idea strange at first.
14790 @node timeout invocation
14791 @section @command{timeout}: Run a command with a time limit
14795 @cindex run commands with bounded time
14797 @command{timeout} runs the given @var{command} and kills it if it is
14798 still running after the specified time interval. Synopsis:
14801 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14805 @var{number} is an integer followed by an optional unit; the default
14806 is seconds. The units are:
14819 @var{command} must not be a special built-in utility (@pxref{Special
14820 built-in utilities}).
14822 The program accepts the following option. Also see @ref{Common options}.
14823 Options must precede operands.
14826 @item -s @var{signal}
14827 @itemx --signal=@var{signal}
14830 Send this @var{signal} to @var{command} on timeout, rather than the
14831 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14832 or a number. Also see @xref{Signal specifications}.
14836 @cindex exit status of @command{timeout}
14840 124 if @var{command} times out
14841 125 if @command{timeout} itself fails
14842 126 if @var{command} is found but cannot be invoked
14843 127 if @var{command} cannot be found
14844 the exit status of @var{command} otherwise
14848 @node Process control
14849 @chapter Process control
14851 @cindex processes, commands for controlling
14852 @cindex commands for controlling processes
14855 * kill invocation:: Sending a signal to processes.
14859 @node kill invocation
14860 @section @command{kill}: Send a signal to processes
14863 @cindex send a signal to processes
14865 The @command{kill} command sends a signal to processes, causing them
14866 to terminate or otherwise act upon receiving the signal in some way.
14867 Alternatively, it lists information about signals. Synopses:
14870 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14871 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14874 @mayConflictWithShellBuiltIn{kill}
14876 The first form of the @command{kill} command sends a signal to all
14877 @var{pid} arguments. The default signal to send if none is specified
14878 is @samp{TERM}. The special signal number @samp{0} does not denote a
14879 valid signal, but can be used to test whether the @var{pid} arguments
14880 specify processes to which a signal could be sent.
14882 If @var{pid} is positive, the signal is sent to the process with the
14883 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14884 processes in the process group of the current process. If @var{pid}
14885 is @minus{}1, the signal is sent to all processes for which the user has
14886 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14887 is sent to all processes in the process group that equals the absolute
14888 value of @var{pid}.
14890 If @var{pid} is not positive, a system-dependent set of system
14891 processes is excluded from the list of processes to which the signal
14894 If a negative @var{pid} argument is desired as the first one, it
14895 should be preceded by @option{--}. However, as a common extension to
14896 @acronym{POSIX}, @option{--} is not required with @samp{kill
14897 -@var{signal} -@var{pid}}. The following commands are equivalent:
14906 The first form of the @command{kill} command succeeds if every @var{pid}
14907 argument specifies at least one process that the signal was sent to.
14909 The second form of the @command{kill} command lists signal information.
14910 Either the @option{-l} or @option{--list} option, or the @option{-t}
14911 or @option{--table} option must be specified. Without any
14912 @var{signal} argument, all supported signals are listed. The output
14913 of @option{-l} or @option{--list} is a list of the signal names, one
14914 per line; if @var{signal} is already a name, the signal number is
14915 printed instead. The output of @option{-t} or @option{--table} is a
14916 table of signal numbers, names, and descriptions. This form of the
14917 @command{kill} command succeeds if all @var{signal} arguments are valid
14918 and if there is no output error.
14920 The @command{kill} command also supports the @option{--help} and
14921 @option{--version} options. @xref{Common options}.
14923 A @var{signal} may be a signal name like @samp{HUP}, or a signal
14924 number like @samp{1}, or an exit status of a process terminated by the
14925 signal. A signal name can be given in canonical form or prefixed by
14926 @samp{SIG}. The case of the letters is ignored, except for the
14927 @option{-@var{signal}} option which must use upper case to avoid
14928 ambiguity with lower case option letters. For a list of supported
14929 signal names and numbers see @xref{Signal specifications}.
14934 @cindex delaying commands
14935 @cindex commands for delaying
14937 @c Perhaps @command{wait} or other commands should be described here also?
14940 * sleep invocation:: Delay for a specified time.
14944 @node sleep invocation
14945 @section @command{sleep}: Delay for a specified time
14948 @cindex delay for a specified time
14950 @command{sleep} pauses for an amount of time specified by the sum of
14951 the values of the command line arguments.
14955 sleep @var{number}[smhd]@dots{}
14959 Each argument is a number followed by an optional unit; the default
14960 is seconds. The units are:
14973 Historical implementations of @command{sleep} have required that
14974 @var{number} be an integer, and only accepted a single argument
14975 without a suffix. However, GNU @command{sleep} accepts
14976 arbitrary floating point numbers (using a period before any fractional
14979 The only options are @option{--help} and @option{--version}. @xref{Common
14982 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
14983 @mayConflictWithShellBuiltIn{sleep}
14988 @node Numeric operations
14989 @chapter Numeric operations
14991 @cindex numeric operations
14992 These programs do numerically-related operations.
14995 * factor invocation:: Show factors of numbers.
14996 * seq invocation:: Print sequences of numbers.
15000 @node factor invocation
15001 @section @command{factor}: Print prime factors
15004 @cindex prime factors
15006 @command{factor} prints prime factors. Synopses:
15009 factor [@var{number}]@dots{}
15010 factor @var{option}
15013 If no @var{number} is specified on the command line, @command{factor} reads
15014 numbers from standard input, delimited by newlines, tabs, or spaces.
15016 The @command{factor} command supports only a small number of options:
15020 Print a short help on standard output, then exit without further
15024 Print the program version on standard output, then exit without further
15028 Factoring the product of the eighth and ninth Mersenne primes
15029 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15032 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15033 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15034 4951760154835678088235319297: 2147483647 2305843009213693951
15038 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15039 about 20 seconds on the same machine.
15041 Factoring large prime numbers is, in general, hard. The Pollard Rho
15042 algorithm used by @command{factor} is particularly effective for
15043 numbers with relatively small factors. If you wish to factor large
15044 numbers which do not have small factors (for example, numbers which
15045 are the product of two large primes), other methods are far better.
15047 If @command{factor} is built without using GNU MP, only
15048 single-precision arithmetic is available, and so large numbers
15049 (typically @math{2^{64}} and above) will not be supported. The single-precision
15050 code uses an algorithm which is designed for factoring smaller
15056 @node seq invocation
15057 @section @command{seq}: Print numeric sequences
15060 @cindex numeric sequences
15061 @cindex sequence of numbers
15063 @command{seq} prints a sequence of numbers to standard output. Synopses:
15066 seq [@var{option}]@dots{} @var{last}
15067 seq [@var{option}]@dots{} @var{first} @var{last}
15068 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15071 @command{seq} prints the numbers from @var{first} to @var{last} by
15072 @var{increment}. By default, each number is printed on a separate line.
15073 When @var{increment} is not specified, it defaults to @samp{1},
15074 even when @var{first} is larger than @var{last}.
15075 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15076 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15077 Floating-point numbers
15078 may be specified (using a period before any fractional digits).
15080 The program accepts the following options. Also see @ref{Common options}.
15081 Options must precede operands.
15084 @item -f @var{format}
15085 @itemx --format=@var{format}
15086 @opindex -f @var{format}
15087 @opindex --format=@var{format}
15088 @cindex formatting of numbers in @command{seq}
15089 Print all numbers using @var{format}.
15090 @var{format} must contain exactly one of the @samp{printf}-style
15091 floating point conversion specifications @samp{%a}, @samp{%e},
15092 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15093 The @samp{%} may be followed by zero or more flags taken from the set
15094 @samp{-+#0 '}, then an optional width containing one or more digits,
15095 then an optional precision consisting of a @samp{.} followed by zero
15096 or more digits. @var{format} may also contain any number of @samp{%%}
15097 conversion specifications. All conversion specifications have the
15098 same meaning as with @samp{printf}.
15100 The default format is derived from @var{first}, @var{step}, and
15101 @var{last}. If these all use a fixed point decimal representation,
15102 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15103 precision that can represent the output numbers exactly. Otherwise,
15104 the default format is @samp{%g}.
15106 @item -s @var{string}
15107 @itemx --separator=@var{string}
15108 @cindex separator for numbers in @command{seq}
15109 Separate numbers with @var{string}; default is a newline.
15110 The output always terminates with a newline.
15113 @itemx --equal-width
15114 Print all numbers with the same width, by padding with leading zeros.
15115 @var{first}, @var{step}, and @var{last} should all use a fixed point
15116 decimal representation.
15117 (To have other kinds of padding, use @option{--format}).
15121 You can get finer-grained control over output with @option{-f}:
15124 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15130 If you want hexadecimal integer output, you can use @command{printf}
15131 to perform the conversion:
15134 $ printf '%x\n' `seq 1048575 1024 1050623`
15140 For very long lists of numbers, use xargs to avoid
15141 system limitations on the length of an argument list:
15144 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15150 To generate octal output, use the printf @code{%o} format instead
15153 On most systems, seq can produce whole-number output for values up to
15154 at least @math{2^{53}}. Larger integers are approximated. The details
15155 differ depending on your floating-point implementation, but a common
15156 case is that @command{seq} works with integers through @math{2^{64}},
15157 and larger integers may not be numerically correct:
15160 $ seq 18446744073709551616 1 18446744073709551618
15161 18446744073709551616
15162 18446744073709551616
15163 18446744073709551618
15166 Be careful when using @command{seq} with outlandish values: otherwise
15167 you may see surprising results, as @command{seq} uses floating point
15168 internally. For example, on the x86 platform, where the internal
15169 representation uses a 64-bit fraction, the command:
15172 seq 1 0.0000000000000000001 1.0000000000000000009
15175 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15180 @node File permissions
15181 @chapter File permissions
15184 @include getdate.texi
15188 @node Opening the software toolbox
15189 @chapter Opening the Software Toolbox
15191 An earlier version of this chapter appeared in
15192 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15193 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15194 It was written by Arnold Robbins.
15197 * Toolbox introduction:: Toolbox introduction
15198 * I/O redirection:: I/O redirection
15199 * The who command:: The @command{who} command
15200 * The cut command:: The @command{cut} command
15201 * The sort command:: The @command{sort} command
15202 * The uniq command:: The @command{uniq} command
15203 * Putting the tools together:: Putting the tools together
15207 @node Toolbox introduction
15208 @unnumberedsec Toolbox Introduction
15210 This month's column is only peripherally related to the GNU Project, in
15211 that it describes a number of the GNU tools on your GNU/Linux system and how they
15212 might be used. What it's really about is the ``Software Tools'' philosophy
15213 of program development and usage.
15215 The software tools philosophy was an important and integral concept
15216 in the initial design and development of Unix (of which Linux and GNU are
15217 essentially clones). Unfortunately, in the modern day press of
15218 Internetworking and flashy GUIs, it seems to have fallen by the
15219 wayside. This is a shame, since it provides a powerful mental model
15220 for solving many kinds of problems.
15222 Many people carry a Swiss Army knife around in their pants pockets (or
15223 purse). A Swiss Army knife is a handy tool to have: it has several knife
15224 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15225 a number of other things on it. For the everyday, small miscellaneous jobs
15226 where you need a simple, general purpose tool, it's just the thing.
15228 On the other hand, an experienced carpenter doesn't build a house using
15229 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15230 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15231 exactly when and where to use each tool; you won't catch him hammering nails
15232 with the handle of his screwdriver.
15234 The Unix developers at Bell Labs were all professional programmers and trained
15235 computer scientists. They had found that while a one-size-fits-all program
15236 might appeal to a user because there's only one program to use, in practice
15241 difficult to write,
15244 difficult to maintain and
15248 difficult to extend to meet new situations.
15251 Instead, they felt that programs should be specialized tools. In short, each
15252 program ``should do one thing well.'' No more and no less. Such programs are
15253 simpler to design, write, and get right---they only do one thing.
15255 Furthermore, they found that with the right machinery for hooking programs
15256 together, that the whole was greater than the sum of the parts. By combining
15257 several special purpose programs, you could accomplish a specific task
15258 that none of the programs was designed for, and accomplish it much more
15259 quickly and easily than if you had to write a special purpose program.
15260 We will see some (classic) examples of this further on in the column.
15261 (An important additional point was that, if necessary, take a detour
15262 and build any software tools you may need first, if you don't already
15263 have something appropriate in the toolbox.)
15265 @node I/O redirection
15266 @unnumberedsec I/O Redirection
15268 Hopefully, you are familiar with the basics of I/O redirection in the
15269 shell, in particular the concepts of ``standard input,'' ``standard output,''
15270 and ``standard error''. Briefly, ``standard input'' is a data source, where
15271 data comes from. A program should not need to either know or care if the
15272 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15273 card reader. Similarly, ``standard output'' is a data sink, where data goes
15274 to. The program should neither know nor care where this might be.
15275 Programs that only read their standard input, do something to the data,
15276 and then send it on, are called @dfn{filters}, by analogy to filters in a
15279 With the Unix shell, it's very easy to set up data pipelines:
15282 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15285 We start out by creating the raw data; each filter applies some successive
15286 transformation to the data, until by the time it comes out of the pipeline,
15287 it is in the desired form.
15289 This is fine and good for standard input and standard output. Where does the
15290 standard error come in to play? Well, think about @command{filter1} in
15291 the pipeline above. What happens if it encounters an error in the data it
15292 sees? If it writes an error message to standard output, it will just
15293 disappear down the pipeline into @command{filter2}'s input, and the
15294 user will probably never see it. So programs need a place where they can send
15295 error messages so that the user will notice them. This is standard error,
15296 and it is usually connected to your console or window, even if you have
15297 redirected standard output of your program away from your screen.
15299 For filter programs to work together, the format of the data has to be
15300 agreed upon. The most straightforward and easiest format to use is simply
15301 lines of text. Unix data files are generally just streams of bytes, with
15302 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15303 conventionally called a ``newline'' in the Unix literature. (This is
15304 @code{'\n'} if you're a C programmer.) This is the format used by all
15305 the traditional filtering programs. (Many earlier operating systems
15306 had elaborate facilities and special purpose programs for managing
15307 binary data. Unix has always shied away from such things, under the
15308 philosophy that it's easiest to simply be able to view and edit your
15309 data with a text editor.)
15311 OK, enough introduction. Let's take a look at some of the tools, and then
15312 we'll see how to hook them together in interesting ways. In the following
15313 discussion, we will only present those command line options that interest
15314 us. As you should always do, double check your system documentation
15315 for the full story.
15317 @node The who command
15318 @unnumberedsec The @command{who} Command
15320 The first program is the @command{who} command. By itself, it generates a
15321 list of the users who are currently logged in. Although I'm writing
15322 this on a single-user system, we'll pretend that several people are
15327 @print{} arnold console Jan 22 19:57
15328 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15329 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15330 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15333 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15334 There are three people logged in, and I am logged in twice. On traditional
15335 Unix systems, user names are never more than eight characters long. This
15336 little bit of trivia will be useful later. The output of @command{who} is nice,
15337 but the data is not all that exciting.
15339 @node The cut command
15340 @unnumberedsec The @command{cut} Command
15342 The next program we'll look at is the @command{cut} command. This program
15343 cuts out columns or fields of input data. For example, we can tell it
15344 to print just the login name and full name from the @file{/etc/passwd}
15345 file. The @file{/etc/passwd} file has seven fields, separated by
15349 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15352 To get the first and fifth fields, we would use @command{cut} like this:
15355 $ cut -d: -f1,5 /etc/passwd
15356 @print{} root:Operator
15358 @print{} arnold:Arnold D. Robbins
15359 @print{} miriam:Miriam A. Robbins
15363 With the @option{-c} option, @command{cut} will cut out specific characters
15364 (i.e., columns) in the input lines. This is useful for input data
15365 that has fixed width fields, and does not have a field separator. For
15366 example, list the Monday dates for the current month:
15368 @c Is using cal ok? Looked at gcal, but I don't like it.
15379 @node The sort command
15380 @unnumberedsec The @command{sort} Command
15382 Next we'll look at the @command{sort} command. This is one of the most
15383 powerful commands on a Unix-style system; one that you will often find
15384 yourself using when setting up fancy data plumbing.
15387 command reads and sorts each file named on the command line. It then
15388 merges the sorted data and writes it to standard output. It will read
15389 standard input if no files are given on the command line (thus
15390 making it into a filter). The sort is based on the character collating
15391 sequence or based on user-supplied ordering criteria.
15394 @node The uniq command
15395 @unnumberedsec The @command{uniq} Command
15397 Finally (at least for now), we'll look at the @command{uniq} program. When
15398 sorting data, you will often end up with duplicate lines, lines that
15399 are identical. Usually, all you need is one instance of each line.
15400 This is where @command{uniq} comes in. The @command{uniq} program reads its
15401 standard input. It prints only one
15402 copy of each repeated line. It does have several options. Later on,
15403 we'll use the @option{-c} option, which prints each unique line, preceded
15404 by a count of the number of times that line occurred in the input.
15407 @node Putting the tools together
15408 @unnumberedsec Putting the Tools Together
15410 Now, let's suppose this is a large ISP server system with dozens of users
15411 logged in. The management wants the system administrator to write a program that will
15412 generate a sorted list of logged in users. Furthermore, even if a user
15413 is logged in multiple times, his or her name should only show up in the
15416 The administrator could sit down with the system documentation and write a C
15417 program that did this. It would take perhaps a couple of hundred lines
15418 of code and about two hours to write it, test it, and debug it.
15419 However, knowing the software toolbox, the administrator can instead start out
15420 by generating just a list of logged on users:
15430 Next, sort the list:
15433 $ who | cut -c1-8 | sort
15440 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15443 $ who | cut -c1-8 | sort | uniq
15449 The @command{sort} command actually has a @option{-u} option that does what
15450 @command{uniq} does. However, @command{uniq} has other uses for which one
15451 cannot substitute @samp{sort -u}.
15453 The administrator puts this pipeline into a shell script, and makes it available for
15454 all the users on the system (@samp{#} is the system administrator,
15455 or @code{root}, prompt):
15458 # cat > /usr/local/bin/listusers
15459 who | cut -c1-8 | sort | uniq
15461 # chmod +x /usr/local/bin/listusers
15464 There are four major points to note here. First, with just four
15465 programs, on one command line, the administrator was able to save about two
15466 hours worth of work. Furthermore, the shell pipeline is just about as
15467 efficient as the C program would be, and it is much more efficient in
15468 terms of programmer time. People time is much more expensive than
15469 computer time, and in our modern ``there's never enough time to do
15470 everything'' society, saving two hours of programmer time is no mean
15473 Second, it is also important to emphasize that with the
15474 @emph{combination} of the tools, it is possible to do a special
15475 purpose job never imagined by the authors of the individual programs.
15477 Third, it is also valuable to build up your pipeline in stages, as we did here.
15478 This allows you to view the data at each stage in the pipeline, which helps
15479 you acquire the confidence that you are indeed using these tools correctly.
15481 Finally, by bundling the pipeline in a shell script, other users can use
15482 your command, without having to remember the fancy plumbing you set up for
15483 them. In terms of how you run them, shell scripts and compiled programs are
15486 After the previous warm-up exercise, we'll look at two additional, more
15487 complicated pipelines. For them, we need to introduce two more tools.
15489 The first is the @command{tr} command, which stands for ``transliterate.''
15490 The @command{tr} command works on a character-by-character basis, changing
15491 characters. Normally it is used for things like mapping upper case to
15495 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15496 @print{} this example has mixed case!
15499 There are several options of interest:
15503 work on the complement of the listed characters, i.e.,
15504 operations apply to characters not in the given set
15507 delete characters in the first set from the output
15510 squeeze repeated characters in the output into just one character.
15513 We will be using all three options in a moment.
15515 The other command we'll look at is @command{comm}. The @command{comm}
15516 command takes two sorted input files as input data, and prints out the
15517 files' lines in three columns. The output columns are the data lines
15518 unique to the first file, the data lines unique to the second file, and
15519 the data lines that are common to both. The @option{-1}, @option{-2}, and
15520 @option{-3} command line options @emph{omit} the respective columns. (This is
15521 non-intuitive and takes a little getting used to.) For example:
15543 The file name @file{-} tells @command{comm} to read standard input
15544 instead of a regular file.
15546 Now we're ready to build a fancy pipeline. The first application is a word
15547 frequency counter. This helps an author determine if he or she is over-using
15550 The first step is to change the case of all the letters in our input file
15551 to one case. ``The'' and ``the'' are the same word when doing counting.
15554 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15557 The next step is to get rid of punctuation. Quoted words and unquoted words
15558 should be treated identically; it's easiest to just get the punctuation out of
15562 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15565 The second @command{tr} command operates on the complement of the listed
15566 characters, which are all the letters, the digits, the underscore, and
15567 the blank. The @samp{\n} represents the newline character; it has to
15568 be left alone. (The @acronym{ASCII} tab character should also be included for
15569 good measure in a production script.)
15571 At this point, we have data consisting of words separated by blank space.
15572 The words only contain alphanumeric characters (and the underscore). The
15573 next step is break the data apart so that we have one word per line. This
15574 makes the counting operation much easier, as we will see shortly.
15577 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15578 > tr -s ' ' '\n' | ...
15581 This command turns blanks into newlines. The @option{-s} option squeezes
15582 multiple newline characters in the output into just one. This helps us
15583 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15584 This is what the shell prints when it notices you haven't finished
15585 typing in all of a command.)
15587 We now have data consisting of one word per line, no punctuation, all one
15588 case. We're ready to count each word:
15591 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15592 > tr -s ' ' '\n' | sort | uniq -c | ...
15595 At this point, the data might look something like this:
15608 The output is sorted by word, not by count! What we want is the most
15609 frequently used words first. Fortunately, this is easy to accomplish,
15610 with the help of two more @command{sort} options:
15614 do a numeric sort, not a textual one
15617 reverse the order of the sort
15620 The final pipeline looks like this:
15623 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15624 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15633 Whew! That's a lot to digest. Yet, the same principles apply. With six
15634 commands, on two lines (really one long one split for convenience), we've
15635 created a program that does something interesting and useful, in much
15636 less time than we could have written a C program to do the same thing.
15638 A minor modification to the above pipeline can give us a simple spelling
15639 checker! To determine if you've spelled a word correctly, all you have to
15640 do is look it up in a dictionary. If it is not there, then chances are
15641 that your spelling is incorrect. So, we need a dictionary.
15642 The conventional location for a dictionary is @file{/usr/dict/words}.
15643 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15644 revision of this article.}
15645 this is a sorted, 45,402 word dictionary.
15647 Now, how to compare our file with the dictionary? As before, we generate
15648 a sorted list of words, one per line:
15651 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15652 > tr -s ' ' '\n' | sort -u | ...
15655 Now, all we need is a list of words that are @emph{not} in the
15656 dictionary. Here is where the @command{comm} command comes in.
15659 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15660 > tr -s ' ' '\n' | sort -u |
15661 > comm -23 - /usr/dict/words
15664 The @option{-2} and @option{-3} options eliminate lines that are only in the
15665 dictionary (the second file), and lines that are in both files. Lines
15666 only in the first file (standard input, our stream of words), are
15667 words that are not in the dictionary. These are likely candidates for
15668 spelling errors. This pipeline was the first cut at a production
15669 spelling checker on Unix.
15671 There are some other tools that deserve brief mention.
15675 search files for text that matches a regular expression
15678 count lines, words, characters
15681 a T-fitting for data pipes, copies data to files and to standard output
15684 the stream editor, an advanced tool
15687 a data manipulation language, another advanced tool
15690 The software tools philosophy also espoused the following bit of
15691 advice: ``Let someone else do the hard part.'' This means, take
15692 something that gives you most of what you need, and then massage it the
15693 rest of the way until it's in the form that you want.
15699 Each program should do one thing well. No more, no less.
15702 Combining programs with appropriate plumbing leads to results where
15703 the whole is greater than the sum of the parts. It also leads to novel
15704 uses of programs that the authors might never have imagined.
15707 Programs should never print extraneous header or trailer data, since these
15708 could get sent on down a pipeline. (A point we didn't mention earlier.)
15711 Let someone else do the hard part.
15714 Know your toolbox! Use each program appropriately. If you don't have an
15715 appropriate tool, build one.
15718 As of this writing, all the programs we've discussed are available via
15719 anonymous @command{ftp} from: @*
15720 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15721 be more recent versions available now.)
15723 None of what I have presented in this column is new. The Software Tools
15724 philosophy was first introduced in the book @cite{Software Tools}, by
15725 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15726 This book showed how to write and use software tools. It was written in
15727 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15728 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15729 was. The last chapter presented a @command{ratfor} to FORTRAN
15730 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15731 lot like C; if you know C, you won't have any problem following the
15734 In 1981, the book was updated and made available as @cite{Software Tools
15735 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15736 still in print and are well worth
15737 reading if you're a programmer. They certainly made a major change in
15738 how I view programming.
15740 The programs in both books are available from
15741 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15742 For a number of years, there was an active
15743 Software Tools Users Group, whose members had ported the original
15744 @command{ratfor} programs to essentially every computer system with a
15745 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15746 as Unix began to spread beyond universities.
15748 With the current proliferation of GNU code and other clones of Unix programs,
15749 these programs now receive little attention; modern C versions are
15750 much more efficient and do more than these programs do. Nevertheless, as
15751 exposition of good programming style, and evangelism for a still-valuable
15752 philosophy, these books are unparalleled, and I recommend them highly.
15754 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15755 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15757 @node GNU Free Documentation License
15758 @appendix GNU Free Documentation License
15762 @node Concept index
15769 @c Local variables:
15770 @c texinfo-column-for-description: 32