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 base64
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:: 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:: mkdir rmdir unlink mkfifo mknod ln link readlink
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 arch 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}
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 * Details about version sort:: More details about version sort
306 * General output formatting:: General output formatting
307 * Formatting the file names:: Formatting the file names
311 * cp invocation:: Copy files and directories
312 * dd invocation:: Convert and copy a file
313 * install invocation:: Copy files and set attributes
314 * mv invocation:: Move (rename) files
315 * rm invocation:: Remove files or directories
316 * shred invocation:: Remove files more securely
320 * link invocation:: Make a hard link via the link syscall
321 * ln invocation:: Make links between files
322 * mkdir invocation:: Make directories
323 * mkfifo invocation:: Make FIFOs (named pipes)
324 * mknod invocation:: Make block or character special files
325 * readlink invocation:: Print value of a symlink or canonical file name
326 * rmdir invocation:: Remove empty directories
327 * unlink invocation:: Remove files via unlink syscall
329 Changing file attributes
331 * chown invocation:: Change file owner and group
332 * chgrp invocation:: Change group ownership
333 * chmod invocation:: Change access permissions
334 * touch invocation:: Change file timestamps
338 * df invocation:: Report file system disk space usage
339 * du invocation:: Estimate file space usage
340 * stat invocation:: Report file or file system status
341 * sync invocation:: Synchronize data on disk with memory
342 * truncate invocation:: Shrink or extend the size of a file
346 * echo invocation:: Print a line of text
347 * printf invocation:: Format and print data
348 * yes invocation:: Print a string until interrupted
352 * false invocation:: Do nothing, unsuccessfully
353 * true invocation:: Do nothing, successfully
354 * test invocation:: Check file types and compare values
355 * expr invocation:: Evaluate expressions
357 @command{test}: Check file types and compare values
359 * File type tests:: File type tests
360 * Access permission tests:: Access permission tests
361 * File characteristic tests:: File characteristic tests
362 * String tests:: String tests
363 * Numeric tests:: Numeric tests
365 @command{expr}: Evaluate expression
367 * String expressions:: + : match substr index length
368 * Numeric expressions:: + - * / %
369 * Relations for expr:: | & < <= = == != >= >
370 * Examples of expr:: Examples of using @command{expr}
374 * tee invocation:: Redirect output to multiple files or processes
376 File name manipulation
378 * basename invocation:: Strip directory and suffix from a file name
379 * dirname invocation:: Strip non-directory suffix from a file name
380 * pathchk invocation:: Check file name validity and portability
384 * pwd invocation:: Print working directory
385 * stty invocation:: Print or change terminal characteristics
386 * printenv invocation:: Print all or some environment variables
387 * tty invocation:: Print file name of terminal on standard input
389 @command{stty}: Print or change terminal characteristics
391 * Control:: Control settings
392 * Input:: Input settings
393 * Output:: Output settings
394 * Local:: Local settings
395 * Combination:: Combination settings
396 * Characters:: Special characters
397 * Special:: Special settings
401 * id invocation:: Print user identity
402 * logname invocation:: Print current login name
403 * whoami invocation:: Print effective user ID
404 * groups invocation:: Print group names a user is in
405 * users invocation:: Print login names of users currently logged in
406 * who invocation:: Print who is currently logged in
410 * arch invocation:: Print machine hardware name
411 * date invocation:: Print or set system date and time
412 * uname invocation:: Print system information
413 * hostname invocation:: Print or set system name
414 * hostid invocation:: Print numeric host identifier
415 * uptime invocation:: Print system uptime and load
417 @command{date}: Print or set system date and time
419 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
420 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
421 * Literal conversion specifiers:: %[%nt]
422 * Padding and other flags:: Pad with zeros, spaces, etc.
423 * Setting the time:: Changing the system clock
424 * Options for date:: Instead of the current time
425 * Date input formats:: Specifying date strings
426 * Examples of date:: Examples
430 * chcon invocation:: Change SELinux context of file
431 * runcon invocation:: Run a command in specified SELinux context
433 Modified command invocation
435 * chroot invocation:: Run a command with a different root directory
436 * env invocation:: Run a command in a modified environment
437 * nice invocation:: Run a command with modified niceness
438 * nohup invocation:: Run a command immune to hangups
439 * stdbuf invocation:: Run a command with modified I/O buffering
440 * su invocation:: Run a command with substitute user and group ID
441 * timeout invocation:: Run a command with a time limit
445 * kill invocation:: Sending a signal to processes.
449 * sleep invocation:: Delay for a specified time
453 * factor invocation:: Print prime factors
454 * seq invocation:: Print numeric sequences
458 * Mode Structure:: Structure of file mode bits
459 * Symbolic Modes:: Mnemonic representation of file mode bits
460 * Numeric Modes:: File mode bits as octal numbers
461 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
465 * General date syntax:: Common rules
466 * Calendar date items:: 19 Dec 1994
467 * Time of day items:: 9:20pm
468 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
469 * Day of week items:: Monday and others
470 * Relative items in date strings:: next tuesday, 2 years ago
471 * Pure numbers in date strings:: 19931219, 1440
472 * Seconds since the Epoch:: @@1078100502
473 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
474 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al
476 Opening the software toolbox
478 * Toolbox introduction:: Toolbox introduction
479 * I/O redirection:: I/O redirection
480 * The who command:: The @command{who} command
481 * The cut command:: The @command{cut} command
482 * The sort command:: The @command{sort} command
483 * The uniq command:: The @command{uniq} command
484 * Putting the tools together:: Putting the tools together
488 * GNU Free Documentation License:: Copying and sharing this manual
495 @chapter Introduction
497 This manual is a work in progress: many sections make no attempt to explain
498 basic concepts in a way suitable for novices. Thus, if you are interested,
499 please get involved in improving this manual. The entire @sc{gnu} community
502 @cindex @acronym{POSIX}
503 The @sc{gnu} utilities documented here are mostly compatible with the
504 @acronym{POSIX} standard.
505 @cindex bugs, reporting
506 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
507 to include the version number, machine architecture, input files, and
508 any other information needed to reproduce the bug: your input, what you
509 expected, what you got, and why it is wrong. Diffs are welcome, but
510 please include a description of the problem as well, since this is
511 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
517 @cindex MacKenzie, D.
520 This manual was originally derived from the Unix man pages in the
521 distributions, which were written by David MacKenzie and updated by Jim
522 Meyering. What you are reading now is the authoritative documentation
523 for these utilities; the man pages are no longer being maintained. The
524 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
525 Pinard did the initial conversion to Texinfo format. Karl Berry did the
526 indexing, some reorganization, and editing of the results. Brian
527 Youmans of the Free Software Foundation office staff combined the
528 manuals for textutils, fileutils, and sh-utils to produce the present
529 omnibus manual. Richard Stallman contributed his usual invaluable
530 insights to the overall process.
533 @chapter Common options
537 @itemx @w{@kbd{--backup}[=@var{method}]}
540 @vindex VERSION_CONTROL
541 @cindex backups, making
542 @xref{Backup options}.
543 Make a backup of each file that would otherwise be overwritten or removed.
546 @macro optBackupSuffix
547 @item -S @var{suffix}
548 @itemx --suffix=@var{suffix}
551 Append @var{suffix} to each backup file made with @option{-b}.
552 @xref{Backup options}.
555 @macro optTargetDirectory
556 @item -t @var{directory}
557 @itemx @w{@kbd{--target-directory}=@var{directory}}
559 @opindex --target-directory
560 @cindex target directory
561 @cindex destination directory
562 Specify the destination @var{directory}.
563 @xref{Target directory}.
566 @macro optNoTargetDirectory
568 @itemx --no-target-directory
570 @opindex --no-target-directory
571 @cindex target directory
572 @cindex destination directory
573 Do not treat the last operand specially when it is a directory or a
574 symbolic link to a directory. @xref{Target directory}.
582 @cindex output @sc{nul}-byte-terminated lines
583 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
584 rather than a newline. This option enables other programs to parse the
585 output of @command{\cmd\} even when that output would contain data
586 with embedded newlines.
593 Append an SI-style abbreviation to each size, such as @samp{M} for
594 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
595 1,000,000 bytes. This option is equivalent to
596 @option{--block-size=si}. Use the @option{-h} or
597 @option{--human-readable} option if
598 you prefer powers of 1024.
601 @macro optHumanReadable
603 @itemx --human-readable
605 @opindex --human-readable
606 @cindex human-readable output
607 Append a size letter to each size, such as @samp{M} for mebibytes.
608 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
609 This option is equivalent to @option{--block-size=human-readable}.
610 Use the @option{--si} option if you prefer powers of 1000.
613 @macro optStripTrailingSlashes
614 @itemx @w{@kbd{--strip-trailing-slashes}}
615 @opindex --strip-trailing-slashes
616 @cindex stripping trailing slashes
617 Remove any trailing slashes from each @var{source} argument.
618 @xref{Trailing slashes}.
621 @macro mayConflictWithShellBuiltIn{cmd}
622 @cindex conflicts with shell built-ins
623 @cindex built-in shell commands, conflicts with
624 Due to shell aliases and built-in @command{\cmd\} command, using an
625 unadorned @command{\cmd\} interactively or in a script may get you
626 different functionality than that described here. Invoke it via
627 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
632 @macro multiplierSuffixes{varName}
633 @var{\varName\} may be, or may be an integer optionally followed by,
634 one of the following multiplicative suffixes:
636 @samp{b} => 512 ("blocks")
637 @samp{KB} => 1000 (KiloBytes)
638 @samp{K} => 1024 (KibiBytes)
639 @samp{MB} => 1000*1000 (MegaBytes)
640 @samp{M} => 1024*1024 (MebiBytes)
641 @samp{GB} => 1000*1000*1000 (GigaBytes)
642 @samp{G} => 1024*1024*1024 (GibiBytes)
644 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
647 @c FIXME: same as above, but no ``blocks'' line.
648 @macro multiplierSuffixesNoBlocks{varName}
649 @var{\varName\} may be, or may be an integer optionally followed by,
650 one of the following multiplicative suffixes:
652 @samp{KB} => 1000 (KiloBytes)
653 @samp{K} => 1024 (KibiBytes)
654 @samp{MB} => 1000*1000 (MegaBytes)
655 @samp{M} => 1024*1024 (MebiBytes)
656 @samp{GB} => 1000*1000*1000 (GigaBytes)
657 @samp{G} => 1024*1024*1024 (GibiBytes)
659 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
662 @cindex common options
664 Certain options are available in all of these programs. Rather than
665 writing identical descriptions for each of the programs, they are
666 described here. (In fact, every @sc{gnu} program accepts (or should accept)
669 @vindex POSIXLY_CORRECT
670 Normally options and operands can appear in any order, and programs act
671 as if all the options appear before any operands. For example,
672 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
673 @samp{:} is an option-argument of @option{-t}. However, if the
674 @env{POSIXLY_CORRECT} environment variable is set, options must appear
675 before operands, unless otherwise specified for a particular command.
677 A few programs can usefully have trailing operands with leading
678 @samp{-}. With such a program, options must precede operands even if
679 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
680 program description. For example, the @command{env} command's options
681 must appear before its operands, since in some cases the operands
682 specify a command that itself contains options.
684 Most programs that accept long options recognize unambiguous
685 abbreviations of those options. For example, @samp{rmdir
686 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
687 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
688 @samp{ls --h}, are identified as such.
690 Some of these programs recognize the @option{--help} and @option{--version}
691 options only when one of them is the sole command line argument. For
692 these programs, abbreviations of the long options are not always recognized.
699 Print a usage message listing all available options, then exit successfully.
703 @cindex version number, finding
704 Print the version number, then exit successfully.
708 @cindex option delimiter
709 Delimit the option list. Later arguments, if any, are treated as
710 operands even if they begin with @samp{-}. For example, @samp{sort --
711 -r} reads from the file named @file{-r}.
715 @cindex standard input
716 @cindex standard output
717 A single @samp{-} operand is not really an option, though it looks like one. It
718 stands for standard input, or for standard output if that is clear from
719 the context. For example, @samp{sort -} reads from standard input,
720 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
721 extra copy of its input to standard output. Unless otherwise
722 specified, @samp{-} can appear as any operand that requires a file
726 * Exit status:: Indicating program success or failure.
727 * Backup options:: -b -S, in some programs.
728 * Block size:: BLOCK_SIZE and --block-size, in some programs.
729 * Signal specifications:: Specifying signals using the --signal option.
730 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
731 * Random sources:: --random-source, in some programs.
732 * Target directory:: Specifying a target directory, in some programs.
733 * Trailing slashes:: --strip-trailing-slashes, in some programs.
734 * Traversing symlinks:: -H, -L, or -P, in some programs.
735 * Treating / specially:: --preserve-root and --no-preserve-root.
736 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
737 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
745 An exit status of zero indicates success,
746 and a nonzero value indicates failure.
749 Nearly every command invocation yields an integral @dfn{exit status}
750 that can be used to change how other commands work.
751 For the vast majority of commands, an exit status of zero indicates
752 success. Failure is indicated by a nonzero value---typically
753 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
754 requires only that it be nonzero.
756 However, some of the programs documented here do produce
757 other exit status values and a few associate different
758 meanings with the values @samp{0} and @samp{1}.
759 Here are some of the exceptions:
760 @command{chroot}, @command{env}, @command{expr}, @command{nice},
761 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
762 @command{su}, @command{test}, @command{timeout}, @command{tty}.
766 @section Backup options
768 @cindex backup options
770 Some @sc{gnu} programs (at least @command{cp}, @command{install},
771 @command{ln}, and @command{mv}) optionally make backups of files
772 before writing new versions.
773 These options control the details of these backups. The options are also
774 briefly mentioned in the descriptions of the particular programs.
779 @itemx @w{@kbd{--backup}[=@var{method}]}
782 @vindex VERSION_CONTROL
783 @cindex backups, making
784 Make a backup of each file that would otherwise be overwritten or removed.
785 Without this option, the original versions are destroyed.
786 Use @var{method} to determine the type of backups to make.
787 When this option is used but @var{method} is not specified,
788 then the value of the @env{VERSION_CONTROL}
789 environment variable is used. And if @env{VERSION_CONTROL} is not set,
790 the default backup type is @samp{existing}.
792 Note that the short form of this option, @option{-b} does not accept any
793 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
795 @vindex version-control @r{Emacs variable}
796 This option corresponds to the Emacs variable @samp{version-control};
797 the values for @var{method} are the same as those used in Emacs.
798 This option also accepts more descriptive names.
799 The valid @var{method}s are (unique abbreviations are accepted):
804 @opindex none @r{backup method}
809 @opindex numbered @r{backup method}
810 Always make numbered backups.
814 @opindex existing @r{backup method}
815 Make numbered backups of files that already have them, simple backups
820 @opindex simple @r{backup method}
821 Always make simple backups. Please note @samp{never} is not to be
822 confused with @samp{none}.
826 @item -S @var{suffix}
827 @itemx --suffix=@var{suffix}
830 @cindex backup suffix
831 @vindex SIMPLE_BACKUP_SUFFIX
832 Append @var{suffix} to each backup file made with @option{-b}. If this
833 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
834 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
835 set, the default is @samp{~}, just as in Emacs.
844 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
845 @command{ls}) display sizes in ``blocks''. You can adjust the block size
846 and method of display to make sizes easier to read. The block size
847 used for display is independent of any file system block size.
848 Fractional block counts are rounded up to the nearest integer.
850 @opindex --block-size=@var{size}
853 @vindex DF_BLOCK_SIZE
854 @vindex DU_BLOCK_SIZE
855 @vindex LS_BLOCK_SIZE
856 @vindex POSIXLY_CORRECT@r{, and block size}
858 The default block size is chosen by examining the following environment
859 variables in turn; the first one that is set determines the block size.
864 This specifies the default block size for the @command{df} command.
865 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
866 @env{LS_BLOCK_SIZE} for @command{ls}.
869 This specifies the default block size for all three commands, if the
870 above command-specific environment variables are not set.
873 This specifies the default block size for all values that are normally
874 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
875 command-specific environment variables are set. Unlike the other
876 environment variables, @env{BLOCKSIZE} does not affect values that are
877 normally printed as byte counts, e.g., the file sizes contained in
880 @item POSIXLY_CORRECT
881 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
882 @env{BLOCKSIZE} is set, but this variable is set, the block size
887 If none of the above environment variables are set, the block size
888 currently defaults to 1024 bytes in most contexts, but this number may
889 change in the future. For @command{ls} file sizes, the block size
892 @cindex human-readable output
895 A block size specification can be a positive integer specifying the number
896 of bytes per block, or it can be @code{human-readable} or @code{si} to
897 select a human-readable format. Integers may be followed by suffixes
898 that are upward compatible with the
899 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
900 for decimal multiples and with the
901 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
902 prefixes for binary multiples}.
904 With human-readable formats, output sizes are followed by a size letter
905 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
906 powers of 1024; @samp{M} stands for 1,048,576 bytes.
907 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
908 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
911 A block size specification preceded by @samp{'} causes output sizes to
912 be displayed with thousands separators. The @env{LC_NUMERIC} locale
913 specifies the thousands separator and grouping. For example, in an
914 American English locale, @samp{--block-size="'1kB"} would cause a size
915 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
916 locale, there is no thousands separator so a leading @samp{'} has no
919 An integer block size can be followed by a suffix to specify a
920 multiple of that size. A bare size letter,
921 or one followed by @samp{iB}, specifies
922 a multiple using powers of 1024. A size letter followed by @samp{B}
923 specifies powers of 1000 instead. For example, @samp{1M} and
924 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
925 equivalent to @samp{1000000}.
927 A plain suffix without a preceding integer acts as if @samp{1} were
928 prepended, except that it causes a size indication to be appended to
929 the output. For example, @samp{--block-size="kB"} displays 3000 as
932 The following suffixes are defined. Large sizes like @code{1Y}
933 may be rejected by your computer due to limitations of its arithmetic.
937 @cindex kilobyte, definition of
938 kilobyte: @math{10^3 = 1000}.
942 @cindex kibibyte, definition of
943 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
944 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
945 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
947 @cindex megabyte, definition of
948 megabyte: @math{10^6 = 1,000,000}.
951 @cindex mebibyte, definition of
952 mebibyte: @math{2^{20} = 1,048,576}.
954 @cindex gigabyte, definition of
955 gigabyte: @math{10^9 = 1,000,000,000}.
958 @cindex gibibyte, definition of
959 gibibyte: @math{2^{30} = 1,073,741,824}.
961 @cindex terabyte, definition of
962 terabyte: @math{10^{12} = 1,000,000,000,000}.
965 @cindex tebibyte, definition of
966 tebibyte: @math{2^{40} = 1,099,511,627,776}.
968 @cindex petabyte, definition of
969 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
972 @cindex pebibyte, definition of
973 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
975 @cindex exabyte, definition of
976 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
979 @cindex exbibyte, definition of
980 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
982 @cindex zettabyte, definition of
983 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
986 @math{2^{70} = 1,180,591,620,717,411,303,424}.
987 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
989 @cindex yottabyte, definition of
990 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
993 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
994 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
999 @opindex --block-size
1000 @opindex --human-readable
1003 Block size defaults can be overridden by an explicit
1004 @option{--block-size=@var{size}} option. The @option{-k}
1005 option is equivalent to @option{--block-size=1K}, which
1006 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1007 set. The @option{-h} or @option{--human-readable} option is equivalent to
1008 @option{--block-size=human-readable}. The @option{--si} option is
1009 equivalent to @option{--block-size=si}.
1011 @node Signal specifications
1012 @section Signal specifications
1013 @cindex signals, specifying
1015 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1016 number like @samp{1}, or an exit status of a process terminated by the
1017 signal. A signal name can be given in canonical form or prefixed by
1018 @samp{SIG}. The case of the letters is ignored. The following signal names
1019 and numbers are supported on all @acronym{POSIX} compliant systems:
1025 2. Terminal interrupt.
1031 9. Kill (cannot be caught or ignored).
1039 Other supported signal names have system-dependent corresponding
1040 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1041 support the following signals:
1045 Access to an undefined portion of a memory object.
1047 Child process terminated, stopped, or continued.
1049 Continue executing, if stopped.
1051 Erroneous arithmetic operation.
1053 Illegal Instruction.
1055 Write on a pipe with no one to read it.
1057 Invalid memory reference.
1059 Stop executing (cannot be caught or ignored).
1063 Background process attempting read.
1065 Background process attempting write.
1067 High bandwidth data is available at a socket.
1069 User-defined signal 1.
1071 User-defined signal 2.
1075 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1076 also support the following signals:
1082 Profiling timer expired.
1086 Trace/breakpoint trap.
1088 Virtual timer expired.
1090 CPU time limit exceeded.
1092 File size limit exceeded.
1096 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1097 also support at least eight real-time signals called @samp{RTMIN},
1098 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1100 @node Disambiguating names and IDs
1101 @section chown and chgrp: Disambiguating user names and IDs
1102 @cindex user names, disambiguating
1103 @cindex user IDs, disambiguating
1104 @cindex group names, disambiguating
1105 @cindex group IDs, disambiguating
1106 @cindex disambiguating group names and IDs
1108 Since the @var{owner} and @var{group} arguments to @command{chown} and
1109 @command{chgrp} may be specified as names or numeric IDs, there is an
1111 What if a user or group @emph{name} is a string of digits?
1112 @footnote{Using a number as a user name is common in some environments.}
1113 Should the command interpret it as a user name or as an ID?
1114 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1115 first attempt to resolve the specified string as a name, and
1116 only once that fails, then try to interpret it as an ID.
1117 This is troublesome when you want to specify a numeric ID, say 42,
1118 and it must work even in a pathological situation where
1119 @samp{42} is a user name that maps to some other user ID, say 1000.
1120 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1121 1000---not what you intended.
1123 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1124 that at the same time may result in a significant performance improvement
1125 by eliminating a database look-up.
1126 Simply precede each numeric user ID and/or group ID with a @samp{+},
1127 in order to force its interpretation as an integer:
1131 chgrp +$numeric_group_id another-file
1135 GNU @command{chown} and @command{chgrp}
1136 skip the name look-up process for each @samp{+}-prefixed string,
1137 because a string containing @samp{+} is never a valid user or group name.
1138 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1140 @node Random sources
1141 @section Sources of random data
1143 @cindex random sources
1145 The @command{shuf}, @command{shred}, and @command{sort} commands
1146 sometimes need random data to do their work. For example, @samp{sort
1147 -R} must choose a hash function at random, and it needs random data to
1148 make this selection.
1150 By default these commands use an internal pseudorandom generator
1151 initialized by a small amount of entropy, but can be directed to use
1152 an external source with the @option{--random-source=@var{file}} option.
1153 An error is reported if @var{file} does not contain enough bytes.
1155 For example, the device file @file{/dev/urandom} could be used as the
1156 source of random data. Typically, this device gathers environmental
1157 noise from device drivers and other sources into an entropy pool, and
1158 uses the pool to generate random bits. If the pool is short of data,
1159 the device reuses the internal pool to produce more bits, using a
1160 cryptographically secure pseudorandom number generator. But be aware
1161 that this device is not designed for bulk random data generation
1162 and is relatively slow.
1164 @file{/dev/urandom} suffices for most practical uses, but applications
1165 requiring high-value or long-term protection of private data may
1166 require an alternate data source like @file{/dev/random} or
1167 @file{/dev/arandom}. The set of available sources depends on your
1170 To reproduce the results of an earlier invocation of a command, you
1171 can save some random data into a file and then use that file as the
1172 random source in earlier and later invocations of the command.
1174 @node Target directory
1175 @section Target directory
1177 @cindex target directory
1179 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1180 commands normally treat the last operand specially when it is a
1181 directory or a symbolic link to a directory. For example, @samp{cp
1182 source dest} is equivalent to @samp{cp source dest/source} if
1183 @file{dest} is a directory. Sometimes this behavior is not exactly
1184 what is wanted, so these commands support the following options to
1185 allow more fine-grained control:
1190 @itemx --no-target-directory
1191 @opindex --no-target-directory
1192 @cindex target directory
1193 @cindex destination directory
1194 Do not treat the last operand specially when it is a directory or a
1195 symbolic link to a directory. This can help avoid race conditions in
1196 programs that operate in a shared area. For example, when the command
1197 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1198 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1199 renamed to @file{/tmp/dest/source} instead, if some other process
1200 created @file{/tmp/dest} as a directory. However, if @file{mv
1201 -T /tmp/source /tmp/dest} succeeds, there is no
1202 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1204 In the opposite situation, where you want the last operand to be
1205 treated as a directory and want a diagnostic otherwise, you can use
1206 the @option{--target-directory} (@option{-t}) option.
1208 @item -t @var{directory}
1209 @itemx @w{@kbd{--target-directory}=@var{directory}}
1210 @opindex --target-directory
1211 @cindex target directory
1212 @cindex destination directory
1213 Use @var{directory} as the directory component of each destination
1216 The interface for most programs is that after processing options and a
1217 finite (possibly zero) number of fixed-position arguments, the remaining
1218 argument list is either expected to be empty, or is a list of items
1219 (usually files) that will all be handled identically. The @command{xargs}
1220 program is designed to work well with this convention.
1222 The commands in the @command{mv}-family are unusual in that they take
1223 a variable number of arguments with a special case at the @emph{end}
1224 (namely, the target directory). This makes it nontrivial to perform some
1225 operations, e.g., ``move all files from here to ../d/'', because
1226 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1227 doesn't have a clean way to specify an extra final argument for each
1228 invocation of the subject command. (It can be done by going through a
1229 shell command, but that requires more human labor and brain power than
1232 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1233 @command{install}, @command{ln}, and @command{mv} programs to be used
1234 conveniently with @command{xargs}. For example, you can move the files
1235 from the current directory to a sibling directory, @code{d} like this:
1238 ls | xargs mv -t ../d --
1241 However, this doesn't move files whose names begin with @samp{.}.
1242 If you use the @sc{gnu} @command{find} program, you can move those
1243 files too, with this command:
1246 find . -mindepth 1 -maxdepth 1 \
1250 But both of the above approaches fail if there are no files in the
1251 current directory, or if any file has a name containing a blank or
1252 some other special characters.
1253 The following example removes those limitations and requires both
1254 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1257 find . -mindepth 1 -maxdepth 1 -print0 \
1258 | xargs --null --no-run-if-empty \
1265 The @option{--target-directory} (@option{-t}) and
1266 @option{--no-target-directory} (@option{-T})
1267 options cannot be combined.
1269 @node Trailing slashes
1270 @section Trailing slashes
1272 @cindex trailing slashes
1274 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1275 remove any trailing slashes from each @var{source} argument before
1276 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1279 This is useful when a @var{source} argument may have a trailing slash and
1280 @c FIXME: mv's behavior in this case is system-dependent
1281 specify a symbolic link to a directory. This scenario is in fact rather
1282 common because some shells can automatically append a trailing slash when
1283 performing file name completion on such symbolic links. Without this
1284 option, @command{mv}, for example, (via the system's rename function) must
1285 interpret a trailing slash as a request to dereference the symbolic link
1286 and so must rename the indirectly referenced @emph{directory} and not
1287 the symbolic link. Although it may seem surprising that such behavior
1288 be the default, it is required by @acronym{POSIX} and is consistent with
1289 other parts of that standard.
1291 @node Traversing symlinks
1292 @section Traversing symlinks
1294 @cindex symbolic link to directory, controlling traversal of
1296 The following options modify how @command{chown} and @command{chgrp}
1297 @c FIXME: note that `du' has these options, too, but they have slightly
1298 @c different meaning.
1299 traverse a hierarchy when the @option{--recursive} (@option{-R})
1300 option is also specified.
1301 If more than one of the following options is specified, only the final
1303 These options specify whether processing a symbolic link to a directory
1304 entails operating on just the symbolic link or on all files in the
1305 hierarchy rooted at that directory.
1307 These options are independent of @option{--dereference} and
1308 @option{--no-dereference} (@option{-h}), which control whether to modify
1309 a symlink or its referent.
1316 @cindex symbolic link to directory, traverse each that is specified on the command line
1317 If @option{--recursive} (@option{-R}) is specified and
1318 a command line argument is a symbolic link to a directory, traverse it.
1325 @cindex symbolic link to directory, traverse each that is encountered
1326 In a recursive traversal, traverse every symbolic link to a directory
1327 that is encountered.
1334 @cindex symbolic link to directory, never traverse
1335 Do not traverse any symbolic links.
1336 This is the default if none of @option{-H}, @option{-L},
1337 or @option{-P} is specified.
1344 @node Treating / specially
1345 @section Treating @file{/} specially
1347 Certain commands can operate destructively on entire hierarchies.
1348 For example, if a user with appropriate privileges mistakenly runs
1349 @samp{rm -rf / tmp/junk}, that may remove
1350 all files on the entire system. Since there are so few
1351 legitimate uses for such a command,
1352 @sc{gnu} @command{rm} normally declines to operate on any directory
1353 that resolves to @file{/}. If you really want to try to remove all
1354 the files on your system, you can use the @option{--no-preserve-root}
1355 option, but the default behavior, specified by the
1356 @option{--preserve-option}, is safer for most purposes.
1358 The commands @command{chgrp}, @command{chmod} and @command{chown}
1359 can also operate destructively on entire hierarchies, so they too
1360 support these options. Although, unlike @command{rm}, they don't
1361 actually unlink files, these commands are arguably more dangerous
1362 when operating recursively on @file{/}, since they often work much
1363 more quickly, and hence damage more files before an alert user can
1364 interrupt them. Tradition and @acronym{POSIX} require these commands
1365 to operate recursively on @file{/}, so they default to
1366 @option{--no-preserve-root}, but using the @option{--preserve-root}
1367 option makes them safer for most purposes. For convenience you can
1368 specify @option{--preserve-root} in an alias or in a shell function.
1370 Note that the @option{--preserve-root} option also ensures
1371 that @command{chgrp} and @command{chown} do not modify @file{/}
1372 even when dereferencing a symlink pointing to @file{/}.
1374 @node Special built-in utilities
1375 @section Special built-in utilities
1377 Some programs like @command{nice} can invoke other programs; for
1378 example, the command @samp{nice cat file} invokes the program
1379 @command{cat} by executing the command @samp{cat file}. However,
1380 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1381 this way. For example, the command @samp{nice exit} does not have a
1382 well-defined behavior: it may generate an error message instead of
1385 Here is a list of the special built-in utilities that are standardized
1386 by @acronym{POSIX} 1003.1-2004.
1389 @t{.@: : break continue eval exec exit export readonly
1390 return set shift times trap unset}
1393 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1394 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1395 pwd} do not work as you might expect.
1397 Many shells extend this list. For example, Bash has several extra
1398 special built-in utilities like @command{history}, and
1399 @command{suspend}, and with Bash the command @samp{nice suspend}
1400 generates an error message instead of suspending.
1402 @node Standards conformance
1403 @section Standards conformance
1405 @vindex POSIXLY_CORRECT
1406 In a few cases, the @sc{gnu} utilities' default behavior is
1407 incompatible with the @acronym{POSIX} standard. To suppress these
1408 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1409 variable. Unless you are checking for @acronym{POSIX} conformance, you
1410 probably do not need to define @env{POSIXLY_CORRECT}.
1412 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1413 versions. For example, older versions of @acronym{POSIX} required the
1414 command @samp{sort +1} to sort based on the second and succeeding
1415 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1416 the same command is required to sort the file named @file{+1}, and you
1417 must instead use the command @samp{sort -k 2} to get the field-based
1420 @vindex _POSIX2_VERSION
1421 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1422 that is standard for your system. To cause them to conform to a
1423 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1424 environment variable to a value of the form @var{yyyymm} specifying
1425 the year and month the standard was adopted. Two values are currently
1426 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1427 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1428 1003.1-2001. For example, if you have a newer system but are running software
1429 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1430 or @samp{tail +10}, you can work around any compatibility problems by setting
1431 @samp{_POSIX2_VERSION=199209} in your environment.
1433 @node Output of entire files
1434 @chapter Output of entire files
1436 @cindex output of entire files
1437 @cindex entire files, output of
1439 These commands read and write entire files, possibly transforming them
1443 * cat invocation:: Concatenate and write files.
1444 * tac invocation:: Concatenate and write files in reverse.
1445 * nl invocation:: Number lines and write files.
1446 * od invocation:: Write files in octal or other formats.
1447 * base64 invocation:: Transform data into printable data.
1450 @node cat invocation
1451 @section @command{cat}: Concatenate and write files
1454 @cindex concatenate and write files
1455 @cindex copying files
1457 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1458 standard input if none are given, to standard output. Synopsis:
1461 cat [@var{option}] [@var{file}]@dots{}
1464 The program accepts the following options. Also see @ref{Common options}.
1472 Equivalent to @option{-vET}.
1475 @itemx --number-nonblank
1477 @opindex --number-nonblank
1478 Number all nonempty output lines, starting with 1.
1482 Equivalent to @option{-vE}.
1487 @opindex --show-ends
1488 Display a @samp{$} after the end of each line.
1494 Number all output lines, starting with 1.
1497 @itemx --squeeze-blank
1499 @opindex --squeeze-blank
1500 @cindex squeezing empty lines
1501 Suppress repeated adjacent empty lines; output just one empty line
1506 Equivalent to @option{-vT}.
1511 @opindex --show-tabs
1512 Display TAB characters as @samp{^I}.
1516 Ignored; for @acronym{POSIX} compatibility.
1519 @itemx --show-nonprinting
1521 @opindex --show-nonprinting
1522 Display control characters except for LFD and TAB using
1523 @samp{^} notation and precede characters that have the high bit set with
1528 On systems like MS-DOS that distinguish between text and binary files,
1529 @command{cat} normally reads and writes in binary mode. However,
1530 @command{cat} reads in text mode if one of the options
1531 @option{-bensAE} is used or if @command{cat} is reading from standard
1532 input and standard input is a terminal. Similarly, @command{cat}
1533 writes in text mode if one of the options @option{-bensAE} is used or
1534 if standard output is a terminal.
1541 # Output f's contents, then standard input, then g's contents.
1544 # Copy standard input to standard output.
1549 @node tac invocation
1550 @section @command{tac}: Concatenate and write files in reverse
1553 @cindex reversing files
1555 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1556 standard input if none are given, to standard output, reversing the
1557 records (lines by default) in each separately. Synopsis:
1560 tac [@var{option}]@dots{} [@var{file}]@dots{}
1563 @dfn{Records} are separated by instances of a string (newline by
1564 default). By default, this separator string is attached to the end of
1565 the record that it follows in the file.
1567 The program accepts the following options. Also see @ref{Common options}.
1575 The separator is attached to the beginning of the record that it
1576 precedes in the file.
1582 Treat the separator string as a regular expression. Users of @command{tac}
1583 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1584 binary mode, each line of a text file might end with a CR/LF pair
1585 instead of the Unix-style LF.
1587 @item -s @var{separator}
1588 @itemx --separator=@var{separator}
1590 @opindex --separator
1591 Use @var{separator} as the record separator, instead of newline.
1599 @section @command{nl}: Number lines and write files
1602 @cindex numbering lines
1603 @cindex line numbering
1605 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1606 standard input if none are given, to standard output, with line numbers
1607 added to some or all of the lines. Synopsis:
1610 nl [@var{option}]@dots{} [@var{file}]@dots{}
1613 @cindex logical pages, numbering on
1614 @command{nl} decomposes its input into (logical) pages; by default, the
1615 line number is reset to 1 at the top of each logical page. @command{nl}
1616 treats all of the input files as a single document; it does not reset
1617 line numbers or logical pages between files.
1619 @cindex headers, numbering
1620 @cindex body, numbering
1621 @cindex footers, numbering
1622 A logical page consists of three sections: header, body, and footer.
1623 Any of the sections can be empty. Each can be numbered in a different
1624 style from the others.
1626 The beginnings of the sections of logical pages are indicated in the
1627 input file by a line containing exactly one of these delimiter strings:
1638 The two characters from which these strings are made can be changed from
1639 @samp{\} and @samp{:} via options (see below), but the pattern and
1640 length of each string cannot be changed.
1642 A section delimiter is replaced by an empty line on output. Any text
1643 that comes before the first section delimiter string in the input file
1644 is considered to be part of a body section, so @command{nl} treats a
1645 file that contains no section delimiters as a single body section.
1647 The program accepts the following options. Also see @ref{Common options}.
1651 @item -b @var{style}
1652 @itemx --body-numbering=@var{style}
1654 @opindex --body-numbering
1655 Select the numbering style for lines in the body section of each
1656 logical page. When a line is not numbered, the current line number
1657 is not incremented, but the line number separator character is still
1658 prepended to the line. The styles are:
1664 number only nonempty lines (default for body),
1666 do not number lines (default for header and footer),
1668 number only lines that contain a match for the basic regular
1669 expression @var{bre}.
1670 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1674 @itemx --section-delimiter=@var{cd}
1676 @opindex --section-delimiter
1677 @cindex section delimiters of pages
1678 Set the section delimiter characters to @var{cd}; default is
1679 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1680 (Remember to protect @samp{\} or other metacharacters from shell
1681 expansion with quotes or extra backslashes.)
1683 @item -f @var{style}
1684 @itemx --footer-numbering=@var{style}
1686 @opindex --footer-numbering
1687 Analogous to @option{--body-numbering}.
1689 @item -h @var{style}
1690 @itemx --header-numbering=@var{style}
1692 @opindex --header-numbering
1693 Analogous to @option{--body-numbering}.
1695 @item -i @var{number}
1696 @itemx --line-increment=@var{number}
1698 @opindex --line-increment
1699 Increment line numbers by @var{number} (default 1).
1701 @item -l @var{number}
1702 @itemx --join-blank-lines=@var{number}
1704 @opindex --join-blank-lines
1705 @cindex empty lines, numbering
1706 @cindex blank lines, numbering
1707 Consider @var{number} (default 1) consecutive empty lines to be one
1708 logical line for numbering, and only number the last one. Where fewer
1709 than @var{number} consecutive empty lines occur, do not number them.
1710 An empty line is one that contains no characters, not even spaces
1713 @item -n @var{format}
1714 @itemx --number-format=@var{format}
1716 @opindex --number-format
1717 Select the line numbering format (default is @code{rn}):
1721 @opindex ln @r{format for @command{nl}}
1722 left justified, no leading zeros;
1724 @opindex rn @r{format for @command{nl}}
1725 right justified, no leading zeros;
1727 @opindex rz @r{format for @command{nl}}
1728 right justified, leading zeros.
1732 @itemx --no-renumber
1734 @opindex --no-renumber
1735 Do not reset the line number at the start of a logical page.
1737 @item -s @var{string}
1738 @itemx --number-separator=@var{string}
1740 @opindex --number-separator
1741 Separate the line number from the text line in the output with
1742 @var{string} (default is the TAB character).
1744 @item -v @var{number}
1745 @itemx --starting-line-number=@var{number}
1747 @opindex --starting-line-number
1748 Set the initial line number on each logical page to @var{number} (default 1).
1750 @item -w @var{number}
1751 @itemx --number-width=@var{number}
1753 @opindex --number-width
1754 Use @var{number} characters for line numbers (default 6).
1762 @section @command{od}: Write files in octal or other formats
1765 @cindex octal dump of files
1766 @cindex hex dump of files
1767 @cindex ASCII dump of files
1768 @cindex file contents, dumping unambiguously
1770 @command{od} writes an unambiguous representation of each @var{file}
1771 (@samp{-} means standard input), or standard input if none are given.
1775 od [@var{option}]@dots{} [@var{file}]@dots{}
1776 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1777 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1780 Each line of output consists of the offset in the input, followed by
1781 groups of data from the file. By default, @command{od} prints the offset in
1782 octal, and each group of file data is a C @code{short int}'s worth of input
1783 printed as a single octal number.
1785 If @var{offset} is given, it specifies how many input bytes to skip
1786 before formatting and writing. By default, it is interpreted as an
1787 octal number, but the optional trailing decimal point causes it to be
1788 interpreted as decimal. If no decimal is specified and the offset
1789 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1790 number. If there is a trailing @samp{b}, the number of bytes skipped
1791 will be @var{offset} multiplied by 512.
1793 If a command is of both the first and second forms, the second form is
1794 assumed if the last operand begins with @samp{+} or (if there are two
1795 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1796 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1799 The program accepts the following options. Also see @ref{Common options}.
1803 @item -A @var{radix}
1804 @itemx --address-radix=@var{radix}
1806 @opindex --address-radix
1807 @cindex radix for file offsets
1808 @cindex file offset radix
1809 Select the base in which file offsets are printed. @var{radix} can
1810 be one of the following:
1820 none (do not print offsets).
1823 The default is octal.
1825 @item -j @var{bytes}
1826 @itemx --skip-bytes=@var{bytes}
1828 @opindex --skip-bytes
1829 Skip @var{bytes} input bytes before formatting and writing. If
1830 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1831 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1833 @multiplierSuffixes{bytes}
1835 @item -N @var{bytes}
1836 @itemx --read-bytes=@var{bytes}
1838 @opindex --read-bytes
1839 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1840 @code{bytes} are interpreted as for the @option{-j} option.
1842 @item -S @var{bytes}
1843 @itemx --strings[=@var{bytes}]
1846 @cindex string constants, outputting
1847 Instead of the normal output, output only @dfn{string constants}: at
1848 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1849 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1850 Prefixes and suffixes on @code{bytes} are interpreted as for the
1853 If @var{n} is omitted with @option{--strings}, the default is 3.
1856 @itemx --format=@var{type}
1859 Select the format in which to output the file data. @var{type} is a
1860 string of one or more of the below type indicator characters. If you
1861 include more than one type indicator character in a single @var{type}
1862 string, or use this option more than once, @command{od} writes one copy
1863 of each output line using each of the data types that you specified,
1864 in the order that you specified.
1866 Adding a trailing ``z'' to any type specification appends a display
1867 of the @acronym{ASCII} character representation of the printable characters
1868 to the output line generated by the type specification.
1872 named character, ignoring high-order bit
1874 @acronym{ASCII} character or backslash escape,
1887 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1888 newline, and @samp{nul} for a zero byte. Only the least significant
1889 seven bits of each byte is used; the high-order bit is ignored.
1890 Type @code{c} outputs
1891 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1894 Except for types @samp{a} and @samp{c}, you can specify the number
1895 of bytes to use in interpreting each number in the given data type
1896 by following the type indicator character with a decimal integer.
1897 Alternately, you can specify the size of one of the C compiler's
1898 built-in data types by following the type indicator character with
1899 one of the following characters. For integers (@samp{d}, @samp{o},
1900 @samp{u}, @samp{x}):
1913 For floating point (@code{f}):
1925 @itemx --output-duplicates
1927 @opindex --output-duplicates
1928 Output consecutive lines that are identical. By default, when two or
1929 more consecutive output lines would be identical, @command{od} outputs only
1930 the first line, and puts just an asterisk on the following line to
1931 indicate the elision.
1934 @itemx --width[=@var{n}]
1937 Dump @code{n} input bytes per output line. This must be a multiple of
1938 the least common multiple of the sizes associated with the specified
1941 If this option is not given at all, the default is 16. If @var{n} is
1942 omitted, the default is 32.
1946 The next several options are shorthands for format specifications.
1947 @sc{gnu} @command{od} accepts any combination of shorthands and format
1948 specification options. These options accumulate.
1954 Output as named characters. Equivalent to @samp{-t a}.
1958 Output as octal bytes. Equivalent to @samp{-t o1}.
1962 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1967 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1971 Output as floats. Equivalent to @samp{-t fF}.
1975 Output as decimal ints. Equivalent to @samp{-t dI}.
1979 Output as decimal long ints. Equivalent to @samp{-t dL}.
1983 Output as octal two-byte units. Equivalent to @option{-t o2}.
1987 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1991 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1994 @opindex --traditional
1995 Recognize the non-option label argument that traditional @command{od}
1996 accepted. The following syntax:
1999 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2003 can be used to specify at most one file and optional arguments
2004 specifying an offset and a pseudo-start address, @var{label}.
2005 The @var{label} argument is interpreted
2006 just like @var{offset}, but it specifies an initial pseudo-address. The
2007 pseudo-addresses are displayed in parentheses following any normal
2014 @node base64 invocation
2015 @section @command{base64}: Transform data into printable data
2018 @cindex base64 encoding
2020 @command{base64} transforms data read from a file, or standard input,
2021 into (or from) base64 encoded form. The base64 encoded form uses
2022 printable @acronym{ASCII} characters to represent binary data.
2026 base64 [@var{option}]@dots{} [@var{file}]
2027 base64 --decode [@var{option}]@dots{} [@var{file}]
2030 The base64 encoding expands data to roughly 133% of the original.
2031 The format conforms to
2032 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2034 The program accepts the following options. Also see @ref{Common options}.
2039 @itemx --wrap=@var{cols}
2043 @cindex column to wrap data after
2044 During encoding, wrap lines after @var{cols} characters. This must be
2047 The default is to wrap after 76 characters. Use the value 0 to
2048 disable line wrapping altogether.
2054 @cindex Decode base64 data
2055 @cindex Base64 decoding
2056 Change the mode of operation, from the default of encoding data, to
2057 decoding data. Input is expected to be base64 encoded data, and the
2058 output will be the original data.
2061 @itemx --ignore-garbage
2063 @opindex --ignore-garbage
2064 @cindex Ignore garbage in base64 stream
2065 When decoding, newlines are always accepted.
2066 During decoding, ignore unrecognized bytes,
2067 to permit distorted data to be decoded.
2074 @node Formatting file contents
2075 @chapter Formatting file contents
2077 @cindex formatting file contents
2079 These commands reformat the contents of files.
2082 * fmt invocation:: Reformat paragraph text.
2083 * pr invocation:: Paginate or columnate files for printing.
2084 * fold invocation:: Wrap input lines to fit in specified width.
2088 @node fmt invocation
2089 @section @command{fmt}: Reformat paragraph text
2092 @cindex reformatting paragraph text
2093 @cindex paragraphs, reformatting
2094 @cindex text, reformatting
2096 @command{fmt} fills and joins lines to produce output lines of (at most)
2097 a given number of characters (75 by default). Synopsis:
2100 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2103 @command{fmt} reads from the specified @var{file} arguments (or standard
2104 input if none are given), and writes to standard output.
2106 By default, blank lines, spaces between words, and indentation are
2107 preserved in the output; successive input lines with different
2108 indentation are not joined; tabs are expanded on input and introduced on
2111 @cindex line-breaking
2112 @cindex sentences and line-breaking
2113 @cindex Knuth, Donald E.
2114 @cindex Plass, Michael F.
2115 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2116 avoid line breaks after the first word of a sentence or before the last
2117 word of a sentence. A @dfn{sentence break} is defined as either the end
2118 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2119 spaces or end of line, ignoring any intervening parentheses or quotes.
2120 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2121 breaks; the algorithm is a variant of that given by Donald E. Knuth
2122 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2123 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2126 The program accepts the following options. Also see @ref{Common options}.
2131 @itemx --crown-margin
2133 @opindex --crown-margin
2134 @cindex crown margin
2135 @dfn{Crown margin} mode: preserve the indentation of the first two
2136 lines within a paragraph, and align the left margin of each subsequent
2137 line with that of the second line.
2140 @itemx --tagged-paragraph
2142 @opindex --tagged-paragraph
2143 @cindex tagged paragraphs
2144 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2145 indentation of the first line of a paragraph is the same as the
2146 indentation of the second, the first line is treated as a one-line
2152 @opindex --split-only
2153 Split lines only. Do not join short lines to form longer ones. This
2154 prevents sample lines of code, and other such ``formatted'' text from
2155 being unduly combined.
2158 @itemx --uniform-spacing
2160 @opindex --uniform-spacing
2161 Uniform spacing. Reduce spacing between words to one space, and spacing
2162 between sentences to two spaces.
2165 @itemx -w @var{width}
2166 @itemx --width=@var{width}
2167 @opindex -@var{width}
2170 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2171 initially tries to make lines about 7% shorter than this, to give it
2172 room to balance line lengths.
2174 @item -p @var{prefix}
2175 @itemx --prefix=@var{prefix}
2176 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2177 are subject to formatting. The prefix and any preceding whitespace are
2178 stripped for the formatting and then re-attached to each formatted output
2179 line. One use is to format certain kinds of program comments, while
2180 leaving the code unchanged.
2188 @section @command{pr}: Paginate or columnate files for printing
2191 @cindex printing, preparing files for
2192 @cindex multicolumn output, generating
2193 @cindex merging files in parallel
2195 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2196 standard input if none are given, to standard output, paginating and
2197 optionally outputting in multicolumn format; optionally merges all
2198 @var{file}s, printing all in parallel, one per column. Synopsis:
2201 pr [@var{option}]@dots{} [@var{file}]@dots{}
2205 By default, a 5-line header is printed at each page: two blank lines;
2206 a line with the date, the file name, and the page count; and two more
2207 blank lines. A footer of five blank lines is also printed.
2208 The default @var{page_length} is 66
2209 lines. The default number of text lines is therefore 56.
2210 The text line of the header takes the form
2211 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2212 @var{string} so that the line takes up the full @var{page_width}. Here,
2213 @var{date} is the date (see the @option{-D} or @option{--date-format}
2214 option for details), @var{string} is the centered header string, and
2215 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2216 category affects the spelling of @var{page}; in the default C locale, it
2217 is @samp{Page @var{number}} where @var{number} is the decimal page
2220 Form feeds in the input cause page breaks in the output. Multiple form
2221 feeds produce empty pages.
2223 Columns are of equal width, separated by an optional string (default
2224 is @samp{space}). For multicolumn output, lines will always be truncated to
2225 @var{page_width} (default 72), unless you use the @option{-J} option.
2227 column output no line truncation occurs by default. Use @option{-W} option to
2228 truncate lines in that case.
2230 The following changes were made in version 1.22i and apply to later
2231 versions of @command{pr}:
2232 @c FIXME: this whole section here sounds very awkward to me. I
2233 @c made a few small changes, but really it all needs to be redone. - Brian
2234 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2239 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2240 redefined for better @acronym{POSIX} compliance. The output of some further
2241 cases has been adapted to other Unix systems. These changes are not
2242 compatible with earlier versions of the program.
2245 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2246 have been introduced to turn off unexpected interferences of small letter
2247 options. The @option{-N} option and the second argument @var{last_page}
2248 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2249 form feeds set in the input files requires the @option{-T} option.
2252 Capital letter options override small letter ones.
2255 Some of the option-arguments (compare @option{-s}, @option{-e},
2256 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2257 preceding option letter (already stated in the @acronym{POSIX} specification).
2260 The program accepts the following options. Also see @ref{Common options}.
2264 @item +@var{first_page}[:@var{last_page}]
2265 @itemx --pages=@var{first_page}[:@var{last_page}]
2266 @c The two following @opindex lines evoke warnings because they contain `:'
2267 @c The `info' spec does not permit that. If we use those lines, we end
2268 @c up with truncated index entries that don't work.
2269 @c @opindex +@var{first_page}[:@var{last_page}]
2270 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2271 @opindex +@var{page_range}
2272 @opindex --pages=@var{page_range}
2273 Begin printing with page @var{first_page} and stop with @var{last_page}.
2274 Missing @samp{:@var{last_page}} implies end of file. While estimating
2275 the number of skipped pages each form feed in the input file results
2276 in a new page. Page counting with and without @samp{+@var{first_page}}
2277 is identical. By default, counting starts with the first page of input
2278 file (not first page printed). Line numbering may be altered by @option{-N}
2282 @itemx --columns=@var{column}
2283 @opindex -@var{column}
2285 @cindex down columns
2286 With each single @var{file}, produce @var{column} columns of output
2287 (default is 1) and print columns down, unless @option{-a} is used. The
2288 column width is automatically decreased as @var{column} increases; unless
2289 you use the @option{-W/-w} option to increase @var{page_width} as well.
2290 This option might well cause some lines to be truncated. The number of
2291 lines in the columns on each page are balanced. The options @option{-e}
2292 and @option{-i} are on for multiple text-column output. Together with
2293 @option{-J} option column alignment and line truncation is turned off.
2294 Lines of full length are joined in a free field format and @option{-S}
2295 option may set field separators. @option{-@var{column}} may not be used
2296 with @option{-m} option.
2302 @cindex across columns
2303 With each single @var{file}, print columns across rather than down. The
2304 @option{-@var{column}} option must be given with @var{column} greater than one.
2305 If a line is too long to fit in a column, it is truncated.
2308 @itemx --show-control-chars
2310 @opindex --show-control-chars
2311 Print control characters using hat notation (e.g., @samp{^G}); print
2312 other nonprinting characters in octal backslash notation. By default,
2313 nonprinting characters are not changed.
2316 @itemx --double-space
2318 @opindex --double-space
2319 @cindex double spacing
2320 Double space the output.
2322 @item -D @var{format}
2323 @itemx --date-format=@var{format}
2324 @cindex time formats
2325 @cindex formatting times
2326 Format header dates using @var{format}, using the same conventions as
2327 for the command @samp{date +@var{format}}; @xref{date invocation}.
2328 Except for directives, which start with
2329 @samp{%}, characters in @var{format} are printed unchanged. You can use
2330 this option to specify an arbitrary string in place of the header date,
2331 e.g., @option{--date-format="Monday morning"}.
2333 @vindex POSIXLY_CORRECT
2335 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2336 @samp{2001-12-04 23:59});
2337 but if the @env{POSIXLY_CORRECT} environment variable is set
2338 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2339 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2340 @samp{Dec@ @ 4 23:59 2001}.
2343 Time stamps are listed according to the time zone rules specified by
2344 the @env{TZ} environment variable, or by the system default rules if
2345 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2346 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2348 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2349 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2351 @opindex --expand-tabs
2353 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2354 the input tab character (default is the TAB character). Second optional
2355 argument @var{in-tabwidth} is the input tab character's width (default
2363 @opindex --form-feed
2364 Use a form feed instead of newlines to separate output pages. This does
2365 not alter the default page length of 66 lines.
2367 @item -h @var{header}
2368 @itemx --header=@var{header}
2371 Replace the file name in the header with the centered string @var{header}.
2372 When using the shell, @var{header} should be quoted and should be
2373 separated from @option{-h} by a space.
2375 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2376 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2378 @opindex --output-tabs
2380 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2381 is the output tab character (default is the TAB character). Second optional
2382 argument @var{out-tabwidth} is the output tab character's width (default
2388 @opindex --join-lines
2389 Merge lines of full length. Used together with the column options
2390 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2391 @option{-W/-w} line truncation;
2392 no column alignment used; may be used with
2393 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2394 (together with @option{-W} and @option{--sep-string})
2395 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2396 @option{-s} along with the three column options.
2399 @item -l @var{page_length}
2400 @itemx --length=@var{page_length}
2403 Set the page length to @var{page_length} (default 66) lines, including
2404 the lines of the header [and the footer]. If @var{page_length} is less
2405 than or equal to 10, the header and footer are omitted, as if the
2406 @option{-t} option had been given.
2412 Merge and print all @var{file}s in parallel, one in each column. If a
2413 line is too long to fit in a column, it is truncated, unless the @option{-J}
2414 option is used. @option{--sep-string[=@var{string}]} may be used.
2416 some @var{file}s (form feeds set) produce empty columns, still marked
2417 by @var{string}. The result is a continuous line numbering and column
2418 marking throughout the whole merged file. Completely empty merged pages
2419 show no separators or line numbers. The default header becomes
2420 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2421 may be used with the @option{-h} or @option{--header} option to fill up
2422 the middle blank part.
2424 @item -n[@var{number-separator}[@var{digits}]]
2425 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2427 @opindex --number-lines
2428 Provide @var{digits} digit line numbering (default for @var{digits} is
2429 5). With multicolumn output the number occupies the first @var{digits}
2430 column positions of each text column or only each line of @option{-m}
2431 output. With single column output the number precedes each line just as
2432 @option{-m} does. Default counting of the line numbers starts with the
2433 first line of the input file (not the first line printed, compare the
2434 @option{--page} option and @option{-N} option).
2435 Optional argument @var{number-separator} is the character appended to
2436 the line number to separate it from the text followed. The default
2437 separator is the TAB character. In a strict sense a TAB is always
2438 printed with single column output only. The TAB width varies
2439 with the TAB position, e.g., with the left @var{margin} specified
2440 by @option{-o} option. With multicolumn output priority is given to
2441 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2442 The TAB width is fixed to the value of the first column and does
2443 not change with different values of left @var{margin}. That means a
2444 fixed number of spaces is always printed in the place of the
2445 @var{number-separator} TAB. The tabification depends upon the output
2448 @item -N @var{line_number}
2449 @itemx --first-line-number=@var{line_number}
2451 @opindex --first-line-number
2452 Start line counting with the number @var{line_number} at first line of
2453 first page printed (in most cases not the first line of the input file).
2455 @item -o @var{margin}
2456 @itemx --indent=@var{margin}
2459 @cindex indenting lines
2461 Indent each line with a margin @var{margin} spaces wide (default is zero).
2462 The total page width is the size of the margin plus the @var{page_width}
2463 set with the @option{-W/-w} option. A limited overflow may occur with
2464 numbered single column output (compare @option{-n} option).
2467 @itemx --no-file-warnings
2469 @opindex --no-file-warnings
2470 Do not print a warning message when an argument @var{file} cannot be
2471 opened. (The exit status will still be nonzero, however.)
2473 @item -s[@var{char}]
2474 @itemx --separator[=@var{char}]
2476 @opindex --separator
2477 Separate columns by a single character @var{char}. The default for
2478 @var{char} is the TAB character without @option{-w} and @samp{no
2479 character} with @option{-w}. Without @option{-s} the default separator
2480 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2481 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2482 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2485 @item -S@var{string}
2486 @itemx --sep-string[=@var{string}]
2488 @opindex --sep-string
2489 Use @var{string} to separate output columns. The @option{-S} option doesn't
2490 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2491 does not affect line truncation or column alignment.
2492 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2494 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2495 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2496 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2499 @itemx --omit-header
2501 @opindex --omit-header
2502 Do not print the usual header [and footer] on each page, and do not fill
2503 out the bottom of pages (with blank lines or a form feed). No page
2504 structure is produced, but form feeds set in the input files are retained.
2505 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2506 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2507 in the input file to 4 spaces but don't make any other changes. Use of
2508 @option{-t} overrides @option{-h}.
2511 @itemx --omit-pagination
2513 @opindex --omit-pagination
2514 Do not print header [and footer]. In addition eliminate all form feeds
2515 set in the input files.
2518 @itemx --show-nonprinting
2520 @opindex --show-nonprinting
2521 Print nonprinting characters in octal backslash notation.
2523 @item -w @var{page_width}
2524 @itemx --width=@var{page_width}
2527 Set page width to @var{page_width} characters for multiple text-column
2528 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2529 off the default page width and any line truncation and column alignment.
2530 Lines of full length are merged, regardless of the column options
2531 set. No @var{page_width} setting is possible with single column output.
2532 A @acronym{POSIX}-compliant formulation.
2534 @item -W @var{page_width}
2535 @itemx --page_width=@var{page_width}
2537 @opindex --page_width
2538 Set the page width to @var{page_width} characters. That's valid with and
2539 without a column option. Text lines are truncated, unless @option{-J}
2540 is used. Together with one of the three column options
2541 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2542 alignment is always used. The separator options @option{-S} or @option{-s}
2543 don't affect the @option{-W} option. Default is 72 characters. Without
2544 @option{-W @var{page_width}} and without any of the column options NO line
2545 truncation is used (defined to keep downward compatibility and to meet
2546 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2547 line is never truncated.
2554 @node fold invocation
2555 @section @command{fold}: Wrap input lines to fit in specified width
2558 @cindex wrapping long input lines
2559 @cindex folding long input lines
2561 @command{fold} writes each @var{file} (@option{-} means standard input), or
2562 standard input if none are given, to standard output, breaking long
2566 fold [@var{option}]@dots{} [@var{file}]@dots{}
2569 By default, @command{fold} breaks lines wider than 80 columns. The output
2570 is split into as many lines as necessary.
2572 @cindex screen columns
2573 @command{fold} counts screen columns by default; thus, a tab may count more
2574 than one column, backspace decreases the column count, and carriage
2575 return sets the column to zero.
2577 The program accepts the following options. Also see @ref{Common options}.
2585 Count bytes rather than columns, so that tabs, backspaces, and carriage
2586 returns are each counted as taking up one column, just like other
2593 Break at word boundaries: the line is broken after the last blank before
2594 the maximum line length. If the line contains no such blanks, the line
2595 is broken at the maximum line length as usual.
2597 @item -w @var{width}
2598 @itemx --width=@var{width}
2601 Use a maximum line length of @var{width} columns instead of 80.
2603 For compatibility @command{fold} supports an obsolete option syntax
2604 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2612 @node Output of parts of files
2613 @chapter Output of parts of files
2615 @cindex output of parts of files
2616 @cindex parts of files, output of
2618 These commands output pieces of the input.
2621 * head invocation:: Output the first part of files.
2622 * tail invocation:: Output the last part of files.
2623 * split invocation:: Split a file into fixed-size pieces.
2624 * csplit invocation:: Split a file into context-determined pieces.
2627 @node head invocation
2628 @section @command{head}: Output the first part of files
2631 @cindex initial part of files, outputting
2632 @cindex first part of files, outputting
2634 @command{head} prints the first part (10 lines by default) of each
2635 @var{file}; it reads from standard input if no files are given or
2636 when given a @var{file} of @option{-}. Synopsis:
2639 head [@var{option}]@dots{} [@var{file}]@dots{}
2642 If more than one @var{file} is specified, @command{head} prints a
2643 one-line header consisting of:
2646 ==> @var{file name} <==
2650 before the output for each @var{file}.
2652 The program accepts the following options. Also see @ref{Common options}.
2657 @itemx --bytes=@var{k}
2660 Print the first @var{k} bytes, instead of initial lines.
2661 However, if @var{k} starts with a @samp{-},
2662 print all but the last @var{k} bytes of each file.
2663 @multiplierSuffixes{k}
2666 @itemx --lines=@var{k}
2669 Output the first @var{k} lines.
2670 However, if @var{k} starts with a @samp{-},
2671 print all but the last @var{k} lines of each file.
2672 Size multiplier suffixes are the same as with the @option{-c} option.
2680 Never print file name headers.
2686 Always print file name headers.
2690 For compatibility @command{head} also supports an obsolete option syntax
2691 @option{-@var{count}@var{options}}, which is recognized only if it is
2692 specified first. @var{count} is a decimal number optionally followed
2693 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2694 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2695 Scripts intended for standard hosts should use @option{-c @var{count}}
2696 or @option{-n @var{count}} instead. If your script must also run on
2697 hosts that support only the obsolete syntax, it is usually simpler to
2698 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2704 @node tail invocation
2705 @section @command{tail}: Output the last part of files
2708 @cindex last part of files, outputting
2710 @command{tail} prints the last part (10 lines by default) of each
2711 @var{file}; it reads from standard input if no files are given or
2712 when given a @var{file} of @samp{-}. Synopsis:
2715 tail [@var{option}]@dots{} [@var{file}]@dots{}
2718 If more than one @var{file} is specified, @command{tail} prints a
2719 one-line header consisting of:
2722 ==> @var{file name} <==
2726 before the output for each @var{file}.
2728 @cindex BSD @command{tail}
2729 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2730 @command{tail} cannot). It also has no @option{-r} option (print in
2731 reverse), since reversing a file is really a different job from printing
2732 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2733 only reverse files that are at most as large as its buffer, which is
2734 typically 32 KiB@. A more reliable and versatile way to reverse files is
2735 the @sc{gnu} @command{tac} command.
2737 The program accepts the following options. Also see @ref{Common options}.
2742 @itemx --bytes=@var{k}
2745 Output the last @var{k} bytes, instead of final lines.
2746 However, if @var{k} starts with a @samp{+}, start printing with the
2747 @var{k}th byte from the start of each file, instead of from the end.
2748 @multiplierSuffixes{k}
2751 @itemx --follow[=@var{how}]
2754 @cindex growing files
2755 @vindex name @r{follow option}
2756 @vindex descriptor @r{follow option}
2757 Loop forever trying to read more characters at the end of the file,
2758 presumably because the file is growing.
2759 If more than one file is given, @command{tail} prints a header whenever it
2760 gets output from a different file, to indicate which file that output is
2763 There are two ways to specify how you'd like to track files with this option,
2764 but that difference is noticeable only when a followed file is removed or
2766 If you'd like to continue to track the end of a growing file even after
2767 it has been unlinked, use @option{--follow=descriptor}. This is the default
2768 behavior, but it is not useful if you're tracking a log file that may be
2769 rotated (removed or renamed, then reopened). In that case, use
2770 @option{--follow=name} to track the named file by reopening it periodically
2771 to see if it has been removed and recreated by some other program.
2773 No matter which method you use, if the tracked file is determined to have
2774 shrunk, @command{tail} prints a message saying the file has been truncated
2775 and resumes tracking the end of the file from the newly-determined endpoint.
2777 When a file is removed, @command{tail}'s behavior depends on whether it is
2778 following the name or the descriptor. When following by name, tail can
2779 detect that a file has been removed and gives a message to that effect,
2780 and if @option{--retry} has been specified it will continue checking
2781 periodically to see if the file reappears.
2782 When following a descriptor, tail does not detect that the file has
2783 been unlinked or renamed and issues no message; even though the file
2784 may no longer be accessible via its original name, it may still be
2787 The option values @samp{descriptor} and @samp{name} may be specified only
2788 with the long form of the option, not with @option{-f}.
2790 The @option{-f} option is ignored if
2791 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2792 Likewise, the @option{-f} option has no effect for any
2793 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2797 This option is the same as @option{--follow=name --retry}. That is, tail
2798 will attempt to reopen a file when it is removed. Should this fail, tail
2799 will keep trying until it becomes accessible again.
2803 This option is useful mainly when following by name (i.e., with
2804 @option{--follow=name}).
2805 Without this option, when tail encounters a file that doesn't
2806 exist or is otherwise inaccessible, it reports that fact and
2807 never checks it again.
2809 @itemx --sleep-interval=@var{number}
2810 @opindex --sleep-interval
2811 Change the number of seconds to wait between iterations (the default is 1.0).
2812 During one iteration, every specified file is checked to see if it has
2814 Historical implementations of @command{tail} have required that
2815 @var{number} be an integer. However, GNU @command{tail} accepts
2816 an arbitrary floating point number (using a period before any
2819 @itemx --pid=@var{pid}
2821 When following by name or by descriptor, you may specify the process ID,
2822 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2823 after that process terminates, tail will also terminate. This will
2824 work properly only if the writer and the tailing process are running on
2825 the same machine. For example, to save the output of a build in a file
2826 and to watch the file grow, if you invoke @command{make} and @command{tail}
2827 like this then the tail process will stop when your build completes.
2828 Without this option, you would have had to kill the @code{tail -f}
2832 $ make >& makerr & tail --pid=$! -f makerr
2835 If you specify a @var{pid} that is not in use or that does not correspond
2836 to the process that is writing to the tailed files, then @command{tail}
2837 may terminate long before any @var{file}s stop growing or it may not
2838 terminate until long after the real writer has terminated.
2839 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2840 will print a warning if this is the case.
2842 @itemx --max-unchanged-stats=@var{n}
2843 @opindex --max-unchanged-stats
2844 When tailing a file by name, if there have been @var{n} (default
2845 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2846 iterations for which the file has not changed, then
2847 @code{open}/@code{fstat} the file to determine if that file name is
2848 still associated with the same device/inode-number pair as before.
2849 When following a log file that is rotated, this is approximately the
2850 number of seconds between when tail prints the last pre-rotation lines
2851 and when it prints the lines that have accumulated in the new log file.
2852 This option is meaningful only when following by name.
2855 @itemx --lines=@var{k}
2858 Output the last @var{k} lines.
2859 However, if @var{k} starts with a @samp{+}, start printing with the
2860 @var{k}th line from the start of each file, instead of from the end.
2861 Size multiplier suffixes are the same as with the @option{-c} option.
2869 Never print file name headers.
2875 Always print file name headers.
2879 For compatibility @command{tail} also supports an obsolete usage
2880 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2881 only if it does not conflict with the usage described
2882 above. This obsolete form uses exactly one option and at most one
2883 file. In the option, @var{count} is an optional decimal number optionally
2884 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2885 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2886 which has the same meaning as @option{-f}.
2888 @vindex _POSIX2_VERSION
2889 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2890 the obsolete option syntax with the same meaning as in counts, and
2891 obsolete usage overrides normal usage when the two conflict.
2892 This obsolete behavior can be enabled or disabled with the
2893 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2896 Scripts intended for use on standard hosts should avoid obsolete
2897 syntax and should use @option{-c @var{count}[b]}, @option{-n
2898 @var{count}}, and/or @option{-f} instead. If your script must also
2899 run on hosts that support only the obsolete syntax, you can often
2900 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2901 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2902 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2903 then @dots{}} to decide which syntax to use.
2905 Even if your script assumes the standard behavior, you should still
2906 beware usages whose behaviors differ depending on the @acronym{POSIX}
2907 version. For example, avoid @samp{tail - main.c}, since it might be
2908 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2909 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2910 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2911 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2916 @node split invocation
2917 @section @command{split}: Split a file into fixed-size pieces
2920 @cindex splitting a file into pieces
2921 @cindex pieces, splitting a file into
2923 @command{split} creates output files containing consecutive sections of
2924 @var{input} (standard input if none is given or @var{input} is
2925 @samp{-}). Synopsis:
2928 split [@var{option}] [@var{input} [@var{prefix}]]
2931 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2932 left over for the last section), into each output file.
2934 @cindex output file name prefix
2935 The output files' names consist of @var{prefix} (@samp{x} by default)
2936 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2937 default), such that concatenating the output files in traditional
2938 sorted order by file name produces
2939 the original input file. If the output file names are exhausted,
2940 @command{split} reports an error without deleting the output files
2943 The program accepts the following options. Also see @ref{Common options}.
2947 @item -l @var{lines}
2948 @itemx --lines=@var{lines}
2951 Put @var{lines} lines of @var{input} into each output file.
2953 For compatibility @command{split} also supports an obsolete
2954 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2955 @var{lines}} instead.
2958 @itemx --bytes=@var{size}
2961 Put @var{size} bytes of @var{input} into each output file.
2962 @multiplierSuffixes{size}
2965 @itemx --line-bytes=@var{size}
2967 @opindex --line-bytes
2968 Put into each output file as many complete lines of @var{input} as
2969 possible without exceeding @var{size} bytes. Individual lines longer than
2970 @var{size} bytes are broken into multiple files.
2971 @var{size} has the same format as for the @option{--bytes} option.
2973 @item -a @var{length}
2974 @itemx --suffix-length=@var{length}
2976 @opindex --suffix-length
2977 Use suffixes of length @var{length}. The default @var{length} is 2.
2980 @itemx --numeric-suffixes
2982 @opindex --numeric-suffixes
2983 Use digits in suffixes rather than lower-case letters.
2987 Write a diagnostic just before each output file is opened.
2994 @node csplit invocation
2995 @section @command{csplit}: Split a file into context-determined pieces
2998 @cindex context splitting
2999 @cindex splitting a file into pieces by context
3001 @command{csplit} creates zero or more output files containing sections of
3002 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3005 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3008 The contents of the output files are determined by the @var{pattern}
3009 arguments, as detailed below. An error occurs if a @var{pattern}
3010 argument refers to a nonexistent line of the input file (e.g., if no
3011 remaining line matches a given regular expression). After every
3012 @var{pattern} has been matched, any remaining input is copied into one
3015 By default, @command{csplit} prints the number of bytes written to each
3016 output file after it has been created.
3018 The types of pattern arguments are:
3023 Create an output file containing the input up to but not including line
3024 @var{n} (a positive integer). If followed by a repeat count, also
3025 create an output file containing the next @var{n} lines of the input
3026 file once for each repeat.
3028 @item /@var{regexp}/[@var{offset}]
3029 Create an output file containing the current line up to (but not
3030 including) the next line of the input file that contains a match for
3031 @var{regexp}. The optional @var{offset} is an integer.
3032 If it is given, the input up to (but not including) the
3033 matching line plus or minus @var{offset} is put into the output file,
3034 and the line after that begins the next section of input.
3036 @item %@var{regexp}%[@var{offset}]
3037 Like the previous type, except that it does not create an output
3038 file, so that section of the input file is effectively ignored.
3040 @item @{@var{repeat-count}@}
3041 Repeat the previous pattern @var{repeat-count} additional
3042 times. The @var{repeat-count} can either be a positive integer or an
3043 asterisk, meaning repeat as many times as necessary until the input is
3048 The output files' names consist of a prefix (@samp{xx} by default)
3049 followed by a suffix. By default, the suffix is an ascending sequence
3050 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3051 concatenating the output files in sorted order by file name produces the
3052 original input file.
3054 By default, if @command{csplit} encounters an error or receives a hangup,
3055 interrupt, quit, or terminate signal, it removes any output files
3056 that it has created so far before it exits.
3058 The program accepts the following options. Also see @ref{Common options}.
3062 @item -f @var{prefix}
3063 @itemx --prefix=@var{prefix}
3066 @cindex output file name prefix
3067 Use @var{prefix} as the output file name prefix.
3069 @item -b @var{suffix}
3070 @itemx --suffix=@var{suffix}
3073 @cindex output file name suffix
3074 Use @var{suffix} as the output file name suffix. When this option is
3075 specified, the suffix string must include exactly one
3076 @code{printf(3)}-style conversion specification, possibly including
3077 format specification flags, a field width, a precision specifications,
3078 or all of these kinds of modifiers. The format letter must convert a
3079 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3080 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3081 entire @var{suffix} is given (with the current output file number) to
3082 @code{sprintf(3)} to form the file name suffixes for each of the
3083 individual output files in turn. If this option is used, the
3084 @option{--digits} option is ignored.
3086 @item -n @var{digits}
3087 @itemx --digits=@var{digits}
3090 Use output file names containing numbers that are @var{digits} digits
3091 long instead of the default 2.
3096 @opindex --keep-files
3097 Do not remove output files when errors are encountered.
3100 @itemx --elide-empty-files
3102 @opindex --elide-empty-files
3103 Suppress the generation of zero-length output files. (In cases where
3104 the section delimiters of the input file are supposed to mark the first
3105 lines of each of the sections, the first output file will generally be a
3106 zero-length file unless you use this option.) The output file sequence
3107 numbers always run consecutively starting from 0, even when this option
3118 Do not print counts of output file sizes.
3124 Here is an example of its usage.
3125 First, create an empty directory for the exercise,
3132 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3135 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3141 Each number printed above is the size of an output
3142 file that csplit has just created.
3143 List the names of those output files:
3150 Use @command{head} to show their contents:
3175 @node Summarizing files
3176 @chapter Summarizing files
3178 @cindex summarizing files
3180 These commands generate just a few numbers representing entire
3184 * wc invocation:: Print newline, word, and byte counts.
3185 * sum invocation:: Print checksum and block counts.
3186 * cksum invocation:: Print CRC checksum and byte counts.
3187 * md5sum invocation:: Print or check MD5 digests.
3188 * sha1sum invocation:: Print or check SHA-1 digests.
3189 * sha2 utilities:: Print or check SHA-2 digests.
3194 @section @command{wc}: Print newline, word, and byte counts
3198 @cindex character count
3202 @command{wc} counts the number of bytes, characters, whitespace-separated
3203 words, and newlines in each given @var{file}, or standard input if none
3204 are given or for a @var{file} of @samp{-}. Synopsis:
3207 wc [@var{option}]@dots{} [@var{file}]@dots{}
3210 @cindex total counts
3211 @command{wc} prints one line of counts for each file, and if the file was
3212 given as an argument, it prints the file name following the counts. If
3213 more than one @var{file} is given, @command{wc} prints a final line
3214 containing the cumulative counts, with the file name @file{total}. The
3215 counts are printed in this order: newlines, words, characters, bytes,
3216 maximum line length.
3217 Each count is printed right-justified in a field with at least one
3218 space between fields so that the numbers and file names normally line
3219 up nicely in columns. The width of the count fields varies depending
3220 on the inputs, so you should not depend on a particular field width.
3221 However, as a @acronym{GNU} extension, if only one count is printed,
3222 it is guaranteed to be printed without leading spaces.
3224 By default, @command{wc} prints three counts: the newline, words, and byte
3225 counts. Options can specify that only certain counts be printed.
3226 Options do not undo others previously given, so
3233 prints both the byte counts and the word counts.
3235 With the @option{--max-line-length} option, @command{wc} prints the length
3236 of the longest line per file, and if there is more than one file it
3237 prints the maximum (not the sum) of those lengths. The line lengths here
3238 are measured in screen columns, according to the current locale and
3239 assuming tab positions in every 8th column.
3241 The program accepts the following options. Also see @ref{Common options}.
3249 Print only the byte counts.
3255 Print only the character counts.
3261 Print only the word counts.
3267 Print only the newline counts.
3270 @itemx --max-line-length
3272 @opindex --max-line-length
3273 Print only the maximum line lengths.
3275 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3276 @itemx --files0-from=@var{file}
3277 @opindex --files0-from=@var{file}
3278 @c This is commented out to avoid a texi2dvi failure.
3279 @c texi2dvi (GNU Texinfo 4.11) 1.104
3280 @c @cindex including files from @command{\cmd\}
3281 Disallow processing files named on the command line, and instead process
3282 those named in file @var{file}; each name being terminated by a zero byte
3283 (@acronym{ASCII} @sc{nul}).
3284 This is useful \withTotalOption\
3285 when the list of file names is so long that it may exceed a command line
3287 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3288 because it splits the list into pieces and makes @command{\cmd\} print
3289 \subListOutput\ for each sublist rather than for the entire list.
3290 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3291 @command{find}, using its @option{-print0} predicate.
3292 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3293 are read from standard input.
3295 @filesZeroFromOption{wc,,a total}
3297 For example, to find the length of the longest line in any @file{.c} or
3298 @file{.h} file in the current hierarchy, do this:
3301 find . -name '*.[ch]' -print0 |
3302 wc -L --files0-from=- | tail -n1
3310 @node sum invocation
3311 @section @command{sum}: Print checksum and block counts
3314 @cindex 16-bit checksum
3315 @cindex checksum, 16-bit
3317 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3318 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3321 sum [@var{option}]@dots{} [@var{file}]@dots{}
3324 @command{sum} prints the checksum for each @var{file} followed by the
3325 number of blocks in the file (rounded up). If more than one @var{file}
3326 is given, file names are also printed (by default). (With the
3327 @option{--sysv} option, corresponding file names are printed when there is
3328 at least one file argument.)
3330 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3331 compatible with BSD @command{sum} and prints file sizes in units of
3334 The program accepts the following options. Also see @ref{Common options}.
3340 @cindex BSD @command{sum}
3341 Use the default (BSD compatible) algorithm. This option is included for
3342 compatibility with the System V @command{sum}. Unless @option{-s} was also
3343 given, it has no effect.
3349 @cindex System V @command{sum}
3350 Compute checksums using an algorithm compatible with System V
3351 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3355 @command{sum} is provided for compatibility; the @command{cksum} program (see
3356 next section) is preferable in new applications.
3361 @node cksum invocation
3362 @section @command{cksum}: Print CRC checksum and byte counts
3365 @cindex cyclic redundancy check
3366 @cindex CRC checksum
3368 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3369 given @var{file}, or standard input if none are given or for a
3370 @var{file} of @samp{-}. Synopsis:
3373 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3376 @command{cksum} prints the CRC checksum for each file along with the number
3377 of bytes in the file, and the file name unless no arguments were given.
3379 @command{cksum} is typically used to ensure that files
3380 transferred by unreliable means (e.g., netnews) have not been corrupted,
3381 by comparing the @command{cksum} output for the received files with the
3382 @command{cksum} output for the original files (typically given in the
3385 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3386 compatible with the BSD or System V @command{sum} algorithms (see the
3387 previous section); it is more robust.
3389 The only options are @option{--help} and @option{--version}. @xref{Common
3395 @node md5sum invocation
3396 @section @command{md5sum}: Print or check MD5 digests
3400 @cindex 128-bit checksum
3401 @cindex checksum, 128-bit
3402 @cindex fingerprint, 128-bit
3403 @cindex message-digest, 128-bit
3405 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3406 @dfn{message-digest}) for each specified @var{file}.
3408 Note: The MD5 digest is more reliable than a simple CRC (provided by
3409 the @command{cksum} command) for detecting accidental file corruption,
3410 as the chances of accidentally having two files with identical MD5
3411 are vanishingly small. However, it should not be considered truly
3412 secure against malicious tampering: although finding a file with a
3413 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3414 considered infeasible at the moment, it is known how to produce
3415 different files with identical MD5 (a ``collision''), something which
3416 can be a security issue in certain contexts. For more secure hashes,
3417 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3418 @ref{sha2 utilities}.
3420 If a @var{file} is specified as @samp{-} or if no files are given
3421 @command{md5sum} computes the checksum for the standard input.
3422 @command{md5sum} can also determine whether a file and checksum are
3423 consistent. Synopsis:
3426 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3429 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3430 indicating a binary or text input file, and the file name.
3431 If @var{file} contains a backslash or newline, the
3432 line is started with a backslash, and each problematic character in
3433 the file name is escaped with a backslash, making the output
3434 unambiguous even in the presence of arbitrary file names.
3435 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3437 The program accepts the following options. Also see @ref{Common options}.
3445 @cindex binary input files
3446 Treat each input file as binary, by reading it in binary mode and
3447 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3448 On systems like @acronym{GNU} that do not distinguish between binary
3449 and text files, this option merely flags each input file as binary:
3450 the MD5 checksum is unaffected. This option is the default on systems
3451 like MS-DOS that distinguish between binary and text files, except
3452 for reading standard input when standard input is a terminal.
3456 Read file names and checksum information (not data) from each
3457 @var{file} (or from stdin if no @var{file} was specified) and report
3458 whether the checksums match the contents of the named files.
3459 The input to this mode of @command{md5sum} is usually the output of
3460 a prior, checksum-generating run of @samp{md5sum}.
3461 Each valid line of input consists of an MD5 checksum, a binary/text
3462 flag, and then a file name.
3463 Binary files are marked with @samp{*}, text with @samp{ }.
3464 For each such line, @command{md5sum} reads the named file and computes its
3465 MD5 checksum. Then, if the computed message digest does not match the
3466 one on the line with the file name, the file is noted as having
3467 failed the test. Otherwise, the file passes the test.
3468 By default, for each valid line, one line is written to standard
3469 output indicating whether the named file passed the test.
3470 After all checks have been performed, if there were any failures,
3471 a warning is issued to standard error.
3472 Use the @option{--status} option to inhibit that output.
3473 If any listed file cannot be opened or read, if any valid line has
3474 an MD5 checksum inconsistent with the associated file, or if no valid
3475 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3476 it exits successfully.
3480 @cindex verifying MD5 checksums
3481 This option is useful only when verifying checksums.
3482 When verifying checksums, don't generate an 'OK' message per successfully
3483 checked file. Files that fail the verification are reported in the
3484 default one-line-per-file format. If there is any checksum mismatch,
3485 print a warning summarizing the failures to standard error.
3489 @cindex verifying MD5 checksums
3490 This option is useful only when verifying checksums.
3491 When verifying checksums, don't generate the default one-line-per-file
3492 diagnostic and don't output the warning summarizing any failures.
3493 Failures to open or read a file still evoke individual diagnostics to
3495 If all listed files are readable and are consistent with the associated
3496 MD5 checksums, exit successfully. Otherwise exit with a status code
3497 indicating there was a failure.
3503 @cindex text input files
3504 Treat each input file as text, by reading it in text mode and
3505 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3506 This option is the default on systems like @acronym{GNU} that do not
3507 distinguish between binary and text files. On other systems, it is
3508 the default for reading standard input when standard input is a
3515 @cindex verifying MD5 checksums
3516 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3517 This option is useful only if all but a few lines in the checked input
3525 @node sha1sum invocation
3526 @section @command{sha1sum}: Print or check SHA-1 digests
3530 @cindex 160-bit checksum
3531 @cindex checksum, 160-bit
3532 @cindex fingerprint, 160-bit
3533 @cindex message-digest, 160-bit
3535 @command{sha1sum} computes a 160-bit checksum for each specified
3536 @var{file}. The usage and options of this command are precisely the
3537 same as for @command{md5sum}. @xref{md5sum invocation}.
3539 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3540 it are known (different files having the same fingerprint). However,
3541 it is known that they can be produced with considerable, but not
3542 unreasonable, resources. For this reason, it is generally considered
3543 that SHA-1 should be gradually phased out in favor of the more secure
3544 SHA-2 hash algorithms. @xref{sha2 utilities}.
3547 @node sha2 utilities
3548 @section sha2 utilities: Print or check SHA-2 digests
3555 @cindex 224-bit checksum
3556 @cindex 256-bit checksum
3557 @cindex 384-bit checksum
3558 @cindex 512-bit checksum
3559 @cindex checksum, 224-bit
3560 @cindex checksum, 256-bit
3561 @cindex checksum, 384-bit
3562 @cindex checksum, 512-bit
3563 @cindex fingerprint, 224-bit
3564 @cindex fingerprint, 256-bit
3565 @cindex fingerprint, 384-bit
3566 @cindex fingerprint, 512-bit
3567 @cindex message-digest, 224-bit
3568 @cindex message-digest, 256-bit
3569 @cindex message-digest, 384-bit
3570 @cindex message-digest, 512-bit
3572 The commands @command{sha224sum}, @command{sha256sum},
3573 @command{sha384sum} and @command{sha512sum} compute checksums of
3574 various lengths (respectively 224, 256, 384 and 512 bits),
3575 collectively known as the SHA-2 hashes. The usage and options of
3576 these commands are precisely the same as for @command{md5sum}.
3577 @xref{md5sum invocation}.
3579 Note: The SHA384 and SHA512 digests are considerably slower to
3580 compute, especially on 32-bit computers, than SHA224 or SHA256.
3583 @node Operating on sorted files
3584 @chapter Operating on sorted files
3586 @cindex operating on sorted files
3587 @cindex sorted files, operations on
3589 These commands work with (or produce) sorted files.
3592 * sort invocation:: Sort text files.
3593 * shuf invocation:: Shuffle text files.
3594 * uniq invocation:: Uniquify files.
3595 * comm invocation:: Compare two sorted files line by line.
3596 * ptx invocation:: Produce a permuted index of file contents.
3597 * tsort invocation:: Topological sort.
3601 @node sort invocation
3602 @section @command{sort}: Sort text files
3605 @cindex sorting files
3607 @command{sort} sorts, merges, or compares all the lines from the given
3608 files, or standard input if none are given or for a @var{file} of
3609 @samp{-}. By default, @command{sort} writes the results to standard
3613 sort [@var{option}]@dots{} [@var{file}]@dots{}
3616 @command{sort} has three modes of operation: sort (the default), merge,
3617 and check for sortedness. The following options change the operation
3624 @itemx --check=diagnose-first
3627 @cindex checking for sortedness
3628 Check whether the given file is already sorted: if it is not all
3629 sorted, print a diagnostic containing the first out-of-order line and
3630 exit with a status of 1.
3631 Otherwise, exit successfully.
3632 At most one input file can be given.
3635 @itemx --check=quiet
3636 @itemx --check=silent
3639 @cindex checking for sortedness
3640 Exit successfully if the given file is already sorted, and
3641 exit with status 1 otherwise.
3642 At most one input file can be given.
3643 This is like @option{-c}, except it does not print a diagnostic.
3649 @cindex merging sorted files
3650 Merge the given files by sorting them as a group. Each input file must
3651 always be individually sorted. It always works to sort instead of
3652 merge; merging is provided because it is faster, in the case where it
3657 @cindex sort stability
3658 @cindex sort's last-resort comparison
3659 A pair of lines is compared as follows:
3660 @command{sort} compares each pair of fields, in the
3661 order specified on the command line, according to the associated
3662 ordering options, until a difference is found or no fields are left.
3663 If no key fields are specified, @command{sort} uses a default key of
3664 the entire line. Finally, as a last resort when all keys compare
3665 equal, @command{sort} compares entire lines as if no ordering options
3666 other than @option{--reverse} (@option{-r}) were specified. The
3667 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3668 comparison} so that lines in which all fields compare equal are left
3669 in their original relative order. The @option{--unique}
3670 (@option{-u}) option also disables the last-resort comparison.
3674 Unless otherwise specified, all comparisons use the character collating
3675 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3676 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3677 to @samp{en_US}), then @command{sort} may produce output that is sorted
3678 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3679 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3680 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3681 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3682 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3683 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3684 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3686 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3687 limit on input line length or restrictions on bytes allowed within lines.
3688 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3689 @command{sort} silently supplies one. A line's trailing newline is not
3690 part of the line for comparison purposes.
3692 @cindex exit status of @command{sort}
3696 0 if no error occurred
3697 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3698 2 if an error occurred
3702 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3703 value as the directory for temporary files instead of @file{/tmp}. The
3704 @option{--temporary-directory} (@option{-T}) option in turn overrides
3705 the environment variable.
3707 The following options affect the ordering of output lines. They may be
3708 specified globally or as part of a specific key field. If no key
3709 fields are specified, global options apply to comparison of entire
3710 lines; otherwise the global options are inherited by key fields that do
3711 not specify any special options of their own. In pre-@acronym{POSIX}
3712 versions of @command{sort}, global options affect only later key fields,
3713 so portable shell scripts should specify global options first.
3718 @itemx --ignore-leading-blanks
3720 @opindex --ignore-leading-blanks
3721 @cindex blanks, ignoring leading
3723 Ignore leading blanks when finding sort keys in each line.
3724 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3725 can change this. Note blanks may be ignored by your locale's collating
3726 rules, but without this option they will be significant for character
3727 positions specified in keys with the @option{-k} option.
3730 @itemx --dictionary-order
3732 @opindex --dictionary-order
3733 @cindex dictionary order
3734 @cindex phone directory order
3735 @cindex telephone directory order
3737 Sort in @dfn{phone directory} order: ignore all characters except
3738 letters, digits and blanks when sorting.
3739 By default letters and digits are those of @acronym{ASCII} and a blank
3740 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3743 @itemx --ignore-case
3745 @opindex --ignore-case
3746 @cindex ignoring case
3747 @cindex case folding
3749 Fold lowercase characters into the equivalent uppercase characters when
3750 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3751 The @env{LC_CTYPE} locale determines character types.
3752 When used with @option{--unique} those lower case equivalent lines are
3753 thrown away. (There is currently no way to throw away the upper case
3754 equivalent instead. (Any @option{--reverse} given would only affect
3755 the final result, after the throwing away.))
3758 @itemx --general-numeric-sort
3759 @itemx --sort=general-numeric
3761 @opindex --general-numeric-sort
3763 @cindex general numeric sort
3765 Sort numerically, using the standard C function @code{strtod} to convert
3766 a prefix of each line to a double-precision floating point number.
3767 This allows floating point numbers to be specified in scientific notation,
3768 like @code{1.0e-34} and @code{10e100}.
3769 The @env{LC_NUMERIC} locale determines the decimal-point character.
3770 Do not report overflow, underflow, or conversion errors.
3771 Use the following collating sequence:
3775 Lines that do not start with numbers (all considered to be equal).
3777 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3778 in a consistent but machine-dependent order.
3782 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3787 Use this option only if there is no alternative; it is much slower than
3788 @option{--numeric-sort} (@option{-n}) and it can lose information when
3789 converting to floating point.
3792 @itemx --human-numeric-sort
3793 @itemx --sort=human-numeric
3795 @opindex --human-numeric-sort
3797 @cindex human numeric sort
3799 Sort numerically, as per the @option{--numeric-sort} option below, and in
3800 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3801 Note a mixture of IEC and SI suffixes is not supported and will
3802 be flagged as an error. Also the numbers must be abbreviated uniformly.
3803 I.E. values with different precisions like 6000K and 5M will be sorted
3807 @itemx --ignore-nonprinting
3809 @opindex --ignore-nonprinting
3810 @cindex nonprinting characters, ignoring
3811 @cindex unprintable characters, ignoring
3813 Ignore nonprinting characters.
3814 The @env{LC_CTYPE} locale determines character types.
3815 This option has no effect if the stronger @option{--dictionary-order}
3816 (@option{-d}) option is also given.
3822 @opindex --month-sort
3824 @cindex months, sorting by
3826 An initial string, consisting of any amount of blanks, followed
3827 by a month name abbreviation, is folded to UPPER case and
3828 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3829 Invalid names compare low to valid names. The @env{LC_TIME} locale
3830 category determines the month spellings.
3831 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3835 @itemx --numeric-sort
3836 @itemx --sort=numeric
3838 @opindex --numeric-sort
3840 @cindex numeric sort
3842 Sort numerically. The number begins each line and consists
3843 of optional blanks, an optional @samp{-} sign, and zero or more
3844 digits possibly separated by thousands separators, optionally followed
3845 by a decimal-point character and zero or more digits. An empty
3846 number is treated as @samp{0}. The @env{LC_NUMERIC}
3847 locale specifies the decimal-point character and thousands separator.
3848 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3851 Comparison is exact; there is no rounding error.
3853 Neither a leading @samp{+} nor exponential notation is recognized.
3854 To compare such strings numerically, use the
3855 @option{--general-numeric-sort} (@option{-g}) option.
3858 @itemx --version-sort
3860 @opindex --version-sort
3861 @cindex version number sort
3863 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3864 that embedded decimal numbers are sorted by numeric value
3865 (see @option{--numeric-sort} above).
3871 @cindex reverse sorting
3872 Reverse the result of comparison, so that lines with greater key values
3873 appear earlier in the output instead of later.
3876 @itemx --random-sort
3877 @itemx --sort=random
3879 @opindex --random-sort
3882 Sort by hashing the input keys and then sorting the hash values.
3883 Choose the hash function at random, ensuring that it is free of
3884 collisions so that differing keys have differing hash values. This is
3885 like a random permutation of the inputs (@pxref{shuf invocation}),
3886 except that keys with the same value sort together.
3888 If multiple random sort fields are specified, the same random hash
3889 function is used for all fields. To use different random hash
3890 functions for different fields, you can invoke @command{sort} more
3893 The choice of hash function is affected by the
3894 @option{--random-source} option.
3902 @item --compress-program=@var{prog}
3903 Compress any temporary files with the program @var{prog}.
3905 With no arguments, @var{prog} must compress standard input to standard
3906 output, and when given the @option{-d} option it must decompress
3907 standard input to standard output.
3909 Terminate with an error if @var{prog} exits with nonzero status.
3911 White space and the backslash character should not appear in
3912 @var{prog}; they are reserved for future use.
3914 @filesZeroFromOption{sort,,sorted output}
3916 @item -k @var{pos1}[,@var{pos2}]
3917 @itemx --key=@var{pos1}[,@var{pos2}]
3921 Specify a sort field that consists of the part of the line between
3922 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3923 omitted), @emph{inclusive}.
3925 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3926 where @var{f} is the number of the field to use, and @var{c} is the number
3927 of the first character from the beginning of the field. Fields and character
3928 positions are numbered starting with 1; a character position of zero in
3929 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3930 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3931 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3932 @var{opts} are ordering options, allowing individual keys to be sorted
3933 according to different rules; see below for details. Keys can span
3936 Example: To sort on the second field, use @option{--key=2,2}
3937 (@option{-k 2,2}). See below for more notes on keys and more examples.
3939 @item --batch-size=@var{nmerge}
3940 @opindex --batch-size
3941 @cindex number of inputs to merge, nmerge
3942 Merge at most @var{nmerge} inputs at once.
3944 When @command{sort} has to merge more than @var{nmerge} inputs,
3945 it merges them in groups of @var{nmerge}, saving the result in
3946 a temporary file, which is then used as an input in a subsequent merge.
3948 A large value of @var{nmerge} may improve merge performance and decrease
3949 temporary storage utilization at the expense of increased memory usage
3950 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3951 requirements and I/0 at the expense of temporary storage consumption and
3954 The value of @var{nmerge} must be at least 2. The default value is
3955 currently 16, but this is implementation-dependent and may change in
3958 The value of @var{nmerge} may be bounded by a resource limit for open
3959 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3960 OPEN_MAX} may display limits for your systems; these limits may be
3961 modified further if your program already has some files open, or if
3962 the operating system has other limits on the number of open files. If
3963 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3964 silently uses a smaller value.
3966 @item -o @var{output-file}
3967 @itemx --output=@var{output-file}
3970 @cindex overwriting of input, allowed
3971 Write output to @var{output-file} instead of standard output.
3972 Normally, @command{sort} reads all input before opening
3973 @var{output-file}, so you can safely sort a file in place by using
3974 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3975 However, @command{sort} with @option{--merge} (@option{-m}) can open
3976 the output file before reading all input, so a command like @code{cat
3977 F | sort -m -o F - G} is not safe as @command{sort} might start
3978 writing @file{F} before @command{cat} is done reading it.
3980 @vindex POSIXLY_CORRECT
3981 On newer systems, @option{-o} cannot appear after an input file if
3982 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3983 scripts should specify @option{-o @var{output-file}} before any input
3986 @item --random-source=@var{file}
3987 @opindex --random-source
3988 @cindex random source for sorting
3989 Use @var{file} as a source of random data used to determine which
3990 random hash function to use with the @option{-R} option. @xref{Random
3997 @cindex sort stability
3998 @cindex sort's last-resort comparison
4000 Make @command{sort} stable by disabling its last-resort comparison.
4001 This option has no effect if no fields or global ordering options
4002 other than @option{--reverse} (@option{-r}) are specified.
4005 @itemx --buffer-size=@var{size}
4007 @opindex --buffer-size
4008 @cindex size for main memory sorting
4009 Use a main-memory sort buffer of the given @var{size}. By default,
4010 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4011 @var{size} to be interpreted as a percentage of physical memory.
4012 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4013 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4014 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4015 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4018 This option can improve the performance of @command{sort} by causing it
4019 to start with a larger or smaller sort buffer than the default.
4020 However, this option affects only the initial buffer size. The buffer
4021 grows beyond @var{size} if @command{sort} encounters input lines larger
4024 @item -t @var{separator}
4025 @itemx --field-separator=@var{separator}
4027 @opindex --field-separator
4028 @cindex field separator character
4029 Use character @var{separator} as the field separator when finding the
4030 sort keys in each line. By default, fields are separated by the empty
4031 string between a non-blank character and a blank character.
4032 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4035 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4036 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4037 not considered to be part of either the field preceding or the field
4038 following, so with @samp{sort @w{-t " "}} the same input line has
4039 three fields: an empty field, @samp{foo}, and @samp{bar}.
4040 However, fields that extend to the end of the line,
4041 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4042 retain the field separators present between the endpoints of the range.
4044 To specify @acronym{ASCII} @sc{nul} as the field separator,
4045 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4047 @item -T @var{tempdir}
4048 @itemx --temporary-directory=@var{tempdir}
4050 @opindex --temporary-directory
4051 @cindex temporary directory
4053 Use directory @var{tempdir} to store temporary files, overriding the
4054 @env{TMPDIR} environment variable. If this option is given more than
4055 once, temporary files are stored in all the directories given. If you
4056 have a large sort or merge that is I/O-bound, you can often improve
4057 performance by using this option to specify directories on different
4058 disks and controllers.
4064 @cindex uniquifying output
4066 Normally, output only the first of a sequence of lines that compare
4067 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4068 check that no pair of consecutive lines compares equal.
4070 This option also disables the default last-resort comparison.
4072 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4073 this equivalence does not extend to arbitrary @command{sort} options.
4074 For example, @code{sort -n -u} inspects only the value of the initial
4075 numeric string when checking for uniqueness, whereas @code{sort -n |
4076 uniq} inspects the entire line. @xref{uniq invocation}.
4078 @macro zeroTerminatedOption
4080 @itemx --zero-terminated
4082 @opindex --zero-terminated
4083 @cindex process zero-terminated items
4084 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4085 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4086 and terminate output items with @acronym{ASCII} @sc{nul}.
4087 This option can be useful in conjunction with @samp{perl -0} or
4088 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4089 reliably handle arbitrary file names (even those containing blanks
4090 or other special characters).
4092 @zeroTerminatedOption
4096 Historical (BSD and System V) implementations of @command{sort} have
4097 differed in their interpretation of some options, particularly
4098 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4099 behavior, which is usually (but not always!) like the System V behavior.
4100 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4101 consistency, @option{-M} has been changed in the same way. This may
4102 affect the meaning of character positions in field specifications in
4103 obscure cases. The only fix is to add an explicit @option{-b}.
4105 A position in a sort field specified with @option{-k} may have any
4106 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4107 global ordering options are inherited by that particular field. The
4108 @option{-b} option may be independently attached to either or both of
4109 the start and end positions of a field specification, and if it is
4110 inherited from the global options it will be attached to both.
4111 If input lines can contain leading or adjacent blanks and @option{-t}
4112 is not used, then @option{-k} is typically combined with @option{-b} or
4113 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4114 the varying numbers of leading blanks in fields can cause confusing results.
4116 If the start position in a sort field specifier falls after the end of
4117 the line or after the end field, the field is empty. If the @option{-b}
4118 option was specified, the @samp{.@var{c}} part of a field specification
4119 is counted from the first nonblank character of the field.
4121 @vindex _POSIX2_VERSION
4122 @vindex POSIXLY_CORRECT
4123 On older systems, @command{sort} supports an obsolete origin-zero
4124 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4125 This obsolete behavior can be enabled or disabled with the
4126 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4127 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4128 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4130 Scripts intended for use on standard hosts should avoid obsolete
4131 syntax and should use @option{-k} instead. For example, avoid
4132 @samp{sort +2}, since it might be interpreted as either @samp{sort
4133 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4134 support only the obsolete syntax, it can use a test like @samp{if sort
4135 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4138 Here are some examples to illustrate various combinations of options.
4143 Sort in descending (reverse) numeric order.
4150 Sort alphabetically, omitting the first and second fields
4151 and the blanks at the start of the third field.
4152 This uses a single key composed of the characters beginning
4153 at the start of the first nonblank character in field three
4154 and extending to the end of each line.
4161 Sort numerically on the second field and resolve ties by sorting
4162 alphabetically on the third and fourth characters of field five.
4163 Use @samp{:} as the field delimiter.
4166 sort -t : -k 2,2n -k 5.3,5.4
4169 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4170 @command{sort} would have used all characters beginning in the second field
4171 and extending to the end of the line as the primary @emph{numeric}
4172 key. For the large majority of applications, treating keys spanning
4173 more than one field as numeric will not do what you expect.
4175 Also note that the @samp{n} modifier was applied to the field-end
4176 specifier for the first key. It would have been equivalent to
4177 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4178 @samp{b} apply to the associated @emph{field}, regardless of whether
4179 the modifier character is attached to the field-start and/or the
4180 field-end part of the key specifier.
4183 Sort the password file on the fifth field and ignore any
4184 leading blanks. Sort lines with equal values in field five
4185 on the numeric user ID in field three. Fields are separated
4189 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4190 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4191 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4194 These three commands have equivalent effect. The first specifies that
4195 the first key's start position ignores leading blanks and the second
4196 key is sorted numerically. The other two commands rely on global
4197 options being inherited by sort keys that lack modifiers. The inheritance
4198 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4199 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4200 character position is not affected by whether initial blanks are
4204 Sort a set of log files, primarily by IPv4 address and secondarily by
4205 time stamp. If two lines' primary and secondary keys are identical,
4206 output the lines in the same order that they were input. The log
4207 files contain lines that look like this:
4210 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4211 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4214 Fields are separated by exactly one space. Sort IPv4 addresses
4215 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4216 because 61 is less than 129.
4219 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4220 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4223 This example cannot be done with a single @command{sort} invocation,
4224 since IPv4 address components are separated by @samp{.} while dates
4225 come just after a space. So it is broken down into two invocations of
4226 @command{sort}: the first sorts by time stamp and the second by IPv4
4227 address. The time stamp is sorted by year, then month, then day, and
4228 finally by hour-minute-second field, using @option{-k} to isolate each
4229 field. Except for hour-minute-second there's no need to specify the
4230 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4231 based on leading prefixes that cannot cross field boundaries. The
4232 IPv4 addresses are sorted lexicographically. The second sort uses
4233 @samp{-s} so that ties in the primary key are broken by the secondary
4234 key; the first sort uses @samp{-s} so that the combination of the two
4238 Generate a tags file in case-insensitive sorted order.
4241 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4244 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4245 that file names that contain blanks or other special characters are
4247 by the sort operation.
4249 @c This example is a bit contrived and needs more explanation.
4251 @c Sort records separated by an arbitrary string by using a pipe to convert
4252 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4253 @c and converting each @samp{\0} back to the original record delimiter.
4256 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4260 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4261 sort lines according to their length.
4264 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4267 In general this technique can be used to sort data that the @command{sort}
4268 command does not support, or is inefficient at, sorting directly.
4271 Shuffle a list of directories, but preserve the order of files within
4272 each directory. For instance, one could use this to generate a music
4273 playlist in which albums are shuffled but the songs of each album are
4277 ls */* | sort -t / -k 1,1R -k 2,2
4283 @node shuf invocation
4284 @section @command{shuf}: Shuffling text
4287 @cindex shuffling files
4289 @command{shuf} shuffles its input by outputting a random permutation
4290 of its input lines. Each output permutation is equally likely.
4294 shuf [@var{option}]@dots{} [@var{file}]
4295 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4296 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4299 @command{shuf} has three modes of operation that affect where it
4300 obtains its input lines. By default, it reads lines from standard
4301 input. The following options change the operation mode:
4309 @cindex command-line operands to shuffle
4310 Treat each command-line operand as an input line.
4312 @item -i @var{lo}-@var{hi}
4313 @itemx --input-range=@var{lo}-@var{hi}
4315 @opindex --input-range
4316 @cindex input range to shuffle
4317 Act as if input came from a file containing the range of unsigned
4318 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4322 @command{shuf}'s other options can affect its behavior in all
4327 @item -n @var{lines}
4328 @itemx --head-count=@var{count}
4330 @opindex --head-count
4331 @cindex head of output
4332 Output at most @var{count} lines. By default, all input lines are
4335 @item -o @var{output-file}
4336 @itemx --output=@var{output-file}
4339 @cindex overwriting of input, allowed
4340 Write output to @var{output-file} instead of standard output.
4341 @command{shuf} reads all input before opening
4342 @var{output-file}, so you can safely shuffle a file in place by using
4343 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4345 @item --random-source=@var{file}
4346 @opindex --random-source
4347 @cindex random source for shuffling
4348 Use @var{file} as a source of random data used to determine which
4349 permutation to generate. @xref{Random sources}.
4351 @zeroTerminatedOption
4367 might produce the output
4377 Similarly, the command:
4380 shuf -e clubs hearts diamonds spades
4394 and the command @samp{shuf -i 1-4} might output:
4404 These examples all have four input lines, so @command{shuf} might
4405 produce any of the twenty-four possible permutations of the input. In
4406 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4407 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4408 output permutations.
4413 @node uniq invocation
4414 @section @command{uniq}: Uniquify files
4417 @cindex uniquify files
4419 @command{uniq} writes the unique lines in the given @file{input}, or
4420 standard input if nothing is given or for an @var{input} name of
4424 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4427 By default, @command{uniq} prints its input lines, except that
4428 it discards all but the first of adjacent repeated lines, so that
4429 no output lines are repeated. Optionally, it can instead discard
4430 lines that are not repeated, or all repeated lines.
4432 The input need not be sorted, but repeated input lines are detected
4433 only if they are adjacent. If you want to discard non-adjacent
4434 duplicate lines, perhaps you want to use @code{sort -u}.
4435 @xref{sort invocation}.
4438 Comparisons honor the rules specified by the @env{LC_COLLATE}
4441 If no @var{output} file is specified, @command{uniq} writes to standard
4444 The program accepts the following options. Also see @ref{Common options}.
4449 @itemx --skip-fields=@var{n}
4451 @opindex --skip-fields
4452 Skip @var{n} fields on each line before checking for uniqueness. Use
4453 a null string for comparison if a line has fewer than @var{n} fields. Fields
4454 are sequences of non-space non-tab characters that are separated from
4455 each other by at least one space or tab.
4457 For compatibility @command{uniq} supports an obsolete option syntax
4458 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4461 @itemx --skip-chars=@var{n}
4463 @opindex --skip-chars
4464 Skip @var{n} characters before checking for uniqueness. Use a null string
4465 for comparison if a line has fewer than @var{n} characters. If you use both
4466 the field and character skipping options, fields are skipped over first.
4468 @vindex _POSIX2_VERSION
4469 On older systems, @command{uniq} supports an obsolete option syntax
4471 This obsolete behavior can be enabled or disabled with the
4472 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4473 conformance}), but portable scripts should avoid commands whose
4474 behavior depends on this variable.
4475 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4476 the ambiguous @samp{uniq +10}.
4482 Print the number of times each line occurred along with the line.
4485 @itemx --ignore-case
4487 @opindex --ignore-case
4488 Ignore differences in case when comparing lines.
4494 @cindex repeated lines, outputting
4495 Discard lines that are not repeated. When used by itself, this option
4496 causes @command{uniq} to print the first copy of each repeated line,
4500 @itemx --all-repeated[=@var{delimit-method}]
4502 @opindex --all-repeated
4503 @cindex all repeated lines, outputting
4504 Do not discard the second and subsequent repeated input lines,
4505 but discard lines that are not repeated.
4506 This option is useful mainly in conjunction with other options e.g.,
4507 to ignore case or to compare only selected fields.
4508 The optional @var{delimit-method} tells how to delimit
4509 groups of repeated lines, and must be one of the following:
4514 Do not delimit groups of repeated lines.
4515 This is equivalent to @option{--all-repeated} (@option{-D}).
4518 Output a newline before each group of repeated lines.
4519 With @option{--zero-terminated} (@option{-z}), use a zero
4520 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4523 Separate groups of repeated lines with a single newline.
4524 With @option{--zero-terminated} (@option{-z}), use a zero
4525 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4526 This is the same as using @samp{prepend}, except that
4527 no delimiter is inserted before the first group, and hence
4528 may be better suited for output direct to users.
4531 Note that when groups are delimited and the input stream contains
4532 two or more consecutive blank lines, then the output is ambiguous.
4533 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4534 each sequence of consecutive newlines with a single newline.
4536 This is a @sc{gnu} extension.
4537 @c FIXME: give an example showing *how* it's useful
4543 @cindex unique lines, outputting
4544 Discard the first repeated line. When used by itself, this option
4545 causes @command{uniq} to print unique lines, and nothing else.
4548 @itemx --check-chars=@var{n}
4550 @opindex --check-chars
4551 Compare at most @var{n} characters on each line (after skipping any specified
4552 fields and characters). By default the entire rest of the lines are
4555 @zeroTerminatedOption
4562 @node comm invocation
4563 @section @command{comm}: Compare two sorted files line by line
4566 @cindex line-by-line comparison
4567 @cindex comparing sorted files
4569 @command{comm} writes to standard output lines that are common, and lines
4570 that are unique, to two input files; a file name of @samp{-} means
4571 standard input. Synopsis:
4574 comm [@var{option}]@dots{} @var{file1} @var{file2}
4578 Before @command{comm} can be used, the input files must be sorted using the
4579 collating sequence specified by the @env{LC_COLLATE} locale.
4580 If an input file ends in a non-newline
4581 character, a newline is silently appended. The @command{sort} command with
4582 no options always outputs a file that is suitable input to @command{comm}.
4584 @cindex differing lines
4585 @cindex common lines
4586 With no options, @command{comm} produces three-column output. Column one
4587 contains lines unique to @var{file1}, column two contains lines unique
4588 to @var{file2}, and column three contains lines common to both files.
4589 Columns are separated by a single TAB character.
4590 @c FIXME: when there's an option to supply an alternative separator
4591 @c string, append `by default' to the above sentence.
4596 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4597 the corresponding columns (and separators). Also see @ref{Common options}.
4599 Unlike some other comparison utilities, @command{comm} has an exit
4600 status that does not depend on the result of the comparison.
4601 Upon normal completion @command{comm} produces an exit code of zero.
4602 If there is an error it exits with nonzero status.
4604 @macro checkOrderOption{cmd}
4605 If the @option{--check-order} option is given, unsorted inputs will
4606 cause a fatal error message. If the option @option{--nocheck-order}
4607 is given, unsorted inputs will never cause an error message. If
4608 neither of these options is given, wrongly sorted inputs are diagnosed
4609 only if an input file is found to contain unpairable lines. If an
4610 input file is diagnosed as being unsorted, the @command{\cmd\} command
4611 will exit with a nonzero status (and the output should not be used).
4613 Forcing @command{\cmd\} to process wrongly sorted input files
4614 containing unpairable lines by specifying @option{--nocheck-order} is
4615 not guaranteed to produce any particular output. The output will
4616 probably not correspond with whatever you hoped it would be.
4618 @checkOrderOption{comm}
4623 Fail with an error message if either input file is wrongly ordered.
4625 @item --nocheck-order
4626 Do not check that both input files are in sorted order.
4630 @item --output-delimiter=@var{str}
4631 Print @var{str} between adjacent output columns,
4632 rather than the default of a single TAB character.
4634 The delimiter @var{str} may not be empty.
4638 @node ptx invocation
4639 @section @command{ptx}: Produce permuted indexes
4643 @command{ptx} reads a text file and essentially produces a permuted index, with
4644 each keyword in its context. The calling sketch is either one of:
4647 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4648 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4651 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4652 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4653 limitations and changing several of the program's default option values.
4654 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4655 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4656 document. For the full list, see @xref{Compatibility in ptx}.
4658 Individual options are explained in the following sections.
4660 When @sc{gnu} extensions are enabled, there may be zero, one or several
4661 @var{file}s after the options. If there is no @var{file}, the program
4662 reads the standard input. If there is one or several @var{file}s, they
4663 give the name of input files which are all read in turn, as if all the
4664 input files were concatenated. However, there is a full contextual
4665 break between each file and, when automatic referencing is requested,
4666 file names and line numbers refer to individual text input files. In
4667 all cases, the program outputs the permuted index to the standard
4670 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4671 operates in traditional mode, there may be zero, one or two parameters
4672 besides the options. If there are no parameters, the program reads the
4673 standard input and outputs the permuted index to the standard output.
4674 If there is only one parameter, it names the text @var{input} to be read
4675 instead of the standard input. If two parameters are given, they give
4676 respectively the name of the @var{input} file to read and the name of
4677 the @var{output} file to produce. @emph{Be very careful} to note that,
4678 in this case, the contents of file given by the second parameter is
4679 destroyed. This behavior is dictated by System V @command{ptx}
4680 compatibility; @sc{gnu} Standards normally discourage output parameters not
4681 introduced by an option.
4683 Note that for @emph{any} file named as the value of an option or as an
4684 input text file, a single dash @kbd{-} may be used, in which case
4685 standard input is assumed. However, it would not make sense to use this
4686 convention more than once per program invocation.
4689 * General options in ptx:: Options which affect general program behavior.
4690 * Charset selection in ptx:: Underlying character set considerations.
4691 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4692 * Output formatting in ptx:: Types of output format, and sizing the fields.
4693 * Compatibility in ptx::
4697 @node General options in ptx
4698 @subsection General options
4703 @itemx --traditional
4704 As already explained, this option disables all @sc{gnu} extensions to
4705 @command{ptx} and switches to traditional mode.
4708 Print a short help on standard output, then exit without further
4712 Print the program version on standard output, then exit without further
4720 @node Charset selection in ptx
4721 @subsection Charset selection
4723 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4724 As it is set up now, the program assumes that the input file is coded
4725 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4726 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4727 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4728 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4729 of characters which are letters is different; this alters the behavior
4730 of regular expression matching. Thus, the default regular expression
4731 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4732 however, is still crude; it obeys the underlying character set ordering
4738 @itemx --ignore-case
4739 Fold lower case letters to upper case for sorting.
4744 @node Input processing in ptx
4745 @subsection Word selection and input processing
4750 @itemx --break-file=@var{file}
4752 This option provides an alternative (to @option{-W}) method of describing
4753 which characters make up words. It introduces the name of a
4754 file which contains a list of characters which can@emph{not} be part of
4755 one word; this file is called the @dfn{Break file}. Any character which
4756 is not part of the Break file is a word constituent. If both options
4757 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4758 @option{-b} is ignored.
4760 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4761 break character is to write all the break characters in the file with no
4762 newline at all, not even at the end of the file. When @sc{gnu} extensions
4763 are disabled, spaces, tabs and newlines are always considered as break
4764 characters even if not included in the Break file.
4767 @itemx --ignore-file=@var{file}
4769 The file associated with this option contains a list of words which will
4770 never be taken as keywords in concordance output. It is called the
4771 @dfn{Ignore file}. The file contains exactly one word in each line; the
4772 end of line separation of words is not subject to the value of the
4776 @itemx --only-file=@var{file}
4778 The file associated with this option contains a list of words which will
4779 be retained in concordance output; any word not mentioned in this file
4780 is ignored. The file is called the @dfn{Only file}. The file contains
4781 exactly one word in each line; the end of line separation of words is
4782 not subject to the value of the @option{-S} option.
4784 There is no default for the Only file. When both an Only file and an
4785 Ignore file are specified, a word is considered a keyword only
4786 if it is listed in the Only file and not in the Ignore file.
4791 On each input line, the leading sequence of non-white space characters will be
4792 taken to be a reference that has the purpose of identifying this input
4793 line in the resulting permuted index. For more information about reference
4794 production, see @xref{Output formatting in ptx}.
4795 Using this option changes the default value for option @option{-S}.
4797 Using this option, the program does not try very hard to remove
4798 references from contexts in output, but it succeeds in doing so
4799 @emph{when} the context ends exactly at the newline. If option
4800 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4801 are disabled, this condition is always met and references are completely
4802 excluded from the output contexts.
4804 @item -S @var{regexp}
4805 @itemx --sentence-regexp=@var{regexp}
4807 This option selects which regular expression will describe the end of a
4808 line or the end of a sentence. In fact, this regular expression is not
4809 the only distinction between end of lines or end of sentences, and input
4810 line boundaries have no special significance outside this option. By
4811 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4812 used, end of sentences are used. In this case, this @var{regex} is
4813 imported from @sc{gnu} Emacs:
4816 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4819 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4820 of lines are used; in this case, the default @var{regexp} is just:
4826 Using an empty @var{regexp} is equivalent to completely disabling end of
4827 line or end of sentence recognition. In this case, the whole file is
4828 considered to be a single big line or sentence. The user might want to
4829 disallow all truncation flag generation as well, through option @option{-F
4830 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4833 When the keywords happen to be near the beginning of the input line or
4834 sentence, this often creates an unused area at the beginning of the
4835 output context line; when the keywords happen to be near the end of the
4836 input line or sentence, this often creates an unused area at the end of
4837 the output context line. The program tries to fill those unused areas
4838 by wrapping around context in them; the tail of the input line or
4839 sentence is used to fill the unused area on the left of the output line;
4840 the head of the input line or sentence is used to fill the unused area
4841 on the right of the output line.
4843 As a matter of convenience to the user, many usual backslashed escape
4844 sequences from the C language are recognized and converted to the
4845 corresponding characters by @command{ptx} itself.
4847 @item -W @var{regexp}
4848 @itemx --word-regexp=@var{regexp}
4850 This option selects which regular expression will describe each keyword.
4851 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4852 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4853 disabled, a word is by default anything which ends with a space, a tab
4854 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4856 An empty @var{regexp} is equivalent to not using this option.
4857 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4860 As a matter of convenience to the user, many usual backslashed escape
4861 sequences, as found in the C language, are recognized and converted to
4862 the corresponding characters by @command{ptx} itself.
4867 @node Output formatting in ptx
4868 @subsection Output formatting
4870 Output format is mainly controlled by the @option{-O} and @option{-T} options
4871 described in the table below. When neither @option{-O} nor @option{-T} are
4872 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4873 output format suitable for a dumb terminal. Each keyword occurrence is
4874 output to the center of one line, surrounded by its left and right
4875 contexts. Each field is properly justified, so the concordance output
4876 can be readily observed. As a special feature, if automatic
4877 references are selected by option @option{-A} and are output before the
4878 left context, that is, if option @option{-R} is @emph{not} selected, then
4879 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4880 Emacs @code{next-error} processing. In this default output format, each
4881 white space character, like newline and tab, is merely changed to
4882 exactly one space, with no special attempt to compress consecutive
4883 spaces. This might change in the future. Except for those white space
4884 characters, every other character of the underlying set of 256
4885 characters is transmitted verbatim.
4887 Output format is further controlled by the following options.
4891 @item -g @var{number}
4892 @itemx --gap-size=@var{number}
4894 Select the size of the minimum white space gap between the fields on the
4897 @item -w @var{number}
4898 @itemx --width=@var{number}
4900 Select the maximum output width of each final line. If references are
4901 used, they are included or excluded from the maximum output width
4902 depending on the value of option @option{-R}. If this option is not
4903 selected, that is, when references are output before the left context,
4904 the maximum output width takes into account the maximum length of all
4905 references. If this option is selected, that is, when references are
4906 output after the right context, the maximum output width does not take
4907 into account the space taken by references, nor the gap that precedes
4911 @itemx --auto-reference
4913 Select automatic references. Each input line will have an automatic
4914 reference made up of the file name and the line ordinal, with a single
4915 colon between them. However, the file name will be empty when standard
4916 input is being read. If both @option{-A} and @option{-r} are selected, then
4917 the input reference is still read and skipped, but the automatic
4918 reference is used at output time, overriding the input reference.
4921 @itemx --right-side-refs
4923 In the default output format, when option @option{-R} is not used, any
4924 references produced by the effect of options @option{-r} or @option{-A} are
4925 placed to the far right of output lines, after the right context. With
4926 default output format, when the @option{-R} option is specified, references
4927 are rather placed at the beginning of each output line, before the left
4928 context. For any other output format, option @option{-R} is
4929 ignored, with one exception: with @option{-R} the width of references
4930 is @emph{not} taken into account in total output width given by @option{-w}.
4932 This option is automatically selected whenever @sc{gnu} extensions are
4935 @item -F @var{string}
4936 @itemx --flac-truncation=@var{string}
4938 This option will request that any truncation in the output be reported
4939 using the string @var{string}. Most output fields theoretically extend
4940 towards the beginning or the end of the current line, or current
4941 sentence, as selected with option @option{-S}. But there is a maximum
4942 allowed output line width, changeable through option @option{-w}, which is
4943 further divided into space for various output fields. When a field has
4944 to be truncated because it cannot extend beyond the beginning or the end of
4945 the current line to fit in, then a truncation occurs. By default,
4946 the string used is a single slash, as in @option{-F /}.
4948 @var{string} may have more than one character, as in @option{-F ...}.
4949 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4950 truncation flagging is disabled, and no truncation marks are appended in
4953 As a matter of convenience to the user, many usual backslashed escape
4954 sequences, as found in the C language, are recognized and converted to
4955 the corresponding characters by @command{ptx} itself.
4957 @item -M @var{string}
4958 @itemx --macro-name=@var{string}
4960 Select another @var{string} to be used instead of @samp{xx}, while
4961 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4964 @itemx --format=roff
4966 Choose an output format suitable for @command{nroff} or @command{troff}
4967 processing. Each output line will look like:
4970 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4973 so it will be possible to write a @samp{.xx} roff macro to take care of
4974 the output typesetting. This is the default output format when @sc{gnu}
4975 extensions are disabled. Option @option{-M} can be used to change
4976 @samp{xx} to another macro name.
4978 In this output format, each non-graphical character, like newline and
4979 tab, is merely changed to exactly one space, with no special attempt to
4980 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4981 so it will be correctly processed by @command{nroff} or @command{troff}.
4986 Choose an output format suitable for @TeX{} processing. Each output
4987 line will look like:
4990 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4994 so it will be possible to write a @code{\xx} definition to take care of
4995 the output typesetting. Note that when references are not being
4996 produced, that is, neither option @option{-A} nor option @option{-r} is
4997 selected, the last parameter of each @code{\xx} call is inhibited.
4998 Option @option{-M} can be used to change @samp{xx} to another macro
5001 In this output format, some special characters, like @kbd{$}, @kbd{%},
5002 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5003 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5004 backslash and a pair of dollar signs (to force mathematical mode). The
5005 backslash itself produces the sequence @code{\backslash@{@}}.
5006 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5007 @code{~\@{ @}} respectively. Other diacriticized characters of the
5008 underlying character set produce an appropriate @TeX{} sequence as far
5009 as possible. The other non-graphical characters, like newline and tab,
5010 and all other characters which are not part of @acronym{ASCII}, are merely
5011 changed to exactly one space, with no special attempt to compress
5012 consecutive spaces. Let me know how to improve this special character
5013 processing for @TeX{}.
5018 @node Compatibility in ptx
5019 @subsection The @sc{gnu} extensions to @command{ptx}
5021 This version of @command{ptx} contains a few features which do not exist in
5022 System V @command{ptx}. These extra features are suppressed by using the
5023 @option{-G} command line option, unless overridden by other command line
5024 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5025 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5026 Here are the differences between this program and System V @command{ptx}.
5031 This program can read many input files at once, it always writes the
5032 resulting concordance on standard output. On the other hand, System V
5033 @command{ptx} reads only one file and sends the result to standard output
5034 or, if a second @var{file} parameter is given on the command, to that
5037 Having output parameters not introduced by options is a dangerous
5038 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5039 portably between @sc{gnu} and System V, you should always use it with a
5040 single input file, and always expect the result on standard output. You
5041 might also want to automatically configure in a @option{-G} option to
5042 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5043 that the installed @command{ptx} accepts @option{-G}.
5046 The only options available in System V @command{ptx} are options @option{-b},
5047 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5048 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5049 this enumeration. Moreover, some options have a slightly different
5050 meaning when @sc{gnu} extensions are enabled, as explained below.
5053 By default, concordance output is not formatted for @command{troff} or
5054 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5055 or @command{nroff} output may still be selected through option @option{-O}.
5058 Unless @option{-R} option is used, the maximum reference width is
5059 subtracted from the total output line width. With @sc{gnu} extensions
5060 disabled, width of references is not taken into account in the output
5061 line width computations.
5064 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5065 processed from input file with no adverse effect, even if @sc{gnu} extensions
5066 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5067 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5070 Input line length is only limited by available memory, even if @sc{gnu}
5071 extensions are disabled. However, System V @command{ptx} processes only
5072 the first 200 characters in each line.
5075 The break (non-word) characters default to be every character except all
5076 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5077 extensions are disabled, the break characters default to space, tab and
5081 The program makes better use of output line width. If @sc{gnu} extensions
5082 are disabled, the program rather tries to imitate System V @command{ptx},
5083 but still, there are some slight disposition glitches this program does
5084 not completely reproduce.
5087 The user can specify both an Ignore file and an Only file. This is not
5088 allowed with System V @command{ptx}.
5093 @node tsort invocation
5094 @section @command{tsort}: Topological sort
5097 @cindex topological sort
5099 @command{tsort} performs a topological sort on the given @var{file}, or
5100 standard input if no input file is given or for a @var{file} of
5101 @samp{-}. For more details and some history, see @ref{tsort background}.
5105 tsort [@var{option}] [@var{file}]
5108 @command{tsort} reads its input as pairs of strings, separated by blanks,
5109 indicating a partial ordering. The output is a total ordering that
5110 corresponds to the given partial ordering.
5124 will produce the output
5135 Consider a more realistic example.
5136 You have a large set of functions all in one file, and they may all be
5137 declared static except one. Currently that one (say @code{main}) is the
5138 first function defined in the file, and the ones it calls directly follow
5139 it, followed by those they call, etc. Let's say that you are determined
5140 to take advantage of prototypes, so you have to choose between declaring
5141 all of those functions (which means duplicating a lot of information from
5142 the definitions) and rearranging the functions so that as many as possible
5143 are defined before they are used. One way to automate the latter process
5144 is to get a list for each function of the functions it calls directly.
5145 Many programs can generate such lists. They describe a call graph.
5146 Consider the following list, in which a given line indicates that the
5147 function on the left calls the one on the right directly.
5153 tail_file pretty_name
5154 tail_file write_header
5156 tail_forever recheck
5157 tail_forever pretty_name
5158 tail_forever write_header
5159 tail_forever dump_remainder
5162 tail_lines start_lines
5163 tail_lines dump_remainder
5164 tail_lines file_lines
5165 tail_lines pipe_lines
5167 tail_bytes start_bytes
5168 tail_bytes dump_remainder
5169 tail_bytes pipe_bytes
5170 file_lines dump_remainder
5174 then you can use @command{tsort} to produce an ordering of those
5175 functions that satisfies your requirement.
5178 example$ tsort call-graph | tac
5198 @command{tsort} detects any cycles in the input and writes the first cycle
5199 encountered to standard error.
5201 Note that for a given partial ordering, generally there is no unique
5202 total ordering. In the context of the call graph above, the function
5203 @code{parse_options} may be placed anywhere in the list as long as it
5204 precedes @code{main}.
5206 The only options are @option{--help} and @option{--version}. @xref{Common
5212 * tsort background:: Where tsort came from.
5215 @node tsort background
5216 @subsection @command{tsort}: Background
5218 @command{tsort} exists because very early versions of the Unix linker processed
5219 an archive file exactly once, and in order. As @command{ld} read each object
5220 in the archive, it decided whether it was needed in the program based on
5221 whether it defined any symbols which were undefined at that point in
5224 This meant that dependencies within the archive had to be handled
5225 specially. For example, @code{scanf} probably calls @code{read}. That means
5226 that in a single pass through an archive, it was important for @code{scanf.o}
5227 to appear before read.o, because otherwise a program which calls
5228 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5229 reference to @code{read}.
5231 The way to address this problem was to first generate a set of
5232 dependencies of one object file on another. This was done by a shell
5233 script called @command{lorder}. The GNU tools don't provide a version of
5234 lorder, as far as I know, but you can still find it in BSD
5237 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5238 resulting sort to define the order in which you added objects to the archive.
5240 This whole procedure has been obsolete since about 1980, because
5241 Unix archives now contain a symbol table (traditionally built by
5242 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5243 linker uses the symbol table to effectively make multiple passes over
5246 Anyhow, that's where tsort came from. To solve an old problem with
5247 the way the linker handled archive files, which has since been solved
5251 @node Operating on fields
5252 @chapter Operating on fields
5255 * cut invocation:: Print selected parts of lines.
5256 * paste invocation:: Merge lines of files.
5257 * join invocation:: Join lines on a common field.
5261 @node cut invocation
5262 @section @command{cut}: Print selected parts of lines
5265 @command{cut} writes to standard output selected parts of each line of each
5266 input file, or standard input if no files are given or for a file name of
5270 cut @var{option}@dots{} [@var{file}]@dots{}
5273 In the table which follows, the @var{byte-list}, @var{character-list},
5274 and @var{field-list} are one or more numbers or ranges (two numbers
5275 separated by a dash) separated by commas. Bytes, characters, and
5276 fields are numbered starting at 1. Incomplete ranges may be
5277 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5278 @samp{@var{n}} through end of line or last field. The list elements
5279 can be repeated, can overlap, and can be specified in any order; but
5280 the selected input is written in the same order that it is read, and
5281 is written exactly once.
5283 The program accepts the following options. Also see @ref{Common
5288 @item -b @var{byte-list}
5289 @itemx --bytes=@var{byte-list}
5292 Select for printing only the bytes in positions listed in
5293 @var{byte-list}. Tabs and backspaces are treated like any other
5294 character; they take up 1 byte. If an output delimiter is specified,
5295 (see the description of @option{--output-delimiter}), then output that
5296 string between ranges of selected bytes.
5298 @item -c @var{character-list}
5299 @itemx --characters=@var{character-list}
5301 @opindex --characters
5302 Select for printing only the characters in positions listed in
5303 @var{character-list}. The same as @option{-b} for now, but
5304 internationalization will change that. Tabs and backspaces are
5305 treated like any other character; they take up 1 character. If an
5306 output delimiter is specified, (see the description of
5307 @option{--output-delimiter}), then output that string between ranges
5310 @item -f @var{field-list}
5311 @itemx --fields=@var{field-list}
5314 Select for printing only the fields listed in @var{field-list}.
5315 Fields are separated by a TAB character by default. Also print any
5316 line that contains no delimiter character, unless the
5317 @option{--only-delimited} (@option{-s}) option is specified
5319 @item -d @var{input_delim_byte}
5320 @itemx --delimiter=@var{input_delim_byte}
5322 @opindex --delimiter
5323 With @option{-f}, use the first byte of @var{input_delim_byte} as
5324 the input fields separator (default is TAB).
5328 Do not split multi-byte characters (no-op for now).
5331 @itemx --only-delimited
5333 @opindex --only-delimited
5334 For @option{-f}, do not print lines that do not contain the field separator
5335 character. Normally, any line without a field separator is printed verbatim.
5337 @item --output-delimiter=@var{output_delim_string}
5338 @opindex --output-delimiter
5339 With @option{-f}, output fields are separated by @var{output_delim_string}.
5340 The default with @option{-f} is to use the input delimiter.
5341 When using @option{-b} or @option{-c} to select ranges of byte or
5342 character offsets (as opposed to ranges of fields),
5343 output @var{output_delim_string} between non-overlapping
5344 ranges of selected bytes.
5347 @opindex --complement
5348 This option is a @acronym{GNU} extension.
5349 Select for printing the complement of the bytes, characters or fields
5350 selected with the @option{-b}, @option{-c} or @option{-f} options.
5351 In other words, do @emph{not} print the bytes, characters or fields
5352 specified via those options. This option is useful when you have
5353 many fields and want to print all but a few of them.
5360 @node paste invocation
5361 @section @command{paste}: Merge lines of files
5364 @cindex merging files
5366 @command{paste} writes to standard output lines consisting of sequentially
5367 corresponding lines of each given file, separated by a TAB character.
5368 Standard input is used for a file name of @samp{-} or if no input files
5390 paste [@var{option}]@dots{} [@var{file}]@dots{}
5393 The program accepts the following options. Also see @ref{Common options}.
5401 Paste the lines of one file at a time rather than one line from each
5402 file. Using the above example data:
5405 $ paste -s num2 let3
5410 @item -d @var{delim-list}
5411 @itemx --delimiters=@var{delim-list}
5413 @opindex --delimiters
5414 Consecutively use the characters in @var{delim-list} instead of
5415 TAB to separate merged lines. When @var{delim-list} is
5416 exhausted, start again at its beginning. Using the above example data:
5419 $ paste -d '%_' num2 let3 num2
5430 @node join invocation
5431 @section @command{join}: Join lines on a common field
5434 @cindex common field, joining on
5436 @command{join} writes to standard output a line for each pair of input
5437 lines that have identical join fields. Synopsis:
5440 join [@var{option}]@dots{} @var{file1} @var{file2}
5443 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5444 meaning standard input. @var{file1} and @var{file2} should be
5445 sorted on the join fields.
5448 Normally, the sort order is that of the
5449 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5450 the @option{-t} option is given, the sort comparison ignores blanks at
5451 the start of the join field, as in @code{sort -b}. If the
5452 @option{--ignore-case} option is given, the sort comparison ignores
5453 the case of characters in the join field, as in @code{sort -f}.
5455 The @command{sort} and @command{join} commands should use consistent
5456 locales and options if the output of @command{sort} is fed to
5457 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5458 sort a file on its default join field, but if you select a non-default
5459 locale, join field, separator, or comparison options, then you should
5460 do so consistently between @command{join} and @command{sort}.
5462 If the input has no unpairable lines, a @acronym{GNU} extension is
5463 available; the sort order can be any order that considers two fields
5464 to be equal if and only if the sort comparison described above
5465 considers them to be equal. For example:
5482 @checkOrderOption{join}
5486 @item the join field is the first field in each line;
5487 @item fields in the input are separated by one or more blanks, with leading
5488 blanks on the line ignored;
5489 @item fields in the output are separated by a space;
5490 @item each output line consists of the join field, the remaining
5491 fields from @var{file1}, then the remaining fields from @var{file2}.
5494 The program accepts the following options. Also see @ref{Common options}.
5498 @item -a @var{file-number}
5500 Print a line for each unpairable line in file @var{file-number} (either
5501 @samp{1} or @samp{2}), in addition to the normal output.
5504 Fail with an error message if either input file is wrongly ordered.
5506 @item --nocheck-order
5507 Do not check that both input files are in sorted order. This is the default.
5509 @item -e @var{string}
5511 Replace those output fields that are missing in the input with
5515 @itemx --ignore-case
5517 @opindex --ignore-case
5518 Ignore differences in case when comparing keys.
5519 With this option, the lines of the input files must be ordered in the same way.
5520 Use @samp{sort -f} to produce this ordering.
5522 @item -1 @var{field}
5524 Join on field @var{field} (a positive integer) of file 1.
5526 @item -2 @var{field}
5528 Join on field @var{field} (a positive integer) of file 2.
5530 @item -j @var{field}
5531 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5533 @item -o @var{field-list}
5534 Construct each output line according to the format in @var{field-list}.
5535 Each element in @var{field-list} is either the single character @samp{0} or
5536 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5537 @samp{2} and @var{n} is a positive field number.
5539 A field specification of @samp{0} denotes the join field.
5540 In most cases, the functionality of the @samp{0} field spec
5541 may be reproduced using the explicit @var{m.n} that corresponds
5542 to the join field. However, when printing unpairable lines
5543 (using either of the @option{-a} or @option{-v} options), there is no way
5544 to specify the join field using @var{m.n} in @var{field-list}
5545 if there are unpairable lines in both files.
5546 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5547 field specification notation.
5549 The elements in @var{field-list}
5550 are separated by commas or blanks.
5551 Blank separators typically need to be quoted for the shell. For
5552 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5553 2.2'} are equivalent.
5555 All output lines---including those printed because of any -a or -v
5556 option---are subject to the specified @var{field-list}.
5559 Use character @var{char} as the input and output field separator.
5560 Treat as significant each occurrence of @var{char} in the input file.
5561 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5562 @samp{sort}, to produce this ordering.
5564 @item -v @var{file-number}
5565 Print a line for each unpairable line in file @var{file-number}
5566 (either @samp{1} or @samp{2}), instead of the normal output.
5573 @node Operating on characters
5574 @chapter Operating on characters
5576 @cindex operating on characters
5578 This commands operate on individual characters.
5581 * tr invocation:: Translate, squeeze, and/or delete characters.
5582 * expand invocation:: Convert tabs to spaces.
5583 * unexpand invocation:: Convert spaces to tabs.
5588 @section @command{tr}: Translate, squeeze, and/or delete characters
5595 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5598 @command{tr} copies standard input to standard output, performing
5599 one of the following operations:
5603 translate, and optionally squeeze repeated characters in the result,
5605 squeeze repeated characters,
5609 delete characters, then squeeze repeated characters from the result.
5612 The @var{set1} and (if given) @var{set2} arguments define ordered
5613 sets of characters, referred to below as @var{set1} and @var{set2}. These
5614 sets are the characters of the input that @command{tr} operates on.
5615 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5617 complement (all of the characters that are not in @var{set1}).
5619 Currently @command{tr} fully supports only single-byte characters.
5620 Eventually it will support multibyte characters; when it does, the
5621 @option{-C} option will cause it to complement the set of characters,
5622 whereas @option{-c} will cause it to complement the set of values.
5623 This distinction will matter only when some values are not characters,
5624 and this is possible only in locales using multibyte encodings when
5625 the input contains encoding errors.
5627 The program accepts the @option{--help} and @option{--version}
5628 options. @xref{Common options}. Options must precede operands.
5633 * Character sets:: Specifying sets of characters.
5634 * Translating:: Changing one set of characters to another.
5635 * Squeezing:: Squeezing repeats and deleting.
5639 @node Character sets
5640 @subsection Specifying sets of characters
5642 @cindex specifying sets of characters
5644 The format of the @var{set1} and @var{set2} arguments resembles
5645 the format of regular expressions; however, they are not regular
5646 expressions, only lists of characters. Most characters simply
5647 represent themselves in these strings, but the strings can contain
5648 the shorthands listed below, for convenience. Some of them can be
5649 used only in @var{set1} or @var{set2}, as noted below.
5653 @item Backslash escapes
5654 @cindex backslash escapes
5656 The following backslash escape sequences are recognized:
5674 The character with the value given by @var{ooo}, which is 1 to 3
5680 While a backslash followed by a character not listed above is
5681 interpreted as that character, the backslash also effectively
5682 removes any special significance, so it is useful to escape
5683 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5688 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5689 from @var{m} through @var{n}, in ascending order. @var{m} should
5690 collate before @var{n}; if it doesn't, an error results. As an example,
5691 @samp{0-9} is the same as @samp{0123456789}.
5693 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5694 brackets to enclose ranges. Translations specified in that format
5695 sometimes work as expected, since the brackets are often transliterated
5696 to themselves. However, they should be avoided because they sometimes
5697 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5700 Many historically common and even accepted uses of ranges are not
5701 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5702 range will not do what most would expect because @samp{A} through @samp{Z}
5703 are not contiguous as they are in @acronym{ASCII}.
5704 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5705 the best way to work around this is to use character classes (see below).
5706 Otherwise, it is most portable (and most ugly) to enumerate the members
5709 @item Repeated characters
5710 @cindex repeated characters
5712 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5713 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5714 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5715 to as many copies of @var{c} as are needed to make @var{set2} as long as
5716 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5717 octal, otherwise in decimal.
5719 @item Character classes
5720 @cindex character classes
5722 The notation @samp{[:@var{class}:]} expands to all of the characters in
5723 the (predefined) class @var{class}. The characters expand in no
5724 particular order, except for the @code{upper} and @code{lower} classes,
5725 which expand in ascending order. When the @option{--delete} (@option{-d})
5726 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5727 character class can be used in @var{set2}. Otherwise, only the
5728 character classes @code{lower} and @code{upper} are accepted in
5729 @var{set2}, and then only if the corresponding character class
5730 (@code{upper} and @code{lower}, respectively) is specified in the same
5731 relative position in @var{set1}. Doing this specifies case conversion.
5732 The class names are given below; an error results when an invalid class
5744 Horizontal whitespace.
5753 Printable characters, not including space.
5759 Printable characters, including space.
5762 Punctuation characters.
5765 Horizontal or vertical whitespace.
5774 @item Equivalence classes
5775 @cindex equivalence classes
5777 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5778 equivalent to @var{c}, in no particular order. Equivalence classes are
5779 a relatively recent invention intended to support non-English alphabets.
5780 But there seems to be no standard way to define them or determine their
5781 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5782 each character's equivalence class consists only of that character,
5783 which is of no particular use.
5789 @subsection Translating
5791 @cindex translating characters
5793 @command{tr} performs translation when @var{set1} and @var{set2} are
5794 both given and the @option{--delete} (@option{-d}) option is not given.
5795 @command{tr} translates each character of its input that is in @var{set1}
5796 to the corresponding character in @var{set2}. Characters not in
5797 @var{set1} are passed through unchanged. When a character appears more
5798 than once in @var{set1} and the corresponding characters in @var{set2}
5799 are not all the same, only the final one is used. For example, these
5800 two commands are equivalent:
5807 A common use of @command{tr} is to convert lowercase characters to
5808 uppercase. This can be done in many ways. Here are three of them:
5811 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5813 tr '[:lower:]' '[:upper:]'
5817 But note that using ranges like @code{a-z} above is not portable.
5819 When @command{tr} is performing translation, @var{set1} and @var{set2}
5820 typically have the same length. If @var{set1} is shorter than
5821 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5823 On the other hand, making @var{set1} longer than @var{set2} is not
5824 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5825 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5826 the last character of @var{set2} as many times as necessary. System V
5827 @command{tr} truncates @var{set1} to the length of @var{set2}.
5829 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5830 When the @option{--truncate-set1} (@option{-t}) option is given,
5831 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5832 instead. This option is ignored for operations other than translation.
5834 Acting like System V @command{tr} in this case breaks the relatively common
5838 tr -cs A-Za-z0-9 '\012'
5842 because it converts only zero bytes (the first element in the
5843 complement of @var{set1}), rather than all non-alphanumerics, to
5847 By the way, the above idiom is not portable because it uses ranges, and
5848 it assumes that the octal code for newline is 012.
5849 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5852 tr -cs '[:alnum:]' '[\n*]'
5857 @subsection Squeezing repeats and deleting
5859 @cindex squeezing repeat characters
5860 @cindex deleting characters
5862 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5863 removes any input characters that are in @var{set1}.
5865 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5866 @command{tr} replaces each input sequence of a repeated character that
5867 is in @var{set1} with a single occurrence of that character.
5869 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5870 first performs any deletions using @var{set1}, then squeezes repeats
5871 from any remaining characters using @var{set2}.
5873 The @option{--squeeze-repeats} option may also be used when translating,
5874 in which case @command{tr} first performs translation, then squeezes
5875 repeats from any remaining characters using @var{set2}.
5877 Here are some examples to illustrate various combinations of options:
5882 Remove all zero bytes:
5889 Put all words on lines by themselves. This converts all
5890 non-alphanumeric characters to newlines, then squeezes each string
5891 of repeated newlines into a single newline:
5894 tr -cs '[:alnum:]' '[\n*]'
5898 Convert each sequence of repeated newlines to a single newline:
5905 Find doubled occurrences of words in a document.
5906 @c Separate the following two "the"s, so typo checkers don't complain.
5907 For example, people often write ``the @w{}the'' with the repeated words
5908 separated by a newline. The Bourne shell script below works first
5909 by converting each sequence of punctuation and blank characters to a
5910 single newline. That puts each ``word'' on a line by itself.
5911 Next it maps all uppercase characters to lower case, and finally it
5912 runs @command{uniq} with the @option{-d} option to print out only the words
5918 | tr -s '[:punct:][:blank:]' '[\n*]' \
5919 | tr '[:upper:]' '[:lower:]' \
5924 Deleting a small set of characters is usually straightforward. For example,
5925 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5931 However, when @samp{-} is one of those characters, it can be tricky because
5932 @samp{-} has special meanings. Performing the same task as above but also
5933 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5934 that would fail because @command{tr} would try to interpret @option{-a} as
5935 a command-line option. Alternatively, we could try putting the hyphen
5936 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5937 it would make @command{tr} interpret @code{a-x} as the range of characters
5938 @samp{a}@dots{}@samp{x} rather than the three.
5939 One way to solve the problem is to put the hyphen at the end of the list
5946 Or you can use @samp{--} to terminate option processing:
5952 More generally, use the character class notation @code{[=c=]}
5953 with @samp{-} (or any other character) in place of the @samp{c}:
5959 Note how single quotes are used in the above example to protect the
5960 square brackets from interpretation by a shell.
5965 @node expand invocation
5966 @section @command{expand}: Convert tabs to spaces
5969 @cindex tabs to spaces, converting
5970 @cindex converting tabs to spaces
5972 @command{expand} writes the contents of each given @var{file}, or standard
5973 input if none are given or for a @var{file} of @samp{-}, to standard
5974 output, with tab characters converted to the appropriate number of
5978 expand [@var{option}]@dots{} [@var{file}]@dots{}
5981 By default, @command{expand} converts all tabs to spaces. It preserves
5982 backspace characters in the output; they decrement the column count for
5983 tab calculations. The default action is equivalent to @option{-t 8} (set
5984 tabs every 8 columns).
5986 The program accepts the following options. Also see @ref{Common options}.
5990 @item -t @var{tab1}[,@var{tab2}]@dots{}
5991 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5994 @cindex tab stops, setting
5995 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5996 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5997 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5998 last tab stop given with single spaces. Tab stops can be separated by
5999 blanks as well as by commas.
6001 For compatibility, GNU @command{expand} also accepts the obsolete
6002 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6003 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6009 @cindex initial tabs, converting
6010 Only convert initial tabs (those that precede all non-space or non-tab
6011 characters) on each line to spaces.
6018 @node unexpand invocation
6019 @section @command{unexpand}: Convert spaces to tabs
6023 @command{unexpand} writes the contents of each given @var{file}, or
6024 standard input if none are given or for a @var{file} of @samp{-}, to
6025 standard output, converting blanks at the beginning of each line into
6026 as many tab characters as needed. In the default @acronym{POSIX}
6027 locale, a @dfn{blank} is a space or a tab; other locales may specify
6028 additional blank characters. Synopsis:
6031 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6034 By default, @command{unexpand} converts only initial blanks (those
6035 that precede all non-blank characters) on each line. It
6036 preserves backspace characters in the output; they decrement the column
6037 count for tab calculations. By default, tabs are set at every 8th
6040 The program accepts the following options. Also see @ref{Common options}.
6044 @item -t @var{tab1}[,@var{tab2}]@dots{}
6045 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6048 If only one tab stop is given, set the tabs @var{tab1} columns apart
6049 instead of the default 8. Otherwise, set the tabs at columns
6050 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6051 beyond the tab stops given unchanged. Tab stops can be separated by
6052 blanks as well as by commas. This option implies the @option{-a} option.
6054 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6055 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6056 separated by commas. (Unlike @option{-t}, this obsolete option does
6057 not imply @option{-a}.) New scripts should use @option{--first-only -t
6058 @var{tab1}[,@var{tab2}]@dots{}} instead.
6064 Also convert all sequences of two or more blanks just before a tab stop,
6065 even if they occur after non-blank characters in a line.
6072 @node Directory listing
6073 @chapter Directory listing
6075 This chapter describes the @command{ls} command and its variants @command{dir}
6076 and @command{vdir}, which list information about files.
6079 * ls invocation:: List directory contents.
6080 * dir invocation:: Briefly ls.
6081 * vdir invocation:: Verbosely ls.
6082 * dircolors invocation:: Color setup for ls, etc.
6087 @section @command{ls}: List directory contents
6090 @cindex directory listing
6092 The @command{ls} program lists information about files (of any type,
6093 including directories). Options and file arguments can be intermixed
6094 arbitrarily, as usual.
6096 For non-option command-line arguments that are directories, by default
6097 @command{ls} lists the contents of directories, not recursively, and
6098 omitting files with names beginning with @samp{.}. For other non-option
6099 arguments, by default @command{ls} lists just the file name. If no
6100 non-option argument is specified, @command{ls} operates on the current
6101 directory, acting as if it had been invoked with a single argument of @samp{.}.
6104 By default, the output is sorted alphabetically, according to the locale
6105 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6106 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6107 produce output that is sorted differently than you're accustomed to.
6108 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6109 If standard output is
6110 a terminal, the output is in columns (sorted vertically) and control
6111 characters are output as question marks; otherwise, the output is listed
6112 one per line and control characters are output as-is.
6114 Because @command{ls} is such a fundamental program, it has accumulated many
6115 options over the years. They are described in the subsections below;
6116 within each section, options are listed alphabetically (ignoring case).
6117 The division of options into the subsections is not absolute, since some
6118 options affect more than one aspect of @command{ls}'s operation.
6120 @cindex exit status of @command{ls}
6125 1 minor problems (e.g., failure to access a file or directory not
6126 specified as a command line argument. This happens when listing a
6127 directory in which entries are actively being removed or renamed.)
6128 2 serious trouble (e.g., memory exhausted, invalid option, failure
6129 to access a file or directory specified as a command line argument
6130 or a directory loop)
6133 Also see @ref{Common options}.
6136 * Which files are listed::
6137 * What information is listed::
6138 * Sorting the output::
6139 * 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{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 Details about version sort
6683 @subsection 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 On older systems, it is not possible to preserve these attributes
7448 when the affected file is a symbolic link.
7449 However, many systems now provide the @code{utimensat} function,
7450 which makes it possible even for symbolic links.
7452 Preserve in the destination files
7453 any links between corresponding source files.
7454 Note that with @option{-L} or @option{-H}, this option can convert
7455 symbolic links to hard links. For example,
7457 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7462 Note the inputs: @file{b} is a symlink to regular file @file{a},
7463 yet the files in destination directory, @file{c/}, are hard-linked.
7464 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7465 tells @command{cp} to dereference command line arguments, it sees two files
7466 with the same inode number, and preserves the perceived hard link.
7468 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7470 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7476 Preserve SELinux security context of the file. @command{cp} will fail
7477 if the preserving of SELinux security context is not succesful.
7479 Preserve extended attributes if @command{cp} is built with xattr support,
7480 and xattrs are supported and enabled on your file system.
7481 If SELinux context and/or ACLs are implemented using xattrs,
7482 they are preserved by this option as well.
7484 Preserve all file attributes.
7485 Equivalent to specifying all of the above, but with the difference
7486 that failure to preserve SELinux security context or extended attributes
7487 does not change @command{cp}'s exit status.
7488 @command{cp} does diagnose such failures.
7491 Using @option{--preserve} with no @var{attribute_list} is equivalent
7492 to @option{--preserve=mode,ownership,timestamps}.
7494 In the absence of this option, each destination file is created with the
7495 mode bits of the corresponding source file, minus the bits set in the
7496 umask and minus the set-user-ID and set-group-ID bits.
7497 @xref{File permissions}.
7499 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7500 @cindex file information, preserving
7501 Do not preserve the specified attributes. The @var{attribute_list}
7502 has the same form as for @option{--preserve}.
7506 @cindex parent directories and @command{cp}
7507 Form the name of each destination file by appending to the target
7508 directory a slash and the specified name of the source file. The last
7509 argument given to @command{cp} must be the name of an existing directory.
7510 For example, the command:
7513 cp --parents a/b/c existing_dir
7517 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7518 any missing intermediate directories.
7525 @opindex --recursive
7526 @cindex directories, copying recursively
7527 @cindex copying directories recursively
7528 @cindex recursively copying directories
7529 @cindex non-directories, copying as special files
7530 Copy directories recursively. By default, do not follow symbolic
7531 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7532 @option{--dereference} (@option{-L}), @option{--no-dereference}
7533 (@option{-P}), and @option{-H} options. Special files are copied by
7534 creating a destination file of the same type as the source; see the
7535 @option{--copy-contents} option. It is not portable to use
7536 @option{-r} to copy symbolic links or special files. On some
7537 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7538 @option{-L} and @option{--copy-contents} for historical reasons.
7539 Also, it is not portable to use @option{-R} to copy symbolic links
7540 unless you also specify @option{-P}, as @acronym{POSIX} allows
7541 implementations that dereference symbolic links by default.
7543 @item --reflink[=@var{when}]
7544 @opindex --reflink[=@var{when}]
7547 @cindex copy on write
7548 Perform a lightweight, copy-on-write (COW) copy.
7549 Copying with this option can succeed only on some file systems.
7550 Once it has succeeded, beware that the source and destination files
7551 share the same disk data blocks as long as they remain unmodified.
7552 Thus, if a disk I/O error affects data blocks of one of the files,
7553 the other suffers the exact same fate.
7555 The @var{when} value can be one of the following:
7559 The default behavior: if the copy-on-write operation is not supported
7560 then report the failure for each file and exit with a failure status.
7563 If the copy-on-write operation is not supported then fall back
7564 to the standard copy behaviour.
7568 @item --remove-destination
7569 @opindex --remove-destination
7570 Remove each existing destination file before attempting to open it
7571 (contrast with @option{-f} above).
7573 @item --sparse=@var{when}
7574 @opindex --sparse=@var{when}
7575 @cindex sparse files, copying
7576 @cindex holes, copying files with
7577 @findex read @r{system call, and holes}
7578 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7579 does not occupy any physical disk blocks; the @samp{read} system call
7580 reads these as zeros. This can both save considerable disk space and
7581 increase speed, since many binary files contain lots of consecutive zero
7582 bytes. By default, @command{cp} detects holes in input source files via a crude
7583 heuristic and makes the corresponding output file sparse as well.
7584 Only regular files may be sparse.
7586 The @var{when} value can be one of the following:
7590 The default behavior: if the input file is sparse, attempt to make
7591 the output file sparse, too. However, if an output file exists but
7592 refers to a non-regular file, then do not attempt to make it sparse.
7595 For each sufficiently long sequence of zero bytes in the input file,
7596 attempt to create a corresponding hole in the output file, even if the
7597 input file does not appear to be sparse.
7598 This is useful when the input file resides on a file system
7599 that does not support sparse files
7600 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7601 but the output file is on a type of file system that does support them.
7602 Holes may be created only in regular files, so if the destination file
7603 is of some other type, @command{cp} does not even try to make it sparse.
7606 Never make the output file sparse.
7607 This is useful in creating a file for use with the @command{mkswap} command,
7608 since such a file must not have any holes.
7611 @optStripTrailingSlashes
7614 @itemx --symbolic-link
7616 @opindex --symbolic-link
7617 @cindex symbolic links, copying with
7618 Make symbolic links instead of copies of non-directories. All source
7619 file names must be absolute (starting with @samp{/}) unless the
7620 destination files are in the current directory. This option merely
7621 results in an error message on systems that do not support symbolic links.
7627 @optNoTargetDirectory
7633 @cindex newer files, copying only
7634 Do not copy a non-directory that has an existing destination with the
7635 same or newer modification time. If time stamps are being preserved,
7636 the comparison is to the source time stamp truncated to the
7637 resolutions of the destination file system and of the system calls
7638 used to update time stamps; this avoids duplicate work if several
7639 @samp{cp -pu} commands are executed with the same source and
7646 Print the name of each file before copying it.
7649 @itemx --one-file-system
7651 @opindex --one-file-system
7652 @cindex file systems, omitting copying to different
7653 Skip subdirectories that are on different file systems from the one that
7654 the copy started on.
7655 However, mount point directories @emph{are} copied.
7663 @section @command{dd}: Convert and copy a file
7666 @cindex converting while copying a file
7668 @command{dd} copies a file (from standard input to standard output, by
7669 default) with a changeable I/O block size, while optionally performing
7670 conversions on it. Synopses:
7673 dd [@var{operand}]@dots{}
7677 The only options are @option{--help} and @option{--version}.
7678 @xref{Common options}. @command{dd} accepts the following operands.
7684 Read from @var{file} instead of standard input.
7688 Write to @var{file} instead of standard output. Unless
7689 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7690 bytes (or the size specified with @samp{seek=}).
7692 @item ibs=@var{bytes}
7694 @cindex block size of input
7695 @cindex input block size
7696 Set the input block size to @var{bytes}.
7697 This makes @command{dd} read @var{bytes} per block.
7698 The default is 512 bytes.
7700 @item obs=@var{bytes}
7702 @cindex block size of output
7703 @cindex output block size
7704 Set the output block size to @var{bytes}.
7705 This makes @command{dd} write @var{bytes} per block.
7706 The default is 512 bytes.
7708 @item bs=@var{bytes}
7711 Set both input and output block sizes to @var{bytes}.
7712 This makes @command{dd} read and write @var{bytes} per block,
7713 overriding any @samp{ibs} and @samp{obs} settings.
7714 In addition, if no data-transforming @option{conv} option is specified,
7715 each input block is copied to the output as a single block,
7716 without aggregating short reads.
7718 @item cbs=@var{bytes}
7720 @cindex block size of conversion
7721 @cindex conversion block size
7722 @cindex fixed-length records, converting to variable-length
7723 @cindex variable-length records, converting to fixed-length
7724 Set the conversion block size to @var{bytes}.
7725 When converting variable-length records to fixed-length ones
7726 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7727 use @var{bytes} as the fixed record length.
7729 @item skip=@var{blocks}
7731 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7733 @item seek=@var{blocks}
7735 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7737 @item count=@var{blocks}
7739 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7740 of everything until the end of the file.
7744 Do not print the overall transfer rate and volume statistics
7745 that normally make up the third status line when @command{dd} exits.
7747 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7749 Convert the file as specified by the @var{conversion} argument(s).
7750 (No spaces around any comma(s).)
7757 @opindex ascii@r{, converting to}
7758 Convert @acronym{EBCDIC} to @acronym{ASCII},
7759 using the conversion table specified by @acronym{POSIX}.
7760 This provides a 1:1 translation for all 256 bytes.
7763 @opindex ebcdic@r{, converting to}
7764 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7765 This is the inverse of the @samp{ascii} conversion.
7768 @opindex alternate ebcdic@r{, converting to}
7769 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7770 using the alternate conversion table specified by @acronym{POSIX}.
7771 This is not a 1:1 translation, but reflects common historical practice
7772 for @samp{~}, @samp{[}, and @samp{]}.
7774 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7778 @opindex block @r{(space-padding)}
7779 For each line in the input, output @samp{cbs} bytes, replacing the
7780 input newline with a space and padding with spaces as necessary.
7784 Remove any trailing spaces in each @samp{cbs}-sized input block,
7785 and append a newline.
7787 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7790 @opindex lcase@r{, converting to}
7791 Change uppercase letters to lowercase.
7794 @opindex ucase@r{, converting to}
7795 Change lowercase letters to uppercase.
7797 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7800 @opindex swab @r{(byte-swapping)}
7801 @cindex byte-swapping
7802 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7803 when an odd number of bytes are read---the last byte is simply copied
7804 (since there is nothing to swap it with).
7808 @cindex read errors, ignoring
7809 Continue after read errors.
7813 @cindex creating output file, avoiding
7814 Do not create the output file; the output file must already exist.
7818 @cindex creating output file, requiring
7819 Fail if the output file already exists; @command{dd} must create the
7822 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7826 @cindex truncating output file, avoiding
7827 Do not truncate the output file.
7830 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7831 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7832 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7837 @cindex synchronized data writes, before finishing
7838 Synchronize output data just before finishing. This forces a physical
7839 write of output data.
7843 @cindex synchronized data and metadata writes, before finishing
7844 Synchronize output data and metadata just before finishing. This
7845 forces a physical write of output data and metadata.
7849 @item iflag=@var{flag}[,@var{flag}]@dots{}
7851 Access the input file using the flags specified by the @var{flag}
7852 argument(s). (No spaces around any comma(s).)
7854 @item oflag=@var{flag}[,@var{flag}]@dots{}
7856 Access the output file using the flags specified by the @var{flag}
7857 argument(s). (No spaces around any comma(s).)
7859 Here are the flags. Not every flag is supported on every operating
7866 @cindex appending to the output file
7867 Write in append mode, so that even if some other process is writing to
7868 this file, every @command{dd} write will append to the current
7869 contents of the file. This flag makes sense only for output.
7870 If you combine this flag with the @samp{of=@var{file}} operand,
7871 you should also specify @samp{conv=notrunc} unless you want the
7872 output file to be truncated before being appended to.
7876 @cindex concurrent I/O
7877 Use concurrent I/O mode for data. This mode performs direct I/O
7878 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7879 A file cannot be opened in CIO mode and with a standard open at the
7885 Use direct I/O for data, avoiding the buffer cache.
7886 Note that the kernel may impose restrictions on read or write buffer sizes.
7887 For example, with an ext4 destination file system and a linux-based kernel,
7888 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7889 output buffer size is not a multiple of 512.
7893 @cindex directory I/O
7895 Fail unless the file is a directory. Most operating systems do not
7896 allow I/O to a directory, so this flag has limited utility.
7900 @cindex synchronized data reads
7901 Use synchronized I/O for data. For the output file, this forces a
7902 physical write of output data on each write. For the input file,
7903 this flag can matter when reading from a remote file that has been
7904 written to synchronously by some other process. Metadata (e.g.,
7905 last-access and last-modified time) is not necessarily synchronized.
7909 @cindex synchronized data and metadata I/O
7910 Use synchronized I/O for both data and metadata.
7914 @cindex nonblocking I/O
7915 Use non-blocking I/O.
7920 Do not update the file's access time.
7921 Some older file systems silently ignore this flag, so it is a good
7922 idea to test it on your files before relying on it.
7926 @cindex controlling terminal
7927 Do not assign the file to be a controlling terminal for @command{dd}.
7928 This has no effect when the file is not a terminal.
7929 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7934 @cindex symbolic links, following
7935 Do not follow symbolic links.
7940 Fail if the file has multiple hard links.
7945 Use binary I/O. This option has an effect only on nonstandard
7946 platforms that distinguish binary from text I/O.
7951 Use text I/O. Like @samp{binary}, this option has no effect on
7956 Accumulate full blocks from input. The @code{read} system call
7957 may return early if a full block is not available.
7958 When that happens, continue calling @code{read} to fill the remainder
7960 This flag can be used only with @code{iflag}.
7964 These flags are not supported on all systems, and @samp{dd} rejects
7965 attempts to use them when they are not supported. When reading from
7966 standard input or writing to standard output, the @samp{nofollow} and
7967 @samp{noctty} flags should not be specified, and the other flags
7968 (e.g., @samp{nonblock}) can affect how other processes behave with the
7969 affected file descriptors, even after @command{dd} exits.
7973 @cindex multipliers after numbers
7974 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7975 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7976 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7977 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7979 Use different @command{dd} invocations to use different block sizes for
7980 skipping and I/O@. For example, the following shell commands copy data
7981 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7982 4 KiB label at the start of the disk:
7985 disk=/dev/rdsk/c0t1d0s2
7988 # Copy all but the label from disk to tape.
7989 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7991 # Copy from tape back to disk, but leave the disk label alone.
7992 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7995 Sending an @samp{INFO} signal to a running @command{dd}
7996 process makes it print I/O statistics to standard error
7997 and then resume copying. In the example below,
7998 @command{dd} is run in the background to copy 10 million blocks.
7999 The @command{kill} command makes it output intermediate I/O statistics,
8000 and when @command{dd} completes normally or is killed by the
8001 @code{SIGINT} signal, it outputs the final statistics.
8004 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8005 $ kill -s INFO $pid; wait $pid
8006 3385223+0 records in
8007 3385223+0 records out
8008 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8009 10000000+0 records in
8010 10000000+0 records out
8011 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8014 @vindex POSIXLY_CORRECT
8015 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8016 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8017 environment variable is set.
8022 @node install invocation
8023 @section @command{install}: Copy files and set attributes
8026 @cindex copying files and setting attributes
8028 @command{install} copies files while setting their file mode bits and, if
8029 possible, their owner and group. Synopses:
8032 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8033 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8034 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8035 install [@var{option}]@dots{} -d @var{directory}@dots{}
8040 If two file names are given, @command{install} copies the first file to the
8044 If the @option{--target-directory} (@option{-t}) option is given, or
8045 failing that if the last file is a directory and the
8046 @option{--no-target-directory} (@option{-T}) option is not given,
8047 @command{install} copies each @var{source} file to the specified
8048 directory, using the @var{source}s' names.
8051 If the @option{--directory} (@option{-d}) option is given,
8052 @command{install} creates each @var{directory} and any missing parent
8053 directories. Parent directories are created with mode
8054 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8055 current umask. @xref{Directory Setuid and Setgid}, for how the
8056 set-user-ID and set-group-ID bits of parent directories are inherited.
8059 @cindex Makefiles, installing programs in
8060 @command{install} is similar to @command{cp}, but allows you to control the
8061 attributes of destination files. It is typically used in Makefiles to
8062 copy programs into their destination directories. It refuses to copy
8063 files onto themselves.
8065 @cindex extended attributes, xattr
8066 @command{install} never preserves extended attributes (xattr).
8068 The program accepts the following options. Also see @ref{Common options}.
8078 Compare each pair of source and destination files, and if the destination has
8079 identical content and any specified owner, group, permissions, and possibly
8080 SELinux context, then do not modify the destination at all.
8084 Ignored; for compatibility with old Unix versions of @command{install}.
8088 Create any missing parent directories of @var{dest},
8089 then copy @var{source} to @var{dest}.
8090 This option is ignored if a destination directory is specified
8091 via @option{--target-directory=DIR}.
8096 @opindex --directory
8097 @cindex directories, creating with given attributes
8098 @cindex parent directories, creating missing
8099 @cindex leading directories, creating missing
8100 Create any missing parent directories, giving them the default
8101 attributes. Then create each given directory, setting their owner,
8102 group and mode as given on the command line or to the defaults.
8104 @item -g @var{group}
8105 @itemx --group=@var{group}
8108 @cindex group ownership of installed files, setting
8109 Set the group ownership of installed files or directories to
8110 @var{group}. The default is the process's current group. @var{group}
8111 may be either a group name or a numeric group ID.
8114 @itemx --mode=@var{mode}
8117 @cindex permissions of installed files, setting
8118 Set the file mode bits for the installed file or directory to @var{mode},
8119 which can be either an octal number, or a symbolic mode as in
8120 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8121 point of departure (@pxref{File permissions}).
8122 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8123 execute for the owner, read and execute for group and other, and with
8124 set-user-ID and set-group-ID disabled.
8125 This default is not quite the same as @samp{755}, since it disables
8126 instead of preserving set-user-ID and set-group-ID on directories.
8127 @xref{Directory Setuid and Setgid}.
8129 @item -o @var{owner}
8130 @itemx --owner=@var{owner}
8133 @cindex ownership of installed files, setting
8134 @cindex appropriate privileges
8135 @vindex root @r{as default owner}
8136 If @command{install} has appropriate privileges (is run as root), set the
8137 ownership of installed files or directories to @var{owner}. The default
8138 is @code{root}. @var{owner} may be either a user name or a numeric user
8141 @item --preserve-context
8142 @opindex --preserve-context
8144 @cindex security context
8145 Preserve the SELinux security context of files and directories.
8146 Failure to preserve the context in all of the files or directories
8147 will result in an exit status of 1. If SELinux is disabled then
8148 print a warning and ignore the option.
8151 @itemx --preserve-timestamps
8153 @opindex --preserve-timestamps
8154 @cindex timestamps of installed files, preserving
8155 Set the time of last access and the time of last modification of each
8156 installed file to match those of each corresponding original file.
8157 When a file is installed without this option, its last access and
8158 last modification times are both set to the time of installation.
8159 This option is useful if you want to use the last modification times
8160 of installed files to keep track of when they were last built as opposed
8161 to when they were last installed.
8167 @cindex symbol table information, stripping
8168 @cindex stripping symbol table information
8169 Strip the symbol tables from installed binary executables.
8171 @itemx --strip-program=@var{program}
8172 @opindex --strip-program
8173 @cindex symbol table information, stripping, program
8174 Program used to strip binaries.
8180 @optNoTargetDirectory
8186 Print the name of each file before copying it.
8188 @item -Z @var{context}
8189 @itemx --context=@var{context}
8193 @cindex security context
8194 Set the default SELinux security context to be used for any
8195 created files and directories. If SELinux is disabled then
8196 print a warning and ignore the option.
8204 @section @command{mv}: Move (rename) files
8208 @command{mv} moves or renames files (or directories). Synopses:
8211 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8212 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8213 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8218 If two file names are given, @command{mv} moves the first file to the
8222 If the @option{--target-directory} (@option{-t}) option is given, or
8223 failing that if the last file is a directory and the
8224 @option{--no-target-directory} (@option{-T}) option is not given,
8225 @command{mv} moves each @var{source} file to the specified
8226 directory, using the @var{source}s' names.
8229 @command{mv} can move any type of file from one file system to another.
8230 Prior to version @code{4.0} of the fileutils,
8231 @command{mv} could move only regular files between file systems.
8232 For example, now @command{mv} can move an entire directory hierarchy
8233 including special device files from one partition to another. It first
8234 uses some of the same code that's used by @code{cp -a} to copy the
8235 requested directories and files, then (assuming the copy succeeded)
8236 it removes the originals. If the copy fails, then the part that was
8237 copied to the destination partition is removed. If you were to copy
8238 three directories from one partition to another and the copy of the first
8239 directory succeeded, but the second didn't, the first would be left on
8240 the destination partition and the second and third would be left on the
8243 @cindex extended attributes, xattr
8244 @command{mv} always tries to copy extended attributes (xattr).
8246 @cindex prompting, and @command{mv}
8247 If a destination file exists but is normally unwritable, standard input
8248 is a terminal, and the @option{-f} or @option{--force} option is not given,
8249 @command{mv} prompts the user for whether to replace the file. (You might
8250 own the file, or have write permission on its directory.) If the
8251 response is not affirmative, the file is skipped.
8253 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8254 when it might be a symlink to a directory.
8255 Otherwise, @command{mv} may do something very surprising, since
8256 its behavior depends on the underlying rename system call.
8257 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8258 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8259 renames not the symlink but rather the directory referenced by the symlink.
8260 @xref{Trailing slashes}.
8262 The program accepts the following options. Also see @ref{Common options}.
8272 @cindex prompts, omitting
8273 Do not prompt the user before removing a destination file.
8275 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8276 options, only the final one takes effect.
8281 @itemx --interactive
8283 @opindex --interactive
8284 @cindex prompts, forcing
8285 Prompt whether to overwrite each existing destination file, regardless
8287 If the response is not affirmative, the file is skipped.
8293 @opindex --no-clobber
8294 @cindex prompts, omitting
8295 Do not overwrite an existing file.
8297 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8303 @cindex newer files, moving only
8304 Do not move a non-directory that has an existing destination with the
8305 same or newer modification time.
8306 If the move is across file system boundaries, the comparison is to the
8307 source time stamp truncated to the resolutions of the destination file
8308 system and of the system calls used to update time stamps; this avoids
8309 duplicate work if several @samp{mv -u} commands are executed with the
8310 same source and destination.
8316 Print the name of each file before moving it.
8318 @optStripTrailingSlashes
8324 @optNoTargetDirectory
8332 @section @command{rm}: Remove files or directories
8335 @cindex removing files or directories
8337 @command{rm} removes each given @var{file}. By default, it does not remove
8338 directories. Synopsis:
8341 rm [@var{option}]@dots{} [@var{file}]@dots{}
8344 @cindex prompting, and @command{rm}
8345 If the @option{-I} or @option{--interactive=once} option is given,
8346 and there are more than three files or the @option{-r}, @option{-R},
8347 or @option{--recursive} are given, then @command{rm} prompts the user
8348 for whether to proceed with the entire operation. If the response is
8349 not affirmative, the entire command is aborted.
8351 Otherwise, if a file is unwritable, standard input is a terminal, and
8352 the @option{-f} or @option{--force} option is not given, or the
8353 @option{-i} or @option{--interactive=always} option @emph{is} given,
8354 @command{rm} prompts the user for whether to remove the file.
8355 If the response is not affirmative, the file is skipped.
8357 Any attempt to remove a file whose last file name component is
8358 @file{.} or @file{..} is rejected without any prompting.
8360 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8361 possible to recover the contents of that file. If you want more assurance
8362 that the contents are truly unrecoverable, consider using @command{shred}.
8364 The program accepts the following options. Also see @ref{Common options}.
8372 Ignore nonexistent files and never prompt the user.
8373 Ignore any previous @option{--interactive} (@option{-i}) option.
8377 Prompt whether to remove each file.
8378 If the response is not affirmative, the file is skipped.
8379 Ignore any previous @option{--force} (@option{-f}) option.
8380 Equivalent to @option{--interactive=always}.
8384 Prompt once whether to proceed with the command, if more than three
8385 files are named or if a recursive removal is requested. Ignore any
8386 previous @option{--force} (@option{-f}) option. Equivalent to
8387 @option{--interactive=once}.
8389 @itemx --interactive [=@var{when}]
8390 @opindex --interactive
8391 Specify when to issue an interactive prompt. @var{when} may be
8395 @vindex never @r{interactive option}
8396 - Do not prompt at all.
8398 @vindex once @r{interactive option}
8399 - Prompt once if more than three files are named or if a recursive
8400 removal is requested. Equivalent to @option{-I}.
8402 @vindex always @r{interactive option}
8403 - Prompt for every file being removed. Equivalent to @option{-i}.
8405 @option{--interactive} with no @var{when} is equivalent to
8406 @option{--interactive=always}.
8408 @itemx --one-file-system
8409 @opindex --one-file-system
8410 @cindex one file system, restricting @command{rm} to
8411 When removing a hierarchy recursively, skip any directory that is on a
8412 file system different from that of the corresponding command line argument.
8414 This option is useful when removing a build ``chroot'' hierarchy,
8415 which normally contains no valuable data. However, it is not uncommon
8416 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8417 use one's start-up file. The catch is that it's easy to forget to
8418 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8419 your normally throw-away chroot, that command will remove everything
8420 under @file{/home}, too.
8421 Use the @option{--one-file-system} option, and it will
8422 warn about and skip directories on other file systems.
8423 Of course, this will not save your @file{/home} if it and your
8424 chroot happen to be on the same file system.
8426 @itemx --preserve-root
8427 @opindex --preserve-root
8428 @cindex root directory, disallow recursive destruction
8429 Fail upon any attempt to remove the root directory, @file{/},
8430 when used with the @option{--recursive} option.
8431 This is the default behavior.
8432 @xref{Treating / specially}.
8434 @itemx --no-preserve-root
8435 @opindex --no-preserve-root
8436 @cindex root directory, allow recursive destruction
8437 Do not treat @file{/} specially when removing recursively.
8438 This option is not recommended unless you really want to
8439 remove all the files on your computer.
8440 @xref{Treating / specially}.
8447 @opindex --recursive
8448 @cindex directories, removing (recursively)
8449 Remove the listed directories and their contents recursively.
8455 Print the name of each file before removing it.
8459 @cindex files beginning with @samp{-}, removing
8460 @cindex @samp{-}, removing files beginning with
8461 One common question is how to remove files whose names begin with a
8462 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8463 function to parse its arguments, lets you use the @samp{--} option to
8464 indicate that all following arguments are non-options. To remove a file
8465 called @file{-f} in the current directory, you could type either:
8478 @opindex - @r{and Unix @command{rm}}
8479 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8480 predates the development of the getopt standard syntax.
8485 @node shred invocation
8486 @section @command{shred}: Remove files more securely
8489 @cindex data, erasing
8490 @cindex erasing data
8492 @command{shred} overwrites devices or files, to help prevent even
8493 very expensive hardware from recovering the data.
8495 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8496 not actually destroyed. Only the index listing where the file is
8497 stored is destroyed, and the storage is made available for reuse.
8498 There are undelete utilities that will attempt to reconstruct the index
8499 and can bring the file back if the parts were not reused.
8501 On a busy system with a nearly-full drive, space can get reused in a few
8502 seconds. But there is no way to know for sure. If you have sensitive
8503 data, you may want to be sure that recovery is not possible by actually
8504 overwriting the file with non-sensitive data.
8506 However, even after doing that, it is possible to take the disk back
8507 to a laboratory and use a lot of sensitive (and expensive) equipment
8508 to look for the faint ``echoes'' of the original data underneath the
8509 overwritten data. If the data has only been overwritten once, it's not
8512 The best way to remove something irretrievably is to destroy the media
8513 it's on with acid, melt it down, or the like. For cheap removable media
8514 like floppy disks, this is the preferred method. However, hard drives
8515 are expensive and hard to melt, so the @command{shred} utility tries
8516 to achieve a similar effect non-destructively.
8518 This uses many overwrite passes, with the data patterns chosen to
8519 maximize the damage they do to the old data. While this will work on
8520 floppies, the patterns are designed for best effect on hard drives.
8521 For more details, see the source code and Peter Gutmann's paper
8522 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8523 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8524 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8525 California, July 22--25, 1996).
8527 @strong{Please note} that @command{shred} relies on a very important assumption:
8528 that the file system overwrites data in place. This is the traditional
8529 way to do things, but many modern file system designs do not satisfy this
8530 assumption. Exceptions include:
8535 Log-structured or journaled file systems, such as those supplied with
8536 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8537 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8540 File systems that write redundant data and carry on even if some writes
8541 fail, such as RAID-based file systems.
8544 File systems that make snapshots, such as Network Appliance's NFS server.
8547 File systems that cache in temporary locations, such as NFS version 3
8551 Compressed file systems.
8554 In the particular case of ext3 file systems, the above disclaimer applies (and
8555 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8556 mode, which journals file data in addition to just metadata. In both
8557 the @code{data=ordered} (default) and @code{data=writeback} modes,
8558 @command{shred} works as usual. Ext3 journaling modes can be changed
8559 by adding the @code{data=something} option to the mount options for a
8560 particular file system in the @file{/etc/fstab} file, as documented in
8561 the mount man page (man mount).
8563 If you are not sure how your file system operates, then you should assume
8564 that it does not overwrite data in place, which means that shred cannot
8565 reliably operate on regular files in your file system.
8567 Generally speaking, it is more reliable to shred a device than a file,
8568 since this bypasses the problem of file system design mentioned above.
8569 However, even shredding devices is not always completely reliable. For
8570 example, most disks map out bad sectors invisibly to the application; if
8571 the bad sectors contain sensitive data, @command{shred} won't be able to
8574 @command{shred} makes no attempt to detect or report this problem, just as
8575 it makes no attempt to do anything about backups. However, since it is
8576 more reliable to shred devices than files, @command{shred} by default does
8577 not truncate or remove the output file. This default is more suitable
8578 for devices, which typically cannot be truncated and should not be
8581 Finally, consider the risk of backups and mirrors.
8582 File system backups and remote mirrors may contain copies of the
8583 file that cannot be removed, and that will allow a shredded file
8584 to be recovered later. So if you keep any data you may later want
8585 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8588 shred [@var{option}]@dots{} @var{file}[@dots{}]
8591 The program accepts the following options. Also see @ref{Common options}.
8599 @cindex force deletion
8600 Override file permissions if necessary to allow overwriting.
8603 @itemx -n @var{number}
8604 @itemx --iterations=@var{number}
8605 @opindex -n @var{number}
8606 @opindex --iterations=@var{number}
8607 @cindex iterations, selecting the number of
8608 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8609 overwrite. You can reduce this to save time, or increase it if you think it's
8610 appropriate. After 25 passes all of the internal overwrite patterns will have
8611 been used at least once.
8613 @item --random-source=@var{file}
8614 @opindex --random-source
8615 @cindex random source for shredding
8616 Use @var{file} as a source of random data used to overwrite and to
8617 choose pass ordering. @xref{Random sources}.
8619 @item -s @var{bytes}
8620 @itemx --size=@var{bytes}
8621 @opindex -s @var{bytes}
8622 @opindex --size=@var{bytes}
8623 @cindex size of file to shred
8624 Shred the first @var{bytes} bytes of the file. The default is to shred
8625 the whole file. @var{bytes} can be followed by a size specification like
8626 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8632 @cindex removing files after shredding
8633 After shredding a file, truncate it (if possible) and then remove it.
8634 If a file has multiple links, only the named links will be removed.
8640 Display to standard error all status updates as sterilization proceeds.
8646 By default, @command{shred} rounds the size of a regular file up to the next
8647 multiple of the file system block size to fully erase the last block of the file.
8648 Use @option{--exact} to suppress that behavior.
8649 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8650 blocks, the resulting file will be 512 bytes long. With this option,
8651 shred does not increase the apparent size of the file.
8657 Normally, the last pass that @command{shred} writes is made up of
8658 random data. If this would be conspicuous on your hard drive (for
8659 example, because it looks like encrypted data), or you just think
8660 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8661 all zero bits. This is in addition to the number of passes specified
8662 by the @option{--iterations} option.
8666 You might use the following command to erase all trace of the
8667 file system you'd created on the floppy disk in your first drive.
8668 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8672 shred --verbose /dev/fd0
8675 Similarly, to erase all data on a selected partition of
8676 your hard disk, you could give a command like this:
8679 shred --verbose /dev/sda5
8682 A @var{file} of @samp{-} denotes standard output.
8683 The intended use of this is to shred a removed temporary file.
8687 i=`tempfile -m 0600`
8690 echo "Hello, world" >&3
8695 However, the command @samp{shred - >file} does not shred the contents
8696 of @var{file}, since the shell truncates @var{file} before invoking
8697 @command{shred}. Use the command @samp{shred file} or (if using a
8698 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8703 @node Special file types
8704 @chapter Special file types
8706 @cindex special file types
8707 @cindex file types, special
8709 This chapter describes commands which create special types of files (and
8710 @command{rmdir}, which removes directories, one special file type).
8712 @cindex special file types
8714 Although Unix-like operating systems have markedly fewer special file
8715 types than others, not @emph{everything} can be treated only as the
8716 undifferentiated byte stream of @dfn{normal files}. For example, when a
8717 file is created or removed, the system must record this information,
8718 which it does in a @dfn{directory}---a special type of file. Although
8719 you can read directories as normal files, if you're curious, in order
8720 for the system to do its job it must impose a structure, a certain
8721 order, on the bytes of the file. Thus it is a ``special'' type of file.
8723 Besides directories, other special file types include named pipes
8724 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8727 * link invocation:: Make a hard link via the link syscall
8728 * ln invocation:: Make links between files.
8729 * mkdir invocation:: Make directories.
8730 * mkfifo invocation:: Make FIFOs (named pipes).
8731 * mknod invocation:: Make block or character special files.
8732 * readlink invocation:: Print value of a symlink or canonical file name.
8733 * rmdir invocation:: Remove empty directories.
8734 * unlink invocation:: Remove files via the unlink syscall
8738 @node link invocation
8739 @section @command{link}: Make a hard link via the link syscall
8742 @cindex links, creating
8743 @cindex hard links, creating
8744 @cindex creating links (hard only)
8746 @command{link} creates a single hard link at a time.
8747 It is a minimalist interface to the system-provided
8748 @code{link} function. @xref{Hard Links, , , libc,
8749 The GNU C Library Reference Manual}.
8750 It avoids the bells and whistles of the more commonly-used
8751 @command{ln} command (@pxref{ln invocation}).
8755 link @var{filename} @var{linkname}
8758 @var{filename} must specify an existing file, and @var{linkname}
8759 must specify a nonexistent entry in an existing directory.
8760 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8763 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8764 --no-target-directory @var{filename} @var{linkname}}. However, the
8765 @option{--directory} and @option{--no-target-directory} options are
8766 not specified by @acronym{POSIX}, and the @command{link} command is
8767 more portable in practice.
8769 If @var{filename} is a symbolic link, it is unspecified whether
8770 @var{linkname} will be a hard link to the symbolic link or to the
8771 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8772 to specify which behavior is desired.
8778 @section @command{ln}: Make links between files
8781 @cindex links, creating
8782 @cindex hard links, creating
8783 @cindex symbolic (soft) links, creating
8784 @cindex creating links (hard or soft)
8786 @cindex file systems and hard links
8787 @command{ln} makes links between files. By default, it makes hard links;
8788 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8792 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8793 ln [@var{option}]@dots{} @var{target}
8794 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8795 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8801 If two file names are given, @command{ln} creates a link to the first
8802 file from the second.
8805 If one @var{target} is given, @command{ln} creates a link to that file
8806 in the current directory.
8809 If the @option{--target-directory} (@option{-t}) option is given, or
8810 failing that if the last file is a directory and the
8811 @option{--no-target-directory} (@option{-T}) option is not given,
8812 @command{ln} creates a link to each @var{target} file in the specified
8813 directory, using the @var{target}s' names.
8817 Normally @command{ln} does not remove existing files. Use the
8818 @option{--force} (@option{-f}) option to remove them unconditionally,
8819 the @option{--interactive} (@option{-i}) option to remove them
8820 conditionally, and the @option{--backup} (@option{-b}) option to
8823 @cindex hard link, defined
8824 @cindex inode, and hard links
8825 A @dfn{hard link} is another name for an existing file; the link and the
8826 original are indistinguishable. Technically speaking, they share the
8827 same inode, and the inode contains all the information about a
8828 file---indeed, it is not incorrect to say that the inode @emph{is} the
8829 file. Most systems prohibit making a hard link to
8830 a directory; on those where it is allowed, only the super-user can do
8831 so (and with caution, since creating a cycle will cause problems to many
8832 other utilities). Hard links cannot cross file system boundaries. (These
8833 restrictions are not mandated by @acronym{POSIX}, however.)
8835 @cindex dereferencing symbolic links
8836 @cindex symbolic link, defined
8837 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8838 a special file type (which not all kernels support: System V release 3
8839 (and older) systems lack symlinks) in which the link file actually
8840 refers to a different file, by name. When most operations (opening,
8841 reading, writing, and so on) are passed the symbolic link file, the
8842 kernel automatically @dfn{dereferences} the link and operates on the
8843 target of the link. But some operations (e.g., removing) work on the
8844 link file itself, rather than on its target. The owner and group of a
8845 symlink are not significant to file access performed through
8846 the link, but do have implications on deleting a symbolic link from a
8847 directory with the restricted deletion bit set. On the GNU system,
8848 the mode of a symlink has no significance and cannot be changed, but
8849 on some BSD systems, the mode can be changed and will affect whether
8850 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8851 libc, The GNU C Library Reference Manual}.
8853 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8854 occurs when the string in the symlink does not resolve to a file.
8855 There are no restrictions against creating dangling symbolic links.
8856 There are trade-offs to using absolute or relative symlinks. An
8857 absolute symlink always points to the same file, even if the directory
8858 containing the link is moved. However, if the symlink is visible from
8859 more than one machine (such as on a networked file system), the file
8860 pointed to might not always be the same. A relative symbolic link is
8861 resolved in relation to the directory that contains the link, and is
8862 often useful in referring to files on the same device without regards
8863 to what name that device is mounted on when accessed via networked
8866 When creating a relative symlink in a different location than the
8867 current directory, the resolution of the symlink will be different
8868 than the resolution of the same string from the current directory.
8869 Therefore, many users prefer to first change directories to the
8870 location where the relative symlink will be created, so that
8871 tab-completion or other file resolution will find the same target as
8872 what will be placed in the symlink.
8874 The program accepts the following options. Also see @ref{Common options}.
8885 @opindex --directory
8886 @cindex hard links to directories
8887 Allow users with appropriate privileges to attempt to make hard links
8889 However, note that this will probably fail due to
8890 system restrictions, even for the super-user.
8896 Remove existing destination files.
8899 @itemx --interactive
8901 @opindex --interactive
8902 @cindex prompting, and @command{ln}
8903 Prompt whether to remove existing destination files.
8909 If @option{-s} is not in effect, and the source file is a symbolic
8910 link, create the hard link to the file referred to by the symbolic
8911 link, rather than the symbolic link itself.
8914 @itemx --no-dereference
8916 @opindex --no-dereference
8917 Do not treat the last operand specially when it is a symbolic link to
8918 a directory. Instead, treat it as if it were a normal file.
8920 When the destination is an actual directory (not a symlink to one),
8921 there is no ambiguity. The link is created in that directory.
8922 But when the specified destination is a symlink to a directory,
8923 there are two ways to treat the user's request. @command{ln} can
8924 treat the destination just as it would a normal directory and create
8925 the link in it. On the other hand, the destination can be viewed as a
8926 non-directory---as the symlink itself. In that case, @command{ln}
8927 must delete or backup that symlink before creating the new link.
8928 The default is to treat a destination that is a symlink to a directory
8929 just like a directory.
8931 This option is weaker than the @option{--no-target-directory}
8932 (@option{-T}) option, so it has no effect if both options are given.
8938 If @option{-s} is not in effect, and the source file is a symbolic
8939 link, create the hard link to the symbolic link itself. On platforms
8940 where this is not supported by the kernel, this option creates a
8941 symbolic link with identical contents; since symbolic link contents
8942 cannot be edited, any file name resolution performed through either
8943 link will be the same as if a hard link had been created.
8949 Make symbolic links instead of hard links. This option merely produces
8950 an error message on systems that do not support symbolic links.
8956 @optNoTargetDirectory
8962 Print the name of each file after linking it successfully.
8966 @cindex hard links to symbolic links
8967 @cindex symbolic links and @command{ln}
8968 If @option{-L} and @option{-P} are both given, the last one takes
8969 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
8970 are silently ignored. If neither option is given, then this
8971 implementation defaults to @option{-P} if the system @code{link} supports
8972 hard links to symbolic links (such as the GNU system), and @option{-L}
8973 if @code{link} follows symbolic links (such as on BSD).
8982 # Create link ../a pointing to a in that directory.
8983 # Not really useful because it points to itself.
8988 # Change to the target before creating symlinks to avoid being confused.
8994 # Hard coded file names don't move well.
8995 ln -s $(pwd)/a /some/dir/
8999 # Relative file names survive directory moves and also
9000 # work across networked file systems.
9001 ln -s afile anotherfile
9002 ln -s ../adir/afile yetanotherfile
9006 @node mkdir invocation
9007 @section @command{mkdir}: Make directories
9010 @cindex directories, creating
9011 @cindex creating directories
9013 @command{mkdir} creates directories with the specified names. Synopsis:
9016 mkdir [@var{option}]@dots{} @var{name}@dots{}
9019 @command{mkdir} creates each directory @var{name} in the order given.
9020 It reports an error if @var{name} already exists, unless the
9021 @option{-p} option is given and @var{name} is a directory.
9023 The program accepts the following options. Also see @ref{Common options}.
9028 @itemx --mode=@var{mode}
9031 @cindex modes of created directories, setting
9032 Set the file permission bits of created directories to @var{mode},
9033 which uses the same syntax as
9034 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9035 everyone) for the point of the departure. @xref{File permissions}.
9037 Normally the directory has the desired file mode bits at the moment it
9038 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9039 special mode bits, but in this case there may be a temporary window
9040 during which the directory exists but its special mode bits are
9041 incorrect. @xref{Directory Setuid and Setgid}, for how the
9042 set-user-ID and set-group-ID bits of directories are inherited unless
9043 overridden in this way.
9049 @cindex parent directories, creating
9050 Make any missing parent directories for each argument, setting their
9051 file permission bits to the umask modified by @samp{u+wx}. Ignore
9052 existing parent directories, and do not change their file permission
9055 To set the file permission bits of any newly-created parent
9056 directories to a value that includes @samp{u+wx}, you can set the
9057 umask before invoking @command{mkdir}. For example, if the shell
9058 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9059 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9060 To set a parent's special mode bits as well, you can invoke
9061 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9062 Setgid}, for how the set-user-ID and set-group-ID bits of
9063 newly-created parent directories are inherited.
9069 Print a message for each created directory. This is most useful with
9072 @item -Z @var{context}
9073 @itemx --context=@var{context}
9077 @cindex security context
9078 Set the default SELinux security context to be used for created directories.
9085 @node mkfifo invocation
9086 @section @command{mkfifo}: Make FIFOs (named pipes)
9089 @cindex FIFOs, creating
9090 @cindex named pipes, creating
9091 @cindex creating FIFOs (named pipes)
9093 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9094 specified names. Synopsis:
9097 mkfifo [@var{option}] @var{name}@dots{}
9100 A @dfn{FIFO} is a special file type that permits independent processes
9101 to communicate. One process opens the FIFO file for writing, and
9102 another for reading, after which data can flow as with the usual
9103 anonymous pipe in shells or elsewhere.
9105 The program accepts the following option. Also see @ref{Common options}.
9110 @itemx --mode=@var{mode}
9113 @cindex modes of created FIFOs, setting
9114 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9115 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9116 for the point of departure. @var{mode} should specify only file
9117 permission bits. @xref{File permissions}.
9119 @item -Z @var{context}
9120 @itemx --context=@var{context}
9124 @cindex security context
9125 Set the default SELinux security context to be used for created FIFOs.
9132 @node mknod invocation
9133 @section @command{mknod}: Make block or character special files
9136 @cindex block special files, creating
9137 @cindex character special files, creating
9139 @command{mknod} creates a FIFO, character special file, or block special
9140 file with the specified name. Synopsis:
9143 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9146 @cindex special files
9147 @cindex block special files
9148 @cindex character special files
9149 Unlike the phrase ``special file type'' above, the term @dfn{special
9150 file} has a technical meaning on Unix: something that can generate or
9151 receive data. Usually this corresponds to a physical piece of hardware,
9152 e.g., a printer or a disk. (These files are typically created at
9153 system-configuration time.) The @command{mknod} command is what creates
9154 files of this type. Such devices can be read either a character at a
9155 time or a ``block'' (many characters) at a time, hence we say there are
9156 @dfn{block special} files and @dfn{character special} files.
9158 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9159 @mayConflictWithShellBuiltIn{mknod}
9161 The arguments after @var{name} specify the type of file to make:
9166 @opindex p @r{for FIFO file}
9170 @opindex b @r{for block special file}
9171 for a block special file
9174 @c Don't document the `u' option -- it's just a synonym for `c'.
9175 @c Do *any* versions of mknod still use it?
9177 @opindex c @r{for character special file}
9178 @c @opindex u @r{for character special file}
9179 for a character special file
9183 When making a block or character special file, the major and minor
9184 device numbers must be given after the file type.
9185 If a major or minor device number begins with @samp{0x} or @samp{0X},
9186 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9187 as octal; otherwise, as decimal.
9189 The program accepts the following option. Also see @ref{Common options}.
9194 @itemx --mode=@var{mode}
9197 Set the mode of created files to @var{mode}, which is symbolic as in
9198 @command{chmod} and uses @samp{a=rw} as the point of departure.
9199 @var{mode} should specify only file permission bits.
9200 @xref{File permissions}.
9202 @item -Z @var{context}
9203 @itemx --context=@var{context}
9207 @cindex security context
9208 Set the default SELinux security context to be used for created files.
9215 @node readlink invocation
9216 @section @command{readlink}: Print value of a symlink or canonical file name
9219 @cindex displaying value of a symbolic link
9220 @cindex canonical file name
9221 @cindex canonicalize a file name
9225 @command{readlink} may work in one of two supported modes:
9231 @command{readlink} outputs the value of the given symbolic link.
9232 If @command{readlink} is invoked with an argument other than the name
9233 of a symbolic link, it produces no output and exits with a nonzero exit code.
9235 @item Canonicalize mode
9237 @command{readlink} outputs the absolute name of the given file which contains
9238 no @file{.}, @file{..} components nor any repeated separators
9239 (@file{/}) or symbolic links.
9244 readlink [@var{option}] @var{file}
9247 By default, @command{readlink} operates in readlink mode.
9249 The program accepts the following options. Also see @ref{Common options}.
9254 @itemx --canonicalize
9256 @opindex --canonicalize
9257 Activate canonicalize mode.
9258 If any component of the file name except the last one is missing or unavailable,
9259 @command{readlink} produces no output and exits with a nonzero exit
9260 code. A trailing slash is ignored.
9263 @itemx --canonicalize-existing
9265 @opindex --canonicalize-existing
9266 Activate canonicalize mode.
9267 If any component is missing or unavailable, @command{readlink} produces
9268 no output and exits with a nonzero exit code. A trailing slash
9269 requires that the name resolve to a directory.
9272 @itemx --canonicalize-missing
9274 @opindex --canonicalize-missing
9275 Activate canonicalize mode.
9276 If any component is missing or unavailable, @command{readlink} treats it
9282 @opindex --no-newline
9283 Do not output the trailing newline.
9293 Suppress most error messages.
9299 Report error messages.
9303 The @command{readlink} utility first appeared in OpenBSD 2.1.
9305 There is a @command{realpath} command on some systems
9306 which operates like @command{readlink} in canonicalize mode.
9311 @node rmdir invocation
9312 @section @command{rmdir}: Remove empty directories
9315 @cindex removing empty directories
9316 @cindex directories, removing empty
9318 @command{rmdir} removes empty directories. Synopsis:
9321 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9324 If any @var{directory} argument does not refer to an existing empty
9325 directory, it is an error.
9327 The program accepts the following options. Also see @ref{Common options}.
9331 @item --ignore-fail-on-non-empty
9332 @opindex --ignore-fail-on-non-empty
9333 @cindex directory deletion, ignoring failures
9334 Ignore each failure to remove a directory that is solely because
9335 the directory is non-empty.
9341 @cindex parent directories, removing
9342 Remove @var{directory}, then try to remove each component of @var{directory}.
9343 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9344 As such, it fails if any of those directories turns out not to be empty.
9345 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9346 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9347 exit unsuccessfully.
9353 @cindex directory deletion, reporting
9354 Give a diagnostic for each successful removal.
9355 @var{directory} is removed.
9359 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9364 @node unlink invocation
9365 @section @command{unlink}: Remove files via the unlink syscall
9368 @cindex removing files or directories (via the unlink syscall)
9370 @command{unlink} deletes a single specified file name.
9371 It is a minimalist interface to the system-provided
9372 @code{unlink} function. @xref{Deleting Files, , , libc,
9373 The GNU C Library Reference Manual}. Synopsis:
9374 It avoids the bells and whistles of the more commonly-used
9375 @command{rm} command (@pxref{rm invocation}).
9378 unlink @var{filename}
9381 On some systems @code{unlink} can be used to delete the name of a
9382 directory. On others, it can be used that way only by a privileged user.
9383 In the GNU system @code{unlink} can never delete the name of a directory.
9385 The @command{unlink} command honors the @option{--help} and
9386 @option{--version} options. To remove a file whose name begins with
9387 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9392 @node Changing file attributes
9393 @chapter Changing file attributes
9395 @cindex changing file attributes
9396 @cindex file attributes, changing
9397 @cindex attributes, file
9399 A file is not merely its contents, a name, and a file type
9400 (@pxref{Special file types}). A file also has an owner (a user ID), a
9401 group (a group ID), permissions (what the owner can do with the file,
9402 what people in the group can do, and what everyone else can do), various
9403 timestamps, and other information. Collectively, we call these a file's
9406 These commands change file attributes.
9409 * chgrp invocation:: Change file groups.
9410 * chmod invocation:: Change access permissions.
9411 * chown invocation:: Change file owners and groups.
9412 * touch invocation:: Change file timestamps.
9416 @node chown invocation
9417 @section @command{chown}: Change file owner and group
9420 @cindex file ownership, changing
9421 @cindex group ownership, changing
9422 @cindex changing file ownership
9423 @cindex changing group ownership
9425 @command{chown} changes the user and/or group ownership of each given @var{file}
9426 to @var{new-owner} or to the user and group of an existing reference file.
9430 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9433 If used, @var{new-owner} specifies the new owner and/or group as follows
9434 (with no embedded white space):
9437 [@var{owner}] [ : [@var{group}] ]
9444 If only an @var{owner} (a user name or numeric user ID) is given, that
9445 user is made the owner of each given file, and the files' group is not
9448 @item owner@samp{:}group
9449 If the @var{owner} is followed by a colon and a @var{group} (a
9450 group name or numeric group ID), with no spaces between them, the group
9451 ownership of the files is changed as well (to @var{group}).
9454 If a colon but no group name follows @var{owner}, that user is
9455 made the owner of the files and the group of the files is changed to
9456 @var{owner}'s login group.
9459 If the colon and following @var{group} are given, but the owner
9460 is omitted, only the group of the files is changed; in this case,
9461 @command{chown} performs the same function as @command{chgrp}.
9464 If only a colon is given, or if @var{new-owner} is empty, neither the
9465 owner nor the group is changed.
9469 If @var{owner} or @var{group} is intended to represent a numeric user
9470 or group ID, then you may specify it with a leading @samp{+}.
9471 @xref{Disambiguating names and IDs}.
9473 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9474 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9475 require support for that, but for backward compatibility @acronym{GNU}
9476 @command{chown} supports @samp{.} so long as no ambiguity results.
9477 New scripts should avoid the use of @samp{.} because it is not
9478 portable, and because it has undesirable results if the entire
9479 @var{owner@samp{.}group} happens to identify a user whose name
9482 The @command{chown} command sometimes clears the set-user-ID or
9483 set-group-ID permission bits. This behavior depends on the policy and
9484 functionality of the underlying @code{chown} system call, which may
9485 make system-dependent file mode modifications outside the control of
9486 the @command{chown} command. For example, the @command{chown} command
9487 might not affect those bits when invoked by a user with appropriate
9488 privileges, or when the
9489 bits signify some function other than executable permission (e.g.,
9491 When in doubt, check the underlying system behavior.
9493 The program accepts the following options. Also see @ref{Common options}.
9501 @cindex changed owners, verbosely describing
9502 Verbosely describe the action for each @var{file} whose ownership
9511 @cindex error messages, omitting
9512 Do not print error messages about files whose ownership cannot be
9515 @itemx @w{@kbd{--from}=@var{old-owner}}
9517 @cindex symbolic links, changing owner
9518 Change a @var{file}'s ownership only if it has current attributes specified
9519 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9521 This option is useful primarily from a security standpoint in that
9522 it narrows considerably the window of potential abuse.
9523 For example, to reflect a user ID numbering change for one user's files
9524 without an option like this, @code{root} might run
9527 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9530 But that is dangerous because the interval between when the @command{find}
9531 tests the existing file's owner and when the @command{chown} is actually run
9533 One way to narrow the gap would be to invoke chown for each file
9537 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9540 But that is very slow if there are many affected files.
9541 With this option, it is safer (the gap is narrower still)
9542 though still not perfect:
9545 chown -h -R --from=OLDUSER NEWUSER /
9549 @opindex --dereference
9550 @cindex symbolic links, changing owner
9552 Do not act on symbolic links themselves but rather on what they point to.
9553 This is the default.
9556 @itemx --no-dereference
9558 @opindex --no-dereference
9559 @cindex symbolic links, changing owner
9561 Act on symbolic links themselves instead of what they point to.
9562 This mode relies on the @code{lchown} system call.
9563 On systems that do not provide the @code{lchown} system call,
9564 @command{chown} fails when a file specified on the command line
9566 By default, no diagnostic is issued for symbolic links encountered
9567 during a recursive traversal, but see @option{--verbose}.
9569 @itemx --preserve-root
9570 @opindex --preserve-root
9571 @cindex root directory, disallow recursive modification
9572 Fail upon any attempt to recursively change the root directory, @file{/}.
9573 Without @option{--recursive}, this option has no effect.
9574 @xref{Treating / specially}.
9576 @itemx --no-preserve-root
9577 @opindex --no-preserve-root
9578 @cindex root directory, allow recursive modification
9579 Cancel the effect of any preceding @option{--preserve-root} option.
9580 @xref{Treating / specially}.
9582 @item --reference=@var{ref_file}
9583 @opindex --reference
9584 Change the user and group of each @var{file} to be the same as those of
9585 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9586 user and group of the symbolic link, but rather those of the file it
9593 Output a diagnostic for every file processed.
9594 If a symbolic link is encountered during a recursive traversal
9595 on a system without the @code{lchown} system call, and @option{--no-dereference}
9596 is in effect, then issue a diagnostic saying neither the symbolic link nor
9597 its referent is being changed.
9602 @opindex --recursive
9603 @cindex recursively changing file ownership
9604 Recursively change ownership of directories and their contents.
9607 @xref{Traversing symlinks}.
9610 @xref{Traversing symlinks}.
9613 @xref{Traversing symlinks}.
9622 # Change the owner of /u to "root".
9625 # Likewise, but also change its group to "staff".
9628 # Change the owner of /u and subfiles to "root".
9633 @node chgrp invocation
9634 @section @command{chgrp}: Change group ownership
9637 @cindex group ownership, changing
9638 @cindex changing group ownership
9640 @command{chgrp} changes the group ownership of each given @var{file}
9641 to @var{group} (which can be either a group name or a numeric group ID)
9642 or to the group of an existing reference file. Synopsis:
9645 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9648 If @var{group} is intended to represent a
9649 numeric group ID, then you may specify it with a leading @samp{+}.
9650 @xref{Disambiguating names and IDs}.
9652 The program accepts the following options. Also see @ref{Common options}.
9660 @cindex changed files, verbosely describing
9661 Verbosely describe the action for each @var{file} whose group actually
9670 @cindex error messages, omitting
9671 Do not print error messages about files whose group cannot be
9675 @opindex --dereference
9676 @cindex symbolic links, changing owner
9678 Do not act on symbolic links themselves but rather on what they point to.
9679 This is the default.
9682 @itemx --no-dereference
9684 @opindex --no-dereference
9685 @cindex symbolic links, changing group
9687 Act on symbolic links themselves instead of what they point to.
9688 This mode relies on the @code{lchown} system call.
9689 On systems that do not provide the @code{lchown} system call,
9690 @command{chgrp} fails when a file specified on the command line
9692 By default, no diagnostic is issued for symbolic links encountered
9693 during a recursive traversal, but see @option{--verbose}.
9695 @itemx --preserve-root
9696 @opindex --preserve-root
9697 @cindex root directory, disallow recursive modification
9698 Fail upon any attempt to recursively change the root directory, @file{/}.
9699 Without @option{--recursive}, this option has no effect.
9700 @xref{Treating / specially}.
9702 @itemx --no-preserve-root
9703 @opindex --no-preserve-root
9704 @cindex root directory, allow recursive modification
9705 Cancel the effect of any preceding @option{--preserve-root} option.
9706 @xref{Treating / specially}.
9708 @item --reference=@var{ref_file}
9709 @opindex --reference
9710 Change the group of each @var{file} to be the same as that of
9711 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9712 group of the symbolic link, but rather that of the file it refers to.
9718 Output a diagnostic for every file processed.
9719 If a symbolic link is encountered during a recursive traversal
9720 on a system without the @code{lchown} system call, and @option{--no-dereference}
9721 is in effect, then issue a diagnostic saying neither the symbolic link nor
9722 its referent is being changed.
9727 @opindex --recursive
9728 @cindex recursively changing group ownership
9729 Recursively change the group ownership of directories and their contents.
9732 @xref{Traversing symlinks}.
9735 @xref{Traversing symlinks}.
9738 @xref{Traversing symlinks}.
9747 # Change the group of /u to "staff".
9750 # Change the group of /u and subfiles to "staff".
9755 @node chmod invocation
9756 @section @command{chmod}: Change access permissions
9759 @cindex changing access permissions
9760 @cindex access permissions, changing
9761 @cindex permissions, changing access
9763 @command{chmod} changes the access permissions of the named files. Synopsis:
9766 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9769 @cindex symbolic links, permissions of
9770 @command{chmod} never changes the permissions of symbolic links, since
9771 the @command{chmod} system call cannot change their permissions.
9772 This is not a problem since the permissions of symbolic links are
9773 never used. However, for each symbolic link listed on the command
9774 line, @command{chmod} changes the permissions of the pointed-to file.
9775 In contrast, @command{chmod} ignores symbolic links encountered during
9776 recursive directory traversals.
9778 A successful use of @command{chmod} clears the set-group-ID bit of a
9779 regular file if the file's group ID does not match the user's
9780 effective group ID or one of the user's supplementary group IDs,
9781 unless the user has appropriate privileges. Additional restrictions
9782 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9783 @var{ref_file} to be ignored. This behavior depends on the policy and
9784 functionality of the underlying @code{chmod} system call. When in
9785 doubt, check the underlying system behavior.
9787 If used, @var{mode} specifies the new file mode bits.
9788 For details, see the section on @ref{File permissions}.
9789 If you really want @var{mode} to have a leading @samp{-}, you should
9790 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9791 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9792 file} (without the @option{--}) complains if it behaves differently
9793 from what @samp{chmod a-w file} would do.
9795 The program accepts the following options. Also see @ref{Common options}.
9803 Verbosely describe the action for each @var{file} whose permissions
9812 @cindex error messages, omitting
9813 Do not print error messages about files whose permissions cannot be
9816 @itemx --preserve-root
9817 @opindex --preserve-root
9818 @cindex root directory, disallow recursive modification
9819 Fail upon any attempt to recursively change the root directory, @file{/}.
9820 Without @option{--recursive}, this option has no effect.
9821 @xref{Treating / specially}.
9823 @itemx --no-preserve-root
9824 @opindex --no-preserve-root
9825 @cindex root directory, allow recursive modification
9826 Cancel the effect of any preceding @option{--preserve-root} option.
9827 @xref{Treating / specially}.
9833 Verbosely describe the action or non-action taken for every @var{file}.
9835 @item --reference=@var{ref_file}
9836 @opindex --reference
9837 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9838 @xref{File permissions}.
9839 If @var{ref_file} is a symbolic link, do not use the mode
9840 of the symbolic link, but rather that of the file it refers to.
9845 @opindex --recursive
9846 @cindex recursively changing access permissions
9847 Recursively change permissions of directories and their contents.
9854 @node touch invocation
9855 @section @command{touch}: Change file timestamps
9858 @cindex changing file timestamps
9859 @cindex file timestamps, changing
9860 @cindex timestamps, changing file
9862 @command{touch} changes the access and/or modification times of the
9863 specified files. Synopsis:
9866 touch [@var{option}]@dots{} @var{file}@dots{}
9869 @cindex empty files, creating
9870 Any @var{file} argument that does not exist is created empty, unless
9871 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9872 (@option{-h}) was in effect.
9874 A @var{file} argument string of @samp{-} is handled specially and
9875 causes @command{touch} to change the times of the file associated with
9878 @cindex permissions, for changing file timestamps
9879 If changing both the access and modification times to the current
9880 time, @command{touch} can change the timestamps for files that the user
9881 running it does not own but has write permission for. Otherwise, the
9882 user must own the files.
9884 Although @command{touch} provides options for changing two of the times---the
9885 times of last access and modification---of a file, there is actually
9886 a standard third one as well: the inode change time. This is often
9887 referred to as a file's @code{ctime}.
9888 The inode change time represents the time when the file's meta-information
9889 last changed. One common example of this is when the permissions of a
9890 file change. Changing the permissions doesn't access the file, so
9891 the atime doesn't change, nor does it modify the file, so the mtime
9892 doesn't change. Yet, something about the file itself has changed,
9893 and this must be noted somewhere. This is the job of the ctime field.
9894 This is necessary, so that, for example, a backup program can make a
9895 fresh copy of the file, including the new permissions value.
9896 Another operation that modifies a file's ctime without affecting
9897 the others is renaming. In any case, it is not possible, in normal
9898 operations, for a user to change the ctime field to a user-specified value.
9899 Some operating systems and file systems support a fourth time: the
9900 birth time, when the file was first created; by definition, this
9901 timestamp never changes.
9904 Time stamps assume the time zone rules specified by the @env{TZ}
9905 environment variable, or by the system default rules if @env{TZ} is
9906 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9907 libc, The GNU C Library Reference Manual}.
9908 You can avoid ambiguities during
9909 daylight saving transitions by using @sc{utc} time stamps.
9911 The program accepts the following options. Also see @ref{Common options}.
9917 @itemx --time=access
9921 @opindex atime@r{, changing}
9922 @opindex access @r{time, changing}
9923 @opindex use @r{time, changing}
9924 Change the access time only.
9929 @opindex --no-create
9930 Do not warn about or create files that do not exist.
9933 @itemx --date=@var{time}
9937 Use @var{time} instead of the current time. It can contain month names,
9938 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9939 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9940 specifies the instant of time that is 489,392,193 nanoseconds after
9941 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9942 minutes east of @acronym{UTC}. @xref{Date input formats}.
9943 File systems that do not support high-resolution time stamps
9944 silently ignore any excess precision here.
9948 @cindex BSD @command{touch} compatibility
9949 Ignored; for compatibility with BSD versions of @command{touch}.
9952 @itemx --no-dereference
9954 @opindex --no-dereference
9955 @cindex symbolic links, changing time
9957 Attempt to change the timestamps of a symbolic link, rather than what
9958 the link refers to. When using this option, empty files are not
9959 created, but option @option{-c} must also be used to avoid warning
9960 about files that do not exist. Not all systems support changing the
9961 timestamps of symlinks, since underlying system support for this
9962 action was not required until @acronym{POSIX} 2008. Also, on some
9963 systems, the mere act of examining a symbolic link changes the access
9964 time, such that only changes to the modification time will persist
9965 long enough to be observable. When coupled with option @option{-r}, a
9966 reference timestamp is taken from a symbolic link rather than the file
9971 @itemx --time=modify
9974 @opindex mtime@r{, changing}
9975 @opindex modify @r{time, changing}
9976 Change the modification time only.
9979 @itemx --reference=@var{file}
9981 @opindex --reference
9982 Use the times of the reference @var{file} instead of the current time.
9983 If this option is combined with the @option{--date=@var{time}}
9984 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9985 the origin for any relative @var{time}s given, but is otherwise ignored.
9986 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9987 equal to five seconds before the corresponding time stamp for @file{foo}.
9988 If @var{file} is a symbolic link, the reference timestamp is taken
9989 from the target of the symlink, unless @option{-h} was also in effect.
9991 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9992 Use the argument (optional four-digit or two-digit years, months,
9993 days, hours, minutes, optional seconds) instead of the current time.
9994 If the year is specified with only two digits, then @var{cc}
9995 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9996 69 @dots{} 99. If no digits of the year are specified,
9997 the argument is interpreted as a date in the current year.
9998 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10002 @vindex _POSIX2_VERSION
10003 On older systems, @command{touch} supports an obsolete syntax, as follows.
10004 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10005 @option{-t} options, and if there are two or more @var{file}s and the
10006 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10007 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10008 any, were moved to the front), and if the represented year
10009 is in the range 1969--1999, that argument is interpreted as the time
10010 for the other files instead of as a file name.
10011 This obsolete behavior can be enabled or disabled with the
10012 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10013 conformance}), but portable scripts should avoid commands whose
10014 behavior depends on this variable.
10015 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10016 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10022 @chapter Disk usage
10026 No disk can hold an infinite amount of data. These commands report
10027 how much disk storage is in use or available, report other file and
10028 file status information, and write buffers to disk.
10031 * df invocation:: Report file system disk space usage.
10032 * du invocation:: Estimate file space usage.
10033 * stat invocation:: Report file or file system status.
10034 * sync invocation:: Synchronize memory and disk.
10035 * truncate invocation:: Shrink or extend the size of a file.
10039 @node df invocation
10040 @section @command{df}: Report file system disk space usage
10043 @cindex file system disk usage
10044 @cindex disk usage by file system
10046 @command{df} reports the amount of disk space used and available on
10047 file systems. Synopsis:
10050 df [@var{option}]@dots{} [@var{file}]@dots{}
10053 With no arguments, @command{df} reports the space used and available on all
10054 currently mounted file systems (of all types). Otherwise, @command{df}
10055 reports on the file system containing each argument @var{file}.
10057 Normally the disk space is printed in units of
10058 1024 bytes, but this can be overridden (@pxref{Block size}).
10059 Non-integer quantities are rounded up to the next higher unit.
10061 @cindex disk device file
10062 @cindex device file, disk
10063 If an argument @var{file} is a disk device file containing a mounted
10064 file system, @command{df} shows the space available on that file system
10065 rather than on the file system containing the device node (i.e., the root
10066 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10067 on unmounted file systems, because on most kinds of systems doing so
10068 requires extremely nonportable intimate knowledge of file system
10071 The program accepts the following options. Also see @ref{Common options}.
10079 @cindex automounter file systems
10080 @cindex ignore file systems
10081 Include in the listing dummy file systems, which
10082 are omitted by default. Such file systems are typically special-purpose
10083 pseudo-file-systems, such as automounter entries.
10085 @item -B @var{size}
10086 @itemx --block-size=@var{size}
10088 @opindex --block-size
10089 @cindex file system sizes
10090 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10091 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10095 @cindex grand total of disk size, usage and available space
10096 Print a grand total of all arguments after all arguments have
10097 been processed. This can be used to find out the total disk size, usage
10098 and available space of all listed devices.
10104 Equivalent to @option{--si}.
10110 @cindex inode usage
10111 List inode usage information instead of block usage. An inode (short
10112 for index node) contains information about a file such as its owner,
10113 permissions, timestamps, and location on the disk.
10117 @cindex kibibytes for file system sizes
10118 Print sizes in 1024-byte blocks, overriding the default block size
10119 (@pxref{Block size}).
10120 This option is equivalent to @option{--block-size=1K}.
10126 @cindex file system types, limiting output to certain
10127 Limit the listing to local file systems. By default, remote file systems
10132 @cindex file system space, retrieving old data more quickly
10133 Do not invoke the @code{sync} system call before getting any usage data.
10134 This may make @command{df} run significantly faster on systems with many
10135 disks, but on some systems (notably SunOS) the results may be slightly
10136 out of date. This is the default.
10139 @itemx --portability
10141 @opindex --portability
10142 @cindex one-line output format
10143 @cindex @acronym{POSIX} output format
10144 @cindex portable output format
10145 @cindex output format, portable
10146 Use the @acronym{POSIX} output format. This is like the default format except
10151 The information about each file system is always printed on exactly
10152 one line; a mount device is never put on a line by itself. This means
10153 that if the mount device name is more than 20 characters long (e.g., for
10154 some network mounts), the columns are misaligned.
10157 The labels in the header output line are changed to conform to @acronym{POSIX}.
10160 The default block size and output format are unaffected by the
10161 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10162 variables. However, the default block size is still affected by
10163 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10164 otherwise. @xref{Block size}.
10171 @cindex file system space, retrieving current data more slowly
10172 Invoke the @code{sync} system call before getting any usage data. On
10173 some systems (notably SunOS), doing this yields more up to date results,
10174 but in general this option makes @command{df} much slower, especially when
10175 there are many or very busy file systems.
10177 @item -t @var{fstype}
10178 @itemx --type=@var{fstype}
10181 @cindex file system types, limiting output to certain
10182 Limit the listing to file systems of type @var{fstype}. Multiple
10183 file system types can be specified by giving multiple @option{-t} options.
10184 By default, nothing is omitted.
10187 @itemx --print-type
10189 @opindex --print-type
10190 @cindex file system types, printing
10191 Print each file system's type. The types printed here are the same ones
10192 you can include or exclude with @option{-t} and @option{-x}. The particular
10193 types printed are whatever is supported by the system. Here are some of
10194 the common names (this list is certainly not exhaustive):
10199 @cindex @acronym{NFS} file system type
10200 An @acronym{NFS} file system, i.e., one mounted over a network from another
10201 machine. This is the one type name which seems to be used uniformly by
10204 @item 4.2@r{, }ufs@r{, }efs@dots{}
10205 @cindex Linux file system types
10206 @cindex local file system types
10207 @opindex 4.2 @r{file system type}
10208 @opindex ufs @r{file system type}
10209 @opindex efs @r{file system type}
10210 A file system on a locally-mounted hard disk. (The system might even
10211 support more than one type here; Linux does.)
10213 @item hsfs@r{, }cdfs
10214 @cindex CD-ROM file system type
10215 @cindex High Sierra file system
10216 @opindex hsfs @r{file system type}
10217 @opindex cdfs @r{file system type}
10218 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10219 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10222 @cindex PC file system
10223 @cindex DOS file system
10224 @cindex MS-DOS file system
10225 @cindex diskette file system
10227 An MS-DOS file system, usually on a diskette.
10231 @item -x @var{fstype}
10232 @itemx --exclude-type=@var{fstype}
10234 @opindex --exclude-type
10235 Limit the listing to file systems not of type @var{fstype}.
10236 Multiple file system types can be eliminated by giving multiple
10237 @option{-x} options. By default, no file system types are omitted.
10240 Ignored; for compatibility with System V versions of @command{df}.
10245 Failure includes the case where no output is generated, so you can
10246 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10247 @var{dir}} to test whether @var{dir} is on a file system of type
10248 @samp{ext3} or @samp{reiserfs}.
10251 @node du invocation
10252 @section @command{du}: Estimate file space usage
10255 @cindex file space usage
10256 @cindex disk usage for files
10258 @command{du} reports the amount of disk space used by the specified files
10259 and for each subdirectory (of directory arguments). Synopsis:
10262 du [@var{option}]@dots{} [@var{file}]@dots{}
10265 With no arguments, @command{du} reports the disk space for the current
10266 directory. Normally the disk space is printed in units of
10267 1024 bytes, but this can be overridden (@pxref{Block size}).
10268 Non-integer quantities are rounded up to the next higher unit.
10270 If two or more hard links point to the same file, only one of the hard
10271 links is counted. The @var{file} argument order affects which links
10272 are counted, and changing the argument order may change the numbers
10273 that @command{du} outputs.
10275 The program accepts the following options. Also see @ref{Common options}.
10283 Show counts for all files, not just directories.
10285 @itemx --apparent-size
10286 @opindex --apparent-size
10287 Print apparent sizes, rather than disk usage. The apparent size of a
10288 file is the number of bytes reported by @code{wc -c} on regular files,
10289 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10290 For example, a file containing the word @samp{zoo} with no newline would,
10291 of course, have an apparent size of 3. Such a small file may require
10292 anywhere from 0 to 16 KiB or more of disk space, depending on
10293 the type and configuration of the file system on which the file resides.
10294 However, a sparse file created with this command:
10297 dd bs=1 seek=2GiB if=/dev/null of=big
10301 has an apparent size of 2 GiB, yet on most modern
10302 systems, it actually uses almost no disk space.
10308 Equivalent to @code{--apparent-size --block-size=1}.
10310 @item -B @var{size}
10311 @itemx --block-size=@var{size}
10313 @opindex --block-size
10315 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10316 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10322 @cindex grand total of disk space
10323 Print a grand total of all arguments after all arguments have
10324 been processed. This can be used to find out the total disk usage of
10325 a given set of files or directories.
10328 @itemx --dereference-args
10330 @opindex --dereference-args
10331 Dereference symbolic links that are command line arguments.
10332 Does not affect other symbolic links. This is helpful for finding
10333 out the disk usage of directories, such as @file{/usr/tmp}, which
10334 are often symbolic links.
10336 @c --files0-from=FILE
10337 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10343 Equivalent to @option{--dereference-args} (@option{-D}).
10347 @cindex kibibytes for file sizes
10348 Print sizes in 1024-byte blocks, overriding the default block size
10349 (@pxref{Block size}).
10350 This option is equivalent to @option{--block-size=1K}.
10353 @itemx --count-links
10355 @opindex --count-links
10356 @cindex hard links, counting in @command{du}
10357 Count the size of all files, even if they have appeared already (as a
10361 @itemx --dereference
10363 @opindex --dereference
10364 @cindex symbolic links, dereferencing in @command{du}
10365 Dereference symbolic links (show the disk space used by the file
10366 or directory that the link points to instead of the space used by
10371 @cindex mebibytes for file sizes
10372 Print sizes in 1,048,576-byte blocks, overriding the default block size
10373 (@pxref{Block size}).
10374 This option is equivalent to @option{--block-size=1M}.
10377 @itemx --no-dereference
10379 @opindex --no-dereference
10380 @cindex symbolic links, dereferencing in @command{du}
10381 For each symbolic links encountered by @command{du},
10382 consider the disk space used by the symbolic link.
10384 @item --max-depth=@var{depth}
10385 @opindex --max-depth=@var{depth}
10386 @cindex limiting output of @command{du}
10387 Show the total for each directory (and file if --all) that is at
10388 most MAX_DEPTH levels down from the root of the hierarchy. The root
10389 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10398 @opindex --summarize
10399 Display only a total for each argument.
10402 @itemx --separate-dirs
10404 @opindex --separate-dirs
10405 Normally, in the output of @command{du} (when not using @option{--summarize}),
10406 the size listed next to a directory name, @var{d}, represents the sum
10407 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10408 With @option{--separate-dirs}, the size reported for a directory name,
10409 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10414 @cindex last modified dates, displaying in @command{du}
10415 Show time of the most recent modification of any file in the directory,
10416 or any of its subdirectories.
10418 @itemx --time=ctime
10419 @itemx --time=status
10422 @opindex ctime@r{, show the most recent}
10423 @opindex status time@r{, show the most recent}
10424 @opindex use time@r{, show the most recent}
10425 Show the most recent status change time (the @samp{ctime} in the inode) of
10426 any file in the directory, instead of the modification time.
10428 @itemx --time=atime
10429 @itemx --time=access
10431 @opindex atime@r{, show the most recent}
10432 @opindex access time@r{, show the most recent}
10433 Show the most recent access time (the @samp{atime} in the inode) of
10434 any file in the directory, instead of the modification time.
10436 @item --time-style=@var{style}
10437 @opindex --time-style
10439 List timestamps in style @var{style}. This option has an effect only if
10440 the @option{--time} option is also specified. The @var{style} should
10441 be one of the following:
10444 @item +@var{format}
10446 List timestamps using @var{format}, where @var{format} is interpreted
10447 like the format argument of @command{date} (@pxref{date invocation}).
10448 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10449 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10450 with @command{date}, @var{format}'s interpretation is affected by the
10451 @env{LC_TIME} locale category.
10454 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10455 format with nanosecond precision, e.g., @samp{2002-03-30
10456 23:45:56.477817180 -0700}. This style is equivalent to
10457 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10460 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10461 @samp{2002-03-30 23:45}. These timestamps are shorter than
10462 @samp{full-iso} timestamps, and are usually good enough for everyday
10463 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10466 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10467 This style is equivalent to @samp{+%Y-%m-%d}.
10471 You can specify the default value of the @option{--time-style} option
10472 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10473 the default style is @samp{long-iso}. For compatibility with @command{ls},
10474 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10475 the newline and any later characters are ignored; if @env{TIME_STYLE}
10476 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10477 @env{TIME_STYLE} is @samp{locale} it is ignored.
10480 @itemx --one-file-system
10482 @opindex --one-file-system
10483 @cindex one file system, restricting @command{du} to
10484 Skip directories that are on different file systems from the one that
10485 the argument being processed is on.
10487 @item --exclude=@var{pattern}
10488 @opindex --exclude=@var{pattern}
10489 @cindex excluding files from @command{du}
10490 When recursing, skip subdirectories or files matching @var{pattern}.
10491 For example, @code{du --exclude='*.o'} excludes files whose names
10494 @item -X @var{file}
10495 @itemx --exclude-from=@var{file}
10496 @opindex -X @var{file}
10497 @opindex --exclude-from=@var{file}
10498 @cindex excluding files from @command{du}
10499 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10500 one per line. If @var{file} is @samp{-}, take the patterns from standard
10505 @cindex NFS mounts from BSD to HP-UX
10506 On BSD systems, @command{du} reports sizes that are half the correct
10507 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10508 systems, it reports sizes that are twice the correct values for
10509 files that are NFS-mounted from BSD systems. This is due to a flaw
10510 in HP-UX; it also affects the HP-UX @command{du} program.
10515 @node stat invocation
10516 @section @command{stat}: Report file or file system status
10519 @cindex file status
10520 @cindex file system status
10522 @command{stat} displays information about the specified file(s). Synopsis:
10525 stat [@var{option}]@dots{} [@var{file}]@dots{}
10528 With no option, @command{stat} reports all information about the given files.
10529 But it also can be used to report the information of the file systems the
10530 given files are located on. If the files are links, @command{stat} can
10531 also give information about the files the links point to.
10533 @mayConflictWithShellBuiltIn{stat}
10538 @itemx --dereference
10540 @opindex --dereference
10541 @cindex symbolic links, dereferencing in @command{stat}
10542 Change how @command{stat} treats symbolic links.
10543 With this option, @command{stat} acts on the file referenced
10544 by each symbolic link argument.
10545 Without it, @command{stat} acts on any symbolic link argument directly.
10548 @itemx --file-system
10550 @opindex --file-system
10551 @cindex file systems
10552 Report information about the file systems where the given files are located
10553 instead of information about the files themselves.
10556 @itemx --format=@var{format}
10558 @opindex --format=@var{format}
10559 @cindex output format
10560 Use @var{format} rather than the default format.
10561 @var{format} is automatically newline-terminated, so
10562 running a command like the following with two or more @var{file}
10563 operands produces a line of output for each operand:
10565 $ stat --format=%d:%i / /usr
10570 @itemx --printf=@var{format}
10571 @opindex --printf=@var{format}
10572 @cindex output format
10573 Use @var{format} rather than the default format.
10574 Like @option{--format}, but interpret backslash escapes,
10575 and do not output a mandatory trailing newline.
10576 If you want a newline, include @samp{\n} in the @var{format}.
10577 Here's how you would use @option{--printf} to print the device
10578 and inode numbers of @file{/} and @file{/usr}:
10580 $ stat --printf='%d:%i\n' / /usr
10589 @cindex terse output
10590 Print the information in terse form, suitable for parsing by other programs.
10594 The valid @var{format} directives for files with @option{--format} and
10595 @option{--printf} are:
10598 @item %a - Access rights in octal
10599 @item %A - Access rights in human readable form
10600 @item %b - Number of blocks allocated (see @samp{%B})
10601 @item %B - The size in bytes of each block reported by @samp{%b}
10602 @item %d - Device number in decimal
10603 @item %D - Device number in hex
10604 @item %f - Raw mode in hex
10605 @item %F - File type
10606 @item %g - Group ID of owner
10607 @item %G - Group name of owner
10608 @item %h - Number of hard links
10609 @item %i - Inode number
10610 @item %n - File name
10611 @item %N - Quoted file name with dereference if symbolic link
10612 @item %o - I/O block size
10613 @item %s - Total size, in bytes
10614 @item %t - Major device type in hex
10615 @item %T - Minor device type in hex
10616 @item %u - User ID of owner
10617 @item %U - User name of owner
10618 @item %x - Time of last access
10619 @item %X - Time of last access as seconds since Epoch
10620 @item %y - Time of last modification
10621 @item %Y - Time of last modification as seconds since Epoch
10622 @item %z - Time of last change
10623 @item %Z - Time of last change as seconds since Epoch
10626 When listing file system information (@option{--file-system} (@option{-f})),
10627 you must use a different set of @var{format} directives:
10630 @item %a - Free blocks available to non-super-user
10631 @item %b - Total data blocks in file system
10632 @item %c - Total file nodes in file system
10633 @item %d - Free file nodes in file system
10634 @item %f - Free blocks in file system
10635 @item %i - File System ID in hex
10636 @item %l - Maximum length of file names
10637 @item %n - File name
10638 @item %s - Block size (for faster transfers)
10639 @item %S - Fundamental block size (for block counts)
10640 @item %t - Type in hex
10641 @item %T - Type in human readable form
10645 Time stamps are listed according to the time zone rules specified by
10646 the @env{TZ} environment variable, or by the system default rules if
10647 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10648 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10653 @node sync invocation
10654 @section @command{sync}: Synchronize data on disk with memory
10657 @cindex synchronize disk and memory
10659 @cindex superblock, writing
10660 @cindex inodes, written buffered
10661 @command{sync} writes any data buffered in memory out to disk. This can
10662 include (but is not limited to) modified superblocks, modified inodes,
10663 and delayed reads and writes. This must be implemented by the kernel;
10664 The @command{sync} program does nothing but exercise the @code{sync} system
10667 @cindex crashes and corruption
10668 The kernel keeps data in memory to avoid doing (relatively slow) disk
10669 reads and writes. This improves performance, but if the computer
10670 crashes, data may be lost or the file system corrupted as a
10671 result. The @command{sync} command ensures everything in memory
10672 is written to disk.
10674 Any arguments are ignored, except for a lone @option{--help} or
10675 @option{--version} (@pxref{Common options}).
10680 @node truncate invocation
10681 @section @command{truncate}: Shrink or extend the size of a file
10684 @cindex truncating, file sizes
10686 @command{truncate} shrinks or extends the size of each @var{file} to the
10687 specified size. Synopsis:
10690 truncate @var{option}@dots{} @var{file}@dots{}
10693 @cindex files, creating
10694 Any @var{file} that does not exist is created.
10696 @cindex sparse files, creating
10697 @cindex holes, creating files with
10698 If a @var{file} is larger than the specified size, the extra data is lost.
10699 If a @var{file} is shorter, it is extended and the extended part (or hole)
10700 reads as zero bytes.
10702 The program accepts the following options. Also see @ref{Common options}.
10709 @opindex --no-create
10710 Do not create files that do not exist.
10715 @opindex --io-blocks
10716 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10718 @item -r @var{rfile}
10719 @itemx --reference=@var{rfile}
10721 @opindex --reference
10722 Set the size of each @var{file} to the same size as @var{rfile}.
10724 @item -s @var{size}
10725 @itemx --size=@var{size}
10728 Set the size of each @var{file} to this @var{size}.
10729 @multiplierSuffixesNoBlocks{size}
10731 @var{size} may also be prefixed by one of the following to adjust
10732 the size of each @var{file} based on their current size:
10734 @samp{+} => extend by
10735 @samp{-} => reduce by
10736 @samp{<} => at most
10737 @samp{>} => at least
10738 @samp{/} => round down to multiple of
10739 @samp{%} => round up to multiple of
10747 @node Printing text
10748 @chapter Printing text
10750 @cindex printing text, commands for
10751 @cindex commands for printing text
10753 This section describes commands that display text strings.
10756 * echo invocation:: Print a line of text.
10757 * printf invocation:: Format and print data.
10758 * yes invocation:: Print a string until interrupted.
10762 @node echo invocation
10763 @section @command{echo}: Print a line of text
10766 @cindex displaying text
10767 @cindex printing text
10768 @cindex text, displaying
10769 @cindex arbitrary text, displaying
10771 @command{echo} writes each given @var{string} to standard output, with a
10772 space between each and a newline after the last one. Synopsis:
10775 echo [@var{option}]@dots{} [@var{string}]@dots{}
10778 @mayConflictWithShellBuiltIn{echo}
10780 The program accepts the following options. Also see @ref{Common options}.
10781 Options must precede operands, and the normally-special argument
10782 @samp{--} has no special meaning and is treated like any other
10788 Do not output the trailing newline.
10792 @cindex backslash escapes
10793 Enable interpretation of the following backslash-escaped characters in
10802 produce no further output
10818 the eight-bit value that is the octal number @var{nnn}
10819 (zero to three octal digits)
10821 the eight-bit value that is the octal number @var{nnn}
10822 (one to three octal digits)
10824 the eight-bit value that is the hexadecimal number @var{hh}
10825 (one or two hexadecimal digits)
10830 @cindex backslash escapes
10831 Disable interpretation of backslash escapes in each @var{string}.
10832 This is the default. If @option{-e} and @option{-E} are both
10833 specified, the last one given takes effect.
10837 @vindex POSIXLY_CORRECT
10838 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10839 @command{echo}'s first argument is not @option{-n} it outputs
10840 option-like arguments instead of treating them as options. For
10841 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10842 plain @samp{hello}.
10844 @acronym{POSIX} does not require support for any options, and says
10845 that the behavior of @command{echo} is implementation-defined if any
10846 @var{string} contains a backslash or if the first argument is
10847 @option{-n}. Portable programs can use the @command{printf} command
10848 if they need to omit trailing newlines or output control characters or
10849 backslashes. @xref{printf invocation}.
10854 @node printf invocation
10855 @section @command{printf}: Format and print data
10858 @command{printf} does formatted printing of text. Synopsis:
10861 printf @var{format} [@var{argument}]@dots{}
10864 @command{printf} prints the @var{format} string, interpreting @samp{%}
10865 directives and @samp{\} escapes to format numeric and string arguments
10866 in a way that is mostly similar to the C @samp{printf} function.
10867 @xref{Output Conversion Syntax,, @command{printf} format directives,
10868 libc, The GNU C Library Reference Manual}, for details.
10869 The differences are listed below.
10871 @mayConflictWithShellBuiltIn{printf}
10876 The @var{format} argument is reused as necessary to convert all the
10877 given @var{argument}s. For example, the command @samp{printf %s a b}
10881 Missing @var{argument}s are treated as null strings or as zeros,
10882 depending on whether the context expects a string or a number. For
10883 example, the command @samp{printf %sx%d} prints @samp{x0}.
10887 An additional escape, @samp{\c}, causes @command{printf} to produce no
10888 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10889 E} prints @samp{ABC}.
10892 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10893 digits, as opposed to C where it can have an unlimited number of
10894 digits. For example, the command @samp{printf '\x07e'} prints two
10895 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10900 @command{printf} has an additional directive, @samp{%b}, which prints its
10901 argument string with @samp{\} escapes interpreted in the same way as in
10902 the @var{format} string, except that octal escapes are of the form
10903 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10904 If a precision is also given, it limits the number of bytes printed
10905 from the converted string.
10908 Numeric arguments must be single C constants, possibly with leading
10909 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10913 @vindex POSIXLY_CORRECT
10914 If the leading character of a numeric argument is @samp{"} or @samp{'}
10915 then its value is the numeric value of the immediately following
10916 character. Any remaining characters are silently ignored if the
10917 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10918 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10919 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10920 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10925 A floating-point argument must use a period before any fractional
10926 digits, but is printed according to the @env{LC_NUMERIC} category of the
10927 current locale. For example, in a locale whose radix character is a
10928 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10929 the command @samp{printf %g 3,14} is an error.
10933 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10934 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10935 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10936 digits) specifying a character to print.
10941 @cindex ISO/IEC 10646
10943 @command{printf} interprets two character syntaxes introduced in
10944 @acronym{ISO} C 99:
10945 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10946 characters, specified as
10947 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10948 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10949 @command{printf} outputs the Unicode characters
10950 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10951 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10952 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10954 The processing of @samp{\u} and @samp{\U} requires a full-featured
10955 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10956 or when @code{libiconv} is installed prior to this package. Otherwise
10957 @samp{\u} and @samp{\U} will print as-is.
10959 The only options are a lone @option{--help} or
10960 @option{--version}. @xref{Common options}.
10961 Options must precede operands.
10963 The Unicode character syntaxes are useful for writing strings in a locale
10964 independent way. For example, a string containing the Euro currency symbol
10967 $ env printf '\u20AC 14.95'
10971 will be output correctly in all locales supporting the Euro symbol
10972 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10975 $ env printf '\u4e2d\u6587'
10979 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10981 Note that in these examples, the @command{printf} command has been
10982 invoked via @command{env} to ensure that we run the program found via
10983 your shell's search path, and not a shell alias or a built-in function.
10985 For larger strings, you don't need to look up the hexadecimal code
10986 values of each character one by one. @acronym{ASCII} characters mixed with \u
10987 escape sequences is also known as the JAVA source file encoding. You can
10988 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10989 is how to convert a piece of text into a shell script which will output
10990 this text in a locale-independent way:
10993 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10994 '\u4e2d\u6587\n' > sample.txt
10995 $ recode BIG5..JAVA < sample.txt \
10996 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11003 @node yes invocation
11004 @section @command{yes}: Print a string until interrupted
11007 @cindex repeated output of a string
11009 @command{yes} prints the command line arguments, separated by spaces and
11010 followed by a newline, forever until it is killed. If no arguments are
11011 given, it prints @samp{y} followed by a newline forever until killed.
11013 Upon a write error, @command{yes} exits with status @samp{1}.
11015 The only options are a lone @option{--help} or @option{--version}.
11016 To output an argument that begins with
11017 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11018 @xref{Common options}.
11022 @chapter Conditions
11025 @cindex commands for exit status
11026 @cindex exit status commands
11028 This section describes commands that are primarily useful for their exit
11029 status, rather than their output. Thus, they are often used as the
11030 condition of shell @code{if} statements, or as the last command in a
11034 * false invocation:: Do nothing, unsuccessfully.
11035 * true invocation:: Do nothing, successfully.
11036 * test invocation:: Check file types and compare values.
11037 * expr invocation:: Evaluate expressions.
11041 @node false invocation
11042 @section @command{false}: Do nothing, unsuccessfully
11045 @cindex do nothing, unsuccessfully
11046 @cindex failure exit status
11047 @cindex exit status of @command{false}
11049 @command{false} does nothing except return an exit status of 1, meaning
11050 @dfn{failure}. It can be used as a place holder in shell scripts
11051 where an unsuccessful command is needed.
11052 In most modern shells, @command{false} is a built-in command, so when
11053 you use @samp{false} in a script, you're probably using the built-in
11054 command, not the one documented here.
11056 @command{false} honors the @option{--help} and @option{--version} options.
11058 This version of @command{false} is implemented as a C program, and is thus
11059 more secure and faster than a shell script implementation, and may safely
11060 be used as a dummy shell for the purpose of disabling accounts.
11062 Note that @command{false} (unlike all other programs documented herein)
11063 exits unsuccessfully, even when invoked with
11064 @option{--help} or @option{--version}.
11066 Portable programs should not assume that the exit status of
11067 @command{false} is 1, as it is greater than 1 on some
11068 non-@acronym{GNU} hosts.
11071 @node true invocation
11072 @section @command{true}: Do nothing, successfully
11075 @cindex do nothing, successfully
11077 @cindex successful exit
11078 @cindex exit status of @command{true}
11080 @command{true} does nothing except return an exit status of 0, meaning
11081 @dfn{success}. It can be used as a place holder in shell scripts
11082 where a successful command is needed, although the shell built-in
11083 command @code{:} (colon) may do the same thing faster.
11084 In most modern shells, @command{true} is a built-in command, so when
11085 you use @samp{true} in a script, you're probably using the built-in
11086 command, not the one documented here.
11088 @command{true} honors the @option{--help} and @option{--version} options.
11090 Note, however, that it is possible to cause @command{true}
11091 to exit with nonzero status: with the @option{--help} or @option{--version}
11092 option, and with standard
11093 output already closed or redirected to a file that evokes an I/O error.
11094 For example, using a Bourne-compatible shell:
11097 $ ./true --version >&-
11098 ./true: write error: Bad file number
11099 $ ./true --version > /dev/full
11100 ./true: write error: No space left on device
11103 This version of @command{true} is implemented as a C program, and is thus
11104 more secure and faster than a shell script implementation, and may safely
11105 be used as a dummy shell for the purpose of disabling accounts.
11107 @node test invocation
11108 @section @command{test}: Check file types and compare values
11111 @cindex check file types
11112 @cindex compare values
11113 @cindex expression evaluation
11115 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11116 evaluation of the conditional expression @var{expr}. Each part of the
11117 expression must be a separate argument.
11119 @command{test} has file status checks, string operators, and numeric
11120 comparison operators.
11122 @command{test} has an alternate form that uses opening and closing
11123 square brackets instead a leading @samp{test}. For example, instead
11124 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11125 brackets must be separate arguments; for example, @samp{[-d /]} does
11126 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11127 @var{expr} ]} have the same meaning, only the former form is discussed
11133 test @var{expression}
11135 [ @var{expression} ]
11140 @mayConflictWithShellBuiltIn{test}
11142 If @var{expression} is omitted, @command{test} returns false.
11143 If @var{expression} is a single argument,
11144 @command{test} returns false if the argument is null and true otherwise. The argument
11145 can be any string, including strings like @samp{-d}, @samp{-1},
11146 @samp{--}, @samp{--help}, and @samp{--version} that most other
11147 programs would treat as options. To get help and version information,
11148 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11149 the usual closing brackets. @xref{Common options}.
11151 @cindex exit status of @command{test}
11155 0 if the expression is true,
11156 1 if the expression is false,
11157 2 if an error occurred.
11161 * File type tests:: -[bcdfhLpSt]
11162 * Access permission tests:: -[gkruwxOG]
11163 * File characteristic tests:: -e -s -nt -ot -ef
11164 * String tests:: -z -n = !=
11165 * Numeric tests:: -eq -ne -lt -le -gt -ge
11166 * Connectives for test:: ! -a -o
11170 @node File type tests
11171 @subsection File type tests
11173 @cindex file type tests
11175 These options test for particular types of files. (Everything's a file,
11176 but not all files are the same!)
11180 @item -b @var{file}
11182 @cindex block special check
11183 True if @var{file} exists and is a block special device.
11185 @item -c @var{file}
11187 @cindex character special check
11188 True if @var{file} exists and is a character special device.
11190 @item -d @var{file}
11192 @cindex directory check
11193 True if @var{file} exists and is a directory.
11195 @item -f @var{file}
11197 @cindex regular file check
11198 True if @var{file} exists and is a regular file.
11200 @item -h @var{file}
11201 @itemx -L @var{file}
11204 @cindex symbolic link check
11205 True if @var{file} exists and is a symbolic link.
11206 Unlike all other file-related tests, this test does not dereference
11207 @var{file} if it is a symbolic link.
11209 @item -p @var{file}
11211 @cindex named pipe check
11212 True if @var{file} exists and is a named pipe.
11214 @item -S @var{file}
11216 @cindex socket check
11217 True if @var{file} exists and is a socket.
11221 @cindex terminal check
11222 True if @var{fd} is a file descriptor that is associated with a
11228 @node Access permission tests
11229 @subsection Access permission tests
11231 @cindex access permission tests
11232 @cindex permission tests
11234 These options test for particular access permissions.
11238 @item -g @var{file}
11240 @cindex set-group-ID check
11241 True if @var{file} exists and has its set-group-ID bit set.
11243 @item -k @var{file}
11245 @cindex sticky bit check
11246 True if @var{file} exists and has its @dfn{sticky} bit set.
11248 @item -r @var{file}
11250 @cindex readable file check
11251 True if @var{file} exists and read permission is granted.
11253 @item -u @var{file}
11255 @cindex set-user-ID check
11256 True if @var{file} exists and has its set-user-ID bit set.
11258 @item -w @var{file}
11260 @cindex writable file check
11261 True if @var{file} exists and write permission is granted.
11263 @item -x @var{file}
11265 @cindex executable file check
11266 True if @var{file} exists and execute permission is granted
11267 (or search permission, if it is a directory).
11269 @item -O @var{file}
11271 @cindex owned by effective user ID check
11272 True if @var{file} exists and is owned by the current effective user ID.
11274 @item -G @var{file}
11276 @cindex owned by effective group ID check
11277 True if @var{file} exists and is owned by the current effective group ID.
11281 @node File characteristic tests
11282 @subsection File characteristic tests
11284 @cindex file characteristic tests
11286 These options test other file characteristics.
11290 @item -e @var{file}
11292 @cindex existence-of-file check
11293 True if @var{file} exists.
11295 @item -s @var{file}
11297 @cindex nonempty file check
11298 True if @var{file} exists and has a size greater than zero.
11300 @item @var{file1} -nt @var{file2}
11302 @cindex newer-than file check
11303 True if @var{file1} is newer (according to modification date) than
11304 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11306 @item @var{file1} -ot @var{file2}
11308 @cindex older-than file check
11309 True if @var{file1} is older (according to modification date) than
11310 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11312 @item @var{file1} -ef @var{file2}
11314 @cindex same file check
11315 @cindex hard link check
11316 True if @var{file1} and @var{file2} have the same device and inode
11317 numbers, i.e., if they are hard links to each other.
11323 @subsection String tests
11325 @cindex string tests
11327 These options test string characteristics. You may need to quote
11328 @var{string} arguments for the shell. For example:
11334 The quotes here prevent the wrong arguments from being passed to
11335 @command{test} if @samp{$V} is empty or contains special characters.
11339 @item -z @var{string}
11341 @cindex zero-length string check
11342 True if the length of @var{string} is zero.
11344 @item -n @var{string}
11345 @itemx @var{string}
11347 @cindex nonzero-length string check
11348 True if the length of @var{string} is nonzero.
11350 @item @var{string1} = @var{string2}
11352 @cindex equal string check
11353 True if the strings are equal.
11355 @item @var{string1} != @var{string2}
11357 @cindex not-equal string check
11358 True if the strings are not equal.
11363 @node Numeric tests
11364 @subsection Numeric tests
11366 @cindex numeric tests
11367 @cindex arithmetic tests
11369 Numeric relational operators. The arguments must be entirely numeric
11370 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11371 which evaluates to the length of @var{string}.
11375 @item @var{arg1} -eq @var{arg2}
11376 @itemx @var{arg1} -ne @var{arg2}
11377 @itemx @var{arg1} -lt @var{arg2}
11378 @itemx @var{arg1} -le @var{arg2}
11379 @itemx @var{arg1} -gt @var{arg2}
11380 @itemx @var{arg1} -ge @var{arg2}
11387 These arithmetic binary operators return true if @var{arg1} is equal,
11388 not-equal, less-than, less-than-or-equal, greater-than, or
11389 greater-than-or-equal than @var{arg2}, respectively.
11396 test -1 -gt -2 && echo yes
11398 test -l abc -gt 1 && echo yes
11401 @error{} test: integer expression expected before -eq
11405 @node Connectives for test
11406 @subsection Connectives for @command{test}
11408 @cindex logical connectives
11409 @cindex connectives, logical
11411 The usual logical connectives.
11417 True if @var{expr} is false.
11419 @item @var{expr1} -a @var{expr2}
11421 @cindex logical and operator
11422 @cindex and operator
11423 True if both @var{expr1} and @var{expr2} are true.
11425 @item @var{expr1} -o @var{expr2}
11427 @cindex logical or operator
11428 @cindex or operator
11429 True if either @var{expr1} or @var{expr2} is true.
11434 @node expr invocation
11435 @section @command{expr}: Evaluate expressions
11438 @cindex expression evaluation
11439 @cindex evaluation of expressions
11441 @command{expr} evaluates an expression and writes the result on standard
11442 output. Each token of the expression must be a separate argument.
11444 Operands are either integers or strings. Integers consist of one or
11445 more decimal digits, with an optional leading @samp{-}.
11446 @command{expr} converts
11447 anything appearing in an operand position to an integer or a string
11448 depending on the operation being applied to it.
11450 Strings are not quoted for @command{expr} itself, though you may need to
11451 quote them to protect characters with special meaning to the shell,
11452 e.g., spaces. However, regardless of whether it is quoted, a string
11453 operand should not be a parenthesis or any of @command{expr}'s
11454 operators like @code{+}, so you cannot safely pass an arbitrary string
11455 @code{$str} to expr merely by quoting it to the shell. One way to
11456 work around this is to use the @sc{gnu} extension @code{+},
11457 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11458 @code{@w{" $str"}} and to adjust the rest of the expression to take
11459 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11461 You should not pass a negative integer or a string with leading
11462 @samp{-} as @command{expr}'s first argument, as it might be
11463 misinterpreted as an option; this can be avoided by parenthesization.
11464 Also, portable scripts should not use a string operand that happens to
11465 take the form of an integer; this can be worked around by inserting
11466 leading spaces as mentioned above.
11468 @cindex parentheses for grouping
11469 Operators may be given as infix symbols or prefix keywords. Parentheses
11470 may be used for grouping in the usual manner. You must quote
11471 parentheses and many operators to avoid the shell evaluating them,
11474 When built with support for the GNU MP library, @command{expr} uses
11475 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11476 types and may fail due to arithmetic overflow.
11478 The only options are @option{--help} and @option{--version}. @xref{Common
11479 options}. Options must precede operands.
11481 @cindex exit status of @command{expr}
11485 0 if the expression is neither null nor 0,
11486 1 if the expression is null or 0,
11487 2 if the expression is invalid,
11488 3 if an internal error occurred (e.g., arithmetic overflow).
11492 * String expressions:: + : match substr index length
11493 * Numeric expressions:: + - * / %
11494 * Relations for expr:: | & < <= = == != >= >
11495 * Examples of expr:: Examples.
11499 @node String expressions
11500 @subsection String expressions
11502 @cindex string expressions
11503 @cindex expressions, string
11505 @command{expr} supports pattern matching and other string operators. These
11506 have higher precedence than both the numeric and relational operators (in
11507 the next sections).
11511 @item @var{string} : @var{regex}
11512 @cindex pattern matching
11513 @cindex regular expression matching
11514 @cindex matching patterns
11515 Perform pattern matching. The arguments are converted to strings and the
11516 second is considered to be a (basic, a la GNU @code{grep}) regular
11517 expression, with a @code{^} implicitly prepended. The first argument is
11518 then matched against this regular expression.
11520 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11521 @code{:} expression returns the part of @var{string} that matched the
11522 subexpression; otherwise, it returns the number of characters matched.
11524 If the match fails, the @code{:} operator returns the null string if
11525 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11527 @kindex \( @r{regexp operator}
11528 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11529 value; additional pairs are meaningful only for grouping the regular
11530 expression operators.
11532 @kindex \+ @r{regexp operator}
11533 @kindex \? @r{regexp operator}
11534 @kindex \| @r{regexp operator}
11535 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11536 operators which respectively match one or more, zero or one, or separate
11537 alternatives. SunOS and other @command{expr}'s treat these as regular
11538 characters. (@acronym{POSIX} allows either behavior.)
11539 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11540 regular expression syntax. Some examples are in @ref{Examples of expr}.
11542 @item match @var{string} @var{regex}
11544 An alternative way to do pattern matching. This is the same as
11545 @w{@samp{@var{string} : @var{regex}}}.
11547 @item substr @var{string} @var{position} @var{length}
11549 Returns the substring of @var{string} beginning at @var{position}
11550 with length at most @var{length}. If either @var{position} or
11551 @var{length} is negative, zero, or non-numeric, returns the null string.
11553 @item index @var{string} @var{charset}
11555 Returns the first position in @var{string} where the first character in
11556 @var{charset} was found. If no character in @var{charset} is found in
11557 @var{string}, return 0.
11559 @item length @var{string}
11561 Returns the length of @var{string}.
11563 @item + @var{token}
11565 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11566 or an operator like @code{/}.
11567 This makes it possible to test @code{expr length + "$x"} or
11568 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11569 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11570 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11571 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11575 To make @command{expr} interpret keywords as strings, you must use the
11576 @code{quote} operator.
11579 @node Numeric expressions
11580 @subsection Numeric expressions
11582 @cindex numeric expressions
11583 @cindex expressions, numeric
11585 @command{expr} supports the usual numeric operators, in order of increasing
11586 precedence. These numeric operators have lower precedence than the
11587 string operators described in the previous section, and higher precedence
11588 than the connectives (next section).
11596 @cindex subtraction
11597 Addition and subtraction. Both arguments are converted to integers;
11598 an error occurs if this cannot be done.
11604 @cindex multiplication
11607 Multiplication, division, remainder. Both arguments are converted to
11608 integers; an error occurs if this cannot be done.
11613 @node Relations for expr
11614 @subsection Relations for @command{expr}
11616 @cindex connectives, logical
11617 @cindex logical connectives
11618 @cindex relations, numeric or string
11620 @command{expr} supports the usual logical connectives and relations. These
11621 have lower precedence than the string and numeric operators
11622 (previous sections). Here is the list, lowest-precedence operator first.
11628 @cindex logical or operator
11629 @cindex or operator
11630 Returns its first argument if that is neither null nor zero, otherwise
11631 its second argument if it is neither null nor zero, otherwise 0. It
11632 does not evaluate its second argument if its first argument is neither
11637 @cindex logical and operator
11638 @cindex and operator
11639 Return its first argument if neither argument is null or zero, otherwise
11640 0. It does not evaluate its second argument if its first argument is
11643 @item < <= = == != >= >
11650 @cindex comparison operators
11652 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11653 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11654 both arguments to integers and do a numeric comparison; if either
11655 conversion fails, it does a lexicographic comparison using the character
11656 collating sequence specified by the @env{LC_COLLATE} locale.
11661 @node Examples of expr
11662 @subsection Examples of using @command{expr}
11664 @cindex examples of @command{expr}
11665 Here are a few examples, including quoting for shell metacharacters.
11667 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11670 foo=`expr $foo + 1`
11673 To print the non-directory part of the file name stored in
11674 @code{$fname}, which need not contain a @code{/}:
11677 expr $fname : '.*/\(.*\)' '|' $fname
11680 An example showing that @code{\+} is an operator:
11688 expr abc : 'a\(.\)c'
11690 expr index abcdef cz
11693 @error{} expr: syntax error
11694 expr index + index a
11700 @chapter Redirection
11702 @cindex redirection
11703 @cindex commands for redirection
11705 Unix shells commonly provide several forms of @dfn{redirection}---ways
11706 to change the input source or output destination of a command. But one
11707 useful redirection is performed by a separate command, not by the shell;
11708 it's described here.
11711 * tee invocation:: Redirect output to multiple files or processes.
11715 @node tee invocation
11716 @section @command{tee}: Redirect output to multiple files or processes
11719 @cindex pipe fitting
11720 @cindex destinations, multiple output
11721 @cindex read from stdin and write to stdout and files
11723 The @command{tee} command copies standard input to standard output and also
11724 to any files given as arguments. This is useful when you want not only
11725 to send some data down a pipe, but also to save a copy. Synopsis:
11728 tee [@var{option}]@dots{} [@var{file}]@dots{}
11731 If a file being written to does not already exist, it is created. If a
11732 file being written to already exists, the data it previously contained
11733 is overwritten unless the @option{-a} option is used.
11735 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11736 input to standard output, but this is typically not that useful as the
11737 copies are interleaved.
11739 The program accepts the following options. Also see @ref{Common options}.
11746 Append standard input to the given files rather than overwriting
11750 @itemx --ignore-interrupts
11752 @opindex --ignore-interrupts
11753 Ignore interrupt signals.
11757 The @command{tee} command is useful when you happen to be transferring a large
11758 amount of data and also want to summarize that data without reading
11759 it a second time. For example, when you are downloading a DVD image,
11760 you often want to verify its signature or checksum right away.
11761 The inefficient way to do it is simply:
11764 wget http://example.com/some.iso && sha1sum some.iso
11767 One problem with the above is that it makes you wait for the
11768 download to complete before starting the time-consuming SHA1 computation.
11769 Perhaps even more importantly, the above requires reading
11770 the DVD image a second time (the first was from the network).
11772 The efficient way to do it is to interleave the download
11773 and SHA1 computation. Then, you'll get the checksum for
11774 free, because the entire process parallelizes so well:
11777 # slightly contrived, to demonstrate process substitution
11778 wget -O - http://example.com/dvd.iso \
11779 | tee >(sha1sum > dvd.sha1) > dvd.iso
11782 That makes @command{tee} write not just to the expected output file,
11783 but also to a pipe running @command{sha1sum} and saving the final
11784 checksum in a file named @file{dvd.sha1}.
11786 Note, however, that this example relies on a feature of modern shells
11787 called @dfn{process substitution}
11788 (the @samp{>(command)} syntax, above;
11789 @xref{Process Substitution,,Process Substitution, bashref,
11790 The Bash Reference Manual}.),
11791 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11792 but not with @command{/bin/sh}. So if you write code like this
11793 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11795 Since the above example writes to one file and one process,
11796 a more conventional and portable use of @command{tee} is even better:
11799 wget -O - http://example.com/dvd.iso \
11800 | tee dvd.iso | sha1sum > dvd.sha1
11803 You can extend this example to make @command{tee} write to two processes,
11804 computing MD5 and SHA1 checksums in parallel. In this case,
11805 process substitution is required:
11808 wget -O - http://example.com/dvd.iso \
11809 | tee >(sha1sum > dvd.sha1) \
11810 >(md5sum > dvd.md5) \
11814 This technique is also useful when you want to make a @emph{compressed}
11815 copy of the contents of a pipe.
11816 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11817 For a large hierarchy, @samp{du -ak} can run for a long time,
11818 and can easily produce terabytes of data, so you won't want to
11819 rerun the command unnecessarily. Nor will you want to save
11820 the uncompressed output.
11822 Doing it the inefficient way, you can't even start the GUI
11823 until after you've compressed all of the @command{du} output:
11826 du -ak | gzip -9 > /tmp/du.gz
11827 gzip -d /tmp/du.gz | xdiskusage -a
11830 With @command{tee} and process substitution, you start the GUI
11831 right away and eliminate the decompression completely:
11834 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11837 Finally, if you regularly create more than one type of
11838 compressed tarball at once, for example when @code{make dist} creates
11839 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11840 there may be a better way.
11841 Typical @command{automake}-generated @file{Makefile} rules create
11842 the two compressed tar archives with commands in sequence, like this
11843 (slightly simplified):
11846 tardir=your-pkg-M.N
11847 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11848 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11851 However, if the hierarchy you are archiving and compressing is larger
11852 than a couple megabytes, and especially if you are using a multi-processor
11853 system with plenty of memory, then you can do much better by reading the
11854 directory contents only once and running the compression programs in parallel:
11857 tardir=your-pkg-M.N
11858 tar chof - "$tardir" \
11859 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11860 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11866 @node File name manipulation
11867 @chapter File name manipulation
11869 @cindex file name manipulation
11870 @cindex manipulation of file names
11871 @cindex commands for file name manipulation
11873 This section describes commands that manipulate file names.
11876 * basename invocation:: Strip directory and suffix from a file name.
11877 * dirname invocation:: Strip non-directory suffix from a file name.
11878 * pathchk invocation:: Check file name validity and portability.
11882 @node basename invocation
11883 @section @command{basename}: Strip directory and suffix from a file name
11886 @cindex strip directory and suffix from file names
11887 @cindex directory, stripping from file names
11888 @cindex suffix, stripping from file names
11889 @cindex file names, stripping directory and suffix
11890 @cindex leading directory components, stripping
11892 @command{basename} removes any leading directory components from
11893 @var{name}. Synopsis:
11896 basename @var{name} [@var{suffix}]
11899 If @var{suffix} is specified and is identical to the end of @var{name},
11900 it is removed from @var{name} as well. Note that since trailing slashes
11901 are removed prior to suffix matching, @var{suffix} will do nothing if it
11902 contains slashes. @command{basename} prints the result on standard
11905 @c This test is used both here and in the section on dirname.
11906 @macro basenameAndDirname
11907 Together, @command{basename} and @command{dirname} are designed such
11908 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11909 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11910 for everything except file names containing a trailing newline.
11912 @basenameAndDirname
11914 @acronym{POSIX} allows the implementation to define the results if
11915 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11916 @command{basename} returns the empty string. In the latter case, the
11917 result is @samp{//} on platforms where @var{//} is distinct from
11918 @var{/}, and @samp{/} on platforms where there is no difference.
11920 The only options are @option{--help} and @option{--version}. @xref{Common
11921 options}. Options must precede operands.
11929 basename /usr/bin/sort
11932 basename include/stdio.h .h
11936 @node dirname invocation
11937 @section @command{dirname}: Strip non-directory suffix from a file name
11940 @cindex directory components, printing
11941 @cindex stripping non-directory suffix
11942 @cindex non-directory suffix, stripping
11944 @command{dirname} prints all but the final slash-delimited component of
11945 a string (presumably a file name). Synopsis:
11951 If @var{name} is a single component, @command{dirname} prints @samp{.}
11952 (meaning the current directory).
11954 @basenameAndDirname
11956 @acronym{POSIX} allows the implementation to define the results if
11957 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11958 result is @samp{//} on platforms where @var{//} is distinct from
11959 @var{/}, and @samp{/} on platforms where there is no difference.
11961 The only options are @option{--help} and @option{--version}. @xref{Common
11969 # Output "/usr/bin".
11970 dirname /usr/bin/sort
11977 @node pathchk invocation
11978 @section @command{pathchk}: Check file name validity and portability
11981 @cindex file names, checking validity and portability
11982 @cindex valid file names, checking for
11983 @cindex portable file names, checking for
11985 @command{pathchk} checks validity and portability of file names. Synopsis:
11988 pathchk [@var{option}]@dots{} @var{name}@dots{}
11991 For each @var{name}, @command{pathchk} prints an error message if any of
11992 these conditions is true:
11996 One of the existing directories in @var{name} does not have search
11997 (execute) permission,
11999 The length of @var{name} is larger than the maximum supported by the
12002 The length of one component of @var{name} is longer than
12003 its file system's maximum.
12006 A nonexistent @var{name} is not an error, so long a file with that
12007 name could be created under the above conditions.
12009 The program accepts the following options. Also see @ref{Common options}.
12010 Options must precede operands.
12016 Instead of performing checks based on the underlying file system,
12017 print an error message if any of these conditions is true:
12021 A file name is empty.
12024 A file name contains a character outside the @acronym{POSIX} portable file
12025 name character set, namely, the ASCII letters and digits, @samp{.},
12026 @samp{_}, @samp{-}, and @samp{/}.
12029 The length of a file name or one of its components exceeds the
12030 @acronym{POSIX} minimum limits for portability.
12035 Print an error message if a file name is empty, or if it contains a component
12036 that begins with @samp{-}.
12038 @item --portability
12039 @opindex --portability
12040 Print an error message if a file name is not portable to all @acronym{POSIX}
12041 hosts. This option is equivalent to @samp{-p -P}.
12045 @cindex exit status of @command{pathchk}
12049 0 if all specified file names passed all checks,
12054 @node Working context
12055 @chapter Working context
12057 @cindex working context
12058 @cindex commands for printing the working context
12060 This section describes commands that display or alter the context in
12061 which you are working: the current directory, the terminal settings, and
12062 so forth. See also the user-related commands in the next section.
12065 * pwd invocation:: Print working directory.
12066 * stty invocation:: Print or change terminal characteristics.
12067 * printenv invocation:: Print environment variables.
12068 * tty invocation:: Print file name of terminal on standard input.
12072 @node pwd invocation
12073 @section @command{pwd}: Print working directory
12076 @cindex print name of current directory
12077 @cindex current working directory, printing
12078 @cindex working directory, printing
12081 @command{pwd} prints the name of the current directory. Synopsis:
12084 pwd [@var{option}]@dots{}
12087 The program accepts the following options. Also see @ref{Common options}.
12094 If the contents of the environment variable @env{PWD} provide an
12095 absolute name of the current directory with no @samp{.} or @samp{..}
12096 components, but possibly with symbolic links, then output those
12097 contents. Otherwise, fall back to default @option{-P} handling.
12102 @opindex --physical
12103 Print a fully resolved name for the current directory. That is, all
12104 components of the printed name will be actual directory names---none
12105 will be symbolic links.
12108 @cindex symbolic links and @command{pwd}
12109 If @option{-L} and @option{-P} are both given, the last one takes
12110 precedence. If neither option is given, then this implementation uses
12111 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12112 environment variable is set.
12114 @mayConflictWithShellBuiltIn{pwd}
12119 @node stty invocation
12120 @section @command{stty}: Print or change terminal characteristics
12123 @cindex change or print terminal settings
12124 @cindex terminal settings
12125 @cindex line settings of terminal
12127 @command{stty} prints or changes terminal characteristics, such as baud rate.
12131 stty [@var{option}] [@var{setting}]@dots{}
12132 stty [@var{option}]
12135 If given no line settings, @command{stty} prints the baud rate, line
12136 discipline number (on systems that support it), and line settings
12137 that have been changed from the values set by @samp{stty sane}.
12138 By default, mode reading and setting are performed on the tty line
12139 connected to standard input, although this can be modified by the
12140 @option{--file} option.
12142 @command{stty} accepts many non-option arguments that change aspects of
12143 the terminal line operation, as described below.
12145 The program accepts the following options. Also see @ref{Common options}.
12152 Print all current settings in human-readable form. This option may not
12153 be used in combination with any line settings.
12155 @item -F @var{device}
12156 @itemx --file=@var{device}
12159 Set the line opened by the file name specified in @var{device} instead of
12160 the tty line connected to standard input. This option is necessary
12161 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12162 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12163 the @code{clocal} flag is not set. Hence, it is not always possible
12164 to allow the shell to open the device in the traditional manner.
12170 @cindex machine-readable @command{stty} output
12171 Print all current settings in a form that can be used as an argument to
12172 another @command{stty} command to restore the current settings. This option
12173 may not be used in combination with any line settings.
12177 Many settings can be turned off by preceding them with a @samp{-}.
12178 Such arguments are marked below with ``May be negated'' in their
12179 description. The descriptions themselves refer to the positive
12180 case, that is, when @emph{not} negated (unless stated otherwise,
12183 Some settings are not available on all @acronym{POSIX} systems, since they use
12184 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12185 description. On non-@acronym{POSIX} systems, those or other settings also may not
12186 be available, but it's not feasible to document all the variations: just
12192 * Control:: Control settings
12193 * Input:: Input settings
12194 * Output:: Output settings
12195 * Local:: Local settings
12196 * Combination:: Combination settings
12197 * Characters:: Special characters
12198 * Special:: Special settings
12203 @subsection Control settings
12205 @cindex control settings
12211 @cindex two-way parity
12212 Generate parity bit in output and expect parity bit in input.
12218 @cindex even parity
12219 Set odd parity (even if negated). May be negated.
12226 @cindex character size
12227 @cindex eight-bit characters
12228 Set character size to 5, 6, 7, or 8 bits.
12233 Send a hangup signal when the last process closes the tty. May be
12239 Use two stop bits per character (one if negated). May be negated.
12243 Allow input to be received. May be negated.
12247 @cindex modem control
12248 Disable modem control signals. May be negated.
12252 @cindex hardware flow control
12253 @cindex flow control, hardware
12254 @cindex RTS/CTS flow control
12255 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12260 @subsection Input settings
12262 @cindex input settings
12263 These settings control operations on data received from the terminal.
12268 @cindex breaks, ignoring
12269 Ignore break characters. May be negated.
12273 @cindex breaks, cause interrupts
12274 Make breaks cause an interrupt signal. May be negated.
12278 @cindex parity, ignoring
12279 Ignore characters with parity errors. May be negated.
12283 @cindex parity errors, marking
12284 Mark parity errors (with a 255-0-character sequence). May be negated.
12288 Enable input parity checking. May be negated.
12292 @cindex eight-bit input
12293 Clear high (8th) bit of input characters. May be negated.
12297 @cindex newline, translating to return
12298 Translate newline to carriage return. May be negated.
12302 @cindex return, ignoring
12303 Ignore carriage return. May be negated.
12307 @cindex return, translating to newline
12308 Translate carriage return to newline. May be negated.
12312 @cindex input encoding, UTF-8
12313 Assume input characters are UTF-8 encoded. May be negated.
12317 @kindex C-s/C-q flow control
12318 @cindex XON/XOFF flow control
12319 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12326 @cindex software flow control
12327 @cindex flow control, software
12328 Enable sending of @code{stop} character when the system input buffer
12329 is almost full, and @code{start} character when it becomes almost
12330 empty again. May be negated.
12334 @cindex uppercase, translating to lowercase
12335 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12336 negated. Note ilcuc is not implemented, as one would not be able to issue
12337 almost any (lowercase) Unix command, after invoking it.
12341 Allow any character to restart output (only the start character
12342 if negated). Non-@acronym{POSIX}. May be negated.
12346 @cindex beeping at input buffer full
12347 Enable beeping and not flushing input buffer if a character arrives
12348 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12353 @subsection Output settings
12355 @cindex output settings
12356 These settings control operations on data sent to the terminal.
12361 Postprocess output. May be negated.
12365 @cindex lowercase, translating to output
12366 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12367 negated. (Note ouclc is not currently implemented.)
12371 @cindex return, translating to newline
12372 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12376 @cindex newline, translating to crlf
12377 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12382 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12387 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12391 @cindex pad instead of timing for delaying
12392 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12397 @cindex pad character
12398 Use @acronym{ASCII} @sc{del} characters for fill instead of
12399 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12405 Newline delay style. Non-@acronym{POSIX}.
12412 Carriage return delay style. Non-@acronym{POSIX}.
12418 @opindex tab@var{n}
12419 Horizontal tab delay style. Non-@acronym{POSIX}.
12424 Backspace delay style. Non-@acronym{POSIX}.
12429 Vertical tab delay style. Non-@acronym{POSIX}.
12434 Form feed delay style. Non-@acronym{POSIX}.
12439 @subsection Local settings
12441 @cindex local settings
12446 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12447 characters. May be negated.
12451 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12452 special characters. May be negated.
12456 Enable non-@acronym{POSIX} special characters. May be negated.
12460 Echo input characters. May be negated.
12466 Echo @code{erase} characters as backspace-space-backspace. May be
12471 @cindex newline echoing after @code{kill}
12472 Echo a newline after a @code{kill} character. May be negated.
12476 @cindex newline, echoing
12477 Echo newline even if not echoing other characters. May be negated.
12481 @cindex flushing, disabling
12482 Disable flushing after @code{interrupt} and @code{quit} special
12483 characters. May be negated.
12487 @cindex case translation
12488 Enable input and output of uppercase characters by preceding their
12489 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12490 Non-@acronym{POSIX}. May be negated.
12494 @cindex background jobs, stopping at terminal write
12495 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12502 Echo erased characters backward, between @samp{\} and @samp{/}.
12503 Non-@acronym{POSIX}. May be negated.
12509 @cindex control characters, using @samp{^@var{c}}
12510 @cindex hat notation for control characters
12511 Echo control characters in hat notation (@samp{^@var{c}}) instead
12512 of literally. Non-@acronym{POSIX}. May be negated.
12518 Echo the @code{kill} special character by erasing each character on
12519 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12520 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12526 @subsection Combination settings
12528 @cindex combination settings
12529 Combination settings:
12536 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12537 as @code{-parenb cs8}.
12541 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12542 as @code{-parenb cs8}.
12546 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12547 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12551 Reset the @code{erase} and @code{kill} special characters to their default
12558 @c This is too long to write inline.
12560 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12561 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12562 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12563 ff0 isig icanon iexten echo echoe echok -echonl
12564 -noflsh -xcase -tostop -echoprt echoctl echoke
12568 and also sets all special characters to their default values.
12572 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12573 sets the @code{eof} and @code{eol} characters to their default values
12574 if they are the same as the @code{min} and @code{time} characters.
12575 May be negated. If negated, same as @code{raw}.
12582 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12583 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12584 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12588 May be negated. If negated, same as @code{cooked}.
12592 Same as @option{-icanon}. May be negated. If negated, same as
12597 @cindex eight-bit characters
12598 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12599 same as @code{parenb istrip cs7}.
12603 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12604 If negated, same as @code{parenb istrip opost cs7}.
12608 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12612 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12619 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12620 (Used for terminals with uppercase characters only.)
12624 Same as @code{echoe echoctl echoke}.
12628 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12633 @subsection Special characters
12635 @cindex special characters
12636 @cindex characters, special
12638 The special characters' default values vary from system to system.
12639 They are set with the syntax @samp{name value}, where the names are
12640 listed below and the value can be given either literally, in hat
12641 notation (@samp{^@var{c}}), or as an integer which may start with
12642 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12643 any other digit to indicate decimal.
12645 @cindex disabling special characters
12646 @kindex u@r{, and disabling special characters}
12647 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12648 special character. (This is incompatible with Ultrix @command{stty},
12649 which uses a value of @samp{u} to disable a special character. GNU
12650 @command{stty} treats a value @samp{u} like any other, namely to set that
12651 special character to @key{U}.)
12657 Send an interrupt signal.
12661 Send a quit signal.
12665 Erase the last character typed.
12669 Erase the current line.
12673 Send an end of file (terminate the input).
12681 Alternate character to end the line. Non-@acronym{POSIX}.
12685 Switch to a different shell layer. Non-@acronym{POSIX}.
12689 Restart the output after stopping it.
12697 Send a terminal stop signal.
12701 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12705 Redraw the current line. Non-@acronym{POSIX}.
12709 Erase the last word typed. Non-@acronym{POSIX}.
12713 Enter the next character typed literally, even if it is a special
12714 character. Non-@acronym{POSIX}.
12719 @subsection Special settings
12721 @cindex special settings
12726 Set the minimum number of characters that will satisfy a read until
12727 the time value has expired, when @option{-icanon} is set.
12731 Set the number of tenths of a second before reads time out if the minimum
12732 number of characters have not been read, when @option{-icanon} is set.
12734 @item ispeed @var{n}
12736 Set the input speed to @var{n}.
12738 @item ospeed @var{n}
12740 Set the output speed to @var{n}.
12744 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12747 @itemx columns @var{n}
12750 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12756 Print the number of rows and columns that the kernel thinks the
12757 terminal has. (Systems that don't support rows and columns in the kernel
12758 typically use the environment variables @env{LINES} and @env{COLUMNS}
12759 instead; however, GNU @command{stty} does not know anything about them.)
12760 Non-@acronym{POSIX}.
12764 Use line discipline @var{n}. Non-@acronym{POSIX}.
12768 Print the terminal speed.
12771 @cindex baud rate, setting
12772 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12773 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12774 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12775 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12776 support higher speeds. The @command{stty} command includes support
12793 4000000 where the system supports these.
12794 0 hangs up the line if @option{-clocal} is set.
12798 @node printenv invocation
12799 @section @command{printenv}: Print all or some environment variables
12802 @cindex printing all or some environment variables
12803 @cindex environment variables, printing
12805 @command{printenv} prints environment variable values. Synopsis:
12808 printenv [@var{option}] [@var{variable}]@dots{}
12811 If no @var{variable}s are specified, @command{printenv} prints the value of
12812 every environment variable. Otherwise, it prints the value of each
12813 @var{variable} that is set, and nothing for those that are not set.
12815 The program accepts the following option. Also see @ref{Common options}.
12823 @cindex exit status of @command{printenv}
12827 0 if all variables specified were found
12828 1 if at least one specified variable was not found
12829 2 if a write error occurred
12833 @node tty invocation
12834 @section @command{tty}: Print file name of terminal on standard input
12837 @cindex print terminal file name
12838 @cindex terminal file name, printing
12840 @command{tty} prints the file name of the terminal connected to its standard
12841 input. It prints @samp{not a tty} if standard input is not a terminal.
12845 tty [@var{option}]@dots{}
12848 The program accepts the following option. Also see @ref{Common options}.
12858 Print nothing; only return an exit status.
12862 @cindex exit status of @command{tty}
12866 0 if standard input is a terminal
12867 1 if standard input is not a terminal
12868 2 if given incorrect arguments
12869 3 if a write error occurs
12873 @node User information
12874 @chapter User information
12876 @cindex user information, commands for
12877 @cindex commands for printing user information
12879 This section describes commands that print user-related information:
12880 logins, groups, and so forth.
12883 * id invocation:: Print user identity.
12884 * logname invocation:: Print current login name.
12885 * whoami invocation:: Print effective user ID.
12886 * groups invocation:: Print group names a user is in.
12887 * users invocation:: Print login names of users currently logged in.
12888 * who invocation:: Print who is currently logged in.
12892 @node id invocation
12893 @section @command{id}: Print user identity
12896 @cindex real user and group IDs, printing
12897 @cindex effective user and group IDs, printing
12898 @cindex printing real and effective user and group IDs
12900 @command{id} prints information about the given user, or the process
12901 running it if no user is specified. Synopsis:
12904 id [@var{option}]@dots{} [@var{username}]
12907 @vindex POSIXLY_CORRECT
12908 By default, it prints the real user ID, real group ID, effective user ID
12909 if different from the real user ID, effective group ID if different from
12910 the real group ID, and supplemental group IDs.
12911 In addition, if SELinux
12912 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
12913 then print @samp{context=@var{c}}, where @var{c} is the security context.
12915 Each of these numeric values is preceded by an identifying string and
12916 followed by the corresponding user or group name in parentheses.
12918 The options cause @command{id} to print only part of the above information.
12919 Also see @ref{Common options}.
12926 Print only the group ID.
12932 Print only the group ID and the supplementary groups.
12938 Print the user or group name instead of the ID number. Requires
12939 @option{-u}, @option{-g}, or @option{-G}.
12945 Print the real, instead of effective, user or group ID. Requires
12946 @option{-u}, @option{-g}, or @option{-G}.
12952 Print only the user ID.
12959 @cindex security context
12960 Print only the security context of the current user.
12961 If SELinux is disabled then print a warning and
12962 set the exit status to 1.
12968 @macro primaryAndSupplementaryGroups{cmd,arg}
12969 Primary and supplementary groups for a process are normally inherited
12970 from its parent and are usually unchanged since login. This means
12971 that if you change the group database after logging in, @command{\cmd\}
12972 will not reflect your changes within your existing login session.
12973 Running @command{\cmd\} with a \arg\ causes the user and group
12974 database to be consulted afresh, and so will give a different result.
12976 @primaryAndSupplementaryGroups{id,user argument}
12978 @node logname invocation
12979 @section @command{logname}: Print current login name
12982 @cindex printing user's login name
12983 @cindex login name, printing
12984 @cindex user name, printing
12987 @command{logname} prints the calling user's name, as found in a
12988 system-maintained file (often @file{/var/run/utmp} or
12989 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
12990 for the calling process, @command{logname} prints
12991 an error message and exits with a status of 1.
12993 The only options are @option{--help} and @option{--version}. @xref{Common
12999 @node whoami invocation
13000 @section @command{whoami}: Print effective user ID
13003 @cindex effective user ID, printing
13004 @cindex printing the effective user ID
13006 @command{whoami} prints the user name associated with the current
13007 effective user ID. It is equivalent to the command @samp{id -un}.
13009 The only options are @option{--help} and @option{--version}. @xref{Common
13015 @node groups invocation
13016 @section @command{groups}: Print group names a user is in
13019 @cindex printing groups a user is in
13020 @cindex supplementary groups, printing
13022 @command{groups} prints the names of the primary and any supplementary
13023 groups for each given @var{username}, or the current process if no names
13024 are given. If more than one name is given, the name of each user is
13026 the list of that user's groups and the user name is separated from the
13027 group list by a colon. Synopsis:
13030 groups [@var{username}]@dots{}
13033 The group lists are equivalent to the output of the command @samp{id -Gn}.
13035 @primaryAndSupplementaryGroups{groups,list of users}
13037 The only options are @option{--help} and @option{--version}. @xref{Common
13043 @node users invocation
13044 @section @command{users}: Print login names of users currently logged in
13047 @cindex printing current usernames
13048 @cindex usernames, printing current
13050 @cindex login sessions, printing users with
13051 @command{users} prints on a single line a blank-separated list of user
13052 names of users currently logged in to the current host. Each user name
13053 corresponds to a login session, so if a user has more than one login
13054 session, that user's name will appear the same number of times in the
13063 With no @var{file} argument, @command{users} extracts its information from
13064 a system-maintained file (often @file{/var/run/utmp} or
13065 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13066 that file instead. A common choice is @file{/var/log/wtmp}.
13068 The only options are @option{--help} and @option{--version}. @xref{Common
13074 @node who invocation
13075 @section @command{who}: Print who is currently logged in
13078 @cindex printing current user information
13079 @cindex information, about current users
13081 @command{who} prints information about users who are currently logged on.
13085 @command{who} [@var{option}] [@var{file}] [am i]
13088 @cindex terminal lines, currently used
13090 @cindex remote hostname
13091 If given no non-option arguments, @command{who} prints the following
13092 information for each user currently logged on: login name, terminal
13093 line, login time, and remote hostname or X display.
13097 If given one non-option argument, @command{who} uses that instead of
13098 a default system-maintained file (often @file{/var/run/utmp} or
13099 @file{/etc/utmp}) as the name of the file containing the record of
13100 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13101 to @command{who} to look at who has previously logged on.
13105 If given two non-option arguments, @command{who} prints only the entry
13106 for the user running it (determined from its standard input), preceded
13107 by the hostname. Traditionally, the two arguments given are @samp{am
13108 i}, as in @samp{who am i}.
13111 Time stamps are listed according to the time zone rules specified by
13112 the @env{TZ} environment variable, or by the system default rules if
13113 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13114 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13116 The program accepts the following options. Also see @ref{Common options}.
13124 Same as @samp{-b -d --login -p -r -t -T -u}.
13130 Print the date and time of last system boot.
13136 Print information corresponding to dead processes.
13142 Print a line of column headings.
13148 List only the entries that correspond to processes via which the
13149 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13153 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13154 is not the default because it can cause significant delays on systems with
13155 automatic dial-up internet access.
13159 Same as @samp{who am i}.
13165 List active processes spawned by init.
13171 Print only the login names and the number of users logged on.
13172 Overrides all other options.
13177 @opindex --runlevel
13178 Print the current (and maybe previous) run-level of the init process.
13182 Ignored; for compatibility with other versions of @command{who}.
13188 Print last system clock change.
13193 After the login time, print the number of hours and minutes that the
13194 user has been idle. @samp{.} means the user was active in the last minute.
13195 @samp{old} means the user has been idle for more than 24 hours.
13206 @opindex --writable
13207 @cindex message status
13208 @pindex write@r{, allowed}
13209 After each login name print a character indicating the user's message status:
13212 @samp{+} allowing @code{write} messages
13213 @samp{-} disallowing @code{write} messages
13214 @samp{?} cannot find terminal device
13222 @node System context
13223 @chapter System context
13225 @cindex system context
13226 @cindex context, system
13227 @cindex commands for system context
13229 This section describes commands that print or change system-wide
13233 * date invocation:: Print or set system date and time.
13234 * arch invocation:: Print machine hardware name.
13235 * uname invocation:: Print system information.
13236 * hostname invocation:: Print or set system name.
13237 * hostid invocation:: Print numeric host identifier.
13238 * uptime invocation:: Print system uptime and load.
13241 @node date invocation
13242 @section @command{date}: Print or set system date and time
13245 @cindex time, printing or setting
13246 @cindex printing the current time
13251 date [@var{option}]@dots{} [+@var{format}]
13252 date [-u|--utc|--universal] @c this avoids a newline in the output
13253 [ MMDDhhmm[[CC]YY][.ss] ]
13257 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13258 it with a default format that depends on the @env{LC_TIME} locale category.
13259 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13260 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13263 Normally, @command{date} uses the time zone rules indicated by the
13264 @env{TZ} environment variable, or the system default rules if @env{TZ}
13265 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13266 @env{TZ}, libc, The GNU C Library Reference Manual}.
13268 @findex strftime @r{and @command{date}}
13269 @cindex time formats
13270 @cindex formatting times
13271 If given an argument that starts with a @samp{+}, @command{date} prints the
13272 current date and time (or the date and time specified by the
13273 @option{--date} option, see below) in the format defined by that argument,
13274 which is similar to that of the @code{strftime} function. Except for
13275 conversion specifiers, which start with @samp{%}, characters in the
13276 format string are printed unchanged. The conversion specifiers are
13282 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13283 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13284 * Literal conversion specifiers:: %[%nt]
13285 * Padding and other flags:: Pad with zeros, spaces, etc.
13286 * Setting the time:: Changing the system clock.
13287 * Options for date:: Instead of the current time.
13289 * Date input formats:: Specifying date strings.
13291 * Examples of date:: Examples.
13294 @node Time conversion specifiers
13295 @subsection Time conversion specifiers
13297 @cindex time conversion specifiers
13298 @cindex conversion specifiers, time
13300 @command{date} conversion specifiers related to times.
13304 hour (@samp{00}@dots{}@samp{23})
13306 hour (@samp{01}@dots{}@samp{12})
13308 hour (@samp{ 0}@dots{}@samp{23}).
13309 This is a @acronym{GNU} extension.
13311 hour (@samp{ 1}@dots{}@samp{12}).
13312 This is a @acronym{GNU} extension.
13314 minute (@samp{00}@dots{}@samp{59})
13316 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13317 This is a @acronym{GNU} extension.
13319 locale's equivalent of either @samp{AM} or @samp{PM};
13320 blank in many locales.
13321 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13323 like @samp{%p}, except lower case.
13324 This is a @acronym{GNU} extension.
13326 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13328 24-hour hour and minute. Same as @samp{%H:%M}.
13329 This is a @acronym{GNU} extension.
13331 @cindex epoch, seconds since
13332 @cindex seconds since the epoch
13333 @cindex beginning of time
13334 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13335 Leap seconds are not counted unless leap second support is available.
13336 @xref{%s-examples}, for examples.
13337 This is a @acronym{GNU} extension.
13339 second (@samp{00}@dots{}@samp{60}).
13340 This may be @samp{60} if leap seconds are supported.
13342 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13344 locale's time representation (e.g., @samp{23:13:48})
13346 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13347 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13348 time zone is determinable. This value reflects the numeric time zone
13349 appropriate for the current time, using the time zone rules specified
13350 by the @env{TZ} environment variable.
13351 The time (and optionally, the time zone rules) can be overridden
13352 by the @option{--date} option.
13353 This is a @acronym{GNU} extension.
13355 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13356 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13357 zone is determinable.
13358 This is a @acronym{GNU} extension.
13360 Numeric time zone to the nearest second with @samp{:} (e.g.,
13361 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13363 This is a @acronym{GNU} extension.
13365 Numeric time zone with @samp{:} using the minimum necessary precision
13366 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13367 no time zone is determinable.
13368 This is a @acronym{GNU} extension.
13370 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13371 time zone is determinable. See @samp{%z} for how it is determined.
13375 @node Date conversion specifiers
13376 @subsection Date conversion specifiers
13378 @cindex date conversion specifiers
13379 @cindex conversion specifiers, date
13381 @command{date} conversion specifiers related to dates.
13385 locale's abbreviated weekday name (e.g., @samp{Sun})
13387 locale's full weekday name, variable length (e.g., @samp{Sunday})
13389 locale's abbreviated month name (e.g., @samp{Jan})
13391 locale's full month name, variable length (e.g., @samp{January})
13393 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13395 century. This is like @samp{%Y}, except the last two digits are omitted.
13396 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13397 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13398 It is normally at least two characters, but it may be more.
13400 day of month (e.g., @samp{01})
13402 date; same as @samp{%m/%d/%y}
13404 day of month, space padded; same as @samp{%_d}
13406 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13407 This is a good choice for a date format, as it is standard and
13408 is easy to sort in the usual case where years are in the range
13410 This is a @acronym{GNU} extension.
13412 year corresponding to the @acronym{ISO} week number, but without the century
13413 (range @samp{00} through @samp{99}). This has the same format and value
13414 as @samp{%y}, except that if the @acronym{ISO} week number (see
13416 to the previous or next year, that year is used instead.
13417 This is a @acronym{GNU} extension.
13419 year corresponding to the @acronym{ISO} week number. This has the
13420 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13422 @samp{%V}) belongs to the previous or next year, that year is used
13424 It is normally useful only if @samp{%V} is also used;
13425 for example, the format @samp{%G-%m-%d} is probably a mistake,
13426 since it combines the ISO week number year with the conventional month and day.
13427 This is a @acronym{GNU} extension.
13431 day of year (@samp{001}@dots{}@samp{366})
13433 month (@samp{01}@dots{}@samp{12})
13435 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13437 week number of year, with Sunday as the first day of the week
13438 (@samp{00}@dots{}@samp{53}).
13439 Days in a new year preceding the first Sunday are in week zero.
13441 @acronym{ISO} week number, that is, the
13442 week number of year, with Monday as the first day of the week
13443 (@samp{01}@dots{}@samp{53}).
13444 If the week containing January 1 has four or more days in
13445 the new year, then it is considered week 1; otherwise, it is week 53 of
13446 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13449 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13451 week number of year, with Monday as first day of week
13452 (@samp{00}@dots{}@samp{53}).
13453 Days in a new year preceding the first Monday are in week zero.
13455 locale's date representation (e.g., @samp{12/31/99})
13457 last two digits of year (@samp{00}@dots{}@samp{99})
13459 year. This is normally at least four characters, but it may be more.
13460 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13461 precedes year @samp{0000}.
13465 @node Literal conversion specifiers
13466 @subsection Literal conversion specifiers
13468 @cindex literal conversion specifiers
13469 @cindex conversion specifiers, literal
13471 @command{date} conversion specifiers that produce literal strings.
13483 @node Padding and other flags
13484 @subsection Padding and other flags
13486 @cindex numeric field padding
13487 @cindex padding of numeric fields
13488 @cindex fields, padding numeric
13490 Unless otherwise specified, @command{date} normally pads numeric fields
13491 with zeros, so that, for
13492 example, numeric months are always output as two digits.
13493 Seconds since the epoch are not padded, though,
13494 since there is no natural width for them.
13496 As a @acronym{GNU} extension, @command{date} recognizes any of the
13497 following optional flags after the @samp{%}:
13501 (hyphen) Do not pad the field; useful if the output is intended for
13504 (underscore) Pad with spaces; useful if you need a fixed
13505 number of characters in the output, but zeros are too distracting.
13507 (zero) Pad with zeros even if the conversion specifier
13508 would normally pad with spaces.
13510 Use upper case characters if possible.
13512 Use opposite case characters if possible.
13513 A field that is normally upper case becomes lower case, and vice versa.
13517 Here are some examples of padding:
13520 date +%d/%m -d "Feb 1"
13522 date +%-d/%-m -d "Feb 1"
13524 date +%_d/%_m -d "Feb 1"
13528 As a @acronym{GNU} extension, you can specify the field width
13529 (after any flag, if present) as a decimal number. If the natural size of the
13530 output of the field has less than the specified number of characters,
13531 the result is written right adjusted and padded to the given
13532 size. For example, @samp{%9B} prints the right adjusted month name in
13533 a field of width 9.
13535 An optional modifier can follow the optional flag and width
13536 specification. The modifiers are:
13540 Use the locale's alternate representation for date and time. This
13541 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13542 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13543 example, @samp{%Ex} might yield a date format based on the Japanese
13547 Use the locale's alternate numeric symbols for numbers. This modifier
13548 applies only to numeric conversion specifiers.
13551 If the format supports the modifier but no alternate representation
13552 is available, it is ignored.
13555 @node Setting the time
13556 @subsection Setting the time
13558 @cindex setting the time
13559 @cindex time setting
13560 @cindex appropriate privileges
13562 If given an argument that does not start with @samp{+}, @command{date} sets
13563 the system clock to the date and time specified by that argument (as
13564 described below). You must have appropriate privileges to set the
13565 system clock. The @option{--date} and @option{--set} options may not be
13566 used with such an argument. The @option{--universal} option may be used
13567 with such an argument to indicate that the specified date and time are
13568 relative to Coordinated Universal Time rather than to the local time
13571 The argument must consist entirely of digits, which have the following
13584 first two digits of year (optional)
13586 last two digits of year (optional)
13591 The @option{--set} option also sets the system clock; see the next section.
13594 @node Options for date
13595 @subsection Options for @command{date}
13597 @cindex @command{date} options
13598 @cindex options for @command{date}
13600 The program accepts the following options. Also see @ref{Common options}.
13604 @item -d @var{datestr}
13605 @itemx --date=@var{datestr}
13608 @cindex parsing date strings
13609 @cindex date strings, parsing
13610 @cindex arbitrary date strings, parsing
13613 @opindex next @var{day}
13614 @opindex last @var{day}
13615 Display the date and time specified in @var{datestr} instead of the
13616 current date and time. @var{datestr} can be in almost any common
13617 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13618 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13619 14:19:13.489392193 +0530"} specifies the instant of time that is
13620 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13621 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13622 Note: input currently must be in locale independent format. E.g., the
13623 LC_TIME=C below is needed to print back the correct date in many locales:
13625 date -d "$(LC_TIME=C date)"
13627 @xref{Date input formats}.
13629 @item -f @var{datefile}
13630 @itemx --file=@var{datefile}
13633 Parse each line in @var{datefile} as with @option{-d} and display the
13634 resulting date and time. If @var{datefile} is @samp{-}, use standard
13635 input. This is useful when you have many dates to process, because the
13636 system overhead of starting up the @command{date} executable many times can
13639 @item -r @var{file}
13640 @itemx --reference=@var{file}
13642 @opindex --reference
13643 Display the date and time of the last modification of @var{file},
13644 instead of the current date and time.
13651 @opindex --rfc-2822
13652 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13653 %z}, evaluated in the C locale so abbreviations are always in English.
13657 Fri, 09 Sep 2005 13:51:39 -0700
13660 This format conforms to
13661 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13662 @acronym{RFCs} 2822} and
13663 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13664 current and previous standards for Internet email.
13666 @item --rfc-3339=@var{timespec}
13667 @opindex --rfc-3339=@var{timespec}
13668 Display the date using a format specified by
13669 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13670 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13671 format, except that it also permits applications to use a space rather
13672 than a @samp{T} to separate dates from times. Unlike the other
13673 standard formats, @acronym{RFC} 3339 format is always suitable as
13674 input for the @option{--date} (@option{-d}) and @option{--file}
13675 (@option{-f}) options, regardless of the current locale.
13677 The argument @var{timespec} specifies how much of the time to include.
13678 It can be one of the following:
13682 Print just the full-date, e.g., @samp{2005-09-14}.
13683 This is equivalent to the format @samp{%Y-%m-%d}.
13686 Print the full-date and full-time separated by a space, e.g.,
13687 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13688 time-offset; here the @samp{+05:30} means that local time is five
13689 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13690 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13693 Like @samp{seconds}, but also print nanoseconds, e.g.,
13694 @samp{2005-09-14 00:56:06.998458565+05:30}.
13695 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13699 @item -s @var{datestr}
13700 @itemx --set=@var{datestr}
13703 Set the date and time to @var{datestr}. See @option{-d} above.
13710 @opindex --universal
13711 @cindex Coordinated Universal Time
13713 @cindex Greenwich Mean Time
13716 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13717 @env{TZ} environment variable were set to the string @samp{UTC0}.
13719 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13720 historical reasons.
13724 @node Examples of date
13725 @subsection Examples of @command{date}
13727 @cindex examples of @command{date}
13729 Here are a few examples. Also see the documentation for the @option{-d}
13730 option in the previous section.
13735 To print the date of the day before yesterday:
13738 date --date='2 days ago'
13742 To print the date of the day three months and one day hence:
13745 date --date='3 months 1 day'
13749 To print the day of year of Christmas in the current year:
13752 date --date='25 Dec' +%j
13756 To print the current full month name and the day of the month:
13762 But this may not be what you want because for the first nine days of
13763 the month, the @samp{%d} expands to a zero-padded two-digit field,
13764 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13767 To print a date without the leading zero for one-digit days
13768 of the month, you can use the (@acronym{GNU} extension)
13769 @samp{-} flag to suppress
13770 the padding altogether:
13773 date -d 1may '+%B %-d
13777 To print the current date and time in the format required by many
13778 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13781 date +%m%d%H%M%Y.%S
13785 To set the system clock forward by two minutes:
13788 date --set='+2 minutes'
13792 To print the date in @acronym{RFC} 2822 format,
13793 use @samp{date --rfc-2822}. Here is some example output:
13796 Fri, 09 Sep 2005 13:51:39 -0700
13799 @anchor{%s-examples}
13801 To convert a date string to the number of seconds since the epoch
13802 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13803 the @samp{%s} format. That can be useful in sorting and/or graphing
13804 and/or comparing data by date. The following command outputs the
13805 number of the seconds since the epoch for the time two minutes after the
13809 date --date='1970-01-01 00:02:00 +0000' +%s
13813 If you do not specify time zone information in the date string,
13814 @command{date} uses your computer's idea of the time zone when
13815 interpreting the string. For example, if your computer's time zone is
13816 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13817 seconds) behind UTC:
13820 # local time zone used
13821 date --date='1970-01-01 00:02:00' +%s
13826 If you're sorting or graphing dated data, your raw date values may be
13827 represented as seconds since the epoch. But few people can look at
13828 the date @samp{946684800} and casually note ``Oh, that's the first second
13829 of the year 2000 in Greenwich, England.''
13832 date --date='2000-01-01 UTC' +%s
13836 An alternative is to use the @option{--utc} (@option{-u}) option.
13837 Then you may omit @samp{UTC} from the date string. Although this
13838 produces the same result for @samp{%s} and many other format sequences,
13839 with a time zone offset different from zero, it would give a different
13840 result for zone-dependent formats like @samp{%z}.
13843 date -u --date=2000-01-01 +%s
13847 To convert such an unwieldy number of seconds back to
13848 a more readable form, use a command like this:
13851 # local time zone used
13852 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
13853 1999-12-31 19:00:00 -0500
13856 Or if you do not mind depending on the @samp{@@} feature present since
13857 coreutils 5.3.0, you could shorten this to:
13860 date -d @@946684800 +"%F %T %z"
13861 1999-12-31 19:00:00 -0500
13864 Often it is better to output UTC-relative date and time:
13867 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
13868 2000-01-01 00:00:00 +0000
13874 @node arch invocation
13875 @section @command{arch}: Print machine hardware name
13878 @cindex print machine hardware name
13879 @cindex system information, printing
13881 @command{arch} prints the machine hardware name,
13882 and is equivalent to @samp{uname -m}.
13886 arch [@var{option}]
13889 The program accepts the @ref{Common options} only.
13894 @node uname invocation
13895 @section @command{uname}: Print system information
13898 @cindex print system information
13899 @cindex system information, printing
13901 @command{uname} prints information about the machine and operating system
13902 it is run on. If no options are given, @command{uname} acts as if the
13903 @option{-s} option were given. Synopsis:
13906 uname [@var{option}]@dots{}
13909 If multiple options or @option{-a} are given, the selected information is
13910 printed in this order:
13913 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
13914 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
13917 The information may contain internal spaces, so such output cannot be
13918 parsed reliably. In the following example, @var{release} is
13919 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
13923 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
13927 The program accepts the following options. Also see @ref{Common options}.
13935 Print all of the below information, except omit the processor type
13936 and the hardware platform name if they are unknown.
13939 @itemx --hardware-platform
13941 @opindex --hardware-platform
13942 @cindex implementation, hardware
13943 @cindex hardware platform
13944 @cindex platform, hardware
13945 Print the hardware platform name
13946 (sometimes called the hardware implementation).
13947 Print @samp{unknown} if the kernel does not make this information
13948 easily available, as is the case with Linux kernels.
13954 @cindex machine type
13955 @cindex hardware class
13956 @cindex hardware type
13957 Print the machine hardware name (sometimes called the hardware class
13963 @opindex --nodename
13966 @cindex network node name
13967 Print the network node hostname.
13972 @opindex --processor
13973 @cindex host processor type
13974 Print the processor type (sometimes called the instruction set
13975 architecture or ISA).
13976 Print @samp{unknown} if the kernel does not make this information
13977 easily available, as is the case with Linux kernels.
13980 @itemx --operating-system
13982 @opindex --operating-system
13983 @cindex operating system name
13984 Print the name of the operating system.
13987 @itemx --kernel-release
13989 @opindex --kernel-release
13990 @cindex kernel release
13991 @cindex release of kernel
13992 Print the kernel release.
13995 @itemx --kernel-name
13997 @opindex --kernel-name
13998 @cindex kernel name
13999 @cindex name of kernel
14000 Print the kernel name.
14001 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14002 ``the implementation of the operating system'', because the
14003 @acronym{POSIX} specification itself has no notion of ``kernel''.
14004 The kernel name might be the same as the operating system name printed
14005 by the @option{-o} or @option{--operating-system} option, but it might
14006 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14007 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14011 @itemx --kernel-version
14013 @opindex --kernel-version
14014 @cindex kernel version
14015 @cindex version of kernel
14016 Print the kernel version.
14023 @node hostname invocation
14024 @section @command{hostname}: Print or set system name
14027 @cindex setting the hostname
14028 @cindex printing the hostname
14029 @cindex system name, printing
14030 @cindex appropriate privileges
14032 With no arguments, @command{hostname} prints the name of the current host
14033 system. With one argument, it sets the current host name to the
14034 specified string. You must have appropriate privileges to set the host
14038 hostname [@var{name}]
14041 The only options are @option{--help} and @option{--version}. @xref{Common
14047 @node hostid invocation
14048 @section @command{hostid}: Print numeric host identifier
14051 @cindex printing the host identifier
14053 @command{hostid} prints the numeric identifier of the current host
14054 in hexadecimal. This command accepts no arguments.
14055 The only options are @option{--help} and @option{--version}.
14056 @xref{Common options}.
14058 For example, here's what it prints on one system I use:
14065 On that system, the 32-bit quantity happens to be closely
14066 related to the system's Internet address, but that isn't always
14071 @node uptime invocation
14072 @section @command{uptime}: Print system uptime and load
14075 @cindex printing the system uptime and load
14077 @command{uptime} prints the current time, the system's uptime, the
14078 number of logged-in users and the current load average.
14080 If an argument is specified, it is used as the file to be read
14081 to discover how many users are logged in. If no argument is
14082 specified, a system default is used (@command{uptime --help} indicates
14083 the default setting).
14085 The only options are @option{--help} and @option{--version}.
14086 @xref{Common options}.
14088 For example, here's what it prints right now on one system I use:
14092 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14095 The precise method of calculation of load average varies somewhat
14096 between systems. Some systems calculate it as the average number of
14097 runnable processes over the last 1, 5 and 15 minutes, but some systems
14098 also include processes in the uninterruptible sleep state (that is,
14099 those processes which are waiting for disk I/O). The Linux kernel
14100 includes uninterruptible processes.
14102 @node SELinux context
14103 @chapter SELinux context
14105 @cindex SELinux context
14106 @cindex SELinux, context
14107 @cindex commands for SELinux context
14109 This section describes commands for operations with SELinux
14113 * chcon invocation:: Change SELinux context of file
14114 * runcon invocation:: Run a command in specified SELinux context
14117 @node chcon invocation
14118 @section @command{chcon}: Change SELinux context of file
14121 @cindex changing security context
14122 @cindex change SELinux context
14124 @command{chcon} changes the SELinux security context of the selected files.
14128 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14129 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14130 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14133 Change the SELinux security context of each @var{file} to @var{context}.
14134 With @option{--reference}, change the security context of each @var{file}
14135 to that of @var{rfile}.
14137 The program accepts the following options. Also see @ref{Common options}.
14142 @itemx --no-dereference
14144 @opindex --no-dereference
14145 @cindex no dereference
14146 Affect symbolic links instead of any referenced file.
14148 @item --reference=@var{rfile}
14149 @opindex --reference
14150 @cindex reference file
14151 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14156 @opindex --recursive
14157 Operate on files and directories recursively.
14160 @xref{Traversing symlinks}.
14163 @xref{Traversing symlinks}.
14166 @xref{Traversing symlinks}.
14173 Output a diagnostic for every file processed.
14175 @item -u @var{user}
14176 @itemx --user=@var{user}
14179 Set user @var{user} in the target security context.
14181 @item -r @var{role}
14182 @itemx --role=@var{role}
14185 Set role @var{role} in the target security context.
14187 @item -t @var{type}
14188 @itemx --type=@var{type}
14191 Set type @var{type} in the target security context.
14193 @item -l @var{range}
14194 @itemx --range=@var{range}
14197 Set range @var{range} in the target security context.
14203 @node runcon invocation
14204 @section @command{runcon}: Run a command in specified SELinux context
14207 @cindex run with security context
14210 @command{runcon} runs file in specified SELinux security context.
14214 runcon @var{context} @var{command} [@var{args}]
14215 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14218 Run @var{command} with completely-specified @var{context}, or with
14219 current or transitioned security context modified by one or more of @var{level},
14220 @var{role}, @var{type} and @var{user}.
14222 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14223 is specified, the first argument is used as the complete context.
14224 Any additional arguments after @var{command}
14225 are interpreted as arguments to the command.
14227 With neither @var{context} nor @var{command}, print the current security context.
14229 The program accepts the following options. Also see @ref{Common options}.
14237 Compute process transition context before modifying.
14239 @item -u @var{user}
14240 @itemx --user=@var{user}
14243 Set user @var{user} in the target security context.
14245 @item -r @var{role}
14246 @itemx --role=@var{role}
14249 Set role @var{role} in the target security context.
14251 @item -t @var{type}
14252 @itemx --type=@var{type}
14255 Set type @var{type} in the target security context.
14257 @item -l @var{range}
14258 @itemx --range=@var{range}
14261 Set range @var{range} in the target security context.
14265 @cindex exit status of @command{runcon}
14269 126 if @var{command} is found but cannot be invoked
14270 127 if @command{runcon} itself fails or if @var{command} cannot be found
14271 the exit status of @var{command} otherwise
14274 @node Modified command invocation
14275 @chapter Modified command invocation
14277 @cindex modified command invocation
14278 @cindex invocation of commands, modified
14279 @cindex commands for invoking other commands
14281 This section describes commands that run other commands in some context
14282 different than the current one: a modified environment, as a different
14286 * chroot invocation:: Modify the root directory.
14287 * env invocation:: Modify environment variables.
14288 * nice invocation:: Modify niceness.
14289 * nohup invocation:: Immunize to hangups.
14290 * stdbuf invocation:: Modify buffering of standard streams.
14291 * su invocation:: Modify user and group ID.
14292 * timeout invocation:: Run with time limit.
14296 @node chroot invocation
14297 @section @command{chroot}: Run a command with a different root directory
14300 @cindex running a program in a specified root directory
14301 @cindex root directory, running a program in a specified
14303 @command{chroot} runs a command with a specified root directory.
14304 On many systems, only the super-user can do this.@footnote{However,
14305 some systems (e.g., FreeBSD) can be configured to allow certain regular
14306 users to use the @code{chroot} system call, and hence to run this program.
14307 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14308 underlying function is non-privileged due to lack of support in MS-Windows.}
14312 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14313 chroot @var{option}
14316 Ordinarily, file names are looked up starting at the root of the
14317 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14318 the directory @var{newroot} (which must exist) and then runs
14319 @var{command} with optional @var{args}. If @var{command} is not
14320 specified, the default is the value of the @env{SHELL} environment
14321 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14322 @var{command} must not be a special built-in utility
14323 (@pxref{Special built-in utilities}).
14325 The program accepts the following options. Also see @ref{Common options}.
14326 Options must precede operands.
14330 @itemx --userspec=@var{user}[:@var{group}]
14331 @opindex --userspec
14332 By default, @var{command} is run with the same credentials
14333 as the invoking process.
14334 Use this option to run it as a different @var{user} and/or with a
14335 different primary @var{group}.
14337 @itemx --groups=@var{groups}
14339 Use this option to specify the supplementary @var{groups} to be
14340 used by the new process.
14341 The items in the list (names or numeric IDs) must be separated by commas.
14345 Here are a few tips to help avoid common problems in using chroot.
14346 To start with a simple example, make @var{command} refer to a statically
14347 linked binary. If you were to use a dynamically linked executable, then
14348 you'd have to arrange to have the shared libraries in the right place under
14349 your new root directory.
14351 For example, if you create a statically linked @command{ls} executable,
14352 and put it in @file{/tmp/empty}, you can run this command as root:
14355 $ chroot /tmp/empty /ls -Rl /
14358 Then you'll see output like this:
14363 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14366 If you want to use a dynamically linked executable, say @command{bash},
14367 then first run @samp{ldd bash} to see what shared objects it needs.
14368 Then, in addition to copying the actual binary, also copy the listed
14369 files to the required positions under your intended new root directory.
14370 Finally, if the executable requires any other files (e.g., data, state,
14371 device files), copy them into place, too.
14373 @cindex exit status of @command{chroot}
14377 125 if @command{chroot} itself fails
14378 126 if @var{command} is found but cannot be invoked
14379 127 if @var{command} cannot be found
14380 the exit status of @var{command} otherwise
14384 @node env invocation
14385 @section @command{env}: Run a command in a modified environment
14388 @cindex environment, running a program in a modified
14389 @cindex modified environment, running a program in a
14390 @cindex running a program in a modified environment
14392 @command{env} runs a command with a modified environment. Synopses:
14395 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14396 [@var{command} [@var{args}]@dots{}]
14400 Operands of the form @samp{@var{variable}=@var{value}} set
14401 the environment variable @var{variable} to value @var{value}.
14402 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14403 to an empty value is different from unsetting it.
14404 These operands are evaluated left-to-right, so if two operands
14405 mention the same variable the earlier is ignored.
14407 Environment variable names can be empty, and can contain any
14408 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14409 However, it is wise to limit yourself to names that
14410 consist solely of underscores, digits, and @acronym{ASCII} letters,
14411 and that begin with a non-digit, as applications like the shell do not
14412 work well with other names.
14415 The first operand that does not contain the character @samp{=}
14416 specifies the program to invoke; it is
14417 searched for according to the @env{PATH} environment variable. Any
14418 remaining arguments are passed as arguments to that program.
14419 The program should not be a special built-in utility
14420 (@pxref{Special built-in utilities}).
14422 Modifications to @env{PATH} take effect prior to searching for
14423 @var{command}. Use caution when reducing @env{PATH}; behavior is
14424 not portable when @env{PATH} is undefined or omits key directories
14425 such as @file{/bin}.
14427 In the rare case that a utility contains a @samp{=} in the name, the
14428 only way to disambiguate it from a variable assignment is to use an
14429 intermediate command for @var{command}, and pass the problematic
14430 program name via @var{args}. For example, if @file{./prog=} is an
14431 executable in the current @env{PATH}:
14434 env prog= true # runs 'true', with prog= in environment
14435 env ./prog= true # runs 'true', with ./prog= in environment
14436 env -- prog= true # runs 'true', with prog= in environment
14437 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14438 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14441 @cindex environment, printing
14443 If no command name is specified following the environment
14444 specifications, the resulting environment is printed. This is like
14445 specifying the @command{printenv} program.
14447 For some examples, suppose the environment passed to @command{env}
14448 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14449 @samp{PATH=.:/gnubin:/hacks}:
14454 Output the current environment.
14456 $ env | LC_ALL=C sort
14459 PATH=.:/gnubin:/hacks
14463 Run @command{foo} with a reduced environment, preserving only the
14464 original @env{PATH} to avoid problems in locating @command{foo}.
14466 env - PATH="$PATH" foo
14470 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14471 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14472 that @command{foo} was found in the file system rather than a shell
14479 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14480 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14481 @samp{DISPLAY=gnu:0}.
14483 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14487 Attempt to run the program @command{/energy/--} (as that is the only
14488 possible path search result); if the command exists, the environment
14489 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14490 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14492 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14498 The program accepts the following options. Also see @ref{Common options}.
14499 Options must precede operands.
14505 @item -u @var{name}
14506 @itemx --unset=@var{name}
14509 Remove variable @var{name} from the environment, if it was in the
14514 @itemx --ignore-environment
14517 @opindex --ignore-environment
14518 Start with an empty environment, ignoring the inherited environment.
14522 @cindex exit status of @command{env}
14526 0 if no @var{command} is specified and the environment is output
14527 125 if @command{env} itself fails
14528 126 if @var{command} is found but cannot be invoked
14529 127 if @var{command} cannot be found
14530 the exit status of @var{command} otherwise
14534 @node nice invocation
14535 @section @command{nice}: Run a command with modified niceness
14539 @cindex scheduling, affecting
14540 @cindex appropriate privileges
14542 @command{nice} prints or modifies a process's @dfn{niceness},
14543 a parameter that affects whether the process is scheduled favorably.
14547 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14550 If no arguments are given, @command{nice} prints the current niceness.
14551 Otherwise, @command{nice} runs the given @var{command} with its
14552 niceness adjusted. By default, its niceness is incremented by 10.
14554 Niceness values range at least from @minus{}20 (process has high priority
14555 and gets more resources, thus slowing down other processes) through 19
14556 (process has lower priority and runs slowly itself, but has less impact
14557 on the speed of other running processes). Some systems
14558 may have a wider range of nicenesses; conversely, other systems may
14559 enforce more restrictive limits. An attempt to set the niceness
14560 outside the supported range is treated as an attempt to use the
14561 minimum or maximum supported value.
14563 A niceness should not be confused with a scheduling priority, which
14564 lets applications determine the order in which threads are scheduled
14565 to run. Unlike a priority, a niceness is merely advice to the
14566 scheduler, which the scheduler is free to ignore. Also, as a point of
14567 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14568 terms of a @dfn{nice value}, which is the nonnegative difference
14569 between a niceness and the minimum niceness. Though @command{nice}
14570 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14571 term ``niceness'' for compatibility with historical practice.
14573 @var{command} must not be a special built-in utility (@pxref{Special
14574 built-in utilities}).
14576 @mayConflictWithShellBuiltIn{nice}
14578 The program accepts the following option. Also see @ref{Common options}.
14579 Options must precede operands.
14582 @item -n @var{adjustment}
14583 @itemx --adjustment=@var{adjustment}
14585 @opindex --adjustment
14586 Add @var{adjustment} instead of 10 to the command's niceness. If
14587 @var{adjustment} is negative and you lack appropriate privileges,
14588 @command{nice} issues a warning but otherwise acts as if you specified
14591 For compatibility @command{nice} also supports an obsolete
14592 option syntax @option{-@var{adjustment}}. New scripts should use
14593 @option{-n @var{adjustment}} instead.
14597 @cindex exit status of @command{nice}
14601 0 if no @var{command} is specified and the niceness is output
14602 125 if @command{nice} itself fails
14603 126 if @var{command} is found but cannot be invoked
14604 127 if @var{command} cannot be found
14605 the exit status of @var{command} otherwise
14608 It is sometimes useful to run a non-interactive program with reduced niceness.
14611 $ nice factor 4611686018427387903
14614 Since @command{nice} prints the current niceness,
14615 you can invoke it through itself to demonstrate how it works.
14617 The default behavior is to increase the niceness by @samp{10}:
14628 The @var{adjustment} is relative to the current niceness. In the
14629 next example, the first @command{nice} invocation runs the second one
14630 with niceness 10, and it in turn runs the final one with a niceness
14634 $ nice nice -n 3 nice
14638 Specifying a niceness larger than the supported range
14639 is the same as specifying the maximum supported value:
14642 $ nice -n 10000000000 nice
14646 Only a privileged user may run a process with lower niceness:
14650 nice: cannot set niceness: Permission denied
14652 $ sudo nice -n -1 nice
14657 @node nohup invocation
14658 @section @command{nohup}: Run a command immune to hangups
14661 @cindex hangups, immunity to
14662 @cindex immunity to hangups
14663 @cindex logging out and continuing to run
14666 @command{nohup} runs the given @var{command} with hangup signals ignored,
14667 so that the command can continue running in the background after you log
14671 nohup @var{command} [@var{arg}]@dots{}
14674 If standard input is a terminal, it is redirected from
14675 @file{/dev/null} so that terminal sessions do not mistakenly consider
14676 the terminal to be used by the command. This is a @acronym{GNU}
14677 extension; programs intended to be portable to non-@acronym{GNU} hosts
14678 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14682 If standard output is a terminal, the command's standard output is appended
14683 to the file @file{nohup.out}; if that cannot be written to, it is appended
14684 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14685 command is not run.
14686 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14687 @command{nohup} is made readable and writable only to the user,
14688 regardless of the current umask settings.
14690 If standard error is a terminal, it is normally redirected to the same file
14691 descriptor as the (possibly-redirected) standard output.
14692 However, if standard output is closed, standard error terminal output
14693 is instead appended to the file @file{nohup.out} or
14694 @file{$HOME/nohup.out} as above.
14696 To capture the command's output to a file other than @file{nohup.out}
14697 you can redirect it. For example, to capture the output of
14701 nohup make > make.log
14704 @command{nohup} does not automatically put the command it runs in the
14705 background; you must do that explicitly, by ending the command line
14706 with an @samp{&}. Also, @command{nohup} does not alter the
14707 niceness of @var{command}; use @command{nice} for that,
14708 e.g., @samp{nohup nice @var{command}}.
14710 @var{command} must not be a special built-in utility (@pxref{Special
14711 built-in utilities}).
14713 The only options are @option{--help} and @option{--version}. @xref{Common
14714 options}. Options must precede operands.
14716 @cindex exit status of @command{nohup}
14720 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14721 126 if @var{command} is found but cannot be invoked
14722 127 if @var{command} cannot be found
14723 the exit status of @var{command} otherwise
14726 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
14730 @node stdbuf invocation
14731 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14734 @cindex standard streams, buffering
14735 @cindex line buffered
14737 @command{stdbuf} allows one to modify the buffering operations of the
14738 three standard I/O streams associated with a program. Synopsis:
14741 stdbuf @var{option}@dots{} @var{command}
14744 Any additional @var{arg}s are passed as additional arguments to the
14747 The program accepts the following options. Also see @ref{Common options}.
14751 @item -i @var{mode}
14752 @itemx --input=@var{mode}
14755 Adjust the standard input stream buffering.
14757 @item -o @var{mode}
14758 @itemx --output=@var{mode}
14761 Adjust the standard output stream buffering.
14763 @item -e @var{mode}
14764 @itemx --error=@var{mode}
14767 Adjust the standard error stream buffering.
14771 The @var{mode} can be specified as follows:
14776 Set the stream to line buffered mode.
14777 In this mode data is coalesced until a newline is output or
14778 input is read from any stream attached to a terminal device.
14779 This option is invalid with standard input.
14782 Disable buffering of the selected stream.
14783 In this mode data is output immediately and only the
14784 amount of data requested is read from input.
14787 Specify the size of the buffer to use in fully buffered mode.
14788 @multiplierSuffixesNoBlocks{size}
14792 NOTE: If @var{command} adjusts the buffering of its standard streams
14793 (@command{tee} does for e.g.) then that will override corresponding settings
14794 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14795 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14796 by @command{stdbuf} settings.
14798 @cindex exit status of @command{stdbuf}
14802 125 if @command{stdbuf} itself fails
14803 126 if @var{command} is found but cannot be invoked
14804 127 if @var{command} cannot be found
14805 the exit status of @var{command} otherwise
14809 @node su invocation
14810 @section @command{su}: Run a command with substitute user and group ID
14813 @cindex substitute user and group IDs
14814 @cindex user ID, switching
14815 @cindex super-user, becoming
14816 @cindex root, becoming
14818 @command{su} allows one user to temporarily become another user. It runs a
14819 command (often an interactive shell) with the real and effective user
14820 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14823 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14826 @cindex passwd entry, and @command{su} shell
14828 @flindex /etc/passwd
14829 If no @var{user} is given, the default is @code{root}, the super-user.
14830 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14831 @file{/bin/sh} if none is specified there. If @var{user} has a
14832 password, @command{su} prompts for the password unless run by a user with
14833 effective user ID of zero (the super-user).
14839 @cindex login shell
14840 By default, @command{su} does not change the current directory.
14841 It sets the environment variables @env{HOME} and @env{SHELL}
14842 from the password entry for @var{user}, and if @var{user} is not
14843 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
14844 By default, the shell is not a login shell.
14846 Any additional @var{arg}s are passed as additional arguments to the
14849 @cindex @option{-su}
14850 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
14851 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
14852 to certain shells, etc.).
14855 @command{su} can optionally be compiled to use @code{syslog} to report
14856 failed, and optionally successful, @command{su} attempts. (If the system
14857 supports @code{syslog}.) However, GNU @command{su} does not check if the
14858 user is a member of the @code{wheel} group; see below.
14860 The program accepts the following options. Also see @ref{Common options}.
14863 @item -c @var{command}
14864 @itemx --command=@var{command}
14867 Pass @var{command}, a single command line to run, to the shell with
14868 a @option{-c} option instead of starting an interactive shell.
14875 @cindex file name pattern expansion, disabled
14876 @cindex globbing, disabled
14877 Pass the @option{-f} option to the shell. This probably only makes sense
14878 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
14879 option prevents reading the startup file (@file{.cshrc}). With
14880 Bourne-like shells, the @option{-f} option disables file name pattern
14881 expansion (globbing), which is not likely to be useful.
14889 @c other variables already indexed above
14892 @cindex login shell, creating
14893 Make the shell a login shell. This means the following. Unset all
14894 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
14895 (which are set as described above), and @env{USER} and @env{LOGNAME}
14896 (which are set, even for the super-user, as described above), and set
14897 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
14898 directory. Prepend @samp{-} to the shell's name, intended to make it
14899 read its login startup file(s).
14903 @itemx --preserve-environment
14906 @opindex --preserve-environment
14907 @cindex environment, preserving
14908 @flindex /etc/shells
14909 @cindex restricted shell
14910 Do not change the environment variables @env{HOME}, @env{USER},
14911 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
14912 variable @env{SHELL} instead of the shell from @var{user}'s passwd
14913 entry, unless the user running @command{su} is not the super-user and
14914 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
14915 is not listed in the file @file{/etc/shells}, or in a compiled-in list
14916 if that file does not exist. Parts of what this option does can be
14917 overridden by @option{--login} and @option{--shell}.
14919 @item -s @var{shell}
14920 @itemx --shell=@var{shell}
14923 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
14924 unless the user running @command{su} is not the super-user and @var{user}'s
14925 shell is restricted (see @option{-m} just above).
14929 @cindex exit status of @command{su}
14933 125 if @command{su} itself fails
14934 126 if subshell is found but cannot be invoked
14935 127 if subshell cannot be found
14936 the exit status of the subshell otherwise
14939 @cindex wheel group, not supported
14940 @cindex group wheel, not supported
14942 @subsection Why GNU @command{su} does not support the @samp{wheel} group
14944 (This section is by Richard Stallman.)
14948 Sometimes a few of the users try to hold total power over all the
14949 rest. For example, in 1984, a few users at the MIT AI lab decided to
14950 seize power by changing the operator password on the Twenex system and
14951 keeping it secret from everyone else. (I was able to thwart this coup
14952 and give power back to the users by patching the kernel, but I
14953 wouldn't know how to do that in Unix.)
14955 However, occasionally the rulers do tell someone. Under the usual
14956 @command{su} mechanism, once someone learns the root password who
14957 sympathizes with the ordinary users, he or she can tell the rest. The
14958 ``wheel group'' feature would make this impossible, and thus cement the
14959 power of the rulers.
14961 I'm on the side of the masses, not that of the rulers. If you are
14962 used to supporting the bosses and sysadmins in whatever they do, you
14963 might find this idea strange at first.
14966 @node timeout invocation
14967 @section @command{timeout}: Run a command with a time limit
14971 @cindex run commands with bounded time
14973 @command{timeout} runs the given @var{command} and kills it if it is
14974 still running after the specified time interval. Synopsis:
14977 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
14981 @var{number} is an integer followed by an optional unit; the default
14982 is seconds. The units are:
14995 @var{command} must not be a special built-in utility (@pxref{Special
14996 built-in utilities}).
14998 The program accepts the following option. Also see @ref{Common options}.
14999 Options must precede operands.
15002 @item -s @var{signal}
15003 @itemx --signal=@var{signal}
15006 Send this @var{signal} to @var{command} on timeout, rather than the
15007 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15008 or a number. Also see @xref{Signal specifications}.
15012 @cindex exit status of @command{timeout}
15016 124 if @var{command} times out
15017 125 if @command{timeout} itself fails
15018 126 if @var{command} is found but cannot be invoked
15019 127 if @var{command} cannot be found
15020 the exit status of @var{command} otherwise
15024 @node Process control
15025 @chapter Process control
15027 @cindex processes, commands for controlling
15028 @cindex commands for controlling processes
15031 * kill invocation:: Sending a signal to processes.
15035 @node kill invocation
15036 @section @command{kill}: Send a signal to processes
15039 @cindex send a signal to processes
15041 The @command{kill} command sends a signal to processes, causing them
15042 to terminate or otherwise act upon receiving the signal in some way.
15043 Alternatively, it lists information about signals. Synopses:
15046 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15047 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15050 @mayConflictWithShellBuiltIn{kill}
15052 The first form of the @command{kill} command sends a signal to all
15053 @var{pid} arguments. The default signal to send if none is specified
15054 is @samp{TERM}. The special signal number @samp{0} does not denote a
15055 valid signal, but can be used to test whether the @var{pid} arguments
15056 specify processes to which a signal could be sent.
15058 If @var{pid} is positive, the signal is sent to the process with the
15059 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15060 processes in the process group of the current process. If @var{pid}
15061 is @minus{}1, the signal is sent to all processes for which the user has
15062 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15063 is sent to all processes in the process group that equals the absolute
15064 value of @var{pid}.
15066 If @var{pid} is not positive, a system-dependent set of system
15067 processes is excluded from the list of processes to which the signal
15070 If a negative @var{pid} argument is desired as the first one, it
15071 should be preceded by @option{--}. However, as a common extension to
15072 @acronym{POSIX}, @option{--} is not required with @samp{kill
15073 -@var{signal} -@var{pid}}. The following commands are equivalent:
15082 The first form of the @command{kill} command succeeds if every @var{pid}
15083 argument specifies at least one process that the signal was sent to.
15085 The second form of the @command{kill} command lists signal information.
15086 Either the @option{-l} or @option{--list} option, or the @option{-t}
15087 or @option{--table} option must be specified. Without any
15088 @var{signal} argument, all supported signals are listed. The output
15089 of @option{-l} or @option{--list} is a list of the signal names, one
15090 per line; if @var{signal} is already a name, the signal number is
15091 printed instead. The output of @option{-t} or @option{--table} is a
15092 table of signal numbers, names, and descriptions. This form of the
15093 @command{kill} command succeeds if all @var{signal} arguments are valid
15094 and if there is no output error.
15096 The @command{kill} command also supports the @option{--help} and
15097 @option{--version} options. @xref{Common options}.
15099 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15100 number like @samp{1}, or an exit status of a process terminated by the
15101 signal. A signal name can be given in canonical form or prefixed by
15102 @samp{SIG}. The case of the letters is ignored, except for the
15103 @option{-@var{signal}} option which must use upper case to avoid
15104 ambiguity with lower case option letters. For a list of supported
15105 signal names and numbers see @xref{Signal specifications}.
15110 @cindex delaying commands
15111 @cindex commands for delaying
15113 @c Perhaps @command{wait} or other commands should be described here also?
15116 * sleep invocation:: Delay for a specified time.
15120 @node sleep invocation
15121 @section @command{sleep}: Delay for a specified time
15124 @cindex delay for a specified time
15126 @command{sleep} pauses for an amount of time specified by the sum of
15127 the values of the command line arguments.
15131 sleep @var{number}[smhd]@dots{}
15135 Each argument is a number followed by an optional unit; the default
15136 is seconds. The units are:
15149 Historical implementations of @command{sleep} have required that
15150 @var{number} be an integer, and only accepted a single argument
15151 without a suffix. However, GNU @command{sleep} accepts
15152 arbitrary floating point numbers (using a period before any fractional
15155 The only options are @option{--help} and @option{--version}. @xref{Common
15158 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15159 @mayConflictWithShellBuiltIn{sleep}
15164 @node Numeric operations
15165 @chapter Numeric operations
15167 @cindex numeric operations
15168 These programs do numerically-related operations.
15171 * factor invocation:: Show factors of numbers.
15172 * seq invocation:: Print sequences of numbers.
15176 @node factor invocation
15177 @section @command{factor}: Print prime factors
15180 @cindex prime factors
15182 @command{factor} prints prime factors. Synopses:
15185 factor [@var{number}]@dots{}
15186 factor @var{option}
15189 If no @var{number} is specified on the command line, @command{factor} reads
15190 numbers from standard input, delimited by newlines, tabs, or spaces.
15192 The @command{factor} command supports only a small number of options:
15196 Print a short help on standard output, then exit without further
15200 Print the program version on standard output, then exit without further
15204 Factoring the product of the eighth and ninth Mersenne primes
15205 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15208 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15209 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15210 4951760154835678088235319297: 2147483647 2305843009213693951
15214 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15215 about 20 seconds on the same machine.
15217 Factoring large prime numbers is, in general, hard. The Pollard Rho
15218 algorithm used by @command{factor} is particularly effective for
15219 numbers with relatively small factors. If you wish to factor large
15220 numbers which do not have small factors (for example, numbers which
15221 are the product of two large primes), other methods are far better.
15223 If @command{factor} is built without using GNU MP, only
15224 single-precision arithmetic is available, and so large numbers
15225 (typically @math{2^{64}} and above) will not be supported. The single-precision
15226 code uses an algorithm which is designed for factoring smaller
15232 @node seq invocation
15233 @section @command{seq}: Print numeric sequences
15236 @cindex numeric sequences
15237 @cindex sequence of numbers
15239 @command{seq} prints a sequence of numbers to standard output. Synopses:
15242 seq [@var{option}]@dots{} @var{last}
15243 seq [@var{option}]@dots{} @var{first} @var{last}
15244 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15247 @command{seq} prints the numbers from @var{first} to @var{last} by
15248 @var{increment}. By default, each number is printed on a separate line.
15249 When @var{increment} is not specified, it defaults to @samp{1},
15250 even when @var{first} is larger than @var{last}.
15251 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15252 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15253 Floating-point numbers
15254 may be specified (using a period before any fractional digits).
15256 The program accepts the following options. Also see @ref{Common options}.
15257 Options must precede operands.
15260 @item -f @var{format}
15261 @itemx --format=@var{format}
15262 @opindex -f @var{format}
15263 @opindex --format=@var{format}
15264 @cindex formatting of numbers in @command{seq}
15265 Print all numbers using @var{format}.
15266 @var{format} must contain exactly one of the @samp{printf}-style
15267 floating point conversion specifications @samp{%a}, @samp{%e},
15268 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15269 The @samp{%} may be followed by zero or more flags taken from the set
15270 @samp{-+#0 '}, then an optional width containing one or more digits,
15271 then an optional precision consisting of a @samp{.} followed by zero
15272 or more digits. @var{format} may also contain any number of @samp{%%}
15273 conversion specifications. All conversion specifications have the
15274 same meaning as with @samp{printf}.
15276 The default format is derived from @var{first}, @var{step}, and
15277 @var{last}. If these all use a fixed point decimal representation,
15278 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15279 precision that can represent the output numbers exactly. Otherwise,
15280 the default format is @samp{%g}.
15282 @item -s @var{string}
15283 @itemx --separator=@var{string}
15284 @cindex separator for numbers in @command{seq}
15285 Separate numbers with @var{string}; default is a newline.
15286 The output always terminates with a newline.
15289 @itemx --equal-width
15290 Print all numbers with the same width, by padding with leading zeros.
15291 @var{first}, @var{step}, and @var{last} should all use a fixed point
15292 decimal representation.
15293 (To have other kinds of padding, use @option{--format}).
15297 You can get finer-grained control over output with @option{-f}:
15300 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15306 If you want hexadecimal integer output, you can use @command{printf}
15307 to perform the conversion:
15310 $ printf '%x\n' `seq 1048575 1024 1050623`
15316 For very long lists of numbers, use xargs to avoid
15317 system limitations on the length of an argument list:
15320 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15326 To generate octal output, use the printf @code{%o} format instead
15329 On most systems, seq can produce whole-number output for values up to
15330 at least @math{2^{53}}. Larger integers are approximated. The details
15331 differ depending on your floating-point implementation, but a common
15332 case is that @command{seq} works with integers through @math{2^{64}},
15333 and larger integers may not be numerically correct:
15336 $ seq 18446744073709551616 1 18446744073709551618
15337 18446744073709551616
15338 18446744073709551616
15339 18446744073709551618
15342 Be careful when using @command{seq} with outlandish values: otherwise
15343 you may see surprising results, as @command{seq} uses floating point
15344 internally. For example, on the x86 platform, where the internal
15345 representation uses a 64-bit fraction, the command:
15348 seq 1 0.0000000000000000001 1.0000000000000000009
15351 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15356 @node File permissions
15357 @chapter File permissions
15360 @include getdate.texi
15364 @node Opening the software toolbox
15365 @chapter Opening the Software Toolbox
15367 An earlier version of this chapter appeared in
15368 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15369 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15370 It was written by Arnold Robbins.
15373 * Toolbox introduction:: Toolbox introduction
15374 * I/O redirection:: I/O redirection
15375 * The who command:: The @command{who} command
15376 * The cut command:: The @command{cut} command
15377 * The sort command:: The @command{sort} command
15378 * The uniq command:: The @command{uniq} command
15379 * Putting the tools together:: Putting the tools together
15383 @node Toolbox introduction
15384 @unnumberedsec Toolbox Introduction
15386 This month's column is only peripherally related to the GNU Project, in
15387 that it describes a number of the GNU tools on your GNU/Linux system and how they
15388 might be used. What it's really about is the ``Software Tools'' philosophy
15389 of program development and usage.
15391 The software tools philosophy was an important and integral concept
15392 in the initial design and development of Unix (of which Linux and GNU are
15393 essentially clones). Unfortunately, in the modern day press of
15394 Internetworking and flashy GUIs, it seems to have fallen by the
15395 wayside. This is a shame, since it provides a powerful mental model
15396 for solving many kinds of problems.
15398 Many people carry a Swiss Army knife around in their pants pockets (or
15399 purse). A Swiss Army knife is a handy tool to have: it has several knife
15400 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15401 a number of other things on it. For the everyday, small miscellaneous jobs
15402 where you need a simple, general purpose tool, it's just the thing.
15404 On the other hand, an experienced carpenter doesn't build a house using
15405 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15406 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15407 exactly when and where to use each tool; you won't catch him hammering nails
15408 with the handle of his screwdriver.
15410 The Unix developers at Bell Labs were all professional programmers and trained
15411 computer scientists. They had found that while a one-size-fits-all program
15412 might appeal to a user because there's only one program to use, in practice
15417 difficult to write,
15420 difficult to maintain and
15424 difficult to extend to meet new situations.
15427 Instead, they felt that programs should be specialized tools. In short, each
15428 program ``should do one thing well.'' No more and no less. Such programs are
15429 simpler to design, write, and get right---they only do one thing.
15431 Furthermore, they found that with the right machinery for hooking programs
15432 together, that the whole was greater than the sum of the parts. By combining
15433 several special purpose programs, you could accomplish a specific task
15434 that none of the programs was designed for, and accomplish it much more
15435 quickly and easily than if you had to write a special purpose program.
15436 We will see some (classic) examples of this further on in the column.
15437 (An important additional point was that, if necessary, take a detour
15438 and build any software tools you may need first, if you don't already
15439 have something appropriate in the toolbox.)
15441 @node I/O redirection
15442 @unnumberedsec I/O Redirection
15444 Hopefully, you are familiar with the basics of I/O redirection in the
15445 shell, in particular the concepts of ``standard input,'' ``standard output,''
15446 and ``standard error''. Briefly, ``standard input'' is a data source, where
15447 data comes from. A program should not need to either know or care if the
15448 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15449 card reader. Similarly, ``standard output'' is a data sink, where data goes
15450 to. The program should neither know nor care where this might be.
15451 Programs that only read their standard input, do something to the data,
15452 and then send it on, are called @dfn{filters}, by analogy to filters in a
15455 With the Unix shell, it's very easy to set up data pipelines:
15458 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15461 We start out by creating the raw data; each filter applies some successive
15462 transformation to the data, until by the time it comes out of the pipeline,
15463 it is in the desired form.
15465 This is fine and good for standard input and standard output. Where does the
15466 standard error come in to play? Well, think about @command{filter1} in
15467 the pipeline above. What happens if it encounters an error in the data it
15468 sees? If it writes an error message to standard output, it will just
15469 disappear down the pipeline into @command{filter2}'s input, and the
15470 user will probably never see it. So programs need a place where they can send
15471 error messages so that the user will notice them. This is standard error,
15472 and it is usually connected to your console or window, even if you have
15473 redirected standard output of your program away from your screen.
15475 For filter programs to work together, the format of the data has to be
15476 agreed upon. The most straightforward and easiest format to use is simply
15477 lines of text. Unix data files are generally just streams of bytes, with
15478 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15479 conventionally called a ``newline'' in the Unix literature. (This is
15480 @code{'\n'} if you're a C programmer.) This is the format used by all
15481 the traditional filtering programs. (Many earlier operating systems
15482 had elaborate facilities and special purpose programs for managing
15483 binary data. Unix has always shied away from such things, under the
15484 philosophy that it's easiest to simply be able to view and edit your
15485 data with a text editor.)
15487 OK, enough introduction. Let's take a look at some of the tools, and then
15488 we'll see how to hook them together in interesting ways. In the following
15489 discussion, we will only present those command line options that interest
15490 us. As you should always do, double check your system documentation
15491 for the full story.
15493 @node The who command
15494 @unnumberedsec The @command{who} Command
15496 The first program is the @command{who} command. By itself, it generates a
15497 list of the users who are currently logged in. Although I'm writing
15498 this on a single-user system, we'll pretend that several people are
15503 @print{} arnold console Jan 22 19:57
15504 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15505 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15506 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15509 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15510 There are three people logged in, and I am logged in twice. On traditional
15511 Unix systems, user names are never more than eight characters long. This
15512 little bit of trivia will be useful later. The output of @command{who} is nice,
15513 but the data is not all that exciting.
15515 @node The cut command
15516 @unnumberedsec The @command{cut} Command
15518 The next program we'll look at is the @command{cut} command. This program
15519 cuts out columns or fields of input data. For example, we can tell it
15520 to print just the login name and full name from the @file{/etc/passwd}
15521 file. The @file{/etc/passwd} file has seven fields, separated by
15525 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15528 To get the first and fifth fields, we would use @command{cut} like this:
15531 $ cut -d: -f1,5 /etc/passwd
15532 @print{} root:Operator
15534 @print{} arnold:Arnold D. Robbins
15535 @print{} miriam:Miriam A. Robbins
15539 With the @option{-c} option, @command{cut} will cut out specific characters
15540 (i.e., columns) in the input lines. This is useful for input data
15541 that has fixed width fields, and does not have a field separator. For
15542 example, list the Monday dates for the current month:
15544 @c Is using cal ok? Looked at gcal, but I don't like it.
15555 @node The sort command
15556 @unnumberedsec The @command{sort} Command
15558 Next we'll look at the @command{sort} command. This is one of the most
15559 powerful commands on a Unix-style system; one that you will often find
15560 yourself using when setting up fancy data plumbing.
15563 command reads and sorts each file named on the command line. It then
15564 merges the sorted data and writes it to standard output. It will read
15565 standard input if no files are given on the command line (thus
15566 making it into a filter). The sort is based on the character collating
15567 sequence or based on user-supplied ordering criteria.
15570 @node The uniq command
15571 @unnumberedsec The @command{uniq} Command
15573 Finally (at least for now), we'll look at the @command{uniq} program. When
15574 sorting data, you will often end up with duplicate lines, lines that
15575 are identical. Usually, all you need is one instance of each line.
15576 This is where @command{uniq} comes in. The @command{uniq} program reads its
15577 standard input. It prints only one
15578 copy of each repeated line. It does have several options. Later on,
15579 we'll use the @option{-c} option, which prints each unique line, preceded
15580 by a count of the number of times that line occurred in the input.
15583 @node Putting the tools together
15584 @unnumberedsec Putting the Tools Together
15586 Now, let's suppose this is a large ISP server system with dozens of users
15587 logged in. The management wants the system administrator to write a program that will
15588 generate a sorted list of logged in users. Furthermore, even if a user
15589 is logged in multiple times, his or her name should only show up in the
15592 The administrator could sit down with the system documentation and write a C
15593 program that did this. It would take perhaps a couple of hundred lines
15594 of code and about two hours to write it, test it, and debug it.
15595 However, knowing the software toolbox, the administrator can instead start out
15596 by generating just a list of logged on users:
15606 Next, sort the list:
15609 $ who | cut -c1-8 | sort
15616 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15619 $ who | cut -c1-8 | sort | uniq
15625 The @command{sort} command actually has a @option{-u} option that does what
15626 @command{uniq} does. However, @command{uniq} has other uses for which one
15627 cannot substitute @samp{sort -u}.
15629 The administrator puts this pipeline into a shell script, and makes it available for
15630 all the users on the system (@samp{#} is the system administrator,
15631 or @code{root}, prompt):
15634 # cat > /usr/local/bin/listusers
15635 who | cut -c1-8 | sort | uniq
15637 # chmod +x /usr/local/bin/listusers
15640 There are four major points to note here. First, with just four
15641 programs, on one command line, the administrator was able to save about two
15642 hours worth of work. Furthermore, the shell pipeline is just about as
15643 efficient as the C program would be, and it is much more efficient in
15644 terms of programmer time. People time is much more expensive than
15645 computer time, and in our modern ``there's never enough time to do
15646 everything'' society, saving two hours of programmer time is no mean
15649 Second, it is also important to emphasize that with the
15650 @emph{combination} of the tools, it is possible to do a special
15651 purpose job never imagined by the authors of the individual programs.
15653 Third, it is also valuable to build up your pipeline in stages, as we did here.
15654 This allows you to view the data at each stage in the pipeline, which helps
15655 you acquire the confidence that you are indeed using these tools correctly.
15657 Finally, by bundling the pipeline in a shell script, other users can use
15658 your command, without having to remember the fancy plumbing you set up for
15659 them. In terms of how you run them, shell scripts and compiled programs are
15662 After the previous warm-up exercise, we'll look at two additional, more
15663 complicated pipelines. For them, we need to introduce two more tools.
15665 The first is the @command{tr} command, which stands for ``transliterate.''
15666 The @command{tr} command works on a character-by-character basis, changing
15667 characters. Normally it is used for things like mapping upper case to
15671 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15672 @print{} this example has mixed case!
15675 There are several options of interest:
15679 work on the complement of the listed characters, i.e.,
15680 operations apply to characters not in the given set
15683 delete characters in the first set from the output
15686 squeeze repeated characters in the output into just one character.
15689 We will be using all three options in a moment.
15691 The other command we'll look at is @command{comm}. The @command{comm}
15692 command takes two sorted input files as input data, and prints out the
15693 files' lines in three columns. The output columns are the data lines
15694 unique to the first file, the data lines unique to the second file, and
15695 the data lines that are common to both. The @option{-1}, @option{-2}, and
15696 @option{-3} command line options @emph{omit} the respective columns. (This is
15697 non-intuitive and takes a little getting used to.) For example:
15719 The file name @file{-} tells @command{comm} to read standard input
15720 instead of a regular file.
15722 Now we're ready to build a fancy pipeline. The first application is a word
15723 frequency counter. This helps an author determine if he or she is over-using
15726 The first step is to change the case of all the letters in our input file
15727 to one case. ``The'' and ``the'' are the same word when doing counting.
15730 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15733 The next step is to get rid of punctuation. Quoted words and unquoted words
15734 should be treated identically; it's easiest to just get the punctuation out of
15738 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15741 The second @command{tr} command operates on the complement of the listed
15742 characters, which are all the letters, the digits, the underscore, and
15743 the blank. The @samp{\n} represents the newline character; it has to
15744 be left alone. (The @acronym{ASCII} tab character should also be included for
15745 good measure in a production script.)
15747 At this point, we have data consisting of words separated by blank space.
15748 The words only contain alphanumeric characters (and the underscore). The
15749 next step is break the data apart so that we have one word per line. This
15750 makes the counting operation much easier, as we will see shortly.
15753 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15754 > tr -s ' ' '\n' | ...
15757 This command turns blanks into newlines. The @option{-s} option squeezes
15758 multiple newline characters in the output into just one. This helps us
15759 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15760 This is what the shell prints when it notices you haven't finished
15761 typing in all of a command.)
15763 We now have data consisting of one word per line, no punctuation, all one
15764 case. We're ready to count each word:
15767 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15768 > tr -s ' ' '\n' | sort | uniq -c | ...
15771 At this point, the data might look something like this:
15784 The output is sorted by word, not by count! What we want is the most
15785 frequently used words first. Fortunately, this is easy to accomplish,
15786 with the help of two more @command{sort} options:
15790 do a numeric sort, not a textual one
15793 reverse the order of the sort
15796 The final pipeline looks like this:
15799 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15800 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15809 Whew! That's a lot to digest. Yet, the same principles apply. With six
15810 commands, on two lines (really one long one split for convenience), we've
15811 created a program that does something interesting and useful, in much
15812 less time than we could have written a C program to do the same thing.
15814 A minor modification to the above pipeline can give us a simple spelling
15815 checker! To determine if you've spelled a word correctly, all you have to
15816 do is look it up in a dictionary. If it is not there, then chances are
15817 that your spelling is incorrect. So, we need a dictionary.
15818 The conventional location for a dictionary is @file{/usr/dict/words}.
15819 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15820 revision of this article.}
15821 this is a sorted, 45,402 word dictionary.
15823 Now, how to compare our file with the dictionary? As before, we generate
15824 a sorted list of words, one per line:
15827 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15828 > tr -s ' ' '\n' | sort -u | ...
15831 Now, all we need is a list of words that are @emph{not} in the
15832 dictionary. Here is where the @command{comm} command comes in.
15835 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15836 > tr -s ' ' '\n' | sort -u |
15837 > comm -23 - /usr/dict/words
15840 The @option{-2} and @option{-3} options eliminate lines that are only in the
15841 dictionary (the second file), and lines that are in both files. Lines
15842 only in the first file (standard input, our stream of words), are
15843 words that are not in the dictionary. These are likely candidates for
15844 spelling errors. This pipeline was the first cut at a production
15845 spelling checker on Unix.
15847 There are some other tools that deserve brief mention.
15851 search files for text that matches a regular expression
15854 count lines, words, characters
15857 a T-fitting for data pipes, copies data to files and to standard output
15860 the stream editor, an advanced tool
15863 a data manipulation language, another advanced tool
15866 The software tools philosophy also espoused the following bit of
15867 advice: ``Let someone else do the hard part.'' This means, take
15868 something that gives you most of what you need, and then massage it the
15869 rest of the way until it's in the form that you want.
15875 Each program should do one thing well. No more, no less.
15878 Combining programs with appropriate plumbing leads to results where
15879 the whole is greater than the sum of the parts. It also leads to novel
15880 uses of programs that the authors might never have imagined.
15883 Programs should never print extraneous header or trailer data, since these
15884 could get sent on down a pipeline. (A point we didn't mention earlier.)
15887 Let someone else do the hard part.
15890 Know your toolbox! Use each program appropriately. If you don't have an
15891 appropriate tool, build one.
15894 As of this writing, all the programs we've discussed are available via
15895 anonymous @command{ftp} from: @*
15896 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
15897 be more recent versions available now.)
15899 None of what I have presented in this column is new. The Software Tools
15900 philosophy was first introduced in the book @cite{Software Tools}, by
15901 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
15902 This book showed how to write and use software tools. It was written in
15903 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
15904 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
15905 was. The last chapter presented a @command{ratfor} to FORTRAN
15906 processor, written in @command{ratfor}. @command{ratfor} looks an awful
15907 lot like C; if you know C, you won't have any problem following the
15910 In 1981, the book was updated and made available as @cite{Software Tools
15911 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
15912 still in print and are well worth
15913 reading if you're a programmer. They certainly made a major change in
15914 how I view programming.
15916 The programs in both books are available from
15917 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
15918 For a number of years, there was an active
15919 Software Tools Users Group, whose members had ported the original
15920 @command{ratfor} programs to essentially every computer system with a
15921 FORTRAN compiler. The popularity of the group waned in the middle 1980s
15922 as Unix began to spread beyond universities.
15924 With the current proliferation of GNU code and other clones of Unix programs,
15925 these programs now receive little attention; modern C versions are
15926 much more efficient and do more than these programs do. Nevertheless, as
15927 exposition of good programming style, and evangelism for a still-valuable
15928 philosophy, these books are unparalleled, and I recommend them highly.
15930 Acknowledgment: I would like to express my gratitude to Brian Kernighan
15931 of Bell Labs, the original Software Toolsmith, for reviewing this column.
15933 @node GNU Free Documentation License
15934 @appendix GNU Free Documentation License
15938 @node Concept index
15945 @c Local variables:
15946 @c texinfo-column-for-description: 32