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.
429 * chcon invocation:: Change SELinux context of file
430 * runcon invocation:: Run a command in specified SELinux context
432 Modified command invocation
434 * chroot invocation:: Run a command with a different root directory
435 * env invocation:: Run a command in a modified environment
436 * nice invocation:: Run a command with modified niceness
437 * nohup invocation:: Run a command immune to hangups
438 * stdbuf invocation:: Run a command with modified I/O buffering
439 * su invocation:: Run a command with substitute user and group ID
440 * timeout invocation:: Run a command with a time limit
444 * kill invocation:: Sending a signal to processes.
448 * sleep invocation:: Delay for a specified time
452 * factor invocation:: Print prime factors
453 * seq invocation:: Print numeric sequences
457 * Mode Structure:: Structure of file mode bits.
458 * Symbolic Modes:: Mnemonic representation of file mode bits.
459 * Numeric Modes:: File mode bits as octal numbers.
460 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories.
464 * General date syntax:: Common rules.
465 * Calendar date items:: 19 Dec 1994.
466 * Time of day items:: 9:20pm.
467 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}.
468 * Day of week items:: Monday and others.
469 * Relative items in date strings:: next tuesday, 2 years ago.
470 * Pure numbers in date strings:: 19931219, 1440.
471 * Seconds since the Epoch:: @@1078100502.
472 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0".
473 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al.
475 Opening the software toolbox
477 * Toolbox introduction:: Toolbox introduction
478 * I/O redirection:: I/O redirection
479 * The who command:: The @command{who} command
480 * The cut command:: The @command{cut} command
481 * The sort command:: The @command{sort} command
482 * The uniq command:: The @command{uniq} command
483 * Putting the tools together:: Putting the tools together
487 * GNU Free Documentation License:: Copying and sharing this manual.
494 @chapter Introduction
496 This manual is a work in progress: many sections make no attempt to explain
497 basic concepts in a way suitable for novices. Thus, if you are interested,
498 please get involved in improving this manual. The entire @sc{gnu} community
501 @cindex @acronym{POSIX}
502 The @sc{gnu} utilities documented here are mostly compatible with the
503 @acronym{POSIX} standard.
504 @cindex bugs, reporting
505 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
506 to include the version number, machine architecture, input files, and
507 any other information needed to reproduce the bug: your input, what you
508 expected, what you got, and why it is wrong. Diffs are welcome, but
509 please include a description of the problem as well, since this is
510 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
516 @cindex MacKenzie, D.
519 This manual was originally derived from the Unix man pages in the
520 distributions, which were written by David MacKenzie and updated by Jim
521 Meyering. What you are reading now is the authoritative documentation
522 for these utilities; the man pages are no longer being maintained. The
523 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
524 Pinard did the initial conversion to Texinfo format. Karl Berry did the
525 indexing, some reorganization, and editing of the results. Brian
526 Youmans of the Free Software Foundation office staff combined the
527 manuals for textutils, fileutils, and sh-utils to produce the present
528 omnibus manual. Richard Stallman contributed his usual invaluable
529 insights to the overall process.
532 @chapter Common options
536 @itemx @w{@kbd{--backup}[=@var{method}]}
539 @vindex VERSION_CONTROL
540 @cindex backups, making
541 @xref{Backup options}.
542 Make a backup of each file that would otherwise be overwritten or removed.
545 @macro optBackupSuffix
546 @item -S @var{suffix}
547 @itemx --suffix=@var{suffix}
550 Append @var{suffix} to each backup file made with @option{-b}.
551 @xref{Backup options}.
554 @macro optTargetDirectory
555 @item -t @var{directory}
556 @itemx @w{@kbd{--target-directory}=@var{directory}}
558 @opindex --target-directory
559 @cindex target directory
560 @cindex destination directory
561 Specify the destination @var{directory}.
562 @xref{Target directory}.
565 @macro optNoTargetDirectory
567 @itemx --no-target-directory
569 @opindex --no-target-directory
570 @cindex target directory
571 @cindex destination directory
572 Do not treat the last operand specially when it is a directory or a
573 symbolic link to a directory. @xref{Target directory}.
580 Append an SI-style abbreviation to each size, such as @samp{M} for
581 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
582 1,000,000 bytes. This option is equivalent to
583 @option{--block-size=si}. Use the @option{-h} or
584 @option{--human-readable} option if
585 you prefer powers of 1024.
588 @macro optHumanReadable
590 @itemx --human-readable
592 @opindex --human-readable
593 @cindex human-readable output
594 Append a size letter to each size, such as @samp{M} for mebibytes.
595 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
596 This option is equivalent to @option{--block-size=human-readable}.
597 Use the @option{--si} option if you prefer powers of 1000.
600 @macro optStripTrailingSlashes
601 @itemx @w{@kbd{--strip-trailing-slashes}}
602 @opindex --strip-trailing-slashes
603 @cindex stripping trailing slashes
604 Remove any trailing slashes from each @var{source} argument.
605 @xref{Trailing slashes}.
608 @macro mayConflictWithShellBuiltIn{cmd}
609 @cindex conflicts with shell built-ins
610 @cindex built-in shell commands, conflicts with
611 Due to shell aliases and built-in @command{\cmd\} command, using an
612 unadorned @command{\cmd\} interactively or in a script may get you
613 different functionality than that described here. Invoke it via
614 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
619 @macro multiplierSuffixes{varName}
621 Appending @samp{b} multiplies @var{\varName\} by 512,
622 @samp{kB} by 1000, @samp{K} by 1024,
623 @samp{MB} by 1000*1000, @samp{M} by 1024*1024,
624 @samp{GB} by 1000*1000*1000, @samp{G} by 1024*1024*1024,
625 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
627 @var{\varName\} is a number which may have one of the following
628 multiplicative suffixes:
630 @samp{b} => 512 ("blocks")
631 @samp{KB} => 1000 (KiloBytes)
632 @samp{K} => 1024 (KibiBytes)
633 @samp{MB} => 1000*1000 (MegaBytes)
634 @samp{M} => 1024*1024 (MebiBytes)
635 @samp{GB} => 1000*1000*1000 (GigaBytes)
636 @samp{G} => 1024*1024*1024 (GibiBytes)
638 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
641 @c FIXME: same as above, but no ``blocks'' line.
642 @macro multiplierSuffixesNoBlocks{varName}
643 @var{\varName\} is a number which may have one of the following
644 multiplicative suffixes:
646 @samp{KB} => 1000 (KiloBytes)
647 @samp{K} => 1024 (KibiBytes)
648 @samp{MB} => 1000*1000 (MegaBytes)
649 @samp{M} => 1024*1024 (MebiBytes)
650 @samp{GB} => 1000*1000*1000 (GigaBytes)
651 @samp{G} => 1024*1024*1024 (GibiBytes)
653 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
656 @cindex common options
658 Certain options are available in all of these programs. Rather than
659 writing identical descriptions for each of the programs, they are
660 described here. (In fact, every @sc{gnu} program accepts (or should accept)
663 @vindex POSIXLY_CORRECT
664 Normally options and operands can appear in any order, and programs act
665 as if all the options appear before any operands. For example,
666 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
667 @samp{:} is an option-argument of @option{-t}. However, if the
668 @env{POSIXLY_CORRECT} environment variable is set, options must appear
669 before operands, unless otherwise specified for a particular command.
671 A few programs can usefully have trailing operands with leading
672 @samp{-}. With such a program, options must precede operands even if
673 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
674 program description. For example, the @command{env} command's options
675 must appear before its operands, since in some cases the operands
676 specify a command that itself contains options.
678 Most programs that accept long options recognize unambiguous
679 abbreviations of those options. For example, @samp{rmdir
680 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
681 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
682 @samp{ls --h}, are identified as such.
684 Some of these programs recognize the @option{--help} and @option{--version}
685 options only when one of them is the sole command line argument. For
686 these programs, abbreviations of the long options are not always recognized.
693 Print a usage message listing all available options, then exit successfully.
697 @cindex version number, finding
698 Print the version number, then exit successfully.
702 @cindex option delimiter
703 Delimit the option list. Later arguments, if any, are treated as
704 operands even if they begin with @samp{-}. For example, @samp{sort --
705 -r} reads from the file named @file{-r}.
709 @cindex standard input
710 @cindex standard output
711 A single @samp{-} operand is not really an option, though it looks like one. It
712 stands for standard input, or for standard output if that is clear from
713 the context. For example, @samp{sort -} reads from standard input,
714 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
715 extra copy of its input to standard output. Unless otherwise
716 specified, @samp{-} can appear as any operand that requires a file
720 * Exit status:: Indicating program success or failure.
721 * Backup options:: -b -S, in some programs.
722 * Block size:: BLOCK_SIZE and --block-size, in some programs.
723 * Signal specifications:: Specifying signals using the --signal option.
724 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
725 * Random sources:: --random-source, in some programs.
726 * Target directory:: Specifying a target directory, in some programs.
727 * Trailing slashes:: --strip-trailing-slashes, in some programs.
728 * Traversing symlinks:: -H, -L, or -P, in some programs.
729 * Treating / specially:: --preserve-root and --no-preserve-root.
730 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
731 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
739 An exit status of zero indicates success,
740 and a nonzero value indicates failure.
743 Nearly every command invocation yields an integral @dfn{exit status}
744 that can be used to change how other commands work.
745 For the vast majority of commands, an exit status of zero indicates
746 success. Failure is indicated by a nonzero value---typically
747 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
748 requires only that it be nonzero.
750 However, some of the programs documented here do produce
751 other exit status values and a few associate different
752 meanings with the values @samp{0} and @samp{1}.
753 Here are some of the exceptions:
754 @command{chroot}, @command{env}, @command{expr},
755 @command{nice}, @command{nohup}, @command{printenv}, @command{sort},
756 @command{su}, @command{test}, @command{timeout}, @command{tty}.
760 @section Backup options
762 @cindex backup options
764 Some @sc{gnu} programs (at least @command{cp}, @command{install},
765 @command{ln}, and @command{mv}) optionally make backups of files
766 before writing new versions.
767 These options control the details of these backups. The options are also
768 briefly mentioned in the descriptions of the particular programs.
773 @itemx @w{@kbd{--backup}[=@var{method}]}
776 @vindex VERSION_CONTROL
777 @cindex backups, making
778 Make a backup of each file that would otherwise be overwritten or removed.
779 Without this option, the original versions are destroyed.
780 Use @var{method} to determine the type of backups to make.
781 When this option is used but @var{method} is not specified,
782 then the value of the @env{VERSION_CONTROL}
783 environment variable is used. And if @env{VERSION_CONTROL} is not set,
784 the default backup type is @samp{existing}.
786 Note that the short form of this option, @option{-b} does not accept any
787 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
789 @vindex version-control @r{Emacs variable}
790 This option corresponds to the Emacs variable @samp{version-control};
791 the values for @var{method} are the same as those used in Emacs.
792 This option also accepts more descriptive names.
793 The valid @var{method}s are (unique abbreviations are accepted):
798 @opindex none @r{backup method}
803 @opindex numbered @r{backup method}
804 Always make numbered backups.
808 @opindex existing @r{backup method}
809 Make numbered backups of files that already have them, simple backups
814 @opindex simple @r{backup method}
815 Always make simple backups. Please note @samp{never} is not to be
816 confused with @samp{none}.
820 @item -S @var{suffix}
821 @itemx --suffix=@var{suffix}
824 @cindex backup suffix
825 @vindex SIMPLE_BACKUP_SUFFIX
826 Append @var{suffix} to each backup file made with @option{-b}. If this
827 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
828 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
829 set, the default is @samp{~}, just as in Emacs.
838 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
839 @command{ls}) display sizes in ``blocks''. You can adjust the block size
840 and method of display to make sizes easier to read. The block size
841 used for display is independent of any file system block size.
842 Fractional block counts are rounded up to the nearest integer.
844 @opindex --block-size=@var{size}
847 @vindex DF_BLOCK_SIZE
848 @vindex DU_BLOCK_SIZE
849 @vindex LS_BLOCK_SIZE
850 @vindex POSIXLY_CORRECT@r{, and block size}
852 The default block size is chosen by examining the following environment
853 variables in turn; the first one that is set determines the block size.
858 This specifies the default block size for the @command{df} command.
859 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
860 @env{LS_BLOCK_SIZE} for @command{ls}.
863 This specifies the default block size for all three commands, if the
864 above command-specific environment variables are not set.
867 This specifies the default block size for all values that are normally
868 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
869 command-specific environment variables are set. Unlike the other
870 environment variables, @env{BLOCKSIZE} does not affect values that are
871 normally printed as byte counts, e.g., the file sizes contained in
874 @item POSIXLY_CORRECT
875 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
876 @env{BLOCKSIZE} is set, but this variable is set, the block size
881 If none of the above environment variables are set, the block size
882 currently defaults to 1024 bytes in most contexts, but this number may
883 change in the future. For @command{ls} file sizes, the block size
886 @cindex human-readable output
889 A block size specification can be a positive integer specifying the number
890 of bytes per block, or it can be @code{human-readable} or @code{si} to
891 select a human-readable format. Integers may be followed by suffixes
892 that are upward compatible with the
893 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
894 for decimal multiples and with the
895 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
896 prefixes for binary multiples}.
898 With human-readable formats, output sizes are followed by a size letter
899 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
900 powers of 1024; @samp{M} stands for 1,048,576 bytes.
901 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
902 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
905 A block size specification preceded by @samp{'} causes output sizes to
906 be displayed with thousands separators. The @env{LC_NUMERIC} locale
907 specifies the thousands separator and grouping. For example, in an
908 American English locale, @samp{--block-size="'1kB"} would cause a size
909 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
910 locale, there is no thousands separator so a leading @samp{'} has no
913 An integer block size can be followed by a suffix to specify a
914 multiple of that size. A bare size letter,
915 or one followed by @samp{iB}, specifies
916 a multiple using powers of 1024. A size letter followed by @samp{B}
917 specifies powers of 1000 instead. For example, @samp{1M} and
918 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
919 equivalent to @samp{1000000}.
921 A plain suffix without a preceding integer acts as if @samp{1} were
922 prepended, except that it causes a size indication to be appended to
923 the output. For example, @samp{--block-size="kB"} displays 3000 as
926 The following suffixes are defined. Large sizes like @code{1Y}
927 may be rejected by your computer due to limitations of its arithmetic.
931 @cindex kilobyte, definition of
932 kilobyte: @math{10^3 = 1000}.
936 @cindex kibibyte, definition of
937 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
938 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
939 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
941 @cindex megabyte, definition of
942 megabyte: @math{10^6 = 1,000,000}.
945 @cindex mebibyte, definition of
946 mebibyte: @math{2^{20} = 1,048,576}.
948 @cindex gigabyte, definition of
949 gigabyte: @math{10^9 = 1,000,000,000}.
952 @cindex gibibyte, definition of
953 gibibyte: @math{2^{30} = 1,073,741,824}.
955 @cindex terabyte, definition of
956 terabyte: @math{10^{12} = 1,000,000,000,000}.
959 @cindex tebibyte, definition of
960 tebibyte: @math{2^{40} = 1,099,511,627,776}.
962 @cindex petabyte, definition of
963 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
966 @cindex pebibyte, definition of
967 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
969 @cindex exabyte, definition of
970 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
973 @cindex exbibyte, definition of
974 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
976 @cindex zettabyte, definition of
977 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
980 @math{2^{70} = 1,180,591,620,717,411,303,424}.
981 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
983 @cindex yottabyte, definition of
984 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
987 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
988 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
993 @opindex --block-size
994 @opindex --human-readable
997 Block size defaults can be overridden by an explicit
998 @option{--block-size=@var{size}} option. The @option{-k}
999 option is equivalent to @option{--block-size=1K}, which
1000 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1001 set. The @option{-h} or @option{--human-readable} option is equivalent to
1002 @option{--block-size=human-readable}. The @option{--si} option is
1003 equivalent to @option{--block-size=si}.
1005 @node Signal specifications
1006 @section Signal specifications
1007 @cindex signals, specifying
1009 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1010 number like @samp{1}, or an exit status of a process terminated by the
1011 signal. A signal name can be given in canonical form or prefixed by
1012 @samp{SIG}. The case of the letters is ignored. The following signal names
1013 and numbers are supported on all @acronym{POSIX} compliant systems:
1019 2. Terminal interrupt.
1025 9. Kill (cannot be caught or ignored).
1033 Other supported signal names have system-dependent corresponding
1034 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1035 support the following signals:
1039 Access to an undefined portion of a memory object.
1041 Child process terminated, stopped, or continued.
1043 Continue executing, if stopped.
1045 Erroneous arithmetic operation.
1047 Illegal Instruction.
1049 Write on a pipe with no one to read it.
1051 Invalid memory reference.
1053 Stop executing (cannot be caught or ignored).
1057 Background process attempting read.
1059 Background process attempting write.
1061 High bandwidth data is available at a socket.
1063 User-defined signal 1.
1065 User-defined signal 2.
1069 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1070 also support the following signals:
1076 Profiling timer expired.
1080 Trace/breakpoint trap.
1082 Virtual timer expired.
1084 CPU time limit exceeded.
1086 File size limit exceeded.
1090 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1091 also support at least eight real-time signals called @samp{RTMIN},
1092 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1094 @node Disambiguating names and IDs
1095 @section chown and chgrp: Disambiguating user names and IDs
1096 @cindex user names, disambiguating
1097 @cindex user IDs, disambiguating
1098 @cindex group names, disambiguating
1099 @cindex group IDs, disambiguating
1100 @cindex disambiguating group names and IDs
1102 Since the @var{owner} and @var{group} arguments to @command{chown} and
1103 @command{chgrp} may be specified as names or numeric IDs, there is an
1105 What if a user or group @emph{name} is a string of digits?
1106 @footnote{Using a number as a user name is common in some environments.}
1107 Should the command interpret it as a user name or as an ID?
1108 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1109 first attempt to resolve the specified string as a name, and
1110 only once that fails, then try to interpret it as an ID.
1111 This is troublesome when you want to specify a numeric ID, say 42,
1112 and it must work even in a pathological situation where
1113 @samp{42} is a user name that maps to some other user ID, say 1000.
1114 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1115 1000---not what you intended.
1117 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1118 that at the same time may result in a significant performance improvement
1119 by eliminating a database look-up.
1120 Simply precede each numeric user ID and/or group ID with a @samp{+},
1121 in order to force its interpretation as an integer:
1125 chgrp +$numeric_group_id another-file
1129 GNU @command{chown} and @command{chgrp}
1130 skip the name look-up process for each @samp{+}-prefixed string,
1131 because a string containing @samp{+} is never a valid user or group name.
1132 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1134 @node Random sources
1135 @section Sources of random data
1137 @cindex random sources
1139 The @command{shuf}, @command{shred}, and @command{sort} commands
1140 sometimes need random data to do their work. For example, @samp{sort
1141 -R} must choose a hash function at random, and it needs random data to
1142 make this selection.
1144 By default these commands use an internal pseudorandom generator
1145 initialized by a small amount of entropy, but can be directed to use
1146 an external source with the @option{--random-source=@var{file}} option.
1147 An error is reported if @var{file} does not contain enough bytes.
1149 For example, the device file @file{/dev/urandom} could be used as the
1150 source of random data. Typically, this device gathers environmental
1151 noise from device drivers and other sources into an entropy pool, and
1152 uses the pool to generate random bits. If the pool is short of data,
1153 the device reuses the internal pool to produce more bits, using a
1154 cryptographically secure pseudorandom number generator. But be aware
1155 that this device is not designed for bulk random data generation
1156 and is relatively slow.
1158 @file{/dev/urandom} suffices for most practical uses, but applications
1159 requiring high-value or long-term protection of private data may
1160 require an alternate data source like @file{/dev/random} or
1161 @file{/dev/arandom}. The set of available sources depends on your
1164 To reproduce the results of an earlier invocation of a command, you
1165 can save some random data into a file and then use that file as the
1166 random source in earlier and later invocations of the command.
1168 @node Target directory
1169 @section Target directory
1171 @cindex target directory
1173 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1174 commands normally treat the last operand specially when it is a
1175 directory or a symbolic link to a directory. For example, @samp{cp
1176 source dest} is equivalent to @samp{cp source dest/source} if
1177 @file{dest} is a directory. Sometimes this behavior is not exactly
1178 what is wanted, so these commands support the following options to
1179 allow more fine-grained control:
1184 @itemx --no-target-directory
1185 @opindex --no-target-directory
1186 @cindex target directory
1187 @cindex destination directory
1188 Do not treat the last operand specially when it is a directory or a
1189 symbolic link to a directory. This can help avoid race conditions in
1190 programs that operate in a shared area. For example, when the command
1191 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1192 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1193 renamed to @file{/tmp/dest/source} instead, if some other process
1194 created @file{/tmp/dest} as a directory. However, if @file{mv
1195 -T /tmp/source /tmp/dest} succeeds, there is no
1196 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1198 In the opposite situation, where you want the last operand to be
1199 treated as a directory and want a diagnostic otherwise, you can use
1200 the @option{--target-directory} (@option{-t}) option.
1202 @item -t @var{directory}
1203 @itemx @w{@kbd{--target-directory}=@var{directory}}
1204 @opindex --target-directory
1205 @cindex target directory
1206 @cindex destination directory
1207 Use @var{directory} as the directory component of each destination
1210 The interface for most programs is that after processing options and a
1211 finite (possibly zero) number of fixed-position arguments, the remaining
1212 argument list is either expected to be empty, or is a list of items
1213 (usually files) that will all be handled identically. The @command{xargs}
1214 program is designed to work well with this convention.
1216 The commands in the @command{mv}-family are unusual in that they take
1217 a variable number of arguments with a special case at the @emph{end}
1218 (namely, the target directory). This makes it nontrivial to perform some
1219 operations, e.g., ``move all files from here to ../d/'', because
1220 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1221 doesn't have a clean way to specify an extra final argument for each
1222 invocation of the subject command. (It can be done by going through a
1223 shell command, but that requires more human labor and brain power than
1226 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1227 @command{install}, @command{ln}, and @command{mv} programs to be used
1228 conveniently with @command{xargs}. For example, you can move the files
1229 from the current directory to a sibling directory, @code{d} like this:
1232 ls | xargs mv -t ../d --
1235 However, this doesn't move files whose names begin with @samp{.}.
1236 If you use the @sc{gnu} @command{find} program, you can move those
1237 files too, with this command:
1240 find . -mindepth 1 -maxdepth 1 \
1244 But both of the above approaches fail if there are no files in the
1245 current directory, or if any file has a name containing a blank or
1246 some other special characters.
1247 The following example removes those limitations and requires both
1248 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1251 find . -mindepth 1 -maxdepth 1 -print0 \
1252 | xargs --null --no-run-if-empty \
1259 The @option{--target-directory} (@option{-t}) and
1260 @option{--no-target-directory} (@option{-T})
1261 options cannot be combined.
1263 @node Trailing slashes
1264 @section Trailing slashes
1266 @cindex trailing slashes
1268 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1269 remove any trailing slashes from each @var{source} argument before
1270 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1273 This is useful when a @var{source} argument may have a trailing slash and
1274 @c FIXME: mv's behavior in this case is system-dependent
1275 specify a symbolic link to a directory. This scenario is in fact rather
1276 common because some shells can automatically append a trailing slash when
1277 performing file name completion on such symbolic links. Without this
1278 option, @command{mv}, for example, (via the system's rename function) must
1279 interpret a trailing slash as a request to dereference the symbolic link
1280 and so must rename the indirectly referenced @emph{directory} and not
1281 the symbolic link. Although it may seem surprising that such behavior
1282 be the default, it is required by @acronym{POSIX} and is consistent with
1283 other parts of that standard.
1285 @node Traversing symlinks
1286 @section Traversing symlinks
1288 @cindex symbolic link to directory, controlling traversal of
1290 The following options modify how @command{chown} and @command{chgrp}
1291 @c FIXME: note that `du' has these options, too, but they have slightly
1292 @c different meaning.
1293 traverse a hierarchy when the @option{--recursive} (@option{-R})
1294 option is also specified.
1295 If more than one of the following options is specified, only the final
1297 These options specify whether processing a symbolic link to a directory
1298 entails operating on just the symbolic link or on all files in the
1299 hierarchy rooted at that directory.
1301 These options are independent of @option{--dereference} and
1302 @option{--no-dereference} (@option{-h}), which control whether to modify
1303 a symlink or its referent.
1310 @cindex symbolic link to directory, traverse each that is specified on the command line
1311 If @option{--recursive} (@option{-R}) is specified and
1312 a command line argument is a symbolic link to a directory, traverse it.
1319 @cindex symbolic link to directory, traverse each that is encountered
1320 In a recursive traversal, traverse every symbolic link to a directory
1321 that is encountered.
1328 @cindex symbolic link to directory, never traverse
1329 Do not traverse any symbolic links.
1330 This is the default if none of @option{-H}, @option{-L},
1331 or @option{-P} is specified.
1338 @node Treating / specially
1339 @section Treating @file{/} specially
1341 Certain commands can operate destructively on entire hierarchies.
1342 For example, if a user with appropriate privileges mistakenly runs
1343 @samp{rm -rf / tmp/junk}, that may remove
1344 all files on the entire system. Since there are so few
1345 legitimate uses for such a command,
1346 @sc{gnu} @command{rm} normally declines to operate on any directory
1347 that resolves to @file{/}. If you really want to try to remove all
1348 the files on your system, you can use the @option{--no-preserve-root}
1349 option, but the default behavior, specified by the
1350 @option{--preserve-option}, is safer for most purposes.
1352 The commands @command{chgrp}, @command{chmod} and @command{chown}
1353 can also operate destructively on entire hierarchies, so they too
1354 support these options. Although, unlike @command{rm}, they don't
1355 actually unlink files, these commands are arguably more dangerous
1356 when operating recursively on @file{/}, since they often work much
1357 more quickly, and hence damage more files before an alert user can
1358 interrupt them. Tradition and @acronym{POSIX} require these commands
1359 to operate recursively on @file{/}, so they default to
1360 @option{--no-preserve-root}, but using the @option{--preserve-root}
1361 option makes them safer for most purposes. For convenience you can
1362 specify @option{--preserve-root} in an alias or in a shell function.
1364 Note that the @option{--preserve-root} option also ensures
1365 that @command{chgrp} and @command{chown} do not modify @file{/}
1366 even when dereferencing a symlink pointing to @file{/}.
1368 @node Special built-in utilities
1369 @section Special built-in utilities
1371 Some programs like @command{nice} can invoke other programs; for
1372 example, the command @samp{nice cat file} invokes the program
1373 @command{cat} by executing the command @samp{cat file}. However,
1374 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1375 this way. For example, the command @samp{nice exit} does not have a
1376 well-defined behavior: it may generate an error message instead of
1379 Here is a list of the special built-in utilities that are standardized
1380 by @acronym{POSIX} 1003.1-2004.
1383 @t{.@: : break continue eval exec exit export readonly
1384 return set shift times trap unset}
1387 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1388 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1389 pwd} do not work as you might expect.
1391 Many shells extend this list. For example, Bash has several extra
1392 special built-in utilities like @command{history}, and
1393 @command{suspend}, and with Bash the command @samp{nice suspend}
1394 generates an error message instead of suspending.
1396 @node Standards conformance
1397 @section Standards conformance
1399 @vindex POSIXLY_CORRECT
1400 In a few cases, the @sc{gnu} utilities' default behavior is
1401 incompatible with the @acronym{POSIX} standard. To suppress these
1402 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1403 variable. Unless you are checking for @acronym{POSIX} conformance, you
1404 probably do not need to define @env{POSIXLY_CORRECT}.
1406 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1407 versions. For example, older versions of @acronym{POSIX} required the
1408 command @samp{sort +1} to sort based on the second and succeeding
1409 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1410 the same command is required to sort the file named @file{+1}, and you
1411 must instead use the command @samp{sort -k 2} to get the field-based
1414 @vindex _POSIX2_VERSION
1415 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1416 that is standard for your system. To cause them to conform to a
1417 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1418 environment variable to a value of the form @var{yyyymm} specifying
1419 the year and month the standard was adopted. Two values are currently
1420 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1421 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1422 1003.1-2001. For example, if you have a newer system but are running software
1423 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1424 or @samp{tail +10}, you can work around any compatibility problems by setting
1425 @samp{_POSIX2_VERSION=199209} in your environment.
1427 @node Output of entire files
1428 @chapter Output of entire files
1430 @cindex output of entire files
1431 @cindex entire files, output of
1433 These commands read and write entire files, possibly transforming them
1437 * cat invocation:: Concatenate and write files.
1438 * tac invocation:: Concatenate and write files in reverse.
1439 * nl invocation:: Number lines and write files.
1440 * od invocation:: Write files in octal or other formats.
1441 * base64 invocation:: Transform data into printable data.
1444 @node cat invocation
1445 @section @command{cat}: Concatenate and write files
1448 @cindex concatenate and write files
1449 @cindex copying files
1451 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1452 standard input if none are given, to standard output. Synopsis:
1455 cat [@var{option}] [@var{file}]@dots{}
1458 The program accepts the following options. Also see @ref{Common options}.
1466 Equivalent to @option{-vET}.
1469 @itemx --number-nonblank
1471 @opindex --number-nonblank
1472 Number all nonempty output lines, starting with 1.
1476 Equivalent to @option{-vE}.
1481 @opindex --show-ends
1482 Display a @samp{$} after the end of each line.
1488 Number all output lines, starting with 1.
1491 @itemx --squeeze-blank
1493 @opindex --squeeze-blank
1494 @cindex squeezing empty lines
1495 Suppress repeated adjacent empty lines; output just one empty line
1500 Equivalent to @option{-vT}.
1505 @opindex --show-tabs
1506 Display TAB characters as @samp{^I}.
1510 Ignored; for @acronym{POSIX} compatibility.
1513 @itemx --show-nonprinting
1515 @opindex --show-nonprinting
1516 Display control characters except for LFD and TAB using
1517 @samp{^} notation and precede characters that have the high bit set with
1522 On systems like MS-DOS that distinguish between text and binary files,
1523 @command{cat} normally reads and writes in binary mode. However,
1524 @command{cat} reads in text mode if one of the options
1525 @option{-bensAE} is used or if @command{cat} is reading from standard
1526 input and standard input is a terminal. Similarly, @command{cat}
1527 writes in text mode if one of the options @option{-bensAE} is used or
1528 if standard output is a terminal.
1535 # Output f's contents, then standard input, then g's contents.
1538 # Copy standard input to standard output.
1543 @node tac invocation
1544 @section @command{tac}: Concatenate and write files in reverse
1547 @cindex reversing files
1549 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1550 standard input if none are given, to standard output, reversing the
1551 records (lines by default) in each separately. Synopsis:
1554 tac [@var{option}]@dots{} [@var{file}]@dots{}
1557 @dfn{Records} are separated by instances of a string (newline by
1558 default). By default, this separator string is attached to the end of
1559 the record that it follows in the file.
1561 The program accepts the following options. Also see @ref{Common options}.
1569 The separator is attached to the beginning of the record that it
1570 precedes in the file.
1576 Treat the separator string as a regular expression. Users of @command{tac}
1577 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1578 binary mode, each line of a text file might end with a CR/LF pair
1579 instead of the Unix-style LF.
1581 @item -s @var{separator}
1582 @itemx --separator=@var{separator}
1584 @opindex --separator
1585 Use @var{separator} as the record separator, instead of newline.
1593 @section @command{nl}: Number lines and write files
1596 @cindex numbering lines
1597 @cindex line numbering
1599 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1600 standard input if none are given, to standard output, with line numbers
1601 added to some or all of the lines. Synopsis:
1604 nl [@var{option}]@dots{} [@var{file}]@dots{}
1607 @cindex logical pages, numbering on
1608 @command{nl} decomposes its input into (logical) pages; by default, the
1609 line number is reset to 1 at the top of each logical page. @command{nl}
1610 treats all of the input files as a single document; it does not reset
1611 line numbers or logical pages between files.
1613 @cindex headers, numbering
1614 @cindex body, numbering
1615 @cindex footers, numbering
1616 A logical page consists of three sections: header, body, and footer.
1617 Any of the sections can be empty. Each can be numbered in a different
1618 style from the others.
1620 The beginnings of the sections of logical pages are indicated in the
1621 input file by a line containing exactly one of these delimiter strings:
1632 The two characters from which these strings are made can be changed from
1633 @samp{\} and @samp{:} via options (see below), but the pattern and
1634 length of each string cannot be changed.
1636 A section delimiter is replaced by an empty line on output. Any text
1637 that comes before the first section delimiter string in the input file
1638 is considered to be part of a body section, so @command{nl} treats a
1639 file that contains no section delimiters as a single body section.
1641 The program accepts the following options. Also see @ref{Common options}.
1645 @item -b @var{style}
1646 @itemx --body-numbering=@var{style}
1648 @opindex --body-numbering
1649 Select the numbering style for lines in the body section of each
1650 logical page. When a line is not numbered, the current line number
1651 is not incremented, but the line number separator character is still
1652 prepended to the line. The styles are:
1658 number only nonempty lines (default for body),
1660 do not number lines (default for header and footer),
1662 number only lines that contain a match for the basic regular
1663 expression @var{bre}.
1664 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1668 @itemx --section-delimiter=@var{cd}
1670 @opindex --section-delimiter
1671 @cindex section delimiters of pages
1672 Set the section delimiter characters to @var{cd}; default is
1673 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1674 (Remember to protect @samp{\} or other metacharacters from shell
1675 expansion with quotes or extra backslashes.)
1677 @item -f @var{style}
1678 @itemx --footer-numbering=@var{style}
1680 @opindex --footer-numbering
1681 Analogous to @option{--body-numbering}.
1683 @item -h @var{style}
1684 @itemx --header-numbering=@var{style}
1686 @opindex --header-numbering
1687 Analogous to @option{--body-numbering}.
1689 @item -i @var{number}
1690 @itemx --page-increment=@var{number}
1692 @opindex --page-increment
1693 Increment line numbers by @var{number} (default 1).
1695 @item -l @var{number}
1696 @itemx --join-blank-lines=@var{number}
1698 @opindex --join-blank-lines
1699 @cindex empty lines, numbering
1700 @cindex blank lines, numbering
1701 Consider @var{number} (default 1) consecutive empty lines to be one
1702 logical line for numbering, and only number the last one. Where fewer
1703 than @var{number} consecutive empty lines occur, do not number them.
1704 An empty line is one that contains no characters, not even spaces
1707 @item -n @var{format}
1708 @itemx --number-format=@var{format}
1710 @opindex --number-format
1711 Select the line numbering format (default is @code{rn}):
1715 @opindex ln @r{format for @command{nl}}
1716 left justified, no leading zeros;
1718 @opindex rn @r{format for @command{nl}}
1719 right justified, no leading zeros;
1721 @opindex rz @r{format for @command{nl}}
1722 right justified, leading zeros.
1726 @itemx --no-renumber
1728 @opindex --no-renumber
1729 Do not reset the line number at the start of a logical page.
1731 @item -s @var{string}
1732 @itemx --number-separator=@var{string}
1734 @opindex --number-separator
1735 Separate the line number from the text line in the output with
1736 @var{string} (default is the TAB character).
1738 @item -v @var{number}
1739 @itemx --starting-line-number=@var{number}
1741 @opindex --starting-line-number
1742 Set the initial line number on each logical page to @var{number} (default 1).
1744 @item -w @var{number}
1745 @itemx --number-width=@var{number}
1747 @opindex --number-width
1748 Use @var{number} characters for line numbers (default 6).
1756 @section @command{od}: Write files in octal or other formats
1759 @cindex octal dump of files
1760 @cindex hex dump of files
1761 @cindex ASCII dump of files
1762 @cindex file contents, dumping unambiguously
1764 @command{od} writes an unambiguous representation of each @var{file}
1765 (@samp{-} means standard input), or standard input if none are given.
1769 od [@var{option}]@dots{} [@var{file}]@dots{}
1770 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1771 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1774 Each line of output consists of the offset in the input, followed by
1775 groups of data from the file. By default, @command{od} prints the offset in
1776 octal, and each group of file data is a C @code{short int}'s worth of input
1777 printed as a single octal number.
1779 If @var{offset} is given, it specifies how many input bytes to skip
1780 before formatting and writing. By default, it is interpreted as an
1781 octal number, but the optional trailing decimal point causes it to be
1782 interpreted as decimal. If no decimal is specified and the offset
1783 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1784 number. If there is a trailing @samp{b}, the number of bytes skipped
1785 will be @var{offset} multiplied by 512.
1787 If a command is of both the first and second forms, the second form is
1788 assumed if the last operand begins with @samp{+} or (if there are two
1789 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1790 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1793 The program accepts the following options. Also see @ref{Common options}.
1797 @item -A @var{radix}
1798 @itemx --address-radix=@var{radix}
1800 @opindex --address-radix
1801 @cindex radix for file offsets
1802 @cindex file offset radix
1803 Select the base in which file offsets are printed. @var{radix} can
1804 be one of the following:
1814 none (do not print offsets).
1817 The default is octal.
1819 @item -j @var{bytes}
1820 @itemx --skip-bytes=@var{bytes}
1822 @opindex --skip-bytes
1823 Skip @var{bytes} input bytes before formatting and writing. If
1824 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1825 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1827 @multiplierSuffixes{bytes}
1829 @item -N @var{bytes}
1830 @itemx --read-bytes=@var{bytes}
1832 @opindex --read-bytes
1833 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1834 @code{bytes} are interpreted as for the @option{-j} option.
1836 @item -S @var{bytes}
1837 @itemx --strings[=@var{bytes}]
1840 @cindex string constants, outputting
1841 Instead of the normal output, output only @dfn{string constants}: at
1842 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1843 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1844 Prefixes and suffixes on @code{bytes} are interpreted as for the
1847 If @var{n} is omitted with @option{--strings}, the default is 3.
1850 @itemx --format=@var{type}
1853 Select the format in which to output the file data. @var{type} is a
1854 string of one or more of the below type indicator characters. If you
1855 include more than one type indicator character in a single @var{type}
1856 string, or use this option more than once, @command{od} writes one copy
1857 of each output line using each of the data types that you specified,
1858 in the order that you specified.
1860 Adding a trailing ``z'' to any type specification appends a display
1861 of the @acronym{ASCII} character representation of the printable characters
1862 to the output line generated by the type specification.
1866 named character, ignoring high-order bit
1868 @acronym{ASCII} character or backslash escape,
1881 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1882 newline, and @samp{nul} for a zero byte. Only the least significant
1883 seven bits of each byte is used; the high-order bit is ignored.
1884 Type @code{c} outputs
1885 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1888 Except for types @samp{a} and @samp{c}, you can specify the number
1889 of bytes to use in interpreting each number in the given data type
1890 by following the type indicator character with a decimal integer.
1891 Alternately, you can specify the size of one of the C compiler's
1892 built-in data types by following the type indicator character with
1893 one of the following characters. For integers (@samp{d}, @samp{o},
1894 @samp{u}, @samp{x}):
1907 For floating point (@code{f}):
1919 @itemx --output-duplicates
1921 @opindex --output-duplicates
1922 Output consecutive lines that are identical. By default, when two or
1923 more consecutive output lines would be identical, @command{od} outputs only
1924 the first line, and puts just an asterisk on the following line to
1925 indicate the elision.
1928 @itemx --width[=@var{n}]
1931 Dump @code{n} input bytes per output line. This must be a multiple of
1932 the least common multiple of the sizes associated with the specified
1935 If this option is not given at all, the default is 16. If @var{n} is
1936 omitted, the default is 32.
1940 The next several options are shorthands for format specifications.
1941 @sc{gnu} @command{od} accepts any combination of shorthands and format
1942 specification options. These options accumulate.
1948 Output as named characters. Equivalent to @samp{-t a}.
1952 Output as octal bytes. Equivalent to @samp{-t o1}.
1956 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1961 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1965 Output as floats. Equivalent to @samp{-t fF}.
1969 Output as decimal ints. Equivalent to @samp{-t dI}.
1973 Output as decimal long ints. Equivalent to @samp{-t dL}.
1977 Output as octal two-byte units. Equivalent to @option{-t o2}.
1981 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1985 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1988 @opindex --traditional
1989 Recognize the non-option label argument that traditional @command{od}
1990 accepted. The following syntax:
1993 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1997 can be used to specify at most one file and optional arguments
1998 specifying an offset and a pseudo-start address, @var{label}.
1999 The @var{label} argument is interpreted
2000 just like @var{offset}, but it specifies an initial pseudo-address. The
2001 pseudo-addresses are displayed in parentheses following any normal
2008 @node base64 invocation
2009 @section @command{base64}: Transform data into printable data.
2012 @cindex base64 encoding
2014 @command{base64} transforms data read from a file, or standard input,
2015 into (or from) base64 encoded form. The base64 encoded form uses
2016 printable @acronym{ASCII} characters to represent binary data.
2020 base64 [@var{option}]@dots{} [@var{file}]
2021 base64 --decode [@var{option}]@dots{} [@var{file}]
2024 The base64 encoding expands data to roughly 133% of the original.
2025 The format conforms to
2026 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2028 The program accepts the following options. Also see @ref{Common options}.
2033 @itemx --wrap=@var{cols}
2037 @cindex column to wrap data after
2038 During encoding, wrap lines after @var{cols} characters. This must be
2041 The default is to wrap after 76 characters. Use the value 0 to
2042 disable line wrapping altogether.
2048 @cindex Decode base64 data
2049 @cindex Base64 decoding
2050 Change the mode of operation, from the default of encoding data, to
2051 decoding data. Input is expected to be base64 encoded data, and the
2052 output will be the original data.
2055 @itemx --ignore-garbage
2057 @opindex --ignore-garbage
2058 @cindex Ignore garbage in base64 stream
2059 When decoding, newlines are always accepted.
2060 During decoding, ignore unrecognized bytes,
2061 to permit distorted data to be decoded.
2068 @node Formatting file contents
2069 @chapter Formatting file contents
2071 @cindex formatting file contents
2073 These commands reformat the contents of files.
2076 * fmt invocation:: Reformat paragraph text.
2077 * pr invocation:: Paginate or columnate files for printing.
2078 * fold invocation:: Wrap input lines to fit in specified width.
2082 @node fmt invocation
2083 @section @command{fmt}: Reformat paragraph text
2086 @cindex reformatting paragraph text
2087 @cindex paragraphs, reformatting
2088 @cindex text, reformatting
2090 @command{fmt} fills and joins lines to produce output lines of (at most)
2091 a given number of characters (75 by default). Synopsis:
2094 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2097 @command{fmt} reads from the specified @var{file} arguments (or standard
2098 input if none are given), and writes to standard output.
2100 By default, blank lines, spaces between words, and indentation are
2101 preserved in the output; successive input lines with different
2102 indentation are not joined; tabs are expanded on input and introduced on
2105 @cindex line-breaking
2106 @cindex sentences and line-breaking
2107 @cindex Knuth, Donald E.
2108 @cindex Plass, Michael F.
2109 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2110 avoid line breaks after the first word of a sentence or before the last
2111 word of a sentence. A @dfn{sentence break} is defined as either the end
2112 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2113 spaces or end of line, ignoring any intervening parentheses or quotes.
2114 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2115 breaks; the algorithm is a variant of that given by Donald E. Knuth
2116 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2117 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2120 The program accepts the following options. Also see @ref{Common options}.
2128 Compare each pair of source and destination files, and if the destination has
2129 identical content and any specified owner, group, permissions, and possibly
2130 SELinux context, then do not modify the destination at all.
2133 @itemx --crown-margin
2135 @opindex --crown-margin
2136 @cindex crown margin
2137 @dfn{Crown margin} mode: preserve the indentation of the first two
2138 lines within a paragraph, and align the left margin of each subsequent
2139 line with that of the second line.
2142 @itemx --tagged-paragraph
2144 @opindex --tagged-paragraph
2145 @cindex tagged paragraphs
2146 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2147 indentation of the first line of a paragraph is the same as the
2148 indentation of the second, the first line is treated as a one-line
2154 @opindex --split-only
2155 Split lines only. Do not join short lines to form longer ones. This
2156 prevents sample lines of code, and other such ``formatted'' text from
2157 being unduly combined.
2160 @itemx --uniform-spacing
2162 @opindex --uniform-spacing
2163 Uniform spacing. Reduce spacing between words to one space, and spacing
2164 between sentences to two spaces.
2167 @itemx -w @var{width}
2168 @itemx --width=@var{width}
2169 @opindex -@var{width}
2172 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2173 initially tries to make lines about 7% shorter than this, to give it
2174 room to balance line lengths.
2176 @item -p @var{prefix}
2177 @itemx --prefix=@var{prefix}
2178 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2179 are subject to formatting. The prefix and any preceding whitespace are
2180 stripped for the formatting and then re-attached to each formatted output
2181 line. One use is to format certain kinds of program comments, while
2182 leaving the code unchanged.
2190 @section @command{pr}: Paginate or columnate files for printing
2193 @cindex printing, preparing files for
2194 @cindex multicolumn output, generating
2195 @cindex merging files in parallel
2197 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2198 standard input if none are given, to standard output, paginating and
2199 optionally outputting in multicolumn format; optionally merges all
2200 @var{file}s, printing all in parallel, one per column. Synopsis:
2203 pr [@var{option}]@dots{} [@var{file}]@dots{}
2207 By default, a 5-line header is printed at each page: two blank lines;
2208 a line with the date, the file name, and the page count; and two more
2209 blank lines. A footer of five blank lines is also printed.
2210 The default @var{page_length} is 66
2211 lines. The default number of text lines is therefore 56.
2212 The text line of the header takes the form
2213 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2214 @var{string} so that the line takes up the full @var{page_width}. Here,
2215 @var{date} is the date (see the @option{-D} or @option{--date-format}
2216 option for details), @var{string} is the centered header string, and
2217 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2218 category affects the spelling of @var{page}; in the default C locale, it
2219 is @samp{Page @var{number}} where @var{number} is the decimal page
2222 Form feeds in the input cause page breaks in the output. Multiple form
2223 feeds produce empty pages.
2225 Columns are of equal width, separated by an optional string (default
2226 is @samp{space}). For multicolumn output, lines will always be truncated to
2227 @var{page_width} (default 72), unless you use the @option{-J} option.
2229 column output no line truncation occurs by default. Use @option{-W} option to
2230 truncate lines in that case.
2232 The following changes were made in version 1.22i and apply to later
2233 versions of @command{pr}:
2234 @c FIXME: this whole section here sounds very awkward to me. I
2235 @c made a few small changes, but really it all needs to be redone. - Brian
2236 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2241 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2242 redefined for better @acronym{POSIX} compliance. The output of some further
2243 cases has been adapted to other Unix systems. These changes are not
2244 compatible with earlier versions of the program.
2247 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2248 have been introduced to turn off unexpected interferences of small letter
2249 options. The @option{-N} option and the second argument @var{last_page}
2250 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2251 form feeds set in the input files requires the @option{-T} option.
2254 Capital letter options override small letter ones.
2257 Some of the option-arguments (compare @option{-s}, @option{-e},
2258 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2259 preceding option letter (already stated in the @acronym{POSIX} specification).
2262 The program accepts the following options. Also see @ref{Common options}.
2266 @item +@var{first_page}[:@var{last_page}]
2267 @itemx --pages=@var{first_page}[:@var{last_page}]
2268 @c The two following @opindex lines evoke warnings because they contain `:'
2269 @c The `info' spec does not permit that. If we use those lines, we end
2270 @c up with truncated index entries that don't work.
2271 @c @opindex +@var{first_page}[:@var{last_page}]
2272 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2273 @opindex +@var{page_range}
2274 @opindex --pages=@var{page_range}
2275 Begin printing with page @var{first_page} and stop with @var{last_page}.
2276 Missing @samp{:@var{last_page}} implies end of file. While estimating
2277 the number of skipped pages each form feed in the input file results
2278 in a new page. Page counting with and without @samp{+@var{first_page}}
2279 is identical. By default, counting starts with the first page of input
2280 file (not first page printed). Line numbering may be altered by @option{-N}
2284 @itemx --columns=@var{column}
2285 @opindex -@var{column}
2287 @cindex down columns
2288 With each single @var{file}, produce @var{column} columns of output
2289 (default is 1) and print columns down, unless @option{-a} is used. The
2290 column width is automatically decreased as @var{column} increases; unless
2291 you use the @option{-W/-w} option to increase @var{page_width} as well.
2292 This option might well cause some lines to be truncated. The number of
2293 lines in the columns on each page are balanced. The options @option{-e}
2294 and @option{-i} are on for multiple text-column output. Together with
2295 @option{-J} option column alignment and line truncation is turned off.
2296 Lines of full length are joined in a free field format and @option{-S}
2297 option may set field separators. @option{-@var{column}} may not be used
2298 with @option{-m} option.
2304 @cindex across columns
2305 With each single @var{file}, print columns across rather than down. The
2306 @option{-@var{column}} option must be given with @var{column} greater than one.
2307 If a line is too long to fit in a column, it is truncated.
2310 @itemx --show-control-chars
2312 @opindex --show-control-chars
2313 Print control characters using hat notation (e.g., @samp{^G}); print
2314 other nonprinting characters in octal backslash notation. By default,
2315 nonprinting characters are not changed.
2318 @itemx --double-space
2320 @opindex --double-space
2321 @cindex double spacing
2322 Double space the output.
2324 @item -D @var{format}
2325 @itemx --date-format=@var{format}
2326 @cindex time formats
2327 @cindex formatting times
2328 Format header dates using @var{format}, using the same conventions as
2329 for the command @samp{date +@var{format}}; @xref{date invocation}.
2330 Except for directives, which start with
2331 @samp{%}, characters in @var{format} are printed unchanged. You can use
2332 this option to specify an arbitrary string in place of the header date,
2333 e.g., @option{--date-format="Monday morning"}.
2335 @vindex POSIXLY_CORRECT
2337 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2338 @samp{2001-12-04 23:59});
2339 but if the @env{POSIXLY_CORRECT} environment variable is set
2340 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2341 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2342 @samp{Dec@ @ 4 23:59 2001}.
2345 Time stamps are listed according to the time zone rules specified by
2346 the @env{TZ} environment variable, or by the system default rules if
2347 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2348 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2350 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2351 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2353 @opindex --expand-tabs
2355 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2356 the input tab character (default is the TAB character). Second optional
2357 argument @var{in-tabwidth} is the input tab character's width (default
2365 @opindex --form-feed
2366 Use a form feed instead of newlines to separate output pages. This does
2367 not alter the default page length of 66 lines.
2369 @item -h @var{header}
2370 @itemx --header=@var{header}
2373 Replace the file name in the header with the centered string @var{header}.
2374 When using the shell, @var{header} should be quoted and should be
2375 separated from @option{-h} by a space.
2377 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2378 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2380 @opindex --output-tabs
2382 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2383 is the output tab character (default is the TAB character). Second optional
2384 argument @var{out-tabwidth} is the output tab character's width (default
2390 @opindex --join-lines
2391 Merge lines of full length. Used together with the column options
2392 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2393 @option{-W/-w} line truncation;
2394 no column alignment used; may be used with
2395 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2396 (together with @option{-W} and @option{--sep-string})
2397 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2398 @option{-s} along with the three column options.
2401 @item -l @var{page_length}
2402 @itemx --length=@var{page_length}
2405 Set the page length to @var{page_length} (default 66) lines, including
2406 the lines of the header [and the footer]. If @var{page_length} is less
2407 than or equal to 10, the header and footer are omitted, as if the
2408 @option{-t} option had been given.
2414 Merge and print all @var{file}s in parallel, one in each column. If a
2415 line is too long to fit in a column, it is truncated, unless the @option{-J}
2416 option is used. @option{--sep-string[=@var{string}]} may be used.
2418 some @var{file}s (form feeds set) produce empty columns, still marked
2419 by @var{string}. The result is a continuous line numbering and column
2420 marking throughout the whole merged file. Completely empty merged pages
2421 show no separators or line numbers. The default header becomes
2422 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2423 may be used with the @option{-h} or @option{--header} option to fill up
2424 the middle blank part.
2426 @item -n[@var{number-separator}[@var{digits}]]
2427 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2429 @opindex --number-lines
2430 Provide @var{digits} digit line numbering (default for @var{digits} is
2431 5). With multicolumn output the number occupies the first @var{digits}
2432 column positions of each text column or only each line of @option{-m}
2433 output. With single column output the number precedes each line just as
2434 @option{-m} does. Default counting of the line numbers starts with the
2435 first line of the input file (not the first line printed, compare the
2436 @option{--page} option and @option{-N} option).
2437 Optional argument @var{number-separator} is the character appended to
2438 the line number to separate it from the text followed. The default
2439 separator is the TAB character. In a strict sense a TAB is always
2440 printed with single column output only. The TAB width varies
2441 with the TAB position, e.g., with the left @var{margin} specified
2442 by @option{-o} option. With multicolumn output priority is given to
2443 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2444 The TAB width is fixed to the value of the first column and does
2445 not change with different values of left @var{margin}. That means a
2446 fixed number of spaces is always printed in the place of the
2447 @var{number-separator} TAB. The tabification depends upon the output
2450 @item -N @var{line_number}
2451 @itemx --first-line-number=@var{line_number}
2453 @opindex --first-line-number
2454 Start line counting with the number @var{line_number} at first line of
2455 first page printed (in most cases not the first line of the input file).
2457 @item -o @var{margin}
2458 @itemx --indent=@var{margin}
2461 @cindex indenting lines
2463 Indent each line with a margin @var{margin} spaces wide (default is zero).
2464 The total page width is the size of the margin plus the @var{page_width}
2465 set with the @option{-W/-w} option. A limited overflow may occur with
2466 numbered single column output (compare @option{-n} option).
2469 @itemx --no-file-warnings
2471 @opindex --no-file-warnings
2472 Do not print a warning message when an argument @var{file} cannot be
2473 opened. (The exit status will still be nonzero, however.)
2475 @item -s[@var{char}]
2476 @itemx --separator[=@var{char}]
2478 @opindex --separator
2479 Separate columns by a single character @var{char}. The default for
2480 @var{char} is the TAB character without @option{-w} and @samp{no
2481 character} with @option{-w}. Without @option{-s} the default separator
2482 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2483 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2484 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2487 @item -S@var{string}
2488 @itemx --sep-string[=@var{string}]
2490 @opindex --sep-string
2491 Use @var{string} to separate output columns. The @option{-S} option doesn't
2492 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2493 does not affect line truncation or column alignment.
2494 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2496 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2497 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2498 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2501 @itemx --omit-header
2503 @opindex --omit-header
2504 Do not print the usual header [and footer] on each page, and do not fill
2505 out the bottom of pages (with blank lines or a form feed). No page
2506 structure is produced, but form feeds set in the input files are retained.
2507 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2508 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2509 in the input file to 4 spaces but don't make any other changes. Use of
2510 @option{-t} overrides @option{-h}.
2513 @itemx --omit-pagination
2515 @opindex --omit-pagination
2516 Do not print header [and footer]. In addition eliminate all form feeds
2517 set in the input files.
2520 @itemx --show-nonprinting
2522 @opindex --show-nonprinting
2523 Print nonprinting characters in octal backslash notation.
2525 @item -w @var{page_width}
2526 @itemx --width=@var{page_width}
2529 Set page width to @var{page_width} characters for multiple text-column
2530 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2531 off the default page width and any line truncation and column alignment.
2532 Lines of full length are merged, regardless of the column options
2533 set. No @var{page_width} setting is possible with single column output.
2534 A @acronym{POSIX}-compliant formulation.
2536 @item -W @var{page_width}
2537 @itemx --page_width=@var{page_width}
2539 @opindex --page_width
2540 Set the page width to @var{page_width} characters. That's valid with and
2541 without a column option. Text lines are truncated, unless @option{-J}
2542 is used. Together with one of the three column options
2543 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2544 alignment is always used. The separator options @option{-S} or @option{-s}
2545 don't affect the @option{-W} option. Default is 72 characters. Without
2546 @option{-W @var{page_width}} and without any of the column options NO line
2547 truncation is used (defined to keep downward compatibility and to meet
2548 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2549 line is never truncated.
2556 @node fold invocation
2557 @section @command{fold}: Wrap input lines to fit in specified width
2560 @cindex wrapping long input lines
2561 @cindex folding long input lines
2563 @command{fold} writes each @var{file} (@option{-} means standard input), or
2564 standard input if none are given, to standard output, breaking long
2568 fold [@var{option}]@dots{} [@var{file}]@dots{}
2571 By default, @command{fold} breaks lines wider than 80 columns. The output
2572 is split into as many lines as necessary.
2574 @cindex screen columns
2575 @command{fold} counts screen columns by default; thus, a tab may count more
2576 than one column, backspace decreases the column count, and carriage
2577 return sets the column to zero.
2579 The program accepts the following options. Also see @ref{Common options}.
2587 Count bytes rather than columns, so that tabs, backspaces, and carriage
2588 returns are each counted as taking up one column, just like other
2595 Break at word boundaries: the line is broken after the last blank before
2596 the maximum line length. If the line contains no such blanks, the line
2597 is broken at the maximum line length as usual.
2599 @item -w @var{width}
2600 @itemx --width=@var{width}
2603 Use a maximum line length of @var{width} columns instead of 80.
2605 For compatibility @command{fold} supports an obsolete option syntax
2606 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2614 @node Output of parts of files
2615 @chapter Output of parts of files
2617 @cindex output of parts of files
2618 @cindex parts of files, output of
2620 These commands output pieces of the input.
2623 * head invocation:: Output the first part of files.
2624 * tail invocation:: Output the last part of files.
2625 * split invocation:: Split a file into fixed-size pieces.
2626 * csplit invocation:: Split a file into context-determined pieces.
2629 @node head invocation
2630 @section @command{head}: Output the first part of files
2633 @cindex initial part of files, outputting
2634 @cindex first part of files, outputting
2636 @command{head} prints the first part (10 lines by default) of each
2637 @var{file}; it reads from standard input if no files are given or
2638 when given a @var{file} of @option{-}. Synopsis:
2641 head [@var{option}]@dots{} [@var{file}]@dots{}
2644 If more than one @var{file} is specified, @command{head} prints a
2645 one-line header consisting of:
2648 ==> @var{file name} <==
2652 before the output for each @var{file}.
2654 The program accepts the following options. Also see @ref{Common options}.
2659 @itemx --bytes=@var{k}
2662 Print the first @var{k} bytes, instead of initial lines.
2663 However, if @var{k} starts with a @samp{-},
2664 print all but the last @var{k} bytes of each file.
2665 @multiplierSuffixes{k}
2668 @itemx --lines=@var{k}
2671 Output the first @var{k} lines.
2672 However, if @var{k} starts with a @samp{-},
2673 print all but the last @var{k} lines of each file.
2674 Size multiplier suffixes are the same as with the @option{-c} option.
2682 Never print file name headers.
2688 Always print file name headers.
2692 For compatibility @command{head} also supports an obsolete option syntax
2693 @option{-@var{count}@var{options}}, which is recognized only if it is
2694 specified first. @var{count} is a decimal number optionally followed
2695 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2696 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2697 Scripts intended for standard hosts should use @option{-c @var{count}}
2698 or @option{-n @var{count}} instead. If your script must also run on
2699 hosts that support only the obsolete syntax, it is usually simpler to
2700 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2706 @node tail invocation
2707 @section @command{tail}: Output the last part of files
2710 @cindex last part of files, outputting
2712 @command{tail} prints the last part (10 lines by default) of each
2713 @var{file}; it reads from standard input if no files are given or
2714 when given a @var{file} of @samp{-}. Synopsis:
2717 tail [@var{option}]@dots{} [@var{file}]@dots{}
2720 If more than one @var{file} is specified, @command{tail} prints a
2721 one-line header consisting of:
2724 ==> @var{file name} <==
2728 before the output for each @var{file}.
2730 @cindex BSD @command{tail}
2731 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2732 @command{tail} cannot). It also has no @option{-r} option (print in
2733 reverse), since reversing a file is really a different job from printing
2734 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2735 only reverse files that are at most as large as its buffer, which is
2736 typically 32 KiB@. A more reliable and versatile way to reverse files is
2737 the @sc{gnu} @command{tac} command.
2739 The program accepts the following options. Also see @ref{Common options}.
2744 @itemx --bytes=@var{k}
2747 Output the last @var{k} bytes, instead of final lines.
2748 However, if @var{k} starts with a @samp{+}, start printing with the
2749 @var{k}th byte from the start of each file, instead of from the end.
2750 @multiplierSuffixes{k}
2753 @itemx --follow[=@var{how}]
2756 @cindex growing files
2757 @vindex name @r{follow option}
2758 @vindex descriptor @r{follow option}
2759 Loop forever trying to read more characters at the end of the file,
2760 presumably because the file is growing.
2761 If more than one file is given, @command{tail} prints a header whenever it
2762 gets output from a different file, to indicate which file that output is
2765 There are two ways to specify how you'd like to track files with this option,
2766 but that difference is noticeable only when a followed file is removed or
2768 If you'd like to continue to track the end of a growing file even after
2769 it has been unlinked, use @option{--follow=descriptor}. This is the default
2770 behavior, but it is not useful if you're tracking a log file that may be
2771 rotated (removed or renamed, then reopened). In that case, use
2772 @option{--follow=name} to track the named file by reopening it periodically
2773 to see if it has been removed and recreated by some other program.
2775 No matter which method you use, if the tracked file is determined to have
2776 shrunk, @command{tail} prints a message saying the file has been truncated
2777 and resumes tracking the end of the file from the newly-determined endpoint.
2779 When a file is removed, @command{tail}'s behavior depends on whether it is
2780 following the name or the descriptor. When following by name, tail can
2781 detect that a file has been removed and gives a message to that effect,
2782 and if @option{--retry} has been specified it will continue checking
2783 periodically to see if the file reappears.
2784 When following a descriptor, tail does not detect that the file has
2785 been unlinked or renamed and issues no message; even though the file
2786 may no longer be accessible via its original name, it may still be
2789 The option values @samp{descriptor} and @samp{name} may be specified only
2790 with the long form of the option, not with @option{-f}.
2792 @vindex POSIXLY_CORRECT
2793 If @env{POSIXLY_CORRECT} is set, the @option{-f} option is ignored if
2794 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2798 This option is the same as @option{--follow=name --retry}. That is, tail
2799 will attempt to reopen a file when it is removed. Should this fail, tail
2800 will keep trying until it becomes accessible again.
2804 This option is useful mainly when following by name (i.e., with
2805 @option{--follow=name}).
2806 Without this option, when tail encounters a file that doesn't
2807 exist or is otherwise inaccessible, it reports that fact and
2808 never checks it again.
2810 @itemx --sleep-interval=@var{number}
2811 @opindex --sleep-interval
2812 Change the number of seconds to wait between iterations (the default is 1.0).
2813 During one iteration, every specified file is checked to see if it has
2815 Historical implementations of @command{tail} have required that
2816 @var{number} be an integer. However, GNU @command{tail} accepts
2817 an arbitrary floating point number (using a period before any
2820 @itemx --pid=@var{pid}
2822 When following by name or by descriptor, you may specify the process ID,
2823 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2824 after that process terminates, tail will also terminate. This will
2825 work properly only if the writer and the tailing process are running on
2826 the same machine. For example, to save the output of a build in a file
2827 and to watch the file grow, if you invoke @command{make} and @command{tail}
2828 like this then the tail process will stop when your build completes.
2829 Without this option, you would have had to kill the @code{tail -f}
2833 $ make >& makerr & tail --pid=$! -f makerr
2836 If you specify a @var{pid} that is not in use or that does not correspond
2837 to the process that is writing to the tailed files, then @command{tail}
2838 may terminate long before any @var{file}s stop growing or it may not
2839 terminate until long after the real writer has terminated.
2840 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2841 will print a warning if this is the case.
2843 @itemx --max-unchanged-stats=@var{n}
2844 @opindex --max-unchanged-stats
2845 When tailing a file by name, if there have been @var{n} (default
2846 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2847 iterations for which the file has not changed, then
2848 @code{open}/@code{fstat} the file to determine if that file name is
2849 still associated with the same device/inode-number pair as before.
2850 When following a log file that is rotated, this is approximately the
2851 number of seconds between when tail prints the last pre-rotation lines
2852 and when it prints the lines that have accumulated in the new log file.
2853 This option is meaningful only when following by name.
2856 @itemx --lines=@var{k}
2859 Output the last @var{k} lines.
2860 However, if @var{k} starts with a @samp{+}, start printing with the
2861 @var{k}th line from the start of each file, instead of from the end.
2862 Size multiplier suffixes are the same as with the @option{-c} option.
2870 Never print file name headers.
2876 Always print file name headers.
2880 For compatibility @command{tail} also supports an obsolete usage
2881 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2882 only if it does not conflict with the usage described
2883 above. This obsolete form uses exactly one option and at most one
2884 file. In the option, @var{count} is an optional decimal number optionally
2885 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2886 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2887 which has the same meaning as @option{-f}.
2889 @vindex _POSIX2_VERSION
2890 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2891 the obsolete option syntax with the same meaning as in counts, and
2892 obsolete usage overrides normal usage when the two conflict.
2893 This obsolete behavior can be enabled or disabled with the
2894 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2897 Scripts intended for use on standard hosts should avoid obsolete
2898 syntax and should use @option{-c @var{count}[b]}, @option{-n
2899 @var{count}}, and/or @option{-f} instead. If your script must also
2900 run on hosts that support only the obsolete syntax, you can often
2901 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2902 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2903 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2904 then @dots{}} to decide which syntax to use.
2906 Even if your script assumes the standard behavior, you should still
2907 beware usages whose behaviors differ depending on the @acronym{POSIX}
2908 version. For example, avoid @samp{tail - main.c}, since it might be
2909 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2910 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2911 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2912 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2917 @node split invocation
2918 @section @command{split}: Split a file into fixed-size pieces
2921 @cindex splitting a file into pieces
2922 @cindex pieces, splitting a file into
2924 @command{split} creates output files containing consecutive sections of
2925 @var{input} (standard input if none is given or @var{input} is
2926 @samp{-}). Synopsis:
2929 split [@var{option}] [@var{input} [@var{prefix}]]
2932 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2933 left over for the last section), into each output file.
2935 @cindex output file name prefix
2936 The output files' names consist of @var{prefix} (@samp{x} by default)
2937 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2938 default), such that concatenating the output files in traditional
2939 sorted order by file name produces
2940 the original input file. If the output file names are exhausted,
2941 @command{split} reports an error without deleting the output files
2944 The program accepts the following options. Also see @ref{Common options}.
2948 @item -l @var{lines}
2949 @itemx --lines=@var{lines}
2952 Put @var{lines} lines of @var{input} into each output file.
2954 For compatibility @command{split} also supports an obsolete
2955 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2956 @var{lines}} instead.
2959 @itemx --bytes=@var{size}
2962 Put @var{size} bytes of @var{input} into each output file.
2963 @multiplierSuffixes{size}
2966 @itemx --line-bytes=@var{size}
2968 @opindex --line-bytes
2969 Put into each output file as many complete lines of @var{input} as
2970 possible without exceeding @var{size} bytes. Individual lines longer than
2971 @var{size} bytes are broken into multiple files.
2972 @var{size} has the same format as for the @option{--bytes} option.
2974 @item -a @var{length}
2975 @itemx --suffix-length=@var{length}
2977 @opindex --suffix-length
2978 Use suffixes of length @var{length}. The default @var{length} is 2.
2981 @itemx --numeric-suffixes
2983 @opindex --numeric-suffixes
2984 Use digits in suffixes rather than lower-case letters.
2988 Write a diagnostic just before each output file is opened.
2995 @node csplit invocation
2996 @section @command{csplit}: Split a file into context-determined pieces
2999 @cindex context splitting
3000 @cindex splitting a file into pieces by context
3002 @command{csplit} creates zero or more output files containing sections of
3003 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3006 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3009 The contents of the output files are determined by the @var{pattern}
3010 arguments, as detailed below. An error occurs if a @var{pattern}
3011 argument refers to a nonexistent line of the input file (e.g., if no
3012 remaining line matches a given regular expression). After every
3013 @var{pattern} has been matched, any remaining input is copied into one
3016 By default, @command{csplit} prints the number of bytes written to each
3017 output file after it has been created.
3019 The types of pattern arguments are:
3024 Create an output file containing the input up to but not including line
3025 @var{n} (a positive integer). If followed by a repeat count, also
3026 create an output file containing the next @var{n} lines of the input
3027 file once for each repeat.
3029 @item /@var{regexp}/[@var{offset}]
3030 Create an output file containing the current line up to (but not
3031 including) the next line of the input file that contains a match for
3032 @var{regexp}. The optional @var{offset} is an integer.
3033 If it is given, the input up to (but not including) the
3034 matching line plus or minus @var{offset} is put into the output file,
3035 and the line after that begins the next section of input.
3037 @item %@var{regexp}%[@var{offset}]
3038 Like the previous type, except that it does not create an output
3039 file, so that section of the input file is effectively ignored.
3041 @item @{@var{repeat-count}@}
3042 Repeat the previous pattern @var{repeat-count} additional
3043 times. The @var{repeat-count} can either be a positive integer or an
3044 asterisk, meaning repeat as many times as necessary until the input is
3049 The output files' names consist of a prefix (@samp{xx} by default)
3050 followed by a suffix. By default, the suffix is an ascending sequence
3051 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3052 concatenating the output files in sorted order by file name produces the
3053 original input file.
3055 By default, if @command{csplit} encounters an error or receives a hangup,
3056 interrupt, quit, or terminate signal, it removes any output files
3057 that it has created so far before it exits.
3059 The program accepts the following options. Also see @ref{Common options}.
3063 @item -f @var{prefix}
3064 @itemx --prefix=@var{prefix}
3067 @cindex output file name prefix
3068 Use @var{prefix} as the output file name prefix.
3070 @item -b @var{suffix}
3071 @itemx --suffix=@var{suffix}
3074 @cindex output file name suffix
3075 Use @var{suffix} as the output file name suffix. When this option is
3076 specified, the suffix string must include exactly one
3077 @code{printf(3)}-style conversion specification, possibly including
3078 format specification flags, a field width, a precision specifications,
3079 or all of these kinds of modifiers. The format letter must convert a
3080 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3081 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3082 entire @var{suffix} is given (with the current output file number) to
3083 @code{sprintf(3)} to form the file name suffixes for each of the
3084 individual output files in turn. If this option is used, the
3085 @option{--digits} option is ignored.
3087 @item -n @var{digits}
3088 @itemx --digits=@var{digits}
3091 Use output file names containing numbers that are @var{digits} digits
3092 long instead of the default 2.
3097 @opindex --keep-files
3098 Do not remove output files when errors are encountered.
3101 @itemx --elide-empty-files
3103 @opindex --elide-empty-files
3104 Suppress the generation of zero-length output files. (In cases where
3105 the section delimiters of the input file are supposed to mark the first
3106 lines of each of the sections, the first output file will generally be a
3107 zero-length file unless you use this option.) The output file sequence
3108 numbers always run consecutively starting from 0, even when this option
3119 Do not print counts of output file sizes.
3125 Here is an example of its usage.
3126 First, create an empty directory for the exercise,
3133 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3136 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3142 Each number printed above is the size of an output
3143 file that csplit has just created.
3144 List the names of those output files:
3151 Use @command{head} to show their contents:
3176 @node Summarizing files
3177 @chapter Summarizing files
3179 @cindex summarizing files
3181 These commands generate just a few numbers representing entire
3185 * wc invocation:: Print newline, word, and byte counts.
3186 * sum invocation:: Print checksum and block counts.
3187 * cksum invocation:: Print CRC checksum and byte counts.
3188 * md5sum invocation:: Print or check MD5 digests.
3189 * sha1sum invocation:: Print or check SHA-1 digests.
3190 * sha2 utilities:: Print or check SHA-2 digests.
3195 @section @command{wc}: Print newline, word, and byte counts
3199 @cindex character count
3203 @command{wc} counts the number of bytes, characters, whitespace-separated
3204 words, and newlines in each given @var{file}, or standard input if none
3205 are given or for a @var{file} of @samp{-}. Synopsis:
3208 wc [@var{option}]@dots{} [@var{file}]@dots{}
3211 @cindex total counts
3212 @command{wc} prints one line of counts for each file, and if the file was
3213 given as an argument, it prints the file name following the counts. If
3214 more than one @var{file} is given, @command{wc} prints a final line
3215 containing the cumulative counts, with the file name @file{total}. The
3216 counts are printed in this order: newlines, words, characters, bytes,
3217 maximum line length.
3218 Each count is printed right-justified in a field with at least one
3219 space between fields so that the numbers and file names normally line
3220 up nicely in columns. The width of the count fields varies depending
3221 on the inputs, so you should not depend on a particular field width.
3222 However, as a @acronym{GNU} extension, if only one count is printed,
3223 it is guaranteed to be printed without leading spaces.
3225 By default, @command{wc} prints three counts: the newline, words, and byte
3226 counts. Options can specify that only certain counts be printed.
3227 Options do not undo others previously given, so
3234 prints both the byte counts and the word counts.
3236 With the @option{--max-line-length} option, @command{wc} prints the length
3237 of the longest line per file, and if there is more than one file it
3238 prints the maximum (not the sum) of those lengths. The line lengths here
3239 are measured in screen columns, according to the current locale and
3240 assuming tab positions in every 8th column.
3242 The program accepts the following options. Also see @ref{Common options}.
3250 Print only the byte counts.
3256 Print only the character counts.
3262 Print only the word counts.
3268 Print only the newline counts.
3271 @itemx --max-line-length
3273 @opindex --max-line-length
3274 Print only the maximum line lengths.
3276 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3277 @itemx --files0-from=@var{file}
3278 @opindex --files0-from=@var{file}
3279 @c This is commented out to avoid a texi2dvi failure.
3280 @c texi2dvi (GNU Texinfo 4.11) 1.104
3281 @c @cindex including files from @command{\cmd\}
3282 Disallow processing files named on the command line, and instead process
3283 those named in file @var{file}; each name being terminated by a zero byte
3284 (@acronym{ASCII} @sc{nul}).
3285 This is useful \withTotalOption\
3286 when the list of file names is so long that it may exceed a command line
3288 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3289 because it splits the list into pieces and makes @command{\cmd\} print
3290 \subListOutput\ for each sublist rather than for the entire list.
3291 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3292 @command{find}, using its @option{-print0} predicate.
3293 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3294 are read from standard input.
3296 @filesZeroFromOption{wc,,a total}
3298 For example, to find the length of the longest line in any @file{.c} or
3299 @file{.h} file in the current hierarchy, do this:
3302 find . -name '*.[ch]' -print0 |
3303 wc -L --files0-from=- | tail -n1
3311 @node sum invocation
3312 @section @command{sum}: Print checksum and block counts
3315 @cindex 16-bit checksum
3316 @cindex checksum, 16-bit
3318 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3319 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3322 sum [@var{option}]@dots{} [@var{file}]@dots{}
3325 @command{sum} prints the checksum for each @var{file} followed by the
3326 number of blocks in the file (rounded up). If more than one @var{file}
3327 is given, file names are also printed (by default). (With the
3328 @option{--sysv} option, corresponding file names are printed when there is
3329 at least one file argument.)
3331 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3332 compatible with BSD @command{sum} and prints file sizes in units of
3335 The program accepts the following options. Also see @ref{Common options}.
3341 @cindex BSD @command{sum}
3342 Use the default (BSD compatible) algorithm. This option is included for
3343 compatibility with the System V @command{sum}. Unless @option{-s} was also
3344 given, it has no effect.
3350 @cindex System V @command{sum}
3351 Compute checksums using an algorithm compatible with System V
3352 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3356 @command{sum} is provided for compatibility; the @command{cksum} program (see
3357 next section) is preferable in new applications.
3362 @node cksum invocation
3363 @section @command{cksum}: Print CRC checksum and byte counts
3366 @cindex cyclic redundancy check
3367 @cindex CRC checksum
3369 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3370 given @var{file}, or standard input if none are given or for a
3371 @var{file} of @samp{-}. Synopsis:
3374 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3377 @command{cksum} prints the CRC checksum for each file along with the number
3378 of bytes in the file, and the file name unless no arguments were given.
3380 @command{cksum} is typically used to ensure that files
3381 transferred by unreliable means (e.g., netnews) have not been corrupted,
3382 by comparing the @command{cksum} output for the received files with the
3383 @command{cksum} output for the original files (typically given in the
3386 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3387 compatible with the BSD or System V @command{sum} algorithms (see the
3388 previous section); it is more robust.
3390 The only options are @option{--help} and @option{--version}. @xref{Common
3396 @node md5sum invocation
3397 @section @command{md5sum}: Print or check MD5 digests
3401 @cindex 128-bit checksum
3402 @cindex checksum, 128-bit
3403 @cindex fingerprint, 128-bit
3404 @cindex message-digest, 128-bit
3406 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3407 @dfn{message-digest}) for each specified @var{file}.
3409 Note: The MD5 digest is more reliable than a simple CRC (provided by
3410 the @command{cksum} command) for detecting accidental file corruption,
3411 as the chances of accidentally having two files with identical MD5
3412 are vanishingly small. However, it should not be considered truly
3413 secure against malicious tampering: although finding a file with a
3414 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3415 considered infeasible at the moment, it is known how to produce
3416 different files with identical MD5 (a ``collision''), something which
3417 can be a security issue in certain contexts. For more secure hashes,
3418 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3419 @ref{sha2 utilities}.
3421 If a @var{file} is specified as @samp{-} or if no files are given
3422 @command{md5sum} computes the checksum for the standard input.
3423 @command{md5sum} can also determine whether a file and checksum are
3424 consistent. Synopsis:
3427 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3430 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3431 indicating a binary or text input file, and the file name.
3432 If @var{file} contains a backslash or newline, the
3433 line is started with a backslash, and each problematic character in
3434 the file name is escaped with a backslash, making the output
3435 unambiguous even in the presence of arbitrary file names.
3436 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3438 The program accepts the following options. Also see @ref{Common options}.
3446 @cindex binary input files
3447 Treat each input file as binary, by reading it in binary mode and
3448 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3449 On systems like @acronym{GNU} that do not distinguish between binary
3450 and text files, this option merely flags each input file as binary:
3451 the MD5 checksum is unaffected. This option is the default on systems
3452 like MS-DOS that distinguish between binary and text files, except
3453 for reading standard input when standard input is a terminal.
3457 Read file names and checksum information (not data) from each
3458 @var{file} (or from stdin if no @var{file} was specified) and report
3459 whether the checksums match the contents of the named files.
3460 The input to this mode of @command{md5sum} is usually the output of
3461 a prior, checksum-generating run of @samp{md5sum}.
3462 Each valid line of input consists of an MD5 checksum, a binary/text
3463 flag, and then a file name.
3464 Binary files are marked with @samp{*}, text with @samp{ }.
3465 For each such line, @command{md5sum} reads the named file and computes its
3466 MD5 checksum. Then, if the computed message digest does not match the
3467 one on the line with the file name, the file is noted as having
3468 failed the test. Otherwise, the file passes the test.
3469 By default, for each valid line, one line is written to standard
3470 output indicating whether the named file passed the test.
3471 After all checks have been performed, if there were any failures,
3472 a warning is issued to standard error.
3473 Use the @option{--status} option to inhibit that output.
3474 If any listed file cannot be opened or read, if any valid line has
3475 an MD5 checksum inconsistent with the associated file, or if no valid
3476 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3477 it exits successfully.
3481 @cindex verifying MD5 checksums
3482 This option is useful only when verifying checksums.
3483 When verifying checksums, don't generate an 'OK' message per successfully
3484 checked file. Files that fail the verification are reported in the
3485 default one-line-per-file format. If there is any checksum mismatch,
3486 print a warning summarizing the failures to standard error.
3490 @cindex verifying MD5 checksums
3491 This option is useful only when verifying checksums.
3492 When verifying checksums, don't generate the default one-line-per-file
3493 diagnostic and don't output the warning summarizing any failures.
3494 Failures to open or read a file still evoke individual diagnostics to
3496 If all listed files are readable and are consistent with the associated
3497 MD5 checksums, exit successfully. Otherwise exit with a status code
3498 indicating there was a failure.
3504 @cindex text input files
3505 Treat each input file as text, by reading it in text mode and
3506 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3507 This option is the default on systems like @acronym{GNU} that do not
3508 distinguish between binary and text files. On other systems, it is
3509 the default for reading standard input when standard input is a
3516 @cindex verifying MD5 checksums
3517 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3518 This option is useful only if all but a few lines in the checked input
3526 @node sha1sum invocation
3527 @section @command{sha1sum}: Print or check SHA-1 digests
3531 @cindex 160-bit checksum
3532 @cindex checksum, 160-bit
3533 @cindex fingerprint, 160-bit
3534 @cindex message-digest, 160-bit
3536 @command{sha1sum} computes a 160-bit checksum for each specified
3537 @var{file}. The usage and options of this command are precisely the
3538 same as for @command{md5sum}. @xref{md5sum invocation}.
3540 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3541 it are known (different files having the same fingerprint). However,
3542 it is known that they can be produced with considerable, but not
3543 unreasonable, resources. For this reason, it is generally considered
3544 that SHA-1 should be gradually phased out in favor of the more secure
3545 SHA-2 hash algorithms. @xref{sha2 utilities}.
3548 @node sha2 utilities
3549 @section sha2 utilities: Print or check SHA-2 digests
3556 @cindex 224-bit checksum
3557 @cindex 256-bit checksum
3558 @cindex 384-bit checksum
3559 @cindex 512-bit checksum
3560 @cindex checksum, 224-bit
3561 @cindex checksum, 256-bit
3562 @cindex checksum, 384-bit
3563 @cindex checksum, 512-bit
3564 @cindex fingerprint, 224-bit
3565 @cindex fingerprint, 256-bit
3566 @cindex fingerprint, 384-bit
3567 @cindex fingerprint, 512-bit
3568 @cindex message-digest, 224-bit
3569 @cindex message-digest, 256-bit
3570 @cindex message-digest, 384-bit
3571 @cindex message-digest, 512-bit
3573 The commands @command{sha224sum}, @command{sha256sum},
3574 @command{sha384sum} and @command{sha512sum} compute checksums of
3575 various lengths (respectively 224, 256, 384 and 512 bits),
3576 collectively known as the SHA-2 hashes. The usage and options of
3577 these commands are precisely the same as for @command{md5sum}.
3578 @xref{md5sum invocation}.
3580 Note: The SHA384 and SHA512 digests are considerably slower to
3581 compute, especially on 32-bit computers, than SHA224 or SHA256.
3584 @node Operating on sorted files
3585 @chapter Operating on sorted files
3587 @cindex operating on sorted files
3588 @cindex sorted files, operations on
3590 These commands work with (or produce) sorted files.
3593 * sort invocation:: Sort text files.
3594 * shuf invocation:: Shuffle text files.
3595 * uniq invocation:: Uniquify files.
3596 * comm invocation:: Compare two sorted files line by line.
3597 * ptx invocation:: Produce a permuted index of file contents.
3598 * tsort invocation:: Topological sort.
3602 @node sort invocation
3603 @section @command{sort}: Sort text files
3606 @cindex sorting files
3608 @command{sort} sorts, merges, or compares all the lines from the given
3609 files, or standard input if none are given or for a @var{file} of
3610 @samp{-}. By default, @command{sort} writes the results to standard
3614 sort [@var{option}]@dots{} [@var{file}]@dots{}
3617 @command{sort} has three modes of operation: sort (the default), merge,
3618 and check for sortedness. The following options change the operation
3625 @itemx --check=diagnose-first
3628 @cindex checking for sortedness
3629 Check whether the given file is already sorted: if it is not all
3630 sorted, print a diagnostic containing the first out-of-order line and
3631 exit with a status of 1.
3632 Otherwise, exit successfully.
3633 At most one input file can be given.
3636 @itemx --check=quiet
3637 @itemx --check=silent
3640 @cindex checking for sortedness
3641 Exit successfully if the given file is already sorted, and
3642 exit with status 1 otherwise.
3643 At most one input file can be given.
3644 This is like @option{-c}, except it does not print a diagnostic.
3650 @cindex merging sorted files
3651 Merge the given files by sorting them as a group. Each input file must
3652 always be individually sorted. It always works to sort instead of
3653 merge; merging is provided because it is faster, in the case where it
3658 @cindex sort stability
3659 @cindex sort's last-resort comparison
3660 A pair of lines is compared as follows:
3661 @command{sort} compares each pair of fields, in the
3662 order specified on the command line, according to the associated
3663 ordering options, until a difference is found or no fields are left.
3664 If no key fields are specified, @command{sort} uses a default key of
3665 the entire line. Finally, as a last resort when all keys compare
3666 equal, @command{sort} compares entire lines as if no ordering options
3667 other than @option{--reverse} (@option{-r}) were specified. The
3668 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3669 comparison} so that lines in which all fields compare equal are left
3670 in their original relative order. The @option{--unique}
3671 (@option{-u}) option also disables the last-resort comparison.
3675 Unless otherwise specified, all comparisons use the character collating
3676 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3677 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3678 to @samp{en_US}), then @command{sort} may produce output that is sorted
3679 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3680 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3681 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3682 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3683 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3684 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3685 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3687 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3688 limit on input line length or restrictions on bytes allowed within lines.
3689 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3690 @command{sort} silently supplies one. A line's trailing newline is not
3691 part of the line for comparison purposes.
3693 @cindex exit status of @command{sort}
3697 0 if no error occurred
3698 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3699 2 if an error occurred
3703 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3704 value as the directory for temporary files instead of @file{/tmp}. The
3705 @option{--temporary-directory} (@option{-T}) option in turn overrides
3706 the environment variable.
3708 The following options affect the ordering of output lines. They may be
3709 specified globally or as part of a specific key field. If no key
3710 fields are specified, global options apply to comparison of entire
3711 lines; otherwise the global options are inherited by key fields that do
3712 not specify any special options of their own. In pre-@acronym{POSIX}
3713 versions of @command{sort}, global options affect only later key fields,
3714 so portable shell scripts should specify global options first.
3719 @itemx --ignore-leading-blanks
3721 @opindex --ignore-leading-blanks
3722 @cindex blanks, ignoring leading
3724 Ignore leading blanks when finding sort keys in each line.
3725 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3726 can change this. Note blanks may be ignored by your locale's collating
3727 rules, but without this option they will be significant for character
3728 positions specified in keys with the @option{-k} option.
3731 @itemx --dictionary-order
3733 @opindex --dictionary-order
3734 @cindex dictionary order
3735 @cindex phone directory order
3736 @cindex telephone directory order
3738 Sort in @dfn{phone directory} order: ignore all characters except
3739 letters, digits and blanks when sorting.
3740 By default letters and digits are those of @acronym{ASCII} and a blank
3741 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3744 @itemx --ignore-case
3746 @opindex --ignore-case
3747 @cindex ignoring case
3748 @cindex case folding
3750 Fold lowercase characters into the equivalent uppercase characters when
3751 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3752 The @env{LC_CTYPE} locale determines character types.
3753 When used with @option{--unique} those lower case equivalent lines are
3754 thrown away. (There is currently no way to throw away the upper case
3755 equivalent instead. (Any @option{--reverse} given would only affect
3756 the final result, after the throwing away.))
3759 @itemx --general-numeric-sort
3760 @itemx --sort=general-numeric
3762 @opindex --general-numeric-sort
3764 @cindex general numeric sort
3766 Sort numerically, using the standard C function @code{strtod} to convert
3767 a prefix of each line to a double-precision floating point number.
3768 This allows floating point numbers to be specified in scientific notation,
3769 like @code{1.0e-34} and @code{10e100}.
3770 The @env{LC_NUMERIC} locale determines the decimal-point character.
3771 Do not report overflow, underflow, or conversion errors.
3772 Use the following collating sequence:
3776 Lines that do not start with numbers (all considered to be equal).
3778 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3779 in a consistent but machine-dependent order.
3783 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3788 Use this option only if there is no alternative; it is much slower than
3789 @option{--numeric-sort} (@option{-n}) and it can lose information when
3790 converting to floating point.
3793 @itemx --human-numeric-sort
3794 @itemx --sort=human-numeric
3796 @opindex --human-numeric-sort
3798 @cindex human numeric sort
3800 Sort numerically, as per the @option{--numeric-sort} option below, and in
3801 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3802 Note a mixture of IEC and SI suffixes is not supported and will
3803 be flagged as an error. Also the numbers must be abbreviated uniformly.
3804 I.E. values with different precisions like 6000K and 5M will be sorted
3808 @itemx --ignore-nonprinting
3810 @opindex --ignore-nonprinting
3811 @cindex nonprinting characters, ignoring
3812 @cindex unprintable characters, ignoring
3814 Ignore nonprinting characters.
3815 The @env{LC_CTYPE} locale determines character types.
3816 This option has no effect if the stronger @option{--dictionary-order}
3817 (@option{-d}) option is also given.
3823 @opindex --month-sort
3825 @cindex months, sorting by
3827 An initial string, consisting of any amount of blanks, followed
3828 by a month name abbreviation, is folded to UPPER case and
3829 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3830 Invalid names compare low to valid names. The @env{LC_TIME} locale
3831 category determines the month spellings.
3832 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3836 @itemx --numeric-sort
3837 @itemx --sort=numeric
3839 @opindex --numeric-sort
3841 @cindex numeric sort
3843 Sort numerically. The number begins each line and consists
3844 of optional blanks, an optional @samp{-} sign, and zero or more
3845 digits possibly separated by thousands separators, optionally followed
3846 by a decimal-point character and zero or more digits. An empty
3847 number is treated as @samp{0}. The @env{LC_NUMERIC}
3848 locale specifies the decimal-point character and thousands separator.
3849 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3852 Comparison is exact; there is no rounding error.
3854 Neither a leading @samp{+} nor exponential notation is recognized.
3855 To compare such strings numerically, use the
3856 @option{--general-numeric-sort} (@option{-g}) option.
3859 @itemx --version-sort
3861 @opindex --version-sort
3862 @cindex version number sort
3864 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3865 that embedded decimal numbers are sorted by numeric value
3866 (see @option{--numeric-sort} above).
3872 @cindex reverse sorting
3873 Reverse the result of comparison, so that lines with greater key values
3874 appear earlier in the output instead of later.
3877 @itemx --random-sort
3878 @itemx --sort=random
3880 @opindex --random-sort
3883 Sort by hashing the input keys and then sorting the hash values.
3884 Choose the hash function at random, ensuring that it is free of
3885 collisions so that differing keys have differing hash values. This is
3886 like a random permutation of the inputs (@pxref{shuf invocation}),
3887 except that keys with the same value sort together.
3889 If multiple random sort fields are specified, the same random hash
3890 function is used for all fields. To use different random hash
3891 functions for different fields, you can invoke @command{sort} more
3894 The choice of hash function is affected by the
3895 @option{--random-source} option.
3903 @item --compress-program=@var{prog}
3904 Compress any temporary files with the program @var{prog}.
3906 With no arguments, @var{prog} must compress standard input to standard
3907 output, and when given the @option{-d} option it must decompress
3908 standard input to standard output.
3910 Terminate with an error if @var{prog} exits with nonzero status.
3912 White space and the backslash character should not appear in
3913 @var{prog}; they are reserved for future use.
3915 @filesZeroFromOption{sort,,sorted output}
3917 @item -k @var{pos1}[,@var{pos2}]
3918 @itemx --key=@var{pos1}[,@var{pos2}]
3922 Specify a sort field that consists of the part of the line between
3923 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3924 omitted), @emph{inclusive}.
3926 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3927 where @var{f} is the number of the field to use, and @var{c} is the number
3928 of the first character from the beginning of the field. Fields and character
3929 positions are numbered starting with 1; a character position of zero in
3930 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3931 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3932 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3933 @var{opts} are ordering options, allowing individual keys to be sorted
3934 according to different rules; see below for details. Keys can span
3937 Example: To sort on the second field, use @option{--key=2,2}
3938 (@option{-k 2,2}). See below for more notes on keys and more examples.
3940 @item --batch-size=@var{nmerge}
3941 @opindex --batch-size
3942 @cindex number of inputs to merge, nmerge
3943 Merge at most @var{nmerge} inputs at once.
3945 When @command{sort} has to merge more than @var{nmerge} inputs,
3946 it merges them in groups of @var{nmerge}, saving the result in
3947 a temporary file, which is then used as an input in a subsequent merge.
3949 A large value of @var{nmerge} may improve merge performance and decrease
3950 temporary storage utilization at the expense of increased memory usage
3951 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3952 requirements and I/0 at the expense of temporary storage consumption and
3955 The value of @var{nmerge} must be at least 2. The default value is
3956 currently 16, but this is implementation-dependent and may change in
3959 The value of @var{nmerge} may be bounded by a resource limit for open
3960 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3961 OPEN_MAX} may display limits for your systems; these limits may be
3962 modified further if your program already has some files open, or if
3963 the operating system has other limits on the number of open files. If
3964 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3965 silently uses a smaller value.
3967 @item -o @var{output-file}
3968 @itemx --output=@var{output-file}
3971 @cindex overwriting of input, allowed
3972 Write output to @var{output-file} instead of standard output.
3973 Normally, @command{sort} reads all input before opening
3974 @var{output-file}, so you can safely sort a file in place by using
3975 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3976 However, @command{sort} with @option{--merge} (@option{-m}) can open
3977 the output file before reading all input, so a command like @code{cat
3978 F | sort -m -o F - G} is not safe as @command{sort} might start
3979 writing @file{F} before @command{cat} is done reading it.
3981 @vindex POSIXLY_CORRECT
3982 On newer systems, @option{-o} cannot appear after an input file if
3983 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3984 scripts should specify @option{-o @var{output-file}} before any input
3987 @item --random-source=@var{file}
3988 @opindex --random-source
3989 @cindex random source for sorting
3990 Use @var{file} as a source of random data used to determine which
3991 random hash function to use with the @option{-R} option. @xref{Random
3998 @cindex sort stability
3999 @cindex sort's last-resort comparison
4001 Make @command{sort} stable by disabling its last-resort comparison.
4002 This option has no effect if no fields or global ordering options
4003 other than @option{--reverse} (@option{-r}) are specified.
4006 @itemx --buffer-size=@var{size}
4008 @opindex --buffer-size
4009 @cindex size for main memory sorting
4010 Use a main-memory sort buffer of the given @var{size}. By default,
4011 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4012 @var{size} to be interpreted as a percentage of physical memory.
4013 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4014 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4015 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4016 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4019 This option can improve the performance of @command{sort} by causing it
4020 to start with a larger or smaller sort buffer than the default.
4021 However, this option affects only the initial buffer size. The buffer
4022 grows beyond @var{size} if @command{sort} encounters input lines larger
4025 @item -t @var{separator}
4026 @itemx --field-separator=@var{separator}
4028 @opindex --field-separator
4029 @cindex field separator character
4030 Use character @var{separator} as the field separator when finding the
4031 sort keys in each line. By default, fields are separated by the empty
4032 string between a non-blank character and a blank character.
4033 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4036 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4037 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4038 not considered to be part of either the field preceding or the field
4039 following, so with @samp{sort @w{-t " "}} the same input line has
4040 three fields: an empty field, @samp{foo}, and @samp{bar}.
4041 However, fields that extend to the end of the line,
4042 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4043 retain the field separators present between the endpoints of the range.
4045 To specify @acronym{ASCII} @sc{nul} as the field separator,
4046 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4048 @item -T @var{tempdir}
4049 @itemx --temporary-directory=@var{tempdir}
4051 @opindex --temporary-directory
4052 @cindex temporary directory
4054 Use directory @var{tempdir} to store temporary files, overriding the
4055 @env{TMPDIR} environment variable. If this option is given more than
4056 once, temporary files are stored in all the directories given. If you
4057 have a large sort or merge that is I/O-bound, you can often improve
4058 performance by using this option to specify directories on different
4059 disks and controllers.
4065 @cindex uniquifying output
4067 Normally, output only the first of a sequence of lines that compare
4068 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4069 check that no pair of consecutive lines compares equal.
4071 This option also disables the default last-resort comparison.
4073 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4074 this equivalence does not extend to arbitrary @command{sort} options.
4075 For example, @code{sort -n -u} inspects only the value of the initial
4076 numeric string when checking for uniqueness, whereas @code{sort -n |
4077 uniq} inspects the entire line. @xref{uniq invocation}.
4079 @macro zeroTerminatedOption
4081 @itemx --zero-terminated
4083 @opindex --zero-terminated
4084 @cindex process zero-terminated items
4085 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4086 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4087 and terminate output items with @acronym{ASCII} @sc{nul}.
4088 This option can be useful in conjunction with @samp{perl -0} or
4089 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4090 reliably handle arbitrary file names (even those containing blanks
4091 or other special characters).
4093 @zeroTerminatedOption
4097 Historical (BSD and System V) implementations of @command{sort} have
4098 differed in their interpretation of some options, particularly
4099 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4100 behavior, which is usually (but not always!) like the System V behavior.
4101 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4102 consistency, @option{-M} has been changed in the same way. This may
4103 affect the meaning of character positions in field specifications in
4104 obscure cases. The only fix is to add an explicit @option{-b}.
4106 A position in a sort field specified with @option{-k} may have any
4107 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4108 global ordering options are inherited by that particular field. The
4109 @option{-b} option may be independently attached to either or both of
4110 the start and end positions of a field specification, and if it is
4111 inherited from the global options it will be attached to both.
4112 If input lines can contain leading or adjacent blanks and @option{-t}
4113 is not used, then @option{-k} is typically combined with @option{-b} or
4114 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4115 the varying numbers of leading blanks in fields can cause confusing results.
4117 If the start position in a sort field specifier falls after the end of
4118 the line or after the end field, the field is empty. If the @option{-b}
4119 option was specified, the @samp{.@var{c}} part of a field specification
4120 is counted from the first nonblank character of the field.
4122 @vindex _POSIX2_VERSION
4123 @vindex POSIXLY_CORRECT
4124 On older systems, @command{sort} supports an obsolete origin-zero
4125 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4126 This obsolete behavior can be enabled or disabled with the
4127 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4128 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4129 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4131 Scripts intended for use on standard hosts should avoid obsolete
4132 syntax and should use @option{-k} instead. For example, avoid
4133 @samp{sort +2}, since it might be interpreted as either @samp{sort
4134 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4135 support only the obsolete syntax, it can use a test like @samp{if sort
4136 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4139 Here are some examples to illustrate various combinations of options.
4144 Sort in descending (reverse) numeric order.
4151 Sort alphabetically, omitting the first and second fields
4152 and the blanks at the start of the third field.
4153 This uses a single key composed of the characters beginning
4154 at the start of the first nonblank character in field three
4155 and extending to the end of each line.
4162 Sort numerically on the second field and resolve ties by sorting
4163 alphabetically on the third and fourth characters of field five.
4164 Use @samp{:} as the field delimiter.
4167 sort -t : -k 2,2n -k 5.3,5.4
4170 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4171 @command{sort} would have used all characters beginning in the second field
4172 and extending to the end of the line as the primary @emph{numeric}
4173 key. For the large majority of applications, treating keys spanning
4174 more than one field as numeric will not do what you expect.
4176 Also note that the @samp{n} modifier was applied to the field-end
4177 specifier for the first key. It would have been equivalent to
4178 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4179 @samp{b} apply to the associated @emph{field}, regardless of whether
4180 the modifier character is attached to the field-start and/or the
4181 field-end part of the key specifier.
4184 Sort the password file on the fifth field and ignore any
4185 leading blanks. Sort lines with equal values in field five
4186 on the numeric user ID in field three. Fields are separated
4190 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4191 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4192 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4195 These three commands have equivalent effect. The first specifies that
4196 the first key's start position ignores leading blanks and the second
4197 key is sorted numerically. The other two commands rely on global
4198 options being inherited by sort keys that lack modifiers. The inheritance
4199 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4200 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4201 character position is not affected by whether initial blanks are
4205 Sort a set of log files, primarily by IPv4 address and secondarily by
4206 time stamp. If two lines' primary and secondary keys are identical,
4207 output the lines in the same order that they were input. The log
4208 files contain lines that look like this:
4211 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4212 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4215 Fields are separated by exactly one space. Sort IPv4 addresses
4216 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4217 because 61 is less than 129.
4220 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4221 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4224 This example cannot be done with a single @command{sort} invocation,
4225 since IPv4 address components are separated by @samp{.} while dates
4226 come just after a space. So it is broken down into two invocations of
4227 @command{sort}: the first sorts by time stamp and the second by IPv4
4228 address. The time stamp is sorted by year, then month, then day, and
4229 finally by hour-minute-second field, using @option{-k} to isolate each
4230 field. Except for hour-minute-second there's no need to specify the
4231 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4232 based on leading prefixes that cannot cross field boundaries. The
4233 IPv4 addresses are sorted lexicographically. The second sort uses
4234 @samp{-s} so that ties in the primary key are broken by the secondary
4235 key; the first sort uses @samp{-s} so that the combination of the two
4239 Generate a tags file in case-insensitive sorted order.
4242 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4245 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4246 that file names that contain blanks or other special characters are
4248 by the sort operation.
4250 @c This example is a bit contrived and needs more explanation.
4252 @c Sort records separated by an arbitrary string by using a pipe to convert
4253 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4254 @c and converting each @samp{\0} back to the original record delimiter.
4257 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4261 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4262 sort lines according to their length.
4265 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4268 In general this technique can be used to sort data that the @command{sort}
4269 command does not support, or is inefficient at, sorting directly.
4272 Shuffle a list of directories, but preserve the order of files within
4273 each directory. For instance, one could use this to generate a music
4274 playlist in which albums are shuffled but the songs of each album are
4278 ls */* | sort -t / -k 1,1R -k 2,2
4284 @node shuf invocation
4285 @section @command{shuf}: Shuffling text
4288 @cindex shuffling files
4290 @command{shuf} shuffles its input by outputting a random permutation
4291 of its input lines. Each output permutation is equally likely.
4295 shuf [@var{option}]@dots{} [@var{file}]
4296 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4297 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4300 @command{shuf} has three modes of operation that affect where it
4301 obtains its input lines. By default, it reads lines from standard
4302 input. The following options change the operation mode:
4310 @cindex command-line operands to shuffle
4311 Treat each command-line operand as an input line.
4313 @item -i @var{lo}-@var{hi}
4314 @itemx --input-range=@var{lo}-@var{hi}
4316 @opindex --input-range
4317 @cindex input range to shuffle
4318 Act as if input came from a file containing the range of unsigned
4319 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4323 @command{shuf}'s other options can affect its behavior in all
4328 @item -n @var{lines}
4329 @itemx --head-count=@var{count}
4331 @opindex --head-count
4332 @cindex head of output
4333 Output at most @var{count} lines. By default, all input lines are
4336 @item -o @var{output-file}
4337 @itemx --output=@var{output-file}
4340 @cindex overwriting of input, allowed
4341 Write output to @var{output-file} instead of standard output.
4342 @command{shuf} reads all input before opening
4343 @var{output-file}, so you can safely shuffle a file in place by using
4344 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4346 @item --random-source=@var{file}
4347 @opindex --random-source
4348 @cindex random source for shuffling
4349 Use @var{file} as a source of random data used to determine which
4350 permutation to generate. @xref{Random sources}.
4352 @zeroTerminatedOption
4368 might produce the output
4378 Similarly, the command:
4381 shuf -e clubs hearts diamonds spades
4395 and the command @samp{shuf -i 1-4} might output:
4405 These examples all have four input lines, so @command{shuf} might
4406 produce any of the twenty-four possible permutations of the input. In
4407 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4408 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4409 output permutations.
4414 @node uniq invocation
4415 @section @command{uniq}: Uniquify files
4418 @cindex uniquify files
4420 @command{uniq} writes the unique lines in the given @file{input}, or
4421 standard input if nothing is given or for an @var{input} name of
4425 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4428 By default, @command{uniq} prints its input lines, except that
4429 it discards all but the first of adjacent repeated lines, so that
4430 no output lines are repeated. Optionally, it can instead discard
4431 lines that are not repeated, or all repeated lines.
4433 The input need not be sorted, but repeated input lines are detected
4434 only if they are adjacent. If you want to discard non-adjacent
4435 duplicate lines, perhaps you want to use @code{sort -u}.
4436 @xref{sort invocation}.
4439 Comparisons honor the rules specified by the @env{LC_COLLATE}
4442 If no @var{output} file is specified, @command{uniq} writes to standard
4445 The program accepts the following options. Also see @ref{Common options}.
4450 @itemx --skip-fields=@var{n}
4452 @opindex --skip-fields
4453 Skip @var{n} fields on each line before checking for uniqueness. Use
4454 a null string for comparison if a line has fewer than @var{n} fields. Fields
4455 are sequences of non-space non-tab characters that are separated from
4456 each other by at least one space or tab.
4458 For compatibility @command{uniq} supports an obsolete option syntax
4459 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4462 @itemx --skip-chars=@var{n}
4464 @opindex --skip-chars
4465 Skip @var{n} characters before checking for uniqueness. Use a null string
4466 for comparison if a line has fewer than @var{n} characters. If you use both
4467 the field and character skipping options, fields are skipped over first.
4469 @vindex _POSIX2_VERSION
4470 On older systems, @command{uniq} supports an obsolete option syntax
4472 This obsolete behavior can be enabled or disabled with the
4473 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4474 conformance}), but portable scripts should avoid commands whose
4475 behavior depends on this variable.
4476 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4477 the ambiguous @samp{uniq +10}.
4483 Print the number of times each line occurred along with the line.
4486 @itemx --ignore-case
4488 @opindex --ignore-case
4489 Ignore differences in case when comparing lines.
4495 @cindex repeated lines, outputting
4496 Discard lines that are not repeated. When used by itself, this option
4497 causes @command{uniq} to print the first copy of each repeated line,
4501 @itemx --all-repeated[=@var{delimit-method}]
4503 @opindex --all-repeated
4504 @cindex all repeated lines, outputting
4505 Do not discard the second and subsequent repeated input lines,
4506 but discard lines that are not repeated.
4507 This option is useful mainly in conjunction with other options e.g.,
4508 to ignore case or to compare only selected fields.
4509 The optional @var{delimit-method} tells how to delimit
4510 groups of repeated lines, and must be one of the following:
4515 Do not delimit groups of repeated lines.
4516 This is equivalent to @option{--all-repeated} (@option{-D}).
4519 Output a newline before each group of repeated lines.
4520 With @option{--zero-terminated} (@option{-z}), use a zero
4521 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4524 Separate groups of repeated lines with a single newline.
4525 With @option{--zero-terminated} (@option{-z}), use a zero
4526 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4527 This is the same as using @samp{prepend}, except that
4528 no delimiter is inserted before the first group, and hence
4529 may be better suited for output direct to users.
4532 Note that when groups are delimited and the input stream contains
4533 two or more consecutive blank lines, then the output is ambiguous.
4534 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4535 each sequence of consecutive newlines with a single newline.
4537 This is a @sc{gnu} extension.
4538 @c FIXME: give an example showing *how* it's useful
4544 @cindex unique lines, outputting
4545 Discard the first repeated line. When used by itself, this option
4546 causes @command{uniq} to print unique lines, and nothing else.
4549 @itemx --check-chars=@var{n}
4551 @opindex --check-chars
4552 Compare at most @var{n} characters on each line (after skipping any specified
4553 fields and characters). By default the entire rest of the lines are
4556 @zeroTerminatedOption
4563 @node comm invocation
4564 @section @command{comm}: Compare two sorted files line by line
4567 @cindex line-by-line comparison
4568 @cindex comparing sorted files
4570 @command{comm} writes to standard output lines that are common, and lines
4571 that are unique, to two input files; a file name of @samp{-} means
4572 standard input. Synopsis:
4575 comm [@var{option}]@dots{} @var{file1} @var{file2}
4579 Before @command{comm} can be used, the input files must be sorted using the
4580 collating sequence specified by the @env{LC_COLLATE} locale.
4581 If an input file ends in a non-newline
4582 character, a newline is silently appended. The @command{sort} command with
4583 no options always outputs a file that is suitable input to @command{comm}.
4585 @cindex differing lines
4586 @cindex common lines
4587 With no options, @command{comm} produces three-column output. Column one
4588 contains lines unique to @var{file1}, column two contains lines unique
4589 to @var{file2}, and column three contains lines common to both files.
4590 Columns are separated by a single TAB character.
4591 @c FIXME: when there's an option to supply an alternative separator
4592 @c string, append `by default' to the above sentence.
4597 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4598 the corresponding columns (and separators). Also see @ref{Common options}.
4600 Unlike some other comparison utilities, @command{comm} has an exit
4601 status that does not depend on the result of the comparison.
4602 Upon normal completion @command{comm} produces an exit code of zero.
4603 If there is an error it exits with nonzero status.
4605 @macro checkOrderOption{cmd}
4606 If the @option{--check-order} option is given, unsorted inputs will
4607 cause a fatal error message. If the option @option{--nocheck-order}
4608 is given, unsorted inputs will never cause an error message. If
4609 neither of these options is given, wrongly sorted inputs are diagnosed
4610 only if an input file is found to contain unpairable lines. If an
4611 input file is diagnosed as being unsorted, the @command{\cmd\} command
4612 will exit with a nonzero status (and the output should not be used).
4614 Forcing @command{\cmd\} to process wrongly sorted input files
4615 containing unpairable lines by specifying @option{--nocheck-order} is
4616 not guaranteed to produce any particular output. The output will
4617 probably not correspond with whatever you hoped it would be.
4619 @checkOrderOption{comm}
4624 Fail with an error message if either input file is wrongly ordered.
4626 @item --nocheck-order
4627 Do not check that both input files are in sorted order.
4631 @item --output-delimiter=@var{str}
4632 Print @var{str} between adjacent output columns,
4633 rather than the default of a single TAB character.
4635 The delimiter @var{str} may not be empty.
4639 @node ptx invocation
4640 @section @command{ptx}: Produce permuted indexes
4644 @command{ptx} reads a text file and essentially produces a permuted index, with
4645 each keyword in its context. The calling sketch is either one of:
4648 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4649 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4652 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4653 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4654 limitations and changing several of the program's default option values.
4655 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4656 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4657 document. For the full list, see @xref{Compatibility in ptx}.
4659 Individual options are explained in the following sections.
4661 When @sc{gnu} extensions are enabled, there may be zero, one or several
4662 @var{file}s after the options. If there is no @var{file}, the program
4663 reads the standard input. If there is one or several @var{file}s, they
4664 give the name of input files which are all read in turn, as if all the
4665 input files were concatenated. However, there is a full contextual
4666 break between each file and, when automatic referencing is requested,
4667 file names and line numbers refer to individual text input files. In
4668 all cases, the program outputs the permuted index to the standard
4671 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4672 operates in traditional mode, there may be zero, one or two parameters
4673 besides the options. If there are no parameters, the program reads the
4674 standard input and outputs the permuted index to the standard output.
4675 If there is only one parameter, it names the text @var{input} to be read
4676 instead of the standard input. If two parameters are given, they give
4677 respectively the name of the @var{input} file to read and the name of
4678 the @var{output} file to produce. @emph{Be very careful} to note that,
4679 in this case, the contents of file given by the second parameter is
4680 destroyed. This behavior is dictated by System V @command{ptx}
4681 compatibility; @sc{gnu} Standards normally discourage output parameters not
4682 introduced by an option.
4684 Note that for @emph{any} file named as the value of an option or as an
4685 input text file, a single dash @kbd{-} may be used, in which case
4686 standard input is assumed. However, it would not make sense to use this
4687 convention more than once per program invocation.
4690 * General options in ptx:: Options which affect general program behavior.
4691 * Charset selection in ptx:: Underlying character set considerations.
4692 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4693 * Output formatting in ptx:: Types of output format, and sizing the fields.
4694 * Compatibility in ptx::
4698 @node General options in ptx
4699 @subsection General options
4704 @itemx --traditional
4705 As already explained, this option disables all @sc{gnu} extensions to
4706 @command{ptx} and switches to traditional mode.
4709 Print a short help on standard output, then exit without further
4713 Print the program version on standard output, then exit without further
4721 @node Charset selection in ptx
4722 @subsection Charset selection
4724 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4725 As it is set up now, the program assumes that the input file is coded
4726 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4727 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4728 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4729 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4730 of characters which are letters is different; this alters the behavior
4731 of regular expression matching. Thus, the default regular expression
4732 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4733 however, is still crude; it obeys the underlying character set ordering
4739 @itemx --ignore-case
4740 Fold lower case letters to upper case for sorting.
4745 @node Input processing in ptx
4746 @subsection Word selection and input processing
4751 @itemx --break-file=@var{file}
4753 This option provides an alternative (to @option{-W}) method of describing
4754 which characters make up words. It introduces the name of a
4755 file which contains a list of characters which can@emph{not} be part of
4756 one word; this file is called the @dfn{Break file}. Any character which
4757 is not part of the Break file is a word constituent. If both options
4758 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4759 @option{-b} is ignored.
4761 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4762 break character is to write all the break characters in the file with no
4763 newline at all, not even at the end of the file. When @sc{gnu} extensions
4764 are disabled, spaces, tabs and newlines are always considered as break
4765 characters even if not included in the Break file.
4768 @itemx --ignore-file=@var{file}
4770 The file associated with this option contains a list of words which will
4771 never be taken as keywords in concordance output. It is called the
4772 @dfn{Ignore file}. The file contains exactly one word in each line; the
4773 end of line separation of words is not subject to the value of the
4777 @itemx --only-file=@var{file}
4779 The file associated with this option contains a list of words which will
4780 be retained in concordance output; any word not mentioned in this file
4781 is ignored. The file is called the @dfn{Only file}. The file contains
4782 exactly one word in each line; the end of line separation of words is
4783 not subject to the value of the @option{-S} option.
4785 There is no default for the Only file. When both an Only file and an
4786 Ignore file are specified, a word is considered a keyword only
4787 if it is listed in the Only file and not in the Ignore file.
4792 On each input line, the leading sequence of non-white space characters will be
4793 taken to be a reference that has the purpose of identifying this input
4794 line in the resulting permuted index. For more information about reference
4795 production, see @xref{Output formatting in ptx}.
4796 Using this option changes the default value for option @option{-S}.
4798 Using this option, the program does not try very hard to remove
4799 references from contexts in output, but it succeeds in doing so
4800 @emph{when} the context ends exactly at the newline. If option
4801 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4802 are disabled, this condition is always met and references are completely
4803 excluded from the output contexts.
4805 @item -S @var{regexp}
4806 @itemx --sentence-regexp=@var{regexp}
4808 This option selects which regular expression will describe the end of a
4809 line or the end of a sentence. In fact, this regular expression is not
4810 the only distinction between end of lines or end of sentences, and input
4811 line boundaries have no special significance outside this option. By
4812 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4813 used, end of sentences are used. In this case, this @var{regex} is
4814 imported from @sc{gnu} Emacs:
4817 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4820 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4821 of lines are used; in this case, the default @var{regexp} is just:
4827 Using an empty @var{regexp} is equivalent to completely disabling end of
4828 line or end of sentence recognition. In this case, the whole file is
4829 considered to be a single big line or sentence. The user might want to
4830 disallow all truncation flag generation as well, through option @option{-F
4831 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4834 When the keywords happen to be near the beginning of the input line or
4835 sentence, this often creates an unused area at the beginning of the
4836 output context line; when the keywords happen to be near the end of the
4837 input line or sentence, this often creates an unused area at the end of
4838 the output context line. The program tries to fill those unused areas
4839 by wrapping around context in them; the tail of the input line or
4840 sentence is used to fill the unused area on the left of the output line;
4841 the head of the input line or sentence is used to fill the unused area
4842 on the right of the output line.
4844 As a matter of convenience to the user, many usual backslashed escape
4845 sequences from the C language are recognized and converted to the
4846 corresponding characters by @command{ptx} itself.
4848 @item -W @var{regexp}
4849 @itemx --word-regexp=@var{regexp}
4851 This option selects which regular expression will describe each keyword.
4852 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4853 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4854 disabled, a word is by default anything which ends with a space, a tab
4855 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4857 An empty @var{regexp} is equivalent to not using this option.
4858 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4861 As a matter of convenience to the user, many usual backslashed escape
4862 sequences, as found in the C language, are recognized and converted to
4863 the corresponding characters by @command{ptx} itself.
4868 @node Output formatting in ptx
4869 @subsection Output formatting
4871 Output format is mainly controlled by the @option{-O} and @option{-T} options
4872 described in the table below. When neither @option{-O} nor @option{-T} are
4873 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4874 output format suitable for a dumb terminal. Each keyword occurrence is
4875 output to the center of one line, surrounded by its left and right
4876 contexts. Each field is properly justified, so the concordance output
4877 can be readily observed. As a special feature, if automatic
4878 references are selected by option @option{-A} and are output before the
4879 left context, that is, if option @option{-R} is @emph{not} selected, then
4880 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4881 Emacs @code{next-error} processing. In this default output format, each
4882 white space character, like newline and tab, is merely changed to
4883 exactly one space, with no special attempt to compress consecutive
4884 spaces. This might change in the future. Except for those white space
4885 characters, every other character of the underlying set of 256
4886 characters is transmitted verbatim.
4888 Output format is further controlled by the following options.
4892 @item -g @var{number}
4893 @itemx --gap-size=@var{number}
4895 Select the size of the minimum white space gap between the fields on the
4898 @item -w @var{number}
4899 @itemx --width=@var{number}
4901 Select the maximum output width of each final line. If references are
4902 used, they are included or excluded from the maximum output width
4903 depending on the value of option @option{-R}. If this option is not
4904 selected, that is, when references are output before the left context,
4905 the maximum output width takes into account the maximum length of all
4906 references. If this option is selected, that is, when references are
4907 output after the right context, the maximum output width does not take
4908 into account the space taken by references, nor the gap that precedes
4912 @itemx --auto-reference
4914 Select automatic references. Each input line will have an automatic
4915 reference made up of the file name and the line ordinal, with a single
4916 colon between them. However, the file name will be empty when standard
4917 input is being read. If both @option{-A} and @option{-r} are selected, then
4918 the input reference is still read and skipped, but the automatic
4919 reference is used at output time, overriding the input reference.
4922 @itemx --right-side-refs
4924 In the default output format, when option @option{-R} is not used, any
4925 references produced by the effect of options @option{-r} or @option{-A} are
4926 placed to the far right of output lines, after the right context. With
4927 default output format, when the @option{-R} option is specified, references
4928 are rather placed at the beginning of each output line, before the left
4929 context. For any other output format, option @option{-R} is
4930 ignored, with one exception: with @option{-R} the width of references
4931 is @emph{not} taken into account in total output width given by @option{-w}.
4933 This option is automatically selected whenever @sc{gnu} extensions are
4936 @item -F @var{string}
4937 @itemx --flac-truncation=@var{string}
4939 This option will request that any truncation in the output be reported
4940 using the string @var{string}. Most output fields theoretically extend
4941 towards the beginning or the end of the current line, or current
4942 sentence, as selected with option @option{-S}. But there is a maximum
4943 allowed output line width, changeable through option @option{-w}, which is
4944 further divided into space for various output fields. When a field has
4945 to be truncated because it cannot extend beyond the beginning or the end of
4946 the current line to fit in, then a truncation occurs. By default,
4947 the string used is a single slash, as in @option{-F /}.
4949 @var{string} may have more than one character, as in @option{-F ...}.
4950 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4951 truncation flagging is disabled, and no truncation marks are appended in
4954 As a matter of convenience to the user, many usual backslashed escape
4955 sequences, as found in the C language, are recognized and converted to
4956 the corresponding characters by @command{ptx} itself.
4958 @item -M @var{string}
4959 @itemx --macro-name=@var{string}
4961 Select another @var{string} to be used instead of @samp{xx}, while
4962 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4965 @itemx --format=roff
4967 Choose an output format suitable for @command{nroff} or @command{troff}
4968 processing. Each output line will look like:
4971 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4974 so it will be possible to write a @samp{.xx} roff macro to take care of
4975 the output typesetting. This is the default output format when @sc{gnu}
4976 extensions are disabled. Option @option{-M} can be used to change
4977 @samp{xx} to another macro name.
4979 In this output format, each non-graphical character, like newline and
4980 tab, is merely changed to exactly one space, with no special attempt to
4981 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4982 so it will be correctly processed by @command{nroff} or @command{troff}.
4987 Choose an output format suitable for @TeX{} processing. Each output
4988 line will look like:
4991 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4995 so it will be possible to write a @code{\xx} definition to take care of
4996 the output typesetting. Note that when references are not being
4997 produced, that is, neither option @option{-A} nor option @option{-r} is
4998 selected, the last parameter of each @code{\xx} call is inhibited.
4999 Option @option{-M} can be used to change @samp{xx} to another macro
5002 In this output format, some special characters, like @kbd{$}, @kbd{%},
5003 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5004 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5005 backslash and a pair of dollar signs (to force mathematical mode). The
5006 backslash itself produces the sequence @code{\backslash@{@}}.
5007 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5008 @code{~\@{ @}} respectively. Other diacriticized characters of the
5009 underlying character set produce an appropriate @TeX{} sequence as far
5010 as possible. The other non-graphical characters, like newline and tab,
5011 and all other characters which are not part of @acronym{ASCII}, are merely
5012 changed to exactly one space, with no special attempt to compress
5013 consecutive spaces. Let me know how to improve this special character
5014 processing for @TeX{}.
5019 @node Compatibility in ptx
5020 @subsection The @sc{gnu} extensions to @command{ptx}
5022 This version of @command{ptx} contains a few features which do not exist in
5023 System V @command{ptx}. These extra features are suppressed by using the
5024 @option{-G} command line option, unless overridden by other command line
5025 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5026 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5027 Here are the differences between this program and System V @command{ptx}.
5032 This program can read many input files at once, it always writes the
5033 resulting concordance on standard output. On the other hand, System V
5034 @command{ptx} reads only one file and sends the result to standard output
5035 or, if a second @var{file} parameter is given on the command, to that
5038 Having output parameters not introduced by options is a dangerous
5039 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5040 portably between @sc{gnu} and System V, you should always use it with a
5041 single input file, and always expect the result on standard output. You
5042 might also want to automatically configure in a @option{-G} option to
5043 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5044 that the installed @command{ptx} accepts @option{-G}.
5047 The only options available in System V @command{ptx} are options @option{-b},
5048 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5049 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5050 this enumeration. Moreover, some options have a slightly different
5051 meaning when @sc{gnu} extensions are enabled, as explained below.
5054 By default, concordance output is not formatted for @command{troff} or
5055 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5056 or @command{nroff} output may still be selected through option @option{-O}.
5059 Unless @option{-R} option is used, the maximum reference width is
5060 subtracted from the total output line width. With @sc{gnu} extensions
5061 disabled, width of references is not taken into account in the output
5062 line width computations.
5065 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5066 processed from input file with no adverse effect, even if @sc{gnu} extensions
5067 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5068 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5071 Input line length is only limited by available memory, even if @sc{gnu}
5072 extensions are disabled. However, System V @command{ptx} processes only
5073 the first 200 characters in each line.
5076 The break (non-word) characters default to be every character except all
5077 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5078 extensions are disabled, the break characters default to space, tab and
5082 The program makes better use of output line width. If @sc{gnu} extensions
5083 are disabled, the program rather tries to imitate System V @command{ptx},
5084 but still, there are some slight disposition glitches this program does
5085 not completely reproduce.
5088 The user can specify both an Ignore file and an Only file. This is not
5089 allowed with System V @command{ptx}.
5094 @node tsort invocation
5095 @section @command{tsort}: Topological sort
5098 @cindex topological sort
5100 @command{tsort} performs a topological sort on the given @var{file}, or
5101 standard input if no input file is given or for a @var{file} of
5102 @samp{-}. For more details and some history, see @ref{tsort background}.
5106 tsort [@var{option}] [@var{file}]
5109 @command{tsort} reads its input as pairs of strings, separated by blanks,
5110 indicating a partial ordering. The output is a total ordering that
5111 corresponds to the given partial ordering.
5125 will produce the output
5136 Consider a more realistic example.
5137 You have a large set of functions all in one file, and they may all be
5138 declared static except one. Currently that one (say @code{main}) is the
5139 first function defined in the file, and the ones it calls directly follow
5140 it, followed by those they call, etc. Let's say that you are determined
5141 to take advantage of prototypes, so you have to choose between declaring
5142 all of those functions (which means duplicating a lot of information from
5143 the definitions) and rearranging the functions so that as many as possible
5144 are defined before they are used. One way to automate the latter process
5145 is to get a list for each function of the functions it calls directly.
5146 Many programs can generate such lists. They describe a call graph.
5147 Consider the following list, in which a given line indicates that the
5148 function on the left calls the one on the right directly.
5154 tail_file pretty_name
5155 tail_file write_header
5157 tail_forever recheck
5158 tail_forever pretty_name
5159 tail_forever write_header
5160 tail_forever dump_remainder
5163 tail_lines start_lines
5164 tail_lines dump_remainder
5165 tail_lines file_lines
5166 tail_lines pipe_lines
5168 tail_bytes start_bytes
5169 tail_bytes dump_remainder
5170 tail_bytes pipe_bytes
5171 file_lines dump_remainder
5175 then you can use @command{tsort} to produce an ordering of those
5176 functions that satisfies your requirement.
5179 example$ tsort call-graph | tac
5199 @command{tsort} detects any cycles in the input and writes the first cycle
5200 encountered to standard error.
5202 Note that for a given partial ordering, generally there is no unique
5203 total ordering. In the context of the call graph above, the function
5204 @code{parse_options} may be placed anywhere in the list as long as it
5205 precedes @code{main}.
5207 The only options are @option{--help} and @option{--version}. @xref{Common
5213 * tsort background:: Where tsort came from.
5216 @node tsort background
5217 @subsection @command{tsort}: Background
5219 @command{tsort} exists because very early versions of the Unix linker processed
5220 an archive file exactly once, and in order. As @command{ld} read each object
5221 in the archive, it decided whether it was needed in the program based on
5222 whether it defined any symbols which were undefined at that point in
5225 This meant that dependencies within the archive had to be handled
5226 specially. For example, @code{scanf} probably calls @code{read}. That means
5227 that in a single pass through an archive, it was important for @code{scanf.o}
5228 to appear before read.o, because otherwise a program which calls
5229 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5230 reference to @code{read}.
5232 The way to address this problem was to first generate a set of
5233 dependencies of one object file on another. This was done by a shell
5234 script called @command{lorder}. The GNU tools don't provide a version of
5235 lorder, as far as I know, but you can still find it in BSD
5238 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5239 resulting sort to define the order in which you added objects to the archive.
5241 This whole procedure has been obsolete since about 1980, because
5242 Unix archives now contain a symbol table (traditionally built by
5243 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5244 linker uses the symbol table to effectively make multiple passes over
5247 Anyhow, that's where tsort came from. To solve an old problem with
5248 the way the linker handled archive files, which has since been solved
5252 @node Operating on fields within a line
5253 @chapter Operating on fields within a line
5256 * cut invocation:: Print selected parts of lines.
5257 * paste invocation:: Merge lines of files.
5258 * join invocation:: Join lines on a common field.
5262 @node cut invocation
5263 @section @command{cut}: Print selected parts of lines
5266 @command{cut} writes to standard output selected parts of each line of each
5267 input file, or standard input if no files are given or for a file name of
5271 cut @var{option}@dots{} [@var{file}]@dots{}
5274 In the table which follows, the @var{byte-list}, @var{character-list},
5275 and @var{field-list} are one or more numbers or ranges (two numbers
5276 separated by a dash) separated by commas. Bytes, characters, and
5277 fields are numbered starting at 1. Incomplete ranges may be
5278 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5279 @samp{@var{n}} through end of line or last field. The list elements
5280 can be repeated, can overlap, and can be specified in any order; but
5281 the selected input is written in the same order that it is read, and
5282 is written exactly once.
5284 The program accepts the following options. Also see @ref{Common
5289 @item -b @var{byte-list}
5290 @itemx --bytes=@var{byte-list}
5293 Select for printing only the bytes in positions listed in
5294 @var{byte-list}. Tabs and backspaces are treated like any other
5295 character; they take up 1 byte. If an output delimiter is specified,
5296 (see the description of @option{--output-delimiter}), then output that
5297 string between ranges of selected bytes.
5299 @item -c @var{character-list}
5300 @itemx --characters=@var{character-list}
5302 @opindex --characters
5303 Select for printing only the characters in positions listed in
5304 @var{character-list}. The same as @option{-b} for now, but
5305 internationalization will change that. Tabs and backspaces are
5306 treated like any other character; they take up 1 character. If an
5307 output delimiter is specified, (see the description of
5308 @option{--output-delimiter}), then output that string between ranges
5311 @item -f @var{field-list}
5312 @itemx --fields=@var{field-list}
5315 Select for printing only the fields listed in @var{field-list}.
5316 Fields are separated by a TAB character by default. Also print any
5317 line that contains no delimiter character, unless the
5318 @option{--only-delimited} (@option{-s}) option is specified
5320 @item -d @var{input_delim_byte}
5321 @itemx --delimiter=@var{input_delim_byte}
5323 @opindex --delimiter
5324 With @option{-f}, use the first byte of @var{input_delim_byte} as
5325 the input fields separator (default is TAB).
5329 Do not split multi-byte characters (no-op for now).
5332 @itemx --only-delimited
5334 @opindex --only-delimited
5335 For @option{-f}, do not print lines that do not contain the field separator
5336 character. Normally, any line without a field separator is printed verbatim.
5338 @item --output-delimiter=@var{output_delim_string}
5339 @opindex --output-delimiter
5340 With @option{-f}, output fields are separated by @var{output_delim_string}.
5341 The default with @option{-f} is to use the input delimiter.
5342 When using @option{-b} or @option{-c} to select ranges of byte or
5343 character offsets (as opposed to ranges of fields),
5344 output @var{output_delim_string} between non-overlapping
5345 ranges of selected bytes.
5348 @opindex --complement
5349 This option is a @acronym{GNU} extension.
5350 Select for printing the complement of the bytes, characters or fields
5351 selected with the @option{-b}, @option{-c} or @option{-f} options.
5352 In other words, do @emph{not} print the bytes, characters or fields
5353 specified via those options. This option is useful when you have
5354 many fields and want to print all but a few of them.
5361 @node paste invocation
5362 @section @command{paste}: Merge lines of files
5365 @cindex merging files
5367 @command{paste} writes to standard output lines consisting of sequentially
5368 corresponding lines of each given file, separated by a TAB character.
5369 Standard input is used for a file name of @samp{-} or if no input files
5391 paste [@var{option}]@dots{} [@var{file}]@dots{}
5394 The program accepts the following options. Also see @ref{Common options}.
5402 Paste the lines of one file at a time rather than one line from each
5403 file. Using the above example data:
5406 $ paste -s num2 let3
5411 @item -d @var{delim-list}
5412 @itemx --delimiters=@var{delim-list}
5414 @opindex --delimiters
5415 Consecutively use the characters in @var{delim-list} instead of
5416 TAB to separate merged lines. When @var{delim-list} is
5417 exhausted, start again at its beginning. Using the above example data:
5420 $ paste -d '%_' num2 let3 num2
5431 @node join invocation
5432 @section @command{join}: Join lines on a common field
5435 @cindex common field, joining on
5437 @command{join} writes to standard output a line for each pair of input
5438 lines that have identical join fields. Synopsis:
5441 join [@var{option}]@dots{} @var{file1} @var{file2}
5444 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5445 meaning standard input. @var{file1} and @var{file2} should be
5446 sorted on the join fields.
5449 Normally, the sort order is that of the
5450 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5451 the @option{-t} option is given, the sort comparison ignores blanks at
5452 the start of the join field, as in @code{sort -b}. If the
5453 @option{--ignore-case} option is given, the sort comparison ignores
5454 the case of characters in the join field, as in @code{sort -f}.
5456 The @command{sort} and @command{join} commands should use consistent
5457 locales and options if the output of @command{sort} is fed to
5458 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5459 sort a file on its default join field, but if you select a non-default
5460 locale, join field, separator, or comparison options, then you should
5461 do so consistently between @command{join} and @command{sort}.
5463 If the input has no unpairable lines, a @acronym{GNU} extension is
5464 available; the sort order can be any order that considers two fields
5465 to be equal if and only if the sort comparison described above
5466 considers them to be equal. For example:
5483 @checkOrderOption{join}
5487 @item the join field is the first field in each line;
5488 @item fields in the input are separated by one or more blanks, with leading
5489 blanks on the line ignored;
5490 @item fields in the output are separated by a space;
5491 @item each output line consists of the join field, the remaining
5492 fields from @var{file1}, then the remaining fields from @var{file2}.
5495 The program accepts the following options. Also see @ref{Common options}.
5499 @item -a @var{file-number}
5501 Print a line for each unpairable line in file @var{file-number} (either
5502 @samp{1} or @samp{2}), in addition to the normal output.
5505 Fail with an error message if either input file is wrongly ordered.
5507 @item --nocheck-order
5508 Do not check that both input files are in sorted order. This is the default.
5510 @item -e @var{string}
5512 Replace those output fields that are missing in the input with
5516 @itemx --ignore-case
5518 @opindex --ignore-case
5519 Ignore differences in case when comparing keys.
5520 With this option, the lines of the input files must be ordered in the same way.
5521 Use @samp{sort -f} to produce this ordering.
5523 @item -1 @var{field}
5525 Join on field @var{field} (a positive integer) of file 1.
5527 @item -2 @var{field}
5529 Join on field @var{field} (a positive integer) of file 2.
5531 @item -j @var{field}
5532 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5534 @item -o @var{field-list}
5535 Construct each output line according to the format in @var{field-list}.
5536 Each element in @var{field-list} is either the single character @samp{0} or
5537 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5538 @samp{2} and @var{n} is a positive field number.
5540 A field specification of @samp{0} denotes the join field.
5541 In most cases, the functionality of the @samp{0} field spec
5542 may be reproduced using the explicit @var{m.n} that corresponds
5543 to the join field. However, when printing unpairable lines
5544 (using either of the @option{-a} or @option{-v} options), there is no way
5545 to specify the join field using @var{m.n} in @var{field-list}
5546 if there are unpairable lines in both files.
5547 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5548 field specification notation.
5550 The elements in @var{field-list}
5551 are separated by commas or blanks.
5552 Blank separators typically need to be quoted for the shell. For
5553 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5554 2.2'} are equivalent.
5556 All output lines---including those printed because of any -a or -v
5557 option---are subject to the specified @var{field-list}.
5560 Use character @var{char} as the input and output field separator.
5561 Treat as significant each occurrence of @var{char} in the input file.
5562 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5563 @samp{sort}, to produce this ordering.
5565 @item -v @var{file-number}
5566 Print a line for each unpairable line in file @var{file-number}
5567 (either @samp{1} or @samp{2}), instead of the normal output.
5574 @node Operating on characters
5575 @chapter Operating on characters
5577 @cindex operating on characters
5579 This commands operate on individual characters.
5582 * tr invocation:: Translate, squeeze, and/or delete characters.
5583 * expand invocation:: Convert tabs to spaces.
5584 * unexpand invocation:: Convert spaces to tabs.
5589 @section @command{tr}: Translate, squeeze, and/or delete characters
5596 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5599 @command{tr} copies standard input to standard output, performing
5600 one of the following operations:
5604 translate, and optionally squeeze repeated characters in the result,
5606 squeeze repeated characters,
5610 delete characters, then squeeze repeated characters from the result.
5613 The @var{set1} and (if given) @var{set2} arguments define ordered
5614 sets of characters, referred to below as @var{set1} and @var{set2}. These
5615 sets are the characters of the input that @command{tr} operates on.
5616 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5618 complement (all of the characters that are not in @var{set1}).
5620 Currently @command{tr} fully supports only single-byte characters.
5621 Eventually it will support multibyte characters; when it does, the
5622 @option{-C} option will cause it to complement the set of characters,
5623 whereas @option{-c} will cause it to complement the set of values.
5624 This distinction will matter only when some values are not characters,
5625 and this is possible only in locales using multibyte encodings when
5626 the input contains encoding errors.
5628 The program accepts the @option{--help} and @option{--version}
5629 options. @xref{Common options}. Options must precede operands.
5634 * Character sets:: Specifying sets of characters.
5635 * Translating:: Changing one set of characters to another.
5636 * Squeezing:: Squeezing repeats and deleting.
5640 @node Character sets
5641 @subsection Specifying sets of characters
5643 @cindex specifying sets of characters
5645 The format of the @var{set1} and @var{set2} arguments resembles
5646 the format of regular expressions; however, they are not regular
5647 expressions, only lists of characters. Most characters simply
5648 represent themselves in these strings, but the strings can contain
5649 the shorthands listed below, for convenience. Some of them can be
5650 used only in @var{set1} or @var{set2}, as noted below.
5654 @item Backslash escapes
5655 @cindex backslash escapes
5657 The following backslash escape sequences are recognized:
5675 The character with the value given by @var{ooo}, which is 1 to 3
5681 While a backslash followed by a character not listed above is
5682 interpreted as that character, the backslash also effectively
5683 removes any special significance, so it is useful to escape
5684 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5689 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5690 from @var{m} through @var{n}, in ascending order. @var{m} should
5691 collate before @var{n}; if it doesn't, an error results. As an example,
5692 @samp{0-9} is the same as @samp{0123456789}.
5694 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5695 brackets to enclose ranges. Translations specified in that format
5696 sometimes work as expected, since the brackets are often transliterated
5697 to themselves. However, they should be avoided because they sometimes
5698 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5701 Many historically common and even accepted uses of ranges are not
5702 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5703 range will not do what most would expect because @samp{A} through @samp{Z}
5704 are not contiguous as they are in @acronym{ASCII}.
5705 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5706 the best way to work around this is to use character classes (see below).
5707 Otherwise, it is most portable (and most ugly) to enumerate the members
5710 @item Repeated characters
5711 @cindex repeated characters
5713 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5714 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5715 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5716 to as many copies of @var{c} as are needed to make @var{set2} as long as
5717 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5718 octal, otherwise in decimal.
5720 @item Character classes
5721 @cindex character classes
5723 The notation @samp{[:@var{class}:]} expands to all of the characters in
5724 the (predefined) class @var{class}. The characters expand in no
5725 particular order, except for the @code{upper} and @code{lower} classes,
5726 which expand in ascending order. When the @option{--delete} (@option{-d})
5727 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5728 character class can be used in @var{set2}. Otherwise, only the
5729 character classes @code{lower} and @code{upper} are accepted in
5730 @var{set2}, and then only if the corresponding character class
5731 (@code{upper} and @code{lower}, respectively) is specified in the same
5732 relative position in @var{set1}. Doing this specifies case conversion.
5733 The class names are given below; an error results when an invalid class
5745 Horizontal whitespace.
5754 Printable characters, not including space.
5760 Printable characters, including space.
5763 Punctuation characters.
5766 Horizontal or vertical whitespace.
5775 @item Equivalence classes
5776 @cindex equivalence classes
5778 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5779 equivalent to @var{c}, in no particular order. Equivalence classes are
5780 a relatively recent invention intended to support non-English alphabets.
5781 But there seems to be no standard way to define them or determine their
5782 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5783 each character's equivalence class consists only of that character,
5784 which is of no particular use.
5790 @subsection Translating
5792 @cindex translating characters
5794 @command{tr} performs translation when @var{set1} and @var{set2} are
5795 both given and the @option{--delete} (@option{-d}) option is not given.
5796 @command{tr} translates each character of its input that is in @var{set1}
5797 to the corresponding character in @var{set2}. Characters not in
5798 @var{set1} are passed through unchanged. When a character appears more
5799 than once in @var{set1} and the corresponding characters in @var{set2}
5800 are not all the same, only the final one is used. For example, these
5801 two commands are equivalent:
5808 A common use of @command{tr} is to convert lowercase characters to
5809 uppercase. This can be done in many ways. Here are three of them:
5812 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5814 tr '[:lower:]' '[:upper:]'
5818 But note that using ranges like @code{a-z} above is not portable.
5820 When @command{tr} is performing translation, @var{set1} and @var{set2}
5821 typically have the same length. If @var{set1} is shorter than
5822 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5824 On the other hand, making @var{set1} longer than @var{set2} is not
5825 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5826 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5827 the last character of @var{set2} as many times as necessary. System V
5828 @command{tr} truncates @var{set1} to the length of @var{set2}.
5830 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5831 When the @option{--truncate-set1} (@option{-t}) option is given,
5832 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5833 instead. This option is ignored for operations other than translation.
5835 Acting like System V @command{tr} in this case breaks the relatively common
5839 tr -cs A-Za-z0-9 '\012'
5843 because it converts only zero bytes (the first element in the
5844 complement of @var{set1}), rather than all non-alphanumerics, to
5848 By the way, the above idiom is not portable because it uses ranges, and
5849 it assumes that the octal code for newline is 012.
5850 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5853 tr -cs '[:alnum:]' '[\n*]'
5858 @subsection Squeezing repeats and deleting
5860 @cindex squeezing repeat characters
5861 @cindex deleting characters
5863 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5864 removes any input characters that are in @var{set1}.
5866 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5867 @command{tr} replaces each input sequence of a repeated character that
5868 is in @var{set1} with a single occurrence of that character.
5870 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5871 first performs any deletions using @var{set1}, then squeezes repeats
5872 from any remaining characters using @var{set2}.
5874 The @option{--squeeze-repeats} option may also be used when translating,
5875 in which case @command{tr} first performs translation, then squeezes
5876 repeats from any remaining characters using @var{set2}.
5878 Here are some examples to illustrate various combinations of options:
5883 Remove all zero bytes:
5890 Put all words on lines by themselves. This converts all
5891 non-alphanumeric characters to newlines, then squeezes each string
5892 of repeated newlines into a single newline:
5895 tr -cs '[:alnum:]' '[\n*]'
5899 Convert each sequence of repeated newlines to a single newline:
5906 Find doubled occurrences of words in a document.
5907 @c Separate the following two "the"s, so typo checkers don't complain.
5908 For example, people often write ``the @w{}the'' with the repeated words
5909 separated by a newline. The Bourne shell script below works first
5910 by converting each sequence of punctuation and blank characters to a
5911 single newline. That puts each ``word'' on a line by itself.
5912 Next it maps all uppercase characters to lower case, and finally it
5913 runs @command{uniq} with the @option{-d} option to print out only the words
5919 | tr -s '[:punct:][:blank:]' '[\n*]' \
5920 | tr '[:upper:]' '[:lower:]' \
5925 Deleting a small set of characters is usually straightforward. For example,
5926 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5932 However, when @samp{-} is one of those characters, it can be tricky because
5933 @samp{-} has special meanings. Performing the same task as above but also
5934 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5935 that would fail because @command{tr} would try to interpret @option{-a} as
5936 a command-line option. Alternatively, we could try putting the hyphen
5937 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5938 it would make @command{tr} interpret @code{a-x} as the range of characters
5939 @samp{a}@dots{}@samp{x} rather than the three.
5940 One way to solve the problem is to put the hyphen at the end of the list
5947 Or you can use @samp{--} to terminate option processing:
5953 More generally, use the character class notation @code{[=c=]}
5954 with @samp{-} (or any other character) in place of the @samp{c}:
5960 Note how single quotes are used in the above example to protect the
5961 square brackets from interpretation by a shell.
5966 @node expand invocation
5967 @section @command{expand}: Convert tabs to spaces
5970 @cindex tabs to spaces, converting
5971 @cindex converting tabs to spaces
5973 @command{expand} writes the contents of each given @var{file}, or standard
5974 input if none are given or for a @var{file} of @samp{-}, to standard
5975 output, with tab characters converted to the appropriate number of
5979 expand [@var{option}]@dots{} [@var{file}]@dots{}
5982 By default, @command{expand} converts all tabs to spaces. It preserves
5983 backspace characters in the output; they decrement the column count for
5984 tab calculations. The default action is equivalent to @option{-t 8} (set
5985 tabs every 8 columns).
5987 The program accepts the following options. Also see @ref{Common options}.
5991 @item -t @var{tab1}[,@var{tab2}]@dots{}
5992 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5995 @cindex tab stops, setting
5996 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5997 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5998 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5999 last tab stop given with single spaces. Tab stops can be separated by
6000 blanks as well as by commas.
6002 For compatibility, GNU @command{expand} also accepts the obsolete
6003 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6004 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6010 @cindex initial tabs, converting
6011 Only convert initial tabs (those that precede all non-space or non-tab
6012 characters) on each line to spaces.
6019 @node unexpand invocation
6020 @section @command{unexpand}: Convert spaces to tabs
6024 @command{unexpand} writes the contents of each given @var{file}, or
6025 standard input if none are given or for a @var{file} of @samp{-}, to
6026 standard output, converting blanks at the beginning of each line into
6027 as many tab characters as needed. In the default @acronym{POSIX}
6028 locale, a @dfn{blank} is a space or a tab; other locales may specify
6029 additional blank characters. Synopsis:
6032 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6035 By default, @command{unexpand} converts only initial blanks (those
6036 that precede all non-blank characters) on each line. It
6037 preserves backspace characters in the output; they decrement the column
6038 count for tab calculations. By default, tabs are set at every 8th
6041 The program accepts the following options. Also see @ref{Common options}.
6045 @item -t @var{tab1}[,@var{tab2}]@dots{}
6046 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6049 If only one tab stop is given, set the tabs @var{tab1} columns apart
6050 instead of the default 8. Otherwise, set the tabs at columns
6051 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6052 beyond the tab stops given unchanged. Tab stops can be separated by
6053 blanks as well as by commas. This option implies the @option{-a} option.
6055 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6056 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6057 separated by commas. (Unlike @option{-t}, this obsolete option does
6058 not imply @option{-a}.) New scripts should use @option{--first-only -t
6059 @var{tab1}[,@var{tab2}]@dots{}} instead.
6065 Also convert all sequences of two or more blanks just before a tab stop,
6066 even if they occur after non-blank characters in a line.
6073 @node Directory listing
6074 @chapter Directory listing
6076 This chapter describes the @command{ls} command and its variants @command{dir}
6077 and @command{vdir}, which list information about files.
6080 * ls invocation:: List directory contents.
6081 * dir invocation:: Briefly ls.
6082 * vdir invocation:: Verbosely ls.
6083 * dircolors invocation:: Color setup for ls, etc.
6088 @section @command{ls}: List directory contents
6091 @cindex directory listing
6093 The @command{ls} program lists information about files (of any type,
6094 including directories). Options and file arguments can be intermixed
6095 arbitrarily, as usual.
6097 For non-option command-line arguments that are directories, by default
6098 @command{ls} lists the contents of directories, not recursively, and
6099 omitting files with names beginning with @samp{.}. For other non-option
6100 arguments, by default @command{ls} lists just the file name. If no
6101 non-option argument is specified, @command{ls} operates on the current
6102 directory, acting as if it had been invoked with a single argument of @samp{.}.
6105 By default, the output is sorted alphabetically, according to the locale
6106 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6107 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6108 produce output that is sorted differently than you're accustomed to.
6109 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6110 If standard output is
6111 a terminal, the output is in columns (sorted vertically) and control
6112 characters are output as question marks; otherwise, the output is listed
6113 one per line and control characters are output as-is.
6115 Because @command{ls} is such a fundamental program, it has accumulated many
6116 options over the years. They are described in the subsections below;
6117 within each section, options are listed alphabetically (ignoring case).
6118 The division of options into the subsections is not absolute, since some
6119 options affect more than one aspect of @command{ls}'s operation.
6121 @cindex exit status of @command{ls}
6126 1 minor problems (e.g., failure to access a file or directory not
6127 specified as a command line argument. This happens when listing a
6128 directory in which entries are actively being removed or renamed.)
6129 2 serious trouble (e.g., memory exhausted, invalid option or failure
6130 to access file or directory specified as a command line argument)
6133 Also see @ref{Common options}.
6136 * Which files are listed::
6137 * What information is listed::
6138 * Sorting the output::
6139 * More details about version sort::
6140 * General output formatting::
6141 * Formatting file timestamps::
6142 * Formatting the file names::
6146 @node Which files are listed
6147 @subsection Which files are listed
6149 These options determine which files @command{ls} lists information for.
6150 By default, @command{ls} lists files and the contents of any
6151 directories on the command line, except that in directories it ignores
6152 files whose names start with @samp{.}.
6160 In directories, do not ignore file names that start with @samp{.}.
6165 @opindex --almost-all
6166 In directories, do not ignore all file names that start with @samp{.};
6167 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6168 option overrides this option.
6171 @itemx --ignore-backups
6173 @opindex --ignore-backups
6174 @cindex backup files, ignoring
6175 In directories, ignore files that end with @samp{~}. This option is
6176 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6181 @opindex --directory
6182 List just the names of directories, as with other types of files, rather
6183 than listing their contents.
6184 @c The following sentence is the same as the one for -F.
6185 Do not follow symbolic links listed on the
6186 command line unless the @option{--dereference-command-line} (@option{-H}),
6187 @option{--dereference} (@option{-L}), or
6188 @option{--dereference-command-line-symlink-to-dir} options are specified.
6191 @itemx --dereference-command-line
6193 @opindex --dereference-command-line
6194 @cindex symbolic links, dereferencing
6195 If a command line argument specifies a symbolic link, show information
6196 for the file the link references rather than for the link itself.
6198 @itemx --dereference-command-line-symlink-to-dir
6199 @opindex --dereference-command-line-symlink-to-dir
6200 @cindex symbolic links, dereferencing
6201 Do not dereference symbolic links, with one exception:
6202 if a command line argument specifies a symbolic link that refers to
6203 a directory, show information for that directory rather than for the
6205 This is the default behavior when no other dereferencing-related
6206 option has been specified (@option{--classify} (@option{-F}),
6207 @option{--directory} (@option{-d}),
6209 @option{--dereference} (@option{-L}), or
6210 @option{--dereference-command-line} (@option{-H})).
6212 @item --group-directories-first
6213 @opindex --group-directories-first
6214 Group all the directories before the files and then sort the
6215 directories and the files separately using the selected sort key
6216 (see --sort option).
6217 That is, this option specifies a primary sort key,
6218 and the --sort option specifies a secondary key.
6219 However, any use of @option{--sort=none}
6220 (@option{-U}) disables this option altogether.
6222 @item --hide=PATTERN
6223 @opindex --hide=@var{pattern}
6224 In directories, ignore files whose names match the shell pattern
6225 @var{pattern}, unless the @option{--all} (@option{-a}) or
6226 @option{--almost-all} (@option{-A}) is also given. This
6227 option acts like @option{--ignore=@var{pattern}} except that it has no
6228 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6229 (@option{-A}) is also given.
6231 This option can be useful in shell aliases. For example, if
6232 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6233 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6234 lists the file @file{README~} even though @samp{ly -A} would not.
6236 @item -I @var{pattern}
6237 @itemx --ignore=@var{pattern}
6239 @opindex --ignore=@var{pattern}
6240 In directories, ignore files whose names match the shell pattern
6241 (not regular expression) @var{pattern}. As
6242 in the shell, an initial @samp{.} in a file name does not match a
6243 wildcard at the start of @var{pattern}. Sometimes it is useful
6244 to give this option several times. For example,
6247 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6250 The first option ignores names of length 3 or more that start with @samp{.},
6251 the second ignores all two-character names that start with @samp{.}
6252 except @samp{..}, and the third ignores names that start with @samp{#}.
6255 @itemx --dereference
6257 @opindex --dereference
6258 @cindex symbolic links, dereferencing
6259 When showing file information for a symbolic link, show information
6260 for the file the link references rather than the link itself.
6261 However, even with this option, @command{ls} still prints the name
6262 of the link itself, not the name of the file that the link points to.
6267 @opindex --recursive
6268 @cindex recursive directory listing
6269 @cindex directory listing, recursive
6270 List the contents of all directories recursively.
6275 @node What information is listed
6276 @subsection What information is listed
6278 These options affect the information that @command{ls} displays. By
6279 default, only file names are shown.
6285 @cindex hurd, author, printing
6286 List each file's author when producing long format directory listings.
6287 In GNU/Hurd, file authors can differ from their owners, but in other
6288 operating systems the two are the same.
6294 @cindex dired Emacs mode support
6295 With the long listing (@option{-l}) format, print an additional line after
6299 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6303 The @var{begn} and @var{endn} are unsigned integers that record the
6304 byte position of the beginning and end of each file name in the output.
6305 This makes it easy for Emacs to find the names, even when they contain
6306 unusual characters such as space or newline, without fancy searching.
6308 If directories are being listed recursively (@option{-R}), output a similar
6309 line with offsets for each subdirectory name:
6312 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6315 Finally, output a line of the form:
6318 //DIRED-OPTIONS// --quoting-style=@var{word}
6322 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6324 Here is an actual example:
6327 $ mkdir -p a/sub/deeper a/sub2
6329 $ touch a/sub/deeper/file
6330 $ ls -gloRF --dired a
6333 -rw-r--r-- 1 0 Jun 10 12:27 f1
6334 -rw-r--r-- 1 0 Jun 10 12:27 f2
6335 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6336 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6340 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6344 -rw-r--r-- 1 0 Jun 10 12:27 file
6348 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6349 //SUBDIRED// 2 3 167 172 228 240 290 296
6350 //DIRED-OPTIONS// --quoting-style=literal
6353 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6354 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6356 The offsets on the @samp{//SUBDIRED//} line delimit the following
6357 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6359 Here is an example of how to extract the fifth entry name, @samp{deeper},
6360 corresponding to the pair of offsets, 222 and 228:
6363 $ ls -gloRF --dired a > out
6364 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6368 Note that although the listing above includes a trailing slash
6369 for the @samp{deeper} entry, the offsets select the name without
6370 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6371 along with an option like @option{--escape} (aka @option{-b}) and operate
6372 on a file whose name contains special characters, notice that the backslash
6377 $ ls -blog --dired 'a b'
6378 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6380 //DIRED-OPTIONS// --quoting-style=escape
6383 If you use a quoting style that adds quote marks
6384 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6385 So beware that the user may select the quoting style via the environment
6386 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6387 should either specify an explicit @option{--quoting-style=literal} option
6388 (aka @option{-N} or @option{--literal}) on the command line, or else be
6389 prepared to parse the escaped names.
6392 @opindex --full-time
6393 Produce long format directory listings, and list times in full. It is
6394 equivalent to using @option{--format=long} with
6395 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6399 Produce long format directory listings, but don't display owner information.
6405 Inhibit display of group information in a long format directory listing.
6406 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6407 provide this option for compatibility.)
6415 @cindex inode number, printing
6416 Print the inode number (also called the file serial number and index
6417 number) of each file to the left of the file name. (This number
6418 uniquely identifies each file within a particular file system.)
6421 @itemx --format=long
6422 @itemx --format=verbose
6425 @opindex long ls @r{format}
6426 @opindex verbose ls @r{format}
6427 In addition to the name of each file, print the file type, file mode bits,
6428 number of hard links, owner name, group name, size, and
6429 timestamp (@pxref{Formatting file timestamps}), normally
6430 the modification time. Print question marks for information that
6431 cannot be determined.
6433 Normally the size is printed as a byte count without punctuation, but
6434 this can be overridden (@pxref{Block size}). For example, @option{-h}
6435 prints an abbreviated, human-readable count, and
6436 @samp{--block-size="'1"} prints a byte count with the thousands
6437 separator of the current locale.
6439 For each directory that is listed, preface the files with a line
6440 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6441 for all files in that directory. The block size currently defaults to 1024
6442 bytes, but this can be overridden (@pxref{Block size}).
6443 The @var{blocks} computed counts each hard link separately;
6444 this is arguably a deficiency.
6446 The file type is one of the following characters:
6448 @c The commented-out entries are ones we're not sure about.
6456 character special file
6458 high performance (``contiguous data'') file
6462 door (Solaris 2.5 and up)
6464 @c semaphore, if this is a distinct file type
6468 @c multiplexed file (7th edition Unix; obsolete)
6470 off-line (``migrated'') file (Cray DMF)
6472 network special file (HP-UX)
6476 port (Solaris 10 and up)
6478 @c message queue, if this is a distinct file type
6482 @c shared memory object, if this is a distinct file type
6484 @c typed memory object, if this is a distinct file type
6486 @c whiteout (4.4BSD; not implemented)
6488 some other file type
6491 @cindex permissions, output by @command{ls}
6492 The file mode bits listed are similar to symbolic mode specifications
6493 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6494 third character of each set of permissions as follows:
6498 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6502 If the set-user-ID or set-group-ID bit is set but the corresponding
6503 executable bit is not set.
6506 If the restricted deletion flag or sticky bit, and the
6507 other-executable bit, are both set. The restricted deletion flag is
6508 another name for the sticky bit. @xref{Mode Structure}.
6511 If the restricted deletion flag or sticky bit is set but the
6512 other-executable bit is not set.
6515 If the executable bit is set and none of the above apply.
6521 Following the file mode bits is a single character that specifies
6522 whether an alternate access method such as an access control list
6523 applies to the file. When the character following the file mode bits is a
6524 space, there is no alternate access method. When it is a printing
6525 character, then there is such a method.
6527 GNU @command{ls} uses a @samp{.} character to indicate a file
6528 with an SELinux security context, but no other alternate access method.
6530 A file with any other combination of alternate access methods
6531 is marked with a @samp{+} character.
6534 @itemx --numeric-uid-gid
6536 @opindex --numeric-uid-gid
6537 @cindex numeric uid and gid
6538 @cindex numeric user and group IDs
6539 Produce long format directory listings, but
6540 display numeric user and group IDs instead of the owner and group names.
6544 Produce long format directory listings, but don't display group information.
6545 It is equivalent to using @option{--format=long} with @option{--no-group} .
6551 @cindex disk allocation
6552 @cindex size of files, reporting
6553 Print the disk allocation of each file to the left of the file name.
6554 This is the amount of disk space used by the file, which is usually a
6555 bit more than the file's size, but it can be less if the file has holes.
6557 Normally the disk allocation is printed in units of
6558 1024 bytes, but this can be overridden (@pxref{Block size}).
6560 @cindex NFS mounts from BSD to HP-UX
6561 For files that are NFS-mounted from an HP-UX system to a BSD system,
6562 this option reports sizes that are half the correct values. On HP-UX
6563 systems, it reports sizes that are twice the correct values for files
6564 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6565 it also affects the HP-UX @command{ls} program.
6574 @cindex security context
6575 Display the SELinux security context or @samp{?} if none is found.
6576 When used with the @option{-l} option, print the security context
6577 to the left of the size column.
6582 @node Sorting the output
6583 @subsection Sorting the output
6585 @cindex sorting @command{ls} output
6586 These options change the order in which @command{ls} sorts the information
6587 it outputs. By default, sorting is done by character code
6588 (e.g., @acronym{ASCII} order).
6594 @itemx --time=status
6597 @opindex ctime@r{, printing or sorting by}
6598 @opindex status time@r{, printing or sorting by}
6599 @opindex use time@r{, printing or sorting files by}
6600 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6601 print the status change time (the @samp{ctime} in the inode) instead of
6602 the modification time.
6603 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6604 or when not using a long listing format,
6605 sort according to the status change time.
6609 @cindex unsorted directory listing
6610 @cindex directory order, listing by
6611 Primarily, like @option{-U}---do not sort; list the files in whatever
6612 order they are stored in the directory. But also enable @option{-a} (list
6613 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6614 were specified before the @option{-f}).
6620 @cindex reverse sorting
6621 Reverse whatever the sorting method is---e.g., list files in reverse
6622 alphabetical order, youngest first, smallest first, or whatever.
6628 @opindex size of files@r{, sorting files by}
6629 Sort by file size, largest first.
6635 @opindex modification time@r{, sorting files by}
6636 Sort by modification time (the @samp{mtime} in the inode), newest first.
6640 @itemx --time=access
6644 @opindex use time@r{, printing or sorting files by}
6645 @opindex atime@r{, printing or sorting files by}
6646 @opindex access time@r{, printing or sorting files by}
6647 If the long listing format (e.g., @option{--format=long}) is being used,
6648 print the last access time (the @samp{atime} in the inode).
6649 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6650 or when not using a long listing format, sort according to the access time.
6656 @opindex none@r{, sorting option for @command{ls}}
6657 Do not sort; list the files in whatever order they are
6658 stored in the directory. (Do not do any of the other unrelated things
6659 that @option{-f} does.) This is especially useful when listing very large
6660 directories, since not doing any sorting can be noticeably faster.
6663 @itemx --sort=version
6666 @opindex version@r{, sorting option for @command{ls}}
6667 Sort by version name and number, lowest first. It behaves like a default
6668 sort, except that each sequence of decimal digits is treated numerically
6669 as an index/version number. (@xref{More details about version sort}.)
6672 @itemx --sort=extension
6675 @opindex extension@r{, sorting files by}
6676 Sort directory contents alphabetically by file extension (characters
6677 after the last @samp{.}); files with no extension are sorted first.
6682 @node More details about version sort
6683 @subsection More details about version sort
6685 The version sort takes into account the fact that file names frequently include
6686 indices or version numbers. Standard sorting functions usually do not produce
6687 the ordering that people expect because comparisons are made on a
6688 character-by-character basis. The version
6689 sort addresses this problem, and is especially useful when browsing
6690 directories that contain many files with indices/version numbers in their
6695 foo.zml-1.gz foo.zml-1.gz
6696 foo.zml-100.gz foo.zml-2.gz
6697 foo.zml-12.gz foo.zml-6.gz
6698 foo.zml-13.gz foo.zml-12.gz
6699 foo.zml-2.gz foo.zml-13.gz
6700 foo.zml-25.gz foo.zml-25.gz
6701 foo.zml-6.gz foo.zml-100.gz
6704 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6705 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6706 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6707 @var{ver1} < @var{ver2} implies that the name composed of
6708 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6709 ``@var{prefix} @var{ver2} @var{suffix}''.
6711 Note also that leading zeros of numeric parts are ignored:
6715 abc-1.007.tgz abc-1.01a.tgz
6716 abc-1.012b.tgz abc-1.007.tgz
6717 abc-1.01a.tgz abc-1.012b.tgz
6720 This functionality is implemented using gnulib's @code{filevercmp} function.
6721 One result of that implementation decision is that @samp{ls -v}
6722 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6723 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6726 @node General output formatting
6727 @subsection General output formatting
6729 These options affect the appearance of the overall output.
6734 @itemx --format=single-column
6737 @opindex single-column @r{output of files}
6738 List one file per line. This is the default for @command{ls} when standard
6739 output is not a terminal.
6742 @itemx --format=vertical
6745 @opindex vertical @r{sorted files in columns}
6746 List files in columns, sorted vertically. This is the default for
6747 @command{ls} if standard output is a terminal. It is always the default
6748 for the @command{dir} program.
6749 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6750 possible in the fewest lines.
6752 @item --color [=@var{when}]
6754 @cindex color, distinguishing file types with
6755 Specify whether to use color for distinguishing file types. @var{when}
6756 may be omitted, or one of:
6759 @vindex none @r{color option}
6760 - Do not use color at all. This is the default.
6762 @vindex auto @r{color option}
6763 @cindex terminal, using color iff
6764 - Only use color if standard output is a terminal.
6766 @vindex always @r{color option}
6769 Specifying @option{--color} and no @var{when} is equivalent to
6770 @option{--color=always}.
6771 Piping a colorized listing through a pager like @command{more} or
6772 @command{less} usually produces unreadable results. However, using
6773 @code{more -f} does seem to work.
6777 @itemx --indicator-style=classify
6780 @opindex --indicator-style
6781 @cindex file type and executables, marking
6782 @cindex executables and file type, marking
6783 Append a character to each file name indicating the file type. Also,
6784 for regular files that are executable, append @samp{*}. The file type
6785 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6786 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6787 and nothing for regular files.
6788 @c The following sentence is the same as the one for -d.
6789 Do not follow symbolic links listed on the
6790 command line unless the @option{--dereference-command-line} (@option{-H}),
6791 @option{--dereference} (@option{-L}), or
6792 @option{--dereference-command-line-symlink-to-dir} options are specified.
6795 @itemx --indicator-style=file-type
6796 @opindex --file-type
6797 @opindex --indicator-style
6798 @cindex file type, marking
6799 Append a character to each file name indicating the file type. This is
6800 like @option{-F}, except that executables are not marked.
6802 @item --indicator-style=@var{word}
6803 @opindex --indicator-style
6804 Append a character indicator with style @var{word} to entry names,
6809 Do not append any character indicator; this is the default.
6811 Append @samp{/} for directories. This is the same as the @option{-p}
6814 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6815 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6816 the same as the @option{--file-type} option.
6818 Append @samp{*} for executable regular files, otherwise behave as for
6819 @samp{file-type}. This is the same as the @option{-F} or
6820 @option{--classify} option.
6825 Print file sizes in 1024-byte blocks, overriding the default block
6826 size (@pxref{Block size}).
6827 This option is equivalent to @option{--block-size=1K}.
6830 @itemx --format=commas
6833 @opindex commas@r{, outputting between files}
6834 List files horizontally, with as many as will fit on each line,
6835 separated by @samp{, } (a comma and a space).
6838 @itemx --indicator-style=slash
6840 @opindex --indicator-style
6841 @cindex file type, marking
6842 Append a @samp{/} to directory names.
6845 @itemx --format=across
6846 @itemx --format=horizontal
6849 @opindex across@r{, listing files}
6850 @opindex horizontal@r{, listing files}
6851 List the files in columns, sorted horizontally.
6854 @itemx --tabsize=@var{cols}
6857 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6858 @command{ls} uses tabs where possible in the output, for efficiency. If
6859 @var{cols} is zero, do not use tabs at all.
6861 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6862 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6863 do not properly align columns to the right of a TAB following a
6864 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6865 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6866 @command{ls} to align using spaces, not tabs.
6869 @itemx --width=@var{cols}
6873 Assume the screen is @var{cols} columns wide. The default is taken
6874 from the terminal settings if possible; otherwise the environment
6875 variable @env{COLUMNS} is used if it is set; otherwise the default
6881 @node Formatting file timestamps
6882 @subsection Formatting file timestamps
6884 By default, file timestamps are listed in abbreviated form. Most
6885 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6886 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6887 for non-recent timestamps, and a date-without-year and time like
6888 @samp{Mar 30 23:45} for recent timestamps.
6890 A timestamp is considered to be @dfn{recent} if it is less than six
6891 months old, and is not dated in the future. If a timestamp dated
6892 today is not listed in recent form, the timestamp is in the future,
6893 which means you probably have clock skew problems which may break
6894 programs like @command{make} that rely on file timestamps.
6897 Time stamps are listed according to the time zone rules specified by
6898 the @env{TZ} environment variable, or by the system default rules if
6899 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6900 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6902 The following option changes how file timestamps are printed.
6905 @item --time-style=@var{style}
6906 @opindex --time-style
6908 List timestamps in style @var{style}. The @var{style} should
6909 be one of the following:
6914 List timestamps using @var{format}, where @var{format} is interpreted
6915 like the format argument of @command{date} (@pxref{date invocation}).
6916 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6917 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6918 with @command{date}, @var{format}'s interpretation is affected by the
6919 @env{LC_TIME} locale category.
6921 If @var{format} contains two format strings separated by a newline,
6922 the former is used for non-recent files and the latter for recent
6923 files; if you want output columns to line up, you may need to insert
6924 spaces in one of the two formats.
6927 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6928 format with nanosecond precision, e.g., @samp{2002-03-30
6929 23:45:56.477817180 -0700}. This style is equivalent to
6930 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6932 This is useful because the time output includes all the information that
6933 is available from the operating system. For example, this can help
6934 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6935 uses the full timestamp to determine whether a file is out of date.
6938 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6939 @samp{2002-03-30 23:45}. These timestamps are shorter than
6940 @samp{full-iso} timestamps, and are usually good enough for everyday
6941 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6944 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6945 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6946 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6947 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6948 nearly the same information in a smaller space and their brevity helps
6949 @command{ls} output fit within traditional 80-column output lines.
6950 The following two @command{ls} invocations are equivalent:
6955 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6956 ls -l --time-style="iso"
6961 List timestamps in a locale-dependent form. For example, a Finnish
6962 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6963 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6964 timestamps typically consume more space than @samp{iso} timestamps and
6965 are harder for programs to parse because locale conventions vary so
6966 widely, but they are easier for many people to read.
6968 The @env{LC_TIME} locale category specifies the timestamp format. The
6969 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6970 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6971 @command{ls} invocations are equivalent:
6976 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6977 ls -l --time-style="locale"
6980 Other locales behave differently. For example, in a German locale,
6981 @option{--time-style="locale"} might be equivalent to
6982 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6983 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6984 @samp{30. M@"ar 23:45}.
6986 @item posix-@var{style}
6988 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6989 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6990 example, the @samp{posix-long-iso} style lists
6991 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6992 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6997 You can specify the default value of the @option{--time-style} option
6998 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
6999 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7000 later use the @option{--dired} option and therefore can parse any date
7001 format, but if you are using Emacs 21.1 or 21.2 and specify a
7002 non-@acronym{POSIX} locale you may need to set
7003 @samp{TIME_STYLE="posix-long-iso"}.
7005 To avoid certain denial-of-service attacks, timestamps that would be
7006 longer than 1000 bytes may be treated as errors.
7009 @node Formatting the file names
7010 @subsection Formatting the file names
7012 These options change how file names themselves are printed.
7018 @itemx --quoting-style=escape
7021 @opindex --quoting-style
7022 @cindex backslash sequences for file names
7023 Quote nongraphic characters in file names using alphabetic and octal
7024 backslash sequences like those used in C.
7028 @itemx --quoting-style=literal
7031 @opindex --quoting-style
7032 Do not quote file names. However, with @command{ls} nongraphic
7033 characters are still printed as question marks if the output is a
7034 terminal and you do not specify the @option{--show-control-chars}
7038 @itemx --hide-control-chars
7040 @opindex --hide-control-chars
7041 Print question marks instead of nongraphic characters in file names.
7042 This is the default if the output is a terminal and the program is
7047 @itemx --quoting-style=c
7049 @opindex --quote-name
7050 @opindex --quoting-style
7051 Enclose file names in double quotes and quote nongraphic characters as
7054 @item --quoting-style=@var{word}
7055 @opindex --quoting-style
7056 @cindex quoting style
7057 Use style @var{word} to quote file names and other strings that may
7058 contain arbitrary characters. The @var{word} should
7059 be one of the following:
7063 Output strings as-is; this is the same as the @option{-N} or
7064 @option{--literal} option.
7066 Quote strings for the shell if they contain shell metacharacters or would
7067 cause ambiguous output.
7068 The quoting is suitable for @acronym{POSIX}-compatible shells like
7069 @command{bash}, but it does not always work for incompatible shells
7072 Quote strings for the shell, even if they would normally not require quoting.
7074 Quote strings as for C character string literals, including the
7075 surrounding double-quote characters; this is the same as the
7076 @option{-Q} or @option{--quote-name} option.
7078 Quote strings as for C character string literals, except omit the
7079 surrounding double-quote
7080 characters; this is the same as the @option{-b} or @option{--escape} option.
7082 Quote strings as for C character string literals, except use
7083 surrounding quotation marks appropriate for the
7086 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7087 Quote strings as for C character string literals, except use
7088 surrounding quotation marks appropriate for the locale, and quote
7089 @t{`like this'} instead of @t{"like
7090 this"} in the default C locale. This looks nicer on many displays.
7093 You can specify the default value of the @option{--quoting-style} option
7094 with the environment variable @env{QUOTING_STYLE}. If that environment
7095 variable is not set, the default value is @samp{literal}, but this
7096 default may change to @samp{shell} in a future version of this package.
7098 @item --show-control-chars
7099 @opindex --show-control-chars
7100 Print nongraphic characters as-is in file names.
7101 This is the default unless the output is a terminal and the program is
7107 @node dir invocation
7108 @section @command{dir}: Briefly list directory contents
7111 @cindex directory listing, brief
7113 @command{dir} is equivalent to @code{ls -C
7114 -b}; that is, by default files are listed in columns, sorted vertically,
7115 and special characters are represented by backslash escape sequences.
7117 @xref{ls invocation, @command{ls}}.
7120 @node vdir invocation
7121 @section @command{vdir}: Verbosely list directory contents
7124 @cindex directory listing, verbose
7126 @command{vdir} is equivalent to @code{ls -l
7127 -b}; that is, by default files are listed in long format and special
7128 characters are represented by backslash escape sequences.
7130 @node dircolors invocation
7131 @section @command{dircolors}: Color setup for @command{ls}
7135 @cindex setup for color
7137 @command{dircolors} outputs a sequence of shell commands to set up the
7138 terminal for color output from @command{ls} (and @command{dir}, etc.).
7142 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7145 If @var{file} is specified, @command{dircolors} reads it to determine which
7146 colors to use for which file types and extensions. Otherwise, a
7147 precompiled database is used. For details on the format of these files,
7148 run @samp{dircolors --print-database}.
7150 To make @command{dircolors} read a @file{~/.dircolors} file if it
7151 exists, you can put the following lines in your @file{~/.bashrc} (or
7152 adapt them to your favorite shell):
7156 test -r $d && eval "$(dircolors $d)"
7160 @vindex SHELL @r{environment variable, and color}
7161 The output is a shell command to set the @env{LS_COLORS} environment
7162 variable. You can specify the shell syntax to use on the command line,
7163 or @command{dircolors} will guess it from the value of the @env{SHELL}
7164 environment variable.
7166 The program accepts the following options. Also see @ref{Common options}.
7171 @itemx --bourne-shell
7174 @opindex --bourne-shell
7175 @cindex Bourne shell syntax for color setup
7176 @cindex @command{sh} syntax for color setup
7177 Output Bourne shell commands. This is the default if the @env{SHELL}
7178 environment variable is set and does not end with @samp{csh} or
7187 @cindex C shell syntax for color setup
7188 @cindex @command{csh} syntax for color setup
7189 Output C shell commands. This is the default if @code{SHELL} ends with
7190 @command{csh} or @command{tcsh}.
7193 @itemx --print-database
7195 @opindex --print-database
7196 @cindex color database, printing
7197 @cindex database for color setup, printing
7198 @cindex printing color database
7199 Print the (compiled-in) default color configuration database. This
7200 output is itself a valid configuration file, and is fairly descriptive
7201 of the possibilities.
7208 @node Basic operations
7209 @chapter Basic operations
7211 @cindex manipulating files
7213 This chapter describes the commands for basic file manipulation:
7214 copying, moving (renaming), and deleting (removing).
7217 * cp invocation:: Copy files.
7218 * dd invocation:: Convert and copy a file.
7219 * install invocation:: Copy files and set attributes.
7220 * mv invocation:: Move (rename) files.
7221 * rm invocation:: Remove files or directories.
7222 * shred invocation:: Remove files more securely.
7227 @section @command{cp}: Copy files and directories
7230 @cindex copying files and directories
7231 @cindex files, copying
7232 @cindex directories, copying
7234 @command{cp} copies files (or, optionally, directories). The copy is
7235 completely independent of the original. You can either copy one file to
7236 another, or copy arbitrarily many files to a destination directory.
7240 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7241 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7242 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7247 If two file names are given, @command{cp} copies the first file to the
7251 If the @option{--target-directory} (@option{-t}) option is given, or
7252 failing that if the last file is a directory and the
7253 @option{--no-target-directory} (@option{-T}) option is not given,
7254 @command{cp} copies each @var{source} file to the specified directory,
7255 using the @var{source}s' names.
7258 Generally, files are written just as they are read. For exceptions,
7259 see the @option{--sparse} option below.
7261 By default, @command{cp} does not copy directories. However, the
7262 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7263 copy recursively by descending into source directories and copying files
7264 to corresponding destination directories.
7266 When copying from a symbolic link, @command{cp} normally follows the
7267 link only when not copying
7268 recursively. This default can be overridden with the
7269 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7270 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7271 @option{-H} options. If more than one of these options is specified,
7272 the last one silently overrides the others.
7274 When copying to a symbolic link, @command{cp} follows the
7275 link only when it refers to an existing regular file.
7276 However, when copying to a dangling symbolic link, @command{cp}
7277 refuses by default, and fails with a diagnostic, since the operation
7278 is inherently dangerous. This behavior is contrary to historical
7279 practice and to @acronym{POSIX}.
7280 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7281 the target of a dangling destination symlink, in spite of the possible risk.
7282 Also, when an option like
7283 @option{--backup} or @option{--link} acts to rename or remove the
7284 destination before copying, @command{cp} renames or removes the
7285 symbolic link rather than the file it points to.
7287 By default, @command{cp} copies the contents of special files only
7288 when not copying recursively. This default can be overridden with the
7289 @option{--copy-contents} option.
7291 @cindex self-backups
7292 @cindex backups, making only
7293 @command{cp} generally refuses to copy a file onto itself, with the
7294 following exception: if @option{--force --backup} is specified with
7295 @var{source} and @var{dest} identical, and referring to a regular file,
7296 @command{cp} will make a backup file, either regular or numbered, as
7297 specified in the usual ways (@pxref{Backup options}). This is useful when
7298 you simply want to make a backup of an existing file before changing it.
7300 The program accepts the following options. Also see @ref{Common options}.
7307 Preserve as much as possible of the structure and attributes of the
7308 original files in the copy (but do not attempt to preserve internal
7309 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7310 directory in a different order).
7311 Try to preserve SELinux security context and extended attributes (xattr),
7312 but ignore any failure to do that and print no corresponding diagnostic.
7313 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7316 @itemx @w{@kbd{--backup}[=@var{method}]}
7319 @vindex VERSION_CONTROL
7320 @cindex backups, making
7321 @xref{Backup options}.
7322 Make a backup of each file that would otherwise be overwritten or removed.
7323 As a special case, @command{cp} makes a backup of @var{source} when the force
7324 and backup options are given and @var{source} and @var{dest} are the same
7325 name for an existing, regular file. One useful application of this
7326 combination of options is this tiny Bourne shell script:
7330 # Usage: backup FILE...
7331 # Create a @sc{gnu}-style backup of each listed FILE.
7333 cp --backup --force -- "$i" "$i"
7337 @item --copy-contents
7338 @cindex directories, copying recursively
7339 @cindex copying directories recursively
7340 @cindex recursively copying directories
7341 @cindex non-directories, copying as special files
7342 If copying recursively, copy the contents of any special files (e.g.,
7343 FIFOs and device files) as if they were regular files. This means
7344 trying to read the data in each source file and writing it to the
7345 destination. It is usually a mistake to use this option, as it
7346 normally has undesirable effects on special files like FIFOs and the
7347 ones typically found in the @file{/dev} directory. In most cases,
7348 @code{cp -R --copy-contents} will hang indefinitely trying to read
7349 from FIFOs and special files like @file{/dev/console}, and it will
7350 fill up your destination disk if you use it to copy @file{/dev/zero}.
7351 This option has no effect unless copying recursively, and it does not
7352 affect the copying of symbolic links.
7356 @cindex symbolic links, copying
7357 @cindex hard links, preserving
7358 Copy symbolic links as symbolic links rather than copying the files that
7359 they point to, and preserve hard links between source files in the copies.
7360 Equivalent to @option{--no-dereference --preserve=links}.
7366 When copying without this option and an existing destination file cannot
7367 be opened for writing, the copy fails. However, with @option{--force}),
7368 when a destination file cannot be opened, @command{cp} then removes it and
7369 tries to open it again. Contrast this behavior with that enabled by
7370 @option{--link} and @option{--symbolic-link}, whereby the destination file
7371 is never opened but rather is removed unconditionally. Also see the
7372 description of @option{--remove-destination}.
7374 This option is independent of the @option{--interactive} or
7375 @option{-i} option: neither cancels the effect of the other.
7377 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7382 If a command line argument specifies a symbolic link, then copy the
7383 file it points to rather than the symbolic link itself. However,
7384 copy (preserving its nature) any symbolic link that is encountered
7385 via recursive traversal.
7388 @itemx --interactive
7390 @opindex --interactive
7391 When copying a file other than a directory, prompt whether to
7392 overwrite an existing destination file. The @option{-i} option overrides
7393 a previous @option{-n} option.
7399 Make hard links instead of copies of non-directories.
7402 @itemx --dereference
7404 @opindex --dereference
7405 Follow symbolic links when copying from them.
7406 With this option, @command{cp} cannot create a symbolic link.
7407 For example, a symlink (to regular file) in the source tree will be copied to
7408 a regular file in the destination tree.
7413 @opindex --no-clobber
7414 Do not overwrite an existing file. The @option{-n} option overrides a previous
7415 @option{-i} option. This option is mutually exclusive with @option{-b} or
7416 @option{--backup} option.
7419 @itemx --no-dereference
7421 @opindex --no-dereference
7422 @cindex symbolic links, copying
7423 Copy symbolic links as symbolic links rather than copying the files that
7424 they point to. This option affects only symbolic links in the source;
7425 symbolic links in the destination are always followed if possible.
7428 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7431 @cindex file information, preserving, extended attributes, xattr
7432 Preserve the specified attributes of the original files.
7433 If specified, the @var{attribute_list} must be a comma-separated list
7434 of one or more of the following strings:
7438 Preserve the file mode bits and access control lists.
7440 Preserve the owner and group. On most modern systems,
7441 only users with appropriate privileges may change the owner of a file,
7443 may preserve the group ownership of a file only if they happen to be
7444 a member of the desired group.
7446 Preserve the times of last access and last modification, when possible.
7447 In general, it is not possible to preserve these attributes
7448 when the affected file is a symbolic link.
7449 However, FreeBSD now provides the @code{lutimes} function, which makes
7450 it possible even for symbolic links. However, this implementation does
7451 not yet take advantage of that.
7452 @c FIXME: once we provide lutimes support, update the above.
7454 Preserve in the destination files
7455 any links between corresponding source files.
7456 Note that with @option{-L} or @option{-H}, this option can convert
7457 symbolic links to hard links. For example,
7459 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7464 Note the inputs: @file{b} is a symlink to regular file @file{a},
7465 yet the files in destination directory, @file{c/}, are hard-linked.
7466 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7467 tells @command{cp} to dereference command line arguments, it sees two files
7468 with the same inode number, and preserves the perceived hard link.
7470 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7472 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7478 Preserve SELinux security context of the file. @command{cp} will fail
7479 if the preserving of SELinux security context is not succesful.
7481 Preserve extended attributes if @command{cp} is built with xattr support,
7482 and xattrs are supported and enabled on your file system.
7483 If SELinux context and/or ACLs are implemented using xattrs,
7484 they are preserved by this option as well.
7486 Preserve all file attributes.
7487 Equivalent to specifying all of the above, but with the difference
7488 that failure to preserve SELinux security context or extended attributes
7489 does not change @command{cp}'s exit status.
7490 @command{cp} does diagnose such failures.
7493 Using @option{--preserve} with no @var{attribute_list} is equivalent
7494 to @option{--preserve=mode,ownership,timestamps}.
7496 In the absence of this option, each destination file is created with the
7497 mode bits of the corresponding source file, minus the bits set in the
7498 umask and minus the set-user-ID and set-group-ID bits.
7499 @xref{File permissions}.
7501 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7502 @cindex file information, preserving
7503 Do not preserve the specified attributes. The @var{attribute_list}
7504 has the same form as for @option{--preserve}.
7508 @cindex parent directories and @command{cp}
7509 Form the name of each destination file by appending to the target
7510 directory a slash and the specified name of the source file. The last
7511 argument given to @command{cp} must be the name of an existing directory.
7512 For example, the command:
7515 cp --parents a/b/c existing_dir
7519 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7520 any missing intermediate directories.
7527 @opindex --recursive
7528 @cindex directories, copying recursively
7529 @cindex copying directories recursively
7530 @cindex recursively copying directories
7531 @cindex non-directories, copying as special files
7532 Copy directories recursively. By default, do not follow symbolic
7533 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7534 @option{--dereference} (@option{-L}), @option{--no-dereference}
7535 (@option{-P}), and @option{-H} options. Special files are copied by
7536 creating a destination file of the same type as the source; see the
7537 @option{--copy-contents} option. It is not portable to use
7538 @option{-r} to copy symbolic links or special files. On some
7539 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7540 @option{-L} and @option{--copy-contents} for historical reasons.
7541 Also, it is not portable to use @option{-R} to copy symbolic links
7542 unless you also specify @option{-P}, as @acronym{POSIX} allows
7543 implementations that dereference symbolic links by default.
7545 @item --remove-destination
7546 @opindex --remove-destination
7547 Remove each existing destination file before attempting to open it
7548 (contrast with @option{-f} above).
7550 @item --sparse=@var{when}
7551 @opindex --sparse=@var{when}
7552 @cindex sparse files, copying
7553 @cindex holes, copying files with
7554 @findex read @r{system call, and holes}
7555 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7556 does not occupy any physical disk blocks; the @samp{read} system call
7557 reads these as zeros. This can both save considerable disk space and
7558 increase speed, since many binary files contain lots of consecutive zero
7559 bytes. By default, @command{cp} detects holes in input source files via a crude
7560 heuristic and makes the corresponding output file sparse as well.
7561 Only regular files may be sparse.
7563 The @var{when} value can be one of the following:
7567 The default behavior: if the input file is sparse, attempt to make
7568 the output file sparse, too. However, if an output file exists but
7569 refers to a non-regular file, then do not attempt to make it sparse.
7572 For each sufficiently long sequence of zero bytes in the input file,
7573 attempt to create a corresponding hole in the output file, even if the
7574 input file does not appear to be sparse.
7575 This is useful when the input file resides on a file system
7576 that does not support sparse files
7577 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7578 but the output file is on a type of file system that does support them.
7579 Holes may be created only in regular files, so if the destination file
7580 is of some other type, @command{cp} does not even try to make it sparse.
7583 Never make the output file sparse.
7584 This is useful in creating a file for use with the @command{mkswap} command,
7585 since such a file must not have any holes.
7588 @optStripTrailingSlashes
7591 @itemx --symbolic-link
7593 @opindex --symbolic-link
7594 @cindex symbolic links, copying with
7595 Make symbolic links instead of copies of non-directories. All source
7596 file names must be absolute (starting with @samp{/}) unless the
7597 destination files are in the current directory. This option merely
7598 results in an error message on systems that do not support symbolic links.
7604 @optNoTargetDirectory
7610 @cindex newer files, copying only
7611 Do not copy a non-directory that has an existing destination with the
7612 same or newer modification time. If time stamps are being preserved,
7613 the comparison is to the source time stamp truncated to the
7614 resolutions of the destination file system and of the system calls
7615 used to update time stamps; this avoids duplicate work if several
7616 @samp{cp -pu} commands are executed with the same source and
7623 Print the name of each file before copying it.
7626 @itemx --one-file-system
7628 @opindex --one-file-system
7629 @cindex file systems, omitting copying to different
7630 Skip subdirectories that are on different file systems from the one that
7631 the copy started on.
7632 However, mount point directories @emph{are} copied.
7640 @section @command{dd}: Convert and copy a file
7643 @cindex converting while copying a file
7645 @command{dd} copies a file (from standard input to standard output, by
7646 default) with a changeable I/O block size, while optionally performing
7647 conversions on it. Synopses:
7650 dd [@var{operand}]@dots{}
7654 The only options are @option{--help} and @option{--version}.
7655 @xref{Common options}. @command{dd} accepts the following operands.
7661 Read from @var{file} instead of standard input.
7665 Write to @var{file} instead of standard output. Unless
7666 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7667 bytes (or the size specified with @samp{seek=}).
7669 @item ibs=@var{bytes}
7671 @cindex block size of input
7672 @cindex input block size
7673 Set the input block size to @var{bytes}.
7674 This makes @command{dd} read @var{bytes} per block.
7675 The default is 512 bytes.
7677 @item obs=@var{bytes}
7679 @cindex block size of output
7680 @cindex output block size
7681 Set the output block size to @var{bytes}.
7682 This makes @command{dd} write @var{bytes} per block.
7683 The default is 512 bytes.
7685 @item bs=@var{bytes}
7688 Set both input and output block sizes to @var{bytes}.
7689 This makes @command{dd} read and write @var{bytes} per block,
7690 overriding any @samp{ibs} and @samp{obs} settings.
7691 In addition, if no data-transforming @option{conv} option is specified,
7692 each input block is copied to the output as a single block,
7693 without aggregating short reads.
7695 @item cbs=@var{bytes}
7697 @cindex block size of conversion
7698 @cindex conversion block size
7699 @cindex fixed-length records, converting to variable-length
7700 @cindex variable-length records, converting to fixed-length
7701 Set the conversion block size to @var{bytes}.
7702 When converting variable-length records to fixed-length ones
7703 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7704 use @var{bytes} as the fixed record length.
7706 @item skip=@var{blocks}
7708 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7710 @item seek=@var{blocks}
7712 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7714 @item count=@var{blocks}
7716 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7717 of everything until the end of the file.
7721 Do not print the overall transfer rate and volume statistics
7722 that normally make up the third status line when @command{dd} exits.
7724 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7726 Convert the file as specified by the @var{conversion} argument(s).
7727 (No spaces around any comma(s).)
7734 @opindex ascii@r{, converting to}
7735 Convert @acronym{EBCDIC} to @acronym{ASCII},
7736 using the conversion table specified by @acronym{POSIX}.
7737 This provides a 1:1 translation for all 256 bytes.
7740 @opindex ebcdic@r{, converting to}
7741 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7742 This is the inverse of the @samp{ascii} conversion.
7745 @opindex alternate ebcdic@r{, converting to}
7746 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7747 using the alternate conversion table specified by @acronym{POSIX}.
7748 This is not a 1:1 translation, but reflects common historical practice
7749 for @samp{~}, @samp{[}, and @samp{]}.
7751 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7755 @opindex block @r{(space-padding)}
7756 For each line in the input, output @samp{cbs} bytes, replacing the
7757 input newline with a space and padding with spaces as necessary.
7761 Replace trailing spaces in each @samp{cbs}-sized input block with a
7764 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7767 @opindex lcase@r{, converting to}
7768 Change uppercase letters to lowercase.
7771 @opindex ucase@r{, converting to}
7772 Change lowercase letters to uppercase.
7774 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7777 @opindex swab @r{(byte-swapping)}
7778 @cindex byte-swapping
7779 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7780 when an odd number of bytes are read---the last byte is simply copied
7781 (since there is nothing to swap it with).
7785 @cindex read errors, ignoring
7786 Continue after read errors.
7790 @cindex creating output file, avoiding
7791 Do not create the output file; the output file must already exist.
7795 @cindex creating output file, requiring
7796 Fail if the output file already exists; @command{dd} must create the
7799 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7803 @cindex truncating output file, avoiding
7804 Do not truncate the output file.
7807 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7808 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7809 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7814 @cindex synchronized data writes, before finishing
7815 Synchronize output data just before finishing. This forces a physical
7816 write of output data.
7820 @cindex synchronized data and metadata writes, before finishing
7821 Synchronize output data and metadata just before finishing. This
7822 forces a physical write of output data and metadata.
7826 @item iflag=@var{flag}[,@var{flag}]@dots{}
7828 Access the input file using the flags specified by the @var{flag}
7829 argument(s). (No spaces around any comma(s).)
7831 @item oflag=@var{flag}[,@var{flag}]@dots{}
7833 Access the output file using the flags specified by the @var{flag}
7834 argument(s). (No spaces around any comma(s).)
7836 Here are the flags. Not every flag is supported on every operating
7843 @cindex appending to the output file
7844 Write in append mode, so that even if some other process is writing to
7845 this file, every @command{dd} write will append to the current
7846 contents of the file. This flag makes sense only for output.
7847 If you combine this flag with the @samp{of=@var{file}} operand,
7848 you should also specify @samp{conv=notrunc} unless you want the
7849 output file to be truncated before being appended to.
7853 @cindex concurrent I/O
7854 Use concurrent I/O mode for data. This mode performs direct I/O
7855 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7856 A file cannot be opened in CIO mode and with a standard open at the
7862 Use direct I/O for data, avoiding the buffer cache.
7866 @cindex directory I/O
7868 Fail unless the file is a directory. Most operating systems do not
7869 allow I/O to a directory, so this flag has limited utility.
7873 @cindex synchronized data reads
7874 Use synchronized I/O for data. For the output file, this forces a
7875 physical write of output data on each write. For the input file,
7876 this flag can matter when reading from a remote file that has been
7877 written to synchronously by some other process. Metadata (e.g.,
7878 last-access and last-modified time) is not necessarily synchronized.
7882 @cindex synchronized data and metadata I/O
7883 Use synchronized I/O for both data and metadata.
7887 @cindex nonblocking I/O
7888 Use non-blocking I/O.
7893 Do not update the file's access time.
7894 Some older file systems silently ignore this flag, so it is a good
7895 idea to test it on your files before relying on it.
7899 @cindex controlling terminal
7900 Do not assign the file to be a controlling terminal for @command{dd}.
7901 This has no effect when the file is not a terminal.
7902 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7907 @cindex symbolic links, following
7908 Do not follow symbolic links.
7913 Fail if the file has multiple hard links.
7918 Use binary I/O. This option has an effect only on nonstandard
7919 platforms that distinguish binary from text I/O.
7924 Use text I/O. Like @samp{binary}, this option has no effect on
7929 Accumulate full blocks from input. The @code{read} system call
7930 may return early if a full block is not available.
7931 When that happens, continue calling @code{read} to fill the remainder
7933 This flag can be used only with @code{iflag}.
7937 These flags are not supported on all systems, and @samp{dd} rejects
7938 attempts to use them when they are not supported. When reading from
7939 standard input or writing to standard output, the @samp{nofollow} and
7940 @samp{noctty} flags should not be specified, and the other flags
7941 (e.g., @samp{nonblock}) can affect how other processes behave with the
7942 affected file descriptors, even after @command{dd} exits.
7946 @cindex multipliers after numbers
7947 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7948 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7949 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7950 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7952 Use different @command{dd} invocations to use different block sizes for
7953 skipping and I/O@. For example, the following shell commands copy data
7954 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7955 4 KiB label at the start of the disk:
7958 disk=/dev/rdsk/c0t1d0s2
7961 # Copy all but the label from disk to tape.
7962 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7964 # Copy from tape back to disk, but leave the disk label alone.
7965 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7968 Sending an @samp{INFO} signal to a running @command{dd}
7969 process makes it print I/O statistics to standard error
7970 and then resume copying. In the example below,
7971 @command{dd} is run in the background to copy 10 million blocks.
7972 The @command{kill} command makes it output intermediate I/O statistics,
7973 and when @command{dd} completes normally or is killed by the
7974 @code{SIGINT} signal, it outputs the final statistics.
7977 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
7978 $ kill -s INFO $pid; wait $pid
7979 3385223+0 records in
7980 3385223+0 records out
7981 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
7982 10000000+0 records in
7983 10000000+0 records out
7984 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
7987 @vindex POSIXLY_CORRECT
7988 On systems lacking the @samp{INFO} signal @command{dd} responds to the
7989 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
7990 environment variable is set.
7995 @node install invocation
7996 @section @command{install}: Copy files and set attributes
7999 @cindex copying files and setting attributes
8001 @command{install} copies files while setting their file mode bits and, if
8002 possible, their owner and group. Synopses:
8005 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8006 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8007 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8008 install [@var{option}]@dots{} -d @var{directory}@dots{}
8013 If two file names are given, @command{install} copies the first file to the
8017 If the @option{--target-directory} (@option{-t}) option is given, or
8018 failing that if the last file is a directory and the
8019 @option{--no-target-directory} (@option{-T}) option is not given,
8020 @command{install} copies each @var{source} file to the specified
8021 directory, using the @var{source}s' names.
8024 If the @option{--directory} (@option{-d}) option is given,
8025 @command{install} creates each @var{directory} and any missing parent
8026 directories. Parent directories are created with mode
8027 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8028 current umask. @xref{Directory Setuid and Setgid}, for how the
8029 set-user-ID and set-group-ID bits of parent directories are inherited.
8032 @cindex Makefiles, installing programs in
8033 @command{install} is similar to @command{cp}, but allows you to control the
8034 attributes of destination files. It is typically used in Makefiles to
8035 copy programs into their destination directories. It refuses to copy
8036 files onto themselves.
8038 @cindex extended attributes, xattr
8039 @command{install} never preserves extended attributes (xattr).
8041 The program accepts the following options. Also see @ref{Common options}.
8049 Ignored; for compatibility with old Unix versions of @command{install}.
8053 Create any missing parent directories of @var{dest},
8054 then copy @var{source} to @var{dest}.
8055 This option is ignored if a destination directory is specified
8056 via @option{--target-directory=DIR}.
8061 @opindex --directory
8062 @cindex directories, creating with given attributes
8063 @cindex parent directories, creating missing
8064 @cindex leading directories, creating missing
8065 Create any missing parent directories, giving them the default
8066 attributes. Then create each given directory, setting their owner,
8067 group and mode as given on the command line or to the defaults.
8069 @item -g @var{group}
8070 @itemx --group=@var{group}
8073 @cindex group ownership of installed files, setting
8074 Set the group ownership of installed files or directories to
8075 @var{group}. The default is the process's current group. @var{group}
8076 may be either a group name or a numeric group ID.
8079 @itemx --mode=@var{mode}
8082 @cindex permissions of installed files, setting
8083 Set the file mode bits for the installed file or directory to @var{mode},
8084 which can be either an octal number, or a symbolic mode as in
8085 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8086 point of departure (@pxref{File permissions}).
8087 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8088 execute for the owner, read and execute for group and other, and with
8089 set-user-ID and set-group-ID disabled.
8090 This default is not quite the same as @samp{755}, since it disables
8091 instead of preserving set-user-ID and set-group-ID on directories.
8092 @xref{Directory Setuid and Setgid}.
8094 @item -o @var{owner}
8095 @itemx --owner=@var{owner}
8098 @cindex ownership of installed files, setting
8099 @cindex appropriate privileges
8100 @vindex root @r{as default owner}
8101 If @command{install} has appropriate privileges (is run as root), set the
8102 ownership of installed files or directories to @var{owner}. The default
8103 is @code{root}. @var{owner} may be either a user name or a numeric user
8106 @item --preserve-context
8107 @opindex --preserve-context
8109 @cindex security context
8110 Preserve the SELinux security context of files and directories.
8111 Failure to preserve the context in all of the files or directories
8112 will result in an exit status of 1. If SELinux is disabled then
8113 print a warning and ignore the option.
8116 @itemx --preserve-timestamps
8118 @opindex --preserve-timestamps
8119 @cindex timestamps of installed files, preserving
8120 Set the time of last access and the time of last modification of each
8121 installed file to match those of each corresponding original file.
8122 When a file is installed without this option, its last access and
8123 last modification times are both set to the time of installation.
8124 This option is useful if you want to use the last modification times
8125 of installed files to keep track of when they were last built as opposed
8126 to when they were last installed.
8132 @cindex symbol table information, stripping
8133 @cindex stripping symbol table information
8134 Strip the symbol tables from installed binary executables.
8136 @itemx --strip-program=@var{program}
8137 @opindex --strip-program
8138 @cindex symbol table information, stripping, program
8139 Program used to strip binaries.
8145 @optNoTargetDirectory
8151 Print the name of each file before copying it.
8153 @item -Z @var{context}
8154 @itemx --context=@var{context}
8158 @cindex security context
8159 Set the default SELinux security context to be used for any
8160 created files and directories. If SELinux is disabled then
8161 print a warning and ignore the option.
8169 @section @command{mv}: Move (rename) files
8173 @command{mv} moves or renames files (or directories). Synopses:
8176 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8177 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8178 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8183 If two file names are given, @command{mv} moves the first file to the
8187 If the @option{--target-directory} (@option{-t}) option is given, or
8188 failing that if the last file is a directory and the
8189 @option{--no-target-directory} (@option{-T}) option is not given,
8190 @command{mv} moves each @var{source} file to the specified
8191 directory, using the @var{source}s' names.
8194 @command{mv} can move any type of file from one file system to another.
8195 Prior to version @code{4.0} of the fileutils,
8196 @command{mv} could move only regular files between file systems.
8197 For example, now @command{mv} can move an entire directory hierarchy
8198 including special device files from one partition to another. It first
8199 uses some of the same code that's used by @code{cp -a} to copy the
8200 requested directories and files, then (assuming the copy succeeded)
8201 it removes the originals. If the copy fails, then the part that was
8202 copied to the destination partition is removed. If you were to copy
8203 three directories from one partition to another and the copy of the first
8204 directory succeeded, but the second didn't, the first would be left on
8205 the destination partition and the second and third would be left on the
8208 @cindex extended attributes, xattr
8209 @command{mv} always tries to copy extended attributes (xattr).
8211 @cindex prompting, and @command{mv}
8212 If a destination file exists but is normally unwritable, standard input
8213 is a terminal, and the @option{-f} or @option{--force} option is not given,
8214 @command{mv} prompts the user for whether to replace the file. (You might
8215 own the file, or have write permission on its directory.) If the
8216 response is not affirmative, the file is skipped.
8218 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8219 when it might be a symlink to a directory.
8220 Otherwise, @command{mv} may do something very surprising, since
8221 its behavior depends on the underlying rename system call.
8222 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8223 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8224 renames not the symlink but rather the directory referenced by the symlink.
8225 @xref{Trailing slashes}.
8227 The program accepts the following options. Also see @ref{Common options}.
8237 @cindex prompts, omitting
8238 Do not prompt the user before removing a destination file.
8240 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8241 options, only the final one takes effect.
8246 @itemx --interactive
8248 @opindex --interactive
8249 @cindex prompts, forcing
8250 Prompt whether to overwrite each existing destination file, regardless
8252 If the response is not affirmative, the file is skipped.
8258 @opindex --no-clobber
8259 @cindex prompts, omitting
8260 Do not overwrite an existing file.
8262 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8268 @cindex newer files, moving only
8269 Do not move a non-directory that has an existing destination with the
8270 same or newer modification time.
8271 If the move is across file system boundaries, the comparison is to the
8272 source time stamp truncated to the resolutions of the destination file
8273 system and of the system calls used to update time stamps; this avoids
8274 duplicate work if several @samp{mv -u} commands are executed with the
8275 same source and destination.
8281 Print the name of each file before moving it.
8283 @optStripTrailingSlashes
8289 @optNoTargetDirectory
8297 @section @command{rm}: Remove files or directories
8300 @cindex removing files or directories
8302 @command{rm} removes each given @var{file}. By default, it does not remove
8303 directories. Synopsis:
8306 rm [@var{option}]@dots{} [@var{file}]@dots{}
8309 @cindex prompting, and @command{rm}
8310 If the @option{-I} or @option{--interactive=once} option is given,
8311 and there are more than three files or the @option{-r}, @option{-R},
8312 or @option{--recursive} are given, then @command{rm} prompts the user
8313 for whether to proceed with the entire operation. If the response is
8314 not affirmative, the entire command is aborted.
8316 Otherwise, if a file is unwritable, standard input is a terminal, and
8317 the @option{-f} or @option{--force} option is not given, or the
8318 @option{-i} or @option{--interactive=always} option @emph{is} given,
8319 @command{rm} prompts the user for whether to remove the file.
8320 If the response is not affirmative, the file is skipped.
8322 Any attempt to remove a file whose last file name component is
8323 @file{.} or @file{..} is rejected without any prompting.
8325 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8326 possible to recover the contents of that file. If you want more assurance
8327 that the contents are truly unrecoverable, consider using @command{shred}.
8329 The program accepts the following options. Also see @ref{Common options}.
8337 Ignore nonexistent files and never prompt the user.
8338 Ignore any previous @option{--interactive} (@option{-i}) option.
8342 Prompt whether to remove each file.
8343 If the response is not affirmative, the file is skipped.
8344 Ignore any previous @option{--force} (@option{-f}) option.
8345 Equivalent to @option{--interactive=always}.
8349 Prompt once whether to proceed with the command, if more than three
8350 files are named or if a recursive removal is requested. Ignore any
8351 previous @option{--force} (@option{-f}) option. Equivalent to
8352 @option{--interactive=once}.
8354 @itemx --interactive [=@var{when}]
8355 @opindex --interactive
8356 Specify when to issue an interactive prompt. @var{when} may be
8360 @vindex never @r{interactive option}
8361 - Do not prompt at all.
8363 @vindex once @r{interactive option}
8364 - Prompt once if more than three files are named or if a recursive
8365 removal is requested. Equivalent to @option{-I}.
8367 @vindex always @r{interactive option}
8368 - Prompt for every file being removed. Equivalent to @option{-i}.
8370 @option{--interactive} with no @var{when} is equivalent to
8371 @option{--interactive=always}.
8373 @itemx --one-file-system
8374 @opindex --one-file-system
8375 @cindex one file system, restricting @command{rm} to
8376 When removing a hierarchy recursively, skip any directory that is on a
8377 file system different from that of the corresponding command line argument.
8379 This option is useful when removing a build ``chroot'' hierarchy,
8380 which normally contains no valuable data. However, it is not uncommon
8381 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8382 use one's start-up file. The catch is that it's easy to forget to
8383 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8384 your normally throw-away chroot, that command will remove everything
8385 under @file{/home}, too.
8386 Use the @option{--one-file-system} option, and it will
8387 warn about and skip directories on other file systems.
8388 Of course, this will not save your @file{/home} if it and your
8389 chroot happen to be on the same file system.
8391 @itemx --preserve-root
8392 @opindex --preserve-root
8393 @cindex root directory, disallow recursive destruction
8394 Fail upon any attempt to remove the root directory, @file{/},
8395 when used with the @option{--recursive} option.
8396 This is the default behavior.
8397 @xref{Treating / specially}.
8399 @itemx --no-preserve-root
8400 @opindex --no-preserve-root
8401 @cindex root directory, allow recursive destruction
8402 Do not treat @file{/} specially when removing recursively.
8403 This option is not recommended unless you really want to
8404 remove all the files on your computer.
8405 @xref{Treating / specially}.
8412 @opindex --recursive
8413 @cindex directories, removing (recursively)
8414 Remove the listed directories and their contents recursively.
8420 Print the name of each file before removing it.
8424 @cindex files beginning with @samp{-}, removing
8425 @cindex @samp{-}, removing files beginning with
8426 One common question is how to remove files whose names begin with a
8427 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8428 function to parse its arguments, lets you use the @samp{--} option to
8429 indicate that all following arguments are non-options. To remove a file
8430 called @file{-f} in the current directory, you could type either:
8443 @opindex - @r{and Unix @command{rm}}
8444 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8445 predates the development of the getopt standard syntax.
8450 @node shred invocation
8451 @section @command{shred}: Remove files more securely
8454 @cindex data, erasing
8455 @cindex erasing data
8457 @command{shred} overwrites devices or files, to help prevent even
8458 very expensive hardware from recovering the data.
8460 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8461 not actually destroyed. Only the index listing where the file is
8462 stored is destroyed, and the storage is made available for reuse.
8463 There are undelete utilities that will attempt to reconstruct the index
8464 and can bring the file back if the parts were not reused.
8466 On a busy system with a nearly-full drive, space can get reused in a few
8467 seconds. But there is no way to know for sure. If you have sensitive
8468 data, you may want to be sure that recovery is not possible by actually
8469 overwriting the file with non-sensitive data.
8471 However, even after doing that, it is possible to take the disk back
8472 to a laboratory and use a lot of sensitive (and expensive) equipment
8473 to look for the faint ``echoes'' of the original data underneath the
8474 overwritten data. If the data has only been overwritten once, it's not
8477 The best way to remove something irretrievably is to destroy the media
8478 it's on with acid, melt it down, or the like. For cheap removable media
8479 like floppy disks, this is the preferred method. However, hard drives
8480 are expensive and hard to melt, so the @command{shred} utility tries
8481 to achieve a similar effect non-destructively.
8483 This uses many overwrite passes, with the data patterns chosen to
8484 maximize the damage they do to the old data. While this will work on
8485 floppies, the patterns are designed for best effect on hard drives.
8486 For more details, see the source code and Peter Gutmann's paper
8487 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8488 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8489 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8490 California, July 22--25, 1996).
8492 @strong{Please note} that @command{shred} relies on a very important assumption:
8493 that the file system overwrites data in place. This is the traditional
8494 way to do things, but many modern file system designs do not satisfy this
8495 assumption. Exceptions include:
8500 Log-structured or journaled file systems, such as those supplied with
8501 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8502 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8505 File systems that write redundant data and carry on even if some writes
8506 fail, such as RAID-based file systems.
8509 File systems that make snapshots, such as Network Appliance's NFS server.
8512 File systems that cache in temporary locations, such as NFS version 3
8516 Compressed file systems.
8519 In the particular case of ext3 file systems, the above disclaimer applies (and
8520 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8521 mode, which journals file data in addition to just metadata. In both
8522 the @code{data=ordered} (default) and @code{data=writeback} modes,
8523 @command{shred} works as usual. Ext3 journaling modes can be changed
8524 by adding the @code{data=something} option to the mount options for a
8525 particular file system in the @file{/etc/fstab} file, as documented in
8526 the mount man page (man mount).
8528 If you are not sure how your file system operates, then you should assume
8529 that it does not overwrite data in place, which means that shred cannot
8530 reliably operate on regular files in your file system.
8532 Generally speaking, it is more reliable to shred a device than a file,
8533 since this bypasses the problem of file system design mentioned above.
8534 However, even shredding devices is not always completely reliable. For
8535 example, most disks map out bad sectors invisibly to the application; if
8536 the bad sectors contain sensitive data, @command{shred} won't be able to
8539 @command{shred} makes no attempt to detect or report this problem, just as
8540 it makes no attempt to do anything about backups. However, since it is
8541 more reliable to shred devices than files, @command{shred} by default does
8542 not truncate or remove the output file. This default is more suitable
8543 for devices, which typically cannot be truncated and should not be
8546 Finally, consider the risk of backups and mirrors.
8547 File system backups and remote mirrors may contain copies of the
8548 file that cannot be removed, and that will allow a shredded file
8549 to be recovered later. So if you keep any data you may later want
8550 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8553 shred [@var{option}]@dots{} @var{file}[@dots{}]
8556 The program accepts the following options. Also see @ref{Common options}.
8564 @cindex force deletion
8565 Override file permissions if necessary to allow overwriting.
8568 @itemx -n @var{number}
8569 @itemx --iterations=@var{number}
8570 @opindex -n @var{number}
8571 @opindex --iterations=@var{number}
8572 @cindex iterations, selecting the number of
8573 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8574 overwrite. You can reduce this to save time, or increase it if you think it's
8575 appropriate. After 25 passes all of the internal overwrite patterns will have
8576 been used at least once.
8578 @item --random-source=@var{file}
8579 @opindex --random-source
8580 @cindex random source for shredding
8581 Use @var{file} as a source of random data used to overwrite and to
8582 choose pass ordering. @xref{Random sources}.
8584 @item -s @var{bytes}
8585 @itemx --size=@var{bytes}
8586 @opindex -s @var{bytes}
8587 @opindex --size=@var{bytes}
8588 @cindex size of file to shred
8589 Shred the first @var{bytes} bytes of the file. The default is to shred
8590 the whole file. @var{bytes} can be followed by a size specification like
8591 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8597 @cindex removing files after shredding
8598 After shredding a file, truncate it (if possible) and then remove it.
8599 If a file has multiple links, only the named links will be removed.
8605 Display to standard error all status updates as sterilization proceeds.
8611 By default, @command{shred} rounds the size of a regular file up to the next
8612 multiple of the file system block size to fully erase the last block of the file.
8613 Use @option{--exact} to suppress that behavior.
8614 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8615 blocks, the resulting file will be 512 bytes long. With this option,
8616 shred does not increase the apparent size of the file.
8622 Normally, the last pass that @command{shred} writes is made up of
8623 random data. If this would be conspicuous on your hard drive (for
8624 example, because it looks like encrypted data), or you just think
8625 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8626 all zero bits. This is in addition to the number of passes specified
8627 by the @option{--iterations} option.
8631 You might use the following command to erase all trace of the
8632 file system you'd created on the floppy disk in your first drive.
8633 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8637 shred --verbose /dev/fd0
8640 Similarly, to erase all data on a selected partition of
8641 your hard disk, you could give a command like this:
8644 shred --verbose /dev/sda5
8647 A @var{file} of @samp{-} denotes standard output.
8648 The intended use of this is to shred a removed temporary file.
8652 i=`tempfile -m 0600`
8655 echo "Hello, world" >&3
8660 However, the command @samp{shred - >file} does not shred the contents
8661 of @var{file}, since the shell truncates @var{file} before invoking
8662 @command{shred}. Use the command @samp{shred file} or (if using a
8663 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8668 @node Special file types
8669 @chapter Special file types
8671 @cindex special file types
8672 @cindex file types, special
8674 This chapter describes commands which create special types of files (and
8675 @command{rmdir}, which removes directories, one special file type).
8677 @cindex special file types
8679 Although Unix-like operating systems have markedly fewer special file
8680 types than others, not @emph{everything} can be treated only as the
8681 undifferentiated byte stream of @dfn{normal files}. For example, when a
8682 file is created or removed, the system must record this information,
8683 which it does in a @dfn{directory}---a special type of file. Although
8684 you can read directories as normal files, if you're curious, in order
8685 for the system to do its job it must impose a structure, a certain
8686 order, on the bytes of the file. Thus it is a ``special'' type of file.
8688 Besides directories, other special file types include named pipes
8689 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8692 * link invocation:: Make a hard link via the link syscall
8693 * ln invocation:: Make links between files.
8694 * mkdir invocation:: Make directories.
8695 * mkfifo invocation:: Make FIFOs (named pipes).
8696 * mknod invocation:: Make block or character special files.
8697 * readlink invocation:: Print value of a symlink or canonical file name.
8698 * rmdir invocation:: Remove empty directories.
8699 * unlink invocation:: Remove files via the unlink syscall
8703 @node link invocation
8704 @section @command{link}: Make a hard link via the link syscall
8707 @cindex links, creating
8708 @cindex hard links, creating
8709 @cindex creating links (hard only)
8711 @command{link} creates a single hard link at a time.
8712 It is a minimalist interface to the system-provided
8713 @code{link} function. @xref{Hard Links, , , libc,
8714 The GNU C Library Reference Manual}.
8715 It avoids the bells and whistles of the more commonly-used
8716 @command{ln} command (@pxref{ln invocation}).
8720 link @var{filename} @var{linkname}
8723 @var{filename} must specify an existing file, and @var{linkname}
8724 must specify a nonexistent entry in an existing directory.
8725 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8728 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8729 --no-target-directory @var{filename} @var{linkname}}. However, the
8730 @option{--directory} and @option{--no-target-directory} options are
8731 not specified by @acronym{POSIX}, and the @command{link} command is
8732 more portable in practice.
8738 @section @command{ln}: Make links between files
8741 @cindex links, creating
8742 @cindex hard links, creating
8743 @cindex symbolic (soft) links, creating
8744 @cindex creating links (hard or soft)
8746 @cindex file systems and hard links
8747 @command{ln} makes links between files. By default, it makes hard links;
8748 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8752 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8753 ln [@var{option}]@dots{} @var{target}
8754 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8755 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8761 If two file names are given, @command{ln} creates a link to the first
8762 file from the second.
8765 If one @var{target} is given, @command{ln} creates a link to that file
8766 in the current directory.
8769 If the @option{--target-directory} (@option{-t}) option is given, or
8770 failing that if the last file is a directory and the
8771 @option{--no-target-directory} (@option{-T}) option is not given,
8772 @command{ln} creates a link to each @var{target} file in the specified
8773 directory, using the @var{target}s' names.
8777 Normally @command{ln} does not remove existing files. Use the
8778 @option{--force} (@option{-f}) option to remove them unconditionally,
8779 the @option{--interactive} (@option{-i}) option to remove them
8780 conditionally, and the @option{--backup} (@option{-b}) option to
8783 @cindex hard link, defined
8784 @cindex inode, and hard links
8785 A @dfn{hard link} is another name for an existing file; the link and the
8786 original are indistinguishable. Technically speaking, they share the
8787 same inode, and the inode contains all the information about a
8788 file---indeed, it is not incorrect to say that the inode @emph{is} the
8789 file. On all existing implementations, you cannot make a hard link to
8790 a directory, and hard links cannot cross file system boundaries. (These
8791 restrictions are not mandated by @acronym{POSIX}, however.)
8793 @cindex dereferencing symbolic links
8794 @cindex symbolic link, defined
8795 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8796 a special file type (which not all kernels support: System V release 3
8797 (and older) systems lack symlinks) in which the link file actually
8798 refers to a different file, by name. When most operations (opening,
8799 reading, writing, and so on) are passed the symbolic link file, the
8800 kernel automatically @dfn{dereferences} the link and operates on the
8801 target of the link. But some operations (e.g., removing) work on the
8802 link file itself, rather than on its target. The owner, group, and
8803 mode of a symlink are not significant to file access performed through
8804 the link. @xref{Symbolic Links,,,
8805 libc, The GNU C Library Reference Manual}.
8807 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8808 occurs when the string in the symlink does not resolve to a file.
8809 There are no restrictions against creating dangling symbolic links.
8810 There are trade-offs to using absolute or relative symlinks. An
8811 absolute symlink always points to the same file, even if the directory
8812 containing the link is moved. However, if the symlink is visible from
8813 more than one machine (such as on a networked file system), the file
8814 pointed to might not always be the same. A relative symbolic link is
8815 resolved in relation to the directory that contains the link, and is
8816 often useful in referring to files on the same device without regards
8817 to what name that device is mounted on when accessed via networked
8820 When creating a relative symlink in a different location than the
8821 current directory, the resolution of the symlink will be different
8822 than the resolution of the same string from the current directory.
8823 Therefore, many users prefer to first change directories to the
8824 location where the relative symlink will be created, so that
8825 tab-completion or other file resolution will find the same target as
8826 what will be placed in the symlink.
8828 The program accepts the following options. Also see @ref{Common options}.
8839 @opindex --directory
8840 @cindex hard links to directories
8841 Allow users with appropriate privileges to attempt to make hard links
8843 However, note that this will probably fail due to
8844 system restrictions, even for the super-user.
8850 Remove existing destination files.
8853 @itemx --interactive
8855 @opindex --interactive
8856 @cindex prompting, and @command{ln}
8857 Prompt whether to remove existing destination files.
8860 @itemx --no-dereference
8862 @opindex --no-dereference
8863 Do not treat the last operand specially when it is a symbolic link to
8864 a directory. Instead, treat it as if it were a normal file.
8866 When the destination is an actual directory (not a symlink to one),
8867 there is no ambiguity. The link is created in that directory.
8868 But when the specified destination is a symlink to a directory,
8869 there are two ways to treat the user's request. @command{ln} can
8870 treat the destination just as it would a normal directory and create
8871 the link in it. On the other hand, the destination can be viewed as a
8872 non-directory---as the symlink itself. In that case, @command{ln}
8873 must delete or backup that symlink before creating the new link.
8874 The default is to treat a destination that is a symlink to a directory
8875 just like a directory.
8877 This option is weaker than the @option{--no-target-directory}
8878 (@option{-T}) option, so it has no effect if both options are given.
8884 Make symbolic links instead of hard links. This option merely produces
8885 an error message on systems that do not support symbolic links.
8891 @optNoTargetDirectory
8897 Print the name of each file after linking it successfully.
8908 # Create link ../a pointing to a in that directory.
8909 # Not really useful because it points to itself.
8914 # Change to the target before creating symlinks to avoid being confused.
8920 # Hard coded file names don't move well.
8921 ln -s $(pwd)/a /some/dir/
8925 # Relative file names survive directory moves and also
8926 # work across networked file systems.
8927 ln -s afile anotherfile
8928 ln -s ../adir/afile yetanotherfile
8932 @node mkdir invocation
8933 @section @command{mkdir}: Make directories
8936 @cindex directories, creating
8937 @cindex creating directories
8939 @command{mkdir} creates directories with the specified names. Synopsis:
8942 mkdir [@var{option}]@dots{} @var{name}@dots{}
8945 @command{mkdir} creates each directory @var{name} in the order given.
8946 It reports an error if @var{name} already exists, unless the
8947 @option{-p} option is given and @var{name} is a directory.
8949 The program accepts the following options. Also see @ref{Common options}.
8954 @itemx --mode=@var{mode}
8957 @cindex modes of created directories, setting
8958 Set the file permission bits of created directories to @var{mode},
8959 which uses the same syntax as
8960 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
8961 everyone) for the point of the departure. @xref{File permissions}.
8963 Normally the directory has the desired file mode bits at the moment it
8964 is created. As a @acronym{GNU} extension, @var{mode} may also mention
8965 special mode bits, but in this case there may be a temporary window
8966 during which the directory exists but its special mode bits are
8967 incorrect. @xref{Directory Setuid and Setgid}, for how the
8968 set-user-ID and set-group-ID bits of directories are inherited unless
8969 overridden in this way.
8975 @cindex parent directories, creating
8976 Make any missing parent directories for each argument, setting their
8977 file permission bits to the umask modified by @samp{u+wx}. Ignore
8978 existing parent directories, and do not change their file permission
8981 To set the file permission bits of any newly-created parent
8982 directories to a value that includes @samp{u+wx}, you can set the
8983 umask before invoking @command{mkdir}. For example, if the shell
8984 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
8985 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
8986 To set a parent's special mode bits as well, you can invoke
8987 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
8988 Setgid}, for how the set-user-ID and set-group-ID bits of
8989 newly-created parent directories are inherited.
8995 Print a message for each created directory. This is most useful with
8998 @item -Z @var{context}
8999 @itemx --context=@var{context}
9003 @cindex security context
9004 Set the default SELinux security context to be used for created directories.
9011 @node mkfifo invocation
9012 @section @command{mkfifo}: Make FIFOs (named pipes)
9015 @cindex FIFOs, creating
9016 @cindex named pipes, creating
9017 @cindex creating FIFOs (named pipes)
9019 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9020 specified names. Synopsis:
9023 mkfifo [@var{option}] @var{name}@dots{}
9026 A @dfn{FIFO} is a special file type that permits independent processes
9027 to communicate. One process opens the FIFO file for writing, and
9028 another for reading, after which data can flow as with the usual
9029 anonymous pipe in shells or elsewhere.
9031 The program accepts the following option. Also see @ref{Common options}.
9036 @itemx --mode=@var{mode}
9039 @cindex modes of created FIFOs, setting
9040 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9041 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9042 for the point of departure. @var{mode} should specify only file
9043 permission bits. @xref{File permissions}.
9045 @item -Z @var{context}
9046 @itemx --context=@var{context}
9050 @cindex security context
9051 Set the default SELinux security context to be used for created FIFOs.
9058 @node mknod invocation
9059 @section @command{mknod}: Make block or character special files
9062 @cindex block special files, creating
9063 @cindex character special files, creating
9065 @command{mknod} creates a FIFO, character special file, or block special
9066 file with the specified name. Synopsis:
9069 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9072 @cindex special files
9073 @cindex block special files
9074 @cindex character special files
9075 Unlike the phrase ``special file type'' above, the term @dfn{special
9076 file} has a technical meaning on Unix: something that can generate or
9077 receive data. Usually this corresponds to a physical piece of hardware,
9078 e.g., a printer or a disk. (These files are typically created at
9079 system-configuration time.) The @command{mknod} command is what creates
9080 files of this type. Such devices can be read either a character at a
9081 time or a ``block'' (many characters) at a time, hence we say there are
9082 @dfn{block special} files and @dfn{character special} files.
9084 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9085 @mayConflictWithShellBuiltIn{mknod}
9087 The arguments after @var{name} specify the type of file to make:
9092 @opindex p @r{for FIFO file}
9096 @opindex b @r{for block special file}
9097 for a block special file
9100 @c Don't document the `u' option -- it's just a synonym for `c'.
9101 @c Do *any* versions of mknod still use it?
9103 @opindex c @r{for character special file}
9104 @c @opindex u @r{for character special file}
9105 for a character special file
9109 When making a block or character special file, the major and minor
9110 device numbers must be given after the file type.
9111 If a major or minor device number begins with @samp{0x} or @samp{0X},
9112 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9113 as octal; otherwise, as decimal.
9115 The program accepts the following option. Also see @ref{Common options}.
9120 @itemx --mode=@var{mode}
9123 Set the mode of created files to @var{mode}, which is symbolic as in
9124 @command{chmod} and uses @samp{a=rw} as the point of departure.
9125 @var{mode} should specify only file permission bits.
9126 @xref{File permissions}.
9128 @item -Z @var{context}
9129 @itemx --context=@var{context}
9133 @cindex security context
9134 Set the default SELinux security context to be used for created files.
9141 @node readlink invocation
9142 @section @command{readlink}: Print value of a symlink or canonical file name
9145 @cindex displaying value of a symbolic link
9146 @cindex canonical file name
9147 @cindex canonicalize a file name
9151 @command{readlink} may work in one of two supported modes:
9157 @command{readlink} outputs the value of the given symbolic link.
9158 If @command{readlink} is invoked with an argument other than the name
9159 of a symbolic link, it produces no output and exits with a nonzero exit code.
9161 @item Canonicalize mode
9163 @command{readlink} outputs the absolute name of the given file which contains
9164 no @file{.}, @file{..} components nor any repeated separators
9165 (@file{/}) or symbolic links.
9170 readlink [@var{option}] @var{file}
9173 By default, @command{readlink} operates in readlink mode.
9175 The program accepts the following options. Also see @ref{Common options}.
9180 @itemx --canonicalize
9182 @opindex --canonicalize
9183 Activate canonicalize mode.
9184 If any component of the file name except the last one is missing or unavailable,
9185 @command{readlink} produces no output and exits with a nonzero exit code.
9188 @itemx --canonicalize-existing
9190 @opindex --canonicalize-existing
9191 Activate canonicalize mode.
9192 If any component is missing or unavailable, @command{readlink} produces
9193 no output and exits with a nonzero exit code.
9196 @itemx --canonicalize-missing
9198 @opindex --canonicalize-missing
9199 Activate canonicalize mode.
9200 If any component is missing or unavailable, @command{readlink} treats it
9206 @opindex --no-newline
9207 Do not output the trailing newline.
9217 Suppress most error messages.
9223 Report error messages.
9227 The @command{readlink} utility first appeared in OpenBSD 2.1.
9229 There is a @command{realpath} command on some systems
9230 which operates like @command{readlink} in canonicalize mode.
9235 @node rmdir invocation
9236 @section @command{rmdir}: Remove empty directories
9239 @cindex removing empty directories
9240 @cindex directories, removing empty
9242 @command{rmdir} removes empty directories. Synopsis:
9245 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9248 If any @var{directory} argument does not refer to an existing empty
9249 directory, it is an error.
9251 The program accepts the following options. Also see @ref{Common options}.
9255 @item --ignore-fail-on-non-empty
9256 @opindex --ignore-fail-on-non-empty
9257 @cindex directory deletion, ignoring failures
9258 Ignore each failure to remove a directory that is solely because
9259 the directory is non-empty.
9265 @cindex parent directories, removing
9266 Remove @var{directory}, then try to remove each component of @var{directory}.
9267 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9268 As such, it fails if any of those directories turns out not to be empty.
9269 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9270 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9271 exit unsuccessfully.
9277 @cindex directory deletion, reporting
9278 Give a diagnostic for each successful removal.
9279 @var{directory} is removed.
9283 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9288 @node unlink invocation
9289 @section @command{unlink}: Remove files via the unlink syscall
9292 @cindex removing files or directories (via the unlink syscall)
9294 @command{unlink} deletes a single specified file name.
9295 It is a minimalist interface to the system-provided
9296 @code{unlink} function. @xref{Deleting Files, , , libc,
9297 The GNU C Library Reference Manual}. Synopsis:
9298 It avoids the bells and whistles of the more commonly-used
9299 @command{rm} command (@pxref{rm invocation}).
9302 unlink @var{filename}
9305 On some systems @code{unlink} can be used to delete the name of a
9306 directory. On others, it can be used that way only by a privileged user.
9307 In the GNU system @code{unlink} can never delete the name of a directory.
9309 The @command{unlink} command honors the @option{--help} and
9310 @option{--version} options. To remove a file whose name begins with
9311 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9316 @node Changing file attributes
9317 @chapter Changing file attributes
9319 @cindex changing file attributes
9320 @cindex file attributes, changing
9321 @cindex attributes, file
9323 A file is not merely its contents, a name, and a file type
9324 (@pxref{Special file types}). A file also has an owner (a user ID), a
9325 group (a group ID), permissions (what the owner can do with the file,
9326 what people in the group can do, and what everyone else can do), various
9327 timestamps, and other information. Collectively, we call these a file's
9330 These commands change file attributes.
9333 * chgrp invocation:: Change file groups.
9334 * chmod invocation:: Change access permissions.
9335 * chown invocation:: Change file owners and groups.
9336 * touch invocation:: Change file timestamps.
9340 @node chown invocation
9341 @section @command{chown}: Change file owner and group
9344 @cindex file ownership, changing
9345 @cindex group ownership, changing
9346 @cindex changing file ownership
9347 @cindex changing group ownership
9349 @command{chown} changes the user and/or group ownership of each given @var{file}
9350 to @var{new-owner} or to the user and group of an existing reference file.
9354 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9357 If used, @var{new-owner} specifies the new owner and/or group as follows
9358 (with no embedded white space):
9361 [@var{owner}] [ : [@var{group}] ]
9368 If only an @var{owner} (a user name or numeric user ID) is given, that
9369 user is made the owner of each given file, and the files' group is not
9372 @item owner@samp{:}group
9373 If the @var{owner} is followed by a colon and a @var{group} (a
9374 group name or numeric group ID), with no spaces between them, the group
9375 ownership of the files is changed as well (to @var{group}).
9378 If a colon but no group name follows @var{owner}, that user is
9379 made the owner of the files and the group of the files is changed to
9380 @var{owner}'s login group.
9383 If the colon and following @var{group} are given, but the owner
9384 is omitted, only the group of the files is changed; in this case,
9385 @command{chown} performs the same function as @command{chgrp}.
9388 If only a colon is given, or if @var{new-owner} is empty, neither the
9389 owner nor the group is changed.
9393 If @var{owner} or @var{group} is intended to represent a numeric user
9394 or group ID, then you may specify it with a leading @samp{+}.
9395 @xref{Disambiguating names and IDs}.
9397 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9398 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9399 require support for that, but for backward compatibility @acronym{GNU}
9400 @command{chown} supports @samp{.} so long as no ambiguity results.
9401 New scripts should avoid the use of @samp{.} because it is not
9402 portable, and because it has undesirable results if the entire
9403 @var{owner@samp{.}group} happens to identify a user whose name
9406 The @command{chown} command sometimes clears the set-user-ID or
9407 set-group-ID permission bits. This behavior depends on the policy and
9408 functionality of the underlying @code{chown} system call, which may
9409 make system-dependent file mode modifications outside the control of
9410 the @command{chown} command. For example, the @command{chown} command
9411 might not affect those bits when invoked by a user with appropriate
9412 privileges, or when the
9413 bits signify some function other than executable permission (e.g.,
9415 When in doubt, check the underlying system behavior.
9417 The program accepts the following options. Also see @ref{Common options}.
9425 @cindex changed owners, verbosely describing
9426 Verbosely describe the action for each @var{file} whose ownership
9435 @cindex error messages, omitting
9436 Do not print error messages about files whose ownership cannot be
9439 @itemx @w{@kbd{--from}=@var{old-owner}}
9441 @cindex symbolic links, changing owner
9442 Change a @var{file}'s ownership only if it has current attributes specified
9443 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9445 This option is useful primarily from a security standpoint in that
9446 it narrows considerably the window of potential abuse.
9447 For example, to reflect a user ID numbering change for one user's files
9448 without an option like this, @code{root} might run
9451 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9454 But that is dangerous because the interval between when the @command{find}
9455 tests the existing file's owner and when the @command{chown} is actually run
9457 One way to narrow the gap would be to invoke chown for each file
9461 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9464 But that is very slow if there are many affected files.
9465 With this option, it is safer (the gap is narrower still)
9466 though still not perfect:
9469 chown -h -R --from=OLDUSER NEWUSER /
9473 @opindex --dereference
9474 @cindex symbolic links, changing owner
9476 Do not act on symbolic links themselves but rather on what they point to.
9477 This is the default.
9480 @itemx --no-dereference
9482 @opindex --no-dereference
9483 @cindex symbolic links, changing owner
9485 Act on symbolic links themselves instead of what they point to.
9486 This mode relies on the @code{lchown} system call.
9487 On systems that do not provide the @code{lchown} system call,
9488 @command{chown} fails when a file specified on the command line
9490 By default, no diagnostic is issued for symbolic links encountered
9491 during a recursive traversal, but see @option{--verbose}.
9493 @itemx --preserve-root
9494 @opindex --preserve-root
9495 @cindex root directory, disallow recursive modification
9496 Fail upon any attempt to recursively change the root directory, @file{/}.
9497 Without @option{--recursive}, this option has no effect.
9498 @xref{Treating / specially}.
9500 @itemx --no-preserve-root
9501 @opindex --no-preserve-root
9502 @cindex root directory, allow recursive modification
9503 Cancel the effect of any preceding @option{--preserve-root} option.
9504 @xref{Treating / specially}.
9506 @item --reference=@var{ref_file}
9507 @opindex --reference
9508 Change the user and group of each @var{file} to be the same as those of
9509 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9510 user and group of the symbolic link, but rather those of the file it
9517 Output a diagnostic for every file processed.
9518 If a symbolic link is encountered during a recursive traversal
9519 on a system without the @code{lchown} system call, and @option{--no-dereference}
9520 is in effect, then issue a diagnostic saying neither the symbolic link nor
9521 its referent is being changed.
9526 @opindex --recursive
9527 @cindex recursively changing file ownership
9528 Recursively change ownership of directories and their contents.
9531 @xref{Traversing symlinks}.
9534 @xref{Traversing symlinks}.
9537 @xref{Traversing symlinks}.
9546 # Change the owner of /u to "root".
9549 # Likewise, but also change its group to "staff".
9552 # Change the owner of /u and subfiles to "root".
9557 @node chgrp invocation
9558 @section @command{chgrp}: Change group ownership
9561 @cindex group ownership, changing
9562 @cindex changing group ownership
9564 @command{chgrp} changes the group ownership of each given @var{file}
9565 to @var{group} (which can be either a group name or a numeric group ID)
9566 or to the group of an existing reference file. Synopsis:
9569 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9572 If @var{group} is intended to represent a
9573 numeric group ID, then you may specify it with a leading @samp{+}.
9574 @xref{Disambiguating names and IDs}.
9576 The program accepts the following options. Also see @ref{Common options}.
9584 @cindex changed files, verbosely describing
9585 Verbosely describe the action for each @var{file} whose group actually
9594 @cindex error messages, omitting
9595 Do not print error messages about files whose group cannot be
9599 @opindex --dereference
9600 @cindex symbolic links, changing owner
9602 Do not act on symbolic links themselves but rather on what they point to.
9603 This is the default.
9606 @itemx --no-dereference
9608 @opindex --no-dereference
9609 @cindex symbolic links, changing group
9611 Act on symbolic links themselves instead of what they point to.
9612 This mode relies on the @code{lchown} system call.
9613 On systems that do not provide the @code{lchown} system call,
9614 @command{chgrp} fails when a file specified on the command line
9616 By default, no diagnostic is issued for symbolic links encountered
9617 during a recursive traversal, but see @option{--verbose}.
9619 @itemx --preserve-root
9620 @opindex --preserve-root
9621 @cindex root directory, disallow recursive modification
9622 Fail upon any attempt to recursively change the root directory, @file{/}.
9623 Without @option{--recursive}, this option has no effect.
9624 @xref{Treating / specially}.
9626 @itemx --no-preserve-root
9627 @opindex --no-preserve-root
9628 @cindex root directory, allow recursive modification
9629 Cancel the effect of any preceding @option{--preserve-root} option.
9630 @xref{Treating / specially}.
9632 @item --reference=@var{ref_file}
9633 @opindex --reference
9634 Change the group of each @var{file} to be the same as that of
9635 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9636 group of the symbolic link, but rather that of the file it refers to.
9642 Output a diagnostic for every file processed.
9643 If a symbolic link is encountered during a recursive traversal
9644 on a system without the @code{lchown} system call, and @option{--no-dereference}
9645 is in effect, then issue a diagnostic saying neither the symbolic link nor
9646 its referent is being changed.
9651 @opindex --recursive
9652 @cindex recursively changing group ownership
9653 Recursively change the group ownership of directories and their contents.
9656 @xref{Traversing symlinks}.
9659 @xref{Traversing symlinks}.
9662 @xref{Traversing symlinks}.
9671 # Change the group of /u to "staff".
9674 # Change the group of /u and subfiles to "staff".
9679 @node chmod invocation
9680 @section @command{chmod}: Change access permissions
9683 @cindex changing access permissions
9684 @cindex access permissions, changing
9685 @cindex permissions, changing access
9687 @command{chmod} changes the access permissions of the named files. Synopsis:
9690 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9693 @cindex symbolic links, permissions of
9694 @command{chmod} never changes the permissions of symbolic links, since
9695 the @command{chmod} system call cannot change their permissions.
9696 This is not a problem since the permissions of symbolic links are
9697 never used. However, for each symbolic link listed on the command
9698 line, @command{chmod} changes the permissions of the pointed-to file.
9699 In contrast, @command{chmod} ignores symbolic links encountered during
9700 recursive directory traversals.
9702 A successful use of @command{chmod} clears the set-group-ID bit of a
9703 regular file if the file's group ID does not match the user's
9704 effective group ID or one of the user's supplementary group IDs,
9705 unless the user has appropriate privileges. Additional restrictions
9706 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9707 @var{ref_file} to be ignored. This behavior depends on the policy and
9708 functionality of the underlying @code{chmod} system call. When in
9709 doubt, check the underlying system behavior.
9711 If used, @var{mode} specifies the new file mode bits.
9712 For details, see the section on @ref{File permissions}.
9713 If you really want @var{mode} to have a leading @samp{-}, you should
9714 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9715 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9716 file} (without the @option{--}) complains if it behaves differently
9717 from what @samp{chmod a-w file} would do.
9719 The program accepts the following options. Also see @ref{Common options}.
9727 Verbosely describe the action for each @var{file} whose permissions
9736 @cindex error messages, omitting
9737 Do not print error messages about files whose permissions cannot be
9740 @itemx --preserve-root
9741 @opindex --preserve-root
9742 @cindex root directory, disallow recursive modification
9743 Fail upon any attempt to recursively change the root directory, @file{/}.
9744 Without @option{--recursive}, this option has no effect.
9745 @xref{Treating / specially}.
9747 @itemx --no-preserve-root
9748 @opindex --no-preserve-root
9749 @cindex root directory, allow recursive modification
9750 Cancel the effect of any preceding @option{--preserve-root} option.
9751 @xref{Treating / specially}.
9757 Verbosely describe the action or non-action taken for every @var{file}.
9759 @item --reference=@var{ref_file}
9760 @opindex --reference
9761 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9762 @xref{File permissions}.
9763 If @var{ref_file} is a symbolic link, do not use the mode
9764 of the symbolic link, but rather that of the file it refers to.
9769 @opindex --recursive
9770 @cindex recursively changing access permissions
9771 Recursively change permissions of directories and their contents.
9778 @node touch invocation
9779 @section @command{touch}: Change file timestamps
9782 @cindex changing file timestamps
9783 @cindex file timestamps, changing
9784 @cindex timestamps, changing file
9786 @command{touch} changes the access and/or modification times of the
9787 specified files. Synopsis:
9790 touch [@var{option}]@dots{} @var{file}@dots{}
9793 @cindex empty files, creating
9794 Any @var{file} argument that does not exist is created empty.
9796 A @var{file} argument string of @samp{-} is handled specially and
9797 causes @command{touch} to change the times of the file associated with
9800 @cindex permissions, for changing file timestamps
9801 If changing both the access and modification times to the current
9802 time, @command{touch} can change the timestamps for files that the user
9803 running it does not own but has write permission for. Otherwise, the
9804 user must own the files.
9806 Although @command{touch} provides options for changing two of the times---the
9807 times of last access and modification---of a file, there is actually
9808 a third one as well: the inode change time. This is often referred to
9809 as a file's @code{ctime}.
9810 The inode change time represents the time when the file's meta-information
9811 last changed. One common example of this is when the permissions of a
9812 file change. Changing the permissions doesn't access the file, so
9813 the atime doesn't change, nor does it modify the file, so the mtime
9814 doesn't change. Yet, something about the file itself has changed,
9815 and this must be noted somewhere. This is the job of the ctime field.
9816 This is necessary, so that, for example, a backup program can make a
9817 fresh copy of the file, including the new permissions value.
9818 Another operation that modifies a file's ctime without affecting
9819 the others is renaming. In any case, it is not possible, in normal
9820 operations, for a user to change the ctime field to a user-specified value.
9823 Time stamps assume the time zone rules specified by the @env{TZ}
9824 environment variable, or by the system default rules if @env{TZ} is
9825 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9826 libc, The GNU C Library Reference Manual}.
9827 You can avoid ambiguities during
9828 daylight saving transitions by using @sc{utc} time stamps.
9830 The program accepts the following options. Also see @ref{Common options}.
9836 @itemx --time=access
9840 @opindex atime@r{, changing}
9841 @opindex access @r{time, changing}
9842 @opindex use @r{time, changing}
9843 Change the access time only.
9848 @opindex --no-create
9849 Do not create files that do not exist.
9852 @itemx --date=@var{time}
9856 Use @var{time} instead of the current time. It can contain month names,
9857 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9858 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9859 specifies the instant of time that is 489,392,193 nanoseconds after
9860 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9861 minutes east of @acronym{UTC}. @xref{Date input formats}.
9862 File systems that do not support high-resolution time stamps
9863 silently ignore any excess precision here.
9867 @cindex BSD @command{touch} compatibility
9868 Ignored; for compatibility with BSD versions of @command{touch}.
9872 @itemx --time=modify
9875 @opindex mtime@r{, changing}
9876 @opindex modify @r{time, changing}
9877 Change the modification time only.
9880 @itemx --reference=@var{file}
9882 @opindex --reference
9883 Use the times of the reference @var{file} instead of the current time.
9884 If this option is combined with the @option{--date=@var{time}}
9885 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9886 the origin for any relative @var{time}s given, but is otherwise ignored.
9887 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9888 equal to five seconds before the corresponding time stamp for @file{foo}.
9890 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9891 Use the argument (optional four-digit or two-digit years, months,
9892 days, hours, minutes, optional seconds) instead of the current time.
9893 If the year is specified with only two digits, then @var{cc}
9894 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9895 69 @dots{} 99. If no digits of the year are specified,
9896 the argument is interpreted as a date in the current year.
9900 @vindex _POSIX2_VERSION
9901 On older systems, @command{touch} supports an obsolete syntax, as follows.
9902 If no timestamp is given with any of the @option{-d}, @option{-r}, or
9903 @option{-t} options, and if there are two or more @var{file}s and the
9904 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
9905 would be a valid argument to the @option{-t} option (if the @var{yy}, if
9906 any, were moved to the front), and if the represented year
9907 is in the range 1969--1999, that argument is interpreted as the time
9908 for the other files instead of as a file name.
9909 This obsolete behavior can be enabled or disabled with the
9910 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
9911 conformance}), but portable scripts should avoid commands whose
9912 behavior depends on this variable.
9913 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
9914 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
9924 No disk can hold an infinite amount of data. These commands report
9925 how much disk storage is in use or available, report other file and
9926 file status information, and write buffers to disk.
9929 * df invocation:: Report file system disk space usage.
9930 * du invocation:: Estimate file space usage.
9931 * stat invocation:: Report file or file system status.
9932 * sync invocation:: Synchronize memory and disk.
9933 * truncate invocation:: Shrink or extend the size of a file.
9938 @section @command{df}: Report file system disk space usage
9941 @cindex file system disk usage
9942 @cindex disk usage by file system
9944 @command{df} reports the amount of disk space used and available on
9945 file systems. Synopsis:
9948 df [@var{option}]@dots{} [@var{file}]@dots{}
9951 With no arguments, @command{df} reports the space used and available on all
9952 currently mounted file systems (of all types). Otherwise, @command{df}
9953 reports on the file system containing each argument @var{file}.
9955 Normally the disk space is printed in units of
9956 1024 bytes, but this can be overridden (@pxref{Block size}).
9957 Non-integer quantities are rounded up to the next higher unit.
9959 @cindex disk device file
9960 @cindex device file, disk
9961 If an argument @var{file} is a disk device file containing a mounted
9962 file system, @command{df} shows the space available on that file system
9963 rather than on the file system containing the device node (i.e., the root
9964 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
9965 on unmounted file systems, because on most kinds of systems doing so
9966 requires extremely nonportable intimate knowledge of file system
9969 The program accepts the following options. Also see @ref{Common options}.
9977 @cindex automounter file systems
9978 @cindex ignore file systems
9979 Include in the listing dummy file systems, which
9980 are omitted by default. Such file systems are typically special-purpose
9981 pseudo-file-systems, such as automounter entries.
9984 @itemx --block-size=@var{size}
9986 @opindex --block-size
9987 @cindex file system sizes
9988 Scale sizes by @var{size} before printing them (@pxref{Block size}).
9989 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
9993 @cindex grand total of disk size, usage and available space
9994 Print a grand total of all arguments after all arguments have
9995 been processed. This can be used to find out the total disk size, usage
9996 and available space of all listed devices.
10002 Equivalent to @option{--si}.
10008 @cindex inode usage
10009 List inode usage information instead of block usage. An inode (short
10010 for index node) contains information about a file such as its owner,
10011 permissions, timestamps, and location on the disk.
10015 @cindex kibibytes for file system sizes
10016 Print sizes in 1024-byte blocks, overriding the default block size
10017 (@pxref{Block size}).
10018 This option is equivalent to @option{--block-size=1K}.
10024 @cindex file system types, limiting output to certain
10025 Limit the listing to local file systems. By default, remote file systems
10030 @cindex file system space, retrieving old data more quickly
10031 Do not invoke the @code{sync} system call before getting any usage data.
10032 This may make @command{df} run significantly faster on systems with many
10033 disks, but on some systems (notably SunOS) the results may be slightly
10034 out of date. This is the default.
10037 @itemx --portability
10039 @opindex --portability
10040 @cindex one-line output format
10041 @cindex @acronym{POSIX} output format
10042 @cindex portable output format
10043 @cindex output format, portable
10044 Use the @acronym{POSIX} output format. This is like the default format except
10049 The information about each file system is always printed on exactly
10050 one line; a mount device is never put on a line by itself. This means
10051 that if the mount device name is more than 20 characters long (e.g., for
10052 some network mounts), the columns are misaligned.
10055 The labels in the header output line are changed to conform to @acronym{POSIX}.
10058 The default block size and output format are unaffected by the
10059 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10060 variables. However, the default block size is still affected by
10061 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10062 otherwise. @xref{Block size}.
10069 @cindex file system space, retrieving current data more slowly
10070 Invoke the @code{sync} system call before getting any usage data. On
10071 some systems (notably SunOS), doing this yields more up to date results,
10072 but in general this option makes @command{df} much slower, especially when
10073 there are many or very busy file systems.
10075 @item -t @var{fstype}
10076 @itemx --type=@var{fstype}
10079 @cindex file system types, limiting output to certain
10080 Limit the listing to file systems of type @var{fstype}. Multiple
10081 file system types can be specified by giving multiple @option{-t} options.
10082 By default, nothing is omitted.
10085 @itemx --print-type
10087 @opindex --print-type
10088 @cindex file system types, printing
10089 Print each file system's type. The types printed here are the same ones
10090 you can include or exclude with @option{-t} and @option{-x}. The particular
10091 types printed are whatever is supported by the system. Here are some of
10092 the common names (this list is certainly not exhaustive):
10097 @cindex @acronym{NFS} file system type
10098 An @acronym{NFS} file system, i.e., one mounted over a network from another
10099 machine. This is the one type name which seems to be used uniformly by
10102 @item 4.2@r{, }ufs@r{, }efs@dots{}
10103 @cindex Linux file system types
10104 @cindex local file system types
10105 @opindex 4.2 @r{file system type}
10106 @opindex ufs @r{file system type}
10107 @opindex efs @r{file system type}
10108 A file system on a locally-mounted hard disk. (The system might even
10109 support more than one type here; Linux does.)
10111 @item hsfs@r{, }cdfs
10112 @cindex CD-ROM file system type
10113 @cindex High Sierra file system
10114 @opindex hsfs @r{file system type}
10115 @opindex cdfs @r{file system type}
10116 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10117 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10120 @cindex PC file system
10121 @cindex DOS file system
10122 @cindex MS-DOS file system
10123 @cindex diskette file system
10125 An MS-DOS file system, usually on a diskette.
10129 @item -x @var{fstype}
10130 @itemx --exclude-type=@var{fstype}
10132 @opindex --exclude-type
10133 Limit the listing to file systems not of type @var{fstype}.
10134 Multiple file system types can be eliminated by giving multiple
10135 @option{-x} options. By default, no file system types are omitted.
10138 Ignored; for compatibility with System V versions of @command{df}.
10143 Failure includes the case where no output is generated, so you can
10144 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10145 @var{dir}} to test whether @var{dir} is on a file system of type
10146 @samp{ext3} or @samp{reiserfs}.
10149 @node du invocation
10150 @section @command{du}: Estimate file space usage
10153 @cindex file space usage
10154 @cindex disk usage for files
10156 @command{du} reports the amount of disk space used by the specified files
10157 and for each subdirectory (of directory arguments). Synopsis:
10160 du [@var{option}]@dots{} [@var{file}]@dots{}
10163 With no arguments, @command{du} reports the disk space for the current
10164 directory. Normally the disk space is printed in units of
10165 1024 bytes, but this can be overridden (@pxref{Block size}).
10166 Non-integer quantities are rounded up to the next higher unit.
10168 If two or more hard links point to the same file, only one of the hard
10169 links is counted. The @var{file} argument order affects which links
10170 are counted, and changing the argument order may change the numbers
10171 that @command{du} outputs.
10173 The program accepts the following options. Also see @ref{Common options}.
10181 Show counts for all files, not just directories.
10183 @itemx --apparent-size
10184 @opindex --apparent-size
10185 Print apparent sizes, rather than disk usage. The apparent size of a
10186 file is the number of bytes reported by @code{wc -c} on regular files,
10187 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10188 For example, a file containing the word @samp{zoo} with no newline would,
10189 of course, have an apparent size of 3. Such a small file may require
10190 anywhere from 0 to 16 KiB or more of disk space, depending on
10191 the type and configuration of the file system on which the file resides.
10192 However, a sparse file created with this command:
10195 dd bs=1 seek=2GiB if=/dev/null of=big
10199 has an apparent size of 2 GiB, yet on most modern
10200 systems, it actually uses almost no disk space.
10206 Equivalent to @code{--apparent-size --block-size=1}.
10208 @item -B @var{size}
10209 @itemx --block-size=@var{size}
10211 @opindex --block-size
10213 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10214 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10220 @cindex grand total of disk space
10221 Print a grand total of all arguments after all arguments have
10222 been processed. This can be used to find out the total disk usage of
10223 a given set of files or directories.
10226 @itemx --dereference-args
10228 @opindex --dereference-args
10229 Dereference symbolic links that are command line arguments.
10230 Does not affect other symbolic links. This is helpful for finding
10231 out the disk usage of directories, such as @file{/usr/tmp}, which
10232 are often symbolic links.
10234 @c --files0-from=FILE
10235 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10241 Equivalent to @option{--dereference-args} (@option{-D}).
10245 @cindex kibibytes for file sizes
10246 Print sizes in 1024-byte blocks, overriding the default block size
10247 (@pxref{Block size}).
10248 This option is equivalent to @option{--block-size=1K}.
10251 @itemx --count-links
10253 @opindex --count-links
10254 @cindex hard links, counting in @command{du}
10255 Count the size of all files, even if they have appeared already (as a
10259 @itemx --dereference
10261 @opindex --dereference
10262 @cindex symbolic links, dereferencing in @command{du}
10263 Dereference symbolic links (show the disk space used by the file
10264 or directory that the link points to instead of the space used by
10269 @cindex mebibytes for file sizes
10270 Print sizes in 1,048,576-byte blocks, overriding the default block size
10271 (@pxref{Block size}).
10272 This option is equivalent to @option{--block-size=1M}.
10275 @itemx --no-dereference
10277 @opindex --no-dereference
10278 @cindex symbolic links, dereferencing in @command{du}
10279 For each symbolic links encountered by @command{du},
10280 consider the disk space used by the symbolic link.
10282 @item --max-depth=@var{depth}
10283 @opindex --max-depth=@var{depth}
10284 @cindex limiting output of @command{du}
10285 Show the total for each directory (and file if --all) that is at
10286 most MAX_DEPTH levels down from the root of the hierarchy. The root
10287 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10293 @cindex output null-byte-terminated lines
10294 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
10295 rather than a newline. This option enables other programs to parse the
10296 output of @command{du} even when that output would contain file names
10297 with embedded newlines.
10304 @opindex --summarize
10305 Display only a total for each argument.
10308 @itemx --separate-dirs
10310 @opindex --separate-dirs
10311 Normally, in the output of @command{du} (when not using @option{--summarize}),
10312 the size listed next to a directory name, @var{d}, represents the sum
10313 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10314 With @option{--separate-dirs}, the size reported for a directory name,
10315 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10320 @cindex last modified dates, displaying in @command{du}
10321 Show time of the most recent modification of any file in the directory,
10322 or any of its subdirectories.
10324 @itemx --time=ctime
10325 @itemx --time=status
10328 @opindex ctime@r{, show the most recent}
10329 @opindex status time@r{, show the most recent}
10330 @opindex use time@r{, show the most recent}
10331 Show the most recent status change time (the @samp{ctime} in the inode) of
10332 any file in the directory, instead of the modification time.
10334 @itemx --time=atime
10335 @itemx --time=access
10337 @opindex atime@r{, show the most recent}
10338 @opindex access time@r{, show the most recent}
10339 Show the most recent access time (the @samp{atime} in the inode) of
10340 any file in the directory, instead of the modification time.
10342 @item --time-style=@var{style}
10343 @opindex --time-style
10345 List timestamps in style @var{style}. This option has an effect only if
10346 the @option{--time} option is also specified. The @var{style} should
10347 be one of the following:
10350 @item +@var{format}
10352 List timestamps using @var{format}, where @var{format} is interpreted
10353 like the format argument of @command{date} (@pxref{date invocation}).
10354 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10355 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10356 with @command{date}, @var{format}'s interpretation is affected by the
10357 @env{LC_TIME} locale category.
10360 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10361 format with nanosecond precision, e.g., @samp{2002-03-30
10362 23:45:56.477817180 -0700}. This style is equivalent to
10363 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10366 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10367 @samp{2002-03-30 23:45}. These timestamps are shorter than
10368 @samp{full-iso} timestamps, and are usually good enough for everyday
10369 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10372 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10373 This style is equivalent to @samp{+%Y-%m-%d}.
10377 You can specify the default value of the @option{--time-style} option
10378 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10379 the default style is @samp{long-iso}. For compatibility with @command{ls},
10380 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10381 the newline and any later characters are ignored; if @env{TIME_STYLE}
10382 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10383 @env{TIME_STYLE} is @samp{locale} it is ignored.
10386 @itemx --one-file-system
10388 @opindex --one-file-system
10389 @cindex one file system, restricting @command{du} to
10390 Skip directories that are on different file systems from the one that
10391 the argument being processed is on.
10393 @item --exclude=@var{pattern}
10394 @opindex --exclude=@var{pattern}
10395 @cindex excluding files from @command{du}
10396 When recursing, skip subdirectories or files matching @var{pattern}.
10397 For example, @code{du --exclude='*.o'} excludes files whose names
10400 @item -X @var{file}
10401 @itemx --exclude-from=@var{file}
10402 @opindex -X @var{file}
10403 @opindex --exclude-from=@var{file}
10404 @cindex excluding files from @command{du}
10405 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10406 one per line. If @var{file} is @samp{-}, take the patterns from standard
10411 @cindex NFS mounts from BSD to HP-UX
10412 On BSD systems, @command{du} reports sizes that are half the correct
10413 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10414 systems, it reports sizes that are twice the correct values for
10415 files that are NFS-mounted from BSD systems. This is due to a flaw
10416 in HP-UX; it also affects the HP-UX @command{du} program.
10421 @node stat invocation
10422 @section @command{stat}: Report file or file system status
10425 @cindex file status
10426 @cindex file system status
10428 @command{stat} displays information about the specified file(s). Synopsis:
10431 stat [@var{option}]@dots{} [@var{file}]@dots{}
10434 With no option, @command{stat} reports all information about the given files.
10435 But it also can be used to report the information of the file systems the
10436 given files are located on. If the files are links, @command{stat} can
10437 also give information about the files the links point to.
10439 @mayConflictWithShellBuiltIn{stat}
10444 @itemx --dereference
10446 @opindex --dereference
10447 @cindex symbolic links, dereferencing in @command{stat}
10448 Change how @command{stat} treats symbolic links.
10449 With this option, @command{stat} acts on the file referenced
10450 by each symbolic link argument.
10451 Without it, @command{stat} acts on any symbolic link argument directly.
10454 @itemx --file-system
10456 @opindex --file-system
10457 @cindex file systems
10458 Report information about the file systems where the given files are located
10459 instead of information about the files themselves.
10462 @itemx --format=@var{format}
10464 @opindex --format=@var{format}
10465 @cindex output format
10466 Use @var{format} rather than the default format.
10467 @var{format} is automatically newline-terminated, so
10468 running a command like the following with two or more @var{file}
10469 operands produces a line of output for each operand:
10471 $ stat --format=%d:%i / /usr
10476 @itemx --printf=@var{format}
10477 @opindex --printf=@var{format}
10478 @cindex output format
10479 Use @var{format} rather than the default format.
10480 Like @option{--format}, but interpret backslash escapes,
10481 and do not output a mandatory trailing newline.
10482 If you want a newline, include @samp{\n} in the @var{format}.
10483 Here's how you would use @option{--printf} to print the device
10484 and inode numbers of @file{/} and @file{/usr}:
10486 $ stat --printf='%d:%i\n' / /usr
10495 @cindex terse output
10496 Print the information in terse form, suitable for parsing by other programs.
10500 The valid @var{format} directives for files with @option{--format} and
10501 @option{--printf} are:
10504 @item %a - Access rights in octal
10505 @item %A - Access rights in human readable form
10506 @item %b - Number of blocks allocated (see @samp{%B})
10507 @item %B - The size in bytes of each block reported by @samp{%b}
10508 @item %d - Device number in decimal
10509 @item %D - Device number in hex
10510 @item %f - Raw mode in hex
10511 @item %F - File type
10512 @item %g - Group ID of owner
10513 @item %G - Group name of owner
10514 @item %h - Number of hard links
10515 @item %i - Inode number
10516 @item %n - File name
10517 @item %N - Quoted file name with dereference if symbolic link
10518 @item %o - I/O block size
10519 @item %s - Total size, in bytes
10520 @item %t - Major device type in hex
10521 @item %T - Minor device type in hex
10522 @item %u - User ID of owner
10523 @item %U - User name of owner
10524 @item %x - Time of last access
10525 @item %X - Time of last access as seconds since Epoch
10526 @item %y - Time of last modification
10527 @item %Y - Time of last modification as seconds since Epoch
10528 @item %z - Time of last change
10529 @item %Z - Time of last change as seconds since Epoch
10532 When listing file system information (@option{--file-system} (@option{-f})),
10533 you must use a different set of @var{format} directives:
10536 @item %a - Free blocks available to non-super-user
10537 @item %b - Total data blocks in file system
10538 @item %c - Total file nodes in file system
10539 @item %d - Free file nodes in file system
10540 @item %f - Free blocks in file system
10541 @item %i - File System ID in hex
10542 @item %l - Maximum length of file names
10543 @item %n - File name
10544 @item %s - Block size (for faster transfers)
10545 @item %S - Fundamental block size (for block counts)
10546 @item %t - Type in hex
10547 @item %T - Type in human readable form
10551 Time stamps are listed according to the time zone rules specified by
10552 the @env{TZ} environment variable, or by the system default rules if
10553 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10554 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10559 @node sync invocation
10560 @section @command{sync}: Synchronize data on disk with memory
10563 @cindex synchronize disk and memory
10565 @cindex superblock, writing
10566 @cindex inodes, written buffered
10567 @command{sync} writes any data buffered in memory out to disk. This can
10568 include (but is not limited to) modified superblocks, modified inodes,
10569 and delayed reads and writes. This must be implemented by the kernel;
10570 The @command{sync} program does nothing but exercise the @code{sync} system
10573 @cindex crashes and corruption
10574 The kernel keeps data in memory to avoid doing (relatively slow) disk
10575 reads and writes. This improves performance, but if the computer
10576 crashes, data may be lost or the file system corrupted as a
10577 result. The @command{sync} command ensures everything in memory
10578 is written to disk.
10580 Any arguments are ignored, except for a lone @option{--help} or
10581 @option{--version} (@pxref{Common options}).
10586 @node truncate invocation
10587 @section @command{truncate}: Shrink or extend the size of a file
10590 @cindex truncating, file sizes
10592 @command{truncate} shrinks or extends the size of each @var{file} to the
10593 specified size. Synopsis:
10596 truncate @var{option}@dots{} @var{file}@dots{}
10599 @cindex files, creating
10600 Any @var{file} that does not exist is created.
10602 @cindex sparse files, creating
10603 @cindex holes, creating files with
10604 If a @var{file} is larger than the specified size, the extra data is lost.
10605 If a @var{file} is shorter, it is extended and the extended part (or hole)
10606 reads as zero bytes.
10608 The program accepts the following options. Also see @ref{Common options}.
10615 @opindex --no-create
10616 Do not create files that do not exist.
10621 @opindex --io-blocks
10622 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10624 @item -r @var{rfile}
10625 @itemx --reference=@var{rfile}
10627 @opindex --reference
10628 Set the size of each @var{file} to the same size as @var{rfile}.
10630 @item -s @var{size}
10631 @itemx --size=@var{size}
10634 Set the size of each @var{file} to this @var{size}.
10635 @multiplierSuffixesNoBlocks{size}
10637 @var{size} may also be prefixed by one of the following to adjust
10638 the size of each @var{file} based on their current size:
10640 @samp{+} => extend by
10641 @samp{-} => reduce by
10642 @samp{<} => at most
10643 @samp{>} => at least
10644 @samp{/} => round down to multiple of
10645 @samp{%} => round up to multiple of
10653 @node Printing text
10654 @chapter Printing text
10656 @cindex printing text, commands for
10657 @cindex commands for printing text
10659 This section describes commands that display text strings.
10662 * echo invocation:: Print a line of text.
10663 * printf invocation:: Format and print data.
10664 * yes invocation:: Print a string until interrupted.
10668 @node echo invocation
10669 @section @command{echo}: Print a line of text
10672 @cindex displaying text
10673 @cindex printing text
10674 @cindex text, displaying
10675 @cindex arbitrary text, displaying
10677 @command{echo} writes each given @var{string} to standard output, with a
10678 space between each and a newline after the last one. Synopsis:
10681 echo [@var{option}]@dots{} [@var{string}]@dots{}
10684 @mayConflictWithShellBuiltIn{echo}
10686 The program accepts the following options. Also see @ref{Common options}.
10687 Options must precede operands, and the normally-special argument
10688 @samp{--} has no special meaning and is treated like any other
10694 Do not output the trailing newline.
10698 @cindex backslash escapes
10699 Enable interpretation of the following backslash-escaped characters in
10708 produce no further output
10722 the eight-bit value that is the octal number @var{nnn}
10723 (zero to three octal digits)
10725 the eight-bit value that is the octal number @var{nnn}
10726 (one to three octal digits)
10728 the eight-bit value that is the hexadecimal number @var{hh}
10729 (one or two hexadecimal digits)
10734 @cindex backslash escapes
10735 Disable interpretation of backslash escapes in each @var{string}.
10736 This is the default. If @option{-e} and @option{-E} are both
10737 specified, the last one given takes effect.
10741 @vindex POSIXLY_CORRECT
10742 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10743 @command{echo}'s first argument is not @option{-n} it outputs
10744 option-like arguments instead of treating them as options. For
10745 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10746 plain @samp{hello}.
10748 @acronym{POSIX} does not require support for any options, and says
10749 that the behavior of @command{echo} is implementation-defined if any
10750 @var{string} contains a backslash or if the first argument is
10751 @option{-n}. Portable programs can use the @command{printf} command
10752 if they need to omit trailing newlines or output control characters or
10753 backslashes. @xref{printf invocation}.
10758 @node printf invocation
10759 @section @command{printf}: Format and print data
10762 @command{printf} does formatted printing of text. Synopsis:
10765 printf @var{format} [@var{argument}]@dots{}
10768 @command{printf} prints the @var{format} string, interpreting @samp{%}
10769 directives and @samp{\} escapes to format numeric and string arguments
10770 in a way that is mostly similar to the C @samp{printf} function.
10771 @xref{Output Conversion Syntax,, @command{printf} format directives,
10772 libc, The GNU C Library Reference Manual}, for details.
10773 The differences are listed below.
10775 @mayConflictWithShellBuiltIn{printf}
10780 The @var{format} argument is reused as necessary to convert all the
10781 given @var{argument}s. For example, the command @samp{printf %s a b}
10785 Missing @var{argument}s are treated as null strings or as zeros,
10786 depending on whether the context expects a string or a number. For
10787 example, the command @samp{printf %sx%d} prints @samp{x0}.
10791 An additional escape, @samp{\c}, causes @command{printf} to produce no
10792 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10793 E} prints @samp{ABC}.
10796 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10797 digits, as opposed to C where it can have an unlimited number of
10798 digits. For example, the command @samp{printf '\x07e'} prints two
10799 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10804 @command{printf} has an additional directive, @samp{%b}, which prints its
10805 argument string with @samp{\} escapes interpreted in the same way as in
10806 the @var{format} string, except that octal escapes are of the form
10807 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10808 If a precision is also given, it limits the number of bytes printed
10809 from the converted string.
10812 Numeric arguments must be single C constants, possibly with leading
10813 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10817 @vindex POSIXLY_CORRECT
10818 If the leading character of a numeric argument is @samp{"} or @samp{'}
10819 then its value is the numeric value of the immediately following
10820 character. Any remaining characters are silently ignored if the
10821 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10822 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10823 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10824 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10829 A floating-point argument must use a period before any fractional
10830 digits, but is printed according to the @env{LC_NUMERIC} category of the
10831 current locale. For example, in a locale whose radix character is a
10832 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10833 the command @samp{printf %g 3,14} is an error.
10837 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10838 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10839 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10840 digits) specifying a character to print.
10845 @cindex ISO/IEC 10646
10847 @command{printf} interprets two character syntaxes introduced in
10848 @acronym{ISO} C 99:
10849 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10850 characters, specified as
10851 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10852 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10853 @command{printf} outputs the Unicode characters
10854 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10855 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10856 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10858 The processing of @samp{\u} and @samp{\U} requires a full-featured
10859 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10860 or when @code{libiconv} is installed prior to this package. Otherwise
10861 @samp{\u} and @samp{\U} will print as-is.
10863 The only options are a lone @option{--help} or
10864 @option{--version}. @xref{Common options}.
10865 Options must precede operands.
10867 The Unicode character syntaxes are useful for writing strings in a locale
10868 independent way. For example, a string containing the Euro currency symbol
10871 $ env printf '\u20AC 14.95'
10875 will be output correctly in all locales supporting the Euro symbol
10876 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10879 $ env printf '\u4e2d\u6587'
10883 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10885 Note that in these examples, the @command{printf} command has been
10886 invoked via @command{env} to ensure that we run the program found via
10887 your shell's search path, and not a shell alias or a built-in function.
10889 For larger strings, you don't need to look up the hexadecimal code
10890 values of each character one by one. @acronym{ASCII} characters mixed with \u
10891 escape sequences is also known as the JAVA source file encoding. You can
10892 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10893 is how to convert a piece of text into a shell script which will output
10894 this text in a locale-independent way:
10897 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10898 '\u4e2d\u6587\n' > sample.txt
10899 $ recode BIG5..JAVA < sample.txt \
10900 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
10907 @node yes invocation
10908 @section @command{yes}: Print a string until interrupted
10911 @cindex repeated output of a string
10913 @command{yes} prints the command line arguments, separated by spaces and
10914 followed by a newline, forever until it is killed. If no arguments are
10915 given, it prints @samp{y} followed by a newline forever until killed.
10917 Upon a write error, @command{yes} exits with status @samp{1}.
10919 The only options are a lone @option{--help} or @option{--version}.
10920 To output an argument that begins with
10921 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
10922 @xref{Common options}.
10926 @chapter Conditions
10929 @cindex commands for exit status
10930 @cindex exit status commands
10932 This section describes commands that are primarily useful for their exit
10933 status, rather than their output. Thus, they are often used as the
10934 condition of shell @code{if} statements, or as the last command in a
10938 * false invocation:: Do nothing, unsuccessfully.
10939 * true invocation:: Do nothing, successfully.
10940 * test invocation:: Check file types and compare values.
10941 * expr invocation:: Evaluate expressions.
10945 @node false invocation
10946 @section @command{false}: Do nothing, unsuccessfully
10949 @cindex do nothing, unsuccessfully
10950 @cindex failure exit status
10951 @cindex exit status of @command{false}
10953 @command{false} does nothing except return an exit status of 1, meaning
10954 @dfn{failure}. It can be used as a place holder in shell scripts
10955 where an unsuccessful command is needed.
10956 In most modern shells, @command{false} is a built-in command, so when
10957 you use @samp{false} in a script, you're probably using the built-in
10958 command, not the one documented here.
10960 @command{false} honors the @option{--help} and @option{--version} options.
10962 This version of @command{false} is implemented as a C program, and is thus
10963 more secure and faster than a shell script implementation, and may safely
10964 be used as a dummy shell for the purpose of disabling accounts.
10966 Note that @command{false} (unlike all other programs documented herein)
10967 exits unsuccessfully, even when invoked with
10968 @option{--help} or @option{--version}.
10970 Portable programs should not assume that the exit status of
10971 @command{false} is 1, as it is greater than 1 on some
10972 non-@acronym{GNU} hosts.
10975 @node true invocation
10976 @section @command{true}: Do nothing, successfully
10979 @cindex do nothing, successfully
10981 @cindex successful exit
10982 @cindex exit status of @command{true}
10984 @command{true} does nothing except return an exit status of 0, meaning
10985 @dfn{success}. It can be used as a place holder in shell scripts
10986 where a successful command is needed, although the shell built-in
10987 command @code{:} (colon) may do the same thing faster.
10988 In most modern shells, @command{true} is a built-in command, so when
10989 you use @samp{true} in a script, you're probably using the built-in
10990 command, not the one documented here.
10992 @command{true} honors the @option{--help} and @option{--version} options.
10994 Note, however, that it is possible to cause @command{true}
10995 to exit with nonzero status: with the @option{--help} or @option{--version}
10996 option, and with standard
10997 output already closed or redirected to a file that evokes an I/O error.
10998 For example, using a Bourne-compatible shell:
11001 $ ./true --version >&-
11002 ./true: write error: Bad file number
11003 $ ./true --version > /dev/full
11004 ./true: write error: No space left on device
11007 This version of @command{true} is implemented as a C program, and is thus
11008 more secure and faster than a shell script implementation, and may safely
11009 be used as a dummy shell for the purpose of disabling accounts.
11011 @node test invocation
11012 @section @command{test}: Check file types and compare values
11015 @cindex check file types
11016 @cindex compare values
11017 @cindex expression evaluation
11019 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11020 evaluation of the conditional expression @var{expr}. Each part of the
11021 expression must be a separate argument.
11023 @command{test} has file status checks, string operators, and numeric
11024 comparison operators.
11026 @command{test} has an alternate form that uses opening and closing
11027 square brackets instead a leading @samp{test}. For example, instead
11028 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11029 brackets must be separate arguments; for example, @samp{[-d /]} does
11030 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11031 @var{expr} ]} have the same meaning, only the former form is discussed
11037 test @var{expression}
11039 [ @var{expression} ]
11044 @mayConflictWithShellBuiltIn{test}
11046 If @var{expression} is omitted, @command{test} returns false.
11047 If @var{expression} is a single argument,
11048 @command{test} returns false if the argument is null and true otherwise. The argument
11049 can be any string, including strings like @samp{-d}, @samp{-1},
11050 @samp{--}, @samp{--help}, and @samp{--version} that most other
11051 programs would treat as options. To get help and version information,
11052 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11053 the usual closing brackets. @xref{Common options}.
11055 @cindex exit status of @command{test}
11059 0 if the expression is true,
11060 1 if the expression is false,
11061 2 if an error occurred.
11065 * File type tests:: -[bcdfhLpSt]
11066 * Access permission tests:: -[gkruwxOG]
11067 * File characteristic tests:: -e -s -nt -ot -ef
11068 * String tests:: -z -n = !=
11069 * Numeric tests:: -eq -ne -lt -le -gt -ge
11070 * Connectives for test:: ! -a -o
11074 @node File type tests
11075 @subsection File type tests
11077 @cindex file type tests
11079 These options test for particular types of files. (Everything's a file,
11080 but not all files are the same!)
11084 @item -b @var{file}
11086 @cindex block special check
11087 True if @var{file} exists and is a block special device.
11089 @item -c @var{file}
11091 @cindex character special check
11092 True if @var{file} exists and is a character special device.
11094 @item -d @var{file}
11096 @cindex directory check
11097 True if @var{file} exists and is a directory.
11099 @item -f @var{file}
11101 @cindex regular file check
11102 True if @var{file} exists and is a regular file.
11104 @item -h @var{file}
11105 @itemx -L @var{file}
11108 @cindex symbolic link check
11109 True if @var{file} exists and is a symbolic link.
11110 Unlike all other file-related tests, this test does not dereference
11111 @var{file} if it is a symbolic link.
11113 @item -p @var{file}
11115 @cindex named pipe check
11116 True if @var{file} exists and is a named pipe.
11118 @item -S @var{file}
11120 @cindex socket check
11121 True if @var{file} exists and is a socket.
11125 @cindex terminal check
11126 True if @var{fd} is a file descriptor that is associated with a
11132 @node Access permission tests
11133 @subsection Access permission tests
11135 @cindex access permission tests
11136 @cindex permission tests
11138 These options test for particular access permissions.
11142 @item -g @var{file}
11144 @cindex set-group-ID check
11145 True if @var{file} exists and has its set-group-ID bit set.
11147 @item -k @var{file}
11149 @cindex sticky bit check
11150 True if @var{file} exists and has its @dfn{sticky} bit set.
11152 @item -r @var{file}
11154 @cindex readable file check
11155 True if @var{file} exists and read permission is granted.
11157 @item -u @var{file}
11159 @cindex set-user-ID check
11160 True if @var{file} exists and has its set-user-ID bit set.
11162 @item -w @var{file}
11164 @cindex writable file check
11165 True if @var{file} exists and write permission is granted.
11167 @item -x @var{file}
11169 @cindex executable file check
11170 True if @var{file} exists and execute permission is granted
11171 (or search permission, if it is a directory).
11173 @item -O @var{file}
11175 @cindex owned by effective user ID check
11176 True if @var{file} exists and is owned by the current effective user ID.
11178 @item -G @var{file}
11180 @cindex owned by effective group ID check
11181 True if @var{file} exists and is owned by the current effective group ID.
11185 @node File characteristic tests
11186 @subsection File characteristic tests
11188 @cindex file characteristic tests
11190 These options test other file characteristics.
11194 @item -e @var{file}
11196 @cindex existence-of-file check
11197 True if @var{file} exists.
11199 @item -s @var{file}
11201 @cindex nonempty file check
11202 True if @var{file} exists and has a size greater than zero.
11204 @item @var{file1} -nt @var{file2}
11206 @cindex newer-than file check
11207 True if @var{file1} is newer (according to modification date) than
11208 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11210 @item @var{file1} -ot @var{file2}
11212 @cindex older-than file check
11213 True if @var{file1} is older (according to modification date) than
11214 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11216 @item @var{file1} -ef @var{file2}
11218 @cindex same file check
11219 @cindex hard link check
11220 True if @var{file1} and @var{file2} have the same device and inode
11221 numbers, i.e., if they are hard links to each other.
11227 @subsection String tests
11229 @cindex string tests
11231 These options test string characteristics. You may need to quote
11232 @var{string} arguments for the shell. For example:
11238 The quotes here prevent the wrong arguments from being passed to
11239 @command{test} if @samp{$V} is empty or contains special characters.
11243 @item -z @var{string}
11245 @cindex zero-length string check
11246 True if the length of @var{string} is zero.
11248 @item -n @var{string}
11249 @itemx @var{string}
11251 @cindex nonzero-length string check
11252 True if the length of @var{string} is nonzero.
11254 @item @var{string1} = @var{string2}
11256 @cindex equal string check
11257 True if the strings are equal.
11259 @item @var{string1} != @var{string2}
11261 @cindex not-equal string check
11262 True if the strings are not equal.
11267 @node Numeric tests
11268 @subsection Numeric tests
11270 @cindex numeric tests
11271 @cindex arithmetic tests
11273 Numeric relational operators. The arguments must be entirely numeric
11274 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11275 which evaluates to the length of @var{string}.
11279 @item @var{arg1} -eq @var{arg2}
11280 @itemx @var{arg1} -ne @var{arg2}
11281 @itemx @var{arg1} -lt @var{arg2}
11282 @itemx @var{arg1} -le @var{arg2}
11283 @itemx @var{arg1} -gt @var{arg2}
11284 @itemx @var{arg1} -ge @var{arg2}
11291 These arithmetic binary operators return true if @var{arg1} is equal,
11292 not-equal, less-than, less-than-or-equal, greater-than, or
11293 greater-than-or-equal than @var{arg2}, respectively.
11300 test -1 -gt -2 && echo yes
11302 test -l abc -gt 1 && echo yes
11305 @error{} test: integer expression expected before -eq
11309 @node Connectives for test
11310 @subsection Connectives for @command{test}
11312 @cindex logical connectives
11313 @cindex connectives, logical
11315 The usual logical connectives.
11321 True if @var{expr} is false.
11323 @item @var{expr1} -a @var{expr2}
11325 @cindex logical and operator
11326 @cindex and operator
11327 True if both @var{expr1} and @var{expr2} are true.
11329 @item @var{expr1} -o @var{expr2}
11331 @cindex logical or operator
11332 @cindex or operator
11333 True if either @var{expr1} or @var{expr2} is true.
11338 @node expr invocation
11339 @section @command{expr}: Evaluate expressions
11342 @cindex expression evaluation
11343 @cindex evaluation of expressions
11345 @command{expr} evaluates an expression and writes the result on standard
11346 output. Each token of the expression must be a separate argument.
11348 Operands are either integers or strings. Integers consist of one or
11349 more decimal digits, with an optional leading @samp{-}.
11350 @command{expr} converts
11351 anything appearing in an operand position to an integer or a string
11352 depending on the operation being applied to it.
11354 Strings are not quoted for @command{expr} itself, though you may need to
11355 quote them to protect characters with special meaning to the shell,
11356 e.g., spaces. However, regardless of whether it is quoted, a string
11357 operand should not be a parenthesis or any of @command{expr}'s
11358 operators like @code{+}, so you cannot safely pass an arbitrary string
11359 @code{$str} to expr merely by quoting it to the shell. One way to
11360 work around this is to use the @sc{gnu} extension @code{+},
11361 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11362 @code{@w{" $str"}} and to adjust the rest of the expression to take
11363 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11365 You should not pass a negative integer or a string with leading
11366 @samp{-} as @command{expr}'s first argument, as it might be
11367 misinterpreted as an option; this can be avoided by parenthesization.
11368 Also, portable scripts should not use a string operand that happens to
11369 take the form of an integer; this can be worked around by inserting
11370 leading spaces as mentioned above.
11372 @cindex parentheses for grouping
11373 Operators may be given as infix symbols or prefix keywords. Parentheses
11374 may be used for grouping in the usual manner. You must quote
11375 parentheses and many operators to avoid the shell evaluating them,
11378 When built with support for the GNU MP library, @command{expr} uses
11379 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11380 types and may fail due to arithmetic overflow.
11382 The only options are @option{--help} and @option{--version}. @xref{Common
11383 options}. Options must precede operands.
11385 @cindex exit status of @command{expr}
11389 0 if the expression is neither null nor 0,
11390 1 if the expression is null or 0,
11391 2 if the expression is invalid,
11392 3 if an internal error occurred (e.g., arithmetic overflow).
11396 * String expressions:: + : match substr index length
11397 * Numeric expressions:: + - * / %
11398 * Relations for expr:: | & < <= = == != >= >
11399 * Examples of expr:: Examples.
11403 @node String expressions
11404 @subsection String expressions
11406 @cindex string expressions
11407 @cindex expressions, string
11409 @command{expr} supports pattern matching and other string operators. These
11410 have higher precedence than both the numeric and relational operators (in
11411 the next sections).
11415 @item @var{string} : @var{regex}
11416 @cindex pattern matching
11417 @cindex regular expression matching
11418 @cindex matching patterns
11419 Perform pattern matching. The arguments are converted to strings and the
11420 second is considered to be a (basic, a la GNU @code{grep}) regular
11421 expression, with a @code{^} implicitly prepended. The first argument is
11422 then matched against this regular expression.
11424 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11425 @code{:} expression returns the part of @var{string} that matched the
11426 subexpression; otherwise, it returns the number of characters matched.
11428 If the match fails, the @code{:} operator returns the null string if
11429 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11431 @kindex \( @r{regexp operator}
11432 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11433 value; additional pairs are meaningful only for grouping the regular
11434 expression operators.
11436 @kindex \+ @r{regexp operator}
11437 @kindex \? @r{regexp operator}
11438 @kindex \| @r{regexp operator}
11439 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11440 operators which respectively match one or more, zero or one, or separate
11441 alternatives. SunOS and other @command{expr}'s treat these as regular
11442 characters. (@acronym{POSIX} allows either behavior.)
11443 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11444 regular expression syntax. Some examples are in @ref{Examples of expr}.
11446 @item match @var{string} @var{regex}
11448 An alternative way to do pattern matching. This is the same as
11449 @w{@samp{@var{string} : @var{regex}}}.
11451 @item substr @var{string} @var{position} @var{length}
11453 Returns the substring of @var{string} beginning at @var{position}
11454 with length at most @var{length}. If either @var{position} or
11455 @var{length} is negative, zero, or non-numeric, returns the null string.
11457 @item index @var{string} @var{charset}
11459 Returns the first position in @var{string} where the first character in
11460 @var{charset} was found. If no character in @var{charset} is found in
11461 @var{string}, return 0.
11463 @item length @var{string}
11465 Returns the length of @var{string}.
11467 @item + @var{token}
11469 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11470 or an operator like @code{/}.
11471 This makes it possible to test @code{expr length + "$x"} or
11472 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11473 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11474 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11475 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11479 To make @command{expr} interpret keywords as strings, you must use the
11480 @code{quote} operator.
11483 @node Numeric expressions
11484 @subsection Numeric expressions
11486 @cindex numeric expressions
11487 @cindex expressions, numeric
11489 @command{expr} supports the usual numeric operators, in order of increasing
11490 precedence. These numeric operators have lower precedence than the
11491 string operators described in the previous section, and higher precedence
11492 than the connectives (next section).
11500 @cindex subtraction
11501 Addition and subtraction. Both arguments are converted to integers;
11502 an error occurs if this cannot be done.
11508 @cindex multiplication
11511 Multiplication, division, remainder. Both arguments are converted to
11512 integers; an error occurs if this cannot be done.
11517 @node Relations for expr
11518 @subsection Relations for @command{expr}
11520 @cindex connectives, logical
11521 @cindex logical connectives
11522 @cindex relations, numeric or string
11524 @command{expr} supports the usual logical connectives and relations. These
11525 have lower precedence than the string and numeric operators
11526 (previous sections). Here is the list, lowest-precedence operator first.
11532 @cindex logical or operator
11533 @cindex or operator
11534 Returns its first argument if that is neither null nor zero, otherwise
11535 its second argument if it is neither null nor zero, otherwise 0. It
11536 does not evaluate its second argument if its first argument is neither
11541 @cindex logical and operator
11542 @cindex and operator
11543 Return its first argument if neither argument is null or zero, otherwise
11544 0. It does not evaluate its second argument if its first argument is
11547 @item < <= = == != >= >
11554 @cindex comparison operators
11556 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11557 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11558 both arguments to integers and do a numeric comparison; if either
11559 conversion fails, it does a lexicographic comparison using the character
11560 collating sequence specified by the @env{LC_COLLATE} locale.
11565 @node Examples of expr
11566 @subsection Examples of using @command{expr}
11568 @cindex examples of @command{expr}
11569 Here are a few examples, including quoting for shell metacharacters.
11571 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11574 foo=`expr $foo + 1`
11577 To print the non-directory part of the file name stored in
11578 @code{$fname}, which need not contain a @code{/}:
11581 expr $fname : '.*/\(.*\)' '|' $fname
11584 An example showing that @code{\+} is an operator:
11592 expr abc : 'a\(.\)c'
11594 expr index abcdef cz
11597 @error{} expr: syntax error
11598 expr index + index a
11604 @chapter Redirection
11606 @cindex redirection
11607 @cindex commands for redirection
11609 Unix shells commonly provide several forms of @dfn{redirection}---ways
11610 to change the input source or output destination of a command. But one
11611 useful redirection is performed by a separate command, not by the shell;
11612 it's described here.
11615 * tee invocation:: Redirect output to multiple files or processes.
11619 @node tee invocation
11620 @section @command{tee}: Redirect output to multiple files or processes
11623 @cindex pipe fitting
11624 @cindex destinations, multiple output
11625 @cindex read from stdin and write to stdout and files
11627 The @command{tee} command copies standard input to standard output and also
11628 to any files given as arguments. This is useful when you want not only
11629 to send some data down a pipe, but also to save a copy. Synopsis:
11632 tee [@var{option}]@dots{} [@var{file}]@dots{}
11635 If a file being written to does not already exist, it is created. If a
11636 file being written to already exists, the data it previously contained
11637 is overwritten unless the @option{-a} option is used.
11639 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11640 input to standard output, but this is typically not that useful as the
11641 copies are interleaved.
11643 The program accepts the following options. Also see @ref{Common options}.
11650 Append standard input to the given files rather than overwriting
11654 @itemx --ignore-interrupts
11656 @opindex --ignore-interrupts
11657 Ignore interrupt signals.
11661 The @command{tee} command is useful when you happen to be transferring a large
11662 amount of data and also want to summarize that data without reading
11663 it a second time. For example, when you are downloading a DVD image,
11664 you often want to verify its signature or checksum right away.
11665 The inefficient way to do it is simply:
11668 wget http://example.com/some.iso && sha1sum some.iso
11671 One problem with the above is that it makes you wait for the
11672 download to complete before starting the time-consuming SHA1 computation.
11673 Perhaps even more importantly, the above requires reading
11674 the DVD image a second time (the first was from the network).
11676 The efficient way to do it is to interleave the download
11677 and SHA1 computation. Then, you'll get the checksum for
11678 free, because the entire process parallelizes so well:
11681 # slightly contrived, to demonstrate process substitution
11682 wget -O - http://example.com/dvd.iso \
11683 | tee >(sha1sum > dvd.sha1) > dvd.iso
11686 That makes @command{tee} write not just to the expected output file,
11687 but also to a pipe running @command{sha1sum} and saving the final
11688 checksum in a file named @file{dvd.sha1}.
11690 Note, however, that this example relies on a feature of modern shells
11691 called @dfn{process substitution}
11692 (the @samp{>(command)} syntax, above;
11693 @xref{Process Substitution,,Process Substitution, bashref,
11694 The Bash Reference Manual}.),
11695 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11696 but not with @command{/bin/sh}. So if you write code like this
11697 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11699 Since the above example writes to one file and one process,
11700 a more conventional and portable use of @command{tee} is even better:
11703 wget -O - http://example.com/dvd.iso \
11704 | tee dvd.iso | sha1sum > dvd.sha1
11707 You can extend this example to make @command{tee} write to two processes,
11708 computing MD5 and SHA1 checksums in parallel. In this case,
11709 process substitution is required:
11712 wget -O - http://example.com/dvd.iso \
11713 | tee >(sha1sum > dvd.sha1) \
11714 >(md5sum > dvd.md5) \
11718 This technique is also useful when you want to make a @emph{compressed}
11719 copy of the contents of a pipe.
11720 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11721 For a large hierarchy, @samp{du -ak} can run for a long time,
11722 and can easily produce terabytes of data, so you won't want to
11723 rerun the command unnecessarily. Nor will you want to save
11724 the uncompressed output.
11726 Doing it the inefficient way, you can't even start the GUI
11727 until after you've compressed all of the @command{du} output:
11730 du -ak | gzip -9 > /tmp/du.gz
11731 gzip -d /tmp/du.gz | xdiskusage -a
11734 With @command{tee} and process substitution, you start the GUI
11735 right away and eliminate the decompression completely:
11738 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11741 Finally, if you regularly create more than one type of
11742 compressed tarball at once, for example when @code{make dist} creates
11743 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11744 there may be a better way.
11745 Typical @command{automake}-generated @file{Makefile} rules create
11746 the two compressed tar archives with commands in sequence, like this
11747 (slightly simplified):
11750 tardir=your-pkg-M.N
11751 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11752 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11755 However, if the hierarchy you are archiving and compressing is larger
11756 than a couple megabytes, and especially if you are using a multi-processor
11757 system with plenty of memory, then you can do much better by reading the
11758 directory contents only once and running the compression programs in parallel:
11761 tardir=your-pkg-M.N
11762 tar chof - "$tardir" \
11763 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11764 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11770 @node File name manipulation
11771 @chapter File name manipulation
11773 @cindex file name manipulation
11774 @cindex manipulation of file names
11775 @cindex commands for file name manipulation
11777 This section describes commands that manipulate file names.
11780 * basename invocation:: Strip directory and suffix from a file name.
11781 * dirname invocation:: Strip non-directory suffix from a file name.
11782 * pathchk invocation:: Check file name validity and portability.
11786 @node basename invocation
11787 @section @command{basename}: Strip directory and suffix from a file name
11790 @cindex strip directory and suffix from file names
11791 @cindex directory, stripping from file names
11792 @cindex suffix, stripping from file names
11793 @cindex file names, stripping directory and suffix
11794 @cindex leading directory components, stripping
11796 @command{basename} removes any leading directory components from
11797 @var{name}. Synopsis:
11800 basename @var{name} [@var{suffix}]
11803 If @var{suffix} is specified and is identical to the end of @var{name},
11804 it is removed from @var{name} as well. Note that since trailing slashes
11805 are removed prior to suffix matching, @var{suffix} will do nothing if it
11806 contains slashes. @command{basename} prints the result on standard
11809 @c This test is used both here and in the section on dirname.
11810 @macro basenameAndDirname
11811 Together, @command{basename} and @command{dirname} are designed such
11812 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11813 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11814 for everything except file names containing a trailing newline.
11816 @basenameAndDirname
11818 @acronym{POSIX} allows the implementation to define the results if
11819 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11820 @command{basename} returns the empty string. In the latter case, the
11821 result is @samp{//} on platforms where @var{//} is distinct from
11822 @var{/}, and @samp{/} on platforms where there is no difference.
11824 The only options are @option{--help} and @option{--version}. @xref{Common
11825 options}. Options must precede operands.
11833 basename /usr/bin/sort
11836 basename include/stdio.h .h
11840 @node dirname invocation
11841 @section @command{dirname}: Strip non-directory suffix from a file name
11844 @cindex directory components, printing
11845 @cindex stripping non-directory suffix
11846 @cindex non-directory suffix, stripping
11848 @command{dirname} prints all but the final slash-delimited component of
11849 a string (presumably a file name). Synopsis:
11855 If @var{name} is a single component, @command{dirname} prints @samp{.}
11856 (meaning the current directory).
11858 @basenameAndDirname
11860 @acronym{POSIX} allows the implementation to define the results if
11861 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11862 result is @samp{//} on platforms where @var{//} is distinct from
11863 @var{/}, and @samp{/} on platforms where there is no difference.
11865 The only options are @option{--help} and @option{--version}. @xref{Common
11873 # Output "/usr/bin".
11874 dirname /usr/bin/sort
11881 @node pathchk invocation
11882 @section @command{pathchk}: Check file name validity and portability
11885 @cindex file names, checking validity and portability
11886 @cindex valid file names, checking for
11887 @cindex portable file names, checking for
11889 @command{pathchk} checks validity and portability of file names. Synopsis:
11892 pathchk [@var{option}]@dots{} @var{name}@dots{}
11895 For each @var{name}, @command{pathchk} prints an error message if any of
11896 these conditions is true:
11900 One of the existing directories in @var{name} does not have search
11901 (execute) permission,
11903 The length of @var{name} is larger than the maximum supported by the
11906 The length of one component of @var{name} is longer than
11907 its file system's maximum.
11910 A nonexistent @var{name} is not an error, so long a file with that
11911 name could be created under the above conditions.
11913 The program accepts the following options. Also see @ref{Common options}.
11914 Options must precede operands.
11920 Instead of performing checks based on the underlying file system,
11921 print an error message if any of these conditions is true:
11925 A file name is empty.
11928 A file name contains a character outside the @acronym{POSIX} portable file
11929 name character set, namely, the ASCII letters and digits, @samp{.},
11930 @samp{_}, @samp{-}, and @samp{/}.
11933 The length of a file name or one of its components exceeds the
11934 @acronym{POSIX} minimum limits for portability.
11939 Print an error message if a file name is empty, or if it contains a component
11940 that begins with @samp{-}.
11942 @item --portability
11943 @opindex --portability
11944 Print an error message if a file name is not portable to all @acronym{POSIX}
11945 hosts. This option is equivalent to @samp{-p -P}.
11949 @cindex exit status of @command{pathchk}
11953 0 if all specified file names passed all checks,
11958 @node Working context
11959 @chapter Working context
11961 @cindex working context
11962 @cindex commands for printing the working context
11964 This section describes commands that display or alter the context in
11965 which you are working: the current directory, the terminal settings, and
11966 so forth. See also the user-related commands in the next section.
11969 * pwd invocation:: Print working directory.
11970 * stty invocation:: Print or change terminal characteristics.
11971 * printenv invocation:: Print environment variables.
11972 * tty invocation:: Print file name of terminal on standard input.
11976 @node pwd invocation
11977 @section @command{pwd}: Print working directory
11980 @cindex print name of current directory
11981 @cindex current working directory, printing
11982 @cindex working directory, printing
11985 @command{pwd} prints the name of the current directory. Synopsis:
11988 pwd [@var{option}]@dots{}
11991 The program accepts the following options. Also see @ref{Common options}.
11998 If the contents of the environment variable @env{PWD} provide an
11999 absolute name of the current directory with no @samp{.} or @samp{..}
12000 components, but possibly with symbolic links, then output those
12001 contents. Otherwise, fall back to default @option{-P} handling.
12006 @opindex --physical
12007 Print a fully resolved name for the current directory. That is, all
12008 components of the printed name will be actual directory names---none
12009 will be symbolic links.
12012 @cindex symbolic links and @command{pwd}
12013 If @option{-L} and @option{-P} are both given, the last one takes
12014 precedence. If neither option is given, then this implementation uses
12015 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12016 environment variable is set.
12018 @mayConflictWithShellBuiltIn{pwd}
12023 @node stty invocation
12024 @section @command{stty}: Print or change terminal characteristics
12027 @cindex change or print terminal settings
12028 @cindex terminal settings
12029 @cindex line settings of terminal
12031 @command{stty} prints or changes terminal characteristics, such as baud rate.
12035 stty [@var{option}] [@var{setting}]@dots{}
12036 stty [@var{option}]
12039 If given no line settings, @command{stty} prints the baud rate, line
12040 discipline number (on systems that support it), and line settings
12041 that have been changed from the values set by @samp{stty sane}.
12042 By default, mode reading and setting are performed on the tty line
12043 connected to standard input, although this can be modified by the
12044 @option{--file} option.
12046 @command{stty} accepts many non-option arguments that change aspects of
12047 the terminal line operation, as described below.
12049 The program accepts the following options. Also see @ref{Common options}.
12056 Print all current settings in human-readable form. This option may not
12057 be used in combination with any line settings.
12059 @item -F @var{device}
12060 @itemx --file=@var{device}
12063 Set the line opened by the file name specified in @var{device} instead of
12064 the tty line connected to standard input. This option is necessary
12065 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12066 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12067 the @code{clocal} flag is not set. Hence, it is not always possible
12068 to allow the shell to open the device in the traditional manner.
12074 @cindex machine-readable @command{stty} output
12075 Print all current settings in a form that can be used as an argument to
12076 another @command{stty} command to restore the current settings. This option
12077 may not be used in combination with any line settings.
12081 Many settings can be turned off by preceding them with a @samp{-}.
12082 Such arguments are marked below with ``May be negated'' in their
12083 description. The descriptions themselves refer to the positive
12084 case, that is, when @emph{not} negated (unless stated otherwise,
12087 Some settings are not available on all @acronym{POSIX} systems, since they use
12088 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12089 description. On non-@acronym{POSIX} systems, those or other settings also may not
12090 be available, but it's not feasible to document all the variations: just
12096 * Control:: Control settings
12097 * Input:: Input settings
12098 * Output:: Output settings
12099 * Local:: Local settings
12100 * Combination:: Combination settings
12101 * Characters:: Special characters
12102 * Special:: Special settings
12107 @subsection Control settings
12109 @cindex control settings
12115 @cindex two-way parity
12116 Generate parity bit in output and expect parity bit in input.
12122 @cindex even parity
12123 Set odd parity (even if negated). May be negated.
12130 @cindex character size
12131 @cindex eight-bit characters
12132 Set character size to 5, 6, 7, or 8 bits.
12137 Send a hangup signal when the last process closes the tty. May be
12143 Use two stop bits per character (one if negated). May be negated.
12147 Allow input to be received. May be negated.
12151 @cindex modem control
12152 Disable modem control signals. May be negated.
12156 @cindex hardware flow control
12157 @cindex flow control, hardware
12158 @cindex RTS/CTS flow control
12159 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12164 @subsection Input settings
12166 @cindex input settings
12167 These settings control operations on data received from the terminal.
12172 @cindex breaks, ignoring
12173 Ignore break characters. May be negated.
12177 @cindex breaks, cause interrupts
12178 Make breaks cause an interrupt signal. May be negated.
12182 @cindex parity, ignoring
12183 Ignore characters with parity errors. May be negated.
12187 @cindex parity errors, marking
12188 Mark parity errors (with a 255-0-character sequence). May be negated.
12192 Enable input parity checking. May be negated.
12196 @cindex eight-bit input
12197 Clear high (8th) bit of input characters. May be negated.
12201 @cindex newline, translating to return
12202 Translate newline to carriage return. May be negated.
12206 @cindex return, ignoring
12207 Ignore carriage return. May be negated.
12211 @cindex return, translating to newline
12212 Translate carriage return to newline. May be negated.
12216 @cindex input encoding, UTF-8
12217 Assume input characters are UTF-8 encoded. May be negated.
12221 @kindex C-s/C-q flow control
12222 @cindex XON/XOFF flow control
12223 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12230 @cindex software flow control
12231 @cindex flow control, software
12232 Enable sending of @code{stop} character when the system input buffer
12233 is almost full, and @code{start} character when it becomes almost
12234 empty again. May be negated.
12238 @cindex uppercase, translating to lowercase
12239 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12240 negated. Note ilcuc is not implemented, as one would not be able to issue
12241 almost any (lowercase) Unix command, after invoking it.
12245 Allow any character to restart output (only the start character
12246 if negated). Non-@acronym{POSIX}. May be negated.
12250 @cindex beeping at input buffer full
12251 Enable beeping and not flushing input buffer if a character arrives
12252 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12257 @subsection Output settings
12259 @cindex output settings
12260 These settings control operations on data sent to the terminal.
12265 Postprocess output. May be negated.
12269 @cindex lowercase, translating to output
12270 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12271 negated. (Note ouclc is not currently implemented.)
12275 @cindex return, translating to newline
12276 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12280 @cindex newline, translating to crlf
12281 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12286 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12291 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12295 @cindex pad instead of timing for delaying
12296 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12301 @cindex pad character
12302 Use @acronym{ASCII} @sc{del} characters for fill instead of
12303 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12309 Newline delay style. Non-@acronym{POSIX}.
12316 Carriage return delay style. Non-@acronym{POSIX}.
12322 @opindex tab@var{n}
12323 Horizontal tab delay style. Non-@acronym{POSIX}.
12328 Backspace delay style. Non-@acronym{POSIX}.
12333 Vertical tab delay style. Non-@acronym{POSIX}.
12338 Form feed delay style. Non-@acronym{POSIX}.
12343 @subsection Local settings
12345 @cindex local settings
12350 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12351 characters. May be negated.
12355 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12356 special characters. May be negated.
12360 Enable non-@acronym{POSIX} special characters. May be negated.
12364 Echo input characters. May be negated.
12370 Echo @code{erase} characters as backspace-space-backspace. May be
12375 @cindex newline echoing after @code{kill}
12376 Echo a newline after a @code{kill} character. May be negated.
12380 @cindex newline, echoing
12381 Echo newline even if not echoing other characters. May be negated.
12385 @cindex flushing, disabling
12386 Disable flushing after @code{interrupt} and @code{quit} special
12387 characters. May be negated.
12391 @cindex case translation
12392 Enable input and output of uppercase characters by preceding their
12393 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12394 Non-@acronym{POSIX}. May be negated.
12398 @cindex background jobs, stopping at terminal write
12399 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12406 Echo erased characters backward, between @samp{\} and @samp{/}.
12407 Non-@acronym{POSIX}. May be negated.
12413 @cindex control characters, using @samp{^@var{c}}
12414 @cindex hat notation for control characters
12415 Echo control characters in hat notation (@samp{^@var{c}}) instead
12416 of literally. Non-@acronym{POSIX}. May be negated.
12422 Echo the @code{kill} special character by erasing each character on
12423 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12424 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12430 @subsection Combination settings
12432 @cindex combination settings
12433 Combination settings:
12440 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12441 as @code{-parenb cs8}.
12445 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12446 as @code{-parenb cs8}.
12450 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12451 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12455 Reset the @code{erase} and @code{kill} special characters to their default
12462 @c This is too long to write inline.
12464 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12465 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12466 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12467 ff0 isig icanon iexten echo echoe echok -echonl
12468 -noflsh -xcase -tostop -echoprt echoctl echoke
12472 and also sets all special characters to their default values.
12476 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12477 sets the @code{eof} and @code{eol} characters to their default values
12478 if they are the same as the @code{min} and @code{time} characters.
12479 May be negated. If negated, same as @code{raw}.
12486 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12487 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12488 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12492 May be negated. If negated, same as @code{cooked}.
12496 Same as @option{-icanon}. May be negated. If negated, same as
12501 @cindex eight-bit characters
12502 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12503 same as @code{parenb istrip cs7}.
12507 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12508 If negated, same as @code{parenb istrip opost cs7}.
12512 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12516 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12523 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12524 (Used for terminals with uppercase characters only.)
12528 Same as @code{echoe echoctl echoke}.
12532 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12537 @subsection Special characters
12539 @cindex special characters
12540 @cindex characters, special
12542 The special characters' default values vary from system to system.
12543 They are set with the syntax @samp{name value}, where the names are
12544 listed below and the value can be given either literally, in hat
12545 notation (@samp{^@var{c}}), or as an integer which may start with
12546 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12547 any other digit to indicate decimal.
12549 @cindex disabling special characters
12550 @kindex u@r{, and disabling special characters}
12551 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12552 special character. (This is incompatible with Ultrix @command{stty},
12553 which uses a value of @samp{u} to disable a special character. GNU
12554 @command{stty} treats a value @samp{u} like any other, namely to set that
12555 special character to @key{U}.)
12561 Send an interrupt signal.
12565 Send a quit signal.
12569 Erase the last character typed.
12573 Erase the current line.
12577 Send an end of file (terminate the input).
12585 Alternate character to end the line. Non-@acronym{POSIX}.
12589 Switch to a different shell layer. Non-@acronym{POSIX}.
12593 Restart the output after stopping it.
12601 Send a terminal stop signal.
12605 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12609 Redraw the current line. Non-@acronym{POSIX}.
12613 Erase the last word typed. Non-@acronym{POSIX}.
12617 Enter the next character typed literally, even if it is a special
12618 character. Non-@acronym{POSIX}.
12623 @subsection Special settings
12625 @cindex special settings
12630 Set the minimum number of characters that will satisfy a read until
12631 the time value has expired, when @option{-icanon} is set.
12635 Set the number of tenths of a second before reads time out if the minimum
12636 number of characters have not been read, when @option{-icanon} is set.
12638 @item ispeed @var{n}
12640 Set the input speed to @var{n}.
12642 @item ospeed @var{n}
12644 Set the output speed to @var{n}.
12648 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12651 @itemx columns @var{n}
12654 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12660 Print the number of rows and columns that the kernel thinks the
12661 terminal has. (Systems that don't support rows and columns in the kernel
12662 typically use the environment variables @env{LINES} and @env{COLUMNS}
12663 instead; however, GNU @command{stty} does not know anything about them.)
12664 Non-@acronym{POSIX}.
12668 Use line discipline @var{n}. Non-@acronym{POSIX}.
12672 Print the terminal speed.
12675 @cindex baud rate, setting
12676 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12677 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12678 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12679 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12680 support higher speeds. The @command{stty} command includes support
12697 4000000 where the system supports these.
12698 0 hangs up the line if @option{-clocal} is set.
12702 @node printenv invocation
12703 @section @command{printenv}: Print all or some environment variables
12706 @cindex printing all or some environment variables
12707 @cindex environment variables, printing
12709 @command{printenv} prints environment variable values. Synopsis:
12712 printenv [@var{option}] [@var{variable}]@dots{}
12715 If no @var{variable}s are specified, @command{printenv} prints the value of
12716 every environment variable. Otherwise, it prints the value of each
12717 @var{variable} that is set, and nothing for those that are not set.
12719 The only options are a lone @option{--help} or @option{--version}.
12720 @xref{Common options}.
12722 @cindex exit status of @command{printenv}
12726 0 if all variables specified were found
12727 1 if at least one specified variable was not found
12728 2 if a write error occurred
12732 @node tty invocation
12733 @section @command{tty}: Print file name of terminal on standard input
12736 @cindex print terminal file name
12737 @cindex terminal file name, printing
12739 @command{tty} prints the file name of the terminal connected to its standard
12740 input. It prints @samp{not a tty} if standard input is not a terminal.
12744 tty [@var{option}]@dots{}
12747 The program accepts the following option. Also see @ref{Common options}.
12757 Print nothing; only return an exit status.
12761 @cindex exit status of @command{tty}
12765 0 if standard input is a terminal
12766 1 if standard input is not a terminal
12767 2 if given incorrect arguments
12768 3 if a write error occurs
12772 @node User information
12773 @chapter User information
12775 @cindex user information, commands for
12776 @cindex commands for printing user information
12778 This section describes commands that print user-related information:
12779 logins, groups, and so forth.
12782 * id invocation:: Print user identity.
12783 * logname invocation:: Print current login name.
12784 * whoami invocation:: Print effective user ID.
12785 * groups invocation:: Print group names a user is in.
12786 * users invocation:: Print login names of users currently logged in.
12787 * who invocation:: Print who is currently logged in.
12791 @node id invocation
12792 @section @command{id}: Print user identity
12795 @cindex real user and group IDs, printing
12796 @cindex effective user and group IDs, printing
12797 @cindex printing real and effective user and group IDs
12799 @command{id} prints information about the given user, or the process
12800 running it if no user is specified. Synopsis:
12803 id [@var{option}]@dots{} [@var{username}]
12806 By default, it prints the real user ID, real group ID, effective user ID
12807 if different from the real user ID, effective group ID if different from
12808 the real group ID, and supplemental group IDs.
12810 Each of these numeric values is preceded by an identifying string and
12811 followed by the corresponding user or group name in parentheses.
12813 The options cause @command{id} to print only part of the above information.
12814 Also see @ref{Common options}.
12821 Print only the group ID.
12827 Print only the group ID and the supplementary groups.
12833 Print the user or group name instead of the ID number. Requires
12834 @option{-u}, @option{-g}, or @option{-G}.
12840 Print the real, instead of effective, user or group ID. Requires
12841 @option{-u}, @option{-g}, or @option{-G}.
12847 Print only the user ID.
12854 @cindex security context
12855 Print only the security context of the current user.
12856 If SELinux is disabled then print a warning and
12857 set the exit status to 1.
12863 @macro primaryAndSupplementaryGroups{cmd,arg}
12864 Primary and supplementary groups for a process are normally inherited
12865 from its parent and are usually unchanged since login. This means
12866 that if you change the group database after logging in, @command{\cmd\}
12867 will not reflect your changes within your existing login session.
12868 Running @command{\cmd\} with a \arg\ causes the user and group
12869 database to be consulted afresh, and so will give a different result.
12871 @primaryAndSupplementaryGroups{id,user argument}
12873 @node logname invocation
12874 @section @command{logname}: Print current login name
12877 @cindex printing user's login name
12878 @cindex login name, printing
12879 @cindex user name, printing
12882 @command{logname} prints the calling user's name, as found in a
12883 system-maintained file (often @file{/var/run/utmp} or
12884 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12885 for the calling process, @command{logname} prints
12886 an error message and exits with a status of 1.
12888 The only options are @option{--help} and @option{--version}. @xref{Common
12894 @node whoami invocation
12895 @section @command{whoami}: Print effective user ID
12898 @cindex effective user ID, printing
12899 @cindex printing the effective user ID
12901 @command{whoami} prints the user name associated with the current
12902 effective user ID. It is equivalent to the command @samp{id -un}.
12904 The only options are @option{--help} and @option{--version}. @xref{Common
12910 @node groups invocation
12911 @section @command{groups}: Print group names a user is in
12914 @cindex printing groups a user is in
12915 @cindex supplementary groups, printing
12917 @command{groups} prints the names of the primary and any supplementary
12918 groups for each given @var{username}, or the current process if no names
12919 are given. If more than one name is given, the name of each user is
12921 the list of that user's groups and the user name is separated from the
12922 group list by a colon. Synopsis:
12925 groups [@var{username}]@dots{}
12928 The group lists are equivalent to the output of the command @samp{id -Gn}.
12930 @primaryAndSupplementaryGroups{groups,list of users}
12932 The only options are @option{--help} and @option{--version}. @xref{Common
12938 @node users invocation
12939 @section @command{users}: Print login names of users currently logged in
12942 @cindex printing current usernames
12943 @cindex usernames, printing current
12945 @cindex login sessions, printing users with
12946 @command{users} prints on a single line a blank-separated list of user
12947 names of users currently logged in to the current host. Each user name
12948 corresponds to a login session, so if a user has more than one login
12949 session, that user's name will appear the same number of times in the
12958 With no @var{file} argument, @command{users} extracts its information from
12959 a system-maintained file (often @file{/var/run/utmp} or
12960 @file{/etc/utmp}). If a file argument is given, @command{users} uses
12961 that file instead. A common choice is @file{/var/log/wtmp}.
12963 The only options are @option{--help} and @option{--version}. @xref{Common
12969 @node who invocation
12970 @section @command{who}: Print who is currently logged in
12973 @cindex printing current user information
12974 @cindex information, about current users
12976 @command{who} prints information about users who are currently logged on.
12980 @command{who} [@var{option}] [@var{file}] [am i]
12983 @cindex terminal lines, currently used
12985 @cindex remote hostname
12986 If given no non-option arguments, @command{who} prints the following
12987 information for each user currently logged on: login name, terminal
12988 line, login time, and remote hostname or X display.
12992 If given one non-option argument, @command{who} uses that instead of
12993 a default system-maintained file (often @file{/var/run/utmp} or
12994 @file{/etc/utmp}) as the name of the file containing the record of
12995 users logged on. @file{/var/log/wtmp} is commonly given as an argument
12996 to @command{who} to look at who has previously logged on.
13000 If given two non-option arguments, @command{who} prints only the entry
13001 for the user running it (determined from its standard input), preceded
13002 by the hostname. Traditionally, the two arguments given are @samp{am
13003 i}, as in @samp{who am i}.
13006 Time stamps are listed according to the time zone rules specified by
13007 the @env{TZ} environment variable, or by the system default rules if
13008 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13009 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13011 The program accepts the following options. Also see @ref{Common options}.
13019 Same as @samp{-b -d --login -p -r -t -T -u}.
13025 Print the date and time of last system boot.
13031 Print information corresponding to dead processes.
13037 Print a line of column headings.
13043 List only the entries that correspond to processes via which the
13044 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13048 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13049 is not the default because it can cause significant delays on systems with
13050 automatic dial-up internet access.
13054 Same as @samp{who am i}.
13060 List active processes spawned by init.
13066 Print only the login names and the number of users logged on.
13067 Overrides all other options.
13072 @opindex --runlevel
13073 Print the current (and maybe previous) run-level of the init process.
13077 Ignored; for compatibility with other versions of @command{who}.
13083 Print last system clock change.
13088 After the login time, print the number of hours and minutes that the
13089 user has been idle. @samp{.} means the user was active in the last minute.
13090 @samp{old} means the user has been idle for more than 24 hours.
13101 @opindex --writable
13102 @cindex message status
13103 @pindex write@r{, allowed}
13104 After each login name print a character indicating the user's message status:
13107 @samp{+} allowing @code{write} messages
13108 @samp{-} disallowing @code{write} messages
13109 @samp{?} cannot find terminal device
13117 @node System context
13118 @chapter System context
13120 @cindex system context
13121 @cindex context, system
13122 @cindex commands for system context
13124 This section describes commands that print or change system-wide
13128 * arch invocation:: Print machine hardware name.
13129 * date invocation:: Print or set system date and time.
13130 * uname invocation:: Print system information.
13131 * hostname invocation:: Print or set system name.
13132 * hostid invocation:: Print numeric host identifier.
13133 * uptime invocation:: Print system uptime and load
13136 @node SELinux context
13137 @chapter SELinux context
13139 @cindex SELinux context
13140 @cindex SELinux, context
13141 @cindex commands for SELinux context
13143 This section describes commands for operations with SELinux
13147 * chcon invocation:: Change SELinux context of file
13148 * runcon invocation:: Run a command in specified SELinux context
13151 @node chcon invocation
13152 @section @command{chcon}: Change SELinux context of file.
13155 @cindex changing security context
13156 @cindex change SELinux context
13158 @command{chcon} changes the SELinux security context of the selected files.
13162 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
13163 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
13164 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
13167 Change the SELinux security context of each @var{file} to @var{context}.
13168 With @option{--reference}, change the security context of each @var{file}
13169 to that of @var{rfile}.
13171 The program accepts the following options. Also see @ref{Common options}.
13176 @itemx --no-dereference
13178 @opindex --no-dereference
13179 @cindex no dereference
13180 Affect symbolic links instead of any referenced file.
13182 @item --reference=@var{rfile}
13183 @opindex --reference
13184 @cindex reference file
13185 Use @var{rfile}'s security context rather than specifying a @var{context} value.
13190 @opindex --recursive
13191 Operate on files and directories recursively.
13194 @xref{Traversing symlinks}.
13197 @xref{Traversing symlinks}.
13200 @xref{Traversing symlinks}.
13207 Output a diagnostic for every file processed.
13209 @item -u @var{user}
13210 @itemx --user=@var{user}
13213 Set user @var{user} in the target security context.
13215 @item -r @var{role}
13216 @itemx --role=@var{role}
13219 Set role @var{role} in the target security context.
13221 @item -t @var{type}
13222 @itemx --type=@var{type}
13225 Set type @var{type} in the target security context.
13227 @item -l @var{range}
13228 @itemx --range=@var{range}
13231 Set range @var{range} in the target security context.
13237 @node runcon invocation
13238 @section @command{runcon}: Run a command in specified SELinux context
13241 @cindex run with security context
13244 @command{runcon} runs file in specified SELinux security context.
13248 runcon @var{context} @var{command} [@var{args}]
13249 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
13252 Run @var{command} with completely-specified @var{context}, or with
13253 current or transitioned security context modified by one or more of @var{level},
13254 @var{role}, @var{type} and @var{user}.
13256 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
13257 is specified, the first argument is used as the complete context.
13258 Any additional arguments after @var{command}
13259 are interpreted as arguments to the command.
13261 With neither @var{context} nor @var{command}, print the current security context.
13263 The program accepts the following options. Also see @ref{Common options}.
13271 Compute process transition context before modifying.
13273 @item -u @var{user}
13274 @itemx --user=@var{user}
13277 Set user @var{user} in the target security context.
13279 @item -r @var{role}
13280 @itemx --role=@var{role}
13283 Set role @var{role} in the target security context.
13285 @item -t @var{type}
13286 @itemx --type=@var{type}
13289 Set type @var{type} in the target security context.
13291 @item -l @var{range}
13292 @itemx --range=@var{range}
13295 Set range @var{range} in the target security context.
13299 @cindex exit status of @command{runcon}
13303 126 if @var{command} is found but cannot be invoked
13304 127 if @command{runcon} itself fails or if @var{command} cannot be found
13305 the exit status of @var{command} otherwise
13308 @node date invocation
13309 @section @command{date}: Print or set system date and time
13312 @cindex time, printing or setting
13313 @cindex printing the current time
13318 date [@var{option}]@dots{} [+@var{format}]
13319 date [-u|--utc|--universal] @c this avoids a newline in the output
13320 [ MMDDhhmm[[CC]YY][.ss] ]
13324 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13325 it with a default format that depends on the @env{LC_TIME} locale category.
13326 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13327 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13330 Normally, @command{date} uses the time zone rules indicated by the
13331 @env{TZ} environment variable, or the system default rules if @env{TZ}
13332 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13333 @env{TZ}, libc, The GNU C Library Reference Manual}.
13335 @findex strftime @r{and @command{date}}
13336 @cindex time formats
13337 @cindex formatting times
13338 If given an argument that starts with a @samp{+}, @command{date} prints the
13339 current date and time (or the date and time specified by the
13340 @option{--date} option, see below) in the format defined by that argument,
13341 which is similar to that of the @code{strftime} function. Except for
13342 conversion specifiers, which start with @samp{%}, characters in the
13343 format string are printed unchanged. The conversion specifiers are
13349 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13350 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13351 * Literal conversion specifiers:: %[%nt]
13352 * Padding and other flags:: Pad with zeros, spaces, etc.
13353 * Setting the time:: Changing the system clock.
13354 * Options for date:: Instead of the current time.
13356 * Date input formats:: Specifying date strings.
13358 * Examples of date:: Examples.
13361 @node Time conversion specifiers
13362 @subsection Time conversion specifiers
13364 @cindex time conversion specifiers
13365 @cindex conversion specifiers, time
13367 @command{date} conversion specifiers related to times.
13371 hour (@samp{00}@dots{}@samp{23})
13373 hour (@samp{01}@dots{}@samp{12})
13375 hour (@samp{ 0}@dots{}@samp{23}).
13376 This is a @acronym{GNU} extension.
13378 hour (@samp{ 1}@dots{}@samp{12}).
13379 This is a @acronym{GNU} extension.
13381 minute (@samp{00}@dots{}@samp{59})
13383 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13384 This is a @acronym{GNU} extension.
13386 locale's equivalent of either @samp{AM} or @samp{PM};
13387 blank in many locales.
13388 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13390 like @samp{%p}, except lower case.
13391 This is a @acronym{GNU} extension.
13393 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13395 24-hour hour and minute. Same as @samp{%H:%M}.
13396 This is a @acronym{GNU} extension.
13398 @cindex epoch, seconds since
13399 @cindex seconds since the epoch
13400 @cindex beginning of time
13401 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13402 Leap seconds are not counted unless leap second support is available.
13403 @xref{%s-examples}, for examples.
13404 This is a @acronym{GNU} extension.
13406 second (@samp{00}@dots{}@samp{60}).
13407 This may be @samp{60} if leap seconds are supported.
13409 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13411 locale's time representation (e.g., @samp{23:13:48})
13413 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13414 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13415 time zone is determinable. This value reflects the numeric time zone
13416 appropriate for the current time, using the time zone rules specified
13417 by the @env{TZ} environment variable.
13418 The time (and optionally, the time zone rules) can be overridden
13419 by the @option{--date} option.
13420 This is a @acronym{GNU} extension.
13422 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13423 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13424 zone is determinable.
13425 This is a @acronym{GNU} extension.
13427 Numeric time zone to the nearest second with @samp{:} (e.g.,
13428 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13430 This is a @acronym{GNU} extension.
13432 Numeric time zone with @samp{:} using the minimum necessary precision
13433 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13434 no time zone is determinable.
13435 This is a @acronym{GNU} extension.
13437 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13438 time zone is determinable. See @samp{%z} for how it is determined.
13442 @node Date conversion specifiers
13443 @subsection Date conversion specifiers
13445 @cindex date conversion specifiers
13446 @cindex conversion specifiers, date
13448 @command{date} conversion specifiers related to dates.
13452 locale's abbreviated weekday name (e.g., @samp{Sun})
13454 locale's full weekday name, variable length (e.g., @samp{Sunday})
13456 locale's abbreviated month name (e.g., @samp{Jan})
13458 locale's full month name, variable length (e.g., @samp{January})
13460 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13462 century. This is like @samp{%Y}, except the last two digits are omitted.
13463 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13464 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13465 It is normally at least two characters, but it may be more.
13467 day of month (e.g., @samp{01})
13469 date; same as @samp{%m/%d/%y}
13471 day of month, space padded; same as @samp{%_d}
13473 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13474 This is a good choice for a date format, as it is standard and
13475 is easy to sort in the usual case where years are in the range
13477 This is a @acronym{GNU} extension.
13479 year corresponding to the @acronym{ISO} week number, but without the century
13480 (range @samp{00} through @samp{99}). This has the same format and value
13481 as @samp{%y}, except that if the @acronym{ISO} week number (see
13483 to the previous or next year, that year is used instead.
13484 This is a @acronym{GNU} extension.
13486 year corresponding to the @acronym{ISO} week number. This has the
13487 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13489 @samp{%V}) belongs to the previous or next year, that year is used
13491 It is normally useful only if @samp{%V} is also used;
13492 for example, the format @samp{%G-%m-%d} is probably a mistake,
13493 since it combines the ISO week number year with the conventional month and day.
13494 This is a @acronym{GNU} extension.
13498 day of year (@samp{001}@dots{}@samp{366})
13500 month (@samp{01}@dots{}@samp{12})
13502 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13504 week number of year, with Sunday as the first day of the week
13505 (@samp{00}@dots{}@samp{53}).
13506 Days in a new year preceding the first Sunday are in week zero.
13508 @acronym{ISO} week number, that is, the
13509 week number of year, with Monday as the first day of the week
13510 (@samp{01}@dots{}@samp{53}).
13511 If the week containing January 1 has four or more days in
13512 the new year, then it is considered week 1; otherwise, it is week 53 of
13513 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13516 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13518 week number of year, with Monday as first day of week
13519 (@samp{00}@dots{}@samp{53}).
13520 Days in a new year preceding the first Monday are in week zero.
13522 locale's date representation (e.g., @samp{12/31/99})
13524 last two digits of year (@samp{00}@dots{}@samp{99})
13526 year. This is normally at least four characters, but it may be more.
13527 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13528 precedes year @samp{0000}.
13532 @node Literal conversion specifiers
13533 @subsection Literal conversion specifiers
13535 @cindex literal conversion specifiers
13536 @cindex conversion specifiers, literal
13538 @command{date} conversion specifiers that produce literal strings.
13550 @node Padding and other flags
13551 @subsection Padding and other flags
13553 @cindex numeric field padding
13554 @cindex padding of numeric fields
13555 @cindex fields, padding numeric
13557 Unless otherwise specified, @command{date} normally pads numeric fields
13558 with zeros, so that, for
13559 example, numeric months are always output as two digits.
13560 Seconds since the epoch are not padded, though,
13561 since there is no natural width for them.
13563 As a @acronym{GNU} extension, @command{date} recognizes any of the
13564 following optional flags after the @samp{%}:
13568 (hyphen) Do not pad the field; useful if the output is intended for
13571 (underscore) Pad with spaces; useful if you need a fixed
13572 number of characters in the output, but zeros are too distracting.
13574 (zero) Pad with zeros even if the conversion specifier
13575 would normally pad with spaces.
13577 Use upper case characters if possible.
13579 Use opposite case characters if possible.
13580 A field that is normally upper case becomes lower case, and vice versa.
13584 Here are some examples of padding:
13587 date +%d/%m -d "Feb 1"
13589 date +%-d/%-m -d "Feb 1"
13591 date +%_d/%_m -d "Feb 1"
13595 As a @acronym{GNU} extension, you can specify the field width
13596 (after any flag, if present) as a decimal number. If the natural size of the
13597 output of the field has less than the specified number of characters,
13598 the result is written right adjusted and padded to the given
13599 size. For example, @samp{%9B} prints the right adjusted month name in
13600 a field of width 9.
13602 An optional modifier can follow the optional flag and width
13603 specification. The modifiers are:
13607 Use the locale's alternate representation for date and time. This
13608 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13609 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13610 example, @samp{%Ex} might yield a date format based on the Japanese
13614 Use the locale's alternate numeric symbols for numbers. This modifier
13615 applies only to numeric conversion specifiers.
13618 If the format supports the modifier but no alternate representation
13619 is available, it is ignored.
13622 @node Setting the time
13623 @subsection Setting the time
13625 @cindex setting the time
13626 @cindex time setting
13627 @cindex appropriate privileges
13629 If given an argument that does not start with @samp{+}, @command{date} sets
13630 the system clock to the date and time specified by that argument (as
13631 described below). You must have appropriate privileges to set the
13632 system clock. The @option{--date} and @option{--set} options may not be
13633 used with such an argument. The @option{--universal} option may be used
13634 with such an argument to indicate that the specified date and time are
13635 relative to Coordinated Universal Time rather than to the local time
13638 The argument must consist entirely of digits, which have the following
13651 first two digits of year (optional)
13653 last two digits of year (optional)
13658 The @option{--set} option also sets the system clock; see the next section.
13661 @node Options for date
13662 @subsection Options for @command{date}
13664 @cindex @command{date} options
13665 @cindex options for @command{date}
13667 The program accepts the following options. Also see @ref{Common options}.
13671 @item -d @var{datestr}
13672 @itemx --date=@var{datestr}
13675 @cindex parsing date strings
13676 @cindex date strings, parsing
13677 @cindex arbitrary date strings, parsing
13680 @opindex next @var{day}
13681 @opindex last @var{day}
13682 Display the date and time specified in @var{datestr} instead of the
13683 current date and time. @var{datestr} can be in almost any common
13684 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13685 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13686 14:19:13.489392193 +0530"} specifies the instant of time that is
13687 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13688 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13689 Note: input currently must be in locale independent format. E.g., the
13690 LC_TIME=C below is needed to print back the correct date in many locales:
13692 date -d "$(LC_TIME=C date)"
13694 @xref{Date input formats}.
13696 @item -f @var{datefile}
13697 @itemx --file=@var{datefile}
13700 Parse each line in @var{datefile} as with @option{-d} and display the
13701 resulting date and time. If @var{datefile} is @samp{-}, use standard
13702 input. This is useful when you have many dates to process, because the
13703 system overhead of starting up the @command{date} executable many times can
13706 @item -r @var{file}
13707 @itemx --reference=@var{file}
13709 @opindex --reference
13710 Display the date and time of the last modification of @var{file},
13711 instead of the current date and time.
13718 @opindex --rfc-2822
13719 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13720 %z}, evaluated in the C locale so abbreviations are always in English.
13724 Fri, 09 Sep 2005 13:51:39 -0700
13727 This format conforms to
13728 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13729 @acronym{RFCs} 2822} and
13730 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13731 current and previous standards for Internet email.
13733 @item --rfc-3339=@var{timespec}
13734 @opindex --rfc-3339=@var{timespec}
13735 Display the date using a format specified by
13736 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13737 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13738 format, except that it also permits applications to use a space rather
13739 than a @samp{T} to separate dates from times. Unlike the other
13740 standard formats, @acronym{RFC} 3339 format is always suitable as
13741 input for the @option{--date} (@option{-d}) and @option{--file}
13742 (@option{-f}) options, regardless of the current locale.
13744 The argument @var{timespec} specifies how much of the time to include.
13745 It can be one of the following:
13749 Print just the full-date, e.g., @samp{2005-09-14}.
13750 This is equivalent to the format @samp{%Y-%m-%d}.
13753 Print the full-date and full-time separated by a space, e.g.,
13754 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13755 time-offset; here the @samp{+05:30} means that local time is five
13756 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13757 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13760 Like @samp{seconds}, but also print nanoseconds, e.g.,
13761 @samp{2005-09-14 00:56:06.998458565+05:30}.
13762 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13766 @item -s @var{datestr}
13767 @itemx --set=@var{datestr}
13770 Set the date and time to @var{datestr}. See @option{-d} above.
13777 @opindex --universal
13778 @cindex Coordinated Universal Time
13780 @cindex Greenwich Mean Time
13783 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13784 @env{TZ} environment variable were set to the string @samp{UTC0}.
13786 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13787 historical reasons.
13791 @node Examples of date
13792 @subsection Examples of @command{date}
13794 @cindex examples of @command{date}
13796 Here are a few examples. Also see the documentation for the @option{-d}
13797 option in the previous section.
13802 To print the date of the day before yesterday:
13805 date --date='2 days ago'
13809 To print the date of the day three months and one day hence:
13812 date --date='3 months 1 day'
13816 To print the day of year of Christmas in the current year:
13819 date --date='25 Dec' +%j
13823 To print the current full month name and the day of the month:
13829 But this may not be what you want because for the first nine days of
13830 the month, the @samp{%d} expands to a zero-padded two-digit field,
13831 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13834 To print a date without the leading zero for one-digit days
13835 of the month, you can use the (@acronym{GNU} extension)
13836 @samp{-} flag to suppress
13837 the padding altogether:
13840 date -d 1may '+%B %-d
13844 To print the current date and time in the format required by many
13845 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13848 date +%m%d%H%M%Y.%S
13852 To set the system clock forward by two minutes:
13855 date --set='+2 minutes'
13859 To print the date in @acronym{RFC} 2822 format,
13860 use @samp{date --rfc-2822}. Here is some example output:
13863 Fri, 09 Sep 2005 13:51:39 -0700
13866 @anchor{%s-examples}
13868 To convert a date string to the number of seconds since the epoch
13869 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13870 the @samp{%s} format. That can be useful in sorting and/or graphing
13871 and/or comparing data by date. The following command outputs the
13872 number of the seconds since the epoch for the time two minutes after the
13876 date --date='1970-01-01 00:02:00 +0000' +%s
13880 If you do not specify time zone information in the date string,
13881 @command{date} uses your computer's idea of the time zone when
13882 interpreting the string. For example, if your computer's time zone is
13883 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13884 seconds) behind UTC:
13887 # local time zone used
13888 date --date='1970-01-01 00:02:00' +%s
13893 If you're sorting or graphing dated data, your raw date values may be
13894 represented as seconds since the epoch. But few people can look at
13895 the date @samp{946684800} and casually note ``Oh, that's the first second
13896 of the year 2000 in Greenwich, England.''
13899 date --date='2000-01-01 UTC' +%s
13903 An alternative is to use the @option{--utc} (@option{-u}) option.
13904 Then you may omit @samp{UTC} from the date string. Although this
13905 produces the same result for @samp{%s} and many other format sequences,
13906 with a time zone offset different from zero, it would give a different
13907 result for zone-dependent formats like @samp{%z}.
13910 date -u --date=2000-01-01 +%s
13914 To convert such an unwieldy number of seconds back to
13915 a more readable form, use a command like this:
13918 # local time zone used
13919 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13920 1999-12-31 19:00:00 -0500
13923 Or if you do not mind depending on the @samp{@@} feature present since
13924 coreutils 5.3.0, you could shorten this to:
13927 date -d @@946684800 +"%F %T %z"
13928 1999-12-31 19:00:00 -0500
13931 Often it is better to output UTC-relative date and time:
13934 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13935 2000-01-01 00:00:00 +0000
13941 @node arch invocation
13942 @section @command{arch}: Print machine hardware name
13945 @cindex print machine hardware name
13946 @cindex system information, printing
13948 @command{arch} prints the machine hardware name,
13949 and is equivalent to @samp{uname -m}.
13953 arch [@var{option}]
13956 The program accepts the @ref{Common options} only.
13961 @node uname invocation
13962 @section @command{uname}: Print system information
13965 @cindex print system information
13966 @cindex system information, printing
13968 @command{uname} prints information about the machine and operating system
13969 it is run on. If no options are given, @command{uname} acts as if the
13970 @option{-s} option were given. Synopsis:
13973 uname [@var{option}]@dots{}
13976 If multiple options or @option{-a} are given, the selected information is
13977 printed in this order:
13980 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13981 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13984 The information may contain internal spaces, so such output cannot be
13985 parsed reliably. In the following example, @var{release} is
13986 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13990 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13994 The program accepts the following options. Also see @ref{Common options}.
14002 Print all of the below information, except omit the processor type
14003 and the hardware platform name if they are unknown.
14006 @itemx --hardware-platform
14008 @opindex --hardware-platform
14009 @cindex implementation, hardware
14010 @cindex hardware platform
14011 @cindex platform, hardware
14012 Print the hardware platform name
14013 (sometimes called the hardware implementation).
14014 Print @samp{unknown} if the kernel does not make this information
14015 easily available, as is the case with Linux kernels.
14021 @cindex machine type
14022 @cindex hardware class
14023 @cindex hardware type
14024 Print the machine hardware name (sometimes called the hardware class
14030 @opindex --nodename
14033 @cindex network node name
14034 Print the network node hostname.
14039 @opindex --processor
14040 @cindex host processor type
14041 Print the processor type (sometimes called the instruction set
14042 architecture or ISA).
14043 Print @samp{unknown} if the kernel does not make this information
14044 easily available, as is the case with Linux kernels.
14047 @itemx --operating-system
14049 @opindex --operating-system
14050 @cindex operating system name
14051 Print the name of the operating system.
14054 @itemx --kernel-release
14056 @opindex --kernel-release
14057 @cindex kernel release
14058 @cindex release of kernel
14059 Print the kernel release.
14062 @itemx --kernel-name
14064 @opindex --kernel-name
14065 @cindex kernel name
14066 @cindex name of kernel
14067 Print the kernel name.
14068 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14069 ``the implementation of the operating system'', because the
14070 @acronym{POSIX} specification itself has no notion of ``kernel''.
14071 The kernel name might be the same as the operating system name printed
14072 by the @option{-o} or @option{--operating-system} option, but it might
14073 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14074 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14078 @itemx --kernel-version
14080 @opindex --kernel-version
14081 @cindex kernel version
14082 @cindex version of kernel
14083 Print the kernel version.
14090 @node hostname invocation
14091 @section @command{hostname}: Print or set system name
14094 @cindex setting the hostname
14095 @cindex printing the hostname
14096 @cindex system name, printing
14097 @cindex appropriate privileges
14099 With no arguments, @command{hostname} prints the name of the current host
14100 system. With one argument, it sets the current host name to the
14101 specified string. You must have appropriate privileges to set the host
14105 hostname [@var{name}]
14108 The only options are @option{--help} and @option{--version}. @xref{Common
14114 @node hostid invocation
14115 @section @command{hostid}: Print numeric host identifier.
14118 @cindex printing the host identifier
14120 @command{hostid} prints the numeric identifier of the current host
14121 in hexadecimal. This command accepts no arguments.
14122 The only options are @option{--help} and @option{--version}.
14123 @xref{Common options}.
14125 For example, here's what it prints on one system I use:
14132 On that system, the 32-bit quantity happens to be closely
14133 related to the system's Internet address, but that isn't always
14138 @node uptime invocation
14139 @section @command{uptime}: Print system uptime and load
14142 @cindex printing the system uptime and load
14144 @command{uptime} prints the current time, the system's uptime, the
14145 number of logged-in users and the current load average.
14147 If an argument is specified, it is used as the file to be read
14148 to discover how many users are logged in. If no argument is
14149 specified, a system default is used (@command{uptime --help} indicates
14150 the default setting).
14152 The only options are @option{--help} and @option{--version}.
14153 @xref{Common options}.
14155 For example, here's what it prints right now on one system I use:
14159 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14162 The precise method of calculation of load average varies somewhat
14163 between systems. Some systems calculate it as the average number of
14164 runnable processes over the last 1, 5 and 15 minutes, but some systems
14165 also include processes in the uninterruptible sleep state (that is,
14166 those processes which are waiting for disk I/O). The Linux kernel
14167 includes uninterruptible processes.
14169 @node Modified command invocation
14170 @chapter Modified command invocation
14172 @cindex modified command invocation
14173 @cindex invocation of commands, modified
14174 @cindex commands for invoking other commands
14176 This section describes commands that run other commands in some context
14177 different than the current one: a modified environment, as a different
14181 * chroot invocation:: Modify the root directory.
14182 * env invocation:: Modify environment variables.
14183 * nice invocation:: Modify niceness.
14184 * nohup invocation:: Immunize to hangups.
14185 * stdbuf invocation:: Modify buffering of standard streams.
14186 * su invocation:: Modify user and group ID.
14187 * timeout invocation:: Run with time limit.
14191 @node chroot invocation
14192 @section @command{chroot}: Run a command with a different root directory
14195 @cindex running a program in a specified root directory
14196 @cindex root directory, running a program in a specified
14198 @command{chroot} runs a command with a specified root directory.
14199 On many systems, only the super-user can do this.@footnote{However,
14200 some systems (e.g., FreeBSD) can be configured to allow certain regular
14201 users to use the @code{chroot} system call, and hence to run this program.
14202 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14203 underlying function is non-privileged due to lack of support in MS-Windows.}
14207 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14208 chroot @var{option}
14211 Ordinarily, file names are looked up starting at the root of the
14212 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14213 the directory @var{newroot} (which must exist) and then runs
14214 @var{command} with optional @var{args}. If @var{command} is not
14215 specified, the default is the value of the @env{SHELL} environment
14216 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14217 @var{command} must not be a special built-in utility
14218 (@pxref{Special built-in utilities}).
14220 The program accepts the following options. Also see @ref{Common options}.
14221 Options must precede operands.
14225 @itemx --userspec=@var{user}[:@var{group}]
14226 @opindex --userspec
14227 By default, @var{command} is run with the same credentials
14228 as the invoking process.
14229 Use this option to run it as a different @var{user} and/or with a
14230 different primary @var{group}.
14232 @itemx --groups=@var{groups}
14234 Use this option to specify the supplementary @var{groups} to be
14235 used by the new process.
14236 The items in the list (names or numeric IDs) must be separated by commas.
14240 Here are a few tips to help avoid common problems in using chroot.
14241 To start with a simple example, make @var{command} refer to a statically
14242 linked binary. If you were to use a dynamically linked executable, then
14243 you'd have to arrange to have the shared libraries in the right place under
14244 your new root directory.
14246 For example, if you create a statically linked @command{ls} executable,
14247 and put it in @file{/tmp/empty}, you can run this command as root:
14250 $ chroot /tmp/empty /ls -Rl /
14253 Then you'll see output like this:
14258 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14261 If you want to use a dynamically linked executable, say @command{bash},
14262 then first run @samp{ldd bash} to see what shared objects it needs.
14263 Then, in addition to copying the actual binary, also copy the listed
14264 files to the required positions under your intended new root directory.
14265 Finally, if the executable requires any other files (e.g., data, state,
14266 device files), copy them into place, too.
14268 @cindex exit status of @command{chroot}
14272 1 if @command{chroot} itself fails
14273 126 if @var{command} is found but cannot be invoked
14274 127 if @var{command} cannot be found
14275 the exit status of @var{command} otherwise
14279 @node env invocation
14280 @section @command{env}: Run a command in a modified environment
14283 @cindex environment, running a program in a modified
14284 @cindex modified environment, running a program in a
14285 @cindex running a program in a modified environment
14287 @command{env} runs a command with a modified environment. Synopses:
14290 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14291 [@var{command} [@var{args}]@dots{}]
14295 Operands of the form @samp{@var{variable}=@var{value}} set
14296 the environment variable @var{variable} to value @var{value}.
14297 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14298 to an empty value is different from unsetting it.
14299 These operands are evaluated left-to-right, so if two operands
14300 mention the same variable the earlier is ignored.
14302 Environment variable names can be empty, and can contain any
14303 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14304 However, it is wise to limit yourself to names that
14305 consist solely of underscores, digits, and @acronym{ASCII} letters,
14306 and that begin with a non-digit, as applications like the shell do not
14307 work well with other names.
14310 The first operand that does not contain the character @samp{=}
14311 specifies the program to invoke; it is
14312 searched for according to the @env{PATH} environment variable. Any
14313 remaining arguments are passed as arguments to that program.
14314 The program should not be a special built-in utility
14315 (@pxref{Special built-in utilities}).
14317 @cindex environment, printing
14319 If no command name is specified following the environment
14320 specifications, the resulting environment is printed. This is like
14321 specifying the @command{printenv} program.
14323 The program accepts the following options. Also see @ref{Common options}.
14324 Options must precede operands.
14328 @item -u @var{name}
14329 @itemx --unset=@var{name}
14332 Remove variable @var{name} from the environment, if it was in the
14337 @itemx --ignore-environment
14340 @opindex --ignore-environment
14341 Start with an empty environment, ignoring the inherited environment.
14345 @cindex exit status of @command{env}
14349 0 if no @var{command} is specified and the environment is output
14350 1 if @command{env} itself fails
14351 126 if @var{command} is found but cannot be invoked
14352 127 if @var{command} cannot be found
14353 the exit status of @var{command} otherwise
14357 @node nice invocation
14358 @section @command{nice}: Run a command with modified niceness
14362 @cindex scheduling, affecting
14363 @cindex appropriate privileges
14365 @command{nice} prints or modifies a process's @dfn{niceness},
14366 a parameter that affects whether the process is scheduled favorably.
14370 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14373 If no arguments are given, @command{nice} prints the current niceness.
14374 Otherwise, @command{nice} runs the given @var{command} with its
14375 niceness adjusted. By default, its niceness is incremented by 10.
14377 Niceness values range at least from @minus{}20 (process has high priority
14378 and gets more resources, thus slowing down other processes) through 19
14379 (process has lower priority and runs slowly itself, but has less impact
14380 on the speed of other running processes). Some systems
14381 may have a wider range of nicenesses; conversely, other systems may
14382 enforce more restrictive limits. An attempt to set the niceness
14383 outside the supported range is treated as an attempt to use the
14384 minimum or maximum supported value.
14386 A niceness should not be confused with a scheduling priority, which
14387 lets applications determine the order in which threads are scheduled
14388 to run. Unlike a priority, a niceness is merely advice to the
14389 scheduler, which the scheduler is free to ignore. Also, as a point of
14390 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14391 terms of a @dfn{nice value}, which is the nonnegative difference
14392 between a niceness and the minimum niceness. Though @command{nice}
14393 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14394 term ``niceness'' for compatibility with historical practice.
14396 @var{command} must not be a special built-in utility (@pxref{Special
14397 built-in utilities}).
14399 @mayConflictWithShellBuiltIn{nice}
14401 The program accepts the following option. Also see @ref{Common options}.
14402 Options must precede operands.
14405 @item -n @var{adjustment}
14406 @itemx --adjustment=@var{adjustment}
14408 @opindex --adjustment
14409 Add @var{adjustment} instead of 10 to the command's niceness. If
14410 @var{adjustment} is negative and you lack appropriate privileges,
14411 @command{nice} issues a warning but otherwise acts as if you specified
14414 For compatibility @command{nice} also supports an obsolete
14415 option syntax @option{-@var{adjustment}}. New scripts should use
14416 @option{-n @var{adjustment}} instead.
14420 @cindex exit status of @command{nice}
14424 0 if no @var{command} is specified and the niceness is output
14425 1 if @command{nice} itself fails
14426 126 if @var{command} is found but cannot be invoked
14427 127 if @var{command} cannot be found
14428 the exit status of @var{command} otherwise
14431 It is sometimes useful to run a non-interactive program with reduced niceness.
14434 $ nice factor 4611686018427387903
14437 Since @command{nice} prints the current niceness,
14438 you can invoke it through itself to demonstrate how it works.
14440 The default behavior is to increase the niceness by @samp{10}:
14451 The @var{adjustment} is relative to the current niceness. In the
14452 next example, the first @command{nice} invocation runs the second one
14453 with niceness 10, and it in turn runs the final one with a niceness
14457 $ nice nice -n 3 nice
14461 Specifying a niceness larger than the supported range
14462 is the same as specifying the maximum supported value:
14465 $ nice -n 10000000000 nice
14469 Only a privileged user may run a process with lower niceness:
14473 nice: cannot set niceness: Permission denied
14475 $ sudo nice -n -1 nice
14480 @node nohup invocation
14481 @section @command{nohup}: Run a command immune to hangups
14484 @cindex hangups, immunity to
14485 @cindex immunity to hangups
14486 @cindex logging out and continuing to run
14489 @command{nohup} runs the given @var{command} with hangup signals ignored,
14490 so that the command can continue running in the background after you log
14494 nohup @var{command} [@var{arg}]@dots{}
14497 If standard input is a terminal, it is redirected from
14498 @file{/dev/null} so that terminal sessions do not mistakenly consider
14499 the terminal to be used by the command. This is a @acronym{GNU}
14500 extension; programs intended to be portable to non-@acronym{GNU} hosts
14501 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14505 If standard output is a terminal, the command's standard output is appended
14506 to the file @file{nohup.out}; if that cannot be written to, it is appended
14507 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14508 command is not run.
14509 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14510 @command{nohup} is made readable and writable only to the user,
14511 regardless of the current umask settings.
14513 If standard error is a terminal, it is normally redirected to the same file
14514 descriptor as the (possibly-redirected) standard output.
14515 However, if standard output is closed, standard error terminal output
14516 is instead appended to the file @file{nohup.out} or
14517 @file{$HOME/nohup.out} as above.
14519 To capture the command's output to a file other than @file{nohup.out}
14520 you can redirect it. For example, to capture the output of
14524 nohup make > make.log
14527 @command{nohup} does not automatically put the command it runs in the
14528 background; you must do that explicitly, by ending the command line
14529 with an @samp{&}. Also, @command{nohup} does not alter the
14530 niceness of @var{command}; use @command{nice} for that,
14531 e.g., @samp{nohup nice @var{command}}.
14533 @var{command} must not be a special built-in utility (@pxref{Special
14534 built-in utilities}).
14536 The only options are @option{--help} and @option{--version}. @xref{Common
14537 options}. Options must precede operands.
14539 @cindex exit status of @command{nohup}
14543 126 if @var{command} is found but cannot be invoked
14544 127 if @command{nohup} itself fails or if @var{command} cannot be found
14545 the exit status of @var{command} otherwise
14549 @node stdbuf invocation
14550 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14553 @cindex standard streams, buffering
14554 @cindex line buffered
14556 @command{stdbuf} allows one to modify the buffering operations of the
14557 three standard I/O streams associated with a program. Synopsis:
14560 stdbuf @var{option}@dots{} @var{command}
14563 Any additional @var{arg}s are passed as additional arguments to the
14566 The program accepts the following options. Also see @ref{Common options}.
14570 @item -i @var{mode}
14571 @itemx --input=@var{mode}
14574 Adjust the standard input stream buffering.
14576 @item -o @var{mode}
14577 @itemx --output=@var{mode}
14580 Adjust the standard output stream buffering.
14582 @item -e @var{mode}
14583 @itemx --error=@var{mode}
14586 Adjust the standard error stream buffering.
14590 The @var{mode} can be specified as follows:
14595 Set the stream to line buffered mode.
14596 In this mode data is coalesced until a newline is output or
14597 input is read from any stream attached to a terminal device.
14598 This option is invalid with standard input.
14601 Disable buffering of the selected stream.
14602 In this mode data is output immediately and only the
14603 amount of data requested is read from input.
14606 Specify the size of the buffer to use in fully buffered mode.
14607 @multiplierSuffixesNoBlocks{size}
14611 NOTE: If @var{command} adjusts the buffering of its standard streams
14612 (@command{tee} does for e.g.) then that will override corresponding settings
14613 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14614 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14615 by @command{stdbuf} settings.
14617 @cindex exit status of @command{stdbuf}
14621 125 if @command{stdbuf} itself fails
14622 126 if @var{command} is found but cannot be invoked
14623 127 if @var{command} cannot be found
14624 the exit status of @var{command} otherwise
14628 @node su invocation
14629 @section @command{su}: Run a command with substitute user and group ID
14632 @cindex substitute user and group IDs
14633 @cindex user ID, switching
14634 @cindex super-user, becoming
14635 @cindex root, becoming
14637 @command{su} allows one user to temporarily become another user. It runs a
14638 command (often an interactive shell) with the real and effective user
14639 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14642 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14645 @cindex passwd entry, and @command{su} shell
14647 @flindex /etc/passwd
14648 If no @var{user} is given, the default is @code{root}, the super-user.
14649 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14650 @file{/bin/sh} if none is specified there. If @var{user} has a
14651 password, @command{su} prompts for the password unless run by a user with
14652 effective user ID of zero (the super-user).
14658 @cindex login shell
14659 By default, @command{su} does not change the current directory.
14660 It sets the environment variables @env{HOME} and @env{SHELL}
14661 from the password entry for @var{user}, and if @var{user} is not
14662 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14663 By default, the shell is not a login shell.
14665 Any additional @var{arg}s are passed as additional arguments to the
14668 @cindex @option{-su}
14669 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14670 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14671 to certain shells, etc.).
14674 @command{su} can optionally be compiled to use @code{syslog} to report
14675 failed, and optionally successful, @command{su} attempts. (If the system
14676 supports @code{syslog}.) However, GNU @command{su} does not check if the
14677 user is a member of the @code{wheel} group; see below.
14679 The program accepts the following options. Also see @ref{Common options}.
14682 @item -c @var{command}
14683 @itemx --command=@var{command}
14686 Pass @var{command}, a single command line to run, to the shell with
14687 a @option{-c} option instead of starting an interactive shell.
14694 @cindex file name pattern expansion, disabled
14695 @cindex globbing, disabled
14696 Pass the @option{-f} option to the shell. This probably only makes sense
14697 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14698 option prevents reading the startup file (@file{.cshrc}). With
14699 Bourne-like shells, the @option{-f} option disables file name pattern
14700 expansion (globbing), which is not likely to be useful.
14708 @c other variables already indexed above
14711 @cindex login shell, creating
14712 Make the shell a login shell. This means the following. Unset all
14713 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14714 (which are set as described above), and @env{USER} and @env{LOGNAME}
14715 (which are set, even for the super-user, as described above), and set
14716 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14717 directory. Prepend @samp{-} to the shell's name, intended to make it
14718 read its login startup file(s).
14722 @itemx --preserve-environment
14725 @opindex --preserve-environment
14726 @cindex environment, preserving
14727 @flindex /etc/shells
14728 @cindex restricted shell
14729 Do not change the environment variables @env{HOME}, @env{USER},
14730 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14731 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14732 entry, unless the user running @command{su} is not the super-user and
14733 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14734 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14735 if that file does not exist. Parts of what this option does can be
14736 overridden by @option{--login} and @option{--shell}.
14738 @item -s @var{shell}
14739 @itemx --shell=@var{shell}
14742 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14743 unless the user running @command{su} is not the super-user and @var{user}'s
14744 shell is restricted (see @option{-m} just above).
14748 @cindex exit status of @command{su}
14752 1 if @command{su} itself fails
14753 126 if subshell is found but cannot be invoked
14754 127 if subshell cannot be found
14755 the exit status of the subshell otherwise
14758 @cindex wheel group, not supported
14759 @cindex group wheel, not supported
14761 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14763 (This section is by Richard Stallman.)
14767 Sometimes a few of the users try to hold total power over all the
14768 rest. For example, in 1984, a few users at the MIT AI lab decided to
14769 seize power by changing the operator password on the Twenex system and
14770 keeping it secret from everyone else. (I was able to thwart this coup
14771 and give power back to the users by patching the kernel, but I
14772 wouldn't know how to do that in Unix.)
14774 However, occasionally the rulers do tell someone. Under the usual
14775 @command{su} mechanism, once someone learns the root password who
14776 sympathizes with the ordinary users, he or she can tell the rest. The
14777 ``wheel group'' feature would make this impossible, and thus cement the
14778 power of the rulers.
14780 I'm on the side of the masses, not that of the rulers. If you are
14781 used to supporting the bosses and sysadmins in whatever they do, you
14782 might find this idea strange at first.
14785 @node timeout invocation
14786 @section @command{timeout}: Run a command with a time limit
14790 @cindex run commands with bounded time
14792 @command{timeout} runs the given @var{command} and kills it if it is
14793 still running after the specified time interval. Synopsis:
14796 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14800 @var{number} is an integer followed by an optional unit; the default
14801 is seconds. The units are:
14814 @var{command} must not be a special built-in utility (@pxref{Special
14815 built-in utilities}).
14817 The program accepts the following option. Also see @ref{Common options}.
14818 Options must precede operands.
14821 @item -s @var{signal}
14822 @itemx --signal=@var{signal}
14825 Send this @var{signal} to @var{command} on timeout, rather than the
14826 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
14827 or a number. Also see @xref{Signal specifications}.
14831 @cindex exit status of @command{timeout}
14835 124 if @var{command} times out
14836 125 if @command{timeout} itself fails
14837 126 if @var{command} is found but cannot be invoked
14838 127 if @var{command} cannot be found
14839 the exit status of @var{command} otherwise
14843 @node Process control
14844 @chapter Process control
14846 @cindex processes, commands for controlling
14847 @cindex commands for controlling processes
14850 * kill invocation:: Sending a signal to processes.
14854 @node kill invocation
14855 @section @command{kill}: Send a signal to processes
14858 @cindex send a signal to processes
14860 The @command{kill} command sends a signal to processes, causing them
14861 to terminate or otherwise act upon receiving the signal in some way.
14862 Alternatively, it lists information about signals. Synopses:
14865 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
14866 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
14869 @mayConflictWithShellBuiltIn{kill}
14871 The first form of the @command{kill} command sends a signal to all
14872 @var{pid} arguments. The default signal to send if none is specified
14873 is @samp{TERM}. The special signal number @samp{0} does not denote a
14874 valid signal, but can be used to test whether the @var{pid} arguments
14875 specify processes to which a signal could be sent.
14877 If @var{pid} is positive, the signal is sent to the process with the
14878 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
14879 processes in the process group of the current process. If @var{pid}
14880 is @minus{}1, the signal is sent to all processes for which the user has
14881 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
14882 is sent to all processes in the process group that equals the absolute
14883 value of @var{pid}.
14885 If @var{pid} is not positive, a system-dependent set of system
14886 processes is excluded from the list of processes to which the signal
14889 If a negative @var{pid} argument is desired as the first one, it
14890 should be preceded by @option{--}. However, as a common extension to
14891 @acronym{POSIX}, @option{--} is not required with @samp{kill
14892 -@var{signal} -@var{pid}}. The following commands are equivalent:
14901 The first form of the @command{kill} command succeeds if every @var{pid}
14902 argument specifies at least one process that the signal was sent to.
14904 The second form of the @command{kill} command lists signal information.
14905 Either the @option{-l} or @option{--list} option, or the @option{-t}
14906 or @option{--table} option must be specified. Without any
14907 @var{signal} argument, all supported signals are listed. The output
14908 of @option{-l} or @option{--list} is a list of the signal names, one
14909 per line; if @var{signal} is already a name, the signal number is
14910 printed instead. The output of @option{-t} or @option{--table} is a
14911 table of signal numbers, names, and descriptions. This form of the
14912 @command{kill} command succeeds if all @var{signal} arguments are valid
14913 and if there is no output error.
14915 The @command{kill} command also supports the @option{--help} and
14916 @option{--version} options. @xref{Common options}.
14918 A @var{signal} may be a signal name like @samp{HUP}, or a signal
14919 number like @samp{1}, or an exit status of a process terminated by the
14920 signal. A signal name can be given in canonical form or prefixed by
14921 @samp{SIG}. The case of the letters is ignored, except for the
14922 @option{-@var{signal}} option which must use upper case to avoid
14923 ambiguity with lower case option letters. For a list of supported
14924 signal names and numbers see @xref{Signal specifications}.
14929 @cindex delaying commands
14930 @cindex commands for delaying
14932 @c Perhaps @command{wait} or other commands should be described here also?
14935 * sleep invocation:: Delay for a specified time.
14939 @node sleep invocation
14940 @section @command{sleep}: Delay for a specified time
14943 @cindex delay for a specified time
14945 @command{sleep} pauses for an amount of time specified by the sum of
14946 the values of the command line arguments.
14950 sleep @var{number}[smhd]@dots{}
14954 Each argument is a number followed by an optional unit; the default
14955 is seconds. The units are:
14968 Historical implementations of @command{sleep} have required that
14969 @var{number} be an integer, and only accepted a single argument
14970 without a suffix. However, GNU @command{sleep} accepts
14971 arbitrary floating point numbers (using a period before any fractional
14974 The only options are @option{--help} and @option{--version}. @xref{Common
14977 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
14978 @mayConflictWithShellBuiltIn{sleep}
14983 @node Numeric operations
14984 @chapter Numeric operations
14986 @cindex numeric operations
14987 These programs do numerically-related operations.
14990 * factor invocation:: Show factors of numbers.
14991 * seq invocation:: Print sequences of numbers.
14995 @node factor invocation
14996 @section @command{factor}: Print prime factors
14999 @cindex prime factors
15001 @command{factor} prints prime factors. Synopses:
15004 factor [@var{number}]@dots{}
15005 factor @var{option}
15008 If no @var{number} is specified on the command line, @command{factor} reads
15009 numbers from standard input, delimited by newlines, tabs, or spaces.
15011 The @command{factor} command supports only a small number of options:
15015 Print a short help on standard output, then exit without further
15019 Print the program version on standard output, then exit without further
15023 Factoring the product of the eighth and ninth Mersenne primes
15024 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15027 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15028 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15029 4951760154835678088235319297: 2147483647 2305843009213693951
15033 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15034 about 20 seconds on the same machine.
15036 Factoring large prime numbers is, in general, hard. The Pollard Rho
15037 algorithm used by @command{factor} is particularly effective for
15038 numbers with relatively small factors. If you wish to factor large
15039 numbers which do not have small factors (for example, numbers which
15040 are the product of two large primes), other methods are far better.
15042 If @command{factor} is built without using GNU MP, only
15043 single-precision arithmetic is available, and so large numbers
15044 (typically @math{2^{64}} and above) will not be supported. The single-precision
15045 code uses an algorithm which is designed for factoring smaller
15051 @node seq invocation
15052 @section @command{seq}: Print numeric sequences
15055 @cindex numeric sequences
15056 @cindex sequence of numbers
15058 @command{seq} prints a sequence of numbers to standard output. Synopses:
15061 seq [@var{option}]@dots{} @var{last}
15062 seq [@var{option}]@dots{} @var{first} @var{last}
15063 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15066 @command{seq} prints the numbers from @var{first} to @var{last} by
15067 @var{increment}. By default, each number is printed on a separate line.
15068 When @var{increment} is not specified, it defaults to @samp{1},
15069 even when @var{first} is larger than @var{last}.
15070 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15071 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15072 Floating-point numbers
15073 may be specified (using a period before any fractional digits).
15075 The program accepts the following options. Also see @ref{Common options}.
15076 Options must precede operands.
15079 @item -f @var{format}
15080 @itemx --format=@var{format}
15081 @opindex -f @var{format}
15082 @opindex --format=@var{format}
15083 @cindex formatting of numbers in @command{seq}
15084 Print all numbers using @var{format}.
15085 @var{format} must contain exactly one of the @samp{printf}-style
15086 floating point conversion specifications @samp{%a}, @samp{%e},
15087 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15088 The @samp{%} may be followed by zero or more flags taken from the set
15089 @samp{-+#0 '}, then an optional width containing one or more digits,
15090 then an optional precision consisting of a @samp{.} followed by zero
15091 or more digits. @var{format} may also contain any number of @samp{%%}
15092 conversion specifications. All conversion specifications have the
15093 same meaning as with @samp{printf}.
15095 The default format is derived from @var{first}, @var{step}, and
15096 @var{last}. If these all use a fixed point decimal representation,
15097 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15098 precision that can represent the output numbers exactly. Otherwise,
15099 the default format is @samp{%g}.
15101 @item -s @var{string}
15102 @itemx --separator=@var{string}
15103 @cindex separator for numbers in @command{seq}
15104 Separate numbers with @var{string}; default is a newline.
15105 The output always terminates with a newline.
15108 @itemx --equal-width
15109 Print all numbers with the same width, by padding with leading zeros.
15110 @var{first}, @var{step}, and @var{last} should all use a fixed point
15111 decimal representation.
15112 (To have other kinds of padding, use @option{--format}).
15116 You can get finer-grained control over output with @option{-f}:
15119 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15125 If you want hexadecimal integer output, you can use @command{printf}
15126 to perform the conversion:
15129 $ printf '%x\n' `seq 1048575 1024 1050623`
15135 For very long lists of numbers, use xargs to avoid
15136 system limitations on the length of an argument list:
15139 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15145 To generate octal output, use the printf @code{%o} format instead
15148 On most systems, seq can produce whole-number output for values up to
15149 at least @math{2^{53}}. Larger integers are approximated. The details
15150 differ depending on your floating-point implementation, but a common
15151 case is that @command{seq} works with integers through @math{2^{64}},
15152 and larger integers may not be numerically correct:
15155 $ seq 18446744073709551616 1 18446744073709551618
15156 18446744073709551616
15157 18446744073709551616
15158 18446744073709551618
15161 Be careful when using @command{seq} with outlandish values: otherwise
15162 you may see surprising results, as @command{seq} uses floating point
15163 internally. For example, on the x86 platform, where the internal
15164 representation uses a 64-bit fraction, the command:
15167 seq 1 0.0000000000000000001 1.0000000000000000009
15170 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15175 @node File permissions
15176 @chapter File permissions
15179 @include getdate.texi
15183 @node Opening the software toolbox
15184 @chapter Opening the Software Toolbox
15186 An earlier version of this chapter appeared in
15187 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15188 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15189 It was written by Arnold Robbins.
15192 * Toolbox introduction:: Toolbox introduction
15193 * I/O redirection:: I/O redirection
15194 * The who command:: The @command{who} command
15195 * The cut command:: The @command{cut} command
15196 * The sort command:: The @command{sort} command
15197 * The uniq command:: The @command{uniq} command
15198 * Putting the tools together:: Putting the tools together
15202 @node Toolbox introduction
15203 @unnumberedsec Toolbox Introduction
15205 This month's column is only peripherally related to the GNU Project, in
15206 that it describes a number of the GNU tools on your GNU/Linux system and how they
15207 might be used. What it's really about is the ``Software Tools'' philosophy
15208 of program development and usage.
15210 The software tools philosophy was an important and integral concept
15211 in the initial design and development of Unix (of which Linux and GNU are
15212 essentially clones). Unfortunately, in the modern day press of
15213 Internetworking and flashy GUIs, it seems to have fallen by the
15214 wayside. This is a shame, since it provides a powerful mental model
15215 for solving many kinds of problems.
15217 Many people carry a Swiss Army knife around in their pants pockets (or
15218 purse). A Swiss Army knife is a handy tool to have: it has several knife
15219 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15220 a number of other things on it. For the everyday, small miscellaneous jobs
15221 where you need a simple, general purpose tool, it's just the thing.
15223 On the other hand, an experienced carpenter doesn't build a house using
15224 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15225 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15226 exactly when and where to use each tool; you won't catch him hammering nails
15227 with the handle of his screwdriver.
15229 The Unix developers at Bell Labs were all professional programmers and trained
15230 computer scientists. They had found that while a one-size-fits-all program
15231 might appeal to a user because there's only one program to use, in practice
15236 difficult to write,
15239 difficult to maintain and
15243 difficult to extend to meet new situations.
15246 Instead, they felt that programs should be specialized tools. In short, each
15247 program ``should do one thing well.'' No more and no less. Such programs are
15248 simpler to design, write, and get right---they only do one thing.
15250 Furthermore, they found that with the right machinery for hooking programs
15251 together, that the whole was greater than the sum of the parts. By combining
15252 several special purpose programs, you could accomplish a specific task
15253 that none of the programs was designed for, and accomplish it much more
15254 quickly and easily than if you had to write a special purpose program.
15255 We will see some (classic) examples of this further on in the column.
15256 (An important additional point was that, if necessary, take a detour
15257 and build any software tools you may need first, if you don't already
15258 have something appropriate in the toolbox.)
15260 @node I/O redirection
15261 @unnumberedsec I/O Redirection
15263 Hopefully, you are familiar with the basics of I/O redirection in the
15264 shell, in particular the concepts of ``standard input,'' ``standard output,''
15265 and ``standard error''. Briefly, ``standard input'' is a data source, where
15266 data comes from. A program should not need to either know or care if the
15267 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15268 card reader. Similarly, ``standard output'' is a data sink, where data goes
15269 to. The program should neither know nor care where this might be.
15270 Programs that only read their standard input, do something to the data,
15271 and then send it on, are called @dfn{filters}, by analogy to filters in a
15274 With the Unix shell, it's very easy to set up data pipelines:
15277 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15280 We start out by creating the raw data; each filter applies some successive
15281 transformation to the data, until by the time it comes out of the pipeline,
15282 it is in the desired form.
15284 This is fine and good for standard input and standard output. Where does the
15285 standard error come in to play? Well, think about @command{filter1} in
15286 the pipeline above. What happens if it encounters an error in the data it
15287 sees? If it writes an error message to standard output, it will just
15288 disappear down the pipeline into @command{filter2}'s input, and the
15289 user will probably never see it. So programs need a place where they can send
15290 error messages so that the user will notice them. This is standard error,
15291 and it is usually connected to your console or window, even if you have
15292 redirected standard output of your program away from your screen.
15294 For filter programs to work together, the format of the data has to be
15295 agreed upon. The most straightforward and easiest format to use is simply
15296 lines of text. Unix data files are generally just streams of bytes, with
15297 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15298 conventionally called a ``newline'' in the Unix literature. (This is
15299 @code{'\n'} if you're a C programmer.) This is the format used by all
15300 the traditional filtering programs. (Many earlier operating systems
15301 had elaborate facilities and special purpose programs for managing
15302 binary data. Unix has always shied away from such things, under the
15303 philosophy that it's easiest to simply be able to view and edit your
15304 data with a text editor.)
15306 OK, enough introduction. Let's take a look at some of the tools, and then
15307 we'll see how to hook them together in interesting ways. In the following
15308 discussion, we will only present those command line options that interest
15309 us. As you should always do, double check your system documentation
15310 for the full story.
15312 @node The who command
15313 @unnumberedsec The @command{who} Command
15315 The first program is the @command{who} command. By itself, it generates a
15316 list of the users who are currently logged in. Although I'm writing
15317 this on a single-user system, we'll pretend that several people are
15322 @print{} arnold console Jan 22 19:57
15323 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15324 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15325 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15328 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15329 There are three people logged in, and I am logged in twice. On traditional
15330 Unix systems, user names are never more than eight characters long. This
15331 little bit of trivia will be useful later. The output of @command{who} is nice,
15332 but the data is not all that exciting.
15334 @node The cut command
15335 @unnumberedsec The @command{cut} Command
15337 The next program we'll look at is the @command{cut} command. This program
15338 cuts out columns or fields of input data. For example, we can tell it
15339 to print just the login name and full name from the @file{/etc/passwd}
15340 file. The @file{/etc/passwd} file has seven fields, separated by
15344 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15347 To get the first and fifth fields, we would use @command{cut} like this:
15350 $ cut -d: -f1,5 /etc/passwd
15351 @print{} root:Operator
15353 @print{} arnold:Arnold D. Robbins
15354 @print{} miriam:Miriam A. Robbins
15358 With the @option{-c} option, @command{cut} will cut out specific characters
15359 (i.e., columns) in the input lines. This is useful for input data
15360 that has fixed width fields, and does not have a field separator. For
15361 example, list the Monday dates for the current month:
15363 @c Is using cal ok? Looked at gcal, but I don't like it.
15374 @node The sort command
15375 @unnumberedsec The @command{sort} Command
15377 Next we'll look at the @command{sort} command. This is one of the most
15378 powerful commands on a Unix-style system; one that you will often find
15379 yourself using when setting up fancy data plumbing.
15382 command reads and sorts each file named on the command line. It then
15383 merges the sorted data and writes it to standard output. It will read
15384 standard input if no files are given on the command line (thus
15385 making it into a filter). The sort is based on the character collating
15386 sequence or based on user-supplied ordering criteria.
15389 @node The uniq command
15390 @unnumberedsec The @command{uniq} Command
15392 Finally (at least for now), we'll look at the @command{uniq} program. When
15393 sorting data, you will often end up with duplicate lines, lines that
15394 are identical. Usually, all you need is one instance of each line.
15395 This is where @command{uniq} comes in. The @command{uniq} program reads its
15396 standard input. It prints only one
15397 copy of each repeated line. It does have several options. Later on,
15398 we'll use the @option{-c} option, which prints each unique line, preceded
15399 by a count of the number of times that line occurred in the input.
15402 @node Putting the tools together
15403 @unnumberedsec Putting the Tools Together
15405 Now, let's suppose this is a large ISP server system with dozens of users
15406 logged in. The management wants the system administrator to write a program that will
15407 generate a sorted list of logged in users. Furthermore, even if a user
15408 is logged in multiple times, his or her name should only show up in the
15411 The administrator could sit down with the system documentation and write a C
15412 program that did this. It would take perhaps a couple of hundred lines
15413 of code and about two hours to write it, test it, and debug it.
15414 However, knowing the software toolbox, the administrator can instead start out
15415 by generating just a list of logged on users:
15425 Next, sort the list:
15428 $ who | cut -c1-8 | sort
15435 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15438 $ who | cut -c1-8 | sort | uniq
15444 The @command{sort} command actually has a @option{-u} option that does what
15445 @command{uniq} does. However, @command{uniq} has other uses for which one
15446 cannot substitute @samp{sort -u}.
15448 The administrator puts this pipeline into a shell script, and makes it available for
15449 all the users on the system (@samp{#} is the system administrator,
15450 or @code{root}, prompt):
15453 # cat > /usr/local/bin/listusers
15454 who | cut -c1-8 | sort | uniq
15456 # chmod +x /usr/local/bin/listusers
15459 There are four major points to note here. First, with just four
15460 programs, on one command line, the administrator was able to save about two
15461 hours worth of work. Furthermore, the shell pipeline is just about as
15462 efficient as the C program would be, and it is much more efficient in
15463 terms of programmer time. People time is much more expensive than
15464 computer time, and in our modern ``there's never enough time to do
15465 everything'' society, saving two hours of programmer time is no mean
15468 Second, it is also important to emphasize that with the
15469 @emph{combination} of the tools, it is possible to do a special
15470 purpose job never imagined by the authors of the individual programs.
15472 Third, it is also valuable to build up your pipeline in stages, as we did here.
15473 This allows you to view the data at each stage in the pipeline, which helps
15474 you acquire the confidence that you are indeed using these tools correctly.
15476 Finally, by bundling the pipeline in a shell script, other users can use
15477 your command, without having to remember the fancy plumbing you set up for
15478 them. In terms of how you run them, shell scripts and compiled programs are
15481 After the previous warm-up exercise, we'll look at two additional, more
15482 complicated pipelines. For them, we need to introduce two more tools.
15484 The first is the @command{tr} command, which stands for ``transliterate.''
15485 The @command{tr} command works on a character-by-character basis, changing
15486 characters. Normally it is used for things like mapping upper case to
15490 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15491 @print{} this example has mixed case!
15494 There are several options of interest:
15498 work on the complement of the listed characters, i.e.,
15499 operations apply to characters not in the given set
15502 delete characters in the first set from the output
15505 squeeze repeated characters in the output into just one character.
15508 We will be using all three options in a moment.
15510 The other command we'll look at is @command{comm}. The @command{comm}
15511 command takes two sorted input files as input data, and prints out the
15512 files' lines in three columns. The output columns are the data lines
15513 unique to the first file, the data lines unique to the second file, and
15514 the data lines that are common to both. The @option{-1}, @option{-2}, and
15515 @option{-3} command line options @emph{omit} the respective columns. (This is
15516 non-intuitive and takes a little getting used to.) For example:
15538 The file name @file{-} tells @command{comm} to read standard input
15539 instead of a regular file.
15541 Now we're ready to build a fancy pipeline. The first application is a word
15542 frequency counter. This helps an author determine if he or she is over-using
15545 The first step is to change the case of all the letters in our input file
15546 to one case. ``The'' and ``the'' are the same word when doing counting.
15549 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15552 The next step is to get rid of punctuation. Quoted words and unquoted words
15553 should be treated identically; it's easiest to just get the punctuation out of
15557 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15560 The second @command{tr} command operates on the complement of the listed
15561 characters, which are all the letters, the digits, the underscore, and
15562 the blank. The @samp{\n} represents the newline character; it has to
15563 be left alone. (The @acronym{ASCII} tab character should also be included for
15564 good measure in a production script.)
15566 At this point, we have data consisting of words separated by blank space.
15567 The words only contain alphanumeric characters (and the underscore). The
15568 next step is break the data apart so that we have one word per line. This
15569 makes the counting operation much easier, as we will see shortly.
15572 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15573 > tr -s ' ' '\n' | ...
15576 This command turns blanks into newlines. The @option{-s} option squeezes
15577 multiple newline characters in the output into just one. This helps us
15578 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15579 This is what the shell prints when it notices you haven't finished
15580 typing in all of a command.)
15582 We now have data consisting of one word per line, no punctuation, all one
15583 case. We're ready to count each word:
15586 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15587 > tr -s ' ' '\n' | sort | uniq -c | ...
15590 At this point, the data might look something like this:
15603 The output is sorted by word, not by count! What we want is the most
15604 frequently used words first. Fortunately, this is easy to accomplish,
15605 with the help of two more @command{sort} options:
15609 do a numeric sort, not a textual one
15612 reverse the order of the sort
15615 The final pipeline looks like this:
15618 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15619 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15628 Whew! That's a lot to digest. Yet, the same principles apply. With six
15629 commands, on two lines (really one long one split for convenience), we've
15630 created a program that does something interesting and useful, in much
15631 less time than we could have written a C program to do the same thing.
15633 A minor modification to the above pipeline can give us a simple spelling
15634 checker! To determine if you've spelled a word correctly, all you have to
15635 do is look it up in a dictionary. If it is not there, then chances are
15636 that your spelling is incorrect. So, we need a dictionary.
15637 The conventional location for a dictionary is @file{/usr/dict/words}.
15638 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15639 revision of this article.}
15640 this is a sorted, 45,402 word dictionary.
15642 Now, how to compare our file with the dictionary? As before, we generate
15643 a sorted list of words, one per line:
15646 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15647 > tr -s ' ' '\n' | sort -u | ...
15650 Now, all we need is a list of words that are @emph{not} in the
15651 dictionary. Here is where the @command{comm} command comes in.
15654 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15655 > tr -s ' ' '\n' | sort -u |
15656 > comm -23 - /usr/dict/words
15659 The @option{-2} and @option{-3} options eliminate lines that are only in the
15660 dictionary (the second file), and lines that are in both files. Lines
15661 only in the first file (standard input, our stream of words), are
15662 words that are not in the dictionary. These are likely candidates for
15663 spelling errors. This pipeline was the first cut at a production
15664 spelling checker on Unix.
15666 There are some other tools that deserve brief mention.
15670 search files for text that matches a regular expression
15673 count lines, words, characters
15676 a T-fitting for data pipes, copies data to files and to standard output
15679 the stream editor, an advanced tool
15682 a data manipulation language, another advanced tool
15685 The software tools philosophy also espoused the following bit of
15686 advice: ``Let someone else do the hard part.'' This means, take
15687 something that gives you most of what you need, and then massage it the
15688 rest of the way until it's in the form that you want.
15694 Each program should do one thing well. No more, no less.
15697 Combining programs with appropriate plumbing leads to results where
15698 the whole is greater than the sum of the parts. It also leads to novel
15699 uses of programs that the authors might never have imagined.
15702 Programs should never print extraneous header or trailer data, since these
15703 could get sent on down a pipeline. (A point we didn't mention earlier.)
15706 Let someone else do the hard part.
15709 Know your toolbox! Use each program appropriately. If you don't have an
15710 appropriate tool, build one.
15713 As of this writing, all the programs we've discussed are available via
15714 anonymous @command{ftp} from: @*
15715 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15716 be more recent versions available now.)
15718 None of what I have presented in this column is new. The Software Tools
15719 philosophy was first introduced in the book @cite{Software Tools}, by
15720 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15721 This book showed how to write and use software tools. It was written in
15722 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15723 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15724 was. The last chapter presented a @command{ratfor} to FORTRAN
15725 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15726 lot like C; if you know C, you won't have any problem following the
15729 In 1981, the book was updated and made available as @cite{Software Tools
15730 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15731 still in print and are well worth
15732 reading if you're a programmer. They certainly made a major change in
15733 how I view programming.
15735 The programs in both books are available from
15736 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15737 For a number of years, there was an active
15738 Software Tools Users Group, whose members had ported the original
15739 @command{ratfor} programs to essentially every computer system with a
15740 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15741 as Unix began to spread beyond universities.
15743 With the current proliferation of GNU code and other clones of Unix programs,
15744 these programs now receive little attention; modern C versions are
15745 much more efficient and do more than these programs do. Nevertheless, as
15746 exposition of good programming style, and evangelism for a still-valuable
15747 philosophy, these books are unparalleled, and I recommend them highly.
15749 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15750 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15752 @node GNU Free Documentation License
15753 @appendix GNU Free Documentation License
15757 @node Concept index
15764 @c Local variables:
15765 @c texinfo-column-for-description: 32
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