3 @setfilename coreutils.info
4 @settitle @sc{gnu} Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options. Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * realpath: (coreutils)readpath invocation. Print resolved file names.
98 * rm: (coreutils)rm invocation. Remove files.
99 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
100 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
101 * seq: (coreutils)seq invocation. Print numeric sequences
102 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
103 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
104 * shred: (coreutils)shred invocation. Remove files more securely.
105 * shuf: (coreutils)shuf invocation. Shuffling text files.
106 * sleep: (coreutils)sleep invocation. Delay for a specified time.
107 * sort: (coreutils)sort invocation. Sort text files.
108 * split: (coreutils)split invocation. Split into pieces.
109 * stat: (coreutils)stat invocation. Report file(system) status.
110 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
111 * stty: (coreutils)stty invocation. Print/change terminal settings.
112 * su: (coreutils)su invocation. Modify user and group ID.
113 * sum: (coreutils)sum invocation. Print traditional checksum.
114 * sync: (coreutils)sync invocation. Synchronize memory and disk.
115 * tac: (coreutils)tac invocation. Reverse files.
116 * tail: (coreutils)tail invocation. Output the last part of files.
117 * tee: (coreutils)tee invocation. Redirect to multiple files.
118 * test: (coreutils)test invocation. File/string tests.
119 * timeout: (coreutils)timeout invocation. Run with time limit.
120 * touch: (coreutils)touch invocation. Change file timestamps.
121 * tr: (coreutils)tr invocation. Translate characters.
122 * true: (coreutils)true invocation. Do nothing, successfully.
123 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
124 * tsort: (coreutils)tsort invocation. Topological sort.
125 * tty: (coreutils)tty invocation. Print terminal name.
126 * uname: (coreutils)uname invocation. Print system information.
127 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
128 * uniq: (coreutils)uniq invocation. Uniquify files.
129 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
130 * uptime: (coreutils)uptime invocation. Print uptime and load.
131 * users: (coreutils)users invocation. Print current user names.
132 * vdir: (coreutils)vdir invocation. List directories verbosely.
133 * wc: (coreutils)wc invocation. Line, word, and byte counts.
134 * who: (coreutils)who invocation. Print who is logged in.
135 * whoami: (coreutils)whoami invocation. Print effective user ID.
136 * yes: (coreutils)yes invocation. Print a string indefinitely.
140 This manual documents version @value{VERSION} of the @sc{gnu} core
141 utilities, including the standard programs for text and file manipulation.
143 Copyright @copyright{} 1994-2012 Free Software Foundation, Inc.
146 Permission is granted to copy, distribute and/or modify this document
147 under the terms of the GNU Free Documentation License, Version 1.3 or
148 any later version published by the Free Software Foundation; with no
149 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
150 Texts. A copy of the license is included in the section entitled ``GNU
151 Free Documentation License''.
156 @title @sc{gnu} @code{Coreutils}
157 @subtitle Core GNU utilities
158 @subtitle for version @value{VERSION}, @value{UPDATED}
159 @author David MacKenzie et al.
162 @vskip 0pt plus 1filll
175 @cindex core utilities
176 @cindex text utilities
177 @cindex shell utilities
178 @cindex file utilities
181 * Introduction:: Caveats, overview, and authors
182 * Common options:: Common options
183 * Output of entire files:: cat tac nl od base64
184 * Formatting file contents:: fmt pr fold
185 * Output of parts of files:: head tail split csplit
186 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
187 * Operating on sorted files:: sort shuf uniq comm ptx tsort
188 * Operating on fields:: cut paste join
189 * Operating on characters:: tr expand unexpand
190 * Directory listing:: ls dir vdir dircolors
191 * Basic operations:: cp dd install mv rm shred
192 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
193 * Changing file attributes:: chgrp chmod chown touch
194 * Disk usage:: df du stat sync truncate
195 * Printing text:: echo printf yes
196 * Conditions:: false true test expr
198 * File name manipulation:: dirname basename pathchk mktemp realpath
199 * Working context:: pwd stty printenv tty
200 * User information:: id logname whoami groups users who
201 * System context:: date arch nproc uname hostname hostid uptime
202 * SELinux context:: chcon runcon
203 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
204 * Process control:: kill
206 * Numeric operations:: factor seq
207 * File permissions:: Access modes
208 * Date input formats:: Specifying date strings
209 * Opening the software toolbox:: The software tools philosophy
210 * GNU Free Documentation License:: Copying and sharing this manual
211 * Concept index:: General index
214 --- The Detailed Node Listing ---
218 * Exit status:: Indicating program success or failure
219 * Backup options:: Backup options
220 * Block size:: Block size
221 * Floating point:: Floating point number representation
222 * Signal specifications:: Specifying signals
223 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
224 * Random sources:: Sources of random data
225 * Target directory:: Target directory
226 * Trailing slashes:: Trailing slashes
227 * Traversing symlinks:: Traversing symlinks to directories
228 * Treating / specially:: Treating / specially
229 * Standards conformance:: Standards conformance
231 Output of entire files
233 * cat invocation:: Concatenate and write files
234 * tac invocation:: Concatenate and write files in reverse
235 * nl invocation:: Number lines and write files
236 * od invocation:: Write files in octal or other formats
237 * base64 invocation:: Transform data into printable data
239 Formatting file contents
241 * fmt invocation:: Reformat paragraph text
242 * pr invocation:: Paginate or columnate files for printing
243 * fold invocation:: Wrap input lines to fit in specified width
245 Output of parts of files
247 * head invocation:: Output the first part of files
248 * tail invocation:: Output the last part of files
249 * split invocation:: Split a file into fixed-size pieces
250 * csplit invocation:: Split a file into context-determined pieces
254 * wc invocation:: Print newline, word, and byte counts
255 * sum invocation:: Print checksum and block counts
256 * cksum invocation:: Print CRC checksum and byte counts
257 * md5sum invocation:: Print or check MD5 digests
258 * sha1sum invocation:: Print or check SHA-1 digests
259 * sha2 utilities:: Print or check SHA-2 digests
261 Operating on sorted files
263 * sort invocation:: Sort text files
264 * shuf invocation:: Shuffle text files
265 * uniq invocation:: Uniquify files
266 * comm invocation:: Compare two sorted files line by line
267 * ptx invocation:: Produce a permuted index of file contents
268 * tsort invocation:: Topological sort
270 @command{ptx}: Produce permuted indexes
272 * General options in ptx:: Options which affect general program behavior
273 * Charset selection in ptx:: Underlying character set considerations
274 * Input processing in ptx:: Input fields, contexts, and keyword selection
275 * Output formatting in ptx:: Types of output format, and sizing the fields
276 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
280 * cut invocation:: Print selected parts of lines
281 * paste invocation:: Merge lines of files
282 * join invocation:: Join lines on a common field
284 Operating on characters
286 * tr invocation:: Translate, squeeze, and/or delete characters
287 * expand invocation:: Convert tabs to spaces
288 * unexpand invocation:: Convert spaces to tabs
290 @command{tr}: Translate, squeeze, and/or delete characters
292 * Character sets:: Specifying sets of characters
293 * Translating:: Changing one set of characters to another
294 * Squeezing:: Squeezing repeats and deleting
298 * ls invocation:: List directory contents
299 * dir invocation:: Briefly list directory contents
300 * vdir invocation:: Verbosely list directory contents
301 * dircolors invocation:: Color setup for @command{ls}
303 @command{ls}: List directory contents
305 * Which files are listed:: Which files are listed
306 * What information is listed:: What information is listed
307 * Sorting the output:: Sorting the output
308 * Details about version sort:: More details about version sort
309 * General output formatting:: General output formatting
310 * Formatting the file names:: Formatting the file names
314 * cp invocation:: Copy files and directories
315 * dd invocation:: Convert and copy a file
316 * install invocation:: Copy files and set attributes
317 * mv invocation:: Move (rename) files
318 * rm invocation:: Remove files or directories
319 * shred invocation:: Remove files more securely
323 * link invocation:: Make a hard link via the link syscall
324 * ln invocation:: Make links between files
325 * mkdir invocation:: Make directories
326 * mkfifo invocation:: Make FIFOs (named pipes)
327 * mknod invocation:: Make block or character special files
328 * readlink invocation:: Print value of a symlink or canonical file name
329 * rmdir invocation:: Remove empty directories
330 * unlink invocation:: Remove files via unlink syscall
332 Changing file attributes
334 * chown invocation:: Change file owner and group
335 * chgrp invocation:: Change group ownership
336 * chmod invocation:: Change access permissions
337 * touch invocation:: Change file timestamps
341 * df invocation:: Report file system disk space usage
342 * du invocation:: Estimate file space usage
343 * stat invocation:: Report file or file system status
344 * sync invocation:: Synchronize data on disk with memory
345 * truncate invocation:: Shrink or extend the size of a file
349 * echo invocation:: Print a line of text
350 * printf invocation:: Format and print data
351 * yes invocation:: Print a string until interrupted
355 * false invocation:: Do nothing, unsuccessfully
356 * true invocation:: Do nothing, successfully
357 * test invocation:: Check file types and compare values
358 * expr invocation:: Evaluate expressions
360 @command{test}: Check file types and compare values
362 * File type tests:: File type tests
363 * Access permission tests:: Access permission tests
364 * File characteristic tests:: File characteristic tests
365 * String tests:: String tests
366 * Numeric tests:: Numeric tests
368 @command{expr}: Evaluate expression
370 * String expressions:: + : match substr index length
371 * Numeric expressions:: + - * / %
372 * Relations for expr:: | & < <= = == != >= >
373 * Examples of expr:: Examples of using @command{expr}
377 * tee invocation:: Redirect output to multiple files or processes
379 File name manipulation
381 * basename invocation:: Strip directory and suffix from a file name
382 * dirname invocation:: Strip last file name component
383 * pathchk invocation:: Check file name validity and portability
384 * mktemp invocation:: Create temporary file or directory
385 * realpath invocation:: Print resolved file names
389 * pwd invocation:: Print working directory
390 * stty invocation:: Print or change terminal characteristics
391 * printenv invocation:: Print all or some environment variables
392 * tty invocation:: Print file name of terminal on standard input
394 @command{stty}: Print or change terminal characteristics
396 * Control:: Control settings
397 * Input:: Input settings
398 * Output:: Output settings
399 * Local:: Local settings
400 * Combination:: Combination settings
401 * Characters:: Special characters
402 * Special:: Special settings
406 * id invocation:: Print user identity
407 * logname invocation:: Print current login name
408 * whoami invocation:: Print effective user ID
409 * groups invocation:: Print group names a user is in
410 * users invocation:: Print login names of users currently logged in
411 * who invocation:: Print who is currently logged in
415 * arch invocation:: Print machine hardware name
416 * date invocation:: Print or set system date and time
417 * nproc invocation:: Print the number of processors
418 * uname invocation:: Print system information
419 * hostname invocation:: Print or set system name
420 * hostid invocation:: Print numeric host identifier
421 * uptime invocation:: Print system uptime and load
423 @command{date}: Print or set system date and time
425 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
426 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
427 * Literal conversion specifiers:: %[%nt]
428 * Padding and other flags:: Pad with zeros, spaces, etc.
429 * Setting the time:: Changing the system clock
430 * Options for date:: Instead of the current time
431 * Date input formats:: Specifying date strings
432 * Examples of date:: Examples
436 * chcon invocation:: Change SELinux context of file
437 * runcon invocation:: Run a command in specified SELinux context
439 Modified command invocation
441 * chroot invocation:: Run a command with a different root directory
442 * env invocation:: Run a command in a modified environment
443 * nice invocation:: Run a command with modified niceness
444 * nohup invocation:: Run a command immune to hangups
445 * stdbuf invocation:: Run a command with modified I/O buffering
446 * su invocation:: Run a command with substitute user and group ID
447 * timeout invocation:: Run a command with a time limit
451 * kill invocation:: Sending a signal to processes.
455 * sleep invocation:: Delay for a specified time
459 * factor invocation:: Print prime factors
460 * seq invocation:: Print numeric sequences
464 * Mode Structure:: Structure of file mode bits
465 * Symbolic Modes:: Mnemonic representation of file mode bits
466 * Numeric Modes:: File mode bits as octal numbers
467 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
471 * General date syntax:: Common rules
472 * Calendar date items:: 19 Dec 1994
473 * Time of day items:: 9:20pm
474 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
475 * Day of week items:: Monday and others
476 * Relative items in date strings:: next tuesday, 2 years ago
477 * Pure numbers in date strings:: 19931219, 1440
478 * Seconds since the Epoch:: @@1078100502
479 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
480 * Authors of parse_datetime:: Bellovin, Eggert, Salz, Berets, et al
482 Opening the software toolbox
484 * Toolbox introduction:: Toolbox introduction
485 * I/O redirection:: I/O redirection
486 * The who command:: The @command{who} command
487 * The cut command:: The @command{cut} command
488 * The sort command:: The @command{sort} command
489 * The uniq command:: The @command{uniq} command
490 * Putting the tools together:: Putting the tools together
494 * GNU Free Documentation License:: Copying and sharing this manual
501 @chapter Introduction
503 This manual is a work in progress: many sections make no attempt to explain
504 basic concepts in a way suitable for novices. Thus, if you are interested,
505 please get involved in improving this manual. The entire @sc{gnu} community
508 @cindex @acronym{POSIX}
509 The @sc{gnu} utilities documented here are mostly compatible with the
510 @acronym{POSIX} standard.
511 @cindex bugs, reporting
512 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
513 to include the version number, machine architecture, input files, and
514 any other information needed to reproduce the bug: your input, what you
515 expected, what you got, and why it is wrong. Diffs are welcome, but
516 please include a description of the problem as well, since this is
517 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
523 @cindex MacKenzie, D.
526 This manual was originally derived from the Unix man pages in the
527 distributions, which were written by David MacKenzie and updated by Jim
528 Meyering. What you are reading now is the authoritative documentation
529 for these utilities; the man pages are no longer being maintained. The
530 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
531 Pinard did the initial conversion to Texinfo format. Karl Berry did the
532 indexing, some reorganization, and editing of the results. Brian
533 Youmans of the Free Software Foundation office staff combined the
534 manuals for textutils, fileutils, and sh-utils to produce the present
535 omnibus manual. Richard Stallman contributed his usual invaluable
536 insights to the overall process.
539 @chapter Common options
543 @itemx @w{@kbd{--backup}[=@var{method}]}
546 @vindex VERSION_CONTROL
547 @cindex backups, making
548 @xref{Backup options}.
549 Make a backup of each file that would otherwise be overwritten or removed.
552 @macro optBackupSuffix
553 @item -S @var{suffix}
554 @itemx --suffix=@var{suffix}
557 Append @var{suffix} to each backup file made with @option{-b}.
558 @xref{Backup options}.
561 @macro optTargetDirectory
562 @item -t @var{directory}
563 @itemx @w{@kbd{--target-directory}=@var{directory}}
565 @opindex --target-directory
566 @cindex target directory
567 @cindex destination directory
568 Specify the destination @var{directory}.
569 @xref{Target directory}.
572 @macro optNoTargetDirectory
574 @itemx --no-target-directory
576 @opindex --no-target-directory
577 @cindex target directory
578 @cindex destination directory
579 Do not treat the last operand specially when it is a directory or a
580 symbolic link to a directory. @xref{Target directory}.
588 @cindex output @sc{nul}-byte-terminated lines
589 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
590 rather than a newline. This option enables other programs to parse the
591 output of @command{\cmd\} even when that output would contain data
592 with embedded newlines.
599 Append an SI-style abbreviation to each size, such as @samp{M} for
600 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
601 1,000,000 bytes. This option is equivalent to
602 @option{--block-size=si}. Use the @option{-h} or
603 @option{--human-readable} option if
604 you prefer powers of 1024.
607 @macro optHumanReadable
609 @itemx --human-readable
611 @opindex --human-readable
612 @cindex human-readable output
613 Append a size letter to each size, such as @samp{M} for mebibytes.
614 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
615 This option is equivalent to @option{--block-size=human-readable}.
616 Use the @option{--si} option if you prefer powers of 1000.
619 @macro optStripTrailingSlashes
620 @itemx @w{@kbd{--strip-trailing-slashes}}
621 @opindex --strip-trailing-slashes
622 @cindex stripping trailing slashes
623 Remove any trailing slashes from each @var{source} argument.
624 @xref{Trailing slashes}.
627 @macro mayConflictWithShellBuiltIn{cmd}
628 @cindex conflicts with shell built-ins
629 @cindex built-in shell commands, conflicts with
630 Due to shell aliases and built-in @command{\cmd\} functions, using an
631 unadorned @command{\cmd\} interactively or in a script may get you
632 different functionality than that described here. Invoke it via
633 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
638 @macro multiplierSuffixes{varName}
639 @var{\varName\} may be, or may be an integer optionally followed by,
640 one of the following multiplicative suffixes:
642 @samp{b} => 512 ("blocks")
643 @samp{KB} => 1000 (KiloBytes)
644 @samp{K} => 1024 (KibiBytes)
645 @samp{MB} => 1000*1000 (MegaBytes)
646 @samp{M} => 1024*1024 (MebiBytes)
647 @samp{GB} => 1000*1000*1000 (GigaBytes)
648 @samp{G} => 1024*1024*1024 (GibiBytes)
650 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
653 @c FIXME: same as above, but no ``blocks'' line.
654 @macro multiplierSuffixesNoBlocks{varName}
655 @var{\varName\} may be, or may be an integer optionally followed by,
656 one of the following multiplicative suffixes:
658 @samp{KB} => 1000 (KiloBytes)
659 @samp{K} => 1024 (KibiBytes)
660 @samp{MB} => 1000*1000 (MegaBytes)
661 @samp{M} => 1024*1024 (MebiBytes)
662 @samp{GB} => 1000*1000*1000 (GigaBytes)
663 @samp{G} => 1024*1024*1024 (GibiBytes)
665 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
668 @cindex common options
670 Certain options are available in all of these programs. Rather than
671 writing identical descriptions for each of the programs, they are
672 described here. (In fact, every @sc{gnu} program accepts (or should accept)
675 @vindex POSIXLY_CORRECT
676 Normally options and operands can appear in any order, and programs act
677 as if all the options appear before any operands. For example,
678 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
679 @samp{:} is an option-argument of @option{-t}. However, if the
680 @env{POSIXLY_CORRECT} environment variable is set, options must appear
681 before operands, unless otherwise specified for a particular command.
683 A few programs can usefully have trailing operands with leading
684 @samp{-}. With such a program, options must precede operands even if
685 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
686 program description. For example, the @command{env} command's options
687 must appear before its operands, since in some cases the operands
688 specify a command that itself contains options.
690 Most programs that accept long options recognize unambiguous
691 abbreviations of those options. For example, @samp{rmdir
692 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
693 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
694 @samp{ls --h}, are identified as such.
696 Some of these programs recognize the @option{--help} and @option{--version}
697 options only when one of them is the sole command line argument. For
698 these programs, abbreviations of the long options are not always recognized.
705 Print a usage message listing all available options, then exit successfully.
709 @cindex version number, finding
710 Print the version number, then exit successfully.
714 @cindex option delimiter
715 Delimit the option list. Later arguments, if any, are treated as
716 operands even if they begin with @samp{-}. For example, @samp{sort --
717 -r} reads from the file named @file{-r}.
721 @cindex standard input
722 @cindex standard output
723 A single @samp{-} operand is not really an option, though it looks like one. It
724 stands for standard input, or for standard output if that is clear from
725 the context. For example, @samp{sort -} reads from standard input,
726 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
727 extra copy of its input to standard output. Unless otherwise
728 specified, @samp{-} can appear as any operand that requires a file
732 * Exit status:: Indicating program success or failure.
733 * Backup options:: -b -S, in some programs.
734 * Block size:: BLOCK_SIZE and --block-size, in some programs.
735 * Floating point:: Floating point number representation.
736 * Signal specifications:: Specifying signals using the --signal option.
737 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
738 * Random sources:: --random-source, in some programs.
739 * Target directory:: Specifying a target directory, in some programs.
740 * Trailing slashes:: --strip-trailing-slashes, in some programs.
741 * Traversing symlinks:: -H, -L, or -P, in some programs.
742 * Treating / specially:: --preserve-root and --no-preserve-root.
743 * Special built-in utilities:: @command{break}, @command{:}, @dots{}
744 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
752 An exit status of zero indicates success,
753 and a nonzero value indicates failure.
756 Nearly every command invocation yields an integral @dfn{exit status}
757 that can be used to change how other commands work.
758 For the vast majority of commands, an exit status of zero indicates
759 success. Failure is indicated by a nonzero value---typically
760 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
761 requires only that it be nonzero.
763 However, some of the programs documented here do produce
764 other exit status values and a few associate different
765 meanings with the values @samp{0} and @samp{1}.
766 Here are some of the exceptions:
767 @command{chroot}, @command{env}, @command{expr}, @command{nice},
768 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
769 @command{su}, @command{test}, @command{timeout}, @command{tty}.
773 @section Backup options
775 @cindex backup options
777 Some @sc{gnu} programs (at least @command{cp}, @command{install},
778 @command{ln}, and @command{mv}) optionally make backups of files
779 before writing new versions.
780 These options control the details of these backups. The options are also
781 briefly mentioned in the descriptions of the particular programs.
786 @itemx @w{@kbd{--backup}[=@var{method}]}
789 @vindex VERSION_CONTROL
790 @cindex backups, making
791 Make a backup of each file that would otherwise be overwritten or removed.
792 Without this option, the original versions are destroyed.
793 Use @var{method} to determine the type of backups to make.
794 When this option is used but @var{method} is not specified,
795 then the value of the @env{VERSION_CONTROL}
796 environment variable is used. And if @env{VERSION_CONTROL} is not set,
797 the default backup type is @samp{existing}.
799 Note that the short form of this option, @option{-b} does not accept any
800 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
802 @vindex version-control @r{Emacs variable}
803 This option corresponds to the Emacs variable @samp{version-control};
804 the values for @var{method} are the same as those used in Emacs.
805 This option also accepts more descriptive names.
806 The valid @var{method}s are (unique abbreviations are accepted):
811 @opindex none @r{backup method}
816 @opindex numbered @r{backup method}
817 Always make numbered backups.
821 @opindex existing @r{backup method}
822 Make numbered backups of files that already have them, simple backups
827 @opindex simple @r{backup method}
828 Always make simple backups. Please note @samp{never} is not to be
829 confused with @samp{none}.
833 @item -S @var{suffix}
834 @itemx --suffix=@var{suffix}
837 @cindex backup suffix
838 @vindex SIMPLE_BACKUP_SUFFIX
839 Append @var{suffix} to each backup file made with @option{-b}. If this
840 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
841 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
842 set, the default is @samp{~}, just as in Emacs.
851 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
852 @command{ls}) display sizes in ``blocks''. You can adjust the block size
853 and method of display to make sizes easier to read. The block size
854 used for display is independent of any file system block size.
855 Fractional block counts are rounded up to the nearest integer.
857 @opindex --block-size=@var{size}
860 @vindex DF_BLOCK_SIZE
861 @vindex DU_BLOCK_SIZE
862 @vindex LS_BLOCK_SIZE
863 @vindex POSIXLY_CORRECT@r{, and block size}
865 The default block size is chosen by examining the following environment
866 variables in turn; the first one that is set determines the block size.
871 This specifies the default block size for the @command{df} command.
872 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
873 @env{LS_BLOCK_SIZE} for @command{ls}.
876 This specifies the default block size for all three commands, if the
877 above command-specific environment variables are not set.
880 This specifies the default block size for all values that are normally
881 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
882 command-specific environment variables are set. Unlike the other
883 environment variables, @env{BLOCKSIZE} does not affect values that are
884 normally printed as byte counts, e.g., the file sizes contained in
887 @item POSIXLY_CORRECT
888 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
889 @env{BLOCKSIZE} is set, but this variable is set, the block size
894 If none of the above environment variables are set, the block size
895 currently defaults to 1024 bytes in most contexts, but this number may
896 change in the future. For @command{ls} file sizes, the block size
899 @cindex human-readable output
902 A block size specification can be a positive integer specifying the number
903 of bytes per block, or it can be @code{human-readable} or @code{si} to
904 select a human-readable format. Integers may be followed by suffixes
905 that are upward compatible with the
906 @uref{http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html, SI prefixes}
907 for decimal multiples and with the
908 @uref{http://physics.nist.gov/cuu/Units/binary.html, ISO/IEC 80000-13
909 (formerly IEC 60027-2) prefixes} for binary multiples.
911 With human-readable formats, output sizes are followed by a size letter
912 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
913 powers of 1024; @samp{M} stands for 1,048,576 bytes.
914 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
915 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
918 A block size specification preceded by @samp{'} causes output sizes to
919 be displayed with thousands separators. The @env{LC_NUMERIC} locale
920 specifies the thousands separator and grouping. For example, in an
921 American English locale, @samp{--block-size="'1kB"} would cause a size
922 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
923 locale, there is no thousands separator so a leading @samp{'} has no
926 An integer block size can be followed by a suffix to specify a
927 multiple of that size. A bare size letter,
928 or one followed by @samp{iB}, specifies
929 a multiple using powers of 1024. A size letter followed by @samp{B}
930 specifies powers of 1000 instead. For example, @samp{1M} and
931 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
932 equivalent to @samp{1000000}.
934 A plain suffix without a preceding integer acts as if @samp{1} were
935 prepended, except that it causes a size indication to be appended to
936 the output. For example, @samp{--block-size="kB"} displays 3000 as
939 The following suffixes are defined. Large sizes like @code{1Y}
940 may be rejected by your computer due to limitations of its arithmetic.
944 @cindex kilobyte, definition of
945 kilobyte: @math{10^3 = 1000}.
949 @cindex kibibyte, definition of
950 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
951 @samp{k} and the ISO/IEC 80000-13 prefix is @samp{Ki}, but tradition and
952 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
954 @cindex megabyte, definition of
955 megabyte: @math{10^6 = 1,000,000}.
958 @cindex mebibyte, definition of
959 mebibyte: @math{2^{20} = 1,048,576}.
961 @cindex gigabyte, definition of
962 gigabyte: @math{10^9 = 1,000,000,000}.
965 @cindex gibibyte, definition of
966 gibibyte: @math{2^{30} = 1,073,741,824}.
968 @cindex terabyte, definition of
969 terabyte: @math{10^{12} = 1,000,000,000,000}.
972 @cindex tebibyte, definition of
973 tebibyte: @math{2^{40} = 1,099,511,627,776}.
975 @cindex petabyte, definition of
976 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
979 @cindex pebibyte, definition of
980 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
982 @cindex exabyte, definition of
983 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
986 @cindex exbibyte, definition of
987 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
989 @cindex zettabyte, definition of
990 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
993 @math{2^{70} = 1,180,591,620,717,411,303,424}.
995 @cindex yottabyte, definition of
996 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
999 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
1004 @opindex --block-size
1005 @opindex --human-readable
1008 Block size defaults can be overridden by an explicit
1009 @option{--block-size=@var{size}} option. The @option{-k}
1010 option is equivalent to @option{--block-size=1K}, which
1011 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1012 set. The @option{-h} or @option{--human-readable} option is equivalent to
1013 @option{--block-size=human-readable}. The @option{--si} option is
1014 equivalent to @option{--block-size=si}.
1016 @node Floating point
1017 @section Floating point numbers
1018 @cindex floating point
1019 @cindex IEEE floating point
1021 Commands that accept or produce floating point numbers employ the
1022 floating point representation of the underlying system, and suffer
1023 from rounding error, overflow, and similar floating-point issues.
1024 Almost all modern systems use IEEE-754 floating point, and it is
1025 typically portable to assume IEEE-754 behavior these days. IEEE-754
1026 has positive and negative infinity, distinguishes positive from
1027 negative zero, and uses special values called NaNs to represent
1028 invalid computations such as dividing zero by itself. For more
1029 information, please see David Goldberg's paper
1030 @uref{http://@/www.validlab.com/@/goldberg/@/paper.pdf, What Every
1031 Computer Scientist Should Know About Floating-Point Arithmetic}.
1034 Commands that accept floating point numbers as options, operands or
1035 input use the standard C functions @code{strtod} and @code{strtold} to
1036 convert from text to floating point numbers. These floating point
1037 numbers therefore can use scientific notation like @code{1.0e-34} and
1038 @code{-10e100}. Modern C implementations also accept hexadecimal
1039 floating point numbers such as @code{-0x.ep-3}, which stands for
1040 @minus{}14/16 times @math{2^-3}, which equals @minus{}0.109375. The
1041 @env{LC_NUMERIC} locale determines the decimal-point character.
1042 @xref{Parsing of Floats,,, libc, The GNU C Library Reference Manual}.
1044 @node Signal specifications
1045 @section Signal specifications
1046 @cindex signals, specifying
1048 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1049 number like @samp{1}, or an exit status of a process terminated by the
1050 signal. A signal name can be given in canonical form or prefixed by
1051 @samp{SIG}. The case of the letters is ignored. The following signal names
1052 and numbers are supported on all @acronym{POSIX} compliant systems:
1058 2. Terminal interrupt.
1064 9. Kill (cannot be caught or ignored).
1072 Other supported signal names have system-dependent corresponding
1073 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1074 support the following signals:
1078 Access to an undefined portion of a memory object.
1080 Child process terminated, stopped, or continued.
1082 Continue executing, if stopped.
1084 Erroneous arithmetic operation.
1086 Illegal Instruction.
1088 Write on a pipe with no one to read it.
1090 Invalid memory reference.
1092 Stop executing (cannot be caught or ignored).
1096 Background process attempting read.
1098 Background process attempting write.
1100 High bandwidth data is available at a socket.
1102 User-defined signal 1.
1104 User-defined signal 2.
1108 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1109 also support the following signals:
1115 Profiling timer expired.
1119 Trace/breakpoint trap.
1121 Virtual timer expired.
1123 CPU time limit exceeded.
1125 File size limit exceeded.
1129 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1130 also support at least eight real-time signals called @samp{RTMIN},
1131 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1133 @node Disambiguating names and IDs
1134 @section chown and chgrp: Disambiguating user names and IDs
1135 @cindex user names, disambiguating
1136 @cindex user IDs, disambiguating
1137 @cindex group names, disambiguating
1138 @cindex group IDs, disambiguating
1139 @cindex disambiguating group names and IDs
1141 Since the @var{owner} and @var{group} arguments to @command{chown} and
1142 @command{chgrp} may be specified as names or numeric IDs, there is an
1144 What if a user or group @emph{name} is a string of digits?
1145 @footnote{Using a number as a user name is common in some environments.}
1146 Should the command interpret it as a user name or as an ID?
1147 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1148 first attempt to resolve the specified string as a name, and
1149 only once that fails, then try to interpret it as an ID.
1150 This is troublesome when you want to specify a numeric ID, say 42,
1151 and it must work even in a pathological situation where
1152 @samp{42} is a user name that maps to some other user ID, say 1000.
1153 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1154 1000---not what you intended.
1156 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1157 that at the same time may result in a significant performance improvement
1158 by eliminating a database look-up.
1159 Simply precede each numeric user ID and/or group ID with a @samp{+},
1160 in order to force its interpretation as an integer:
1164 chgrp +$numeric_group_id another-file
1168 GNU @command{chown} and @command{chgrp}
1169 skip the name look-up process for each @samp{+}-prefixed string,
1170 because a string containing @samp{+} is never a valid user or group name.
1171 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1173 @node Random sources
1174 @section Sources of random data
1176 @cindex random sources
1178 The @command{shuf}, @command{shred}, and @command{sort} commands
1179 sometimes need random data to do their work. For example, @samp{sort
1180 -R} must choose a hash function at random, and it needs random data to
1181 make this selection.
1183 By default these commands use an internal pseudorandom generator
1184 initialized by a small amount of entropy, but can be directed to use
1185 an external source with the @option{--random-source=@var{file}} option.
1186 An error is reported if @var{file} does not contain enough bytes.
1188 For example, the device file @file{/dev/urandom} could be used as the
1189 source of random data. Typically, this device gathers environmental
1190 noise from device drivers and other sources into an entropy pool, and
1191 uses the pool to generate random bits. If the pool is short of data,
1192 the device reuses the internal pool to produce more bits, using a
1193 cryptographically secure pseudorandom number generator. But be aware
1194 that this device is not designed for bulk random data generation
1195 and is relatively slow.
1197 @file{/dev/urandom} suffices for most practical uses, but applications
1198 requiring high-value or long-term protection of private data may
1199 require an alternate data source like @file{/dev/random} or
1200 @file{/dev/arandom}. The set of available sources depends on your
1203 To reproduce the results of an earlier invocation of a command, you
1204 can save some random data into a file and then use that file as the
1205 random source in earlier and later invocations of the command.
1207 @node Target directory
1208 @section Target directory
1210 @cindex target directory
1212 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1213 commands normally treat the last operand specially when it is a
1214 directory or a symbolic link to a directory. For example, @samp{cp
1215 source dest} is equivalent to @samp{cp source dest/source} if
1216 @file{dest} is a directory. Sometimes this behavior is not exactly
1217 what is wanted, so these commands support the following options to
1218 allow more fine-grained control:
1223 @itemx --no-target-directory
1224 @opindex --no-target-directory
1225 @cindex target directory
1226 @cindex destination directory
1227 Do not treat the last operand specially when it is a directory or a
1228 symbolic link to a directory. This can help avoid race conditions in
1229 programs that operate in a shared area. For example, when the command
1230 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1231 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1232 renamed to @file{/tmp/dest/source} instead, if some other process
1233 created @file{/tmp/dest} as a directory. However, if @file{mv
1234 -T /tmp/source /tmp/dest} succeeds, there is no
1235 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1237 In the opposite situation, where you want the last operand to be
1238 treated as a directory and want a diagnostic otherwise, you can use
1239 the @option{--target-directory} (@option{-t}) option.
1241 @item -t @var{directory}
1242 @itemx @w{@kbd{--target-directory}=@var{directory}}
1243 @opindex --target-directory
1244 @cindex target directory
1245 @cindex destination directory
1246 Use @var{directory} as the directory component of each destination
1249 The interface for most programs is that after processing options and a
1250 finite (possibly zero) number of fixed-position arguments, the remaining
1251 argument list is either expected to be empty, or is a list of items
1252 (usually files) that will all be handled identically. The @command{xargs}
1253 program is designed to work well with this convention.
1255 The commands in the @command{mv}-family are unusual in that they take
1256 a variable number of arguments with a special case at the @emph{end}
1257 (namely, the target directory). This makes it nontrivial to perform some
1258 operations, e.g., ``move all files from here to ../d/'', because
1259 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1260 doesn't have a clean way to specify an extra final argument for each
1261 invocation of the subject command. (It can be done by going through a
1262 shell command, but that requires more human labor and brain power than
1265 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1266 @command{install}, @command{ln}, and @command{mv} programs to be used
1267 conveniently with @command{xargs}. For example, you can move the files
1268 from the current directory to a sibling directory, @code{d} like this:
1271 ls | xargs mv -t ../d --
1274 However, this doesn't move files whose names begin with @samp{.}.
1275 If you use the @sc{gnu} @command{find} program, you can move those
1276 files too, with this command:
1279 find . -mindepth 1 -maxdepth 1 \
1283 But both of the above approaches fail if there are no files in the
1284 current directory, or if any file has a name containing a blank or
1285 some other special characters.
1286 The following example removes those limitations and requires both
1287 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1290 find . -mindepth 1 -maxdepth 1 -print0 \
1291 | xargs --null --no-run-if-empty \
1298 The @option{--target-directory} (@option{-t}) and
1299 @option{--no-target-directory} (@option{-T})
1300 options cannot be combined.
1302 @node Trailing slashes
1303 @section Trailing slashes
1305 @cindex trailing slashes
1307 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1308 remove any trailing slashes from each @var{source} argument before
1309 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1312 This is useful when a @var{source} argument may have a trailing slash and
1313 @c FIXME: mv's behavior in this case is system-dependent
1314 specify a symbolic link to a directory. This scenario is in fact rather
1315 common because some shells can automatically append a trailing slash when
1316 performing file name completion on such symbolic links. Without this
1317 option, @command{mv}, for example, (via the system's rename function) must
1318 interpret a trailing slash as a request to dereference the symbolic link
1319 and so must rename the indirectly referenced @emph{directory} and not
1320 the symbolic link. Although it may seem surprising that such behavior
1321 be the default, it is required by @acronym{POSIX} and is consistent with
1322 other parts of that standard.
1324 @node Traversing symlinks
1325 @section Traversing symlinks
1327 @cindex symbolic link to directory, controlling traversal of
1329 The following options modify how @command{chown} and @command{chgrp}
1330 @c FIXME: note that 'du' has these options, too, but they have slightly
1331 @c different meaning.
1332 traverse a hierarchy when the @option{--recursive} (@option{-R})
1333 option is also specified.
1334 If more than one of the following options is specified, only the final
1336 These options specify whether processing a symbolic link to a directory
1337 entails operating on just the symbolic link or on all files in the
1338 hierarchy rooted at that directory.
1340 These options are independent of @option{--dereference} and
1341 @option{--no-dereference} (@option{-h}), which control whether to modify
1342 a symlink or its referent.
1349 @cindex symbolic link to directory, traverse if on the command line
1350 If @option{--recursive} (@option{-R}) is specified and
1351 a command line argument is a symbolic link to a directory, traverse it.
1358 @cindex symbolic link to directory, traverse each that is encountered
1359 In a recursive traversal, traverse every symbolic link to a directory
1360 that is encountered.
1367 @cindex symbolic link to directory, never traverse
1368 Do not traverse any symbolic links.
1369 This is the default if none of @option{-H}, @option{-L},
1370 or @option{-P} is specified.
1377 @node Treating / specially
1378 @section Treating @file{/} specially
1380 Certain commands can operate destructively on entire hierarchies.
1381 For example, if a user with appropriate privileges mistakenly runs
1382 @samp{rm -rf / tmp/junk}, that may remove
1383 all files on the entire system. Since there are so few
1384 legitimate uses for such a command,
1385 @sc{gnu} @command{rm} normally declines to operate on any directory
1386 that resolves to @file{/}. If you really want to try to remove all
1387 the files on your system, you can use the @option{--no-preserve-root}
1388 option, but the default behavior, specified by the
1389 @option{--preserve-option}, is safer for most purposes.
1391 The commands @command{chgrp}, @command{chmod} and @command{chown}
1392 can also operate destructively on entire hierarchies, so they too
1393 support these options. Although, unlike @command{rm}, they don't
1394 actually unlink files, these commands are arguably more dangerous
1395 when operating recursively on @file{/}, since they often work much
1396 more quickly, and hence damage more files before an alert user can
1397 interrupt them. Tradition and @acronym{POSIX} require these commands
1398 to operate recursively on @file{/}, so they default to
1399 @option{--no-preserve-root}, but using the @option{--preserve-root}
1400 option makes them safer for most purposes. For convenience you can
1401 specify @option{--preserve-root} in an alias or in a shell function.
1403 Note that the @option{--preserve-root} option also ensures
1404 that @command{chgrp} and @command{chown} do not modify @file{/}
1405 even when dereferencing a symlink pointing to @file{/}.
1407 @node Special built-in utilities
1408 @section Special built-in utilities
1410 Some programs like @command{nice} can invoke other programs; for
1411 example, the command @samp{nice cat file} invokes the program
1412 @command{cat} by executing the command @samp{cat file}. However,
1413 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1414 this way. For example, the command @samp{nice exit} does not have a
1415 well-defined behavior: it may generate an error message instead of
1418 Here is a list of the special built-in utilities that are standardized
1419 by @acronym{POSIX} 1003.1-2004.
1422 @t{.@: : break continue eval exec exit export readonly
1423 return set shift times trap unset}
1426 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1427 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1428 pwd} do not work as you might expect.
1430 Many shells extend this list. For example, Bash has several extra
1431 special built-in utilities like @command{history}, and
1432 @command{suspend}, and with Bash the command @samp{nice suspend}
1433 generates an error message instead of suspending.
1435 @node Standards conformance
1436 @section Standards conformance
1438 @vindex POSIXLY_CORRECT
1439 In a few cases, the @sc{gnu} utilities' default behavior is
1440 incompatible with the @acronym{POSIX} standard. To suppress these
1441 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1442 variable. Unless you are checking for @acronym{POSIX} conformance, you
1443 probably do not need to define @env{POSIXLY_CORRECT}.
1445 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1446 versions. For example, older versions of @acronym{POSIX} required the
1447 command @samp{sort +1} to sort based on the second and succeeding
1448 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1449 the same command is required to sort the file named @file{+1}, and you
1450 must instead use the command @samp{sort -k 2} to get the field-based
1453 @vindex _POSIX2_VERSION
1454 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1455 that is standard for your system. To cause them to conform to a
1456 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1457 environment variable to a value of the form @var{yyyymm} specifying
1458 the year and month the standard was adopted. Three values are currently
1459 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1460 @acronym{POSIX} 1003.2-1992, @samp{200112} stands for @acronym{POSIX}
1461 1003.1-2001, and @samp{200809} stands for @acronym{POSIX} 1003.1-2008.
1462 For example, if you have a newer system but are running software
1463 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1464 or @samp{tail +10}, you can work around any compatibility problems by setting
1465 @samp{_POSIX2_VERSION=199209} in your environment.
1467 @node Output of entire files
1468 @chapter Output of entire files
1470 @cindex output of entire files
1471 @cindex entire files, output of
1473 These commands read and write entire files, possibly transforming them
1477 * cat invocation:: Concatenate and write files.
1478 * tac invocation:: Concatenate and write files in reverse.
1479 * nl invocation:: Number lines and write files.
1480 * od invocation:: Write files in octal or other formats.
1481 * base64 invocation:: Transform data into printable data.
1484 @node cat invocation
1485 @section @command{cat}: Concatenate and write files
1488 @cindex concatenate and write files
1489 @cindex copying files
1491 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1492 standard input if none are given, to standard output. Synopsis:
1495 cat [@var{option}] [@var{file}]@dots{}
1498 The program accepts the following options. Also see @ref{Common options}.
1506 Equivalent to @option{-vET}.
1509 @itemx --number-nonblank
1511 @opindex --number-nonblank
1512 Number all nonempty output lines, starting with 1.
1516 Equivalent to @option{-vE}.
1521 @opindex --show-ends
1522 Display a @samp{$} after the end of each line.
1528 Number all output lines, starting with 1. This option is ignored
1529 if @option{-b} is in effect.
1532 @itemx --squeeze-blank
1534 @opindex --squeeze-blank
1535 @cindex squeezing empty lines
1536 Suppress repeated adjacent empty lines; output just one empty line
1541 Equivalent to @option{-vT}.
1546 @opindex --show-tabs
1547 Display TAB characters as @samp{^I}.
1551 Ignored; for @acronym{POSIX} compatibility.
1554 @itemx --show-nonprinting
1556 @opindex --show-nonprinting
1557 Display control characters except for LFD and TAB using
1558 @samp{^} notation and precede characters that have the high bit set with
1563 On systems like MS-DOS that distinguish between text and binary files,
1564 @command{cat} normally reads and writes in binary mode. However,
1565 @command{cat} reads in text mode if one of the options
1566 @option{-bensAE} is used or if @command{cat} is reading from standard
1567 input and standard input is a terminal. Similarly, @command{cat}
1568 writes in text mode if one of the options @option{-bensAE} is used or
1569 if standard output is a terminal.
1576 # Output f's contents, then standard input, then g's contents.
1579 # Copy standard input to standard output.
1584 @node tac invocation
1585 @section @command{tac}: Concatenate and write files in reverse
1588 @cindex reversing files
1590 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1591 standard input if none are given, to standard output, reversing the
1592 records (lines by default) in each separately. Synopsis:
1595 tac [@var{option}]@dots{} [@var{file}]@dots{}
1598 @dfn{Records} are separated by instances of a string (newline by
1599 default). By default, this separator string is attached to the end of
1600 the record that it follows in the file.
1602 The program accepts the following options. Also see @ref{Common options}.
1610 The separator is attached to the beginning of the record that it
1611 precedes in the file.
1617 Treat the separator string as a regular expression. Users of @command{tac}
1618 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1619 binary mode, each line of a text file might end with a CR/LF pair
1620 instead of the Unix-style LF.
1622 @item -s @var{separator}
1623 @itemx --separator=@var{separator}
1625 @opindex --separator
1626 Use @var{separator} as the record separator, instead of newline.
1634 @section @command{nl}: Number lines and write files
1637 @cindex numbering lines
1638 @cindex line numbering
1640 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1641 standard input if none are given, to standard output, with line numbers
1642 added to some or all of the lines. Synopsis:
1645 nl [@var{option}]@dots{} [@var{file}]@dots{}
1648 @cindex logical pages, numbering on
1649 @command{nl} decomposes its input into (logical) pages; by default, the
1650 line number is reset to 1 at the top of each logical page. @command{nl}
1651 treats all of the input files as a single document; it does not reset
1652 line numbers or logical pages between files.
1654 @cindex headers, numbering
1655 @cindex body, numbering
1656 @cindex footers, numbering
1657 A logical page consists of three sections: header, body, and footer.
1658 Any of the sections can be empty. Each can be numbered in a different
1659 style from the others.
1661 The beginnings of the sections of logical pages are indicated in the
1662 input file by a line containing exactly one of these delimiter strings:
1673 The two characters from which these strings are made can be changed from
1674 @samp{\} and @samp{:} via options (see below), but the pattern and
1675 length of each string cannot be changed.
1677 A section delimiter is replaced by an empty line on output. Any text
1678 that comes before the first section delimiter string in the input file
1679 is considered to be part of a body section, so @command{nl} treats a
1680 file that contains no section delimiters as a single body section.
1682 The program accepts the following options. Also see @ref{Common options}.
1686 @item -b @var{style}
1687 @itemx --body-numbering=@var{style}
1689 @opindex --body-numbering
1690 Select the numbering style for lines in the body section of each
1691 logical page. When a line is not numbered, the current line number
1692 is not incremented, but the line number separator character is still
1693 prepended to the line. The styles are:
1699 number only nonempty lines (default for body),
1701 do not number lines (default for header and footer),
1703 number only lines that contain a match for the basic regular
1704 expression @var{bre}.
1705 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1709 @itemx --section-delimiter=@var{cd}
1711 @opindex --section-delimiter
1712 @cindex section delimiters of pages
1713 Set the section delimiter characters to @var{cd}; default is
1714 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1715 (Remember to protect @samp{\} or other metacharacters from shell
1716 expansion with quotes or extra backslashes.)
1718 @item -f @var{style}
1719 @itemx --footer-numbering=@var{style}
1721 @opindex --footer-numbering
1722 Analogous to @option{--body-numbering}.
1724 @item -h @var{style}
1725 @itemx --header-numbering=@var{style}
1727 @opindex --header-numbering
1728 Analogous to @option{--body-numbering}.
1730 @item -i @var{number}
1731 @itemx --line-increment=@var{number}
1733 @opindex --line-increment
1734 Increment line numbers by @var{number} (default 1).
1736 @item -l @var{number}
1737 @itemx --join-blank-lines=@var{number}
1739 @opindex --join-blank-lines
1740 @cindex empty lines, numbering
1741 @cindex blank lines, numbering
1742 Consider @var{number} (default 1) consecutive empty lines to be one
1743 logical line for numbering, and only number the last one. Where fewer
1744 than @var{number} consecutive empty lines occur, do not number them.
1745 An empty line is one that contains no characters, not even spaces
1748 @item -n @var{format}
1749 @itemx --number-format=@var{format}
1751 @opindex --number-format
1752 Select the line numbering format (default is @code{rn}):
1756 @opindex ln @r{format for @command{nl}}
1757 left justified, no leading zeros;
1759 @opindex rn @r{format for @command{nl}}
1760 right justified, no leading zeros;
1762 @opindex rz @r{format for @command{nl}}
1763 right justified, leading zeros.
1767 @itemx --no-renumber
1769 @opindex --no-renumber
1770 Do not reset the line number at the start of a logical page.
1772 @item -s @var{string}
1773 @itemx --number-separator=@var{string}
1775 @opindex --number-separator
1776 Separate the line number from the text line in the output with
1777 @var{string} (default is the TAB character).
1779 @item -v @var{number}
1780 @itemx --starting-line-number=@var{number}
1782 @opindex --starting-line-number
1783 Set the initial line number on each logical page to @var{number} (default 1).
1785 @item -w @var{number}
1786 @itemx --number-width=@var{number}
1788 @opindex --number-width
1789 Use @var{number} characters for line numbers (default 6).
1797 @section @command{od}: Write files in octal or other formats
1800 @cindex octal dump of files
1801 @cindex hex dump of files
1802 @cindex ASCII dump of files
1803 @cindex file contents, dumping unambiguously
1805 @command{od} writes an unambiguous representation of each @var{file}
1806 (@samp{-} means standard input), or standard input if none are given.
1810 od [@var{option}]@dots{} [@var{file}]@dots{}
1811 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1812 od [@var{option}]@dots{} --traditional [@var{file}]@c
1813 [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1816 Each line of output consists of the offset in the input, followed by
1817 groups of data from the file. By default, @command{od} prints the offset in
1818 octal, and each group of file data is a C @code{short int}'s worth of input
1819 printed as a single octal number.
1821 If @var{offset} is given, it specifies how many input bytes to skip
1822 before formatting and writing. By default, it is interpreted as an
1823 octal number, but the optional trailing decimal point causes it to be
1824 interpreted as decimal. If no decimal is specified and the offset
1825 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1826 number. If there is a trailing @samp{b}, the number of bytes skipped
1827 will be @var{offset} multiplied by 512.
1829 If a command is of both the first and second forms, the second form is
1830 assumed if the last operand begins with @samp{+} or (if there are two
1831 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1832 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1835 The program accepts the following options. Also see @ref{Common options}.
1839 @item -A @var{radix}
1840 @itemx --address-radix=@var{radix}
1842 @opindex --address-radix
1843 @cindex radix for file offsets
1844 @cindex file offset radix
1845 Select the base in which file offsets are printed. @var{radix} can
1846 be one of the following:
1856 none (do not print offsets).
1859 The default is octal.
1861 @item -j @var{bytes}
1862 @itemx --skip-bytes=@var{bytes}
1864 @opindex --skip-bytes
1865 Skip @var{bytes} input bytes before formatting and writing. If
1866 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1867 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1869 @multiplierSuffixes{bytes}
1871 @item -N @var{bytes}
1872 @itemx --read-bytes=@var{bytes}
1874 @opindex --read-bytes
1875 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1876 @code{bytes} are interpreted as for the @option{-j} option.
1878 @item -S @var{bytes}
1879 @itemx --strings[=@var{bytes}]
1882 @cindex string constants, outputting
1883 Instead of the normal output, output only @dfn{string constants}: at
1884 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1885 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1886 Prefixes and suffixes on @var{bytes} are interpreted as for the
1889 If @var{n} is omitted with @option{--strings}, the default is 3.
1892 @itemx --format=@var{type}
1895 Select the format in which to output the file data. @var{type} is a
1896 string of one or more of the below type indicator characters. If you
1897 include more than one type indicator character in a single @var{type}
1898 string, or use this option more than once, @command{od} writes one copy
1899 of each output line using each of the data types that you specified,
1900 in the order that you specified.
1902 Adding a trailing ``z'' to any type specification appends a display
1903 of the @acronym{ASCII} character representation of the printable characters
1904 to the output line generated by the type specification.
1908 named character, ignoring high-order bit
1910 @acronym{ASCII} character or backslash escape,
1914 floating point (@pxref{Floating point})
1923 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1924 newline, and @samp{nul} for a zero byte. Only the least significant
1925 seven bits of each byte is used; the high-order bit is ignored.
1926 Type @code{c} outputs
1927 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1930 Except for types @samp{a} and @samp{c}, you can specify the number
1931 of bytes to use in interpreting each number in the given data type
1932 by following the type indicator character with a decimal integer.
1933 Alternately, you can specify the size of one of the C compiler's
1934 built-in data types by following the type indicator character with
1935 one of the following characters. For integers (@samp{d}, @samp{o},
1936 @samp{u}, @samp{x}):
1949 For floating point (@code{f}):
1961 @itemx --output-duplicates
1963 @opindex --output-duplicates
1964 Output consecutive lines that are identical. By default, when two or
1965 more consecutive output lines would be identical, @command{od} outputs only
1966 the first line, and puts just an asterisk on the following line to
1967 indicate the elision.
1970 @itemx --width[=@var{n}]
1973 Dump @code{n} input bytes per output line. This must be a multiple of
1974 the least common multiple of the sizes associated with the specified
1977 If this option is not given at all, the default is 16. If @var{n} is
1978 omitted, the default is 32.
1982 The next several options are shorthands for format specifications.
1983 @sc{gnu} @command{od} accepts any combination of shorthands and format
1984 specification options. These options accumulate.
1990 Output as named characters. Equivalent to @samp{-t a}.
1994 Output as octal bytes. Equivalent to @samp{-t o1}.
1998 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
2003 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
2007 Output as floats. Equivalent to @samp{-t fF}.
2011 Output as decimal ints. Equivalent to @samp{-t dI}.
2015 Output as decimal long ints. Equivalent to @samp{-t dL}.
2019 Output as octal two-byte units. Equivalent to @option{-t o2}.
2023 Output as decimal two-byte units. Equivalent to @option{-t d2}.
2027 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
2030 @opindex --traditional
2031 Recognize the non-option label argument that traditional @command{od}
2032 accepted. The following syntax:
2035 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2039 can be used to specify at most one file and optional arguments
2040 specifying an offset and a pseudo-start address, @var{label}.
2041 The @var{label} argument is interpreted
2042 just like @var{offset}, but it specifies an initial pseudo-address. The
2043 pseudo-addresses are displayed in parentheses following any normal
2050 @node base64 invocation
2051 @section @command{base64}: Transform data into printable data
2054 @cindex base64 encoding
2056 @command{base64} transforms data read from a file, or standard input,
2057 into (or from) base64 encoded form. The base64 encoded form uses
2058 printable @acronym{ASCII} characters to represent binary data.
2062 base64 [@var{option}]@dots{} [@var{file}]
2063 base64 --decode [@var{option}]@dots{} [@var{file}]
2066 The base64 encoding expands data to roughly 133% of the original.
2067 The format conforms to
2068 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2070 The program accepts the following options. Also see @ref{Common options}.
2075 @itemx --wrap=@var{cols}
2079 @cindex column to wrap data after
2080 During encoding, wrap lines after @var{cols} characters. This must be
2083 The default is to wrap after 76 characters. Use the value 0 to
2084 disable line wrapping altogether.
2090 @cindex Decode base64 data
2091 @cindex Base64 decoding
2092 Change the mode of operation, from the default of encoding data, to
2093 decoding data. Input is expected to be base64 encoded data, and the
2094 output will be the original data.
2097 @itemx --ignore-garbage
2099 @opindex --ignore-garbage
2100 @cindex Ignore garbage in base64 stream
2101 When decoding, newlines are always accepted.
2102 During decoding, ignore unrecognized bytes,
2103 to permit distorted data to be decoded.
2110 @node Formatting file contents
2111 @chapter Formatting file contents
2113 @cindex formatting file contents
2115 These commands reformat the contents of files.
2118 * fmt invocation:: Reformat paragraph text.
2119 * pr invocation:: Paginate or columnate files for printing.
2120 * fold invocation:: Wrap input lines to fit in specified width.
2124 @node fmt invocation
2125 @section @command{fmt}: Reformat paragraph text
2128 @cindex reformatting paragraph text
2129 @cindex paragraphs, reformatting
2130 @cindex text, reformatting
2132 @command{fmt} fills and joins lines to produce output lines of (at most)
2133 a given number of characters (75 by default). Synopsis:
2136 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2139 @command{fmt} reads from the specified @var{file} arguments (or standard
2140 input if none are given), and writes to standard output.
2142 By default, blank lines, spaces between words, and indentation are
2143 preserved in the output; successive input lines with different
2144 indentation are not joined; tabs are expanded on input and introduced on
2147 @cindex line-breaking
2148 @cindex sentences and line-breaking
2149 @cindex Knuth, Donald E.
2150 @cindex Plass, Michael F.
2151 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2152 avoid line breaks after the first word of a sentence or before the last
2153 word of a sentence. A @dfn{sentence break} is defined as either the end
2154 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2155 spaces or end of line, ignoring any intervening parentheses or quotes.
2156 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2157 breaks; the algorithm is a variant of that given by Donald E. Knuth
2158 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2159 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2162 The program accepts the following options. Also see @ref{Common options}.
2167 @itemx --crown-margin
2169 @opindex --crown-margin
2170 @cindex crown margin
2171 @dfn{Crown margin} mode: preserve the indentation of the first two
2172 lines within a paragraph, and align the left margin of each subsequent
2173 line with that of the second line.
2176 @itemx --tagged-paragraph
2178 @opindex --tagged-paragraph
2179 @cindex tagged paragraphs
2180 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2181 indentation of the first line of a paragraph is the same as the
2182 indentation of the second, the first line is treated as a one-line
2188 @opindex --split-only
2189 Split lines only. Do not join short lines to form longer ones. This
2190 prevents sample lines of code, and other such ``formatted'' text from
2191 being unduly combined.
2194 @itemx --uniform-spacing
2196 @opindex --uniform-spacing
2197 Uniform spacing. Reduce spacing between words to one space, and spacing
2198 between sentences to two spaces.
2201 @itemx -w @var{width}
2202 @itemx --width=@var{width}
2203 @opindex -@var{width}
2206 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2207 initially tries to make lines about 7% shorter than this, to give it
2208 room to balance line lengths.
2210 @item -p @var{prefix}
2211 @itemx --prefix=@var{prefix}
2212 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2213 are subject to formatting. The prefix and any preceding whitespace are
2214 stripped for the formatting and then re-attached to each formatted output
2215 line. One use is to format certain kinds of program comments, while
2216 leaving the code unchanged.
2224 @section @command{pr}: Paginate or columnate files for printing
2227 @cindex printing, preparing files for
2228 @cindex multicolumn output, generating
2229 @cindex merging files in parallel
2231 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2232 standard input if none are given, to standard output, paginating and
2233 optionally outputting in multicolumn format; optionally merges all
2234 @var{file}s, printing all in parallel, one per column. Synopsis:
2237 pr [@var{option}]@dots{} [@var{file}]@dots{}
2241 By default, a 5-line header is printed at each page: two blank lines;
2242 a line with the date, the file name, and the page count; and two more
2243 blank lines. A footer of five blank lines is also printed.
2244 The default @var{page_length} is 66
2245 lines. The default number of text lines is therefore 56.
2246 The text line of the header takes the form
2247 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2248 @var{string} so that the line takes up the full @var{page_width}. Here,
2249 @var{date} is the date (see the @option{-D} or @option{--date-format}
2250 option for details), @var{string} is the centered header string, and
2251 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2252 category affects the spelling of @var{page}; in the default C locale, it
2253 is @samp{Page @var{number}} where @var{number} is the decimal page
2256 Form feeds in the input cause page breaks in the output. Multiple form
2257 feeds produce empty pages.
2259 Columns are of equal width, separated by an optional string (default
2260 is @samp{space}). For multicolumn output, lines will always be truncated to
2261 @var{page_width} (default 72), unless you use the @option{-J} option.
2263 column output no line truncation occurs by default. Use @option{-W} option to
2264 truncate lines in that case.
2266 The following changes were made in version 1.22i and apply to later
2267 versions of @command{pr}:
2268 @c FIXME: this whole section here sounds very awkward to me. I
2269 @c made a few small changes, but really it all needs to be redone. - Brian
2270 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2275 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2276 redefined for better @acronym{POSIX} compliance. The output of some further
2277 cases has been adapted to other Unix systems. These changes are not
2278 compatible with earlier versions of the program.
2281 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2282 have been introduced to turn off unexpected interferences of small letter
2283 options. The @option{-N} option and the second argument @var{last_page}
2284 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2285 form feeds set in the input files requires the @option{-T} option.
2288 Capital letter options override small letter ones.
2291 Some of the option-arguments (compare @option{-s}, @option{-e},
2292 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2293 preceding option letter (already stated in the @acronym{POSIX} specification).
2296 The program accepts the following options. Also see @ref{Common options}.
2300 @item +@var{first_page}[:@var{last_page}]
2301 @itemx --pages=@var{first_page}[:@var{last_page}]
2302 @c The two following @opindex lines evoke warnings because they contain ':'
2303 @c The 'info' spec does not permit that. If we use those lines, we end
2304 @c up with truncated index entries that don't work.
2305 @c @opindex +@var{first_page}[:@var{last_page}]
2306 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2307 @opindex +@var{page_range}
2308 @opindex --pages=@var{page_range}
2309 Begin printing with page @var{first_page} and stop with @var{last_page}.
2310 Missing @samp{:@var{last_page}} implies end of file. While estimating
2311 the number of skipped pages each form feed in the input file results
2312 in a new page. Page counting with and without @samp{+@var{first_page}}
2313 is identical. By default, counting starts with the first page of input
2314 file (not first page printed). Line numbering may be altered by @option{-N}
2318 @itemx --columns=@var{column}
2319 @opindex -@var{column}
2321 @cindex down columns
2322 With each single @var{file}, produce @var{column} columns of output
2323 (default is 1) and print columns down, unless @option{-a} is used. The
2324 column width is automatically decreased as @var{column} increases; unless
2325 you use the @option{-W/-w} option to increase @var{page_width} as well.
2326 This option might well cause some lines to be truncated. The number of
2327 lines in the columns on each page are balanced. The options @option{-e}
2328 and @option{-i} are on for multiple text-column output. Together with
2329 @option{-J} option column alignment and line truncation is turned off.
2330 Lines of full length are joined in a free field format and @option{-S}
2331 option may set field separators. @option{-@var{column}} may not be used
2332 with @option{-m} option.
2338 @cindex across columns
2339 With each single @var{file}, print columns across rather than down. The
2340 @option{-@var{column}} option must be given with @var{column} greater than one.
2341 If a line is too long to fit in a column, it is truncated.
2344 @itemx --show-control-chars
2346 @opindex --show-control-chars
2347 Print control characters using hat notation (e.g., @samp{^G}); print
2348 other nonprinting characters in octal backslash notation. By default,
2349 nonprinting characters are not changed.
2352 @itemx --double-space
2354 @opindex --double-space
2355 @cindex double spacing
2356 Double space the output.
2358 @item -D @var{format}
2359 @itemx --date-format=@var{format}
2360 @cindex time formats
2361 @cindex formatting times
2362 Format header dates using @var{format}, using the same conventions as
2363 for the command @samp{date +@var{format}}; @xref{date invocation}.
2364 Except for directives, which start with
2365 @samp{%}, characters in @var{format} are printed unchanged. You can use
2366 this option to specify an arbitrary string in place of the header date,
2367 e.g., @option{--date-format="Monday morning"}.
2369 @vindex POSIXLY_CORRECT
2371 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2372 @samp{2001-12-04 23:59});
2373 but if the @env{POSIXLY_CORRECT} environment variable is set
2374 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2375 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2376 @samp{Dec@ @ 4 23:59 2001}.
2379 Time stamps are listed according to the time zone rules specified by
2380 the @env{TZ} environment variable, or by the system default rules if
2381 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2382 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2384 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2385 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2387 @opindex --expand-tabs
2389 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2390 the input tab character (default is the TAB character). Second optional
2391 argument @var{in-tabwidth} is the input tab character's width (default
2399 @opindex --form-feed
2400 Use a form feed instead of newlines to separate output pages. This does
2401 not alter the default page length of 66 lines.
2403 @item -h @var{header}
2404 @itemx --header=@var{header}
2407 Replace the file name in the header with the centered string @var{header}.
2408 When using the shell, @var{header} should be quoted and should be
2409 separated from @option{-h} by a space.
2411 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2412 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2414 @opindex --output-tabs
2416 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2417 is the output tab character (default is the TAB character). Second optional
2418 argument @var{out-tabwidth} is the output tab character's width (default
2424 @opindex --join-lines
2425 Merge lines of full length. Used together with the column options
2426 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2427 @option{-W/-w} line truncation;
2428 no column alignment used; may be used with
2429 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2430 (together with @option{-W} and @option{--sep-string})
2431 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2432 @option{-s} along with the three column options.
2435 @item -l @var{page_length}
2436 @itemx --length=@var{page_length}
2439 Set the page length to @var{page_length} (default 66) lines, including
2440 the lines of the header [and the footer]. If @var{page_length} is less
2441 than or equal to 10, the header and footer are omitted, as if the
2442 @option{-t} option had been given.
2448 Merge and print all @var{file}s in parallel, one in each column. If a
2449 line is too long to fit in a column, it is truncated, unless the @option{-J}
2450 option is used. @option{--sep-string[=@var{string}]} may be used.
2452 some @var{file}s (form feeds set) produce empty columns, still marked
2453 by @var{string}. The result is a continuous line numbering and column
2454 marking throughout the whole merged file. Completely empty merged pages
2455 show no separators or line numbers. The default header becomes
2456 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2457 may be used with the @option{-h} or @option{--header} option to fill up
2458 the middle blank part.
2460 @item -n[@var{number-separator}[@var{digits}]]
2461 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2463 @opindex --number-lines
2464 Provide @var{digits} digit line numbering (default for @var{digits} is
2465 5). With multicolumn output the number occupies the first @var{digits}
2466 column positions of each text column or only each line of @option{-m}
2467 output. With single column output the number precedes each line just as
2468 @option{-m} does. Default counting of the line numbers starts with the
2469 first line of the input file (not the first line printed, compare the
2470 @option{--page} option and @option{-N} option).
2471 Optional argument @var{number-separator} is the character appended to
2472 the line number to separate it from the text followed. The default
2473 separator is the TAB character. In a strict sense a TAB is always
2474 printed with single column output only. The TAB width varies
2475 with the TAB position, e.g., with the left @var{margin} specified
2476 by @option{-o} option. With multicolumn output priority is given to
2477 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2478 The TAB width is fixed to the value of the first column and does
2479 not change with different values of left @var{margin}. That means a
2480 fixed number of spaces is always printed in the place of the
2481 @var{number-separator} TAB. The tabification depends upon the output
2484 @item -N @var{line_number}
2485 @itemx --first-line-number=@var{line_number}
2487 @opindex --first-line-number
2488 Start line counting with the number @var{line_number} at first line of
2489 first page printed (in most cases not the first line of the input file).
2491 @item -o @var{margin}
2492 @itemx --indent=@var{margin}
2495 @cindex indenting lines
2497 Indent each line with a margin @var{margin} spaces wide (default is zero).
2498 The total page width is the size of the margin plus the @var{page_width}
2499 set with the @option{-W/-w} option. A limited overflow may occur with
2500 numbered single column output (compare @option{-n} option).
2503 @itemx --no-file-warnings
2505 @opindex --no-file-warnings
2506 Do not print a warning message when an argument @var{file} cannot be
2507 opened. (The exit status will still be nonzero, however.)
2509 @item -s[@var{char}]
2510 @itemx --separator[=@var{char}]
2512 @opindex --separator
2513 Separate columns by a single character @var{char}. The default for
2514 @var{char} is the TAB character without @option{-w} and @samp{no
2515 character} with @option{-w}. Without @option{-s} the default separator
2516 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2517 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2518 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2521 @item -S[@var{string}]
2522 @itemx --sep-string[=@var{string}]
2524 @opindex --sep-string
2525 Use @var{string} to separate output columns. The @option{-S} option doesn't
2526 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2527 does not affect line truncation or column alignment.
2528 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2530 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2531 (same as @option{-S"@w{ }"}).
2532 If no @samp{@var{string}} argument is specified, @samp{""} is assumed.
2535 @itemx --omit-header
2537 @opindex --omit-header
2538 Do not print the usual header [and footer] on each page, and do not fill
2539 out the bottom of pages (with blank lines or a form feed). No page
2540 structure is produced, but form feeds set in the input files are retained.
2541 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2542 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2543 in the input file to 4 spaces but don't make any other changes. Use of
2544 @option{-t} overrides @option{-h}.
2547 @itemx --omit-pagination
2549 @opindex --omit-pagination
2550 Do not print header [and footer]. In addition eliminate all form feeds
2551 set in the input files.
2554 @itemx --show-nonprinting
2556 @opindex --show-nonprinting
2557 Print nonprinting characters in octal backslash notation.
2559 @item -w @var{page_width}
2560 @itemx --width=@var{page_width}
2563 Set page width to @var{page_width} characters for multiple text-column
2564 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2565 off the default page width and any line truncation and column alignment.
2566 Lines of full length are merged, regardless of the column options
2567 set. No @var{page_width} setting is possible with single column output.
2568 A @acronym{POSIX}-compliant formulation.
2570 @item -W @var{page_width}
2571 @itemx --page_width=@var{page_width}
2573 @opindex --page_width
2574 Set the page width to @var{page_width} characters. That's valid with and
2575 without a column option. Text lines are truncated, unless @option{-J}
2576 is used. Together with one of the three column options
2577 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2578 alignment is always used. The separator options @option{-S} or @option{-s}
2579 don't affect the @option{-W} option. Default is 72 characters. Without
2580 @option{-W @var{page_width}} and without any of the column options NO line
2581 truncation is used (defined to keep downward compatibility and to meet
2582 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2583 line is never truncated.
2590 @node fold invocation
2591 @section @command{fold}: Wrap input lines to fit in specified width
2594 @cindex wrapping long input lines
2595 @cindex folding long input lines
2597 @command{fold} writes each @var{file} (@option{-} means standard input), or
2598 standard input if none are given, to standard output, breaking long
2602 fold [@var{option}]@dots{} [@var{file}]@dots{}
2605 By default, @command{fold} breaks lines wider than 80 columns. The output
2606 is split into as many lines as necessary.
2608 @cindex screen columns
2609 @command{fold} counts screen columns by default; thus, a tab may count more
2610 than one column, backspace decreases the column count, and carriage
2611 return sets the column to zero.
2613 The program accepts the following options. Also see @ref{Common options}.
2621 Count bytes rather than columns, so that tabs, backspaces, and carriage
2622 returns are each counted as taking up one column, just like other
2629 Break at word boundaries: the line is broken after the last blank before
2630 the maximum line length. If the line contains no such blanks, the line
2631 is broken at the maximum line length as usual.
2633 @item -w @var{width}
2634 @itemx --width=@var{width}
2637 Use a maximum line length of @var{width} columns instead of 80.
2639 For compatibility @command{fold} supports an obsolete option syntax
2640 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2648 @node Output of parts of files
2649 @chapter Output of parts of files
2651 @cindex output of parts of files
2652 @cindex parts of files, output of
2654 These commands output pieces of the input.
2657 * head invocation:: Output the first part of files.
2658 * tail invocation:: Output the last part of files.
2659 * split invocation:: Split a file into pieces.
2660 * csplit invocation:: Split a file into context-determined pieces.
2663 @node head invocation
2664 @section @command{head}: Output the first part of files
2667 @cindex initial part of files, outputting
2668 @cindex first part of files, outputting
2670 @command{head} prints the first part (10 lines by default) of each
2671 @var{file}; it reads from standard input if no files are given or
2672 when given a @var{file} of @option{-}. Synopsis:
2675 head [@var{option}]@dots{} [@var{file}]@dots{}
2678 If more than one @var{file} is specified, @command{head} prints a
2679 one-line header consisting of:
2682 ==> @var{file name} <==
2686 before the output for each @var{file}.
2688 The program accepts the following options. Also see @ref{Common options}.
2693 @itemx --bytes=@var{k}
2696 Print the first @var{k} bytes, instead of initial lines.
2697 However, if @var{k} starts with a @samp{-},
2698 print all but the last @var{k} bytes of each file.
2699 @multiplierSuffixes{k}
2702 @itemx --lines=@var{k}
2705 Output the first @var{k} lines.
2706 However, if @var{k} starts with a @samp{-},
2707 print all but the last @var{k} lines of each file.
2708 Size multiplier suffixes are the same as with the @option{-c} option.
2716 Never print file name headers.
2722 Always print file name headers.
2726 For compatibility @command{head} also supports an obsolete option syntax
2727 @option{-@var{count}@var{options}}, which is recognized only if it is
2728 specified first. @var{count} is a decimal number optionally followed
2729 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2730 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2731 Scripts intended for standard hosts should use @option{-c @var{count}}
2732 or @option{-n @var{count}} instead. If your script must also run on
2733 hosts that support only the obsolete syntax, it is usually simpler to
2734 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2740 @node tail invocation
2741 @section @command{tail}: Output the last part of files
2744 @cindex last part of files, outputting
2746 @command{tail} prints the last part (10 lines by default) of each
2747 @var{file}; it reads from standard input if no files are given or
2748 when given a @var{file} of @samp{-}. Synopsis:
2751 tail [@var{option}]@dots{} [@var{file}]@dots{}
2754 If more than one @var{file} is specified, @command{tail} prints a
2755 one-line header consisting of:
2758 ==> @var{file name} <==
2762 before the output for each @var{file}.
2764 @cindex BSD @command{tail}
2765 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2766 @command{tail} cannot). It also has no @option{-r} option (print in
2767 reverse), since reversing a file is really a different job from printing
2768 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2769 only reverse files that are at most as large as its buffer, which is
2770 typically 32 KiB@. A more reliable and versatile way to reverse files is
2771 the @sc{gnu} @command{tac} command.
2773 The program accepts the following options. Also see @ref{Common options}.
2778 @itemx --bytes=@var{k}
2781 Output the last @var{k} bytes, instead of final lines.
2782 However, if @var{k} starts with a @samp{+}, start printing with the
2783 @var{k}th byte from the start of each file, instead of from the end.
2784 @multiplierSuffixes{k}
2787 @itemx --follow[=@var{how}]
2790 @cindex growing files
2791 @vindex name @r{follow option}
2792 @vindex descriptor @r{follow option}
2793 Loop forever trying to read more characters at the end of the file,
2794 presumably because the file is growing.
2795 If more than one file is given, @command{tail} prints a header whenever it
2796 gets output from a different file, to indicate which file that output is
2799 There are two ways to specify how you'd like to track files with this option,
2800 but that difference is noticeable only when a followed file is removed or
2802 If you'd like to continue to track the end of a growing file even after
2803 it has been unlinked, use @option{--follow=descriptor}. This is the default
2804 behavior, but it is not useful if you're tracking a log file that may be
2805 rotated (removed or renamed, then reopened). In that case, use
2806 @option{--follow=name} to track the named file, perhaps by reopening it
2807 periodically to see if it has been removed and recreated by some other program.
2808 Note that the inotify-based implementation handles this case without
2809 the need for any periodic reopening.
2811 No matter which method you use, if the tracked file is determined to have
2812 shrunk, @command{tail} prints a message saying the file has been truncated
2813 and resumes tracking the end of the file from the newly-determined endpoint.
2815 When a file is removed, @command{tail}'s behavior depends on whether it is
2816 following the name or the descriptor. When following by name, tail can
2817 detect that a file has been removed and gives a message to that effect,
2818 and if @option{--retry} has been specified it will continue checking
2819 periodically to see if the file reappears.
2820 When following a descriptor, tail does not detect that the file has
2821 been unlinked or renamed and issues no message; even though the file
2822 may no longer be accessible via its original name, it may still be
2825 The option values @samp{descriptor} and @samp{name} may be specified only
2826 with the long form of the option, not with @option{-f}.
2828 The @option{-f} option is ignored if
2829 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2830 Likewise, the @option{-f} option has no effect for any
2831 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2833 With kernel inotify support, output is triggered by file changes
2834 and is generally very prompt.
2835 Otherwise, @command{tail} sleeps for one second between checks---
2836 use @option{--sleep-interval=@var{n}} to change that default---which can
2837 make the output appear slightly less responsive or bursty.
2838 When using tail without inotify support, you can make it more responsive
2839 by using a sub-second sleep interval, e.g., via an alias like this:
2842 alias tail='tail -s.1'
2847 This option is the same as @option{--follow=name --retry}. That is, tail
2848 will attempt to reopen a file when it is removed. Should this fail, tail
2849 will keep trying until it becomes accessible again.
2853 This option is useful mainly when following by name (i.e., with
2854 @option{--follow=name}).
2855 Without this option, when tail encounters a file that doesn't
2856 exist or is otherwise inaccessible, it reports that fact and
2857 never checks it again.
2859 @itemx --sleep-interval=@var{number}
2860 @opindex --sleep-interval
2861 Change the number of seconds to wait between iterations (the default is 1.0).
2862 During one iteration, every specified file is checked to see if it has
2864 Historical implementations of @command{tail} have required that
2865 @var{number} be an integer. However, GNU @command{tail} accepts
2866 an arbitrary floating point number. @xref{Floating point}.
2867 When @command{tail} uses inotify, this polling-related option
2868 is usually ignored. However, if you also specify @option{--pid=@var{p}},
2869 @command{tail} checks whether process @var{p} is alive at least
2870 every @var{number} seconds.
2872 @itemx --pid=@var{pid}
2874 When following by name or by descriptor, you may specify the process ID,
2875 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2876 after that process terminates, tail will also terminate. This will
2877 work properly only if the writer and the tailing process are running on
2878 the same machine. For example, to save the output of a build in a file
2879 and to watch the file grow, if you invoke @command{make} and @command{tail}
2880 like this then the tail process will stop when your build completes.
2881 Without this option, you would have had to kill the @code{tail -f}
2885 $ make >& makerr & tail --pid=$! -f makerr
2888 If you specify a @var{pid} that is not in use or that does not correspond
2889 to the process that is writing to the tailed files, then @command{tail}
2890 may terminate long before any @var{file}s stop growing or it may not
2891 terminate until long after the real writer has terminated.
2892 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2893 will print a warning if this is the case.
2895 @itemx --max-unchanged-stats=@var{n}
2896 @opindex --max-unchanged-stats
2897 When tailing a file by name, if there have been @var{n} (default
2898 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2899 iterations for which the file has not changed, then
2900 @code{open}/@code{fstat} the file to determine if that file name is
2901 still associated with the same device/inode-number pair as before.
2902 When following a log file that is rotated, this is approximately the
2903 number of seconds between when tail prints the last pre-rotation lines
2904 and when it prints the lines that have accumulated in the new log file.
2905 This option is meaningful only when polling (i.e., without inotify)
2906 and when following by name.
2909 @itemx --lines=@var{k}
2912 Output the last @var{k} lines.
2913 However, if @var{k} starts with a @samp{+}, start printing with the
2914 @var{k}th line from the start of each file, instead of from the end.
2915 Size multiplier suffixes are the same as with the @option{-c} option.
2923 Never print file name headers.
2929 Always print file name headers.
2933 For compatibility @command{tail} also supports an obsolete usage
2934 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2935 only if it does not conflict with the usage described
2936 above. This obsolete form uses exactly one option and at most one
2937 file. In the option, @var{count} is an optional decimal number optionally
2938 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2939 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2940 which has the same meaning as @option{-f}.
2942 @vindex _POSIX2_VERSION
2943 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2944 the obsolete option syntax with the same meaning as in counts, and
2945 obsolete usage overrides normal usage when the two conflict.
2946 This obsolete behavior can be enabled or disabled with the
2947 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2950 Scripts intended for use on standard hosts should avoid obsolete
2951 syntax and should use @option{-c @var{count}[b]}, @option{-n
2952 @var{count}}, and/or @option{-f} instead. If your script must also
2953 run on hosts that support only the obsolete syntax, you can often
2954 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2955 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2956 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2957 then @dots{}} to decide which syntax to use.
2959 Even if your script assumes the standard behavior, you should still
2960 beware usages whose behaviors differ depending on the @acronym{POSIX}
2961 version. For example, avoid @samp{tail - main.c}, since it might be
2962 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2963 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2964 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2965 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2970 @node split invocation
2971 @section @command{split}: Split a file into pieces.
2974 @cindex splitting a file into pieces
2975 @cindex pieces, splitting a file into
2977 @command{split} creates output files containing consecutive or interleaved
2978 sections of @var{input} (standard input if none is given or @var{input}
2979 is @samp{-}). Synopsis:
2982 split [@var{option}] [@var{input} [@var{prefix}]]
2985 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2986 left over for the last section), into each output file.
2988 @cindex output file name prefix
2989 The output files' names consist of @var{prefix} (@samp{x} by default)
2990 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2991 default), such that concatenating the output files in traditional
2992 sorted order by file name produces the original input file (except
2993 @option{-nr/@var{n}}). If the output file names are exhausted,
2994 @command{split} reports an error without deleting the output files
2997 The program accepts the following options. Also see @ref{Common options}.
3001 @item -l @var{lines}
3002 @itemx --lines=@var{lines}
3005 Put @var{lines} lines of @var{input} into each output file.
3007 For compatibility @command{split} also supports an obsolete
3008 option syntax @option{-@var{lines}}. New scripts should use
3009 @option{-l @var{lines}} instead.
3012 @itemx --bytes=@var{size}
3015 Put @var{size} bytes of @var{input} into each output file.
3016 @multiplierSuffixes{size}
3019 @itemx --line-bytes=@var{size}
3021 @opindex --line-bytes
3022 Put into each output file as many complete lines of @var{input} as
3023 possible without exceeding @var{size} bytes. Individual lines longer than
3024 @var{size} bytes are broken into multiple files.
3025 @var{size} has the same format as for the @option{--bytes} option.
3027 @itemx --filter=@var{command}
3029 With this option, rather than simply writing to each output file,
3030 write through a pipe to the specified shell @var{command} for each output file.
3031 @var{command} should use the $FILE environment variable, which is set
3032 to a different output file name for each invocation of the command.
3033 For example, imagine that you have a 1TiB compressed file
3034 that, if uncompressed, would be too large to reside on disk,
3035 yet you must split it into individually-compressed pieces
3036 of a more manageable size.
3037 To do that, you might run this command:
3040 xz -dc BIG.xz | split -b200G --filter='xz > $FILE.xz' - big-
3043 Assuming a 10:1 compression ratio, that would create about fifty 20GiB files
3044 with names @file{big-aa.xz}, @file{big-ab.xz}, @file{big-ac.xz}, etc.
3046 @item -n @var{chunks}
3047 @itemx --number=@var{chunks}
3051 Split @var{input} to @var{chunks} output files where @var{chunks} may be:
3054 @var{n} generate @var{n} files based on current size of @var{input}
3055 @var{k}/@var{n} only output @var{k}th of @var{n} to stdout
3056 l/@var{n} generate @var{n} files without splitting lines
3057 l/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3058 r/@var{n} like @samp{l} but use round robin distribution
3059 r/@var{k}/@var{n} likewise but only output @var{k}th of @var{n} to stdout
3062 Any excess bytes remaining after dividing the @var{input}
3063 into @var{n} chunks, are assigned to the last chunk.
3064 Any excess bytes appearing after the initial calculation are discarded
3065 (except when using @samp{r} mode).
3067 All @var{n} files are created even if there are fewer than @var{n} lines,
3068 or the @var{input} is truncated.
3070 For @samp{l} mode, chunks are approximately @var{input} size / @var{n}.
3071 The @var{input} is partitioned into @var{n} equal sized portions, with
3072 the last assigned any excess. If a line @emph{starts} within a partition
3073 it is written completely to the corresponding file. Since lines
3074 are not split even if they overlap a partition, the files written
3075 can be larger or smaller than the partition size, and even empty
3076 if a line is so long as to completely overlap the partition.
3078 For @samp{r} mode, the size of @var{input} is irrelevant,
3079 and so can be a pipe for example.
3081 @item -a @var{length}
3082 @itemx --suffix-length=@var{length}
3084 @opindex --suffix-length
3085 Use suffixes of length @var{length}. The default @var{length} is 2.
3088 @itemx --numeric-suffixes[=@var{from}]
3090 @opindex --numeric-suffixes
3091 Use digits in suffixes rather than lower-case letters. The numerical
3092 suffix counts from @var{from} if specified, 0 otherwise.
3094 @itemx --additional-suffix=@var{suffix}
3095 @opindex --additional-suffix
3096 Append an additional @var{suffix} to output file names. @var{suffix}
3097 must not contain slash.
3100 @itemx --elide-empty-files
3102 @opindex --elide-empty-files
3103 Suppress the generation of zero-length output files. This can happen
3104 with the @option{--number} option if a file is (truncated to be) shorter
3105 than the number requested, or if a line is so long as to completely
3106 span a chunk. The output file sequence numbers, always run consecutively
3107 even when this option is specified.
3112 @opindex --unbuffered
3113 Immediately copy input to output in @option{--number r/...} mode,
3114 which is a much slower mode of operation.
3118 Write a diagnostic just before each output file is opened.
3124 Here are a few examples to illustrate how the
3125 @option{--number} (@option{-n}) option works:
3127 Notice how, by default, one line may be split onto two or more:
3130 $ seq -w 6 10 > k; split -n3 k; head xa?
3143 Use the "l/" modifier to suppress that:
3146 $ seq -w 6 10 > k; split -nl/3 k; head xa?
3159 Use the "r/" modifier to distribute lines in a round-robin fashion:
3162 $ seq -w 6 10 > k; split -nr/3 k; head xa?
3175 You can also extract just the Kth chunk.
3176 This extracts and prints just the 7th "chunk" of 33:
3179 $ seq 100 > k; split -nl/7/33 k
3186 @node csplit invocation
3187 @section @command{csplit}: Split a file into context-determined pieces
3190 @cindex context splitting
3191 @cindex splitting a file into pieces by context
3193 @command{csplit} creates zero or more output files containing sections of
3194 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3197 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3200 The contents of the output files are determined by the @var{pattern}
3201 arguments, as detailed below. An error occurs if a @var{pattern}
3202 argument refers to a nonexistent line of the input file (e.g., if no
3203 remaining line matches a given regular expression). After every
3204 @var{pattern} has been matched, any remaining input is copied into one
3207 By default, @command{csplit} prints the number of bytes written to each
3208 output file after it has been created.
3210 The types of pattern arguments are:
3215 Create an output file containing the input up to but not including line
3216 @var{n} (a positive integer). If followed by a repeat count, also
3217 create an output file containing the next @var{n} lines of the input
3218 file once for each repeat.
3220 @item /@var{regexp}/[@var{offset}]
3221 Create an output file containing the current line up to (but not
3222 including) the next line of the input file that contains a match for
3223 @var{regexp}. The optional @var{offset} is an integer.
3224 If it is given, the input up to (but not including) the
3225 matching line plus or minus @var{offset} is put into the output file,
3226 and the line after that begins the next section of input.
3228 @item %@var{regexp}%[@var{offset}]
3229 Like the previous type, except that it does not create an output
3230 file, so that section of the input file is effectively ignored.
3232 @item @{@var{repeat-count}@}
3233 Repeat the previous pattern @var{repeat-count} additional
3234 times. The @var{repeat-count} can either be a positive integer or an
3235 asterisk, meaning repeat as many times as necessary until the input is
3240 The output files' names consist of a prefix (@samp{xx} by default)
3241 followed by a suffix. By default, the suffix is an ascending sequence
3242 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3243 concatenating the output files in sorted order by file name produces the
3244 original input file.
3246 By default, if @command{csplit} encounters an error or receives a hangup,
3247 interrupt, quit, or terminate signal, it removes any output files
3248 that it has created so far before it exits.
3250 The program accepts the following options. Also see @ref{Common options}.
3254 @item -f @var{prefix}
3255 @itemx --prefix=@var{prefix}
3258 @cindex output file name prefix
3259 Use @var{prefix} as the output file name prefix.
3261 @item -b @var{suffix}
3262 @itemx --suffix=@var{suffix}
3265 @cindex output file name suffix
3266 Use @var{suffix} as the output file name suffix. When this option is
3267 specified, the suffix string must include exactly one
3268 @code{printf(3)}-style conversion specification, possibly including
3269 format specification flags, a field width, a precision specifications,
3270 or all of these kinds of modifiers. The format letter must convert a
3271 binary unsigned integer argument to readable form. The format letters
3272 @samp{d} and @samp{i} are aliases for @samp{u}, and the
3273 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3274 entire @var{suffix} is given (with the current output file number) to
3275 @code{sprintf(3)} to form the file name suffixes for each of the
3276 individual output files in turn. If this option is used, the
3277 @option{--digits} option is ignored.
3279 @item -n @var{digits}
3280 @itemx --digits=@var{digits}
3283 Use output file names containing numbers that are @var{digits} digits
3284 long instead of the default 2.
3289 @opindex --keep-files
3290 Do not remove output files when errors are encountered.
3293 @itemx --elide-empty-files
3295 @opindex --elide-empty-files
3296 Suppress the generation of zero-length output files. (In cases where
3297 the section delimiters of the input file are supposed to mark the first
3298 lines of each of the sections, the first output file will generally be a
3299 zero-length file unless you use this option.) The output file sequence
3300 numbers always run consecutively starting from 0, even when this option
3311 Do not print counts of output file sizes.
3317 Here is an example of its usage.
3318 First, create an empty directory for the exercise,
3325 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3328 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3334 Each number printed above is the size of an output
3335 file that csplit has just created.
3336 List the names of those output files:
3343 Use @command{head} to show their contents:
3368 @node Summarizing files
3369 @chapter Summarizing files
3371 @cindex summarizing files
3373 These commands generate just a few numbers representing entire
3377 * wc invocation:: Print newline, word, and byte counts.
3378 * sum invocation:: Print checksum and block counts.
3379 * cksum invocation:: Print CRC checksum and byte counts.
3380 * md5sum invocation:: Print or check MD5 digests.
3381 * sha1sum invocation:: Print or check SHA-1 digests.
3382 * sha2 utilities:: Print or check SHA-2 digests.
3387 @section @command{wc}: Print newline, word, and byte counts
3391 @cindex character count
3395 @command{wc} counts the number of bytes, characters, whitespace-separated
3396 words, and newlines in each given @var{file}, or standard input if none
3397 are given or for a @var{file} of @samp{-}. Synopsis:
3400 wc [@var{option}]@dots{} [@var{file}]@dots{}
3403 @cindex total counts
3404 @command{wc} prints one line of counts for each file, and if the file was
3405 given as an argument, it prints the file name following the counts. If
3406 more than one @var{file} is given, @command{wc} prints a final line
3407 containing the cumulative counts, with the file name @file{total}. The
3408 counts are printed in this order: newlines, words, characters, bytes,
3409 maximum line length.
3410 Each count is printed right-justified in a field with at least one
3411 space between fields so that the numbers and file names normally line
3412 up nicely in columns. The width of the count fields varies depending
3413 on the inputs, so you should not depend on a particular field width.
3414 However, as a @acronym{GNU} extension, if only one count is printed,
3415 it is guaranteed to be printed without leading spaces.
3417 By default, @command{wc} prints three counts: the newline, words, and byte
3418 counts. Options can specify that only certain counts be printed.
3419 Options do not undo others previously given, so
3426 prints both the byte counts and the word counts.
3428 With the @option{--max-line-length} option, @command{wc} prints the length
3429 of the longest line per file, and if there is more than one file it
3430 prints the maximum (not the sum) of those lengths. The line lengths here
3431 are measured in screen columns, according to the current locale and
3432 assuming tab positions in every 8th column.
3434 The program accepts the following options. Also see @ref{Common options}.
3442 Print only the byte counts.
3448 Print only the character counts.
3454 Print only the word counts.
3460 Print only the newline counts.
3463 @itemx --max-line-length
3465 @opindex --max-line-length
3466 Print only the maximum line lengths.
3468 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3469 @itemx --files0-from=@var{file}
3470 @opindex --files0-from=@var{file}
3471 @c This is commented out to avoid a texi2dvi failure.
3472 @c texi2dvi (GNU Texinfo 4.11) 1.104
3473 @c @cindex including files from @command{\cmd\}
3474 Disallow processing files named on the command line, and instead process
3475 those named in file @var{file}; each name being terminated by a zero byte
3476 (@acronym{ASCII} @sc{nul}).
3477 This is useful \withTotalOption\
3478 when the list of file names is so long that it may exceed a command line
3480 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3481 because it splits the list into pieces and makes @command{\cmd\} print
3482 \subListOutput\ for each sublist rather than for the entire list.
3483 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file
3484 names is with @sc{gnu}
3485 @command{find}, using its @option{-print0} predicate.
3486 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated
3487 file names are read from standard input.
3489 @filesZeroFromOption{wc,,a total}
3491 For example, to find the length of the longest line in any @file{.c} or
3492 @file{.h} file in the current hierarchy, do this:
3495 find . -name '*.[ch]' -print0 |
3496 wc -L --files0-from=- | tail -n1
3504 @node sum invocation
3505 @section @command{sum}: Print checksum and block counts
3508 @cindex 16-bit checksum
3509 @cindex checksum, 16-bit
3511 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3512 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3515 sum [@var{option}]@dots{} [@var{file}]@dots{}
3518 @command{sum} prints the checksum for each @var{file} followed by the
3519 number of blocks in the file (rounded up). If more than one @var{file}
3520 is given, file names are also printed (by default). (With the
3521 @option{--sysv} option, corresponding file names are printed when there is
3522 at least one file argument.)
3524 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3525 compatible with BSD @command{sum} and prints file sizes in units of
3528 The program accepts the following options. Also see @ref{Common options}.
3534 @cindex BSD @command{sum}
3535 Use the default (BSD compatible) algorithm. This option is included for
3536 compatibility with the System V @command{sum}. Unless @option{-s} was also
3537 given, it has no effect.
3543 @cindex System V @command{sum}
3544 Compute checksums using an algorithm compatible with System V
3545 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3549 @command{sum} is provided for compatibility; the @command{cksum} program (see
3550 next section) is preferable in new applications.
3555 @node cksum invocation
3556 @section @command{cksum}: Print CRC checksum and byte counts
3559 @cindex cyclic redundancy check
3560 @cindex CRC checksum
3562 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3563 given @var{file}, or standard input if none are given or for a
3564 @var{file} of @samp{-}. Synopsis:
3567 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3570 @command{cksum} prints the CRC checksum for each file along with the number
3571 of bytes in the file, and the file name unless no arguments were given.
3573 @command{cksum} is typically used to ensure that files
3574 transferred by unreliable means (e.g., netnews) have not been corrupted,
3575 by comparing the @command{cksum} output for the received files with the
3576 @command{cksum} output for the original files (typically given in the
3579 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3580 compatible with the BSD or System V @command{sum} algorithms (see the
3581 previous section); it is more robust.
3583 The only options are @option{--help} and @option{--version}. @xref{Common
3589 @node md5sum invocation
3590 @section @command{md5sum}: Print or check MD5 digests
3594 @cindex 128-bit checksum
3595 @cindex checksum, 128-bit
3596 @cindex fingerprint, 128-bit
3597 @cindex message-digest, 128-bit
3599 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3600 @dfn{message-digest}) for each specified @var{file}.
3602 Note: The MD5 digest is more reliable than a simple CRC (provided by
3603 the @command{cksum} command) for detecting accidental file corruption,
3604 as the chances of accidentally having two files with identical MD5
3605 are vanishingly small. However, it should not be considered secure
3606 against malicious tampering: although finding a file with a given MD5
3607 fingerprint is considered infeasible at the moment, it is known how
3608 to modify certain files, including digital certificates, so that they
3609 appear valid when signed with an MD5 digest.
3610 For more secure hashes, consider using SHA-2. @xref{sha2 utilities}.
3612 If a @var{file} is specified as @samp{-} or if no files are given
3613 @command{md5sum} computes the checksum for the standard input.
3614 @command{md5sum} can also determine whether a file and checksum are
3615 consistent. Synopsis:
3618 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3621 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3622 indicating binary or text input mode, and the file name.
3623 If @var{file} contains a backslash or newline, the
3624 line is started with a backslash, and each problematic character in
3625 the file name is escaped with a backslash, making the output
3626 unambiguous even in the presence of arbitrary file names.
3627 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3629 The program accepts the following options. Also see @ref{Common options}.
3637 @cindex binary input files
3638 Treat each input file as binary, by reading it in binary mode and
3639 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3640 On systems like @acronym{GNU} that do not distinguish between binary
3641 and text files, this option merely flags each input mode as binary:
3642 the MD5 checksum is unaffected. This option is the default on systems
3643 like MS-DOS that distinguish between binary and text files, except
3644 for reading standard input when standard input is a terminal.
3648 Read file names and checksum information (not data) from each
3649 @var{file} (or from stdin if no @var{file} was specified) and report
3650 whether the checksums match the contents of the named files.
3651 The input to this mode of @command{md5sum} is usually the output of
3652 a prior, checksum-generating run of @samp{md5sum}.
3653 Each valid line of input consists of an MD5 checksum, a binary/text
3654 flag, and then a file name.
3655 Binary mode is indicated with @samp{*}, text with @samp{ } (space).
3656 For each such line, @command{md5sum} reads the named file and computes its
3657 MD5 checksum. Then, if the computed message digest does not match the
3658 one on the line with the file name, the file is noted as having
3659 failed the test. Otherwise, the file passes the test.
3660 By default, for each valid line, one line is written to standard
3661 output indicating whether the named file passed the test.
3662 After all checks have been performed, if there were any failures,
3663 a warning is issued to standard error.
3664 Use the @option{--status} option to inhibit that output.
3665 If any listed file cannot be opened or read, if any valid line has
3666 an MD5 checksum inconsistent with the associated file, or if no valid
3667 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3668 it exits successfully.
3672 @cindex verifying MD5 checksums
3673 This option is useful only when verifying checksums.
3674 When verifying checksums, don't generate an 'OK' message per successfully
3675 checked file. Files that fail the verification are reported in the
3676 default one-line-per-file format. If there is any checksum mismatch,
3677 print a warning summarizing the failures to standard error.
3681 @cindex verifying MD5 checksums
3682 This option is useful only when verifying checksums.
3683 When verifying checksums, don't generate the default one-line-per-file
3684 diagnostic and don't output the warning summarizing any failures.
3685 Failures to open or read a file still evoke individual diagnostics to
3687 If all listed files are readable and are consistent with the associated
3688 MD5 checksums, exit successfully. Otherwise exit with a status code
3689 indicating there was a failure.
3695 @cindex text input files
3696 Treat each input file as text, by reading it in text mode and
3697 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3698 This option is the default on systems like @acronym{GNU} that do not
3699 distinguish between binary and text files. On other systems, it is
3700 the default for reading standard input when standard input is a
3707 @cindex verifying MD5 checksums
3708 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3709 This option is useful only if all but a few lines in the checked input
3714 @cindex verifying MD5 checksums
3715 When verifying checksums,
3716 if one or more input line is invalid,
3717 exit nonzero after all warnings have been issued.
3724 @node sha1sum invocation
3725 @section @command{sha1sum}: Print or check SHA-1 digests
3729 @cindex 160-bit checksum
3730 @cindex checksum, 160-bit
3731 @cindex fingerprint, 160-bit
3732 @cindex message-digest, 160-bit
3734 @command{sha1sum} computes a 160-bit checksum for each specified
3735 @var{file}. The usage and options of this command are precisely the
3736 same as for @command{md5sum}. @xref{md5sum invocation}.
3738 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3739 it are known (different files having the same fingerprint). However,
3740 it is known that they can be produced with considerable, but not
3741 unreasonable, resources. For this reason, it is generally considered
3742 that SHA-1 should be gradually phased out in favor of the more secure
3743 SHA-2 hash algorithms. @xref{sha2 utilities}.
3746 @node sha2 utilities
3747 @section sha2 utilities: Print or check SHA-2 digests
3754 @cindex 224-bit checksum
3755 @cindex 256-bit checksum
3756 @cindex 384-bit checksum
3757 @cindex 512-bit checksum
3758 @cindex checksum, 224-bit
3759 @cindex checksum, 256-bit
3760 @cindex checksum, 384-bit
3761 @cindex checksum, 512-bit
3762 @cindex fingerprint, 224-bit
3763 @cindex fingerprint, 256-bit
3764 @cindex fingerprint, 384-bit
3765 @cindex fingerprint, 512-bit
3766 @cindex message-digest, 224-bit
3767 @cindex message-digest, 256-bit
3768 @cindex message-digest, 384-bit
3769 @cindex message-digest, 512-bit
3771 The commands @command{sha224sum}, @command{sha256sum},
3772 @command{sha384sum} and @command{sha512sum} compute checksums of
3773 various lengths (respectively 224, 256, 384 and 512 bits),
3774 collectively known as the SHA-2 hashes. The usage and options of
3775 these commands are precisely the same as for @command{md5sum}.
3776 @xref{md5sum invocation}.
3778 Note: The SHA384 and SHA512 digests are considerably slower to
3779 compute, especially on 32-bit computers, than SHA224 or SHA256.
3782 @node Operating on sorted files
3783 @chapter Operating on sorted files
3785 @cindex operating on sorted files
3786 @cindex sorted files, operations on
3788 These commands work with (or produce) sorted files.
3791 * sort invocation:: Sort text files.
3792 * shuf invocation:: Shuffle text files.
3793 * uniq invocation:: Uniquify files.
3794 * comm invocation:: Compare two sorted files line by line.
3795 * ptx invocation:: Produce a permuted index of file contents.
3796 * tsort invocation:: Topological sort.
3800 @node sort invocation
3801 @section @command{sort}: Sort text files
3804 @cindex sorting files
3806 @command{sort} sorts, merges, or compares all the lines from the given
3807 files, or standard input if none are given or for a @var{file} of
3808 @samp{-}. By default, @command{sort} writes the results to standard
3812 sort [@var{option}]@dots{} [@var{file}]@dots{}
3815 @command{sort} has three modes of operation: sort (the default), merge,
3816 and check for sortedness. The following options change the operation
3823 @itemx --check=diagnose-first
3826 @cindex checking for sortedness
3827 Check whether the given file is already sorted: if it is not all
3828 sorted, print a diagnostic containing the first out-of-order line and
3829 exit with a status of 1.
3830 Otherwise, exit successfully.
3831 At most one input file can be given.
3834 @itemx --check=quiet
3835 @itemx --check=silent
3838 @cindex checking for sortedness
3839 Exit successfully if the given file is already sorted, and
3840 exit with status 1 otherwise.
3841 At most one input file can be given.
3842 This is like @option{-c}, except it does not print a diagnostic.
3848 @cindex merging sorted files
3849 Merge the given files by sorting them as a group. Each input file must
3850 always be individually sorted. It always works to sort instead of
3851 merge; merging is provided because it is faster, in the case where it
3856 @cindex sort stability
3857 @cindex sort's last-resort comparison
3858 A pair of lines is compared as follows:
3859 @command{sort} compares each pair of fields, in the
3860 order specified on the command line, according to the associated
3861 ordering options, until a difference is found or no fields are left.
3862 If no key fields are specified, @command{sort} uses a default key of
3863 the entire line. Finally, as a last resort when all keys compare
3864 equal, @command{sort} compares entire lines as if no ordering options
3865 other than @option{--reverse} (@option{-r}) were specified. The
3866 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3867 comparison} so that lines in which all fields compare equal are left
3868 in their original relative order. The @option{--unique}
3869 (@option{-u}) option also disables the last-resort comparison.
3873 Unless otherwise specified, all comparisons use the character collating
3874 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3875 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3876 to @samp{en_US}), then @command{sort} may produce output that is sorted
3877 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3878 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3879 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3880 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3881 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3882 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3883 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3885 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3886 limit on input line length or restrictions on bytes allowed within lines.
3887 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3888 @command{sort} silently supplies one. A line's trailing newline is not
3889 part of the line for comparison purposes.
3891 @cindex exit status of @command{sort}
3895 0 if no error occurred
3896 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3897 2 if an error occurred
3901 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3902 value as the directory for temporary files instead of @file{/tmp}. The
3903 @option{--temporary-directory} (@option{-T}) option in turn overrides
3904 the environment variable.
3906 The following options affect the ordering of output lines. They may be
3907 specified globally or as part of a specific key field. If no key
3908 fields are specified, global options apply to comparison of entire
3909 lines; otherwise the global options are inherited by key fields that do
3910 not specify any special options of their own. In pre-@acronym{POSIX}
3911 versions of @command{sort}, global options affect only later key fields,
3912 so portable shell scripts should specify global options first.
3917 @itemx --ignore-leading-blanks
3919 @opindex --ignore-leading-blanks
3920 @cindex blanks, ignoring leading
3922 Ignore leading blanks when finding sort keys in each line.
3923 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3924 can change this. Note blanks may be ignored by your locale's collating
3925 rules, but without this option they will be significant for character
3926 positions specified in keys with the @option{-k} option.
3929 @itemx --dictionary-order
3931 @opindex --dictionary-order
3932 @cindex dictionary order
3933 @cindex phone directory order
3934 @cindex telephone directory order
3936 Sort in @dfn{phone directory} order: ignore all characters except
3937 letters, digits and blanks when sorting.
3938 By default letters and digits are those of @acronym{ASCII} and a blank
3939 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3942 @itemx --ignore-case
3944 @opindex --ignore-case
3945 @cindex ignoring case
3946 @cindex case folding
3948 Fold lowercase characters into the equivalent uppercase characters when
3949 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3950 The @env{LC_CTYPE} locale determines character types.
3951 When used with @option{--unique} those lower case equivalent lines are
3952 thrown away. (There is currently no way to throw away the upper case
3953 equivalent instead. (Any @option{--reverse} given would only affect
3954 the final result, after the throwing away.))
3957 @itemx --general-numeric-sort
3958 @itemx --sort=general-numeric
3960 @opindex --general-numeric-sort
3962 @cindex general numeric sort
3964 Sort numerically, converting a prefix of each line to a long
3965 double-precision floating point number. @xref{Floating point}.
3966 Do not report overflow, underflow, or conversion errors.
3967 Use the following collating sequence:
3971 Lines that do not start with numbers (all considered to be equal).
3973 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3974 in a consistent but machine-dependent order.
3978 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3983 Use this option only if there is no alternative; it is much slower than
3984 @option{--numeric-sort} (@option{-n}) and it can lose information when
3985 converting to floating point.
3988 @itemx --human-numeric-sort
3989 @itemx --sort=human-numeric
3991 @opindex --human-numeric-sort
3993 @cindex human numeric sort
3995 Sort numerically, first by numeric sign (negative, zero, or positive);
3996 then by @acronym{SI} suffix (either empty, or @samp{k} or @samp{K}, or
3997 one of @samp{MGTPEZY}, in that order; @pxref{Block size}); and finally
3998 by numeric value. For example, @samp{1023M} sorts before @samp{1G}
3999 because @samp{M} (mega) precedes @samp{G} (giga) as an @acronym{SI}
4000 suffix. This option sorts values that are consistently scaled to the
4001 nearest suffix, regardless of whether suffixes denote powers of 1000
4002 or 1024, and it therefore sorts the output of any single invocation of
4003 the @command{df}, @command{du}, or @command{ls} commands that are
4004 invoked with their @option{--human-readable} or @option{--si} options.
4005 The syntax for numbers is the same as for the @option{--numeric-sort}
4006 option; the @acronym{SI} suffix must immediately follow the number.
4009 @itemx --ignore-nonprinting
4011 @opindex --ignore-nonprinting
4012 @cindex nonprinting characters, ignoring
4013 @cindex unprintable characters, ignoring
4015 Ignore nonprinting characters.
4016 The @env{LC_CTYPE} locale determines character types.
4017 This option has no effect if the stronger @option{--dictionary-order}
4018 (@option{-d}) option is also given.
4024 @opindex --month-sort
4026 @cindex months, sorting by
4028 An initial string, consisting of any amount of blanks, followed
4029 by a month name abbreviation, is folded to UPPER case and
4030 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
4031 Invalid names compare low to valid names. The @env{LC_TIME} locale
4032 category determines the month spellings.
4033 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4037 @itemx --numeric-sort
4038 @itemx --sort=numeric
4040 @opindex --numeric-sort
4042 @cindex numeric sort
4044 Sort numerically. The number begins each line and consists
4045 of optional blanks, an optional @samp{-} sign, and zero or more
4046 digits possibly separated by thousands separators, optionally followed
4047 by a decimal-point character and zero or more digits. An empty
4048 number is treated as @samp{0}. The @env{LC_NUMERIC}
4049 locale specifies the decimal-point character and thousands separator.
4050 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4053 Comparison is exact; there is no rounding error.
4055 Neither a leading @samp{+} nor exponential notation is recognized.
4056 To compare such strings numerically, use the
4057 @option{--general-numeric-sort} (@option{-g}) option.
4060 @itemx --version-sort
4062 @opindex --version-sort
4063 @cindex version number sort
4064 Sort by version name and number. It behaves like a standard sort,
4065 except that each sequence of decimal digits is treated numerically
4066 as an index/version number. (@xref{Details about version sort}.)
4072 @cindex reverse sorting
4073 Reverse the result of comparison, so that lines with greater key values
4074 appear earlier in the output instead of later.
4077 @itemx --random-sort
4078 @itemx --sort=random
4080 @opindex --random-sort
4083 Sort by hashing the input keys and then sorting the hash values.
4084 Choose the hash function at random, ensuring that it is free of
4085 collisions so that differing keys have differing hash values. This is
4086 like a random permutation of the inputs (@pxref{shuf invocation}),
4087 except that keys with the same value sort together.
4089 If multiple random sort fields are specified, the same random hash
4090 function is used for all fields. To use different random hash
4091 functions for different fields, you can invoke @command{sort} more
4094 The choice of hash function is affected by the
4095 @option{--random-source} option.
4103 @item --compress-program=@var{prog}
4104 Compress any temporary files with the program @var{prog}.
4106 With no arguments, @var{prog} must compress standard input to standard
4107 output, and when given the @option{-d} option it must decompress
4108 standard input to standard output.
4110 Terminate with an error if @var{prog} exits with nonzero status.
4112 White space and the backslash character should not appear in
4113 @var{prog}; they are reserved for future use.
4115 @filesZeroFromOption{sort,,sorted output}
4117 @item -k @var{pos1}[,@var{pos2}]
4118 @itemx --key=@var{pos1}[,@var{pos2}]
4122 Specify a sort field that consists of the part of the line between
4123 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
4124 omitted), @emph{inclusive}.
4126 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
4127 where @var{f} is the number of the field to use, and @var{c} is the number
4128 of the first character from the beginning of the field. Fields and character
4129 positions are numbered starting with 1; a character position of zero in
4130 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
4131 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
4132 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
4133 @var{opts} are ordering options, allowing individual keys to be sorted
4134 according to different rules; see below for details. Keys can span
4137 Example: To sort on the second field, use @option{--key=2,2}
4138 (@option{-k 2,2}). See below for more notes on keys and more examples.
4139 See also the @option{--debug} option to help determine the part
4140 of the line being used in the sort.
4143 Highlight the portion of each line used for sorting.
4144 Also issue warnings about questionable usage to stderr.
4146 @item --batch-size=@var{nmerge}
4147 @opindex --batch-size
4148 @cindex number of inputs to merge, nmerge
4149 Merge at most @var{nmerge} inputs at once.
4151 When @command{sort} has to merge more than @var{nmerge} inputs,
4152 it merges them in groups of @var{nmerge}, saving the result in
4153 a temporary file, which is then used as an input in a subsequent merge.
4155 A large value of @var{nmerge} may improve merge performance and decrease
4156 temporary storage utilization at the expense of increased memory usage
4157 and I/O. Conversely a small value of @var{nmerge} may reduce memory
4158 requirements and I/O at the expense of temporary storage consumption and
4161 The value of @var{nmerge} must be at least 2. The default value is
4162 currently 16, but this is implementation-dependent and may change in
4165 The value of @var{nmerge} may be bounded by a resource limit for open
4166 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
4167 OPEN_MAX} may display limits for your systems; these limits may be
4168 modified further if your program already has some files open, or if
4169 the operating system has other limits on the number of open files. If
4170 the value of @var{nmerge} exceeds the resource limit, @command{sort}
4171 silently uses a smaller value.
4173 @item -o @var{output-file}
4174 @itemx --output=@var{output-file}
4177 @cindex overwriting of input, allowed
4178 Write output to @var{output-file} instead of standard output.
4179 Normally, @command{sort} reads all input before opening
4180 @var{output-file}, so you can safely sort a file in place by using
4181 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
4182 However, @command{sort} with @option{--merge} (@option{-m}) can open
4183 the output file before reading all input, so a command like @code{cat
4184 F | sort -m -o F - G} is not safe as @command{sort} might start
4185 writing @file{F} before @command{cat} is done reading it.
4187 @vindex POSIXLY_CORRECT
4188 On newer systems, @option{-o} cannot appear after an input file if
4189 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
4190 scripts should specify @option{-o @var{output-file}} before any input
4193 @item --random-source=@var{file}
4194 @opindex --random-source
4195 @cindex random source for sorting
4196 Use @var{file} as a source of random data used to determine which
4197 random hash function to use with the @option{-R} option. @xref{Random
4204 @cindex sort stability
4205 @cindex sort's last-resort comparison
4207 Make @command{sort} stable by disabling its last-resort comparison.
4208 This option has no effect if no fields or global ordering options
4209 other than @option{--reverse} (@option{-r}) are specified.
4212 @itemx --buffer-size=@var{size}
4214 @opindex --buffer-size
4215 @cindex size for main memory sorting
4216 Use a main-memory sort buffer of the given @var{size}. By default,
4217 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4218 @var{size} to be interpreted as a percentage of physical memory.
4219 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4220 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4221 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4222 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4225 This option can improve the performance of @command{sort} by causing it
4226 to start with a larger or smaller sort buffer than the default.
4227 However, this option affects only the initial buffer size. The buffer
4228 grows beyond @var{size} if @command{sort} encounters input lines larger
4231 @item -t @var{separator}
4232 @itemx --field-separator=@var{separator}
4234 @opindex --field-separator
4235 @cindex field separator character
4236 Use character @var{separator} as the field separator when finding the
4237 sort keys in each line. By default, fields are separated by the empty
4238 string between a non-blank character and a blank character.
4239 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4242 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4243 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4244 not considered to be part of either the field preceding or the field
4245 following, so with @samp{sort @w{-t " "}} the same input line has
4246 three fields: an empty field, @samp{foo}, and @samp{bar}.
4247 However, fields that extend to the end of the line,
4248 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4249 retain the field separators present between the endpoints of the range.
4251 To specify @acronym{ASCII} @sc{nul} as the field separator,
4252 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4254 @item -T @var{tempdir}
4255 @itemx --temporary-directory=@var{tempdir}
4257 @opindex --temporary-directory
4258 @cindex temporary directory
4260 Use directory @var{tempdir} to store temporary files, overriding the
4261 @env{TMPDIR} environment variable. If this option is given more than
4262 once, temporary files are stored in all the directories given. If you
4263 have a large sort or merge that is I/O-bound, you can often improve
4264 performance by using this option to specify directories on different
4265 disks and controllers.
4267 @item --parallel=@var{n}
4269 @cindex multithreaded sort
4270 Set the number of sorts run in parallel to @var{n}. By default,
4271 @var{n} is set to the number of available processors, but limited
4272 to 8, as there are diminishing performance gains after that.
4273 Note also that using @var{n} threads increases the memory usage by
4274 a factor of log @var{n}. Also see @ref{nproc invocation}.
4280 @cindex uniquifying output
4282 Normally, output only the first of a sequence of lines that compare
4283 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4284 check that no pair of consecutive lines compares equal.
4286 This option also disables the default last-resort comparison.
4288 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4289 this equivalence does not extend to arbitrary @command{sort} options.
4290 For example, @code{sort -n -u} inspects only the value of the initial
4291 numeric string when checking for uniqueness, whereas @code{sort -n |
4292 uniq} inspects the entire line. @xref{uniq invocation}.
4294 @macro zeroTerminatedOption
4296 @itemx --zero-terminated
4298 @opindex --zero-terminated
4299 @cindex process zero-terminated items
4300 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4301 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4302 and terminate output items with @acronym{ASCII} @sc{nul}.
4303 This option can be useful in conjunction with @samp{perl -0} or
4304 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4305 reliably handle arbitrary file names (even those containing blanks
4306 or other special characters).
4308 @zeroTerminatedOption
4312 Historical (BSD and System V) implementations of @command{sort} have
4313 differed in their interpretation of some options, particularly
4314 @option{-b}, @option{-f}, and @option{-n}.
4315 @sc{gnu} sort follows the @acronym{POSIX}
4316 behavior, which is usually (but not always!) like the System V behavior.
4317 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4318 consistency, @option{-M} has been changed in the same way. This may
4319 affect the meaning of character positions in field specifications in
4320 obscure cases. The only fix is to add an explicit @option{-b}.
4322 A position in a sort field specified with @option{-k} may have any
4323 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4324 global ordering options are inherited by that particular field. The
4325 @option{-b} option may be independently attached to either or both of
4326 the start and end positions of a field specification, and if it is
4327 inherited from the global options it will be attached to both.
4328 If input lines can contain leading or adjacent blanks and @option{-t}
4329 is not used, then @option{-k} is typically combined with @option{-b} or
4330 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4331 the varying numbers of leading blanks in fields can cause confusing results.
4333 If the start position in a sort field specifier falls after the end of
4334 the line or after the end field, the field is empty. If the @option{-b}
4335 option was specified, the @samp{.@var{c}} part of a field specification
4336 is counted from the first nonblank character of the field.
4338 @vindex _POSIX2_VERSION
4339 @vindex POSIXLY_CORRECT
4340 On older systems, @command{sort} supports an obsolete origin-zero
4341 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4342 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4343 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4344 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4345 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4347 This obsolete behavior can be enabled or disabled with the
4348 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4349 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4350 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4352 Scripts intended for use on standard hosts should avoid obsolete
4353 syntax and should use @option{-k} instead. For example, avoid
4354 @samp{sort +2}, since it might be interpreted as either @samp{sort
4355 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4356 support only the obsolete syntax, it can use a test like @samp{if sort
4357 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4360 Here are some examples to illustrate various combinations of options.
4365 Sort in descending (reverse) numeric order.
4372 Run no more than 4 sorts concurrently, using a buffer size of 10M.
4375 sort --parallel=4 -S 10M
4379 Sort alphabetically, omitting the first and second fields
4380 and the blanks at the start of the third field.
4381 This uses a single key composed of the characters beginning
4382 at the start of the first nonblank character in field three
4383 and extending to the end of each line.
4390 Sort numerically on the second field and resolve ties by sorting
4391 alphabetically on the third and fourth characters of field five.
4392 Use @samp{:} as the field delimiter.
4395 sort -t : -k 2,2n -k 5.3,5.4
4398 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4399 @command{sort} would have used all characters beginning in the second field
4400 and extending to the end of the line as the primary @emph{numeric}
4401 key. For the large majority of applications, treating keys spanning
4402 more than one field as numeric will not do what you expect.
4404 Also note that the @samp{n} modifier was applied to the field-end
4405 specifier for the first key. It would have been equivalent to
4406 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4407 @samp{b} apply to the associated @emph{field}, regardless of whether
4408 the modifier character is attached to the field-start and/or the
4409 field-end part of the key specifier.
4412 Sort the password file on the fifth field and ignore any
4413 leading blanks. Sort lines with equal values in field five
4414 on the numeric user ID in field three. Fields are separated
4418 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4419 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4420 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4423 These three commands have equivalent effect. The first specifies that
4424 the first key's start position ignores leading blanks and the second
4425 key is sorted numerically. The other two commands rely on global
4426 options being inherited by sort keys that lack modifiers. The inheritance
4427 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4428 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4429 character position is not affected by whether initial blanks are
4433 Sort a set of log files, primarily by IPv4 address and secondarily by
4434 time stamp. If two lines' primary and secondary keys are identical,
4435 output the lines in the same order that they were input. The log
4436 files contain lines that look like this:
4439 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4440 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4443 Fields are separated by exactly one space. Sort IPv4 addresses
4444 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4445 because 61 is less than 129.
4448 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4449 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4452 This example cannot be done with a single @command{sort} invocation,
4453 since IPv4 address components are separated by @samp{.} while dates
4454 come just after a space. So it is broken down into two invocations of
4455 @command{sort}: the first sorts by time stamp and the second by IPv4
4456 address. The time stamp is sorted by year, then month, then day, and
4457 finally by hour-minute-second field, using @option{-k} to isolate each
4458 field. Except for hour-minute-second there's no need to specify the
4459 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4460 based on leading prefixes that cannot cross field boundaries. The
4461 IPv4 addresses are sorted lexicographically. The second sort uses
4462 @samp{-s} so that ties in the primary key are broken by the secondary
4463 key; the first sort uses @samp{-s} so that the combination of the two
4467 Generate a tags file in case-insensitive sorted order.
4470 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4473 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4474 that file names that contain blanks or other special characters are
4476 by the sort operation.
4478 @c This example is a bit contrived and needs more explanation.
4480 @c Sort records separated by an arbitrary string by using a pipe to convert
4481 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4482 @c and converting each @samp{\0} back to the original record delimiter.
4485 @c printf 'c\n\nb\n\na\n' |
4486 @c perl -0pe 's/\n\n/\n\0/g' |
4488 @c perl -0pe 's/\0/\n/g'
4492 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4493 sort lines according to their length.
4496 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4499 In general this technique can be used to sort data that the @command{sort}
4500 command does not support, or is inefficient at, sorting directly.
4503 Shuffle a list of directories, but preserve the order of files within
4504 each directory. For instance, one could use this to generate a music
4505 playlist in which albums are shuffled but the songs of each album are
4509 ls */* | sort -t / -k 1,1R -k 2,2
4515 @node shuf invocation
4516 @section @command{shuf}: Shuffling text
4519 @cindex shuffling files
4521 @command{shuf} shuffles its input by outputting a random permutation
4522 of its input lines. Each output permutation is equally likely.
4526 shuf [@var{option}]@dots{} [@var{file}]
4527 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4528 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4531 @command{shuf} has three modes of operation that affect where it
4532 obtains its input lines. By default, it reads lines from standard
4533 input. The following options change the operation mode:
4541 @cindex command-line operands to shuffle
4542 Treat each command-line operand as an input line.
4544 @item -i @var{lo}-@var{hi}
4545 @itemx --input-range=@var{lo}-@var{hi}
4547 @opindex --input-range
4548 @cindex input range to shuffle
4549 Act as if input came from a file containing the range of unsigned
4550 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4554 @command{shuf}'s other options can affect its behavior in all
4559 @item -n @var{lines}
4560 @itemx --head-count=@var{count}
4562 @opindex --head-count
4563 @cindex head of output
4564 Output at most @var{count} lines. By default, all input lines are
4567 @item -o @var{output-file}
4568 @itemx --output=@var{output-file}
4571 @cindex overwriting of input, allowed
4572 Write output to @var{output-file} instead of standard output.
4573 @command{shuf} reads all input before opening
4574 @var{output-file}, so you can safely shuffle a file in place by using
4575 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4577 @item --random-source=@var{file}
4578 @opindex --random-source
4579 @cindex random source for shuffling
4580 Use @var{file} as a source of random data used to determine which
4581 permutation to generate. @xref{Random sources}.
4583 @zeroTerminatedOption
4599 might produce the output
4609 Similarly, the command:
4612 shuf -e clubs hearts diamonds spades
4626 and the command @samp{shuf -i 1-4} might output:
4636 These examples all have four input lines, so @command{shuf} might
4637 produce any of the twenty-four possible permutations of the input. In
4638 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4639 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4640 output permutations.
4645 @node uniq invocation
4646 @section @command{uniq}: Uniquify files
4649 @cindex uniquify files
4651 @command{uniq} writes the unique lines in the given @file{input}, or
4652 standard input if nothing is given or for an @var{input} name of
4656 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4659 By default, @command{uniq} prints its input lines, except that
4660 it discards all but the first of adjacent repeated lines, so that
4661 no output lines are repeated. Optionally, it can instead discard
4662 lines that are not repeated, or all repeated lines.
4664 The input need not be sorted, but repeated input lines are detected
4665 only if they are adjacent. If you want to discard non-adjacent
4666 duplicate lines, perhaps you want to use @code{sort -u}.
4667 @xref{sort invocation}.
4670 Comparisons honor the rules specified by the @env{LC_COLLATE}
4673 If no @var{output} file is specified, @command{uniq} writes to standard
4676 The program accepts the following options. Also see @ref{Common options}.
4681 @itemx --skip-fields=@var{n}
4683 @opindex --skip-fields
4684 Skip @var{n} fields on each line before checking for uniqueness. Use
4685 a null string for comparison if a line has fewer than @var{n} fields. Fields
4686 are sequences of non-space non-tab characters that are separated from
4687 each other by at least one space or tab.
4689 For compatibility @command{uniq} supports an obsolete option syntax
4690 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4693 @itemx --skip-chars=@var{n}
4695 @opindex --skip-chars
4696 Skip @var{n} characters before checking for uniqueness. Use a null string
4697 for comparison if a line has fewer than @var{n} characters. If you use both
4698 the field and character skipping options, fields are skipped over first.
4700 @vindex _POSIX2_VERSION
4701 On older systems, @command{uniq} supports an obsolete option syntax
4703 This obsolete behavior can be enabled or disabled with the
4704 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4705 conformance}), but portable scripts should avoid commands whose
4706 behavior depends on this variable.
4707 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4708 the ambiguous @samp{uniq +10}.
4714 Print the number of times each line occurred along with the line.
4717 @itemx --ignore-case
4719 @opindex --ignore-case
4720 Ignore differences in case when comparing lines.
4726 @cindex repeated lines, outputting
4727 Discard lines that are not repeated. When used by itself, this option
4728 causes @command{uniq} to print the first copy of each repeated line,
4732 @itemx --all-repeated[=@var{delimit-method}]
4734 @opindex --all-repeated
4735 @cindex all repeated lines, outputting
4736 Do not discard the second and subsequent repeated input lines,
4737 but discard lines that are not repeated.
4738 This option is useful mainly in conjunction with other options e.g.,
4739 to ignore case or to compare only selected fields.
4740 The optional @var{delimit-method} tells how to delimit
4741 groups of repeated lines, and must be one of the following:
4746 Do not delimit groups of repeated lines.
4747 This is equivalent to @option{--all-repeated} (@option{-D}).
4750 Output a newline before each group of repeated lines.
4751 With @option{--zero-terminated} (@option{-z}), use a zero
4752 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4755 Separate groups of repeated lines with a single newline.
4756 With @option{--zero-terminated} (@option{-z}), use a zero
4757 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4758 This is the same as using @samp{prepend}, except that
4759 no delimiter is inserted before the first group, and hence
4760 may be better suited for output direct to users.
4763 Note that when groups are delimited and the input stream contains
4764 two or more consecutive blank lines, then the output is ambiguous.
4765 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4766 each sequence of consecutive newlines with a single newline.
4768 This is a @sc{gnu} extension.
4769 @c FIXME: give an example showing *how* it's useful
4775 @cindex unique lines, outputting
4776 Discard the first repeated line. When used by itself, this option
4777 causes @command{uniq} to print unique lines, and nothing else.
4780 @itemx --check-chars=@var{n}
4782 @opindex --check-chars
4783 Compare at most @var{n} characters on each line (after skipping any specified
4784 fields and characters). By default the entire rest of the lines are
4787 @zeroTerminatedOption
4794 @node comm invocation
4795 @section @command{comm}: Compare two sorted files line by line
4798 @cindex line-by-line comparison
4799 @cindex comparing sorted files
4801 @command{comm} writes to standard output lines that are common, and lines
4802 that are unique, to two input files; a file name of @samp{-} means
4803 standard input. Synopsis:
4806 comm [@var{option}]@dots{} @var{file1} @var{file2}
4810 Before @command{comm} can be used, the input files must be sorted using the
4811 collating sequence specified by the @env{LC_COLLATE} locale.
4812 If an input file ends in a non-newline
4813 character, a newline is silently appended. The @command{sort} command with
4814 no options always outputs a file that is suitable input to @command{comm}.
4816 @cindex differing lines
4817 @cindex common lines
4818 With no options, @command{comm} produces three-column output. Column one
4819 contains lines unique to @var{file1}, column two contains lines unique
4820 to @var{file2}, and column three contains lines common to both files.
4821 Columns are separated by a single TAB character.
4822 @c FIXME: when there's an option to supply an alternative separator
4823 @c string, append "by default" to the above sentence.
4828 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4829 the corresponding columns (and separators). Also see @ref{Common options}.
4831 Unlike some other comparison utilities, @command{comm} has an exit
4832 status that does not depend on the result of the comparison.
4833 Upon normal completion @command{comm} produces an exit code of zero.
4834 If there is an error it exits with nonzero status.
4836 @macro checkOrderOption{cmd}
4837 If the @option{--check-order} option is given, unsorted inputs will
4838 cause a fatal error message. If the option @option{--nocheck-order}
4839 is given, unsorted inputs will never cause an error message. If neither
4840 of these options is given, wrongly sorted inputs are diagnosed
4841 only if an input file is found to contain unpairable
4843 lines, and when both input files are non empty.
4845 @ifclear JOIN_COMMAND
4848 If an input file is diagnosed as being unsorted, the @command{\cmd\}
4849 command will exit with a nonzero status (and the output should not be used).
4851 Forcing @command{\cmd\} to process wrongly sorted input files
4852 containing unpairable lines by specifying @option{--nocheck-order} is
4853 not guaranteed to produce any particular output. The output will
4854 probably not correspond with whatever you hoped it would be.
4856 @checkOrderOption{comm}
4861 Fail with an error message if either input file is wrongly ordered.
4863 @item --nocheck-order
4864 Do not check that both input files are in sorted order.
4868 @item --output-delimiter=@var{str}
4869 Print @var{str} between adjacent output columns,
4870 rather than the default of a single TAB character.
4872 The delimiter @var{str} may not be empty.
4876 @node ptx invocation
4877 @section @command{ptx}: Produce permuted indexes
4881 @command{ptx} reads a text file and essentially produces a permuted index, with
4882 each keyword in its context. The calling sketch is either one of:
4885 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4886 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4889 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4890 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4891 limitations and changing several of the program's default option values.
4892 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4893 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4894 document. For the full list, see @xref{Compatibility in ptx}.
4896 Individual options are explained in the following sections.
4898 When @sc{gnu} extensions are enabled, there may be zero, one or several
4899 @var{file}s after the options. If there is no @var{file}, the program
4900 reads the standard input. If there is one or several @var{file}s, they
4901 give the name of input files which are all read in turn, as if all the
4902 input files were concatenated. However, there is a full contextual
4903 break between each file and, when automatic referencing is requested,
4904 file names and line numbers refer to individual text input files. In
4905 all cases, the program outputs the permuted index to the standard
4908 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4909 operates in traditional mode, there may be zero, one or two parameters
4910 besides the options. If there are no parameters, the program reads the
4911 standard input and outputs the permuted index to the standard output.
4912 If there is only one parameter, it names the text @var{input} to be read
4913 instead of the standard input. If two parameters are given, they give
4914 respectively the name of the @var{input} file to read and the name of
4915 the @var{output} file to produce. @emph{Be very careful} to note that,
4916 in this case, the contents of file given by the second parameter is
4917 destroyed. This behavior is dictated by System V @command{ptx}
4918 compatibility; @sc{gnu} Standards normally discourage output parameters not
4919 introduced by an option.
4921 Note that for @emph{any} file named as the value of an option or as an
4922 input text file, a single dash @kbd{-} may be used, in which case
4923 standard input is assumed. However, it would not make sense to use this
4924 convention more than once per program invocation.
4927 * General options in ptx:: Options which affect general program behavior.
4928 * Charset selection in ptx:: Underlying character set considerations.
4929 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4930 * Output formatting in ptx:: Types of output format, and sizing the fields.
4931 * Compatibility in ptx::
4935 @node General options in ptx
4936 @subsection General options
4941 @itemx --traditional
4942 As already explained, this option disables all @sc{gnu} extensions to
4943 @command{ptx} and switches to traditional mode.
4946 Print a short help on standard output, then exit without further
4950 Print the program version on standard output, then exit without further
4958 @node Charset selection in ptx
4959 @subsection Charset selection
4961 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4962 As it is set up now, the program assumes that the input file is coded
4963 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4964 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4965 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4966 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4967 of characters which are letters is different; this alters the behavior
4968 of regular expression matching. Thus, the default regular expression
4969 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4970 however, is still crude; it obeys the underlying character set ordering
4976 @itemx --ignore-case
4977 Fold lower case letters to upper case for sorting.
4982 @node Input processing in ptx
4983 @subsection Word selection and input processing
4988 @itemx --break-file=@var{file}
4990 This option provides an alternative (to @option{-W}) method of describing
4991 which characters make up words. It introduces the name of a
4992 file which contains a list of characters which can@emph{not} be part of
4993 one word; this file is called the @dfn{Break file}. Any character which
4994 is not part of the Break file is a word constituent. If both options
4995 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4996 @option{-b} is ignored.
4998 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4999 break character is to write all the break characters in the file with no
5000 newline at all, not even at the end of the file. When @sc{gnu} extensions
5001 are disabled, spaces, tabs and newlines are always considered as break
5002 characters even if not included in the Break file.
5005 @itemx --ignore-file=@var{file}
5007 The file associated with this option contains a list of words which will
5008 never be taken as keywords in concordance output. It is called the
5009 @dfn{Ignore file}. The file contains exactly one word in each line; the
5010 end of line separation of words is not subject to the value of the
5014 @itemx --only-file=@var{file}
5016 The file associated with this option contains a list of words which will
5017 be retained in concordance output; any word not mentioned in this file
5018 is ignored. The file is called the @dfn{Only file}. The file contains
5019 exactly one word in each line; the end of line separation of words is
5020 not subject to the value of the @option{-S} option.
5022 There is no default for the Only file. When both an Only file and an
5023 Ignore file are specified, a word is considered a keyword only
5024 if it is listed in the Only file and not in the Ignore file.
5029 On each input line, the leading sequence of non-white space characters will be
5030 taken to be a reference that has the purpose of identifying this input
5031 line in the resulting permuted index. For more information about reference
5032 production, see @xref{Output formatting in ptx}.
5033 Using this option changes the default value for option @option{-S}.
5035 Using this option, the program does not try very hard to remove
5036 references from contexts in output, but it succeeds in doing so
5037 @emph{when} the context ends exactly at the newline. If option
5038 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
5039 are disabled, this condition is always met and references are completely
5040 excluded from the output contexts.
5042 @item -S @var{regexp}
5043 @itemx --sentence-regexp=@var{regexp}
5045 This option selects which regular expression will describe the end of a
5046 line or the end of a sentence. In fact, this regular expression is not
5047 the only distinction between end of lines or end of sentences, and input
5048 line boundaries have no special significance outside this option. By
5049 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
5050 used, end of sentences are used. In this case, this @var{regex} is
5051 imported from @sc{gnu} Emacs:
5054 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
5057 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
5058 of lines are used; in this case, the default @var{regexp} is just:
5064 Using an empty @var{regexp} is equivalent to completely disabling end of
5065 line or end of sentence recognition. In this case, the whole file is
5066 considered to be a single big line or sentence. The user might want to
5067 disallow all truncation flag generation as well, through option @option{-F
5068 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5071 When the keywords happen to be near the beginning of the input line or
5072 sentence, this often creates an unused area at the beginning of the
5073 output context line; when the keywords happen to be near the end of the
5074 input line or sentence, this often creates an unused area at the end of
5075 the output context line. The program tries to fill those unused areas
5076 by wrapping around context in them; the tail of the input line or
5077 sentence is used to fill the unused area on the left of the output line;
5078 the head of the input line or sentence is used to fill the unused area
5079 on the right of the output line.
5081 As a matter of convenience to the user, many usual backslashed escape
5082 sequences from the C language are recognized and converted to the
5083 corresponding characters by @command{ptx} itself.
5085 @item -W @var{regexp}
5086 @itemx --word-regexp=@var{regexp}
5088 This option selects which regular expression will describe each keyword.
5089 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
5090 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
5091 disabled, a word is by default anything which ends with a space, a tab
5092 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
5094 An empty @var{regexp} is equivalent to not using this option.
5095 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
5098 As a matter of convenience to the user, many usual backslashed escape
5099 sequences, as found in the C language, are recognized and converted to
5100 the corresponding characters by @command{ptx} itself.
5105 @node Output formatting in ptx
5106 @subsection Output formatting
5108 Output format is mainly controlled by the @option{-O} and @option{-T} options
5109 described in the table below. When neither @option{-O} nor @option{-T} are
5110 selected, and if @sc{gnu} extensions are enabled, the program chooses an
5111 output format suitable for a dumb terminal. Each keyword occurrence is
5112 output to the center of one line, surrounded by its left and right
5113 contexts. Each field is properly justified, so the concordance output
5114 can be readily observed. As a special feature, if automatic
5115 references are selected by option @option{-A} and are output before the
5116 left context, that is, if option @option{-R} is @emph{not} selected, then
5117 a colon is added after the reference; this nicely interfaces with @sc{gnu}
5118 Emacs @code{next-error} processing. In this default output format, each
5119 white space character, like newline and tab, is merely changed to
5120 exactly one space, with no special attempt to compress consecutive
5121 spaces. This might change in the future. Except for those white space
5122 characters, every other character of the underlying set of 256
5123 characters is transmitted verbatim.
5125 Output format is further controlled by the following options.
5129 @item -g @var{number}
5130 @itemx --gap-size=@var{number}
5132 Select the size of the minimum white space gap between the fields on the
5135 @item -w @var{number}
5136 @itemx --width=@var{number}
5138 Select the maximum output width of each final line. If references are
5139 used, they are included or excluded from the maximum output width
5140 depending on the value of option @option{-R}. If this option is not
5141 selected, that is, when references are output before the left context,
5142 the maximum output width takes into account the maximum length of all
5143 references. If this option is selected, that is, when references are
5144 output after the right context, the maximum output width does not take
5145 into account the space taken by references, nor the gap that precedes
5149 @itemx --auto-reference
5151 Select automatic references. Each input line will have an automatic
5152 reference made up of the file name and the line ordinal, with a single
5153 colon between them. However, the file name will be empty when standard
5154 input is being read. If both @option{-A} and @option{-r} are selected, then
5155 the input reference is still read and skipped, but the automatic
5156 reference is used at output time, overriding the input reference.
5159 @itemx --right-side-refs
5161 In the default output format, when option @option{-R} is not used, any
5162 references produced by the effect of options @option{-r} or @option{-A} are
5163 placed to the far right of output lines, after the right context. With
5164 default output format, when the @option{-R} option is specified, references
5165 are rather placed at the beginning of each output line, before the left
5166 context. For any other output format, option @option{-R} is
5167 ignored, with one exception: with @option{-R} the width of references
5168 is @emph{not} taken into account in total output width given by @option{-w}.
5170 This option is automatically selected whenever @sc{gnu} extensions are
5173 @item -F @var{string}
5174 @itemx --flac-truncation=@var{string}
5176 This option will request that any truncation in the output be reported
5177 using the string @var{string}. Most output fields theoretically extend
5178 towards the beginning or the end of the current line, or current
5179 sentence, as selected with option @option{-S}. But there is a maximum
5180 allowed output line width, changeable through option @option{-w}, which is
5181 further divided into space for various output fields. When a field has
5182 to be truncated because it cannot extend beyond the beginning or the end of
5183 the current line to fit in, then a truncation occurs. By default,
5184 the string used is a single slash, as in @option{-F /}.
5186 @var{string} may have more than one character, as in @option{-F ...}.
5187 Also, in the particular case when @var{string} is empty (@option{-F ""}),
5188 truncation flagging is disabled, and no truncation marks are appended in
5191 As a matter of convenience to the user, many usual backslashed escape
5192 sequences, as found in the C language, are recognized and converted to
5193 the corresponding characters by @command{ptx} itself.
5195 @item -M @var{string}
5196 @itemx --macro-name=@var{string}
5198 Select another @var{string} to be used instead of @samp{xx}, while
5199 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
5202 @itemx --format=roff
5204 Choose an output format suitable for @command{nroff} or @command{troff}
5205 processing. Each output line will look like:
5208 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}"@c
5209 "@var{head}" "@var{ref}"
5212 so it will be possible to write a @samp{.xx} roff macro to take care of
5213 the output typesetting. This is the default output format when @sc{gnu}
5214 extensions are disabled. Option @option{-M} can be used to change
5215 @samp{xx} to another macro name.
5217 In this output format, each non-graphical character, like newline and
5218 tab, is merely changed to exactly one space, with no special attempt to
5219 compress consecutive spaces. Each quote character: @kbd{"} is doubled
5220 so it will be correctly processed by @command{nroff} or @command{troff}.
5225 Choose an output format suitable for @TeX{} processing. Each output
5226 line will look like:
5229 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@c
5230 @{@var{after}@}@{@var{head}@}@{@var{ref}@}
5234 so it will be possible to write a @code{\xx} definition to take care of
5235 the output typesetting. Note that when references are not being
5236 produced, that is, neither option @option{-A} nor option @option{-r} is
5237 selected, the last parameter of each @code{\xx} call is inhibited.
5238 Option @option{-M} can be used to change @samp{xx} to another macro
5241 In this output format, some special characters, like @kbd{$}, @kbd{%},
5242 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5243 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5244 backslash and a pair of dollar signs (to force mathematical mode). The
5245 backslash itself produces the sequence @code{\backslash@{@}}.
5246 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5247 @code{~\@{ @}} respectively. Other diacriticized characters of the
5248 underlying character set produce an appropriate @TeX{} sequence as far
5249 as possible. The other non-graphical characters, like newline and tab,
5250 and all other characters which are not part of @acronym{ASCII}, are merely
5251 changed to exactly one space, with no special attempt to compress
5252 consecutive spaces. Let me know how to improve this special character
5253 processing for @TeX{}.
5258 @node Compatibility in ptx
5259 @subsection The @sc{gnu} extensions to @command{ptx}
5261 This version of @command{ptx} contains a few features which do not exist in
5262 System V @command{ptx}. These extra features are suppressed by using the
5263 @option{-G} command line option, unless overridden by other command line
5264 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5265 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5266 Here are the differences between this program and System V @command{ptx}.
5271 This program can read many input files at once, it always writes the
5272 resulting concordance on standard output. On the other hand, System V
5273 @command{ptx} reads only one file and sends the result to standard output
5274 or, if a second @var{file} parameter is given on the command, to that
5277 Having output parameters not introduced by options is a dangerous
5278 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5279 portably between @sc{gnu} and System V, you should always use it with a
5280 single input file, and always expect the result on standard output. You
5281 might also want to automatically configure in a @option{-G} option to
5282 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5283 that the installed @command{ptx} accepts @option{-G}.
5286 The only options available in System V @command{ptx} are options @option{-b},
5287 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5288 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5289 this enumeration. Moreover, some options have a slightly different
5290 meaning when @sc{gnu} extensions are enabled, as explained below.
5293 By default, concordance output is not formatted for @command{troff} or
5294 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5295 or @command{nroff} output may still be selected through option @option{-O}.
5298 Unless @option{-R} option is used, the maximum reference width is
5299 subtracted from the total output line width. With @sc{gnu} extensions
5300 disabled, width of references is not taken into account in the output
5301 line width computations.
5304 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5305 processed from input file with no adverse effect, even if @sc{gnu} extensions
5306 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5307 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5310 Input line length is only limited by available memory, even if @sc{gnu}
5311 extensions are disabled. However, System V @command{ptx} processes only
5312 the first 200 characters in each line.
5315 The break (non-word) characters default to be every character except all
5316 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5317 extensions are disabled, the break characters default to space, tab and
5321 The program makes better use of output line width. If @sc{gnu} extensions
5322 are disabled, the program rather tries to imitate System V @command{ptx},
5323 but still, there are some slight disposition glitches this program does
5324 not completely reproduce.
5327 The user can specify both an Ignore file and an Only file. This is not
5328 allowed with System V @command{ptx}.
5333 @node tsort invocation
5334 @section @command{tsort}: Topological sort
5337 @cindex topological sort
5339 @command{tsort} performs a topological sort on the given @var{file}, or
5340 standard input if no input file is given or for a @var{file} of
5341 @samp{-}. For more details and some history, see @ref{tsort background}.
5345 tsort [@var{option}] [@var{file}]
5348 @command{tsort} reads its input as pairs of strings, separated by blanks,
5349 indicating a partial ordering. The output is a total ordering that
5350 corresponds to the given partial ordering.
5364 will produce the output
5375 Consider a more realistic example.
5376 You have a large set of functions all in one file, and they may all be
5377 declared static except one. Currently that one (say @code{main}) is the
5378 first function defined in the file, and the ones it calls directly follow
5379 it, followed by those they call, etc. Let's say that you are determined
5380 to take advantage of prototypes, so you have to choose between declaring
5381 all of those functions (which means duplicating a lot of information from
5382 the definitions) and rearranging the functions so that as many as possible
5383 are defined before they are used. One way to automate the latter process
5384 is to get a list for each function of the functions it calls directly.
5385 Many programs can generate such lists. They describe a call graph.
5386 Consider the following list, in which a given line indicates that the
5387 function on the left calls the one on the right directly.
5393 tail_file pretty_name
5394 tail_file write_header
5396 tail_forever recheck
5397 tail_forever pretty_name
5398 tail_forever write_header
5399 tail_forever dump_remainder
5402 tail_lines start_lines
5403 tail_lines dump_remainder
5404 tail_lines file_lines
5405 tail_lines pipe_lines
5407 tail_bytes start_bytes
5408 tail_bytes dump_remainder
5409 tail_bytes pipe_bytes
5410 file_lines dump_remainder
5414 then you can use @command{tsort} to produce an ordering of those
5415 functions that satisfies your requirement.
5418 example$ tsort call-graph | tac
5438 @command{tsort} detects any cycles in the input and writes the first cycle
5439 encountered to standard error.
5441 Note that for a given partial ordering, generally there is no unique
5442 total ordering. In the context of the call graph above, the function
5443 @code{parse_options} may be placed anywhere in the list as long as it
5444 precedes @code{main}.
5446 The only options are @option{--help} and @option{--version}. @xref{Common
5452 * tsort background:: Where tsort came from.
5455 @node tsort background
5456 @subsection @command{tsort}: Background
5458 @command{tsort} exists because very early versions of the Unix linker processed
5459 an archive file exactly once, and in order. As @command{ld} read each object
5460 in the archive, it decided whether it was needed in the program based on
5461 whether it defined any symbols which were undefined at that point in
5464 This meant that dependencies within the archive had to be handled
5465 specially. For example, @code{scanf} probably calls @code{read}. That means
5466 that in a single pass through an archive, it was important for @code{scanf.o}
5467 to appear before read.o, because otherwise a program which calls
5468 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5469 reference to @code{read}.
5471 The way to address this problem was to first generate a set of
5472 dependencies of one object file on another. This was done by a shell
5473 script called @command{lorder}. The GNU tools don't provide a version of
5474 lorder, as far as I know, but you can still find it in BSD
5477 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5478 resulting sort to define the order in which you added objects to the archive.
5480 This whole procedure has been obsolete since about 1980, because
5481 Unix archives now contain a symbol table (traditionally built by
5482 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5483 linker uses the symbol table to effectively make multiple passes over
5486 Anyhow, that's where tsort came from. To solve an old problem with
5487 the way the linker handled archive files, which has since been solved
5491 @node Operating on fields
5492 @chapter Operating on fields
5495 * cut invocation:: Print selected parts of lines.
5496 * paste invocation:: Merge lines of files.
5497 * join invocation:: Join lines on a common field.
5501 @node cut invocation
5502 @section @command{cut}: Print selected parts of lines
5505 @command{cut} writes to standard output selected parts of each line of each
5506 input file, or standard input if no files are given or for a file name of
5510 cut @var{option}@dots{} [@var{file}]@dots{}
5513 In the table which follows, the @var{byte-list}, @var{character-list},
5514 and @var{field-list} are one or more numbers or ranges (two numbers
5515 separated by a dash) separated by commas. Bytes, characters, and
5516 fields are numbered starting at 1. Incomplete ranges may be
5517 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5518 @samp{@var{n}} through end of line or last field. The list elements
5519 can be repeated, can overlap, and can be specified in any order; but
5520 the selected input is written in the same order that it is read, and
5521 is written exactly once.
5523 The program accepts the following options. Also see @ref{Common
5528 @item -b @var{byte-list}
5529 @itemx --bytes=@var{byte-list}
5532 Select for printing only the bytes in positions listed in
5533 @var{byte-list}. Tabs and backspaces are treated like any other
5534 character; they take up 1 byte. If an output delimiter is specified,
5535 (see the description of @option{--output-delimiter}), then output that
5536 string between ranges of selected bytes.
5538 @item -c @var{character-list}
5539 @itemx --characters=@var{character-list}
5541 @opindex --characters
5542 Select for printing only the characters in positions listed in
5543 @var{character-list}. The same as @option{-b} for now, but
5544 internationalization will change that. Tabs and backspaces are
5545 treated like any other character; they take up 1 character. If an
5546 output delimiter is specified, (see the description of
5547 @option{--output-delimiter}), then output that string between ranges
5550 @item -f @var{field-list}
5551 @itemx --fields=@var{field-list}
5554 Select for printing only the fields listed in @var{field-list}.
5555 Fields are separated by a TAB character by default. Also print any
5556 line that contains no delimiter character, unless the
5557 @option{--only-delimited} (@option{-s}) option is specified.
5559 Note @command{awk} supports more sophisticated field processing,
5560 and by default will use (and discard) runs of blank characters to
5561 separate fields, and ignore leading and trailing blanks.
5564 awk '{print $2}' # print the second field
5565 awk '{print $NF-1}' # print the penultimate field
5566 awk '{print $2,$1}' # reorder the first two fields
5570 In the unlikely event that @command{awk} is unavailable,
5571 one can use the @command{join} command, to process blank
5572 characters as @command{awk} does above.
5575 join -a1 -o 1.2 - /dev/null # print the second field
5576 join -a1 -o 1.2,1.1 - /dev/null # reorder the first two fields
5580 @item -d @var{input_delim_byte}
5581 @itemx --delimiter=@var{input_delim_byte}
5583 @opindex --delimiter
5584 With @option{-f}, use the first byte of @var{input_delim_byte} as
5585 the input fields separator (default is TAB).
5589 Do not split multi-byte characters (no-op for now).
5592 @itemx --only-delimited
5594 @opindex --only-delimited
5595 For @option{-f}, do not print lines that do not contain the field separator
5596 character. Normally, any line without a field separator is printed verbatim.
5598 @item --output-delimiter=@var{output_delim_string}
5599 @opindex --output-delimiter
5600 With @option{-f}, output fields are separated by @var{output_delim_string}.
5601 The default with @option{-f} is to use the input delimiter.
5602 When using @option{-b} or @option{-c} to select ranges of byte or
5603 character offsets (as opposed to ranges of fields),
5604 output @var{output_delim_string} between non-overlapping
5605 ranges of selected bytes.
5608 @opindex --complement
5609 This option is a @acronym{GNU} extension.
5610 Select for printing the complement of the bytes, characters or fields
5611 selected with the @option{-b}, @option{-c} or @option{-f} options.
5612 In other words, do @emph{not} print the bytes, characters or fields
5613 specified via those options. This option is useful when you have
5614 many fields and want to print all but a few of them.
5621 @node paste invocation
5622 @section @command{paste}: Merge lines of files
5625 @cindex merging files
5627 @command{paste} writes to standard output lines consisting of sequentially
5628 corresponding lines of each given file, separated by a TAB character.
5629 Standard input is used for a file name of @samp{-} or if no input files
5651 paste [@var{option}]@dots{} [@var{file}]@dots{}
5654 The program accepts the following options. Also see @ref{Common options}.
5662 Paste the lines of one file at a time rather than one line from each
5663 file. Using the above example data:
5666 $ paste -s num2 let3
5671 @item -d @var{delim-list}
5672 @itemx --delimiters=@var{delim-list}
5674 @opindex --delimiters
5675 Consecutively use the characters in @var{delim-list} instead of
5676 TAB to separate merged lines. When @var{delim-list} is
5677 exhausted, start again at its beginning. Using the above example data:
5680 $ paste -d '%_' num2 let3 num2
5691 @node join invocation
5692 @section @command{join}: Join lines on a common field
5695 @cindex common field, joining on
5697 @command{join} writes to standard output a line for each pair of input
5698 lines that have identical join fields. Synopsis:
5701 join [@var{option}]@dots{} @var{file1} @var{file2}
5704 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5705 meaning standard input. @var{file1} and @var{file2} should be
5706 sorted on the join fields.
5709 Normally, the sort order is that of the
5710 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5711 the @option{-t} option is given, the sort comparison ignores blanks at
5712 the start of the join field, as in @code{sort -b}. If the
5713 @option{--ignore-case} option is given, the sort comparison ignores
5714 the case of characters in the join field, as in @code{sort -f}.
5716 The @command{sort} and @command{join} commands should use consistent
5717 locales and options if the output of @command{sort} is fed to
5718 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5719 sort a file on its default join field, but if you select a non-default
5720 locale, join field, separator, or comparison options, then you should
5721 do so consistently between @command{join} and @command{sort}.
5722 If @samp{join -t ''} is specified then the whole line is considered which
5723 matches the default operation of sort.
5725 If the input has no unpairable lines, a @acronym{GNU} extension is
5726 available; the sort order can be any order that considers two fields
5727 to be equal if and only if the sort comparison described above
5728 considers them to be equal. For example:
5746 @checkOrderOption{join}
5751 @item the join field is the first field in each line;
5752 @item fields in the input are separated by one or more blanks, with leading
5753 blanks on the line ignored;
5754 @item fields in the output are separated by a space;
5755 @item each output line consists of the join field, the remaining
5756 fields from @var{file1}, then the remaining fields from @var{file2}.
5759 The program accepts the following options. Also see @ref{Common options}.
5763 @item -a @var{file-number}
5765 Print a line for each unpairable line in file @var{file-number} (either
5766 @samp{1} or @samp{2}), in addition to the normal output.
5769 Fail with an error message if either input file is wrongly ordered.
5771 @item --nocheck-order
5772 Do not check that both input files are in sorted order. This is the default.
5774 @item -e @var{string}
5776 Replace those output fields that are missing in the input with @var{string}.
5777 I.E. missing fields specified with the @option{-12jo} options.
5781 Treat the first line of each input file as a header line. The header lines will
5782 be joined and printed as the first output line. If @option{-o} is used to
5783 specify output format, the header line will be printed according to the
5784 specified format. The header lines will not be checked for ordering even if
5785 @option{--check-order} is specified. Also if the header lines from each file
5786 do not match, the heading fields from the first file will be used.
5789 @itemx --ignore-case
5791 @opindex --ignore-case
5792 Ignore differences in case when comparing keys.
5793 With this option, the lines of the input files must be ordered in the same way.
5794 Use @samp{sort -f} to produce this ordering.
5796 @item -1 @var{field}
5798 Join on field @var{field} (a positive integer) of file 1.
5800 @item -2 @var{field}
5802 Join on field @var{field} (a positive integer) of file 2.
5804 @item -j @var{field}
5805 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5807 @item -o @var{field-list}
5809 If the keyword @samp{auto} is specified, infer the output format from
5810 the first line in each file. This is the same as the default output format
5811 but also ensures the same number of fields are output for each line.
5812 Missing fields are replaced with the @option{-e} option and extra fields
5815 Otherwise, construct each output line according to the format in
5816 @var{field-list}. Each element in @var{field-list} is either the single
5817 character @samp{0} or has the form @var{m.n} where the file number, @var{m},
5818 is @samp{1} or @samp{2} and @var{n} is a positive field number.
5820 A field specification of @samp{0} denotes the join field.
5821 In most cases, the functionality of the @samp{0} field spec
5822 may be reproduced using the explicit @var{m.n} that corresponds
5823 to the join field. However, when printing unpairable lines
5824 (using either of the @option{-a} or @option{-v} options), there is no way
5825 to specify the join field using @var{m.n} in @var{field-list}
5826 if there are unpairable lines in both files.
5827 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5828 field specification notation.
5830 The elements in @var{field-list}
5831 are separated by commas or blanks.
5832 Blank separators typically need to be quoted for the shell. For
5833 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5834 2.2'} are equivalent.
5836 All output lines---including those printed because of any -a or -v
5837 option---are subject to the specified @var{field-list}.
5840 Use character @var{char} as the input and output field separator.
5841 Treat as significant each occurrence of @var{char} in the input file.
5842 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5843 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5844 the whole line is considered, matching the default operation of sort.
5845 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5846 character is used to delimit the fields.
5848 @item -v @var{file-number}
5849 Print a line for each unpairable line in file @var{file-number}
5850 (either @samp{1} or @samp{2}), instead of the normal output.
5857 @node Operating on characters
5858 @chapter Operating on characters
5860 @cindex operating on characters
5862 This commands operate on individual characters.
5865 * tr invocation:: Translate, squeeze, and/or delete characters.
5866 * expand invocation:: Convert tabs to spaces.
5867 * unexpand invocation:: Convert spaces to tabs.
5872 @section @command{tr}: Translate, squeeze, and/or delete characters
5879 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5882 @command{tr} copies standard input to standard output, performing
5883 one of the following operations:
5887 translate, and optionally squeeze repeated characters in the result,
5889 squeeze repeated characters,
5893 delete characters, then squeeze repeated characters from the result.
5896 The @var{set1} and (if given) @var{set2} arguments define ordered
5897 sets of characters, referred to below as @var{set1} and @var{set2}. These
5898 sets are the characters of the input that @command{tr} operates on.
5899 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5901 complement (all of the characters that are not in @var{set1}).
5903 Currently @command{tr} fully supports only single-byte characters.
5904 Eventually it will support multibyte characters; when it does, the
5905 @option{-C} option will cause it to complement the set of characters,
5906 whereas @option{-c} will cause it to complement the set of values.
5907 This distinction will matter only when some values are not characters,
5908 and this is possible only in locales using multibyte encodings when
5909 the input contains encoding errors.
5911 The program accepts the @option{--help} and @option{--version}
5912 options. @xref{Common options}. Options must precede operands.
5917 * Character sets:: Specifying sets of characters.
5918 * Translating:: Changing one set of characters to another.
5919 * Squeezing:: Squeezing repeats and deleting.
5923 @node Character sets
5924 @subsection Specifying sets of characters
5926 @cindex specifying sets of characters
5928 The format of the @var{set1} and @var{set2} arguments resembles
5929 the format of regular expressions; however, they are not regular
5930 expressions, only lists of characters. Most characters simply
5931 represent themselves in these strings, but the strings can contain
5932 the shorthands listed below, for convenience. Some of them can be
5933 used only in @var{set1} or @var{set2}, as noted below.
5937 @item Backslash escapes
5938 @cindex backslash escapes
5940 The following backslash escape sequences are recognized:
5958 The 8-bit character with the value given by @var{ooo}, which is 1 to 3
5959 octal digits. Note that @samp{\400} is interpreted as the two-byte
5960 sequence, @samp{\040} @samp{0}.
5965 While a backslash followed by a character not listed above is
5966 interpreted as that character, the backslash also effectively
5967 removes any special significance, so it is useful to escape
5968 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5973 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5974 from @var{m} through @var{n}, in ascending order. @var{m} should
5975 collate before @var{n}; if it doesn't, an error results. As an example,
5976 @samp{0-9} is the same as @samp{0123456789}.
5978 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5979 brackets to enclose ranges. Translations specified in that format
5980 sometimes work as expected, since the brackets are often transliterated
5981 to themselves. However, they should be avoided because they sometimes
5982 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5985 Many historically common and even accepted uses of ranges are not
5986 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5987 range will not do what most would expect because @samp{A} through @samp{Z}
5988 are not contiguous as they are in @acronym{ASCII}.
5989 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5990 the best way to work around this is to use character classes (see below).
5991 Otherwise, it is most portable (and most ugly) to enumerate the members
5994 @item Repeated characters
5995 @cindex repeated characters
5997 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5998 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5999 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
6000 to as many copies of @var{c} as are needed to make @var{set2} as long as
6001 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
6002 octal, otherwise in decimal.
6004 @item Character classes
6005 @cindex character classes
6007 The notation @samp{[:@var{class}:]} expands to all of the characters in
6008 the (predefined) class @var{class}. The characters expand in no
6009 particular order, except for the @code{upper} and @code{lower} classes,
6010 which expand in ascending order. When the @option{--delete} (@option{-d})
6011 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
6012 character class can be used in @var{set2}. Otherwise, only the
6013 character classes @code{lower} and @code{upper} are accepted in
6014 @var{set2}, and then only if the corresponding character class
6015 (@code{upper} and @code{lower}, respectively) is specified in the same
6016 relative position in @var{set1}. Doing this specifies case conversion.
6017 The class names are given below; an error results when an invalid class
6029 Horizontal whitespace.
6038 Printable characters, not including space.
6044 Printable characters, including space.
6047 Punctuation characters.
6050 Horizontal or vertical whitespace.
6059 @item Equivalence classes
6060 @cindex equivalence classes
6062 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
6063 equivalent to @var{c}, in no particular order. Equivalence classes are
6064 a relatively recent invention intended to support non-English alphabets.
6065 But there seems to be no standard way to define them or determine their
6066 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
6067 each character's equivalence class consists only of that character,
6068 which is of no particular use.
6074 @subsection Translating
6076 @cindex translating characters
6078 @command{tr} performs translation when @var{set1} and @var{set2} are
6079 both given and the @option{--delete} (@option{-d}) option is not given.
6080 @command{tr} translates each character of its input that is in @var{set1}
6081 to the corresponding character in @var{set2}. Characters not in
6082 @var{set1} are passed through unchanged. When a character appears more
6083 than once in @var{set1} and the corresponding characters in @var{set2}
6084 are not all the same, only the final one is used. For example, these
6085 two commands are equivalent:
6092 A common use of @command{tr} is to convert lowercase characters to
6093 uppercase. This can be done in many ways. Here are three of them:
6096 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
6098 tr '[:lower:]' '[:upper:]'
6102 But note that using ranges like @code{a-z} above is not portable.
6104 When @command{tr} is performing translation, @var{set1} and @var{set2}
6105 typically have the same length. If @var{set1} is shorter than
6106 @var{set2}, the extra characters at the end of @var{set2} are ignored.
6108 On the other hand, making @var{set1} longer than @var{set2} is not
6109 portable; @acronym{POSIX} says that the result is undefined. In this situation,
6110 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
6111 the last character of @var{set2} as many times as necessary. System V
6112 @command{tr} truncates @var{set1} to the length of @var{set2}.
6114 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
6115 When the @option{--truncate-set1} (@option{-t}) option is given,
6116 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
6117 instead. This option is ignored for operations other than translation.
6119 Acting like System V @command{tr} in this case breaks the relatively common
6123 tr -cs A-Za-z0-9 '\012'
6127 because it converts only zero bytes (the first element in the
6128 complement of @var{set1}), rather than all non-alphanumerics, to
6132 By the way, the above idiom is not portable because it uses ranges, and
6133 it assumes that the octal code for newline is 012.
6134 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better
6138 tr -cs '[:alnum:]' '[\n*]'
6143 @subsection Squeezing repeats and deleting
6145 @cindex squeezing repeat characters
6146 @cindex deleting characters
6148 When given just the @option{--delete} (@option{-d}) option, @command{tr}
6149 removes any input characters that are in @var{set1}.
6151 When given just the @option{--squeeze-repeats} (@option{-s}) option,
6152 @command{tr} replaces each input sequence of a repeated character that
6153 is in @var{set1} with a single occurrence of that character.
6155 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
6156 first performs any deletions using @var{set1}, then squeezes repeats
6157 from any remaining characters using @var{set2}.
6159 The @option{--squeeze-repeats} option may also be used when translating,
6160 in which case @command{tr} first performs translation, then squeezes
6161 repeats from any remaining characters using @var{set2}.
6163 Here are some examples to illustrate various combinations of options:
6168 Remove all zero bytes:
6175 Put all words on lines by themselves. This converts all
6176 non-alphanumeric characters to newlines, then squeezes each string
6177 of repeated newlines into a single newline:
6180 tr -cs '[:alnum:]' '[\n*]'
6184 Convert each sequence of repeated newlines to a single newline:
6191 Find doubled occurrences of words in a document.
6192 @c Separate the following two "the"s, so typo checkers don't complain.
6193 For example, people often write ``the @w{}the'' with the repeated words
6194 separated by a newline. The Bourne shell script below works first
6195 by converting each sequence of punctuation and blank characters to a
6196 single newline. That puts each ``word'' on a line by itself.
6197 Next it maps all uppercase characters to lower case, and finally it
6198 runs @command{uniq} with the @option{-d} option to print out only the words
6204 | tr -s '[:punct:][:blank:]' '[\n*]' \
6205 | tr '[:upper:]' '[:lower:]' \
6210 Deleting a small set of characters is usually straightforward. For example,
6211 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
6217 However, when @samp{-} is one of those characters, it can be tricky because
6218 @samp{-} has special meanings. Performing the same task as above but also
6219 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
6220 that would fail because @command{tr} would try to interpret @option{-a} as
6221 a command-line option. Alternatively, we could try putting the hyphen
6222 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
6223 it would make @command{tr} interpret @code{a-x} as the range of characters
6224 @samp{a}@dots{}@samp{x} rather than the three.
6225 One way to solve the problem is to put the hyphen at the end of the list
6232 Or you can use @samp{--} to terminate option processing:
6238 More generally, use the character class notation @code{[=c=]}
6239 with @samp{-} (or any other character) in place of the @samp{c}:
6245 Note how single quotes are used in the above example to protect the
6246 square brackets from interpretation by a shell.
6251 @node expand invocation
6252 @section @command{expand}: Convert tabs to spaces
6255 @cindex tabs to spaces, converting
6256 @cindex converting tabs to spaces
6258 @command{expand} writes the contents of each given @var{file}, or standard
6259 input if none are given or for a @var{file} of @samp{-}, to standard
6260 output, with tab characters converted to the appropriate number of
6264 expand [@var{option}]@dots{} [@var{file}]@dots{}
6267 By default, @command{expand} converts all tabs to spaces. It preserves
6268 backspace characters in the output; they decrement the column count for
6269 tab calculations. The default action is equivalent to @option{-t 8} (set
6270 tabs every 8 columns).
6272 The program accepts the following options. Also see @ref{Common options}.
6276 @item -t @var{tab1}[,@var{tab2}]@dots{}
6277 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6280 @cindex tab stops, setting
6281 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6282 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6283 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6284 last tab stop given with single spaces. Tab stops can be separated by
6285 blanks as well as by commas.
6287 For compatibility, GNU @command{expand} also accepts the obsolete
6288 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6289 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6295 @cindex initial tabs, converting
6296 Only convert initial tabs (those that precede all non-space or non-tab
6297 characters) on each line to spaces.
6304 @node unexpand invocation
6305 @section @command{unexpand}: Convert spaces to tabs
6309 @command{unexpand} writes the contents of each given @var{file}, or
6310 standard input if none are given or for a @var{file} of @samp{-}, to
6311 standard output, converting blanks at the beginning of each line into
6312 as many tab characters as needed. In the default @acronym{POSIX}
6313 locale, a @dfn{blank} is a space or a tab; other locales may specify
6314 additional blank characters. Synopsis:
6317 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6320 By default, @command{unexpand} converts only initial blanks (those
6321 that precede all non-blank characters) on each line. It
6322 preserves backspace characters in the output; they decrement the column
6323 count for tab calculations. By default, tabs are set at every 8th
6326 The program accepts the following options. Also see @ref{Common options}.
6330 @item -t @var{tab1}[,@var{tab2}]@dots{}
6331 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6334 If only one tab stop is given, set the tabs @var{tab1} columns apart
6335 instead of the default 8. Otherwise, set the tabs at columns
6336 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6337 beyond the tab stops given unchanged. Tab stops can be separated by
6338 blanks as well as by commas. This option implies the @option{-a} option.
6340 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6341 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6342 separated by commas. (Unlike @option{-t}, this obsolete option does
6343 not imply @option{-a}.) New scripts should use @option{--first-only -t
6344 @var{tab1}[,@var{tab2}]@dots{}} instead.
6350 Also convert all sequences of two or more blanks just before a tab stop,
6351 even if they occur after non-blank characters in a line.
6358 @node Directory listing
6359 @chapter Directory listing
6361 This chapter describes the @command{ls} command and its variants @command{dir}
6362 and @command{vdir}, which list information about files.
6365 * ls invocation:: List directory contents.
6366 * dir invocation:: Briefly ls.
6367 * vdir invocation:: Verbosely ls.
6368 * dircolors invocation:: Color setup for ls, etc.
6373 @section @command{ls}: List directory contents
6376 @cindex directory listing
6378 The @command{ls} program lists information about files (of any type,
6379 including directories). Options and file arguments can be intermixed
6380 arbitrarily, as usual.
6382 For non-option command-line arguments that are directories, by default
6383 @command{ls} lists the contents of directories, not recursively, and
6384 omitting files with names beginning with @samp{.}. For other non-option
6385 arguments, by default @command{ls} lists just the file name. If no
6386 non-option argument is specified, @command{ls} operates on the current
6387 directory, acting as if it had been invoked with a single argument of @samp{.}.
6390 By default, the output is sorted alphabetically, according to the locale
6391 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6392 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6393 produce output that is sorted differently than you're accustomed to.
6394 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6395 If standard output is
6396 a terminal, the output is in columns (sorted vertically) and control
6397 characters are output as question marks; otherwise, the output is listed
6398 one per line and control characters are output as-is.
6400 Because @command{ls} is such a fundamental program, it has accumulated many
6401 options over the years. They are described in the subsections below;
6402 within each section, options are listed alphabetically (ignoring case).
6403 The division of options into the subsections is not absolute, since some
6404 options affect more than one aspect of @command{ls}'s operation.
6406 @cindex exit status of @command{ls}
6411 1 minor problems (e.g., failure to access a file or directory not
6412 specified as a command line argument. This happens when listing a
6413 directory in which entries are actively being removed or renamed.)
6414 2 serious trouble (e.g., memory exhausted, invalid option, failure
6415 to access a file or directory specified as a command line argument
6416 or a directory loop)
6419 Also see @ref{Common options}.
6422 * Which files are listed::
6423 * What information is listed::
6424 * Sorting the output::
6425 * Details about version sort::
6426 * General output formatting::
6427 * Formatting file timestamps::
6428 * Formatting the file names::
6432 @node Which files are listed
6433 @subsection Which files are listed
6435 These options determine which files @command{ls} lists information for.
6436 By default, @command{ls} lists files and the contents of any
6437 directories on the command line, except that in directories it ignores
6438 files whose names start with @samp{.}.
6446 In directories, do not ignore file names that start with @samp{.}.
6451 @opindex --almost-all
6452 In directories, do not ignore all file names that start with @samp{.};
6453 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6454 option overrides this option.
6457 @itemx --ignore-backups
6459 @opindex --ignore-backups
6460 @cindex backup files, ignoring
6461 In directories, ignore files that end with @samp{~}. This option is
6462 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6467 @opindex --directory
6468 List just the names of directories, as with other types of files, rather
6469 than listing their contents.
6470 @c The following sentence is the same as the one for -F.
6471 Do not follow symbolic links listed on the
6472 command line unless the @option{--dereference-command-line} (@option{-H}),
6473 @option{--dereference} (@option{-L}), or
6474 @option{--dereference-command-line-symlink-to-dir} options are specified.
6477 @itemx --dereference-command-line
6479 @opindex --dereference-command-line
6480 @cindex symbolic links, dereferencing
6481 If a command line argument specifies a symbolic link, show information
6482 for the file the link references rather than for the link itself.
6484 @itemx --dereference-command-line-symlink-to-dir
6485 @opindex --dereference-command-line-symlink-to-dir
6486 @cindex symbolic links, dereferencing
6487 Do not dereference symbolic links, with one exception:
6488 if a command line argument specifies a symbolic link that refers to
6489 a directory, show information for that directory rather than for the
6491 This is the default behavior when no other dereferencing-related
6492 option has been specified (@option{--classify} (@option{-F}),
6493 @option{--directory} (@option{-d}),
6495 @option{--dereference} (@option{-L}), or
6496 @option{--dereference-command-line} (@option{-H})).
6498 @item --group-directories-first
6499 @opindex --group-directories-first
6500 Group all the directories before the files and then sort the
6501 directories and the files separately using the selected sort key
6502 (see --sort option).
6503 That is, this option specifies a primary sort key,
6504 and the --sort option specifies a secondary key.
6505 However, any use of @option{--sort=none}
6506 (@option{-U}) disables this option altogether.
6508 @item --hide=PATTERN
6509 @opindex --hide=@var{pattern}
6510 In directories, ignore files whose names match the shell pattern
6511 @var{pattern}, unless the @option{--all} (@option{-a}) or
6512 @option{--almost-all} (@option{-A}) is also given. This
6513 option acts like @option{--ignore=@var{pattern}} except that it has no
6514 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6515 (@option{-A}) is also given.
6517 This option can be useful in shell aliases. For example, if
6518 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6519 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6520 lists the file @file{README~} even though @samp{ly -A} would not.
6522 @item -I @var{pattern}
6523 @itemx --ignore=@var{pattern}
6525 @opindex --ignore=@var{pattern}
6526 In directories, ignore files whose names match the shell pattern
6527 (not regular expression) @var{pattern}. As
6528 in the shell, an initial @samp{.} in a file name does not match a
6529 wildcard at the start of @var{pattern}. Sometimes it is useful
6530 to give this option several times. For example,
6533 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6536 The first option ignores names of length 3 or more that start with @samp{.},
6537 the second ignores all two-character names that start with @samp{.}
6538 except @samp{..}, and the third ignores names that start with @samp{#}.
6541 @itemx --dereference
6543 @opindex --dereference
6544 @cindex symbolic links, dereferencing
6545 When showing file information for a symbolic link, show information
6546 for the file the link references rather than the link itself.
6547 However, even with this option, @command{ls} still prints the name
6548 of the link itself, not the name of the file that the link points to.
6553 @opindex --recursive
6554 @cindex recursive directory listing
6555 @cindex directory listing, recursive
6556 List the contents of all directories recursively.
6561 @node What information is listed
6562 @subsection What information is listed
6564 These options affect the information that @command{ls} displays. By
6565 default, only file names are shown.
6571 @cindex hurd, author, printing
6572 List each file's author when producing long format directory listings.
6573 In GNU/Hurd, file authors can differ from their owners, but in other
6574 operating systems the two are the same.
6580 @cindex dired Emacs mode support
6581 With the long listing (@option{-l}) format, print an additional line after
6585 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6589 The @var{begn} and @var{endn} are unsigned integers that record the
6590 byte position of the beginning and end of each file name in the output.
6591 This makes it easy for Emacs to find the names, even when they contain
6592 unusual characters such as space or newline, without fancy searching.
6594 If directories are being listed recursively (@option{-R}), output a similar
6595 line with offsets for each subdirectory name:
6598 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6601 Finally, output a line of the form:
6604 //DIRED-OPTIONS// --quoting-style=@var{word}
6608 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6610 Here is an actual example:
6613 $ mkdir -p a/sub/deeper a/sub2
6615 $ touch a/sub/deeper/file
6616 $ ls -gloRF --dired a
6619 -rw-r--r-- 1 0 Jun 10 12:27 f1
6620 -rw-r--r-- 1 0 Jun 10 12:27 f2
6621 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6622 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6626 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6630 -rw-r--r-- 1 0 Jun 10 12:27 file
6634 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6635 //SUBDIRED// 2 3 167 172 228 240 290 296
6636 //DIRED-OPTIONS// --quoting-style=literal
6639 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6640 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6642 The offsets on the @samp{//SUBDIRED//} line delimit the following
6643 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6645 Here is an example of how to extract the fifth entry name, @samp{deeper},
6646 corresponding to the pair of offsets, 222 and 228:
6649 $ ls -gloRF --dired a > out
6650 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6654 Note that although the listing above includes a trailing slash
6655 for the @samp{deeper} entry, the offsets select the name without
6656 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6657 along with an option like @option{--escape} (aka @option{-b}) and operate
6658 on a file whose name contains special characters, notice that the backslash
6663 $ ls -blog --dired 'a b'
6664 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6666 //DIRED-OPTIONS// --quoting-style=escape
6669 If you use a quoting style that adds quote marks
6670 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6671 So beware that the user may select the quoting style via the environment
6672 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6673 should either specify an explicit @option{--quoting-style=literal} option
6674 (aka @option{-N} or @option{--literal}) on the command line, or else be
6675 prepared to parse the escaped names.
6678 @opindex --full-time
6679 Produce long format directory listings, and list times in full. It is
6680 equivalent to using @option{--format=long} with
6681 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6685 Produce long format directory listings, but don't display owner information.
6691 Inhibit display of group information in a long format directory listing.
6692 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6693 provide this option for compatibility.)
6701 @cindex inode number, printing
6702 Print the inode number (also called the file serial number and index
6703 number) of each file to the left of the file name. (This number
6704 uniquely identifies each file within a particular file system.)
6707 @itemx --format=long
6708 @itemx --format=verbose
6711 @opindex long ls @r{format}
6712 @opindex verbose ls @r{format}
6713 In addition to the name of each file, print the file type, file mode bits,
6714 number of hard links, owner name, group name, size, and
6715 timestamp (@pxref{Formatting file timestamps}), normally
6716 the modification time. Print question marks for information that
6717 cannot be determined.
6719 Normally the size is printed as a byte count without punctuation, but
6720 this can be overridden (@pxref{Block size}). For example, @option{-h}
6721 prints an abbreviated, human-readable count, and
6722 @samp{--block-size="'1"} prints a byte count with the thousands
6723 separator of the current locale.
6725 For each directory that is listed, preface the files with a line
6726 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6727 for all files in that directory. The block size currently defaults to 1024
6728 bytes, but this can be overridden (@pxref{Block size}).
6729 The @var{blocks} computed counts each hard link separately;
6730 this is arguably a deficiency.
6732 The file type is one of the following characters:
6734 @c The commented-out entries are ones we're not sure about.
6742 character special file
6744 high performance (``contiguous data'') file
6748 door (Solaris 2.5 and up)
6750 @c semaphore, if this is a distinct file type
6754 @c multiplexed file (7th edition Unix; obsolete)
6756 off-line (``migrated'') file (Cray DMF)
6758 network special file (HP-UX)
6762 port (Solaris 10 and up)
6764 @c message queue, if this is a distinct file type
6768 @c shared memory object, if this is a distinct file type
6770 @c typed memory object, if this is a distinct file type
6772 @c whiteout (4.4BSD; not implemented)
6774 some other file type
6777 @cindex permissions, output by @command{ls}
6778 The file mode bits listed are similar to symbolic mode specifications
6779 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6780 third character of each set of permissions as follows:
6784 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6788 If the set-user-ID or set-group-ID bit is set but the corresponding
6789 executable bit is not set.
6792 If the restricted deletion flag or sticky bit, and the
6793 other-executable bit, are both set. The restricted deletion flag is
6794 another name for the sticky bit. @xref{Mode Structure}.
6797 If the restricted deletion flag or sticky bit is set but the
6798 other-executable bit is not set.
6801 If the executable bit is set and none of the above apply.
6807 Following the file mode bits is a single character that specifies
6808 whether an alternate access method such as an access control list
6809 applies to the file. When the character following the file mode bits is a
6810 space, there is no alternate access method. When it is a printing
6811 character, then there is such a method.
6813 GNU @command{ls} uses a @samp{.} character to indicate a file
6814 with an SELinux security context, but no other alternate access method.
6816 A file with any other combination of alternate access methods
6817 is marked with a @samp{+} character.
6820 @itemx --numeric-uid-gid
6822 @opindex --numeric-uid-gid
6823 @cindex numeric uid and gid
6824 @cindex numeric user and group IDs
6825 Produce long format directory listings, but
6826 display numeric user and group IDs instead of the owner and group names.
6830 Produce long format directory listings, but don't display group information.
6831 It is equivalent to using @option{--format=long} with @option{--no-group} .
6837 @cindex disk allocation
6838 @cindex size of files, reporting
6839 Print the disk allocation of each file to the left of the file name.
6840 This is the amount of disk space used by the file, which is usually a
6841 bit more than the file's size, but it can be less if the file has holes.
6843 Normally the disk allocation is printed in units of
6844 1024 bytes, but this can be overridden (@pxref{Block size}).
6846 @cindex NFS mounts from BSD to HP-UX
6847 For files that are NFS-mounted from an HP-UX system to a BSD system,
6848 this option reports sizes that are half the correct values. On HP-UX
6849 systems, it reports sizes that are twice the correct values for files
6850 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6851 it also affects the HP-UX @command{ls} program.
6860 @cindex security context
6861 Display the SELinux security context or @samp{?} if none is found.
6862 When used with the @option{-l} option, print the security context
6863 to the left of the size column.
6868 @node Sorting the output
6869 @subsection Sorting the output
6871 @cindex sorting @command{ls} output
6872 These options change the order in which @command{ls} sorts the information
6873 it outputs. By default, sorting is done by character code
6874 (e.g., @acronym{ASCII} order).
6880 @itemx --time=status
6883 @opindex ctime@r{, printing or sorting by}
6884 @opindex status time@r{, printing or sorting by}
6885 @opindex use time@r{, printing or sorting files by}
6886 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6887 print the status change time (the @samp{ctime} in the inode) instead of
6888 the modification time.
6889 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6890 or when not using a long listing format,
6891 sort according to the status change time.
6895 @cindex unsorted directory listing
6896 @cindex directory order, listing by
6897 Primarily, like @option{-U}---do not sort; list the files in whatever
6898 order they are stored in the directory. But also enable @option{-a} (list
6899 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6900 were specified before the @option{-f}).
6906 @cindex reverse sorting
6907 Reverse whatever the sorting method is---e.g., list files in reverse
6908 alphabetical order, youngest first, smallest first, or whatever.
6914 @opindex size of files@r{, sorting files by}
6915 Sort by file size, largest first.
6921 @opindex modification time@r{, sorting files by}
6922 Sort by modification time (the @samp{mtime} in the inode), newest first.
6926 @itemx --time=access
6930 @opindex use time@r{, printing or sorting files by}
6931 @opindex atime@r{, printing or sorting files by}
6932 @opindex access time@r{, printing or sorting files by}
6933 If the long listing format (e.g., @option{--format=long}) is being used,
6934 print the last access time (the @samp{atime} in the inode).
6935 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6936 or when not using a long listing format, sort according to the access time.
6942 @opindex none@r{, sorting option for @command{ls}}
6943 Do not sort; list the files in whatever order they are
6944 stored in the directory. (Do not do any of the other unrelated things
6945 that @option{-f} does.) This is especially useful when listing very large
6946 directories, since not doing any sorting can be noticeably faster.
6949 @itemx --sort=version
6952 @opindex version@r{, sorting option for @command{ls}}
6953 Sort by version name and number, lowest first. It behaves like a default
6954 sort, except that each sequence of decimal digits is treated numerically
6955 as an index/version number. (@xref{Details about version sort}.)
6958 @itemx --sort=extension
6961 @opindex extension@r{, sorting files by}
6962 Sort directory contents alphabetically by file extension (characters
6963 after the last @samp{.}); files with no extension are sorted first.
6968 @node Details about version sort
6969 @subsection Details about version sort
6971 Version sorting handles the fact that file names frequently include indices or
6972 version numbers. Standard sorting usually does not produce the order that one
6973 expects because comparisons are made on a character-by-character basis.
6974 Version sorting is especially useful when browsing directories that contain
6975 many files with indices/version numbers in their names:
6979 abc.zml-1.gz abc.zml-1.gz
6980 abc.zml-12.gz abc.zml-2.gz
6981 abc.zml-2.gz abc.zml-12.gz
6984 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6985 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6986 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6987 @var{ver1} < @var{ver2} implies that the name composed of
6988 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6989 ``@var{prefix} @var{ver2} @var{suffix}''.
6991 Note also that leading zeros of numeric parts are ignored:
6995 abc-1.007.tgz abc-1.01a.tgz
6996 abc-1.012b.tgz abc-1.007.tgz
6997 abc-1.01a.tgz abc-1.012b.tgz
7000 This functionality is implemented using gnulib's @code{filevercmp} function,
7001 which has some caveats worth noting.
7004 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
7005 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
7006 was set to @samp{C}.
7007 @item Some suffixes will not be matched by the regular
7008 expression mentioned above. Consequently these examples may
7009 not sort as you expect:
7017 abc-1.2.3.4.x86_64.rpm
7018 abc-1.2.3.x86_64.rpm
7022 @node General output formatting
7023 @subsection General output formatting
7025 These options affect the appearance of the overall output.
7030 @itemx --format=single-column
7033 @opindex single-column @r{output of files}
7034 List one file per line. This is the default for @command{ls} when standard
7035 output is not a terminal.
7038 @itemx --format=vertical
7041 @opindex vertical @r{sorted files in columns}
7042 List files in columns, sorted vertically. This is the default for
7043 @command{ls} if standard output is a terminal. It is always the default
7044 for the @command{dir} program.
7045 @sc{gnu} @command{ls} uses variable width columns to display as many files as
7046 possible in the fewest lines.
7048 @item --color [=@var{when}]
7050 @cindex color, distinguishing file types with
7051 Specify whether to use color for distinguishing file types. @var{when}
7052 may be omitted, or one of:
7055 @vindex none @r{color option}
7056 - Do not use color at all. This is the default.
7058 @vindex auto @r{color option}
7059 @cindex terminal, using color iff
7060 - Only use color if standard output is a terminal.
7062 @vindex always @r{color option}
7065 Specifying @option{--color} and no @var{when} is equivalent to
7066 @option{--color=always}.
7067 Piping a colorized listing through a pager like @command{more} or
7068 @command{less} usually produces unreadable results. However, using
7069 @code{more -f} does seem to work.
7072 @vindex SHELL @r{environment variable, and color}
7073 Note that using the @option{--color} option may incur a noticeable
7074 performance penalty when run in a directory with very many entries,
7075 because the default settings require that @command{ls} @code{stat} every
7076 single file it lists.
7077 However, if you would like most of the file-type coloring
7078 but can live without the other coloring options (e.g.,
7079 executable, orphan, sticky, other-writable, capability), use
7080 @command{dircolors} to set the @env{LS_COLORS} environment variable like this,
7082 eval $(dircolors -p | perl -pe \
7083 's/^((CAP|S[ET]|O[TR]|M|E)\w+).*/$1 00/' | dircolors -)
7085 and on a @code{dirent.d_type}-capable file system, @command{ls}
7086 will perform only one @code{stat} call per command line argument.
7090 @itemx --indicator-style=classify
7093 @opindex --indicator-style
7094 @cindex file type and executables, marking
7095 @cindex executables and file type, marking
7096 Append a character to each file name indicating the file type. Also,
7097 for regular files that are executable, append @samp{*}. The file type
7098 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
7099 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
7100 and nothing for regular files.
7101 @c The following sentence is the same as the one for -d.
7102 Do not follow symbolic links listed on the
7103 command line unless the @option{--dereference-command-line} (@option{-H}),
7104 @option{--dereference} (@option{-L}), or
7105 @option{--dereference-command-line-symlink-to-dir} options are specified.
7108 @itemx --indicator-style=file-type
7109 @opindex --file-type
7110 @opindex --indicator-style
7111 @cindex file type, marking
7112 Append a character to each file name indicating the file type. This is
7113 like @option{-F}, except that executables are not marked.
7115 @item --indicator-style=@var{word}
7116 @opindex --indicator-style
7117 Append a character indicator with style @var{word} to entry names,
7122 Do not append any character indicator; this is the default.
7124 Append @samp{/} for directories. This is the same as the @option{-p}
7127 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
7128 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
7129 the same as the @option{--file-type} option.
7131 Append @samp{*} for executable regular files, otherwise behave as for
7132 @samp{file-type}. This is the same as the @option{-F} or
7133 @option{--classify} option.
7139 @opindex --kibibytes
7140 Set the default block size to its normal value of 1024 bytes,
7141 overriding any contrary specification in environment variables
7142 (@pxref{Block size}). This option is in turn overridden by the
7143 @option{--block-size}, @option{-h} or @option{--human-readable}, and
7144 @option{--si} options.
7146 The @option{-k} or @option{--kibibytes} option affects the
7147 per-directory block count written by the @option{-l} and similar
7148 options, and the size written by the @option{-s} or @option{--size}
7149 option. It does not affect the file size written by @option{-l}.
7152 @itemx --format=commas
7155 @opindex commas@r{, outputting between files}
7156 List files horizontally, with as many as will fit on each line,
7157 separated by @samp{, } (a comma and a space).
7160 @itemx --indicator-style=slash
7162 @opindex --indicator-style
7163 @cindex file type, marking
7164 Append a @samp{/} to directory names.
7167 @itemx --format=across
7168 @itemx --format=horizontal
7171 @opindex across@r{, listing files}
7172 @opindex horizontal@r{, listing files}
7173 List the files in columns, sorted horizontally.
7176 @itemx --tabsize=@var{cols}
7179 Assume that each tab stop is @var{cols} columns wide. The default is 8.
7180 @command{ls} uses tabs where possible in the output, for efficiency. If
7181 @var{cols} is zero, do not use tabs at all.
7183 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
7184 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
7185 do not properly align columns to the right of a TAB following a
7186 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
7187 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
7188 @command{ls} to align using spaces, not tabs.
7191 @itemx --width=@var{cols}
7195 Assume the screen is @var{cols} columns wide. The default is taken
7196 from the terminal settings if possible; otherwise the environment
7197 variable @env{COLUMNS} is used if it is set; otherwise the default
7203 @node Formatting file timestamps
7204 @subsection Formatting file timestamps
7206 By default, file timestamps are listed in abbreviated form, using
7207 a date like @samp{Mar 30@ @ 2002} for non-recent timestamps, and a
7208 date-without-year and time like @samp{Mar 30 23:45} for recent timestamps.
7209 This format can change depending on the current locale as detailed below.
7212 A timestamp is considered to be @dfn{recent} if it is less than six
7213 months old, and is not dated in the future. If a timestamp dated
7214 today is not listed in recent form, the timestamp is in the future,
7215 which means you probably have clock skew problems which may break
7216 programs like @command{make} that rely on file timestamps.
7219 Time stamps are listed according to the time zone rules specified by
7220 the @env{TZ} environment variable, or by the system default rules if
7221 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
7222 with @env{TZ}, libc, The GNU C Library Reference Manual}.
7224 The following option changes how file timestamps are printed.
7227 @item --time-style=@var{style}
7228 @opindex --time-style
7230 List timestamps in style @var{style}. The @var{style} should
7231 be one of the following:
7236 List timestamps using @var{format}, where @var{format} is interpreted
7237 like the format argument of @command{date} (@pxref{date invocation}).
7238 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
7239 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
7240 with @command{date}, @var{format}'s interpretation is affected by the
7241 @env{LC_TIME} locale category.
7243 If @var{format} contains two format strings separated by a newline,
7244 the former is used for non-recent files and the latter for recent
7245 files; if you want output columns to line up, you may need to insert
7246 spaces in one of the two formats.
7249 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
7250 format with nanosecond precision, e.g., @samp{2002-03-30
7251 23:45:56.477817180 -0700}. This style is equivalent to
7252 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
7254 This is useful because the time output includes all the information that
7255 is available from the operating system. For example, this can help
7256 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
7257 uses the full timestamp to determine whether a file is out of date.
7260 List @acronym{ISO} 8601 date and time in minutes, e.g.,
7261 @samp{2002-03-30 23:45}. These timestamps are shorter than
7262 @samp{full-iso} timestamps, and are usually good enough for everyday
7263 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
7266 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
7267 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
7268 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
7269 timestamps are uglier than @samp{long-iso} timestamps, but they carry
7270 nearly the same information in a smaller space and their brevity helps
7271 @command{ls} output fit within traditional 80-column output lines.
7272 The following two @command{ls} invocations are equivalent:
7277 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7278 ls -l --time-style="iso"
7283 List timestamps in a locale-dependent form. For example, a Finnish
7284 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7285 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7286 timestamps typically consume more space than @samp{iso} timestamps and
7287 are harder for programs to parse because locale conventions vary so
7288 widely, but they are easier for many people to read.
7290 The @env{LC_TIME} locale category specifies the timestamp format. The
7291 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7292 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7293 @command{ls} invocations are equivalent:
7298 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7299 ls -l --time-style="locale"
7302 Other locales behave differently. For example, in a German locale,
7303 @option{--time-style="locale"} might be equivalent to
7304 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7305 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7306 @samp{30. M@"ar 23:45}.
7308 @item posix-@var{style}
7310 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7311 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7312 example, the @samp{posix-long-iso} style lists
7313 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7314 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7319 You can specify the default value of the @option{--time-style} option
7320 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7321 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7322 later use the @option{--dired} option and therefore can parse any date
7323 format, but if you are using Emacs 21.1 or 21.2 and specify a
7324 non-@acronym{POSIX} locale you may need to set
7325 @samp{TIME_STYLE="posix-long-iso"}.
7327 To avoid certain denial-of-service attacks, timestamps that would be
7328 longer than 1000 bytes may be treated as errors.
7331 @node Formatting the file names
7332 @subsection Formatting the file names
7334 These options change how file names themselves are printed.
7340 @itemx --quoting-style=escape
7343 @opindex --quoting-style
7344 @cindex backslash sequences for file names
7345 Quote nongraphic characters in file names using alphabetic and octal
7346 backslash sequences like those used in C.
7350 @itemx --quoting-style=literal
7353 @opindex --quoting-style
7354 Do not quote file names. However, with @command{ls} nongraphic
7355 characters are still printed as question marks if the output is a
7356 terminal and you do not specify the @option{--show-control-chars}
7360 @itemx --hide-control-chars
7362 @opindex --hide-control-chars
7363 Print question marks instead of nongraphic characters in file names.
7364 This is the default if the output is a terminal and the program is
7369 @itemx --quoting-style=c
7371 @opindex --quote-name
7372 @opindex --quoting-style
7373 Enclose file names in double quotes and quote nongraphic characters as
7376 @item --quoting-style=@var{word}
7377 @opindex --quoting-style
7378 @cindex quoting style
7379 Use style @var{word} to quote file names and other strings that may
7380 contain arbitrary characters. The @var{word} should
7381 be one of the following:
7385 Output strings as-is; this is the same as the @option{-N} or
7386 @option{--literal} option.
7388 Quote strings for the shell if they contain shell metacharacters or would
7389 cause ambiguous output.
7390 The quoting is suitable for @acronym{POSIX}-compatible shells like
7391 @command{bash}, but it does not always work for incompatible shells
7394 Quote strings for the shell, even if they would normally not require quoting.
7396 Quote strings as for C character string literals, including the
7397 surrounding double-quote characters; this is the same as the
7398 @option{-Q} or @option{--quote-name} option.
7400 Quote strings as for C character string literals, except omit the
7401 surrounding double-quote
7402 characters; this is the same as the @option{-b} or @option{--escape} option.
7404 Quote strings as for C character string literals, except use
7405 surrounding quotation marks appropriate for the
7408 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7409 Quote strings as for C character string literals, except use
7410 surrounding quotation marks appropriate for the locale, and quote
7411 @t{'like this'} instead of @t{"like
7412 this"} in the default C locale. This looks nicer on many displays.
7415 You can specify the default value of the @option{--quoting-style} option
7416 with the environment variable @env{QUOTING_STYLE}. If that environment
7417 variable is not set, the default value is @samp{literal}, but this
7418 default may change to @samp{shell} in a future version of this package.
7420 @item --show-control-chars
7421 @opindex --show-control-chars
7422 Print nongraphic characters as-is in file names.
7423 This is the default unless the output is a terminal and the program is
7429 @node dir invocation
7430 @section @command{dir}: Briefly list directory contents
7433 @cindex directory listing, brief
7435 @command{dir} is equivalent to @code{ls -C
7436 -b}; that is, by default files are listed in columns, sorted vertically,
7437 and special characters are represented by backslash escape sequences.
7439 @xref{ls invocation, @command{ls}}.
7442 @node vdir invocation
7443 @section @command{vdir}: Verbosely list directory contents
7446 @cindex directory listing, verbose
7448 @command{vdir} is equivalent to @code{ls -l
7449 -b}; that is, by default files are listed in long format and special
7450 characters are represented by backslash escape sequences.
7452 @node dircolors invocation
7453 @section @command{dircolors}: Color setup for @command{ls}
7457 @cindex setup for color
7459 @command{dircolors} outputs a sequence of shell commands to set up the
7460 terminal for color output from @command{ls} (and @command{dir}, etc.).
7464 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7467 If @var{file} is specified, @command{dircolors} reads it to determine which
7468 colors to use for which file types and extensions. Otherwise, a
7469 precompiled database is used. For details on the format of these files,
7470 run @samp{dircolors --print-database}.
7472 To make @command{dircolors} read a @file{~/.dircolors} file if it
7473 exists, you can put the following lines in your @file{~/.bashrc} (or
7474 adapt them to your favorite shell):
7478 test -r $d && eval "$(dircolors $d)"
7482 @vindex SHELL @r{environment variable, and color}
7483 The output is a shell command to set the @env{LS_COLORS} environment
7484 variable. You can specify the shell syntax to use on the command line,
7485 or @command{dircolors} will guess it from the value of the @env{SHELL}
7486 environment variable.
7488 The program accepts the following options. Also see @ref{Common options}.
7493 @itemx --bourne-shell
7496 @opindex --bourne-shell
7497 @cindex Bourne shell syntax for color setup
7498 @cindex @command{sh} syntax for color setup
7499 Output Bourne shell commands. This is the default if the @env{SHELL}
7500 environment variable is set and does not end with @samp{csh} or
7509 @cindex C shell syntax for color setup
7510 @cindex @command{csh} syntax for color setup
7511 Output C shell commands. This is the default if @code{SHELL} ends with
7512 @command{csh} or @command{tcsh}.
7515 @itemx --print-database
7517 @opindex --print-database
7518 @cindex color database, printing
7519 @cindex database for color setup, printing
7520 @cindex printing color database
7521 Print the (compiled-in) default color configuration database. This
7522 output is itself a valid configuration file, and is fairly descriptive
7523 of the possibilities.
7530 @node Basic operations
7531 @chapter Basic operations
7533 @cindex manipulating files
7535 This chapter describes the commands for basic file manipulation:
7536 copying, moving (renaming), and deleting (removing).
7539 * cp invocation:: Copy files.
7540 * dd invocation:: Convert and copy a file.
7541 * install invocation:: Copy files and set attributes.
7542 * mv invocation:: Move (rename) files.
7543 * rm invocation:: Remove files or directories.
7544 * shred invocation:: Remove files more securely.
7549 @section @command{cp}: Copy files and directories
7552 @cindex copying files and directories
7553 @cindex files, copying
7554 @cindex directories, copying
7556 @command{cp} copies files (or, optionally, directories). The copy is
7557 completely independent of the original. You can either copy one file to
7558 another, or copy arbitrarily many files to a destination directory.
7562 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7563 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7564 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7569 If two file names are given, @command{cp} copies the first file to the
7573 If the @option{--target-directory} (@option{-t}) option is given, or
7574 failing that if the last file is a directory and the
7575 @option{--no-target-directory} (@option{-T}) option is not given,
7576 @command{cp} copies each @var{source} file to the specified directory,
7577 using the @var{source}s' names.
7580 Generally, files are written just as they are read. For exceptions,
7581 see the @option{--sparse} option below.
7583 By default, @command{cp} does not copy directories. However, the
7584 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7585 copy recursively by descending into source directories and copying files
7586 to corresponding destination directories.
7588 When copying from a symbolic link, @command{cp} normally follows the
7589 link only when not copying
7590 recursively. This default can be overridden with the
7591 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7592 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7593 @option{-H} options. If more than one of these options is specified,
7594 the last one silently overrides the others.
7596 When copying to a symbolic link, @command{cp} follows the
7597 link only when it refers to an existing regular file.
7598 However, when copying to a dangling symbolic link, @command{cp}
7599 refuses by default, and fails with a diagnostic, since the operation
7600 is inherently dangerous. This behavior is contrary to historical
7601 practice and to @acronym{POSIX}.
7602 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7603 the target of a dangling destination symlink, in spite of the possible risk.
7604 Also, when an option like
7605 @option{--backup} or @option{--link} acts to rename or remove the
7606 destination before copying, @command{cp} renames or removes the
7607 symbolic link rather than the file it points to.
7609 By default, @command{cp} copies the contents of special files only
7610 when not copying recursively. This default can be overridden with the
7611 @option{--copy-contents} option.
7613 @cindex self-backups
7614 @cindex backups, making only
7615 @command{cp} generally refuses to copy a file onto itself, with the
7616 following exception: if @option{--force --backup} is specified with
7617 @var{source} and @var{dest} identical, and referring to a regular file,
7618 @command{cp} will make a backup file, either regular or numbered, as
7619 specified in the usual ways (@pxref{Backup options}). This is useful when
7620 you simply want to make a backup of an existing file before changing it.
7622 The program accepts the following options. Also see @ref{Common options}.
7629 Preserve as much as possible of the structure and attributes of the
7630 original files in the copy (but do not attempt to preserve internal
7631 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7632 directory in a different order).
7633 Try to preserve SELinux security context and extended attributes (xattr),
7634 but ignore any failure to do that and print no corresponding diagnostic.
7635 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7637 @itemx --attributes-only
7638 @opindex --attributes-only
7639 Preserve the specified attributes of the original files in the copy,
7640 but do not copy any data. See the @option{--preserve} option for
7641 controlling which attributes to copy.
7644 @itemx @w{@kbd{--backup}[=@var{method}]}
7647 @vindex VERSION_CONTROL
7648 @cindex backups, making
7649 @xref{Backup options}.
7650 Make a backup of each file that would otherwise be overwritten or removed.
7651 As a special case, @command{cp} makes a backup of @var{source} when the force
7652 and backup options are given and @var{source} and @var{dest} are the same
7653 name for an existing, regular file. One useful application of this
7654 combination of options is this tiny Bourne shell script:
7658 # Usage: backup FILE...
7659 # Create a @sc{gnu}-style backup of each listed FILE.
7661 cp --backup --force -- "$i" "$i"
7665 @item --copy-contents
7666 @cindex directories, copying recursively
7667 @cindex copying directories recursively
7668 @cindex recursively copying directories
7669 @cindex non-directories, copying as special files
7670 If copying recursively, copy the contents of any special files (e.g.,
7671 FIFOs and device files) as if they were regular files. This means
7672 trying to read the data in each source file and writing it to the
7673 destination. It is usually a mistake to use this option, as it
7674 normally has undesirable effects on special files like FIFOs and the
7675 ones typically found in the @file{/dev} directory. In most cases,
7676 @code{cp -R --copy-contents} will hang indefinitely trying to read
7677 from FIFOs and special files like @file{/dev/console}, and it will
7678 fill up your destination disk if you use it to copy @file{/dev/zero}.
7679 This option has no effect unless copying recursively, and it does not
7680 affect the copying of symbolic links.
7684 @cindex symbolic links, copying
7685 @cindex hard links, preserving
7686 Copy symbolic links as symbolic links rather than copying the files that
7687 they point to, and preserve hard links between source files in the copies.
7688 Equivalent to @option{--no-dereference --preserve=links}.
7694 When copying without this option and an existing destination file cannot
7695 be opened for writing, the copy fails. However, with @option{--force}),
7696 when a destination file cannot be opened, @command{cp} then removes it and
7697 tries to open it again. Contrast this behavior with that enabled by
7698 @option{--link} and @option{--symbolic-link}, whereby the destination file
7699 is never opened but rather is removed unconditionally. Also see the
7700 description of @option{--remove-destination}.
7702 This option is independent of the @option{--interactive} or
7703 @option{-i} option: neither cancels the effect of the other.
7705 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7710 If a command line argument specifies a symbolic link, then copy the
7711 file it points to rather than the symbolic link itself. However,
7712 copy (preserving its nature) any symbolic link that is encountered
7713 via recursive traversal.
7716 @itemx --interactive
7718 @opindex --interactive
7719 When copying a file other than a directory, prompt whether to
7720 overwrite an existing destination file. The @option{-i} option overrides
7721 a previous @option{-n} option.
7727 Make hard links instead of copies of non-directories.
7730 @itemx --dereference
7732 @opindex --dereference
7733 Follow symbolic links when copying from them.
7734 With this option, @command{cp} cannot create a symbolic link.
7735 For example, a symlink (to regular file) in the source tree will be copied to
7736 a regular file in the destination tree.
7741 @opindex --no-clobber
7742 Do not overwrite an existing file. The @option{-n} option overrides a previous
7743 @option{-i} option. This option is mutually exclusive with @option{-b} or
7744 @option{--backup} option.
7747 @itemx --no-dereference
7749 @opindex --no-dereference
7750 @cindex symbolic links, copying
7751 Copy symbolic links as symbolic links rather than copying the files that
7752 they point to. This option affects only symbolic links in the source;
7753 symbolic links in the destination are always followed if possible.
7756 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7759 @cindex file information, preserving, extended attributes, xattr
7760 Preserve the specified attributes of the original files.
7761 If specified, the @var{attribute_list} must be a comma-separated list
7762 of one or more of the following strings:
7766 Preserve the file mode bits and access control lists.
7768 Preserve the owner and group. On most modern systems,
7769 only users with appropriate privileges may change the owner of a file,
7771 may preserve the group ownership of a file only if they happen to be
7772 a member of the desired group.
7774 Preserve the times of last access and last modification, when possible.
7775 On older systems, it is not possible to preserve these attributes
7776 when the affected file is a symbolic link.
7777 However, many systems now provide the @code{utimensat} function,
7778 which makes it possible even for symbolic links.
7780 Preserve in the destination files
7781 any links between corresponding source files.
7782 Note that with @option{-L} or @option{-H}, this option can convert
7783 symbolic links to hard links. For example,
7785 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7790 Note the inputs: @file{b} is a symlink to regular file @file{a},
7791 yet the files in destination directory, @file{c/}, are hard-linked.
7792 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7793 tells @command{cp} to dereference command line arguments, it sees two files
7794 with the same inode number, and preserves the perceived hard link.
7796 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7798 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7804 Preserve SELinux security context of the file, or fail with full diagnostics.
7806 Preserve extended attributes of the file, or fail with full diagnostics.
7807 If @command{cp} is built without xattr support, ignore this option.
7808 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7809 they are preserved by this option as well.
7811 Preserve all file attributes.
7812 Equivalent to specifying all of the above, but with the difference
7813 that failure to preserve SELinux security context or extended attributes
7814 does not change @command{cp}'s exit status. In contrast to @option{-a},
7815 all but @samp{Operation not supported} warnings are output.
7818 Using @option{--preserve} with no @var{attribute_list} is equivalent
7819 to @option{--preserve=mode,ownership,timestamps}.
7821 In the absence of this option, each destination file is created with the
7822 mode bits of the corresponding source file, minus the bits set in the
7823 umask and minus the set-user-ID and set-group-ID bits.
7824 @xref{File permissions}.
7826 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7827 @cindex file information, preserving
7828 Do not preserve the specified attributes. The @var{attribute_list}
7829 has the same form as for @option{--preserve}.
7833 @cindex parent directories and @command{cp}
7834 Form the name of each destination file by appending to the target
7835 directory a slash and the specified name of the source file. The last
7836 argument given to @command{cp} must be the name of an existing directory.
7837 For example, the command:
7840 cp --parents a/b/c existing_dir
7844 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7845 any missing intermediate directories.
7852 @opindex --recursive
7853 @cindex directories, copying recursively
7854 @cindex copying directories recursively
7855 @cindex recursively copying directories
7856 @cindex non-directories, copying as special files
7857 Copy directories recursively. By default, do not follow symbolic
7858 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7859 @option{--dereference} (@option{-L}), @option{--no-dereference}
7860 (@option{-P}), and @option{-H} options. Special files are copied by
7861 creating a destination file of the same type as the source; see the
7862 @option{--copy-contents} option. It is not portable to use
7863 @option{-r} to copy symbolic links or special files. On some
7864 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7865 @option{-L} and @option{--copy-contents} for historical reasons.
7866 Also, it is not portable to use @option{-R} to copy symbolic links
7867 unless you also specify @option{-P}, as @acronym{POSIX} allows
7868 implementations that dereference symbolic links by default.
7870 @item --reflink[=@var{when}]
7871 @opindex --reflink[=@var{when}]
7874 @cindex copy on write
7875 Perform a lightweight, copy-on-write (COW) copy, if supported by the
7876 file system. Once it has succeeded, beware that the source and destination
7877 files share the same disk data blocks as long as they remain unmodified.
7878 Thus, if a disk I/O error affects data blocks of one of the files,
7879 the other suffers the same fate.
7881 The @var{when} value can be one of the following:
7885 The default behavior: if the copy-on-write operation is not supported
7886 then report the failure for each file and exit with a failure status.
7889 If the copy-on-write operation is not supported then fall back
7890 to the standard copy behaviour.
7893 This option is overridden by the @option{--link}, @option{--symbolic-link}
7894 and @option{--attributes-only} options, thus allowing it to be used
7895 to configure the default data copying behavior for @command{cp}.
7896 For example, with the following alias, @command{cp} will use the
7897 minimum amount of space supported by the file system.
7900 alias cp='cp --reflink=auto --sparse=always'
7903 @item --remove-destination
7904 @opindex --remove-destination
7905 Remove each existing destination file before attempting to open it
7906 (contrast with @option{-f} above).
7908 @item --sparse=@var{when}
7909 @opindex --sparse=@var{when}
7910 @cindex sparse files, copying
7911 @cindex holes, copying files with
7912 @findex read @r{system call, and holes}
7913 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7914 does not occupy any physical disk blocks; the @samp{read} system call
7915 reads these as zeros. This can both save considerable disk space and
7916 increase speed, since many binary files contain lots of consecutive zero
7917 bytes. By default, @command{cp} detects holes in input source files via a crude
7918 heuristic and makes the corresponding output file sparse as well.
7919 Only regular files may be sparse.
7921 The @var{when} value can be one of the following:
7925 The default behavior: if the input file is sparse, attempt to make
7926 the output file sparse, too. However, if an output file exists but
7927 refers to a non-regular file, then do not attempt to make it sparse.
7930 For each sufficiently long sequence of zero bytes in the input file,
7931 attempt to create a corresponding hole in the output file, even if the
7932 input file does not appear to be sparse.
7933 This is useful when the input file resides on a file system
7934 that does not support sparse files
7935 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7936 but the output file is on a type of file system that does support them.
7937 Holes may be created only in regular files, so if the destination file
7938 is of some other type, @command{cp} does not even try to make it sparse.
7941 Never make the output file sparse.
7942 This is useful in creating a file for use with the @command{mkswap} command,
7943 since such a file must not have any holes.
7946 @optStripTrailingSlashes
7949 @itemx --symbolic-link
7951 @opindex --symbolic-link
7952 @cindex symbolic links, copying with
7953 Make symbolic links instead of copies of non-directories. All source
7954 file names must be absolute (starting with @samp{/}) unless the
7955 destination files are in the current directory. This option merely
7956 results in an error message on systems that do not support symbolic links.
7962 @optNoTargetDirectory
7968 @cindex newer files, copying only
7969 Do not copy a non-directory that has an existing destination with the
7970 same or newer modification time. If time stamps are being preserved,
7971 the comparison is to the source time stamp truncated to the
7972 resolutions of the destination file system and of the system calls
7973 used to update time stamps; this avoids duplicate work if several
7974 @samp{cp -pu} commands are executed with the same source and destination.
7975 If @option{--preserve=links} is also specified (like with @samp{cp -au}
7976 for example), that will take precedence. Consequently, depending on the
7977 order that files are processed from the source, newer files in the destination
7978 may be replaced, to mirror hard links in the source.
7984 Print the name of each file before copying it.
7987 @itemx --one-file-system
7989 @opindex --one-file-system
7990 @cindex file systems, omitting copying to different
7991 Skip subdirectories that are on different file systems from the one that
7992 the copy started on.
7993 However, mount point directories @emph{are} copied.
8001 @section @command{dd}: Convert and copy a file
8004 @cindex converting while copying a file
8006 @command{dd} copies a file (from standard input to standard output, by
8007 default) with a changeable I/O block size, while optionally performing
8008 conversions on it. Synopses:
8011 dd [@var{operand}]@dots{}
8015 The only options are @option{--help} and @option{--version}.
8016 @xref{Common options}. @command{dd} accepts the following operands.
8022 Read from @var{file} instead of standard input.
8026 Write to @var{file} instead of standard output. Unless
8027 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
8028 bytes (or the size specified with @samp{seek=}).
8030 @item ibs=@var{bytes}
8032 @cindex block size of input
8033 @cindex input block size
8034 Set the input block size to @var{bytes}.
8035 This makes @command{dd} read @var{bytes} per block.
8036 The default is 512 bytes.
8038 @item obs=@var{bytes}
8040 @cindex block size of output
8041 @cindex output block size
8042 Set the output block size to @var{bytes}.
8043 This makes @command{dd} write @var{bytes} per block.
8044 The default is 512 bytes.
8046 @item bs=@var{bytes}
8049 Set both input and output block sizes to @var{bytes}.
8050 This makes @command{dd} read and write @var{bytes} per block,
8051 overriding any @samp{ibs} and @samp{obs} settings.
8052 In addition, if no data-transforming @option{conv} option is specified,
8053 input is copied to the output as soon as it's read,
8054 even if it is smaller than the block size.
8056 @item cbs=@var{bytes}
8058 @cindex block size of conversion
8059 @cindex conversion block size
8060 @cindex fixed-length records, converting to variable-length
8061 @cindex variable-length records, converting to fixed-length
8062 Set the conversion block size to @var{bytes}.
8063 When converting variable-length records to fixed-length ones
8064 (@option{conv=block}) or the reverse (@option{conv=unblock}),
8065 use @var{bytes} as the fixed record length.
8069 Skip @var{n} @samp{ibs}-byte blocks in the input file before copying.
8070 If @samp{iflag=skip_bytes} is specified, @var{n} is interpreted
8071 as a byte count rather than a block count.
8075 Skip @var{n} @samp{obs}-byte blocks in the output file before copying.
8076 if @samp{oflag=seek_bytes} is specified, @var{n} is interpreted
8077 as a byte count rather than a block count.
8081 Copy @var{n} @samp{ibs}-byte blocks from the input file, instead
8082 of everything until the end of the file.
8083 if @samp{iflag=count_bytes} is specified, @var{n} is interpreted
8084 as a byte count rather than a block count.
8088 Do not print the overall transfer rate and volume statistics
8089 that normally make up the third status line when @command{dd} exits.
8091 @item conv=@var{conversion}[,@var{conversion}]@dots{}
8093 Convert the file as specified by the @var{conversion} argument(s).
8094 (No spaces around any comma(s).)
8101 @opindex ascii@r{, converting to}
8102 Convert @acronym{EBCDIC} to @acronym{ASCII},
8103 using the conversion table specified by @acronym{POSIX}.
8104 This provides a 1:1 translation for all 256 bytes.
8107 @opindex ebcdic@r{, converting to}
8108 Convert @acronym{ASCII} to @acronym{EBCDIC}.
8109 This is the inverse of the @samp{ascii} conversion.
8112 @opindex alternate ebcdic@r{, converting to}
8113 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
8114 using the alternate conversion table specified by @acronym{POSIX}.
8115 This is not a 1:1 translation, but reflects common historical practice
8116 for @samp{~}, @samp{[}, and @samp{]}.
8118 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
8122 @opindex block @r{(space-padding)}
8123 For each line in the input, output @samp{cbs} bytes, replacing the
8124 input newline with a space and padding with spaces as necessary.
8128 Remove any trailing spaces in each @samp{cbs}-sized input block,
8129 and append a newline.
8131 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
8134 @opindex lcase@r{, converting to}
8135 Change uppercase letters to lowercase.
8138 @opindex ucase@r{, converting to}
8139 Change lowercase letters to uppercase.
8141 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
8145 Try to seek rather than write @sc{nul} output blocks.
8146 On a file system that supports sparse files, this will create
8147 sparse output when extending the output file.
8148 Be careful when using this option in conjunction with
8149 @samp{conv=notrunc} or @samp{oflag=append}.
8150 With @samp{conv=notrunc}, existing data in the output
8151 corresponding to @sc{nul} blocks from the input, will be untouched.
8152 With @samp{oflag=append} the seeks performed will be ineffective.
8155 @opindex swab @r{(byte-swapping)}
8156 @cindex byte-swapping
8157 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
8158 when an odd number of bytes are read---the last byte is simply copied
8159 (since there is nothing to swap it with).
8162 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
8163 Pad every input block to size of @samp{ibs} with trailing zero bytes.
8164 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
8169 The following ``conversions'' are really file flags
8170 and don't affect internal processing:
8175 @cindex creating output file, requiring
8176 Fail if the output file already exists; @command{dd} must create the
8181 @cindex creating output file, avoiding
8182 Do not create the output file; the output file must already exist.
8184 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
8188 @cindex truncating output file, avoiding
8189 Do not truncate the output file.
8193 @cindex read errors, ignoring
8194 Continue after read errors.
8198 @cindex synchronized data writes, before finishing
8199 Synchronize output data just before finishing. This forces a physical
8200 write of output data.
8204 @cindex synchronized data and metadata writes, before finishing
8205 Synchronize output data and metadata just before finishing. This
8206 forces a physical write of output data and metadata.
8210 @item iflag=@var{flag}[,@var{flag}]@dots{}
8212 Access the input file using the flags specified by the @var{flag}
8213 argument(s). (No spaces around any comma(s).)
8215 @item oflag=@var{flag}[,@var{flag}]@dots{}
8217 Access the output file using the flags specified by the @var{flag}
8218 argument(s). (No spaces around any comma(s).)
8220 Here are the flags. Not every flag is supported on every operating
8227 @cindex appending to the output file
8228 Write in append mode, so that even if some other process is writing to
8229 this file, every @command{dd} write will append to the current
8230 contents of the file. This flag makes sense only for output.
8231 If you combine this flag with the @samp{of=@var{file}} operand,
8232 you should also specify @samp{conv=notrunc} unless you want the
8233 output file to be truncated before being appended to.
8237 @cindex concurrent I/O
8238 Use concurrent I/O mode for data. This mode performs direct I/O
8239 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
8240 A file cannot be opened in CIO mode and with a standard open at the
8246 Use direct I/O for data, avoiding the buffer cache.
8247 Note that the kernel may impose restrictions on read or write buffer sizes.
8248 For example, with an ext4 destination file system and a linux-based kernel,
8249 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
8250 output buffer size is not a multiple of 512.
8254 @cindex directory I/O
8256 Fail unless the file is a directory. Most operating systems do not
8257 allow I/O to a directory, so this flag has limited utility.
8261 @cindex synchronized data reads
8262 Use synchronized I/O for data. For the output file, this forces a
8263 physical write of output data on each write. For the input file,
8264 this flag can matter when reading from a remote file that has been
8265 written to synchronously by some other process. Metadata (e.g.,
8266 last-access and last-modified time) is not necessarily synchronized.
8270 @cindex synchronized data and metadata I/O
8271 Use synchronized I/O for both data and metadata.
8275 @cindex discarding file cache
8276 Discard the data cache for a file.
8277 When count=0 all cache is discarded,
8278 otherwise the cache is dropped for the processed
8279 portion of the file. Also when count=0
8280 failure to discard the cache is diagnosed
8281 and reflected in the exit status.
8282 Here as some usage examples:
8285 # Advise to drop cache for whole file
8286 dd if=ifile iflag=nocache count=0
8288 # Ensure drop cache for the whole file
8289 dd of=ofile oflag=nocache conv=notrunc,fdatasync count=0
8291 # Drop cache for part of file
8292 dd if=ifile iflag=nocache skip=10 count=10 of=/dev/null
8294 # Stream data using just the read-ahead cache
8295 dd if=ifile of=ofile iflag=nocache oflag=nocache
8300 @cindex nonblocking I/O
8301 Use non-blocking I/O.
8306 Do not update the file's access time.
8307 Some older file systems silently ignore this flag, so it is a good
8308 idea to test it on your files before relying on it.
8312 @cindex controlling terminal
8313 Do not assign the file to be a controlling terminal for @command{dd}.
8314 This has no effect when the file is not a terminal.
8315 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
8320 @cindex symbolic links, following
8321 Do not follow symbolic links.
8326 Fail if the file has multiple hard links.
8331 Use binary I/O. This option has an effect only on nonstandard
8332 platforms that distinguish binary from text I/O.
8337 Use text I/O. Like @samp{binary}, this option has no effect on
8342 Accumulate full blocks from input. The @code{read} system call
8343 may return early if a full block is not available.
8344 When that happens, continue calling @code{read} to fill the remainder
8346 This flag can be used only with @code{iflag}.
8349 @opindex count_bytes
8350 Interpret the @samp{count=} operand as a byte count,
8351 rather than a block count, which allows specifying
8352 a length that is not a multiple of the I/O block size.
8353 This flag can be used only with @code{iflag}.
8357 Interpret the @samp{skip=} operand as a byte count,
8358 rather than a block count, which allows specifying
8359 an offset that is not a multiple of the I/O block size.
8360 This flag can be used only with @code{iflag}.
8364 Interpret the @samp{seek=} operand as a byte count,
8365 rather than a block count, which allows specifying
8366 an offset that is not a multiple of the I/O block size.
8367 This flag can be used only with @code{oflag}.
8371 These flags are not supported on all systems, and @samp{dd} rejects
8372 attempts to use them when they are not supported. When reading from
8373 standard input or writing to standard output, the @samp{nofollow} and
8374 @samp{noctty} flags should not be specified, and the other flags
8375 (e.g., @samp{nonblock}) can affect how other processes behave with the
8376 affected file descriptors, even after @command{dd} exits.
8380 @cindex multipliers after numbers
8381 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8382 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8383 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8384 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8386 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8387 should not be too large---values larger than a few megabytes
8388 are generally wasteful or (as in the gigabyte..exabyte case) downright
8389 counterproductive or error-inducing.
8391 To process data that is at an offset or size that is not a
8392 multiple of the I/O@ block size, you can use the @samp{skip_bytes},
8393 @samp{seek_bytes} and @samp{count_bytes} flags. Alternatively
8394 the traditional method of separate @command{dd} invocations can be used.
8395 For example, the following shell commands copy data
8396 in 512 KiB blocks between a disk and a tape, but do not save
8397 or restore a 4 KiB label at the start of the disk:
8400 disk=/dev/rdsk/c0t1d0s2
8403 # Copy all but the label from disk to tape.
8404 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8406 # Copy from tape back to disk, but leave the disk label alone.
8407 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8410 Sending an @samp{INFO} signal to a running @command{dd}
8411 process makes it print I/O statistics to standard error
8412 and then resume copying. In the example below,
8413 @command{dd} is run in the background to copy 10 million blocks.
8414 The @command{kill} command makes it output intermediate I/O statistics,
8415 and when @command{dd} completes normally or is killed by the
8416 @code{SIGINT} signal, it outputs the final statistics.
8419 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8420 $ kill -s INFO $pid; wait $pid
8421 3385223+0 records in
8422 3385223+0 records out
8423 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8424 10000000+0 records in
8425 10000000+0 records out
8426 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8429 @vindex POSIXLY_CORRECT
8430 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8431 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8432 environment variable is set.
8437 @node install invocation
8438 @section @command{install}: Copy files and set attributes
8441 @cindex copying files and setting attributes
8443 @command{install} copies files while setting their file mode bits and, if
8444 possible, their owner and group. Synopses:
8447 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8448 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8449 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8450 install [@var{option}]@dots{} -d @var{directory}@dots{}
8455 If two file names are given, @command{install} copies the first file to the
8459 If the @option{--target-directory} (@option{-t}) option is given, or
8460 failing that if the last file is a directory and the
8461 @option{--no-target-directory} (@option{-T}) option is not given,
8462 @command{install} copies each @var{source} file to the specified
8463 directory, using the @var{source}s' names.
8466 If the @option{--directory} (@option{-d}) option is given,
8467 @command{install} creates each @var{directory} and any missing parent
8468 directories. Parent directories are created with mode
8469 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8470 current umask. @xref{Directory Setuid and Setgid}, for how the
8471 set-user-ID and set-group-ID bits of parent directories are inherited.
8474 @cindex Makefiles, installing programs in
8475 @command{install} is similar to @command{cp}, but allows you to control the
8476 attributes of destination files. It is typically used in Makefiles to
8477 copy programs into their destination directories. It refuses to copy
8478 files onto themselves.
8480 @cindex extended attributes, xattr
8481 @command{install} never preserves extended attributes (xattr).
8483 The program accepts the following options. Also see @ref{Common options}.
8493 Compare each pair of source and destination files, and if the destination has
8494 identical content and any specified owner, group, permissions, and possibly
8495 SELinux context, then do not modify the destination at all.
8499 Ignored; for compatibility with old Unix versions of @command{install}.
8503 Create any missing parent directories of @var{dest},
8504 then copy @var{source} to @var{dest}.
8505 This option is ignored if a destination directory is specified
8506 via @option{--target-directory=DIR}.
8511 @opindex --directory
8512 @cindex directories, creating with given attributes
8513 @cindex parent directories, creating missing
8514 @cindex leading directories, creating missing
8515 Create any missing parent directories, giving them the default
8516 attributes. Then create each given directory, setting their owner,
8517 group and mode as given on the command line or to the defaults.
8519 @item -g @var{group}
8520 @itemx --group=@var{group}
8523 @cindex group ownership of installed files, setting
8524 Set the group ownership of installed files or directories to
8525 @var{group}. The default is the process's current group. @var{group}
8526 may be either a group name or a numeric group ID.
8529 @itemx --mode=@var{mode}
8532 @cindex permissions of installed files, setting
8533 Set the file mode bits for the installed file or directory to @var{mode},
8534 which can be either an octal number, or a symbolic mode as in
8535 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8536 point of departure (@pxref{File permissions}).
8537 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8538 execute for the owner, read and execute for group and other, and with
8539 set-user-ID and set-group-ID disabled.
8540 This default is not quite the same as @samp{755}, since it disables
8541 instead of preserving set-user-ID and set-group-ID on directories.
8542 @xref{Directory Setuid and Setgid}.
8544 @item -o @var{owner}
8545 @itemx --owner=@var{owner}
8548 @cindex ownership of installed files, setting
8549 @cindex appropriate privileges
8550 @vindex root @r{as default owner}
8551 If @command{install} has appropriate privileges (is run as root), set the
8552 ownership of installed files or directories to @var{owner}. The default
8553 is @code{root}. @var{owner} may be either a user name or a numeric user
8556 @item --preserve-context
8557 @opindex --preserve-context
8559 @cindex security context
8560 Preserve the SELinux security context of files and directories.
8561 Failure to preserve the context in all of the files or directories
8562 will result in an exit status of 1. If SELinux is disabled then
8563 print a warning and ignore the option.
8566 @itemx --preserve-timestamps
8568 @opindex --preserve-timestamps
8569 @cindex timestamps of installed files, preserving
8570 Set the time of last access and the time of last modification of each
8571 installed file to match those of each corresponding original file.
8572 When a file is installed without this option, its last access and
8573 last modification times are both set to the time of installation.
8574 This option is useful if you want to use the last modification times
8575 of installed files to keep track of when they were last built as opposed
8576 to when they were last installed.
8582 @cindex symbol table information, stripping
8583 @cindex stripping symbol table information
8584 Strip the symbol tables from installed binary executables.
8586 @itemx --strip-program=@var{program}
8587 @opindex --strip-program
8588 @cindex symbol table information, stripping, program
8589 Program used to strip binaries.
8595 @optNoTargetDirectory
8601 Print the name of each file before copying it.
8603 @item -Z @var{context}
8604 @itemx --context=@var{context}
8608 @cindex security context
8609 Set the default SELinux security context to be used for any
8610 created files and directories. If SELinux is disabled then
8611 print a warning and ignore the option.
8619 @section @command{mv}: Move (rename) files
8623 @command{mv} moves or renames files (or directories). Synopses:
8626 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8627 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8628 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8633 If two file names are given, @command{mv} moves the first file to the
8637 If the @option{--target-directory} (@option{-t}) option is given, or
8638 failing that if the last file is a directory and the
8639 @option{--no-target-directory} (@option{-T}) option is not given,
8640 @command{mv} moves each @var{source} file to the specified
8641 directory, using the @var{source}s' names.
8644 @command{mv} can move any type of file from one file system to another.
8645 Prior to version @code{4.0} of the fileutils,
8646 @command{mv} could move only regular files between file systems.
8647 For example, now @command{mv} can move an entire directory hierarchy
8648 including special device files from one partition to another. It first
8649 uses some of the same code that's used by @code{cp -a} to copy the
8650 requested directories and files, then (assuming the copy succeeded)
8651 it removes the originals. If the copy fails, then the part that was
8652 copied to the destination partition is removed. If you were to copy
8653 three directories from one partition to another and the copy of the first
8654 directory succeeded, but the second didn't, the first would be left on
8655 the destination partition and the second and third would be left on the
8658 @cindex extended attributes, xattr
8659 @command{mv} always tries to copy extended attributes (xattr), which may
8660 include SELinux context, ACLs or Capabilities.
8661 Upon failure all but @samp{Operation not supported} warnings are output.
8663 @cindex prompting, and @command{mv}
8664 If a destination file exists but is normally unwritable, standard input
8665 is a terminal, and the @option{-f} or @option{--force} option is not given,
8666 @command{mv} prompts the user for whether to replace the file. (You might
8667 own the file, or have write permission on its directory.) If the
8668 response is not affirmative, the file is skipped.
8670 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8671 when it might be a symlink to a directory.
8672 Otherwise, @command{mv} may do something very surprising, since
8673 its behavior depends on the underlying rename system call.
8674 On a system with a modern Linux-based kernel, it fails with
8675 @code{errno=ENOTDIR}.
8676 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8677 renames not the symlink but rather the directory referenced by the symlink.
8678 @xref{Trailing slashes}.
8680 The program accepts the following options. Also see @ref{Common options}.
8690 @cindex prompts, omitting
8691 Do not prompt the user before removing a destination file.
8693 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8694 options, only the final one takes effect.
8699 @itemx --interactive
8701 @opindex --interactive
8702 @cindex prompts, forcing
8703 Prompt whether to overwrite each existing destination file, regardless
8705 If the response is not affirmative, the file is skipped.
8711 @opindex --no-clobber
8712 @cindex prompts, omitting
8713 Do not overwrite an existing file.
8715 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8721 @cindex newer files, moving only
8722 Do not move a non-directory that has an existing destination with the
8723 same or newer modification time.
8724 If the move is across file system boundaries, the comparison is to the
8725 source time stamp truncated to the resolutions of the destination file
8726 system and of the system calls used to update time stamps; this avoids
8727 duplicate work if several @samp{mv -u} commands are executed with the
8728 same source and destination.
8734 Print the name of each file before moving it.
8736 @optStripTrailingSlashes
8742 @optNoTargetDirectory
8750 @section @command{rm}: Remove files or directories
8753 @cindex removing files or directories
8755 @command{rm} removes each given @var{file}. By default, it does not remove
8756 directories. Synopsis:
8759 rm [@var{option}]@dots{} [@var{file}]@dots{}
8762 @cindex prompting, and @command{rm}
8763 If the @option{-I} or @option{--interactive=once} option is given,
8764 and there are more than three files or the @option{-r}, @option{-R},
8765 or @option{--recursive} are given, then @command{rm} prompts the user
8766 for whether to proceed with the entire operation. If the response is
8767 not affirmative, the entire command is aborted.
8769 Otherwise, if a file is unwritable, standard input is a terminal, and
8770 the @option{-f} or @option{--force} option is not given, or the
8771 @option{-i} or @option{--interactive=always} option @emph{is} given,
8772 @command{rm} prompts the user for whether to remove the file.
8773 If the response is not affirmative, the file is skipped.
8775 Any attempt to remove a file whose last file name component is
8776 @file{.} or @file{..} is rejected without any prompting.
8778 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8779 possible to recover the contents of that file. If you want more assurance
8780 that the contents are truly unrecoverable, consider using @command{shred}.
8782 The program accepts the following options. Also see @ref{Common options}.
8790 Ignore nonexistent files and missing operands, and never prompt the user.
8791 Ignore any previous @option{--interactive} (@option{-i}) option.
8795 Prompt whether to remove each file.
8796 If the response is not affirmative, the file is skipped.
8797 Ignore any previous @option{--force} (@option{-f}) option.
8798 Equivalent to @option{--interactive=always}.
8802 Prompt once whether to proceed with the command, if more than three
8803 files are named or if a recursive removal is requested. Ignore any
8804 previous @option{--force} (@option{-f}) option. Equivalent to
8805 @option{--interactive=once}.
8807 @itemx --interactive [=@var{when}]
8808 @opindex --interactive
8809 Specify when to issue an interactive prompt. @var{when} may be
8813 @vindex never @r{interactive option}
8814 - Do not prompt at all.
8816 @vindex once @r{interactive option}
8817 - Prompt once if more than three files are named or if a recursive
8818 removal is requested. Equivalent to @option{-I}.
8820 @vindex always @r{interactive option}
8821 - Prompt for every file being removed. Equivalent to @option{-i}.
8823 @option{--interactive} with no @var{when} is equivalent to
8824 @option{--interactive=always}.
8826 @itemx --one-file-system
8827 @opindex --one-file-system
8828 @cindex one file system, restricting @command{rm} to
8829 When removing a hierarchy recursively, skip any directory that is on a
8830 file system different from that of the corresponding command line argument.
8833 This option is useful when removing a build ``chroot'' hierarchy,
8834 which normally contains no valuable data. However, it is not uncommon
8835 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8836 use one's start-up file. The catch is that it's easy to forget to
8837 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8838 your normally throw-away chroot, that command will remove everything
8839 under @file{/home}, too.
8840 Use the @option{--one-file-system} option, and it will
8841 warn about and skip directories on other file systems.
8842 Of course, this will not save your @file{/home} if it and your
8843 chroot happen to be on the same file system.
8845 @itemx --preserve-root
8846 @opindex --preserve-root
8847 @cindex root directory, disallow recursive destruction
8848 Fail upon any attempt to remove the root directory, @file{/},
8849 when used with the @option{--recursive} option.
8850 This is the default behavior.
8851 @xref{Treating / specially}.
8853 @itemx --no-preserve-root
8854 @opindex --no-preserve-root
8855 @cindex root directory, allow recursive destruction
8856 Do not treat @file{/} specially when removing recursively.
8857 This option is not recommended unless you really want to
8858 remove all the files on your computer.
8859 @xref{Treating / specially}.
8866 @opindex --recursive
8867 @cindex directories, removing (recursively)
8868 Remove the listed directories and their contents recursively.
8874 Print the name of each file before removing it.
8878 @cindex files beginning with @samp{-}, removing
8879 @cindex @samp{-}, removing files beginning with
8880 One common question is how to remove files whose names begin with a
8881 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8882 function to parse its arguments, lets you use the @samp{--} option to
8883 indicate that all following arguments are non-options. To remove a file
8884 called @file{-f} in the current directory, you could type either:
8897 @opindex - @r{and Unix @command{rm}}
8898 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8899 predates the development of the getopt standard syntax.
8904 @node shred invocation
8905 @section @command{shred}: Remove files more securely
8908 @cindex data, erasing
8909 @cindex erasing data
8911 @command{shred} overwrites devices or files, to help prevent even
8912 very expensive hardware from recovering the data.
8914 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8915 not actually destroyed. Only the index listing where the file is
8916 stored is destroyed, and the storage is made available for reuse.
8917 There are undelete utilities that will attempt to reconstruct the index
8918 and can bring the file back if the parts were not reused.
8920 On a busy system with a nearly-full drive, space can get reused in a few
8921 seconds. But there is no way to know for sure. If you have sensitive
8922 data, you may want to be sure that recovery is not possible by actually
8923 overwriting the file with non-sensitive data.
8925 However, even after doing that, it is possible to take the disk back
8926 to a laboratory and use a lot of sensitive (and expensive) equipment
8927 to look for the faint ``echoes'' of the original data underneath the
8928 overwritten data. If the data has only been overwritten once, it's not
8931 The best way to remove something irretrievably is to destroy the media
8932 it's on with acid, melt it down, or the like. For cheap removable media
8933 like floppy disks, this is the preferred method. However, hard drives
8934 are expensive and hard to melt, so the @command{shred} utility tries
8935 to achieve a similar effect non-destructively.
8937 This uses many overwrite passes, with the data patterns chosen to
8938 maximize the damage they do to the old data. While this will work on
8939 floppies, the patterns are designed for best effect on hard drives.
8940 For more details, see the source code and Peter Gutmann's paper
8941 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8942 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8943 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8944 California, July 22--25, 1996).
8946 @strong{Please note} that @command{shred} relies on a very important assumption:
8947 that the file system overwrites data in place. This is the traditional
8948 way to do things, but many modern file system designs do not satisfy this
8949 assumption. Exceptions include:
8954 Log-structured or journaled file systems, such as those supplied with
8955 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8956 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8959 File systems that write redundant data and carry on even if some writes
8960 fail, such as RAID-based file systems.
8963 File systems that make snapshots, such as Network Appliance's NFS server.
8966 File systems that cache in temporary locations, such as NFS version 3
8970 Compressed file systems.
8973 In the particular case of ext3 file systems, the above disclaimer applies (and
8974 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8975 mode, which journals file data in addition to just metadata. In both
8976 the @code{data=ordered} (default) and @code{data=writeback} modes,
8977 @command{shred} works as usual. Ext3 journaling modes can be changed
8978 by adding the @code{data=something} option to the mount options for a
8979 particular file system in the @file{/etc/fstab} file, as documented in
8980 the mount man page (man mount).
8982 If you are not sure how your file system operates, then you should assume
8983 that it does not overwrite data in place, which means that shred cannot
8984 reliably operate on regular files in your file system.
8986 Generally speaking, it is more reliable to shred a device than a file,
8987 since this bypasses the problem of file system design mentioned above.
8988 However, even shredding devices is not always completely reliable. For
8989 example, most disks map out bad sectors invisibly to the application; if
8990 the bad sectors contain sensitive data, @command{shred} won't be able to
8993 @command{shred} makes no attempt to detect or report this problem, just as
8994 it makes no attempt to do anything about backups. However, since it is
8995 more reliable to shred devices than files, @command{shred} by default does
8996 not truncate or remove the output file. This default is more suitable
8997 for devices, which typically cannot be truncated and should not be
9000 Finally, consider the risk of backups and mirrors.
9001 File system backups and remote mirrors may contain copies of the
9002 file that cannot be removed, and that will allow a shredded file
9003 to be recovered later. So if you keep any data you may later want
9004 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
9007 shred [@var{option}]@dots{} @var{file}[@dots{}]
9010 The program accepts the following options. Also see @ref{Common options}.
9018 @cindex force deletion
9019 Override file permissions if necessary to allow overwriting.
9022 @itemx -n @var{number}
9023 @itemx --iterations=@var{number}
9024 @opindex -n @var{number}
9025 @opindex --iterations=@var{number}
9026 @cindex iterations, selecting the number of
9027 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
9028 overwrite. You can reduce this to save time, or increase it if you think it's
9029 appropriate. After 25 passes all of the internal overwrite patterns will have
9030 been used at least once.
9032 @item --random-source=@var{file}
9033 @opindex --random-source
9034 @cindex random source for shredding
9035 Use @var{file} as a source of random data used to overwrite and to
9036 choose pass ordering. @xref{Random sources}.
9038 @item -s @var{bytes}
9039 @itemx --size=@var{bytes}
9040 @opindex -s @var{bytes}
9041 @opindex --size=@var{bytes}
9042 @cindex size of file to shred
9043 Shred the first @var{bytes} bytes of the file. The default is to shred
9044 the whole file. @var{bytes} can be followed by a size specification like
9045 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
9051 @cindex removing files after shredding
9052 After shredding a file, truncate it (if possible) and then remove it.
9053 If a file has multiple links, only the named links will be removed.
9059 Display to standard error all status updates as sterilization proceeds.
9065 By default, @command{shred} rounds the size of a regular file up to the next
9066 multiple of the file system block size to fully erase the last block
9068 Use @option{--exact} to suppress that behavior.
9069 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
9070 blocks, the resulting file will be 512 bytes long. With this option,
9071 shred does not increase the apparent size of the file.
9077 Normally, the last pass that @command{shred} writes is made up of
9078 random data. If this would be conspicuous on your hard drive (for
9079 example, because it looks like encrypted data), or you just think
9080 it's tidier, the @option{--zero} option adds an additional overwrite pass with
9081 all zero bits. This is in addition to the number of passes specified
9082 by the @option{--iterations} option.
9086 You might use the following command to erase all trace of the
9087 file system you'd created on the floppy disk in your first drive.
9088 That command takes about 20 minutes to erase a ``1.44MB'' (actually
9092 shred --verbose /dev/fd0
9095 Similarly, to erase all data on a selected partition of
9096 your hard disk, you could give a command like this:
9099 shred --verbose /dev/sda5
9102 On modern disks, a single pass should be adequate,
9103 and it will take one third the time of the default three-pass approach.
9106 # 1 pass, write pseudo-random data; 3x faster than the default
9107 shred --verbose -n1 /dev/sda5
9110 To be on the safe side, use at least one pass that overwrites using
9111 pseudo-random data. I.e., don't be tempted to use @samp{-n0 --zero},
9112 in case some disk controller optimizes the process of writing blocks
9113 of all zeros, and thereby does not clear all bytes in a block.
9114 Some SSDs may do just that.
9116 A @var{file} of @samp{-} denotes standard output.
9117 The intended use of this is to shred a removed temporary file.
9124 echo "Hello, world" >&3
9129 However, the command @samp{shred - >file} does not shred the contents
9130 of @var{file}, since the shell truncates @var{file} before invoking
9131 @command{shred}. Use the command @samp{shred file} or (if using a
9132 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
9137 @node Special file types
9138 @chapter Special file types
9140 @cindex special file types
9141 @cindex file types, special
9143 This chapter describes commands which create special types of files (and
9144 @command{rmdir}, which removes directories, one special file type).
9146 @cindex special file types
9148 Although Unix-like operating systems have markedly fewer special file
9149 types than others, not @emph{everything} can be treated only as the
9150 undifferentiated byte stream of @dfn{normal files}. For example, when a
9151 file is created or removed, the system must record this information,
9152 which it does in a @dfn{directory}---a special type of file. Although
9153 you can read directories as normal files, if you're curious, in order
9154 for the system to do its job it must impose a structure, a certain
9155 order, on the bytes of the file. Thus it is a ``special'' type of file.
9157 Besides directories, other special file types include named pipes
9158 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
9161 * link invocation:: Make a hard link via the link syscall
9162 * ln invocation:: Make links between files.
9163 * mkdir invocation:: Make directories.
9164 * mkfifo invocation:: Make FIFOs (named pipes).
9165 * mknod invocation:: Make block or character special files.
9166 * readlink invocation:: Print value of a symlink or canonical file name.
9167 * rmdir invocation:: Remove empty directories.
9168 * unlink invocation:: Remove files via the unlink syscall
9172 @node link invocation
9173 @section @command{link}: Make a hard link via the link syscall
9176 @cindex links, creating
9177 @cindex hard links, creating
9178 @cindex creating links (hard only)
9180 @command{link} creates a single hard link at a time.
9181 It is a minimalist interface to the system-provided
9182 @code{link} function. @xref{Hard Links, , , libc,
9183 The GNU C Library Reference Manual}.
9184 It avoids the bells and whistles of the more commonly-used
9185 @command{ln} command (@pxref{ln invocation}).
9189 link @var{filename} @var{linkname}
9192 @var{filename} must specify an existing file, and @var{linkname}
9193 must specify a nonexistent entry in an existing directory.
9194 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
9197 On a @acronym{GNU} system, this command acts like @samp{ln --directory
9198 --no-target-directory @var{filename} @var{linkname}}. However, the
9199 @option{--directory} and @option{--no-target-directory} options are
9200 not specified by @acronym{POSIX}, and the @command{link} command is
9201 more portable in practice.
9203 If @var{filename} is a symbolic link, it is unspecified whether
9204 @var{linkname} will be a hard link to the symbolic link or to the
9205 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
9206 to specify which behavior is desired.
9212 @section @command{ln}: Make links between files
9215 @cindex links, creating
9216 @cindex hard links, creating
9217 @cindex symbolic (soft) links, creating
9218 @cindex creating links (hard or soft)
9220 @cindex file systems and hard links
9221 @command{ln} makes links between files. By default, it makes hard links;
9222 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
9226 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
9227 ln [@var{option}]@dots{} @var{target}
9228 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
9229 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
9235 If two file names are given, @command{ln} creates a link to the first
9236 file from the second.
9239 If one @var{target} is given, @command{ln} creates a link to that file
9240 in the current directory.
9243 If the @option{--target-directory} (@option{-t}) option is given, or
9244 failing that if the last file is a directory and the
9245 @option{--no-target-directory} (@option{-T}) option is not given,
9246 @command{ln} creates a link to each @var{target} file in the specified
9247 directory, using the @var{target}s' names.
9251 Normally @command{ln} does not remove existing files. Use the
9252 @option{--force} (@option{-f}) option to remove them unconditionally,
9253 the @option{--interactive} (@option{-i}) option to remove them
9254 conditionally, and the @option{--backup} (@option{-b}) option to
9257 @cindex hard link, defined
9258 @cindex inode, and hard links
9259 A @dfn{hard link} is another name for an existing file; the link and the
9260 original are indistinguishable. Technically speaking, they share the
9261 same inode, and the inode contains all the information about a
9262 file---indeed, it is not incorrect to say that the inode @emph{is} the
9263 file. Most systems prohibit making a hard link to
9264 a directory; on those where it is allowed, only the super-user can do
9265 so (and with caution, since creating a cycle will cause problems to many
9266 other utilities). Hard links cannot cross file system boundaries. (These
9267 restrictions are not mandated by @acronym{POSIX}, however.)
9269 @cindex dereferencing symbolic links
9270 @cindex symbolic link, defined
9271 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
9272 a special file type (which not all kernels support: System V release 3
9273 (and older) systems lack symlinks) in which the link file actually
9274 refers to a different file, by name. When most operations (opening,
9275 reading, writing, and so on) are passed the symbolic link file, the
9276 kernel automatically @dfn{dereferences} the link and operates on the
9277 target of the link. But some operations (e.g., removing) work on the
9278 link file itself, rather than on its target. The owner and group of a
9279 symlink are not significant to file access performed through
9280 the link, but do have implications on deleting a symbolic link from a
9281 directory with the restricted deletion bit set. On the GNU system,
9282 the mode of a symlink has no significance and cannot be changed, but
9283 on some BSD systems, the mode can be changed and will affect whether
9284 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
9285 libc, The GNU C Library Reference Manual}.
9287 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
9288 occurs when the string in the symlink does not resolve to a file.
9289 There are no restrictions against creating dangling symbolic links.
9290 There are trade-offs to using absolute or relative symlinks. An
9291 absolute symlink always points to the same file, even if the directory
9292 containing the link is moved. However, if the symlink is visible from
9293 more than one machine (such as on a networked file system), the file
9294 pointed to might not always be the same. A relative symbolic link is
9295 resolved in relation to the directory that contains the link, and is
9296 often useful in referring to files on the same device without regards
9297 to what name that device is mounted on when accessed via networked
9300 When creating a relative symlink in a different location than the
9301 current directory, the resolution of the symlink will be different
9302 than the resolution of the same string from the current directory.
9303 Therefore, many users prefer to first change directories to the
9304 location where the relative symlink will be created, so that
9305 tab-completion or other file resolution will find the same target as
9306 what will be placed in the symlink.
9308 The program accepts the following options. Also see @ref{Common options}.
9319 @opindex --directory
9320 @cindex hard links to directories
9321 Allow users with appropriate privileges to attempt to make hard links
9323 However, note that this will probably fail due to
9324 system restrictions, even for the super-user.
9330 Remove existing destination files.
9333 @itemx --interactive
9335 @opindex --interactive
9336 @cindex prompting, and @command{ln}
9337 Prompt whether to remove existing destination files.
9343 If @option{-s} is not in effect, and the source file is a symbolic
9344 link, create the hard link to the file referred to by the symbolic
9345 link, rather than the symbolic link itself.
9348 @itemx --no-dereference
9350 @opindex --no-dereference
9351 Do not treat the last operand specially when it is a symbolic link to
9352 a directory. Instead, treat it as if it were a normal file.
9354 When the destination is an actual directory (not a symlink to one),
9355 there is no ambiguity. The link is created in that directory.
9356 But when the specified destination is a symlink to a directory,
9357 there are two ways to treat the user's request. @command{ln} can
9358 treat the destination just as it would a normal directory and create
9359 the link in it. On the other hand, the destination can be viewed as a
9360 non-directory---as the symlink itself. In that case, @command{ln}
9361 must delete or backup that symlink before creating the new link.
9362 The default is to treat a destination that is a symlink to a directory
9363 just like a directory.
9365 This option is weaker than the @option{--no-target-directory}
9366 (@option{-T}) option, so it has no effect if both options are given.
9372 If @option{-s} is not in effect, and the source file is a symbolic
9373 link, create the hard link to the symbolic link itself. On platforms
9374 where this is not supported by the kernel, this option creates a
9375 symbolic link with identical contents; since symbolic link contents
9376 cannot be edited, any file name resolution performed through either
9377 link will be the same as if a hard link had been created.
9383 Make symbolic links instead of hard links. This option merely produces
9384 an error message on systems that do not support symbolic links.
9390 @optNoTargetDirectory
9396 Print the name of each file after linking it successfully.
9400 @cindex hard links to symbolic links
9401 @cindex symbolic links and @command{ln}
9402 If @option{-L} and @option{-P} are both given, the last one takes
9403 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9404 are silently ignored. If neither option is given, then this
9405 implementation defaults to @option{-P} if the system @code{link} supports
9406 hard links to symbolic links (such as the GNU system), and @option{-L}
9407 if @code{link} follows symbolic links (such as on BSD).
9416 # Create link ../a pointing to a in that directory.
9417 # Not really useful because it points to itself.
9422 # Change to the target before creating symlinks to avoid being confused.
9428 # Hard coded file names don't move well.
9429 ln -s $(pwd)/a /some/dir/
9433 # Relative file names survive directory moves and also
9434 # work across networked file systems.
9435 ln -s afile anotherfile
9436 ln -s ../adir/afile yetanotherfile
9440 @node mkdir invocation
9441 @section @command{mkdir}: Make directories
9444 @cindex directories, creating
9445 @cindex creating directories
9447 @command{mkdir} creates directories with the specified names. Synopsis:
9450 mkdir [@var{option}]@dots{} @var{name}@dots{}
9453 @command{mkdir} creates each directory @var{name} in the order given.
9454 It reports an error if @var{name} already exists, unless the
9455 @option{-p} option is given and @var{name} is a directory.
9457 The program accepts the following options. Also see @ref{Common options}.
9462 @itemx --mode=@var{mode}
9465 @cindex modes of created directories, setting
9466 Set the file permission bits of created directories to @var{mode},
9467 which uses the same syntax as
9468 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9469 everyone) for the point of the departure. @xref{File permissions}.
9471 Normally the directory has the desired file mode bits at the moment it
9472 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9473 special mode bits, but in this case there may be a temporary window
9474 during which the directory exists but its special mode bits are
9475 incorrect. @xref{Directory Setuid and Setgid}, for how the
9476 set-user-ID and set-group-ID bits of directories are inherited unless
9477 overridden in this way.
9483 @cindex parent directories, creating
9484 Make any missing parent directories for each argument, setting their
9485 file permission bits to the umask modified by @samp{u+wx}. Ignore
9486 existing parent directories, and do not change their file permission
9489 To set the file permission bits of any newly-created parent
9490 directories to a value that includes @samp{u+wx}, you can set the
9491 umask before invoking @command{mkdir}. For example, if the shell
9492 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9493 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9494 To set a parent's special mode bits as well, you can invoke
9495 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9496 Setgid}, for how the set-user-ID and set-group-ID bits of
9497 newly-created parent directories are inherited.
9503 Print a message for each created directory. This is most useful with
9506 @item -Z @var{context}
9507 @itemx --context=@var{context}
9511 @cindex security context
9512 Set the default SELinux security context to be used for created directories.
9519 @node mkfifo invocation
9520 @section @command{mkfifo}: Make FIFOs (named pipes)
9523 @cindex FIFOs, creating
9524 @cindex named pipes, creating
9525 @cindex creating FIFOs (named pipes)
9527 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9528 specified names. Synopsis:
9531 mkfifo [@var{option}] @var{name}@dots{}
9534 A @dfn{FIFO} is a special file type that permits independent processes
9535 to communicate. One process opens the FIFO file for writing, and
9536 another for reading, after which data can flow as with the usual
9537 anonymous pipe in shells or elsewhere.
9539 The program accepts the following option. Also see @ref{Common options}.
9544 @itemx --mode=@var{mode}
9547 @cindex modes of created FIFOs, setting
9548 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9549 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9550 for the point of departure. @var{mode} should specify only file
9551 permission bits. @xref{File permissions}.
9553 @item -Z @var{context}
9554 @itemx --context=@var{context}
9558 @cindex security context
9559 Set the default SELinux security context to be used for created FIFOs.
9566 @node mknod invocation
9567 @section @command{mknod}: Make block or character special files
9570 @cindex block special files, creating
9571 @cindex character special files, creating
9573 @command{mknod} creates a FIFO, character special file, or block special
9574 file with the specified name. Synopsis:
9577 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9580 @cindex special files
9581 @cindex block special files
9582 @cindex character special files
9583 Unlike the phrase ``special file type'' above, the term @dfn{special
9584 file} has a technical meaning on Unix: something that can generate or
9585 receive data. Usually this corresponds to a physical piece of hardware,
9586 e.g., a printer or a disk. (These files are typically created at
9587 system-configuration time.) The @command{mknod} command is what creates
9588 files of this type. Such devices can be read either a character at a
9589 time or a ``block'' (many characters) at a time, hence we say there are
9590 @dfn{block special} files and @dfn{character special} files.
9592 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9593 @mayConflictWithShellBuiltIn{mknod}
9595 The arguments after @var{name} specify the type of file to make:
9600 @opindex p @r{for FIFO file}
9604 @opindex b @r{for block special file}
9605 for a block special file
9608 @c Don't document the 'u' option -- it's just a synonym for 'c'.
9609 @c Do *any* versions of mknod still use it?
9611 @opindex c @r{for character special file}
9612 @c @opindex u @r{for character special file}
9613 for a character special file
9617 When making a block or character special file, the major and minor
9618 device numbers must be given after the file type.
9619 If a major or minor device number begins with @samp{0x} or @samp{0X},
9620 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9621 as octal; otherwise, as decimal.
9623 The program accepts the following option. Also see @ref{Common options}.
9628 @itemx --mode=@var{mode}
9631 Set the mode of created files to @var{mode}, which is symbolic as in
9632 @command{chmod} and uses @samp{a=rw} as the point of departure.
9633 @var{mode} should specify only file permission bits.
9634 @xref{File permissions}.
9636 @item -Z @var{context}
9637 @itemx --context=@var{context}
9641 @cindex security context
9642 Set the default SELinux security context to be used for created files.
9649 @node readlink invocation
9650 @section @command{readlink}: Print value of a symlink or canonical file name
9653 @cindex displaying value of a symbolic link
9654 @cindex canonical file name
9655 @cindex canonicalize a file name
9658 @command{readlink} may work in one of two supported modes:
9664 @command{readlink} outputs the value of the given symbolic link.
9665 If @command{readlink} is invoked with an argument other than the name
9666 of a symbolic link, it produces no output and exits with a nonzero exit code.
9668 @item Canonicalize mode
9670 @command{readlink} outputs the absolute name of the given file which contains
9671 no @file{.}, @file{..} components nor any repeated separators
9672 (@file{/}) or symbolic links.
9677 readlink [@var{option}] @var{file}
9680 By default, @command{readlink} operates in readlink mode.
9682 The program accepts the following options. Also see @ref{Common options}.
9687 @itemx --canonicalize
9689 @opindex --canonicalize
9690 Activate canonicalize mode.
9691 If any component of the file name except the last one is missing or unavailable,
9692 @command{readlink} produces no output and exits with a nonzero exit
9693 code. A trailing slash is ignored.
9696 @itemx --canonicalize-existing
9698 @opindex --canonicalize-existing
9699 Activate canonicalize mode.
9700 If any component is missing or unavailable, @command{readlink} produces
9701 no output and exits with a nonzero exit code. A trailing slash
9702 requires that the name resolve to a directory.
9705 @itemx --canonicalize-missing
9707 @opindex --canonicalize-missing
9708 Activate canonicalize mode.
9709 If any component is missing or unavailable, @command{readlink} treats it
9715 @opindex --no-newline
9716 Do not output the trailing newline.
9726 Suppress most error messages.
9732 Report error messages.
9736 The @command{readlink} utility first appeared in OpenBSD 2.1.
9738 The @command{realpath} command without options, operates like
9739 @command{readlink} in canonicalize mode.
9744 @node rmdir invocation
9745 @section @command{rmdir}: Remove empty directories
9748 @cindex removing empty directories
9749 @cindex directories, removing empty
9751 @command{rmdir} removes empty directories. Synopsis:
9754 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9757 If any @var{directory} argument does not refer to an existing empty
9758 directory, it is an error.
9760 The program accepts the following options. Also see @ref{Common options}.
9764 @item --ignore-fail-on-non-empty
9765 @opindex --ignore-fail-on-non-empty
9766 @cindex directory deletion, ignoring failures
9767 Ignore each failure to remove a directory that is solely because
9768 the directory is non-empty.
9774 @cindex parent directories, removing
9775 Remove @var{directory}, then try to remove each component of @var{directory}.
9776 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9777 As such, it fails if any of those directories turns out not to be empty.
9778 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9779 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9780 exit unsuccessfully.
9786 @cindex directory deletion, reporting
9787 Give a diagnostic for each successful removal.
9788 @var{directory} is removed.
9792 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9797 @node unlink invocation
9798 @section @command{unlink}: Remove files via the unlink syscall
9801 @cindex removing files or directories (via the unlink syscall)
9803 @command{unlink} deletes a single specified file name.
9804 It is a minimalist interface to the system-provided
9805 @code{unlink} function. @xref{Deleting Files, , , libc,
9806 The GNU C Library Reference Manual}. Synopsis:
9807 It avoids the bells and whistles of the more commonly-used
9808 @command{rm} command (@pxref{rm invocation}).
9811 unlink @var{filename}
9814 On some systems @code{unlink} can be used to delete the name of a
9815 directory. On others, it can be used that way only by a privileged user.
9816 In the GNU system @code{unlink} can never delete the name of a directory.
9818 The @command{unlink} command honors the @option{--help} and
9819 @option{--version} options. To remove a file whose name begins with
9820 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9825 @node Changing file attributes
9826 @chapter Changing file attributes
9828 @cindex changing file attributes
9829 @cindex file attributes, changing
9830 @cindex attributes, file
9832 A file is not merely its contents, a name, and a file type
9833 (@pxref{Special file types}). A file also has an owner (a user ID), a
9834 group (a group ID), permissions (what the owner can do with the file,
9835 what people in the group can do, and what everyone else can do), various
9836 timestamps, and other information. Collectively, we call these a file's
9839 These commands change file attributes.
9842 * chgrp invocation:: Change file groups.
9843 * chmod invocation:: Change access permissions.
9844 * chown invocation:: Change file owners and groups.
9845 * touch invocation:: Change file timestamps.
9849 @node chown invocation
9850 @section @command{chown}: Change file owner and group
9853 @cindex file ownership, changing
9854 @cindex group ownership, changing
9855 @cindex changing file ownership
9856 @cindex changing group ownership
9858 @command{chown} changes the user and/or group ownership of each given @var{file}
9859 to @var{new-owner} or to the user and group of an existing reference file.
9863 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@}@c
9867 If used, @var{new-owner} specifies the new owner and/or group as follows
9868 (with no embedded white space):
9871 [@var{owner}] [ : [@var{group}] ]
9878 If only an @var{owner} (a user name or numeric user ID) is given, that
9879 user is made the owner of each given file, and the files' group is not
9882 @item owner@samp{:}group
9883 If the @var{owner} is followed by a colon and a @var{group} (a
9884 group name or numeric group ID), with no spaces between them, the group
9885 ownership of the files is changed as well (to @var{group}).
9888 If a colon but no group name follows @var{owner}, that user is
9889 made the owner of the files and the group of the files is changed to
9890 @var{owner}'s login group.
9893 If the colon and following @var{group} are given, but the owner
9894 is omitted, only the group of the files is changed; in this case,
9895 @command{chown} performs the same function as @command{chgrp}.
9898 If only a colon is given, or if @var{new-owner} is empty, neither the
9899 owner nor the group is changed.
9903 If @var{owner} or @var{group} is intended to represent a numeric user
9904 or group ID, then you may specify it with a leading @samp{+}.
9905 @xref{Disambiguating names and IDs}.
9907 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9908 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9909 require support for that, but for backward compatibility @acronym{GNU}
9910 @command{chown} supports @samp{.} so long as no ambiguity results.
9911 New scripts should avoid the use of @samp{.} because it is not
9912 portable, and because it has undesirable results if the entire
9913 @var{owner@samp{.}group} happens to identify a user whose name
9916 The @command{chown} command sometimes clears the set-user-ID or
9917 set-group-ID permission bits. This behavior depends on the policy and
9918 functionality of the underlying @code{chown} system call, which may
9919 make system-dependent file mode modifications outside the control of
9920 the @command{chown} command. For example, the @command{chown} command
9921 might not affect those bits when invoked by a user with appropriate
9922 privileges, or when the
9923 bits signify some function other than executable permission (e.g.,
9925 When in doubt, check the underlying system behavior.
9927 The program accepts the following options. Also see @ref{Common options}.
9935 @cindex changed owners, verbosely describing
9936 Verbosely describe the action for each @var{file} whose ownership
9945 @cindex error messages, omitting
9946 Do not print error messages about files whose ownership cannot be
9949 @itemx @w{@kbd{--from}=@var{old-owner}}
9951 @cindex symbolic links, changing owner
9952 Change a @var{file}'s ownership only if it has current attributes specified
9953 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9955 This option is useful primarily from a security standpoint in that
9956 it narrows considerably the window of potential abuse.
9957 For example, to reflect a user ID numbering change for one user's files
9958 without an option like this, @code{root} might run
9961 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9964 But that is dangerous because the interval between when the @command{find}
9965 tests the existing file's owner and when the @command{chown} is actually run
9967 One way to narrow the gap would be to invoke chown for each file
9971 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9974 But that is very slow if there are many affected files.
9975 With this option, it is safer (the gap is narrower still)
9976 though still not perfect:
9979 chown -h -R --from=OLDUSER NEWUSER /
9983 @opindex --dereference
9984 @cindex symbolic links, changing owner
9986 Do not act on symbolic links themselves but rather on what they point to.
9987 This is the default.
9990 @itemx --no-dereference
9992 @opindex --no-dereference
9993 @cindex symbolic links, changing owner
9995 Act on symbolic links themselves instead of what they point to.
9996 This mode relies on the @code{lchown} system call.
9997 On systems that do not provide the @code{lchown} system call,
9998 @command{chown} fails when a file specified on the command line
10000 By default, no diagnostic is issued for symbolic links encountered
10001 during a recursive traversal, but see @option{--verbose}.
10003 @itemx --preserve-root
10004 @opindex --preserve-root
10005 @cindex root directory, disallow recursive modification
10006 Fail upon any attempt to recursively change the root directory, @file{/}.
10007 Without @option{--recursive}, this option has no effect.
10008 @xref{Treating / specially}.
10010 @itemx --no-preserve-root
10011 @opindex --no-preserve-root
10012 @cindex root directory, allow recursive modification
10013 Cancel the effect of any preceding @option{--preserve-root} option.
10014 @xref{Treating / specially}.
10016 @item --reference=@var{ref_file}
10017 @opindex --reference
10018 Change the user and group of each @var{file} to be the same as those of
10019 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10020 user and group of the symbolic link, but rather those of the file it
10027 Output a diagnostic for every file processed.
10028 If a symbolic link is encountered during a recursive traversal
10029 on a system without the @code{lchown} system call, and @option{--no-dereference}
10030 is in effect, then issue a diagnostic saying neither the symbolic link nor
10031 its referent is being changed.
10036 @opindex --recursive
10037 @cindex recursively changing file ownership
10038 Recursively change ownership of directories and their contents.
10041 @xref{Traversing symlinks}.
10044 @xref{Traversing symlinks}.
10047 @xref{Traversing symlinks}.
10056 # Change the owner of /u to "root".
10059 # Likewise, but also change its group to "staff".
10060 chown root:staff /u
10062 # Change the owner of /u and subfiles to "root".
10067 @node chgrp invocation
10068 @section @command{chgrp}: Change group ownership
10071 @cindex group ownership, changing
10072 @cindex changing group ownership
10074 @command{chgrp} changes the group ownership of each given @var{file}
10075 to @var{group} (which can be either a group name or a numeric group ID)
10076 or to the group of an existing reference file. Synopsis:
10079 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@}@c
10083 If @var{group} is intended to represent a
10084 numeric group ID, then you may specify it with a leading @samp{+}.
10085 @xref{Disambiguating names and IDs}.
10087 The program accepts the following options. Also see @ref{Common options}.
10095 @cindex changed files, verbosely describing
10096 Verbosely describe the action for each @var{file} whose group actually
10105 @cindex error messages, omitting
10106 Do not print error messages about files whose group cannot be
10109 @item --dereference
10110 @opindex --dereference
10111 @cindex symbolic links, changing owner
10113 Do not act on symbolic links themselves but rather on what they point to.
10114 This is the default.
10117 @itemx --no-dereference
10119 @opindex --no-dereference
10120 @cindex symbolic links, changing group
10122 Act on symbolic links themselves instead of what they point to.
10123 This mode relies on the @code{lchown} system call.
10124 On systems that do not provide the @code{lchown} system call,
10125 @command{chgrp} fails when a file specified on the command line
10126 is a symbolic link.
10127 By default, no diagnostic is issued for symbolic links encountered
10128 during a recursive traversal, but see @option{--verbose}.
10130 @itemx --preserve-root
10131 @opindex --preserve-root
10132 @cindex root directory, disallow recursive modification
10133 Fail upon any attempt to recursively change the root directory, @file{/}.
10134 Without @option{--recursive}, this option has no effect.
10135 @xref{Treating / specially}.
10137 @itemx --no-preserve-root
10138 @opindex --no-preserve-root
10139 @cindex root directory, allow recursive modification
10140 Cancel the effect of any preceding @option{--preserve-root} option.
10141 @xref{Treating / specially}.
10143 @item --reference=@var{ref_file}
10144 @opindex --reference
10145 Change the group of each @var{file} to be the same as that of
10146 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
10147 group of the symbolic link, but rather that of the file it refers to.
10153 Output a diagnostic for every file processed.
10154 If a symbolic link is encountered during a recursive traversal
10155 on a system without the @code{lchown} system call, and @option{--no-dereference}
10156 is in effect, then issue a diagnostic saying neither the symbolic link nor
10157 its referent is being changed.
10162 @opindex --recursive
10163 @cindex recursively changing group ownership
10164 Recursively change the group ownership of directories and their contents.
10167 @xref{Traversing symlinks}.
10170 @xref{Traversing symlinks}.
10173 @xref{Traversing symlinks}.
10182 # Change the group of /u to "staff".
10185 # Change the group of /u and subfiles to "staff".
10190 @node chmod invocation
10191 @section @command{chmod}: Change access permissions
10194 @cindex changing access permissions
10195 @cindex access permissions, changing
10196 @cindex permissions, changing access
10198 @command{chmod} changes the access permissions of the named files. Synopsis:
10201 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@}@c
10205 @cindex symbolic links, permissions of
10206 @command{chmod} never changes the permissions of symbolic links, since
10207 the @command{chmod} system call cannot change their permissions.
10208 This is not a problem since the permissions of symbolic links are
10209 never used. However, for each symbolic link listed on the command
10210 line, @command{chmod} changes the permissions of the pointed-to file.
10211 In contrast, @command{chmod} ignores symbolic links encountered during
10212 recursive directory traversals.
10214 A successful use of @command{chmod} clears the set-group-ID bit of a
10215 regular file if the file's group ID does not match the user's
10216 effective group ID or one of the user's supplementary group IDs,
10217 unless the user has appropriate privileges. Additional restrictions
10218 may cause the set-user-ID and set-group-ID bits of @var{mode} or
10219 @var{ref_file} to be ignored. This behavior depends on the policy and
10220 functionality of the underlying @code{chmod} system call. When in
10221 doubt, check the underlying system behavior.
10223 If used, @var{mode} specifies the new file mode bits.
10224 For details, see the section on @ref{File permissions}.
10225 If you really want @var{mode} to have a leading @samp{-}, you should
10226 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
10227 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
10228 file} (without the @option{--}) complains if it behaves differently
10229 from what @samp{chmod a-w file} would do.
10231 The program accepts the following options. Also see @ref{Common options}.
10239 Verbosely describe the action for each @var{file} whose permissions
10248 @cindex error messages, omitting
10249 Do not print error messages about files whose permissions cannot be
10252 @itemx --preserve-root
10253 @opindex --preserve-root
10254 @cindex root directory, disallow recursive modification
10255 Fail upon any attempt to recursively change the root directory, @file{/}.
10256 Without @option{--recursive}, this option has no effect.
10257 @xref{Treating / specially}.
10259 @itemx --no-preserve-root
10260 @opindex --no-preserve-root
10261 @cindex root directory, allow recursive modification
10262 Cancel the effect of any preceding @option{--preserve-root} option.
10263 @xref{Treating / specially}.
10269 Verbosely describe the action or non-action taken for every @var{file}.
10271 @item --reference=@var{ref_file}
10272 @opindex --reference
10273 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
10274 @xref{File permissions}.
10275 If @var{ref_file} is a symbolic link, do not use the mode
10276 of the symbolic link, but rather that of the file it refers to.
10281 @opindex --recursive
10282 @cindex recursively changing access permissions
10283 Recursively change permissions of directories and their contents.
10290 @node touch invocation
10291 @section @command{touch}: Change file timestamps
10294 @cindex changing file timestamps
10295 @cindex file timestamps, changing
10296 @cindex timestamps, changing file
10298 @command{touch} changes the access and/or modification times of the
10299 specified files. Synopsis:
10302 touch [@var{option}]@dots{} @var{file}@dots{}
10305 @cindex empty files, creating
10306 Any @var{file} argument that does not exist is created empty, unless
10307 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
10308 (@option{-h}) was in effect.
10310 A @var{file} argument string of @samp{-} is handled specially and
10311 causes @command{touch} to change the times of the file associated with
10315 By default, @command{touch} sets file timestamps to the current time.
10316 Because @command{touch} acts on its operands left to right, the
10317 resulting timestamps of earlier and later operands may disagree.
10318 Also, the determination of what time is ``current'' depends on the
10319 platform. Platforms with network file systems often use different
10320 clocks for the operating system and for file systems; because
10321 @command{touch} typically uses file systems' clocks by default, clock
10322 skew can cause the resulting file timestamps to appear to be in a
10323 program's ``future'' or ``past''.
10325 @cindex file timestamp resolution
10326 The @command{touch} command sets the file's timestamp to the greatest
10327 representable value that is not greater than the requested time. This
10328 can differ from the requested time for several reasons. First, the
10329 requested time may have a higher resolution than supported. Second, a
10330 file system may use different resolutions for different types of
10331 times. Third, file timestamps may use a different resolution than
10332 operating system timestamps. Fourth, the operating system primitives
10333 used to update timestamps may employ yet a different resolution. For
10334 example, in theory a file system might use 10-microsecond resolution
10335 for access time and 100-nanosecond resolution for modification time,
10336 and the operating system might use nanosecond resolution for the
10337 current time and microsecond resolution for the primitive that
10338 @command{touch} uses to set a file's timestamp to an arbitrary value.
10340 @cindex permissions, for changing file timestamps
10341 When setting file timestamps to the current time, @command{touch} can
10342 change the timestamps for files that the user does not own but has
10343 write permission for. Otherwise, the user must own the files. Some
10344 older systems have a further restriction: the user must own the files
10345 unless both the access and modification times are being set to the
10348 Although @command{touch} provides options for changing two of the times---the
10349 times of last access and modification---of a file, there is actually
10350 a standard third one as well: the inode change time. This is often
10351 referred to as a file's @code{ctime}.
10352 The inode change time represents the time when the file's meta-information
10353 last changed. One common example of this is when the permissions of a
10354 file change. Changing the permissions doesn't access the file, so
10355 the atime doesn't change, nor does it modify the file, so the mtime
10356 doesn't change. Yet, something about the file itself has changed,
10357 and this must be noted somewhere. This is the job of the ctime field.
10358 This is necessary, so that, for example, a backup program can make a
10359 fresh copy of the file, including the new permissions value.
10360 Another operation that modifies a file's ctime without affecting
10361 the others is renaming. In any case, it is not possible, in normal
10362 operations, for a user to change the ctime field to a user-specified value.
10363 Some operating systems and file systems support a fourth time: the
10364 birth time, when the file was first created; by definition, this
10365 timestamp never changes.
10368 Time stamps assume the time zone rules specified by the @env{TZ}
10369 environment variable, or by the system default rules if @env{TZ} is
10370 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
10371 libc, The GNU C Library Reference Manual}.
10372 You can avoid ambiguities during
10373 daylight saving transitions by using @sc{utc} time stamps.
10375 The program accepts the following options. Also see @ref{Common options}.
10380 @itemx --time=atime
10381 @itemx --time=access
10385 @opindex atime@r{, changing}
10386 @opindex access @r{time, changing}
10387 @opindex use @r{time, changing}
10388 Change the access time only.
10393 @opindex --no-create
10394 Do not warn about or create files that do not exist.
10397 @itemx --date=@var{time}
10401 Use @var{time} instead of the current time. It can contain month names,
10402 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
10403 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
10404 specifies the instant of time that is 489,392,193 nanoseconds after
10405 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
10406 minutes east of @acronym{UTC}. @xref{Date input formats}.
10407 File systems that do not support high-resolution time stamps
10408 silently ignore any excess precision here.
10412 @cindex BSD @command{touch} compatibility
10413 Ignored; for compatibility with BSD versions of @command{touch}.
10416 @itemx --no-dereference
10418 @opindex --no-dereference
10419 @cindex symbolic links, changing time
10421 Attempt to change the timestamps of a symbolic link, rather than what
10422 the link refers to. When using this option, empty files are not
10423 created, but option @option{-c} must also be used to avoid warning
10424 about files that do not exist. Not all systems support changing the
10425 timestamps of symlinks, since underlying system support for this
10426 action was not required until @acronym{POSIX} 2008. Also, on some
10427 systems, the mere act of examining a symbolic link changes the access
10428 time, such that only changes to the modification time will persist
10429 long enough to be observable. When coupled with option @option{-r}, a
10430 reference timestamp is taken from a symbolic link rather than the file
10434 @itemx --time=mtime
10435 @itemx --time=modify
10438 @opindex mtime@r{, changing}
10439 @opindex modify @r{time, changing}
10440 Change the modification time only.
10442 @item -r @var{file}
10443 @itemx --reference=@var{file}
10445 @opindex --reference
10446 Use the times of the reference @var{file} instead of the current time.
10447 If this option is combined with the @option{--date=@var{time}}
10448 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10449 the origin for any relative @var{time}s given, but is otherwise ignored.
10450 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10451 equal to five seconds before the corresponding time stamp for @file{foo}.
10452 If @var{file} is a symbolic link, the reference timestamp is taken
10453 from the target of the symlink, unless @option{-h} was also in effect.
10455 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10456 Use the argument (optional four-digit or two-digit years, months,
10457 days, hours, minutes, optional seconds) instead of the current time.
10458 If the year is specified with only two digits, then @var{cc}
10459 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10460 69 @dots{} 99. If no digits of the year are specified,
10461 the argument is interpreted as a date in the current year.
10462 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10466 @vindex _POSIX2_VERSION
10467 On older systems, @command{touch} supports an obsolete syntax, as follows.
10468 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10469 @option{-t} options, and if there are two or more @var{file}s and the
10470 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10471 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10472 any, were moved to the front), and if the represented year
10473 is in the range 1969--1999, that argument is interpreted as the time
10474 for the other files instead of as a file name.
10475 This obsolete behavior can be enabled or disabled with the
10476 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10477 conformance}), but portable scripts should avoid commands whose
10478 behavior depends on this variable.
10479 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10480 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10486 @chapter Disk usage
10490 No disk can hold an infinite amount of data. These commands report
10491 how much disk storage is in use or available, report other file and
10492 file status information, and write buffers to disk.
10495 * df invocation:: Report file system disk space usage.
10496 * du invocation:: Estimate file space usage.
10497 * stat invocation:: Report file or file system status.
10498 * sync invocation:: Synchronize memory and disk.
10499 * truncate invocation:: Shrink or extend the size of a file.
10503 @node df invocation
10504 @section @command{df}: Report file system disk space usage
10507 @cindex file system disk usage
10508 @cindex disk usage by file system
10510 @command{df} reports the amount of disk space used and available on
10511 file systems. Synopsis:
10514 df [@var{option}]@dots{} [@var{file}]@dots{}
10517 With no arguments, @command{df} reports the space used and available on all
10518 currently mounted file systems (of all types). Otherwise, @command{df}
10519 reports on the file system containing each argument @var{file}.
10521 Normally the disk space is printed in units of
10522 1024 bytes, but this can be overridden (@pxref{Block size}).
10523 Non-integer quantities are rounded up to the next higher unit.
10525 @cindex disk device file
10526 @cindex device file, disk
10527 If an argument @var{file} is a disk device file containing a mounted
10528 file system, @command{df} shows the space available on that file system
10529 rather than on the file system containing the device node (i.e., the root
10530 file system). @sc{gnu} @command{df} does not attempt to determine the
10532 on unmounted file systems, because on most kinds of systems doing so
10533 requires extremely nonportable intimate knowledge of file system
10536 The program accepts the following options. Also see @ref{Common options}.
10544 @cindex automounter file systems
10545 @cindex ignore file systems
10546 Include in the listing dummy file systems, which
10547 are omitted by default. Such file systems are typically special-purpose
10548 pseudo-file-systems, such as automounter entries.
10550 @item -B @var{size}
10551 @itemx --block-size=@var{size}
10553 @opindex --block-size
10554 @cindex file system sizes
10555 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10556 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10560 @cindex grand total of disk size, usage and available space
10561 Print a grand total of all arguments after all arguments have
10562 been processed. This can be used to find out the total disk size, usage
10563 and available space of all listed devices.
10569 Equivalent to @option{--si}.
10575 @cindex inode usage
10576 List inode usage information instead of block usage. An inode (short
10577 for index node) contains information about a file such as its owner,
10578 permissions, timestamps, and location on the disk.
10582 @cindex kibibytes for file system sizes
10583 Print sizes in 1024-byte blocks, overriding the default block size
10584 (@pxref{Block size}).
10585 This option is equivalent to @option{--block-size=1K}.
10591 @cindex file system types, limiting output to certain
10592 Limit the listing to local file systems. By default, remote file systems
10597 @cindex file system space, retrieving old data more quickly
10598 Do not invoke the @code{sync} system call before getting any usage data.
10599 This may make @command{df} run significantly faster on systems with many
10600 disks, but on some systems (notably SunOS) the results may be slightly
10601 out of date. This is the default.
10604 @itemx --portability
10606 @opindex --portability
10607 @cindex one-line output format
10608 @cindex @acronym{POSIX} output format
10609 @cindex portable output format
10610 @cindex output format, portable
10611 Use the @acronym{POSIX} output format. This is like the default format except
10616 The information about each file system is always printed on exactly
10617 one line; a mount device is never put on a line by itself. This means
10618 that if the mount device name is more than 20 characters long (e.g., for
10619 some network mounts), the columns are misaligned.
10622 The labels in the header output line are changed to conform to @acronym{POSIX}.
10625 The default block size and output format are unaffected by the
10626 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10627 variables. However, the default block size is still affected by
10628 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10629 otherwise. @xref{Block size}.
10636 @cindex file system space, retrieving current data more slowly
10637 Invoke the @code{sync} system call before getting any usage data. On
10638 some systems (notably SunOS), doing this yields more up to date results,
10639 but in general this option makes @command{df} much slower, especially when
10640 there are many or very busy file systems.
10642 @item -t @var{fstype}
10643 @itemx --type=@var{fstype}
10646 @cindex file system types, limiting output to certain
10647 Limit the listing to file systems of type @var{fstype}. Multiple
10648 file system types can be specified by giving multiple @option{-t} options.
10649 By default, nothing is omitted.
10652 @itemx --print-type
10654 @opindex --print-type
10655 @cindex file system types, printing
10656 Print each file system's type. The types printed here are the same ones
10657 you can include or exclude with @option{-t} and @option{-x}. The particular
10658 types printed are whatever is supported by the system. Here are some of
10659 the common names (this list is certainly not exhaustive):
10664 @cindex @acronym{NFS} file system type
10665 An @acronym{NFS} file system, i.e., one mounted over a network from another
10666 machine. This is the one type name which seems to be used uniformly by
10669 @item 4.2@r{, }ufs@r{, }efs@dots{}
10670 @cindex Linux file system types
10671 @cindex local file system types
10672 @opindex 4.2 @r{file system type}
10673 @opindex ufs @r{file system type}
10674 @opindex efs @r{file system type}
10675 A file system on a locally-mounted hard disk. (The system might even
10676 support more than one type here; Linux does.)
10678 @item hsfs@r{, }cdfs
10679 @cindex CD-ROM file system type
10680 @cindex High Sierra file system
10681 @opindex hsfs @r{file system type}
10682 @opindex cdfs @r{file system type}
10683 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10684 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10687 @cindex PC file system
10688 @cindex DOS file system
10689 @cindex MS-DOS file system
10690 @cindex diskette file system
10692 An MS-DOS file system, usually on a diskette.
10696 @item -x @var{fstype}
10697 @itemx --exclude-type=@var{fstype}
10699 @opindex --exclude-type
10700 Limit the listing to file systems not of type @var{fstype}.
10701 Multiple file system types can be eliminated by giving multiple
10702 @option{-x} options. By default, no file system types are omitted.
10705 Ignored; for compatibility with System V versions of @command{df}.
10710 Failure includes the case where no output is generated, so you can
10711 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10712 @var{dir}} to test whether @var{dir} is on a file system of type
10713 @samp{ext3} or @samp{reiserfs}.
10716 @node du invocation
10717 @section @command{du}: Estimate file space usage
10720 @cindex file space usage
10721 @cindex disk usage for files
10723 @command{du} reports the amount of disk space used by the specified files
10724 and for each subdirectory (of directory arguments). Synopsis:
10727 du [@var{option}]@dots{} [@var{file}]@dots{}
10730 With no arguments, @command{du} reports the disk space for the current
10731 directory. Normally the disk space is printed in units of
10732 1024 bytes, but this can be overridden (@pxref{Block size}).
10733 Non-integer quantities are rounded up to the next higher unit.
10735 If two or more hard links point to the same file, only one of the hard
10736 links is counted. The @var{file} argument order affects which links
10737 are counted, and changing the argument order may change the numbers
10738 that @command{du} outputs.
10740 The program accepts the following options. Also see @ref{Common options}.
10748 Show counts for all files, not just directories.
10750 @itemx --apparent-size
10751 @opindex --apparent-size
10752 Print apparent sizes, rather than disk usage. The apparent size of a
10753 file is the number of bytes reported by @code{wc -c} on regular files,
10754 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10755 For example, a file containing the word @samp{zoo} with no newline would,
10756 of course, have an apparent size of 3. Such a small file may require
10757 anywhere from 0 to 16 KiB or more of disk space, depending on
10758 the type and configuration of the file system on which the file resides.
10759 However, a sparse file created with this command:
10762 dd bs=1 seek=2GiB if=/dev/null of=big
10766 has an apparent size of 2 GiB, yet on most modern
10767 systems, it actually uses almost no disk space.
10773 Equivalent to @code{--apparent-size --block-size=1}.
10775 @item -B @var{size}
10776 @itemx --block-size=@var{size}
10778 @opindex --block-size
10780 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10781 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10787 @cindex grand total of disk space
10788 Print a grand total of all arguments after all arguments have
10789 been processed. This can be used to find out the total disk usage of
10790 a given set of files or directories.
10793 @itemx --dereference-args
10795 @opindex --dereference-args
10796 Dereference symbolic links that are command line arguments.
10797 Does not affect other symbolic links. This is helpful for finding
10798 out the disk usage of directories, such as @file{/usr/tmp}, which
10799 are often symbolic links.
10801 @c --files0-from=FILE
10802 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10808 Equivalent to @option{--dereference-args} (@option{-D}).
10812 @cindex kibibytes for file sizes
10813 Print sizes in 1024-byte blocks, overriding the default block size
10814 (@pxref{Block size}).
10815 This option is equivalent to @option{--block-size=1K}.
10818 @itemx --count-links
10820 @opindex --count-links
10821 @cindex hard links, counting in @command{du}
10822 Count the size of all files, even if they have appeared already (as a
10826 @itemx --dereference
10828 @opindex --dereference
10829 @cindex symbolic links, dereferencing in @command{du}
10830 Dereference symbolic links (show the disk space used by the file
10831 or directory that the link points to instead of the space used by
10836 @cindex mebibytes for file sizes
10837 Print sizes in 1,048,576-byte blocks, overriding the default block size
10838 (@pxref{Block size}).
10839 This option is equivalent to @option{--block-size=1M}.
10842 @itemx --no-dereference
10844 @opindex --no-dereference
10845 @cindex symbolic links, dereferencing in @command{du}
10846 For each symbolic links encountered by @command{du},
10847 consider the disk space used by the symbolic link.
10849 @item -d @var{depth}
10850 @item --max-depth=@var{depth}
10851 @opindex -d @var{depth}
10852 @opindex --max-depth=@var{depth}
10853 @cindex limiting output of @command{du}
10854 Show the total for each directory (and file if --all) that is at
10855 most MAX_DEPTH levels down from the root of the hierarchy. The root
10856 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10865 @opindex --summarize
10866 Display only a total for each argument.
10869 @itemx --separate-dirs
10871 @opindex --separate-dirs
10872 Normally, in the output of @command{du} (when not using @option{--summarize}),
10873 the size listed next to a directory name, @var{d}, represents the sum
10874 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10875 With @option{--separate-dirs}, the size reported for a directory name,
10876 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10881 @cindex last modified dates, displaying in @command{du}
10882 Show time of the most recent modification of any file in the directory,
10883 or any of its subdirectories.
10885 @itemx --time=ctime
10886 @itemx --time=status
10889 @opindex ctime@r{, show the most recent}
10890 @opindex status time@r{, show the most recent}
10891 @opindex use time@r{, show the most recent}
10892 Show the most recent status change time (the @samp{ctime} in the inode) of
10893 any file in the directory, instead of the modification time.
10895 @itemx --time=atime
10896 @itemx --time=access
10898 @opindex atime@r{, show the most recent}
10899 @opindex access time@r{, show the most recent}
10900 Show the most recent access time (the @samp{atime} in the inode) of
10901 any file in the directory, instead of the modification time.
10903 @item --time-style=@var{style}
10904 @opindex --time-style
10906 List timestamps in style @var{style}. This option has an effect only if
10907 the @option{--time} option is also specified. The @var{style} should
10908 be one of the following:
10911 @item +@var{format}
10913 List timestamps using @var{format}, where @var{format} is interpreted
10914 like the format argument of @command{date} (@pxref{date invocation}).
10915 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10916 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10917 with @command{date}, @var{format}'s interpretation is affected by the
10918 @env{LC_TIME} locale category.
10921 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10922 format with nanosecond precision, e.g., @samp{2002-03-30
10923 23:45:56.477817180 -0700}. This style is equivalent to
10924 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10927 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10928 @samp{2002-03-30 23:45}. These timestamps are shorter than
10929 @samp{full-iso} timestamps, and are usually good enough for everyday
10930 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10933 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10934 This style is equivalent to @samp{+%Y-%m-%d}.
10938 You can specify the default value of the @option{--time-style} option
10939 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10940 the default style is @samp{long-iso}. For compatibility with @command{ls},
10941 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10942 the newline and any later characters are ignored; if @env{TIME_STYLE}
10943 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10944 @env{TIME_STYLE} is @samp{locale} it is ignored.
10947 @itemx --one-file-system
10949 @opindex --one-file-system
10950 @cindex one file system, restricting @command{du} to
10951 Skip directories that are on different file systems from the one that
10952 the argument being processed is on.
10954 @item --exclude=@var{pattern}
10955 @opindex --exclude=@var{pattern}
10956 @cindex excluding files from @command{du}
10957 When recursing, skip subdirectories or files matching @var{pattern}.
10958 For example, @code{du --exclude='*.o'} excludes files whose names
10961 @item -X @var{file}
10962 @itemx --exclude-from=@var{file}
10963 @opindex -X @var{file}
10964 @opindex --exclude-from=@var{file}
10965 @cindex excluding files from @command{du}
10966 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10967 one per line. If @var{file} is @samp{-}, take the patterns from standard
10972 @cindex NFS mounts from BSD to HP-UX
10973 On BSD systems, @command{du} reports sizes that are half the correct
10974 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10975 systems, it reports sizes that are twice the correct values for
10976 files that are NFS-mounted from BSD systems. This is due to a flaw
10977 in HP-UX; it also affects the HP-UX @command{du} program.
10982 @node stat invocation
10983 @section @command{stat}: Report file or file system status
10986 @cindex file status
10987 @cindex file system status
10989 @command{stat} displays information about the specified file(s). Synopsis:
10992 stat [@var{option}]@dots{} [@var{file}]@dots{}
10995 With no option, @command{stat} reports all information about the given files.
10996 But it also can be used to report the information of the file systems the
10997 given files are located on. If the files are links, @command{stat} can
10998 also give information about the files the links point to.
11000 @mayConflictWithShellBuiltIn{stat}
11005 @itemx --dereference
11007 @opindex --dereference
11008 @cindex symbolic links, dereferencing in @command{stat}
11009 Change how @command{stat} treats symbolic links.
11010 With this option, @command{stat} acts on the file referenced
11011 by each symbolic link argument.
11012 Without it, @command{stat} acts on any symbolic link argument directly.
11015 @itemx --file-system
11017 @opindex --file-system
11018 @cindex file systems
11019 Report information about the file systems where the given files are located
11020 instead of information about the files themselves.
11021 This option implies the @option{-L} option.
11024 @itemx --format=@var{format}
11026 @opindex --format=@var{format}
11027 @cindex output format
11028 Use @var{format} rather than the default format.
11029 @var{format} is automatically newline-terminated, so
11030 running a command like the following with two or more @var{file}
11031 operands produces a line of output for each operand:
11033 $ stat --format=%d:%i / /usr
11038 @itemx --printf=@var{format}
11039 @opindex --printf=@var{format}
11040 @cindex output format
11041 Use @var{format} rather than the default format.
11042 Like @option{--format}, but interpret backslash escapes,
11043 and do not output a mandatory trailing newline.
11044 If you want a newline, include @samp{\n} in the @var{format}.
11045 Here's how you would use @option{--printf} to print the device
11046 and inode numbers of @file{/} and @file{/usr}:
11048 $ stat --printf='%d:%i\n' / /usr
11057 @cindex terse output
11058 Print the information in terse form, suitable for parsing by other programs.
11062 The valid @var{format} directives for files with @option{--format} and
11063 @option{--printf} are:
11066 @item %a - Access rights in octal
11067 @item %A - Access rights in human readable form
11068 @item %b - Number of blocks allocated (see @samp{%B})
11069 @item %B - The size in bytes of each block reported by @samp{%b}
11070 @item %C - The SELinux security context of a file, if available
11071 @item %d - Device number in decimal
11072 @item %D - Device number in hex
11073 @item %f - Raw mode in hex
11074 @item %F - File type
11075 @item %g - Group ID of owner
11076 @item %G - Group name of owner
11077 @item %h - Number of hard links
11078 @item %i - Inode number
11079 @item %m - Mount point (See note below)
11080 @item %n - File name
11081 @item %N - Quoted file name with dereference if symbolic link
11082 @item %o - Optimal I/O transfer size hint
11083 @item %s - Total size, in bytes
11084 @item %t - Major device type in hex
11085 @item %T - Minor device type in hex
11086 @item %u - User ID of owner
11087 @item %U - User name of owner
11088 @item %w - Time of file birth, or @samp{-} if unknown
11089 @item %W - Time of file birth as seconds since Epoch, or @samp{0}
11090 @item %x - Time of last access
11091 @item %X - Time of last access as seconds since Epoch
11092 @item %y - Time of last modification
11093 @item %Y - Time of last modification as seconds since Epoch
11094 @item %z - Time of last change
11095 @item %Z - Time of last change as seconds since Epoch
11098 The @samp{%W}, @samp{%X}, @samp{%Y}, and @samp{%Z} formats accept a
11099 precision preceded by a period to specify the number of digits to
11100 print after the decimal point. For example, @samp{%.3X} outputs the
11101 last access time to millisecond precision. If a period is given but no
11102 precision, @command{stat} uses 9 digits, so @samp{%.X} is equivalent to
11103 @samp{%.9X}. When discarding excess precision, time stamps are truncated
11104 toward minus infinity.
11108 $ stat -c '[%015Y]' /usr
11111 $ stat -c '[%15Y]' /usr
11113 $ stat -c '[%-15Y]' /usr
11116 $ stat -c '[%.3Y]' /usr
11118 $ stat -c '[%.Y]' /usr
11119 [1288929712.114951834]
11122 The mount point printed by @samp{%m} is similar to that output
11123 by @command{df}, except that:
11126 stat does not dereference symlinks by default
11127 (unless @option{-L} is specified)
11129 stat does not search for specified device nodes in the
11130 file system list, instead operating on them directly
11133 stat outputs the alias for a bind mounted file, rather than
11134 the initial mount point of its backing device.
11135 One can recursively call stat until there is no change in output,
11136 to get the current base mount point
11139 When listing file system information (@option{--file-system} (@option{-f})),
11140 you must use a different set of @var{format} directives:
11143 @item %a - Free blocks available to non-super-user
11144 @item %b - Total data blocks in file system
11145 @item %c - Total file nodes in file system
11146 @item %d - Free file nodes in file system
11147 @item %f - Free blocks in file system
11148 @item %i - File System ID in hex
11149 @item %l - Maximum length of file names
11150 @item %n - File name
11151 @item %s - Block size (for faster transfers)
11152 @item %S - Fundamental block size (for block counts)
11153 @item %t - Type in hex
11154 @item %T - Type in human readable form
11158 Time stamps are listed according to the time zone rules specified by
11159 the @env{TZ} environment variable, or by the system default rules if
11160 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
11161 with @env{TZ}, libc, The GNU C Library Reference Manual}.
11166 @node sync invocation
11167 @section @command{sync}: Synchronize data on disk with memory
11170 @cindex synchronize disk and memory
11172 @cindex superblock, writing
11173 @cindex inodes, written buffered
11174 @command{sync} writes any data buffered in memory out to disk. This can
11175 include (but is not limited to) modified superblocks, modified inodes,
11176 and delayed reads and writes. This must be implemented by the kernel;
11177 The @command{sync} program does nothing but exercise the @code{sync} system
11180 @cindex crashes and corruption
11181 The kernel keeps data in memory to avoid doing (relatively slow) disk
11182 reads and writes. This improves performance, but if the computer
11183 crashes, data may be lost or the file system corrupted as a
11184 result. The @command{sync} command ensures everything in memory
11185 is written to disk.
11187 Any arguments are ignored, except for a lone @option{--help} or
11188 @option{--version} (@pxref{Common options}).
11193 @node truncate invocation
11194 @section @command{truncate}: Shrink or extend the size of a file
11197 @cindex truncating, file sizes
11199 @command{truncate} shrinks or extends the size of each @var{file} to the
11200 specified size. Synopsis:
11203 truncate @var{option}@dots{} @var{file}@dots{}
11206 @cindex files, creating
11207 Any @var{file} that does not exist is created.
11209 @cindex sparse files, creating
11210 @cindex holes, creating files with
11211 If a @var{file} is larger than the specified size, the extra data is lost.
11212 If a @var{file} is shorter, it is extended and the extended part (or hole)
11213 reads as zero bytes.
11215 The program accepts the following options. Also see @ref{Common options}.
11222 @opindex --no-create
11223 Do not create files that do not exist.
11228 @opindex --io-blocks
11229 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
11231 @item -r @var{rfile}
11232 @itemx --reference=@var{rfile}
11234 @opindex --reference
11235 Base the size of each @var{file} on the size of @var{rfile}.
11237 @item -s @var{size}
11238 @itemx --size=@var{size}
11241 Set or adjust the size of each @var{file} according to @var{size}.
11242 @multiplierSuffixesNoBlocks{size}
11244 @var{size} may also be prefixed by one of the following to adjust
11245 the size of each @var{file} based on their current size:
11247 @samp{+} => extend by
11248 @samp{-} => reduce by
11249 @samp{<} => at most
11250 @samp{>} => at least
11251 @samp{/} => round down to multiple of
11252 @samp{%} => round up to multiple of
11260 @node Printing text
11261 @chapter Printing text
11263 @cindex printing text, commands for
11264 @cindex commands for printing text
11266 This section describes commands that display text strings.
11269 * echo invocation:: Print a line of text.
11270 * printf invocation:: Format and print data.
11271 * yes invocation:: Print a string until interrupted.
11275 @node echo invocation
11276 @section @command{echo}: Print a line of text
11279 @cindex displaying text
11280 @cindex printing text
11281 @cindex text, displaying
11282 @cindex arbitrary text, displaying
11284 @command{echo} writes each given @var{string} to standard output, with a
11285 space between each and a newline after the last one. Synopsis:
11288 echo [@var{option}]@dots{} [@var{string}]@dots{}
11291 @mayConflictWithShellBuiltIn{echo}
11293 The program accepts the following options. Also see @ref{Common options}.
11294 Options must precede operands, and the normally-special argument
11295 @samp{--} has no special meaning and is treated like any other
11301 Do not output the trailing newline.
11305 @cindex backslash escapes
11306 Enable interpretation of the following backslash-escaped characters in
11315 produce no further output
11331 the eight-bit value that is the octal number @var{nnn}
11332 (zero to three octal digits), if @var{nnn} is
11333 a nine-bit value, the ninth bit is ignored
11335 the eight-bit value that is the octal number @var{nnn}
11336 (one to three octal digits), if @var{nnn} is
11337 a nine-bit value, the ninth bit is ignored
11339 the eight-bit value that is the hexadecimal number @var{hh}
11340 (one or two hexadecimal digits)
11345 @cindex backslash escapes
11346 Disable interpretation of backslash escapes in each @var{string}.
11347 This is the default. If @option{-e} and @option{-E} are both
11348 specified, the last one given takes effect.
11352 @vindex POSIXLY_CORRECT
11353 If the @env{POSIXLY_CORRECT} environment variable is set, then when
11354 @command{echo}'s first argument is not @option{-n} it outputs
11355 option-like arguments instead of treating them as options. For
11356 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
11357 plain @samp{hello}.
11359 @acronym{POSIX} does not require support for any options, and says
11360 that the behavior of @command{echo} is implementation-defined if any
11361 @var{string} contains a backslash or if the first argument is
11362 @option{-n}. Portable programs can use the @command{printf} command
11363 if they need to omit trailing newlines or output control characters or
11364 backslashes. @xref{printf invocation}.
11369 @node printf invocation
11370 @section @command{printf}: Format and print data
11373 @command{printf} does formatted printing of text. Synopsis:
11376 printf @var{format} [@var{argument}]@dots{}
11379 @command{printf} prints the @var{format} string, interpreting @samp{%}
11380 directives and @samp{\} escapes to format numeric and string arguments
11381 in a way that is mostly similar to the C @samp{printf} function.
11382 @xref{Output Conversion Syntax,, @command{printf} format directives,
11383 libc, The GNU C Library Reference Manual}, for details.
11384 The differences are listed below.
11386 @mayConflictWithShellBuiltIn{printf}
11391 The @var{format} argument is reused as necessary to convert all the
11392 given @var{argument}s. For example, the command @samp{printf %s a b}
11396 Missing @var{argument}s are treated as null strings or as zeros,
11397 depending on whether the context expects a string or a number. For
11398 example, the command @samp{printf %sx%d} prints @samp{x0}.
11402 An additional escape, @samp{\c}, causes @command{printf} to produce no
11403 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
11404 E} prints @samp{ABC}.
11407 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
11408 digits, as opposed to C where it can have an unlimited number of
11409 digits. For example, the command @samp{printf '\x07e'} prints two
11410 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
11415 @command{printf} has an additional directive, @samp{%b}, which prints its
11416 argument string with @samp{\} escapes interpreted in the same way as in
11417 the @var{format} string, except that octal escapes are of the form
11418 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits. If
11419 @samp{\@var{ooo}} is nine-bit value, ignore the ninth bit.
11420 If a precision is also given, it limits the number of bytes printed
11421 from the converted string.
11424 Numeric arguments must be single C constants, possibly with leading
11425 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
11429 @vindex POSIXLY_CORRECT
11430 If the leading character of a numeric argument is @samp{"} or @samp{'}
11431 then its value is the numeric value of the immediately following
11432 character. Any remaining characters are silently ignored if the
11433 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
11434 warning is printed. For example, @samp{printf "%d" "'a"} outputs
11435 @samp{97} on hosts that use the @acronym{ASCII} character set, since
11436 @samp{a} has the numeric value 97 in @acronym{ASCII}.
11441 A floating-point argument must use a period before any fractional
11442 digits, but is printed according to the @env{LC_NUMERIC} category of the
11443 current locale. For example, in a locale whose radix character is a
11444 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
11445 the command @samp{printf %g 3,14} is an error.
11446 @xref{Floating point}.
11450 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
11451 (if @var{ooo} is 1 to 3 octal digits) specifying a byte to print,
11452 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
11453 digits) specifying a character to print.
11454 Note however that when @samp{\@var{ooo}} specifies a number larger than 255,
11455 @command{printf} ignores the ninth bit.
11456 For example, @samp{printf '\400'} is equivalent to @samp{printf '\0'}.
11461 @cindex ISO/IEC 10646
11463 @command{printf} interprets two character syntaxes introduced in
11464 @acronym{ISO} C 99:
11465 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
11466 characters, specified as
11467 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11468 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11469 @command{printf} outputs the Unicode characters
11470 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11471 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11472 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11474 The processing of @samp{\u} and @samp{\U} requires a full-featured
11475 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11476 or when @code{libiconv} is installed prior to this package. Otherwise
11477 @samp{\u} and @samp{\U} will print as-is.
11479 The only options are a lone @option{--help} or
11480 @option{--version}. @xref{Common options}.
11481 Options must precede operands.
11483 The Unicode character syntaxes are useful for writing strings in a locale
11484 independent way. For example, a string containing the Euro currency symbol
11487 $ env printf '\u20AC 14.95'
11491 will be output correctly in all locales supporting the Euro symbol
11492 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11495 $ env printf '\u4e2d\u6587'
11499 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11501 Note that in these examples, the @command{printf} command has been
11502 invoked via @command{env} to ensure that we run the program found via
11503 your shell's search path, and not a shell alias or a built-in function.
11505 For larger strings, you don't need to look up the hexadecimal code
11506 values of each character one by one. @acronym{ASCII} characters mixed with \u
11507 escape sequences is also known as the JAVA source file encoding. You can
11508 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11509 is how to convert a piece of text into a shell script which will output
11510 this text in a locale-independent way:
11513 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11514 '\u4e2d\u6587\n' > sample.txt
11515 $ recode BIG5..JAVA < sample.txt \
11516 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11523 @node yes invocation
11524 @section @command{yes}: Print a string until interrupted
11527 @cindex repeated output of a string
11529 @command{yes} prints the command line arguments, separated by spaces and
11530 followed by a newline, forever until it is killed. If no arguments are
11531 given, it prints @samp{y} followed by a newline forever until killed.
11533 Upon a write error, @command{yes} exits with status @samp{1}.
11535 The only options are a lone @option{--help} or @option{--version}.
11536 To output an argument that begins with
11537 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11538 @xref{Common options}.
11542 @chapter Conditions
11545 @cindex commands for exit status
11546 @cindex exit status commands
11548 This section describes commands that are primarily useful for their exit
11549 status, rather than their output. Thus, they are often used as the
11550 condition of shell @code{if} statements, or as the last command in a
11554 * false invocation:: Do nothing, unsuccessfully.
11555 * true invocation:: Do nothing, successfully.
11556 * test invocation:: Check file types and compare values.
11557 * expr invocation:: Evaluate expressions.
11561 @node false invocation
11562 @section @command{false}: Do nothing, unsuccessfully
11565 @cindex do nothing, unsuccessfully
11566 @cindex failure exit status
11567 @cindex exit status of @command{false}
11569 @command{false} does nothing except return an exit status of 1, meaning
11570 @dfn{failure}. It can be used as a place holder in shell scripts
11571 where an unsuccessful command is needed.
11572 In most modern shells, @command{false} is a built-in command, so when
11573 you use @samp{false} in a script, you're probably using the built-in
11574 command, not the one documented here.
11576 @command{false} honors the @option{--help} and @option{--version} options.
11578 This version of @command{false} is implemented as a C program, and is thus
11579 more secure and faster than a shell script implementation, and may safely
11580 be used as a dummy shell for the purpose of disabling accounts.
11582 Note that @command{false} (unlike all other programs documented herein)
11583 exits unsuccessfully, even when invoked with
11584 @option{--help} or @option{--version}.
11586 Portable programs should not assume that the exit status of
11587 @command{false} is 1, as it is greater than 1 on some
11588 non-@acronym{GNU} hosts.
11591 @node true invocation
11592 @section @command{true}: Do nothing, successfully
11595 @cindex do nothing, successfully
11597 @cindex successful exit
11598 @cindex exit status of @command{true}
11600 @command{true} does nothing except return an exit status of 0, meaning
11601 @dfn{success}. It can be used as a place holder in shell scripts
11602 where a successful command is needed, although the shell built-in
11603 command @code{:} (colon) may do the same thing faster.
11604 In most modern shells, @command{true} is a built-in command, so when
11605 you use @samp{true} in a script, you're probably using the built-in
11606 command, not the one documented here.
11608 @command{true} honors the @option{--help} and @option{--version} options.
11610 Note, however, that it is possible to cause @command{true}
11611 to exit with nonzero status: with the @option{--help} or @option{--version}
11612 option, and with standard
11613 output already closed or redirected to a file that evokes an I/O error.
11614 For example, using a Bourne-compatible shell:
11617 $ ./true --version >&-
11618 ./true: write error: Bad file number
11619 $ ./true --version > /dev/full
11620 ./true: write error: No space left on device
11623 This version of @command{true} is implemented as a C program, and is thus
11624 more secure and faster than a shell script implementation, and may safely
11625 be used as a dummy shell for the purpose of disabling accounts.
11627 @node test invocation
11628 @section @command{test}: Check file types and compare values
11631 @cindex check file types
11632 @cindex compare values
11633 @cindex expression evaluation
11635 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11636 evaluation of the conditional expression @var{expr}. Each part of the
11637 expression must be a separate argument.
11639 @command{test} has file status checks, string operators, and numeric
11640 comparison operators.
11642 @command{test} has an alternate form that uses opening and closing
11643 square brackets instead a leading @samp{test}. For example, instead
11644 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11645 brackets must be separate arguments; for example, @samp{[-d /]} does
11646 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11647 @var{expr} ]} have the same meaning, only the former form is discussed
11653 test @var{expression}
11655 [ @var{expression} ]
11660 @mayConflictWithShellBuiltIn{test}
11662 If @var{expression} is omitted, @command{test} returns false.
11663 If @var{expression} is a single argument,
11664 @command{test} returns false if the argument is null and true
11665 otherwise. The argument
11666 can be any string, including strings like @samp{-d}, @samp{-1},
11667 @samp{--}, @samp{--help}, and @samp{--version} that most other
11668 programs would treat as options. To get help and version information,
11669 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11670 the usual closing brackets. @xref{Common options}.
11672 @cindex exit status of @command{test}
11676 0 if the expression is true,
11677 1 if the expression is false,
11678 2 if an error occurred.
11682 * File type tests:: -[bcdfhLpSt]
11683 * Access permission tests:: -[gkruwxOG]
11684 * File characteristic tests:: -e -s -nt -ot -ef
11685 * String tests:: -z -n = == !=
11686 * Numeric tests:: -eq -ne -lt -le -gt -ge
11687 * Connectives for test:: ! -a -o
11691 @node File type tests
11692 @subsection File type tests
11694 @cindex file type tests
11696 These options test for particular types of files. (Everything's a file,
11697 but not all files are the same!)
11701 @item -b @var{file}
11703 @cindex block special check
11704 True if @var{file} exists and is a block special device.
11706 @item -c @var{file}
11708 @cindex character special check
11709 True if @var{file} exists and is a character special device.
11711 @item -d @var{file}
11713 @cindex directory check
11714 True if @var{file} exists and is a directory.
11716 @item -f @var{file}
11718 @cindex regular file check
11719 True if @var{file} exists and is a regular file.
11721 @item -h @var{file}
11722 @itemx -L @var{file}
11725 @cindex symbolic link check
11726 True if @var{file} exists and is a symbolic link.
11727 Unlike all other file-related tests, this test does not dereference
11728 @var{file} if it is a symbolic link.
11730 @item -p @var{file}
11732 @cindex named pipe check
11733 True if @var{file} exists and is a named pipe.
11735 @item -S @var{file}
11737 @cindex socket check
11738 True if @var{file} exists and is a socket.
11742 @cindex terminal check
11743 True if @var{fd} is a file descriptor that is associated with a
11749 @node Access permission tests
11750 @subsection Access permission tests
11752 @cindex access permission tests
11753 @cindex permission tests
11755 These options test for particular access permissions.
11759 @item -g @var{file}
11761 @cindex set-group-ID check
11762 True if @var{file} exists and has its set-group-ID bit set.
11764 @item -k @var{file}
11766 @cindex sticky bit check
11767 True if @var{file} exists and has its @dfn{sticky} bit set.
11769 @item -r @var{file}
11771 @cindex readable file check
11772 True if @var{file} exists and read permission is granted.
11774 @item -u @var{file}
11776 @cindex set-user-ID check
11777 True if @var{file} exists and has its set-user-ID bit set.
11779 @item -w @var{file}
11781 @cindex writable file check
11782 True if @var{file} exists and write permission is granted.
11784 @item -x @var{file}
11786 @cindex executable file check
11787 True if @var{file} exists and execute permission is granted
11788 (or search permission, if it is a directory).
11790 @item -O @var{file}
11792 @cindex owned by effective user ID check
11793 True if @var{file} exists and is owned by the current effective user ID.
11795 @item -G @var{file}
11797 @cindex owned by effective group ID check
11798 True if @var{file} exists and is owned by the current effective group ID.
11802 @node File characteristic tests
11803 @subsection File characteristic tests
11805 @cindex file characteristic tests
11807 These options test other file characteristics.
11811 @item -e @var{file}
11813 @cindex existence-of-file check
11814 True if @var{file} exists.
11816 @item -s @var{file}
11818 @cindex nonempty file check
11819 True if @var{file} exists and has a size greater than zero.
11821 @item @var{file1} -nt @var{file2}
11823 @cindex newer-than file check
11824 True if @var{file1} is newer (according to modification date) than
11825 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11827 @item @var{file1} -ot @var{file2}
11829 @cindex older-than file check
11830 True if @var{file1} is older (according to modification date) than
11831 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11833 @item @var{file1} -ef @var{file2}
11835 @cindex same file check
11836 @cindex hard link check
11837 True if @var{file1} and @var{file2} have the same device and inode
11838 numbers, i.e., if they are hard links to each other.
11844 @subsection String tests
11846 @cindex string tests
11848 These options test string characteristics. You may need to quote
11849 @var{string} arguments for the shell. For example:
11855 The quotes here prevent the wrong arguments from being passed to
11856 @command{test} if @samp{$V} is empty or contains special characters.
11860 @item -z @var{string}
11862 @cindex zero-length string check
11863 True if the length of @var{string} is zero.
11865 @item -n @var{string}
11866 @itemx @var{string}
11868 @cindex nonzero-length string check
11869 True if the length of @var{string} is nonzero.
11871 @item @var{string1} = @var{string2}
11873 @cindex equal string check
11874 True if the strings are equal.
11876 @item @var{string1} == @var{string2}
11878 @cindex equal string check
11879 True if the strings are equal (synonym for =).
11881 @item @var{string1} != @var{string2}
11883 @cindex not-equal string check
11884 True if the strings are not equal.
11889 @node Numeric tests
11890 @subsection Numeric tests
11892 @cindex numeric tests
11893 @cindex arithmetic tests
11895 Numeric relational operators. The arguments must be entirely numeric
11896 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11897 which evaluates to the length of @var{string}.
11901 @item @var{arg1} -eq @var{arg2}
11902 @itemx @var{arg1} -ne @var{arg2}
11903 @itemx @var{arg1} -lt @var{arg2}
11904 @itemx @var{arg1} -le @var{arg2}
11905 @itemx @var{arg1} -gt @var{arg2}
11906 @itemx @var{arg1} -ge @var{arg2}
11913 These arithmetic binary operators return true if @var{arg1} is equal,
11914 not-equal, less-than, less-than-or-equal, greater-than, or
11915 greater-than-or-equal than @var{arg2}, respectively.
11922 test -1 -gt -2 && echo yes
11924 test -l abc -gt 1 && echo yes
11927 @error{} test: integer expression expected before -eq
11931 @node Connectives for test
11932 @subsection Connectives for @command{test}
11934 @cindex logical connectives
11935 @cindex connectives, logical
11937 The usual logical connectives.
11943 True if @var{expr} is false.
11945 @item @var{expr1} -a @var{expr2}
11947 @cindex logical and operator
11948 @cindex and operator
11949 True if both @var{expr1} and @var{expr2} are true.
11951 @item @var{expr1} -o @var{expr2}
11953 @cindex logical or operator
11954 @cindex or operator
11955 True if either @var{expr1} or @var{expr2} is true.
11960 @node expr invocation
11961 @section @command{expr}: Evaluate expressions
11964 @cindex expression evaluation
11965 @cindex evaluation of expressions
11967 @command{expr} evaluates an expression and writes the result on standard
11968 output. Each token of the expression must be a separate argument.
11970 Operands are either integers or strings. Integers consist of one or
11971 more decimal digits, with an optional leading @samp{-}.
11972 @command{expr} converts
11973 anything appearing in an operand position to an integer or a string
11974 depending on the operation being applied to it.
11976 Strings are not quoted for @command{expr} itself, though you may need to
11977 quote them to protect characters with special meaning to the shell,
11978 e.g., spaces. However, regardless of whether it is quoted, a string
11979 operand should not be a parenthesis or any of @command{expr}'s
11980 operators like @code{+}, so you cannot safely pass an arbitrary string
11981 @code{$str} to expr merely by quoting it to the shell. One way to
11982 work around this is to use the @sc{gnu} extension @code{+},
11983 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11984 @code{@w{" $str"}} and to adjust the rest of the expression to take
11985 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11987 You should not pass a negative integer or a string with leading
11988 @samp{-} as @command{expr}'s first argument, as it might be
11989 misinterpreted as an option; this can be avoided by parenthesization.
11990 Also, portable scripts should not use a string operand that happens to
11991 take the form of an integer; this can be worked around by inserting
11992 leading spaces as mentioned above.
11994 @cindex parentheses for grouping
11995 Operators may be given as infix symbols or prefix keywords. Parentheses
11996 may be used for grouping in the usual manner. You must quote
11997 parentheses and many operators to avoid the shell evaluating them,
12000 When built with support for the GNU MP library, @command{expr} uses
12001 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
12002 types and may fail due to arithmetic overflow.
12004 The only options are @option{--help} and @option{--version}. @xref{Common
12005 options}. Options must precede operands.
12007 @cindex exit status of @command{expr}
12011 0 if the expression is neither null nor 0,
12012 1 if the expression is null or 0,
12013 2 if the expression is invalid,
12014 3 if an internal error occurred (e.g., arithmetic overflow).
12018 * String expressions:: + : match substr index length
12019 * Numeric expressions:: + - * / %
12020 * Relations for expr:: | & < <= = == != >= >
12021 * Examples of expr:: Examples.
12025 @node String expressions
12026 @subsection String expressions
12028 @cindex string expressions
12029 @cindex expressions, string
12031 @command{expr} supports pattern matching and other string operators. These
12032 have higher precedence than both the numeric and relational operators (in
12033 the next sections).
12037 @item @var{string} : @var{regex}
12038 @cindex pattern matching
12039 @cindex regular expression matching
12040 @cindex matching patterns
12041 Perform pattern matching. The arguments are converted to strings and the
12042 second is considered to be a (basic, a la GNU @code{grep}) regular
12043 expression, with a @code{^} implicitly prepended. The first argument is
12044 then matched against this regular expression.
12046 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
12047 @code{:} expression returns the part of @var{string} that matched the
12048 subexpression; otherwise, it returns the number of characters matched.
12050 If the match fails, the @code{:} operator returns the null string if
12051 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
12053 @kindex \( @r{regexp operator}
12054 Only the first @samp{\( @dots{} \)} pair is relevant to the return
12055 value; additional pairs are meaningful only for grouping the regular
12056 expression operators.
12058 @kindex \+ @r{regexp operator}
12059 @kindex \? @r{regexp operator}
12060 @kindex \| @r{regexp operator}
12061 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
12062 operators which respectively match one or more, zero or one, or separate
12063 alternatives. SunOS and other @command{expr}'s treat these as regular
12064 characters. (@acronym{POSIX} allows either behavior.)
12065 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
12066 regular expression syntax. Some examples are in @ref{Examples of expr}.
12068 @item match @var{string} @var{regex}
12070 An alternative way to do pattern matching. This is the same as
12071 @w{@samp{@var{string} : @var{regex}}}.
12073 @item substr @var{string} @var{position} @var{length}
12075 Returns the substring of @var{string} beginning at @var{position}
12076 with length at most @var{length}. If either @var{position} or
12077 @var{length} is negative, zero, or non-numeric, returns the null string.
12079 @item index @var{string} @var{charset}
12081 Returns the first position in @var{string} where the first character in
12082 @var{charset} was found. If no character in @var{charset} is found in
12083 @var{string}, return 0.
12085 @item length @var{string}
12087 Returns the length of @var{string}.
12089 @item + @var{token}
12091 Interpret @var{token} as a string, even if it is a keyword like @var{match}
12092 or an operator like @code{/}.
12093 This makes it possible to test @code{expr length + "$x"} or
12094 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
12095 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
12096 This operator is a @acronym{GNU} extension. Portable shell scripts should use
12097 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
12101 To make @command{expr} interpret keywords as strings, you must use the
12102 @code{quote} operator.
12105 @node Numeric expressions
12106 @subsection Numeric expressions
12108 @cindex numeric expressions
12109 @cindex expressions, numeric
12111 @command{expr} supports the usual numeric operators, in order of increasing
12112 precedence. These numeric operators have lower precedence than the
12113 string operators described in the previous section, and higher precedence
12114 than the connectives (next section).
12122 @cindex subtraction
12123 Addition and subtraction. Both arguments are converted to integers;
12124 an error occurs if this cannot be done.
12130 @cindex multiplication
12133 Multiplication, division, remainder. Both arguments are converted to
12134 integers; an error occurs if this cannot be done.
12139 @node Relations for expr
12140 @subsection Relations for @command{expr}
12142 @cindex connectives, logical
12143 @cindex logical connectives
12144 @cindex relations, numeric or string
12146 @command{expr} supports the usual logical connectives and relations. These
12147 have lower precedence than the string and numeric operators
12148 (previous sections). Here is the list, lowest-precedence operator first.
12154 @cindex logical or operator
12155 @cindex or operator
12156 Returns its first argument if that is neither null nor zero, otherwise
12157 its second argument if it is neither null nor zero, otherwise 0. It
12158 does not evaluate its second argument if its first argument is neither
12163 @cindex logical and operator
12164 @cindex and operator
12165 Return its first argument if neither argument is null or zero, otherwise
12166 0. It does not evaluate its second argument if its first argument is
12169 @item < <= = == != >= >
12176 @cindex comparison operators
12178 Compare the arguments and return 1 if the relation is true, 0 otherwise.
12179 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
12180 both arguments to integers and do a numeric comparison; if either
12181 conversion fails, it does a lexicographic comparison using the character
12182 collating sequence specified by the @env{LC_COLLATE} locale.
12187 @node Examples of expr
12188 @subsection Examples of using @command{expr}
12190 @cindex examples of @command{expr}
12191 Here are a few examples, including quoting for shell metacharacters.
12193 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
12196 foo=`expr $foo + 1`
12199 To print the non-directory part of the file name stored in
12200 @code{$fname}, which need not contain a @code{/}:
12203 expr $fname : '.*/\(.*\)' '|' $fname
12206 An example showing that @code{\+} is an operator:
12214 expr abc : 'a\(.\)c'
12216 expr index abcdef cz
12219 @error{} expr: syntax error
12220 expr index + index a
12226 @chapter Redirection
12228 @cindex redirection
12229 @cindex commands for redirection
12231 Unix shells commonly provide several forms of @dfn{redirection}---ways
12232 to change the input source or output destination of a command. But one
12233 useful redirection is performed by a separate command, not by the shell;
12234 it's described here.
12237 * tee invocation:: Redirect output to multiple files or processes.
12241 @node tee invocation
12242 @section @command{tee}: Redirect output to multiple files or processes
12245 @cindex pipe fitting
12246 @cindex destinations, multiple output
12247 @cindex read from stdin and write to stdout and files
12249 The @command{tee} command copies standard input to standard output and also
12250 to any files given as arguments. This is useful when you want not only
12251 to send some data down a pipe, but also to save a copy. Synopsis:
12254 tee [@var{option}]@dots{} [@var{file}]@dots{}
12257 If a file being written to does not already exist, it is created. If a
12258 file being written to already exists, the data it previously contained
12259 is overwritten unless the @option{-a} option is used.
12261 A @var{file} of @samp{-} causes @command{tee} to send another copy of
12262 input to standard output, but this is typically not that useful as the
12263 copies are interleaved.
12265 The program accepts the following options. Also see @ref{Common options}.
12272 Append standard input to the given files rather than overwriting
12276 @itemx --ignore-interrupts
12278 @opindex --ignore-interrupts
12279 Ignore interrupt signals.
12283 The @command{tee} command is useful when you happen to be transferring a large
12284 amount of data and also want to summarize that data without reading
12285 it a second time. For example, when you are downloading a DVD image,
12286 you often want to verify its signature or checksum right away.
12287 The inefficient way to do it is simply:
12290 wget http://example.com/some.iso && sha1sum some.iso
12293 One problem with the above is that it makes you wait for the
12294 download to complete before starting the time-consuming SHA1 computation.
12295 Perhaps even more importantly, the above requires reading
12296 the DVD image a second time (the first was from the network).
12298 The efficient way to do it is to interleave the download
12299 and SHA1 computation. Then, you'll get the checksum for
12300 free, because the entire process parallelizes so well:
12303 # slightly contrived, to demonstrate process substitution
12304 wget -O - http://example.com/dvd.iso \
12305 | tee >(sha1sum > dvd.sha1) > dvd.iso
12308 That makes @command{tee} write not just to the expected output file,
12309 but also to a pipe running @command{sha1sum} and saving the final
12310 checksum in a file named @file{dvd.sha1}.
12312 Note, however, that this example relies on a feature of modern shells
12313 called @dfn{process substitution}
12314 (the @samp{>(command)} syntax, above;
12315 @xref{Process Substitution,,Process Substitution, bashref,
12316 The Bash Reference Manual}.),
12317 so it works with @command{zsh}, @command{bash}, and @command{ksh},
12318 but not with @command{/bin/sh}. So if you write code like this
12319 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
12321 Since the above example writes to one file and one process,
12322 a more conventional and portable use of @command{tee} is even better:
12325 wget -O - http://example.com/dvd.iso \
12326 | tee dvd.iso | sha1sum > dvd.sha1
12329 You can extend this example to make @command{tee} write to two processes,
12330 computing MD5 and SHA1 checksums in parallel. In this case,
12331 process substitution is required:
12334 wget -O - http://example.com/dvd.iso \
12335 | tee >(sha1sum > dvd.sha1) \
12336 >(md5sum > dvd.md5) \
12340 This technique is also useful when you want to make a @emph{compressed}
12341 copy of the contents of a pipe.
12342 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
12343 For a large hierarchy, @samp{du -ak} can run for a long time,
12344 and can easily produce terabytes of data, so you won't want to
12345 rerun the command unnecessarily. Nor will you want to save
12346 the uncompressed output.
12348 Doing it the inefficient way, you can't even start the GUI
12349 until after you've compressed all of the @command{du} output:
12352 du -ak | gzip -9 > /tmp/du.gz
12353 gzip -d /tmp/du.gz | xdiskusage -a
12356 With @command{tee} and process substitution, you start the GUI
12357 right away and eliminate the decompression completely:
12360 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
12363 Finally, if you regularly create more than one type of
12364 compressed tarball at once, for example when @code{make dist} creates
12365 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
12366 there may be a better way.
12367 Typical @command{automake}-generated @file{Makefile} rules create
12368 the two compressed tar archives with commands in sequence, like this
12369 (slightly simplified):
12372 tardir=your-pkg-M.N
12373 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
12374 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12377 However, if the hierarchy you are archiving and compressing is larger
12378 than a couple megabytes, and especially if you are using a multi-processor
12379 system with plenty of memory, then you can do much better by reading the
12380 directory contents only once and running the compression programs in parallel:
12383 tardir=your-pkg-M.N
12384 tar chof - "$tardir" \
12385 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
12386 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
12392 @node File name manipulation
12393 @chapter File name manipulation
12395 @cindex file name manipulation
12396 @cindex manipulation of file names
12397 @cindex commands for file name manipulation
12399 This section describes commands that manipulate file names.
12402 * basename invocation:: Strip directory and suffix from a file name.
12403 * dirname invocation:: Strip last file name component.
12404 * pathchk invocation:: Check file name validity and portability.
12405 * mktemp invocation:: Create temporary file or directory.
12406 * realpath invocation:: Print resolved file names.
12410 @node basename invocation
12411 @section @command{basename}: Strip directory and suffix from a file name
12414 @cindex strip directory and suffix from file names
12415 @cindex directory, stripping from file names
12416 @cindex suffix, stripping from file names
12417 @cindex file names, stripping directory and suffix
12418 @cindex leading directory components, stripping
12420 @command{basename} removes any leading directory components from
12421 @var{name}. Synopsis:
12424 basename @var{name} [@var{suffix}]
12425 basename @var{option}... @var{name}...
12428 If @var{suffix} is specified and is identical to the end of @var{name},
12429 it is removed from @var{name} as well. Note that since trailing slashes
12430 are removed prior to suffix matching, @var{suffix} will do nothing if it
12431 contains slashes. @command{basename} prints the result on standard
12434 @c This test is used both here and in the section on dirname.
12435 @macro basenameAndDirname
12436 Together, @command{basename} and @command{dirname} are designed such
12437 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
12438 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
12439 for everything except file names containing a trailing newline.
12441 @basenameAndDirname
12443 @acronym{POSIX} allows the implementation to define the results if
12444 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
12445 @command{basename} returns the empty string. In the latter case, the
12446 result is @samp{//} on platforms where @var{//} is distinct from
12447 @var{/}, and @samp{/} on platforms where there is no difference.
12449 The program accepts the following options. Also see @ref{Common options}.
12450 Options must precede operands.
12457 @opindex --multiple
12458 Support more than one argument. Treat every argument as a @var{name}.
12459 With this, an optional @var{suffix} must be specified using the
12460 @option{-s} option.
12462 @item -s @var{suffix}
12463 @itemx --suffix=@var{suffix}
12466 Remove a trailing @var{suffix}.
12467 This option implies the @option{-a} option.
12477 basename /usr/bin/sort
12480 basename include/stdio.h .h
12483 basename -s .h include/stdio.h
12485 # Output "stdio" followed by "stdlib"
12486 basename -a -s .h include/stdio.h include/stdlib.h
12490 @node dirname invocation
12491 @section @command{dirname}: Strip last file name component
12494 @cindex directory components, printing
12495 @cindex stripping non-directory suffix
12496 @cindex non-directory suffix, stripping
12498 @command{dirname} prints all but the final slash-delimited component of
12499 @var{name}. Slashes on either side of the final component are also
12500 removed. If the string contains no slash, @command{dirname} prints
12501 @samp{.} (meaning the current directory). Synopsis:
12507 @var{name} need not be a file name, but if it is, this operation
12508 effectively lists the directory that contains the final component,
12509 including the case when the final component is itself a directory.
12511 @basenameAndDirname
12513 @acronym{POSIX} allows the implementation to define the results if
12514 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12515 result is @samp{//} on platforms where @var{//} is distinct from
12516 @var{/}, and @samp{/} on platforms where there is no difference.
12518 The only options are @option{--help} and @option{--version}. @xref{Common
12526 # Output "/usr/bin".
12527 dirname /usr/bin/sort
12528 dirname /usr/bin//.//
12535 @node pathchk invocation
12536 @section @command{pathchk}: Check file name validity and portability
12539 @cindex file names, checking validity and portability
12540 @cindex valid file names, checking for
12541 @cindex portable file names, checking for
12543 @command{pathchk} checks validity and portability of file names. Synopsis:
12546 pathchk [@var{option}]@dots{} @var{name}@dots{}
12549 For each @var{name}, @command{pathchk} prints an error message if any of
12550 these conditions is true:
12554 One of the existing directories in @var{name} does not have search
12555 (execute) permission,
12557 The length of @var{name} is larger than the maximum supported by the
12560 The length of one component of @var{name} is longer than
12561 its file system's maximum.
12564 A nonexistent @var{name} is not an error, so long a file with that
12565 name could be created under the above conditions.
12567 The program accepts the following options. Also see @ref{Common options}.
12568 Options must precede operands.
12574 Instead of performing checks based on the underlying file system,
12575 print an error message if any of these conditions is true:
12579 A file name is empty.
12582 A file name contains a character outside the @acronym{POSIX} portable file
12583 name character set, namely, the ASCII letters and digits, @samp{.},
12584 @samp{_}, @samp{-}, and @samp{/}.
12587 The length of a file name or one of its components exceeds the
12588 @acronym{POSIX} minimum limits for portability.
12593 Print an error message if a file name is empty, or if it contains a component
12594 that begins with @samp{-}.
12596 @item --portability
12597 @opindex --portability
12598 Print an error message if a file name is not portable to all @acronym{POSIX}
12599 hosts. This option is equivalent to @samp{-p -P}.
12603 @cindex exit status of @command{pathchk}
12607 0 if all specified file names passed all checks,
12611 @node mktemp invocation
12612 @section @command{mktemp}: Create temporary file or directory
12615 @cindex file names, creating temporary
12616 @cindex directory, creating temporary
12617 @cindex temporary files and directories
12619 @command{mktemp} manages the creation of temporary files and
12620 directories. Synopsis:
12623 mktemp [@var{option}]@dots{} [@var{template}]
12626 Safely create a temporary file or directory based on @var{template},
12627 and print its name. If given, @var{template} must include at least
12628 three consecutive @samp{X}s in the last component. If omitted, the template
12629 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12630 implied. The final run of @samp{X}s in the @var{template} will be replaced
12631 by alpha-numeric characters; thus, on a case-sensitive file system,
12632 and with a @var{template} including a run of @var{n} instances of @samp{X},
12633 there are @samp{62**@var{n}} potential file names.
12635 Older scripts used to create temporary files by simply joining the
12636 name of the program with the process id (@samp{$$}) as a suffix.
12637 However, that naming scheme is easily predictable, and suffers from a
12638 race condition where the attacker can create an appropriately named
12639 symbolic link, such that when the script then opens a handle to what
12640 it thought was an unused file, it is instead modifying an existing
12641 file. Using the same scheme to create a directory is slightly safer,
12642 since the @command{mkdir} will fail if the target already exists, but
12643 it is still inferior because it allows for denial of service attacks.
12644 Therefore, modern scripts should use the @command{mktemp} command to
12645 guarantee that the generated name will be unpredictable, and that
12646 knowledge of the temporary file name implies that the file was created
12647 by the current script and cannot be modified by other users.
12649 When creating a file, the resulting file has read and write
12650 permissions for the current user, but no permissions for the group or
12651 others; these permissions are reduced if the current umask is more
12654 Here are some examples (although note that if you repeat them, you
12655 will most likely get different file names):
12660 Create a temporary file in the current directory.
12667 Create a temporary file with a known suffix.
12669 $ mktemp --suffix=.txt file-XXXX
12671 $ mktemp file-XXXX-XXXX.txt
12676 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12677 but falling back to the current directory rather than @file{/tmp}.
12678 Note that @command{mktemp} does not create fifos, but can create a
12679 secure directory in which the fifo can live. Exit the shell if the
12680 directory or fifo could not be created.
12682 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12684 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12688 Create and use a temporary file if possible, but ignore failure. The
12689 file will reside in the directory named by @env{TMPDIR}, if specified,
12690 or else in @file{/tmp}.
12692 $ file=$(mktemp -q) && @{
12693 > # Safe to use $file only within this block. Use quotes,
12694 > # since $TMPDIR, and thus $file, may contain whitespace.
12695 > echo ... > "$file"
12701 Act as a semi-random character generator (it is not fully random,
12702 since it is impacted by the contents of the current directory). To
12703 avoid security holes, do not use the resulting names to create a file.
12713 The program accepts the following options. Also see @ref{Common options}.
12720 @opindex --directory
12721 Create a directory rather than a file. The directory will have read,
12722 write, and search permissions for the current user, but no permissions
12723 for the group or others; these permissions are reduced if the current
12724 umask is more restrictive.
12730 Suppress diagnostics about failure to create a file or directory. The
12731 exit status will still reflect whether a file was created.
12737 Generate a temporary name that does not name an existing file, without
12738 changing the file system contents. Using the output of this command
12739 to create a new file is inherently unsafe, as there is a window of
12740 time between generating the name and using it where another process
12741 can create an object by the same name.
12744 @itemx --tmpdir[=@var{dir}]
12747 Treat @var{template} relative to the directory @var{dir}. If
12748 @var{dir} is not specified (only possible with the long option
12749 @option{--tmpdir}) or is the empty string, use the value of
12750 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12751 specified, @var{template} must not be absolute. However,
12752 @var{template} can still contain slashes, although intermediate
12753 directories must already exist.
12755 @item --suffix=@var{suffix}
12757 Append @var{suffix} to the @var{template}. @var{suffix} must not
12758 contain slash. If @option{--suffix} is specified, @var{template} must
12759 end in @samp{X}; if it is not specified, then an appropriate
12760 @option{--suffix} is inferred by finding the last @samp{X} in
12761 @var{template}. This option exists for use with the default
12762 @var{template} and for the creation of a @var{suffix} that starts with
12767 Treat @var{template} as a single file relative to the value of
12768 @env{TMPDIR} if available, or to the directory specified by
12769 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12770 contain slashes. This option is deprecated; the use of @option{-p}
12771 without @option{-t} offers better defaults (by favoring the command
12772 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12777 @cindex exit status of @command{mktemp}
12781 0 if the file was created,
12786 @node realpath invocation
12787 @section @command{realpath}: Print the resolved file name.
12790 @cindex file names, canonicalization
12791 @cindex symlinks, resolution
12792 @cindex canonical file name
12793 @cindex canonicalize a file name
12797 @command{realpath} expands all symbolic links and resolves references to
12798 @samp{/./}, @samp{/../} and extra @samp{/} characters. By default,
12799 all but the last component of the specified files must exist. Synopsis:
12802 realpath [@var{option}]@dots{} @var{file}@dots{}
12805 The program accepts the following options. Also see @ref{Common options}.
12810 @itemx --canonicalize-existing
12812 @opindex --canonicalize-existing
12813 Ensure that all components of the specified file names exist.
12814 If any component is missing or unavailable, @command{realpath} will output
12815 a diagnostic unless the @option{-q} option is specified, and exit with a
12816 nonzero exit code. A trailing slash requires that the name resolve to a
12820 @itemx --canonicalize-missing
12822 @opindex --canonicalize-missing
12823 If any component of a specified file name is missing or unavailable,
12824 treat it as a directory.
12830 Symbolic links are resolved in the specified file names,
12831 but they are resolved after any subsequent @samp{..} components are processed.
12836 @opindex --physical
12837 Symbolic links are resolved in the specified file names,
12838 and they are resolved before any subsequent @samp{..} components are processed.
12839 This is the default mode of operation.
12845 Suppress diagnostic messages for specified file names.
12849 @itemx --no-symlinks
12852 @opindex --no-symlinks
12853 Do not resolve symbolic links. Only resolve references to
12854 @samp{/./}, @samp{/../} and remove extra @samp{/} characters.
12855 When combined with the @option{-m} option, realpath operates
12856 only on the file name, and does not touch any actual file.
12862 Separate output items with @sc{nul} characters.
12864 @itemx --relative-to=@var{file}
12865 @opindex --relative-to
12867 Print the resolved file names relative to the specified file.
12868 Note this option honors the @option{-m} and @option{-e} options
12869 pertaining to file existence.
12871 @itemx --relative-base=@var{base}
12872 @opindex --relative-base
12873 This option is valid when used with @option{--relative-to}, and will restrict
12874 the output of @option{--relative-to} so that relative names are output,
12875 only when @var{file}s are descendants of @var{base}. Otherwise output the
12876 absolute file name. Note: this option honors the @option{-m} and @option{-e}
12877 options pertaining to file existence. For example:
12880 realpath --relative-to=/usr /tmp /usr/bin
12883 realpath --relative-base=/usr --relative-to=/usr /tmp /usr/bin
12890 @cindex exit status of @command{realpath}
12894 0 if all file names were printed without issue.
12899 @node Working context
12900 @chapter Working context
12902 @cindex working context
12903 @cindex commands for printing the working context
12905 This section describes commands that display or alter the context in
12906 which you are working: the current directory, the terminal settings, and
12907 so forth. See also the user-related commands in the next section.
12910 * pwd invocation:: Print working directory.
12911 * stty invocation:: Print or change terminal characteristics.
12912 * printenv invocation:: Print environment variables.
12913 * tty invocation:: Print file name of terminal on standard input.
12917 @node pwd invocation
12918 @section @command{pwd}: Print working directory
12921 @cindex print name of current directory
12922 @cindex current working directory, printing
12923 @cindex working directory, printing
12926 @command{pwd} prints the name of the current directory. Synopsis:
12929 pwd [@var{option}]@dots{}
12932 The program accepts the following options. Also see @ref{Common options}.
12939 If the contents of the environment variable @env{PWD} provide an
12940 absolute name of the current directory with no @samp{.} or @samp{..}
12941 components, but possibly with symbolic links, then output those
12942 contents. Otherwise, fall back to default @option{-P} handling.
12947 @opindex --physical
12948 Print a fully resolved name for the current directory. That is, all
12949 components of the printed name will be actual directory names---none
12950 will be symbolic links.
12953 @cindex symbolic links and @command{pwd}
12954 If @option{-L} and @option{-P} are both given, the last one takes
12955 precedence. If neither option is given, then this implementation uses
12956 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12957 environment variable is set.
12959 @mayConflictWithShellBuiltIn{pwd}
12964 @node stty invocation
12965 @section @command{stty}: Print or change terminal characteristics
12968 @cindex change or print terminal settings
12969 @cindex terminal settings
12970 @cindex line settings of terminal
12972 @command{stty} prints or changes terminal characteristics, such as baud rate.
12976 stty [@var{option}] [@var{setting}]@dots{}
12977 stty [@var{option}]
12980 If given no line settings, @command{stty} prints the baud rate, line
12981 discipline number (on systems that support it), and line settings
12982 that have been changed from the values set by @samp{stty sane}.
12983 By default, mode reading and setting are performed on the tty line
12984 connected to standard input, although this can be modified by the
12985 @option{--file} option.
12987 @command{stty} accepts many non-option arguments that change aspects of
12988 the terminal line operation, as described below.
12990 The program accepts the following options. Also see @ref{Common options}.
12997 Print all current settings in human-readable form. This option may not
12998 be used in combination with any line settings.
13000 @item -F @var{device}
13001 @itemx --file=@var{device}
13004 Set the line opened by the file name specified in @var{device} instead of
13005 the tty line connected to standard input. This option is necessary
13006 because opening a @acronym{POSIX} tty requires use of the
13007 @code{O_NONDELAY} flag to prevent a @acronym{POSIX} tty from blocking
13008 until the carrier detect line is high if
13009 the @code{clocal} flag is not set. Hence, it is not always possible
13010 to allow the shell to open the device in the traditional manner.
13016 @cindex machine-readable @command{stty} output
13017 Print all current settings in a form that can be used as an argument to
13018 another @command{stty} command to restore the current settings. This option
13019 may not be used in combination with any line settings.
13023 Many settings can be turned off by preceding them with a @samp{-}.
13024 Such arguments are marked below with ``May be negated'' in their
13025 description. The descriptions themselves refer to the positive
13026 case, that is, when @emph{not} negated (unless stated otherwise,
13029 Some settings are not available on all @acronym{POSIX} systems, since they use
13030 extensions. Such arguments are marked below with
13031 ``Non-@acronym{POSIX}'' in their description. On non-@acronym{POSIX}
13032 systems, those or other settings also may not
13033 be available, but it's not feasible to document all the variations: just
13039 * Control:: Control settings
13040 * Input:: Input settings
13041 * Output:: Output settings
13042 * Local:: Local settings
13043 * Combination:: Combination settings
13044 * Characters:: Special characters
13045 * Special:: Special settings
13050 @subsection Control settings
13052 @cindex control settings
13058 @cindex two-way parity
13059 Generate parity bit in output and expect parity bit in input.
13065 @cindex even parity
13066 Set odd parity (even if negated). May be negated.
13073 @cindex character size
13074 @cindex eight-bit characters
13075 Set character size to 5, 6, 7, or 8 bits.
13080 Send a hangup signal when the last process closes the tty. May be
13086 Use two stop bits per character (one if negated). May be negated.
13090 Allow input to be received. May be negated.
13094 @cindex modem control
13095 Disable modem control signals. May be negated.
13099 @cindex hardware flow control
13100 @cindex flow control, hardware
13101 @cindex RTS/CTS flow control
13102 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
13107 @subsection Input settings
13109 @cindex input settings
13110 These settings control operations on data received from the terminal.
13115 @cindex breaks, ignoring
13116 Ignore break characters. May be negated.
13120 @cindex breaks, cause interrupts
13121 Make breaks cause an interrupt signal. May be negated.
13125 @cindex parity, ignoring
13126 Ignore characters with parity errors. May be negated.
13130 @cindex parity errors, marking
13131 Mark parity errors (with a 255-0-character sequence). May be negated.
13135 Enable input parity checking. May be negated.
13139 @cindex eight-bit input
13140 Clear high (8th) bit of input characters. May be negated.
13144 @cindex newline, translating to return
13145 Translate newline to carriage return. May be negated.
13149 @cindex return, ignoring
13150 Ignore carriage return. May be negated.
13154 @cindex return, translating to newline
13155 Translate carriage return to newline. May be negated.
13159 @cindex input encoding, UTF-8
13160 Assume input characters are UTF-8 encoded. May be negated.
13164 @kindex C-s/C-q flow control
13165 @cindex XON/XOFF flow control
13166 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
13173 @cindex software flow control
13174 @cindex flow control, software
13175 Enable sending of @code{stop} character when the system input buffer
13176 is almost full, and @code{start} character when it becomes almost
13177 empty again. May be negated.
13181 @cindex uppercase, translating to lowercase
13182 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
13183 negated. Note ilcuc is not implemented, as one would not be able to issue
13184 almost any (lowercase) Unix command, after invoking it.
13188 Allow any character to restart output (only the start character
13189 if negated). Non-@acronym{POSIX}. May be negated.
13193 @cindex beeping at input buffer full
13194 Enable beeping and not flushing input buffer if a character arrives
13195 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
13200 @subsection Output settings
13202 @cindex output settings
13203 These settings control operations on data sent to the terminal.
13208 Postprocess output. May be negated.
13212 @cindex lowercase, translating to output
13213 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
13214 negated. (Note ouclc is not currently implemented.)
13218 @cindex return, translating to newline
13219 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
13223 @cindex newline, translating to crlf
13224 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
13229 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
13234 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
13238 @cindex pad instead of timing for delaying
13239 Use fill (padding) characters instead of timing for delays.
13240 Non-@acronym{POSIX}.
13245 @cindex pad character
13246 Use @acronym{ASCII} @sc{del} characters for fill instead of
13247 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
13253 Newline delay style. Non-@acronym{POSIX}.
13260 Carriage return delay style. Non-@acronym{POSIX}.
13266 @opindex tab@var{n}
13267 Horizontal tab delay style. Non-@acronym{POSIX}.
13272 Backspace delay style. Non-@acronym{POSIX}.
13277 Vertical tab delay style. Non-@acronym{POSIX}.
13282 Form feed delay style. Non-@acronym{POSIX}.
13287 @subsection Local settings
13289 @cindex local settings
13294 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
13295 characters. May be negated.
13299 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
13300 special characters. May be negated.
13304 Enable non-@acronym{POSIX} special characters. May be negated.
13308 Echo input characters. May be negated.
13314 Echo @code{erase} characters as backspace-space-backspace. May be
13319 @cindex newline echoing after @code{kill}
13320 Echo a newline after a @code{kill} character. May be negated.
13324 @cindex newline, echoing
13325 Echo newline even if not echoing other characters. May be negated.
13329 @cindex flushing, disabling
13330 Disable flushing after @code{interrupt} and @code{quit} special
13331 characters. May be negated.
13335 @cindex case translation
13336 Enable input and output of uppercase characters by preceding their
13337 lowercase equivalents with @samp{\}, when @code{icanon} is set.
13338 Non-@acronym{POSIX}. May be negated.
13342 @cindex background jobs, stopping at terminal write
13343 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
13350 Echo erased characters backward, between @samp{\} and @samp{/}.
13351 Non-@acronym{POSIX}. May be negated.
13357 @cindex control characters, using @samp{^@var{c}}
13358 @cindex hat notation for control characters
13359 Echo control characters in hat notation (@samp{^@var{c}}) instead
13360 of literally. Non-@acronym{POSIX}. May be negated.
13366 Echo the @code{kill} special character by erasing each character on
13367 the line as indicated by the @code{echoprt} and @code{echoe} settings,
13368 instead of by the @code{echoctl} and @code{echok} settings.
13369 Non-@acronym{POSIX}.
13375 @subsection Combination settings
13377 @cindex combination settings
13378 Combination settings:
13385 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
13386 as @code{-parenb cs8}.
13390 Same as @code{parenb parodd cs7}. May be negated. If negated, same
13391 as @code{-parenb cs8}.
13395 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
13396 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
13400 Reset the @code{erase} and @code{kill} special characters to their default
13407 @c This is too long to write inline.
13409 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
13410 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
13411 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
13412 ff0 isig icanon iexten echo echoe echok -echonl
13413 -noflsh -xcase -tostop -echoprt echoctl echoke
13417 and also sets all special characters to their default values.
13421 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
13422 sets the @code{eof} and @code{eol} characters to their default values
13423 if they are the same as the @code{min} and @code{time} characters.
13424 May be negated. If negated, same as @code{raw}.
13431 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
13432 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
13433 -imaxbel -opost -isig -icanon -xcase min 1 time 0
13437 May be negated. If negated, same as @code{cooked}.
13441 Same as @option{-icanon}. May be negated. If negated, same as
13446 @cindex eight-bit characters
13447 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
13448 same as @code{parenb istrip cs7}.
13452 Same as @option{-parenb -istrip -opost cs8}. May be negated.
13453 If negated, same as @code{parenb istrip opost cs7}.
13457 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
13461 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
13468 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
13469 (Used for terminals with uppercase characters only.)
13473 Same as @code{echoe echoctl echoke}.
13477 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
13482 @subsection Special characters
13484 @cindex special characters
13485 @cindex characters, special
13487 The special characters' default values vary from system to system.
13488 They are set with the syntax @samp{name value}, where the names are
13489 listed below and the value can be given either literally, in hat
13490 notation (@samp{^@var{c}}), or as an integer which may start with
13491 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
13492 any other digit to indicate decimal.
13494 @cindex disabling special characters
13495 @kindex u@r{, and disabling special characters}
13496 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
13497 special character. (This is incompatible with Ultrix @command{stty},
13498 which uses a value of @samp{u} to disable a special character. GNU
13499 @command{stty} treats a value @samp{u} like any other, namely to set that
13500 special character to @key{U}.)
13506 Send an interrupt signal.
13510 Send a quit signal.
13514 Erase the last character typed.
13518 Erase the current line.
13522 Send an end of file (terminate the input).
13530 Alternate character to end the line. Non-@acronym{POSIX}.
13534 Switch to a different shell layer. Non-@acronym{POSIX}.
13538 Restart the output after stopping it.
13546 Send a terminal stop signal.
13550 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
13554 Redraw the current line. Non-@acronym{POSIX}.
13558 Erase the last word typed. Non-@acronym{POSIX}.
13562 Enter the next character typed literally, even if it is a special
13563 character. Non-@acronym{POSIX}.
13568 @subsection Special settings
13570 @cindex special settings
13575 Set the minimum number of characters that will satisfy a read until
13576 the time value has expired, when @option{-icanon} is set.
13580 Set the number of tenths of a second before reads time out if the minimum
13581 number of characters have not been read, when @option{-icanon} is set.
13583 @item ispeed @var{n}
13585 Set the input speed to @var{n}.
13587 @item ospeed @var{n}
13589 Set the output speed to @var{n}.
13593 Tell the tty kernel driver that the terminal has @var{n} rows.
13594 Non-@acronym{POSIX}.
13597 @itemx columns @var{n}
13600 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
13606 Print the number of rows and columns that the kernel thinks the
13607 terminal has. (Systems that don't support rows and columns in the kernel
13608 typically use the environment variables @env{LINES} and @env{COLUMNS}
13609 instead; however, GNU @command{stty} does not know anything about them.)
13610 Non-@acronym{POSIX}.
13614 Use line discipline @var{n}. Non-@acronym{POSIX}.
13618 Print the terminal speed.
13621 @cindex baud rate, setting
13622 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13623 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13624 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13625 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13626 support higher speeds. The @command{stty} command includes support
13643 4000000 where the system supports these.
13644 0 hangs up the line if @option{-clocal} is set.
13648 @node printenv invocation
13649 @section @command{printenv}: Print all or some environment variables
13652 @cindex printing all or some environment variables
13653 @cindex environment variables, printing
13655 @command{printenv} prints environment variable values. Synopsis:
13658 printenv [@var{option}] [@var{variable}]@dots{}
13661 If no @var{variable}s are specified, @command{printenv} prints the value of
13662 every environment variable. Otherwise, it prints the value of each
13663 @var{variable} that is set, and nothing for those that are not set.
13665 The program accepts the following option. Also see @ref{Common options}.
13673 @cindex exit status of @command{printenv}
13677 0 if all variables specified were found
13678 1 if at least one specified variable was not found
13679 2 if a write error occurred
13683 @node tty invocation
13684 @section @command{tty}: Print file name of terminal on standard input
13687 @cindex print terminal file name
13688 @cindex terminal file name, printing
13690 @command{tty} prints the file name of the terminal connected to its standard
13691 input. It prints @samp{not a tty} if standard input is not a terminal.
13695 tty [@var{option}]@dots{}
13698 The program accepts the following option. Also see @ref{Common options}.
13708 Print nothing; only return an exit status.
13712 @cindex exit status of @command{tty}
13716 0 if standard input is a terminal
13717 1 if standard input is not a terminal
13718 2 if given incorrect arguments
13719 3 if a write error occurs
13723 @node User information
13724 @chapter User information
13726 @cindex user information, commands for
13727 @cindex commands for printing user information
13729 This section describes commands that print user-related information:
13730 logins, groups, and so forth.
13733 * id invocation:: Print user identity.
13734 * logname invocation:: Print current login name.
13735 * whoami invocation:: Print effective user ID.
13736 * groups invocation:: Print group names a user is in.
13737 * users invocation:: Print login names of users currently logged in.
13738 * who invocation:: Print who is currently logged in.
13742 @node id invocation
13743 @section @command{id}: Print user identity
13746 @cindex real user and group IDs, printing
13747 @cindex effective user and group IDs, printing
13748 @cindex printing real and effective user and group IDs
13750 @command{id} prints information about the given user, or the process
13751 running it if no user is specified. Synopsis:
13754 id [@var{option}]@dots{} [@var{username}]
13757 @vindex POSIXLY_CORRECT
13758 By default, it prints the real user ID, real group ID, effective user ID
13759 if different from the real user ID, effective group ID if different from
13760 the real group ID, and supplemental group IDs.
13761 In addition, if SELinux
13762 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13763 then print @samp{context=@var{c}}, where @var{c} is the security context.
13765 Each of these numeric values is preceded by an identifying string and
13766 followed by the corresponding user or group name in parentheses.
13768 The options cause @command{id} to print only part of the above information.
13769 Also see @ref{Common options}.
13776 Print only the group ID.
13782 Print only the group ID and the supplementary groups.
13788 Print the user or group name instead of the ID number. Requires
13789 @option{-u}, @option{-g}, or @option{-G}.
13795 Print the real, instead of effective, user or group ID. Requires
13796 @option{-u}, @option{-g}, or @option{-G}.
13802 Print only the user ID.
13809 @cindex security context
13810 Print only the security context of the current user.
13811 If SELinux is disabled then print a warning and
13812 set the exit status to 1.
13818 @macro primaryAndSupplementaryGroups{cmd,arg}
13819 Primary and supplementary groups for a process are normally inherited
13820 from its parent and are usually unchanged since login. This means
13821 that if you change the group database after logging in, @command{\cmd\}
13822 will not reflect your changes within your existing login session.
13823 Running @command{\cmd\} with a \arg\ causes the user and group
13824 database to be consulted afresh, and so will give a different result.
13826 @primaryAndSupplementaryGroups{id,user argument}
13828 @node logname invocation
13829 @section @command{logname}: Print current login name
13832 @cindex printing user's login name
13833 @cindex login name, printing
13834 @cindex user name, printing
13837 @command{logname} prints the calling user's name, as found in a
13838 system-maintained file (often @file{/var/run/utmp} or
13839 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13840 for the calling process, @command{logname} prints
13841 an error message and exits with a status of 1.
13843 The only options are @option{--help} and @option{--version}. @xref{Common
13849 @node whoami invocation
13850 @section @command{whoami}: Print effective user ID
13853 @cindex effective user ID, printing
13854 @cindex printing the effective user ID
13856 @command{whoami} prints the user name associated with the current
13857 effective user ID. It is equivalent to the command @samp{id -un}.
13859 The only options are @option{--help} and @option{--version}. @xref{Common
13865 @node groups invocation
13866 @section @command{groups}: Print group names a user is in
13869 @cindex printing groups a user is in
13870 @cindex supplementary groups, printing
13872 @command{groups} prints the names of the primary and any supplementary
13873 groups for each given @var{username}, or the current process if no names
13874 are given. If more than one name is given, the name of each user is
13876 the list of that user's groups and the user name is separated from the
13877 group list by a colon. Synopsis:
13880 groups [@var{username}]@dots{}
13883 The group lists are equivalent to the output of the command @samp{id -Gn}.
13885 @primaryAndSupplementaryGroups{groups,list of users}
13887 The only options are @option{--help} and @option{--version}. @xref{Common
13893 @node users invocation
13894 @section @command{users}: Print login names of users currently logged in
13897 @cindex printing current usernames
13898 @cindex usernames, printing current
13900 @cindex login sessions, printing users with
13901 @command{users} prints on a single line a blank-separated list of user
13902 names of users currently logged in to the current host. Each user name
13903 corresponds to a login session, so if a user has more than one login
13904 session, that user's name will appear the same number of times in the
13913 With no @var{file} argument, @command{users} extracts its information from
13914 a system-maintained file (often @file{/var/run/utmp} or
13915 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13916 that file instead. A common choice is @file{/var/log/wtmp}.
13918 The only options are @option{--help} and @option{--version}. @xref{Common
13924 @node who invocation
13925 @section @command{who}: Print who is currently logged in
13928 @cindex printing current user information
13929 @cindex information, about current users
13931 @command{who} prints information about users who are currently logged on.
13935 @command{who} [@var{option}] [@var{file}] [am i]
13938 @cindex terminal lines, currently used
13940 @cindex remote hostname
13941 If given no non-option arguments, @command{who} prints the following
13942 information for each user currently logged on: login name, terminal
13943 line, login time, and remote hostname or X display.
13947 If given one non-option argument, @command{who} uses that instead of
13948 a default system-maintained file (often @file{/var/run/utmp} or
13949 @file{/etc/utmp}) as the name of the file containing the record of
13950 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13951 to @command{who} to look at who has previously logged on.
13955 If given two non-option arguments, @command{who} prints only the entry
13956 for the user running it (determined from its standard input), preceded
13957 by the hostname. Traditionally, the two arguments given are @samp{am
13958 i}, as in @samp{who am i}.
13961 Time stamps are listed according to the time zone rules specified by
13962 the @env{TZ} environment variable, or by the system default rules if
13963 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13964 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13966 The program accepts the following options. Also see @ref{Common options}.
13974 Same as @samp{-b -d --login -p -r -t -T -u}.
13980 Print the date and time of last system boot.
13986 Print information corresponding to dead processes.
13992 Print a line of column headings.
13998 List only the entries that correspond to processes via which the
13999 system is waiting for a user to login. The user name is always @samp{LOGIN}.
14003 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
14004 is not the default because it can cause significant delays on systems with
14005 automatic dial-up internet access.
14009 Same as @samp{who am i}.
14015 List active processes spawned by init.
14021 Print only the login names and the number of users logged on.
14022 Overrides all other options.
14027 @opindex --runlevel
14028 Print the current (and maybe previous) run-level of the init process.
14032 Ignored; for compatibility with other versions of @command{who}.
14038 Print last system clock change.
14043 After the login time, print the number of hours and minutes that the
14044 user has been idle. @samp{.} means the user was active in the last minute.
14045 @samp{old} means the user has been idle for more than 24 hours.
14056 @opindex --writable
14057 @cindex message status
14058 @pindex write@r{, allowed}
14059 After each login name print a character indicating the user's message status:
14062 @samp{+} allowing @code{write} messages
14063 @samp{-} disallowing @code{write} messages
14064 @samp{?} cannot find terminal device
14072 @node System context
14073 @chapter System context
14075 @cindex system context
14076 @cindex context, system
14077 @cindex commands for system context
14079 This section describes commands that print or change system-wide
14083 * date invocation:: Print or set system date and time.
14084 * arch invocation:: Print machine hardware name.
14085 * nproc invocation:: Print the number of processors.
14086 * uname invocation:: Print system information.
14087 * hostname invocation:: Print or set system name.
14088 * hostid invocation:: Print numeric host identifier.
14089 * uptime invocation:: Print system uptime and load.
14092 @node date invocation
14093 @section @command{date}: Print or set system date and time
14096 @cindex time, printing or setting
14097 @cindex printing the current time
14102 date [@var{option}]@dots{} [+@var{format}]
14103 date [-u|--utc|--universal] @c this avoids a newline in the output
14104 [ MMDDhhmm[[CC]YY][.ss] ]
14108 Invoking @command{date} with no @var{format} argument is equivalent to invoking
14109 it with a default format that depends on the @env{LC_TIME} locale category.
14110 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
14111 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
14114 Normally, @command{date} uses the time zone rules indicated by the
14115 @env{TZ} environment variable, or the system default rules if @env{TZ}
14116 is not set. @xref{TZ Variable,, Specifying the Time Zone with
14117 @env{TZ}, libc, The GNU C Library Reference Manual}.
14119 @findex strftime @r{and @command{date}}
14120 @cindex time formats
14121 @cindex formatting times
14122 If given an argument that starts with a @samp{+}, @command{date} prints the
14123 current date and time (or the date and time specified by the
14124 @option{--date} option, see below) in the format defined by that argument,
14125 which is similar to that of the @code{strftime} function. Except for
14126 conversion specifiers, which start with @samp{%}, characters in the
14127 format string are printed unchanged. The conversion specifiers are
14133 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
14134 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
14135 * Literal conversion specifiers:: %[%nt]
14136 * Padding and other flags:: Pad with zeros, spaces, etc.
14137 * Setting the time:: Changing the system clock.
14138 * Options for date:: Instead of the current time.
14140 * Date input formats:: Specifying date strings.
14142 * Examples of date:: Examples.
14145 @node Time conversion specifiers
14146 @subsection Time conversion specifiers
14148 @cindex time conversion specifiers
14149 @cindex conversion specifiers, time
14151 @command{date} conversion specifiers related to times.
14155 hour (@samp{00}@dots{}@samp{23})
14157 hour (@samp{01}@dots{}@samp{12})
14159 hour, space padded (@samp{ 0}@dots{}@samp{23}); equivalent to @samp{%_H}.
14160 This is a @acronym{GNU} extension.
14162 hour, space padded (@samp{ 1}@dots{}@samp{12}); equivalent to @samp{%_I}.
14163 This is a @acronym{GNU} extension.
14165 minute (@samp{00}@dots{}@samp{59})
14167 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
14168 This is a @acronym{GNU} extension.
14170 locale's equivalent of either @samp{AM} or @samp{PM};
14171 blank in many locales.
14172 Noon is treated as @samp{PM} and midnight as @samp{AM}.
14174 like @samp{%p}, except lower case.
14175 This is a @acronym{GNU} extension.
14177 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
14179 24-hour hour and minute. Same as @samp{%H:%M}.
14181 @cindex epoch, seconds since
14182 @cindex seconds since the epoch
14183 @cindex beginning of time
14184 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
14185 Leap seconds are not counted unless leap second support is available.
14186 @xref{%s-examples}, for examples.
14187 This is a @acronym{GNU} extension.
14189 second (@samp{00}@dots{}@samp{60}).
14190 This may be @samp{60} if leap seconds are supported.
14192 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
14194 locale's time representation (e.g., @samp{23:13:48})
14196 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
14197 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
14198 time zone is determinable. This value reflects the numeric time zone
14199 appropriate for the current time, using the time zone rules specified
14200 by the @env{TZ} environment variable.
14201 The time (and optionally, the time zone rules) can be overridden
14202 by the @option{--date} option.
14204 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
14205 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
14206 zone is determinable.
14207 This is a @acronym{GNU} extension.
14209 Numeric time zone to the nearest second with @samp{:} (e.g.,
14210 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
14212 This is a @acronym{GNU} extension.
14214 Numeric time zone with @samp{:} using the minimum necessary precision
14215 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
14216 no time zone is determinable.
14217 This is a @acronym{GNU} extension.
14219 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
14220 time zone is determinable. See @samp{%z} for how it is determined.
14224 @node Date conversion specifiers
14225 @subsection Date conversion specifiers
14227 @cindex date conversion specifiers
14228 @cindex conversion specifiers, date
14230 @command{date} conversion specifiers related to dates.
14234 locale's abbreviated weekday name (e.g., @samp{Sun})
14236 locale's full weekday name, variable length (e.g., @samp{Sunday})
14238 locale's abbreviated month name (e.g., @samp{Jan})
14240 locale's full month name, variable length (e.g., @samp{January})
14242 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
14244 century. This is like @samp{%Y}, except the last two digits are omitted.
14245 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
14246 and is @samp{-0} if @samp{%Y} is @samp{-001}.
14247 It is normally at least two characters, but it may be more.
14249 day of month (e.g., @samp{01})
14251 date; same as @samp{%m/%d/%y}
14253 day of month, space padded; same as @samp{%_d}
14255 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
14256 This is a good choice for a date format, as it is standard and
14257 is easy to sort in the usual case where years are in the range
14260 year corresponding to the @acronym{ISO} week number, but without the century
14261 (range @samp{00} through @samp{99}). This has the same format and value
14262 as @samp{%y}, except that if the @acronym{ISO} week number (see
14264 to the previous or next year, that year is used instead.
14266 year corresponding to the @acronym{ISO} week number. This has the
14267 same format and value as @samp{%Y}, except that if the @acronym{ISO}
14269 @samp{%V}) belongs to the previous or next year, that year is used
14271 It is normally useful only if @samp{%V} is also used;
14272 for example, the format @samp{%G-%m-%d} is probably a mistake,
14273 since it combines the ISO week number year with the conventional month and day.
14277 day of year (@samp{001}@dots{}@samp{366})
14279 month (@samp{01}@dots{}@samp{12})
14281 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
14283 week number of year, with Sunday as the first day of the week
14284 (@samp{00}@dots{}@samp{53}).
14285 Days in a new year preceding the first Sunday are in week zero.
14287 @acronym{ISO} week number, that is, the
14288 week number of year, with Monday as the first day of the week
14289 (@samp{01}@dots{}@samp{53}).
14290 If the week containing January 1 has four or more days in
14291 the new year, then it is considered week 1; otherwise, it is week 53 of
14292 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
14295 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
14297 week number of year, with Monday as first day of week
14298 (@samp{00}@dots{}@samp{53}).
14299 Days in a new year preceding the first Monday are in week zero.
14301 locale's date representation (e.g., @samp{12/31/99})
14303 last two digits of year (@samp{00}@dots{}@samp{99})
14305 year. This is normally at least four characters, but it may be more.
14306 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
14307 precedes year @samp{0000}.
14311 @node Literal conversion specifiers
14312 @subsection Literal conversion specifiers
14314 @cindex literal conversion specifiers
14315 @cindex conversion specifiers, literal
14317 @command{date} conversion specifiers that produce literal strings.
14329 @node Padding and other flags
14330 @subsection Padding and other flags
14332 @cindex numeric field padding
14333 @cindex padding of numeric fields
14334 @cindex fields, padding numeric
14336 Unless otherwise specified, @command{date} normally pads numeric fields
14337 with zeros, so that, for
14338 example, numeric months are always output as two digits.
14339 Seconds since the epoch are not padded, though,
14340 since there is no natural width for them.
14342 As a @acronym{GNU} extension, @command{date} recognizes any of the
14343 following optional flags after the @samp{%}:
14347 (hyphen) Do not pad the field; useful if the output is intended for
14350 (underscore) Pad with spaces; useful if you need a fixed
14351 number of characters in the output, but zeros are too distracting.
14353 (zero) Pad with zeros even if the conversion specifier
14354 would normally pad with spaces.
14356 Use upper case characters if possible.
14358 Use opposite case characters if possible.
14359 A field that is normally upper case becomes lower case, and vice versa.
14363 Here are some examples of padding:
14366 date +%d/%m -d "Feb 1"
14368 date +%-d/%-m -d "Feb 1"
14370 date +%_d/%_m -d "Feb 1"
14374 As a @acronym{GNU} extension, you can specify the field width
14375 (after any flag, if present) as a decimal number. If the natural size of the
14376 output of the field has less than the specified number of characters,
14377 the result is written right adjusted and padded to the given
14378 size. For example, @samp{%9B} prints the right adjusted month name in
14379 a field of width 9.
14381 An optional modifier can follow the optional flag and width
14382 specification. The modifiers are:
14386 Use the locale's alternate representation for date and time. This
14387 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
14388 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
14389 example, @samp{%Ex} might yield a date format based on the Japanese
14393 Use the locale's alternate numeric symbols for numbers. This modifier
14394 applies only to numeric conversion specifiers.
14397 If the format supports the modifier but no alternate representation
14398 is available, it is ignored.
14401 @node Setting the time
14402 @subsection Setting the time
14404 @cindex setting the time
14405 @cindex time setting
14406 @cindex appropriate privileges
14408 If given an argument that does not start with @samp{+}, @command{date} sets
14409 the system clock to the date and time specified by that argument (as
14410 described below). You must have appropriate privileges to set the
14411 system clock. Note for changes to persist across a reboot, the
14412 hardware clock may need to be updated from the system clock, which
14413 might not happen automatically on your system.
14415 The argument must consist entirely of digits, which have the following
14428 first two digits of year (optional)
14430 last two digits of year (optional)
14435 Note, the @option{--date} and @option{--set} options may not be used with an
14436 argument in the above format. The @option{--universal} option may be used
14437 with such an argument to indicate that the specified date and time are
14438 relative to Coordinated Universal Time rather than to the local time zone.
14441 @node Options for date
14442 @subsection Options for @command{date}
14444 @cindex @command{date} options
14445 @cindex options for @command{date}
14447 The program accepts the following options. Also see @ref{Common options}.
14451 @item -d @var{datestr}
14452 @itemx --date=@var{datestr}
14455 @cindex parsing date strings
14456 @cindex date strings, parsing
14457 @cindex arbitrary date strings, parsing
14460 @opindex next @var{day}
14461 @opindex last @var{day}
14462 Display the date and time specified in @var{datestr} instead of the
14463 current date and time. @var{datestr} can be in almost any common
14464 format. It can contain month names, time zones, @samp{am} and @samp{pm},
14465 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
14466 14:19:13.489392193 +0530"} specifies the instant of time that is
14467 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
14468 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
14469 Note: input currently must be in locale independent format. E.g., the
14470 LC_TIME=C below is needed to print back the correct date in many locales:
14472 date -d "$(LC_TIME=C date)"
14474 @xref{Date input formats}.
14476 @item -f @var{datefile}
14477 @itemx --file=@var{datefile}
14480 Parse each line in @var{datefile} as with @option{-d} and display the
14481 resulting date and time. If @var{datefile} is @samp{-}, use standard
14482 input. This is useful when you have many dates to process, because the
14483 system overhead of starting up the @command{date} executable many times can
14486 @item -I[@var{timespec}]
14487 @itemx --iso-8601[=@var{timespec}]
14488 @opindex -I[@var{timespec}]
14489 @opindex --iso-8601[=@var{timespec}]
14490 Display the date using the @acronym{ISO} 8601 format, @samp{%Y-%m-%d}.
14492 The argument @var{timespec} specifies the number of additional
14493 terms of the time to include. It can be one of the following:
14496 Print just the date. This is the default if @var{timespec} is omitted.
14499 Append the hour of the day to the date.
14502 Append the hours and minutes.
14505 Append the hours, minutes and seconds.
14508 Append the hours, minutes, seconds and nanoseconds.
14511 If showing any time terms, then include the time zone using the format
14514 @item -r @var{file}
14515 @itemx --reference=@var{file}
14517 @opindex --reference
14518 Display the date and time of the last modification of @var{file},
14519 instead of the current date and time.
14526 @opindex --rfc-2822
14527 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
14528 %z}, evaluated in the C locale so abbreviations are always in English.
14532 Fri, 09 Sep 2005 13:51:39 -0700
14535 This format conforms to
14536 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
14537 @acronym{RFCs} 2822} and
14538 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
14539 current and previous standards for Internet email.
14541 @item --rfc-3339=@var{timespec}
14542 @opindex --rfc-3339=@var{timespec}
14543 Display the date using a format specified by
14544 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
14545 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
14546 format, except that it also permits applications to use a space rather
14547 than a @samp{T} to separate dates from times. Unlike the other
14548 standard formats, @acronym{RFC} 3339 format is always suitable as
14549 input for the @option{--date} (@option{-d}) and @option{--file}
14550 (@option{-f}) options, regardless of the current locale.
14552 The argument @var{timespec} specifies how much of the time to include.
14553 It can be one of the following:
14557 Print just the full-date, e.g., @samp{2005-09-14}.
14558 This is equivalent to the format @samp{%Y-%m-%d}.
14561 Print the full-date and full-time separated by a space, e.g.,
14562 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
14563 time-offset; here the @samp{+05:30} means that local time is five
14564 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
14565 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
14568 Like @samp{seconds}, but also print nanoseconds, e.g.,
14569 @samp{2005-09-14 00:56:06.998458565+05:30}.
14570 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
14574 @item -s @var{datestr}
14575 @itemx --set=@var{datestr}
14578 Set the date and time to @var{datestr}. See @option{-d} above.
14579 See also @ref{Setting the time}.
14586 @opindex --universal
14587 @cindex Coordinated Universal Time
14589 @cindex Greenwich Mean Time
14592 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
14593 @env{TZ} environment variable were set to the string @samp{UTC0}.
14595 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
14596 historical reasons.
14600 @node Examples of date
14601 @subsection Examples of @command{date}
14603 @cindex examples of @command{date}
14605 Here are a few examples. Also see the documentation for the @option{-d}
14606 option in the previous section.
14611 To print the date of the day before yesterday:
14614 date --date='2 days ago'
14618 To print the date of the day three months and one day hence:
14621 date --date='3 months 1 day'
14625 To print the day of year of Christmas in the current year:
14628 date --date='25 Dec' +%j
14632 To print the current full month name and the day of the month:
14638 But this may not be what you want because for the first nine days of
14639 the month, the @samp{%d} expands to a zero-padded two-digit field,
14640 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14643 To print a date without the leading zero for one-digit days
14644 of the month, you can use the (@acronym{GNU} extension)
14645 @samp{-} flag to suppress
14646 the padding altogether:
14649 date -d 1may '+%B %-d
14653 To print the current date and time in the format required by many
14654 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14657 date +%m%d%H%M%Y.%S
14661 To set the system clock forward by two minutes:
14664 date --set='+2 minutes'
14668 To print the date in @acronym{RFC} 2822 format,
14669 use @samp{date --rfc-2822}. Here is some example output:
14672 Fri, 09 Sep 2005 13:51:39 -0700
14675 @anchor{%s-examples}
14677 To convert a date string to the number of seconds since the epoch
14678 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14679 the @samp{%s} format. That can be useful in sorting and/or graphing
14680 and/or comparing data by date. The following command outputs the
14681 number of the seconds since the epoch for the time two minutes after the
14685 date --date='1970-01-01 00:02:00 +0000' +%s
14689 If you do not specify time zone information in the date string,
14690 @command{date} uses your computer's idea of the time zone when
14691 interpreting the string. For example, if your computer's time zone is
14692 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14693 seconds) behind UTC:
14696 # local time zone used
14697 date --date='1970-01-01 00:02:00' +%s
14702 If you're sorting or graphing dated data, your raw date values may be
14703 represented as seconds since the epoch. But few people can look at
14704 the date @samp{946684800} and casually note ``Oh, that's the first second
14705 of the year 2000 in Greenwich, England.''
14708 date --date='2000-01-01 UTC' +%s
14712 An alternative is to use the @option{--utc} (@option{-u}) option.
14713 Then you may omit @samp{UTC} from the date string. Although this
14714 produces the same result for @samp{%s} and many other format sequences,
14715 with a time zone offset different from zero, it would give a different
14716 result for zone-dependent formats like @samp{%z}.
14719 date -u --date=2000-01-01 +%s
14723 To convert such an unwieldy number of seconds back to
14724 a more readable form, use a command like this:
14727 # local time zone used
14728 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14729 1999-12-31 19:00:00 -0500
14732 Or if you do not mind depending on the @samp{@@} feature present since
14733 coreutils 5.3.0, you could shorten this to:
14736 date -d @@946684800 +"%F %T %z"
14737 1999-12-31 19:00:00 -0500
14740 Often it is better to output UTC-relative date and time:
14743 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14744 2000-01-01 00:00:00 +0000
14750 @node arch invocation
14751 @section @command{arch}: Print machine hardware name
14754 @cindex print machine hardware name
14755 @cindex system information, printing
14757 @command{arch} prints the machine hardware name,
14758 and is equivalent to @samp{uname -m}.
14762 arch [@var{option}]
14765 The program accepts the @ref{Common options} only.
14770 @node nproc invocation
14771 @section @command{nproc}: Print the number of available processors
14774 @cindex Print the number of processors
14775 @cindex system information, printing
14777 Print the number of processing units available to the current process,
14778 which may be less than the number of online processors.
14779 If this information is not accessible, then print the number of
14780 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14781 set, then it will determine the returned value. The result is guaranteed to be
14782 greater than zero. Synopsis:
14785 nproc [@var{option}]
14788 The program accepts the following options. Also see @ref{Common options}.
14794 Print the number of installed processors on the system, which may
14795 be greater than the number online or available to the current process.
14796 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14798 @item --ignore=@var{number}
14800 If possible, exclude this @var{number} of processing units.
14807 @node uname invocation
14808 @section @command{uname}: Print system information
14811 @cindex print system information
14812 @cindex system information, printing
14814 @command{uname} prints information about the machine and operating system
14815 it is run on. If no options are given, @command{uname} acts as if the
14816 @option{-s} option were given. Synopsis:
14819 uname [@var{option}]@dots{}
14822 If multiple options or @option{-a} are given, the selected information is
14823 printed in this order:
14826 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14827 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14830 The information may contain internal spaces, so such output cannot be
14831 parsed reliably. In the following example, @var{release} is
14832 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14836 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686@c
14837 unknown unknown GNU/Linux
14841 The program accepts the following options. Also see @ref{Common options}.
14849 Print all of the below information, except omit the processor type
14850 and the hardware platform name if they are unknown.
14853 @itemx --hardware-platform
14855 @opindex --hardware-platform
14856 @cindex implementation, hardware
14857 @cindex hardware platform
14858 @cindex platform, hardware
14859 Print the hardware platform name
14860 (sometimes called the hardware implementation).
14861 Print @samp{unknown} if the kernel does not make this information
14862 easily available, as is the case with Linux kernels.
14868 @cindex machine type
14869 @cindex hardware class
14870 @cindex hardware type
14871 Print the machine hardware name (sometimes called the hardware class
14877 @opindex --nodename
14880 @cindex network node name
14881 Print the network node hostname.
14886 @opindex --processor
14887 @cindex host processor type
14888 Print the processor type (sometimes called the instruction set
14889 architecture or ISA).
14890 Print @samp{unknown} if the kernel does not make this information
14891 easily available, as is the case with Linux kernels.
14894 @itemx --operating-system
14896 @opindex --operating-system
14897 @cindex operating system name
14898 Print the name of the operating system.
14901 @itemx --kernel-release
14903 @opindex --kernel-release
14904 @cindex kernel release
14905 @cindex release of kernel
14906 Print the kernel release.
14909 @itemx --kernel-name
14911 @opindex --kernel-name
14912 @cindex kernel name
14913 @cindex name of kernel
14914 Print the kernel name.
14915 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14916 ``the implementation of the operating system'', because the
14917 @acronym{POSIX} specification itself has no notion of ``kernel''.
14918 The kernel name might be the same as the operating system name printed
14919 by the @option{-o} or @option{--operating-system} option, but it might
14920 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14921 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14925 @itemx --kernel-version
14927 @opindex --kernel-version
14928 @cindex kernel version
14929 @cindex version of kernel
14930 Print the kernel version.
14937 @node hostname invocation
14938 @section @command{hostname}: Print or set system name
14941 @cindex setting the hostname
14942 @cindex printing the hostname
14943 @cindex system name, printing
14944 @cindex appropriate privileges
14946 With no arguments, @command{hostname} prints the name of the current host
14947 system. With one argument, it sets the current host name to the
14948 specified string. You must have appropriate privileges to set the host
14952 hostname [@var{name}]
14955 The only options are @option{--help} and @option{--version}. @xref{Common
14961 @node hostid invocation
14962 @section @command{hostid}: Print numeric host identifier
14965 @cindex printing the host identifier
14967 @command{hostid} prints the numeric identifier of the current host
14968 in hexadecimal. This command accepts no arguments.
14969 The only options are @option{--help} and @option{--version}.
14970 @xref{Common options}.
14972 For example, here's what it prints on one system I use:
14979 On that system, the 32-bit quantity happens to be closely
14980 related to the system's Internet address, but that isn't always
14985 @node uptime invocation
14986 @section @command{uptime}: Print system uptime and load
14989 @cindex printing the system uptime and load
14991 @command{uptime} prints the current time, the system's uptime, the
14992 number of logged-in users and the current load average.
14994 If an argument is specified, it is used as the file to be read
14995 to discover how many users are logged in. If no argument is
14996 specified, a system default is used (@command{uptime --help} indicates
14997 the default setting).
14999 The only options are @option{--help} and @option{--version}.
15000 @xref{Common options}.
15002 For example, here's what it prints right now on one system I use:
15006 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
15009 The precise method of calculation of load average varies somewhat
15010 between systems. Some systems calculate it as the average number of
15011 runnable processes over the last 1, 5 and 15 minutes, but some systems
15012 also include processes in the uninterruptible sleep state (that is,
15013 those processes which are waiting for disk I/O). The Linux kernel
15014 includes uninterruptible processes.
15016 @node SELinux context
15017 @chapter SELinux context
15019 @cindex SELinux context
15020 @cindex SELinux, context
15021 @cindex commands for SELinux context
15023 This section describes commands for operations with SELinux
15027 * chcon invocation:: Change SELinux context of file
15028 * runcon invocation:: Run a command in specified SELinux context
15031 @node chcon invocation
15032 @section @command{chcon}: Change SELinux context of file
15035 @cindex changing security context
15036 @cindex change SELinux context
15038 @command{chcon} changes the SELinux security context of the selected files.
15042 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
15043 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}]@c
15044 [-t @var{type}] @var{file}@dots{}
15045 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
15048 Change the SELinux security context of each @var{file} to @var{context}.
15049 With @option{--reference}, change the security context of each @var{file}
15050 to that of @var{rfile}.
15052 The program accepts the following options. Also see @ref{Common options}.
15057 @itemx --no-dereference
15059 @opindex --no-dereference
15060 @cindex no dereference
15061 Affect symbolic links instead of any referenced file.
15063 @item --reference=@var{rfile}
15064 @opindex --reference
15065 @cindex reference file
15066 Use @var{rfile}'s security context rather than specifying a @var{context} value.
15071 @opindex --recursive
15072 Operate on files and directories recursively.
15075 @xref{Traversing symlinks}.
15078 @xref{Traversing symlinks}.
15081 @xref{Traversing symlinks}.
15088 Output a diagnostic for every file processed.
15090 @item -u @var{user}
15091 @itemx --user=@var{user}
15094 Set user @var{user} in the target security context.
15096 @item -r @var{role}
15097 @itemx --role=@var{role}
15100 Set role @var{role} in the target security context.
15102 @item -t @var{type}
15103 @itemx --type=@var{type}
15106 Set type @var{type} in the target security context.
15108 @item -l @var{range}
15109 @itemx --range=@var{range}
15112 Set range @var{range} in the target security context.
15118 @node runcon invocation
15119 @section @command{runcon}: Run a command in specified SELinux context
15122 @cindex run with security context
15125 @command{runcon} runs file in specified SELinux security context.
15129 runcon @var{context} @var{command} [@var{args}]
15130 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}]@c
15131 [-l @var{range}] @var{command} [@var{args}]
15134 Run @var{command} with completely-specified @var{context}, or with
15135 current or transitioned security context modified by one or more of @var{level},
15136 @var{role}, @var{type} and @var{user}.
15138 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
15139 is specified, the first argument is used as the complete context.
15140 Any additional arguments after @var{command}
15141 are interpreted as arguments to the command.
15143 With neither @var{context} nor @var{command}, print the current
15146 The program accepts the following options. Also see @ref{Common options}.
15154 Compute process transition context before modifying.
15156 @item -u @var{user}
15157 @itemx --user=@var{user}
15160 Set user @var{user} in the target security context.
15162 @item -r @var{role}
15163 @itemx --role=@var{role}
15166 Set role @var{role} in the target security context.
15168 @item -t @var{type}
15169 @itemx --type=@var{type}
15172 Set type @var{type} in the target security context.
15174 @item -l @var{range}
15175 @itemx --range=@var{range}
15178 Set range @var{range} in the target security context.
15182 @cindex exit status of @command{runcon}
15186 126 if @var{command} is found but cannot be invoked
15187 127 if @command{runcon} itself fails or if @var{command} cannot be found
15188 the exit status of @var{command} otherwise
15191 @node Modified command invocation
15192 @chapter Modified command invocation
15194 @cindex modified command invocation
15195 @cindex invocation of commands, modified
15196 @cindex commands for invoking other commands
15198 This section describes commands that run other commands in some context
15199 different than the current one: a modified environment, as a different
15203 * chroot invocation:: Modify the root directory.
15204 * env invocation:: Modify environment variables.
15205 * nice invocation:: Modify niceness.
15206 * nohup invocation:: Immunize to hangups.
15207 * stdbuf invocation:: Modify buffering of standard streams.
15208 * su invocation:: Modify user and group ID.
15209 * timeout invocation:: Run with time limit.
15213 @node chroot invocation
15214 @section @command{chroot}: Run a command with a different root directory
15217 @cindex running a program in a specified root directory
15218 @cindex root directory, running a program in a specified
15220 @command{chroot} runs a command with a specified root directory.
15221 On many systems, only the super-user can do this.@footnote{However,
15222 some systems (e.g., FreeBSD) can be configured to allow certain regular
15223 users to use the @code{chroot} system call, and hence to run this program.
15224 Also, on Cygwin, anyone can run the @command{chroot} command, because the
15225 underlying function is non-privileged due to lack of support in MS-Windows.}
15229 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
15230 chroot @var{option}
15233 Ordinarily, file names are looked up starting at the root of the
15234 directory structure, i.e., @file{/}. @command{chroot} changes the root to
15235 the directory @var{newroot} (which must exist) and then runs
15236 @var{command} with optional @var{args}. If @var{command} is not
15237 specified, the default is the value of the @env{SHELL} environment
15238 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
15239 @var{command} must not be a special built-in utility
15240 (@pxref{Special built-in utilities}).
15242 The program accepts the following options. Also see @ref{Common options}.
15243 Options must precede operands.
15247 @itemx --userspec=@var{user}[:@var{group}]
15248 @opindex --userspec
15249 By default, @var{command} is run with the same credentials
15250 as the invoking process.
15251 Use this option to run it as a different @var{user} and/or with a
15252 different primary @var{group}.
15254 @itemx --groups=@var{groups}
15256 Use this option to specify the supplementary @var{groups} to be
15257 used by the new process.
15258 The items in the list (names or numeric IDs) must be separated by commas.
15262 Here are a few tips to help avoid common problems in using chroot.
15263 To start with a simple example, make @var{command} refer to a statically
15264 linked binary. If you were to use a dynamically linked executable, then
15265 you'd have to arrange to have the shared libraries in the right place under
15266 your new root directory.
15268 For example, if you create a statically linked @command{ls} executable,
15269 and put it in @file{/tmp/empty}, you can run this command as root:
15272 $ chroot /tmp/empty /ls -Rl /
15275 Then you'll see output like this:
15280 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
15283 If you want to use a dynamically linked executable, say @command{bash},
15284 then first run @samp{ldd bash} to see what shared objects it needs.
15285 Then, in addition to copying the actual binary, also copy the listed
15286 files to the required positions under your intended new root directory.
15287 Finally, if the executable requires any other files (e.g., data, state,
15288 device files), copy them into place, too.
15290 @cindex exit status of @command{chroot}
15294 125 if @command{chroot} itself fails
15295 126 if @var{command} is found but cannot be invoked
15296 127 if @var{command} cannot be found
15297 the exit status of @var{command} otherwise
15301 @node env invocation
15302 @section @command{env}: Run a command in a modified environment
15305 @cindex environment, running a program in a modified
15306 @cindex modified environment, running a program in a
15307 @cindex running a program in a modified environment
15309 @command{env} runs a command with a modified environment. Synopses:
15312 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
15313 [@var{command} [@var{args}]@dots{}]
15317 Operands of the form @samp{@var{variable}=@var{value}} set
15318 the environment variable @var{variable} to value @var{value}.
15319 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
15320 to an empty value is different from unsetting it.
15321 These operands are evaluated left-to-right, so if two operands
15322 mention the same variable the earlier is ignored.
15324 Environment variable names can be empty, and can contain any
15325 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
15326 However, it is wise to limit yourself to names that
15327 consist solely of underscores, digits, and @acronym{ASCII} letters,
15328 and that begin with a non-digit, as applications like the shell do not
15329 work well with other names.
15332 The first operand that does not contain the character @samp{=}
15333 specifies the program to invoke; it is
15334 searched for according to the @env{PATH} environment variable. Any
15335 remaining arguments are passed as arguments to that program.
15336 The program should not be a special built-in utility
15337 (@pxref{Special built-in utilities}).
15339 Modifications to @env{PATH} take effect prior to searching for
15340 @var{command}. Use caution when reducing @env{PATH}; behavior is
15341 not portable when @env{PATH} is undefined or omits key directories
15342 such as @file{/bin}.
15344 In the rare case that a utility contains a @samp{=} in the name, the
15345 only way to disambiguate it from a variable assignment is to use an
15346 intermediate command for @var{command}, and pass the problematic
15347 program name via @var{args}. For example, if @file{./prog=} is an
15348 executable in the current @env{PATH}:
15351 env prog= true # runs 'true', with prog= in environment
15352 env ./prog= true # runs 'true', with ./prog= in environment
15353 env -- prog= true # runs 'true', with prog= in environment
15354 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
15355 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
15358 @cindex environment, printing
15360 If no command name is specified following the environment
15361 specifications, the resulting environment is printed. This is like
15362 specifying the @command{printenv} program.
15364 For some examples, suppose the environment passed to @command{env}
15365 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
15366 @samp{PATH=.:/gnubin:/hacks}:
15371 Output the current environment.
15373 $ env | LC_ALL=C sort
15376 PATH=.:/gnubin:/hacks
15380 Run @command{foo} with a reduced environment, preserving only the
15381 original @env{PATH} to avoid problems in locating @command{foo}.
15383 env - PATH="$PATH" foo
15387 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
15388 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
15389 that @command{foo} was found in the file system rather than as a shell
15396 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
15397 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
15398 @samp{DISPLAY=gnu:0}.
15400 env DISPLAY=gnu:0 LOGNAME=foo nemacs
15404 Attempt to run the program @command{/energy/--} (as that is the only
15405 possible path search result); if the command exists, the environment
15406 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
15407 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
15409 env -u EDITOR PATH=/energy -- e=mc2 bar baz
15415 The program accepts the following options. Also see @ref{Common options}.
15416 Options must precede operands.
15422 @item -u @var{name}
15423 @itemx --unset=@var{name}
15426 Remove variable @var{name} from the environment, if it was in the
15431 @itemx --ignore-environment
15434 @opindex --ignore-environment
15435 Start with an empty environment, ignoring the inherited environment.
15439 @cindex exit status of @command{env}
15443 0 if no @var{command} is specified and the environment is output
15444 125 if @command{env} itself fails
15445 126 if @var{command} is found but cannot be invoked
15446 127 if @var{command} cannot be found
15447 the exit status of @var{command} otherwise
15451 @node nice invocation
15452 @section @command{nice}: Run a command with modified niceness
15456 @cindex scheduling, affecting
15457 @cindex appropriate privileges
15459 @command{nice} prints or modifies a process's @dfn{niceness},
15460 a parameter that affects whether the process is scheduled favorably.
15464 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
15467 If no arguments are given, @command{nice} prints the current niceness.
15468 Otherwise, @command{nice} runs the given @var{command} with its
15469 niceness adjusted. By default, its niceness is incremented by 10.
15471 Niceness values range at least from @minus{}20 (process has high priority
15472 and gets more resources, thus slowing down other processes) through 19
15473 (process has lower priority and runs slowly itself, but has less impact
15474 on the speed of other running processes). Some systems
15475 may have a wider range of nicenesses; conversely, other systems may
15476 enforce more restrictive limits. An attempt to set the niceness
15477 outside the supported range is treated as an attempt to use the
15478 minimum or maximum supported value.
15480 A niceness should not be confused with a scheduling priority, which
15481 lets applications determine the order in which threads are scheduled
15482 to run. Unlike a priority, a niceness is merely advice to the
15483 scheduler, which the scheduler is free to ignore. Also, as a point of
15484 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
15485 terms of a @dfn{nice value}, which is the nonnegative difference
15486 between a niceness and the minimum niceness. Though @command{nice}
15487 conforms to @acronym{POSIX}, its documentation and diagnostics use the
15488 term ``niceness'' for compatibility with historical practice.
15490 @var{command} must not be a special built-in utility (@pxref{Special
15491 built-in utilities}).
15493 @mayConflictWithShellBuiltIn{nice}
15495 The program accepts the following option. Also see @ref{Common options}.
15496 Options must precede operands.
15499 @item -n @var{adjustment}
15500 @itemx --adjustment=@var{adjustment}
15502 @opindex --adjustment
15503 Add @var{adjustment} instead of 10 to the command's niceness. If
15504 @var{adjustment} is negative and you lack appropriate privileges,
15505 @command{nice} issues a warning but otherwise acts as if you specified
15508 For compatibility @command{nice} also supports an obsolete
15509 option syntax @option{-@var{adjustment}}. New scripts should use
15510 @option{-n @var{adjustment}} instead.
15514 @cindex exit status of @command{nice}
15518 0 if no @var{command} is specified and the niceness is output
15519 125 if @command{nice} itself fails
15520 126 if @var{command} is found but cannot be invoked
15521 127 if @var{command} cannot be found
15522 the exit status of @var{command} otherwise
15525 It is sometimes useful to run a non-interactive program with reduced niceness.
15528 $ nice factor 4611686018427387903
15531 Since @command{nice} prints the current niceness,
15532 you can invoke it through itself to demonstrate how it works.
15534 The default behavior is to increase the niceness by @samp{10}:
15545 The @var{adjustment} is relative to the current niceness. In the
15546 next example, the first @command{nice} invocation runs the second one
15547 with niceness 10, and it in turn runs the final one with a niceness
15551 $ nice nice -n 3 nice
15555 Specifying a niceness larger than the supported range
15556 is the same as specifying the maximum supported value:
15559 $ nice -n 10000000000 nice
15563 Only a privileged user may run a process with lower niceness:
15567 nice: cannot set niceness: Permission denied
15569 $ sudo nice -n -1 nice
15574 @node nohup invocation
15575 @section @command{nohup}: Run a command immune to hangups
15578 @cindex hangups, immunity to
15579 @cindex immunity to hangups
15580 @cindex logging out and continuing to run
15583 @command{nohup} runs the given @var{command} with hangup signals ignored,
15584 so that the command can continue running in the background after you log
15588 nohup @var{command} [@var{arg}]@dots{}
15591 If standard input is a terminal, it is redirected from
15592 @file{/dev/null} so that terminal sessions do not mistakenly consider
15593 the terminal to be used by the command. This is a @acronym{GNU}
15594 extension; programs intended to be portable to non-@acronym{GNU} hosts
15595 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
15599 If standard output is a terminal, the command's standard output is appended
15600 to the file @file{nohup.out}; if that cannot be written to, it is appended
15601 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
15602 command is not run.
15603 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
15604 @command{nohup} is made readable and writable only to the user,
15605 regardless of the current umask settings.
15607 If standard error is a terminal, it is normally redirected to the same file
15608 descriptor as the (possibly-redirected) standard output.
15609 However, if standard output is closed, standard error terminal output
15610 is instead appended to the file @file{nohup.out} or
15611 @file{$HOME/nohup.out} as above.
15613 To capture the command's output to a file other than @file{nohup.out}
15614 you can redirect it. For example, to capture the output of
15618 nohup make > make.log
15621 @command{nohup} does not automatically put the command it runs in the
15622 background; you must do that explicitly, by ending the command line
15623 with an @samp{&}. Also, @command{nohup} does not alter the
15624 niceness of @var{command}; use @command{nice} for that,
15625 e.g., @samp{nohup nice @var{command}}.
15627 @var{command} must not be a special built-in utility (@pxref{Special
15628 built-in utilities}).
15630 The only options are @option{--help} and @option{--version}. @xref{Common
15631 options}. Options must precede operands.
15633 @cindex exit status of @command{nohup}
15637 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
15638 126 if @var{command} is found but cannot be invoked
15639 127 if @var{command} cannot be found
15640 the exit status of @var{command} otherwise
15643 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15647 @node stdbuf invocation
15648 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15651 @cindex standard streams, buffering
15652 @cindex line buffered
15654 @command{stdbuf} allows one to modify the buffering operations of the
15655 three standard I/O streams associated with a program. Synopsis:
15658 stdbuf @var{option}@dots{} @var{command}
15661 @var{command} must start with the name of a program that
15664 uses the ISO C @code{FILE} streams for input/output (note the
15665 programs @command{dd} and @command{cat} don't do that),
15668 does not adjust the buffering of its standard streams (note the
15669 program @command{tee} is not in this category).
15672 Any additional @var{arg}s are passed as additional arguments to the
15675 The program accepts the following options. Also see @ref{Common options}.
15679 @item -i @var{mode}
15680 @itemx --input=@var{mode}
15683 Adjust the standard input stream buffering.
15685 @item -o @var{mode}
15686 @itemx --output=@var{mode}
15689 Adjust the standard output stream buffering.
15691 @item -e @var{mode}
15692 @itemx --error=@var{mode}
15695 Adjust the standard error stream buffering.
15699 The @var{mode} can be specified as follows:
15704 Set the stream to line buffered mode.
15705 In this mode data is coalesced until a newline is output or
15706 input is read from any stream attached to a terminal device.
15707 This option is invalid with standard input.
15710 Disable buffering of the selected stream.
15711 In this mode, data is output immediately and only the
15712 amount of data requested is read from input.
15713 Note the difference in function for input and output.
15714 Disabling buffering for input will not influence the responsiveness
15715 or blocking behavior of the stream input functions.
15716 For example @code{fread} will still block until @code{EOF} or error,
15717 even if the underlying @code{read} returns less data than requested.
15720 Specify the size of the buffer to use in fully buffered mode.
15721 @multiplierSuffixesNoBlocks{size}
15725 @cindex exit status of @command{stdbuf}
15729 125 if @command{stdbuf} itself fails
15730 126 if @var{command} is found but cannot be invoked
15731 127 if @var{command} cannot be found
15732 the exit status of @var{command} otherwise
15736 @node su invocation
15737 @section @command{su}: Run a command with substitute user and group ID
15740 @cindex substitute user and group IDs
15741 @cindex user ID, switching
15742 @cindex super-user, becoming
15743 @cindex root, becoming
15745 @command{su} allows one user to temporarily become another user. It runs a
15746 command (often an interactive shell) with the real and effective user
15747 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15750 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15753 @cindex passwd entry, and @command{su} shell
15755 @flindex /etc/passwd
15756 If no @var{user} is given, the default is @code{root}, the super-user.
15757 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15758 @file{/bin/sh} if none is specified there. If @var{user} has a
15759 password, @command{su} prompts for the password unless run by a user with
15760 effective user ID of zero (the super-user).
15766 @cindex login shell
15767 By default, @command{su} does not change the current directory.
15768 It sets the environment variables @env{HOME} and @env{SHELL}
15769 from the password entry for @var{user}, and if @var{user} is not
15770 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15771 By default, the shell is not a login shell.
15773 Any additional @var{arg}s are passed as additional arguments to the
15776 @cindex @option{-su}
15777 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15778 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15779 to certain shells, etc.).
15782 @command{su} can optionally be compiled to use @code{syslog} to report
15783 failed, and optionally successful, @command{su} attempts. (If the system
15784 supports @code{syslog}.) However, GNU @command{su} does not check if the
15785 user is a member of the @code{wheel} group; see below.
15787 The program accepts the following options. Also see @ref{Common options}.
15790 @item -c @var{command}
15791 @itemx --command=@var{command}
15794 Pass @var{command}, a single command line to run, to the shell with
15795 a @option{-c} option instead of starting an interactive shell.
15802 @cindex file name pattern expansion, disabled
15803 @cindex globbing, disabled
15804 Pass the @option{-f} option to the shell. This probably only makes sense
15805 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15806 option prevents reading the startup file (@file{.cshrc}). With
15807 Bourne-like shells, the @option{-f} option disables file name pattern
15808 expansion (globbing), which is not likely to be useful.
15816 @c other variables already indexed above
15819 @cindex login shell, creating
15820 Make the shell a login shell. This means the following. Unset all
15821 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15822 (which are set as described above), and @env{USER} and @env{LOGNAME}
15823 (which are set, even for the super-user, as described above), and set
15824 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15825 directory. Prepend @samp{-} to the shell's name, intended to make it
15826 read its login startup file(s).
15830 @itemx --preserve-environment
15833 @opindex --preserve-environment
15834 @cindex environment, preserving
15835 @flindex /etc/shells
15836 @cindex restricted shell
15837 Do not change the environment variables @env{HOME}, @env{USER},
15838 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15839 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15840 entry, unless the user running @command{su} is not the super-user and
15841 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15842 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15843 if that file does not exist. Parts of what this option does can be
15844 overridden by @option{--login} and @option{--shell}.
15846 @item -s @var{shell}
15847 @itemx --shell=@var{shell}
15850 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15851 unless the user running @command{su} is not the super-user and @var{user}'s
15852 shell is restricted (see @option{-m} just above).
15856 @cindex exit status of @command{su}
15860 125 if @command{su} itself fails
15861 126 if subshell is found but cannot be invoked
15862 127 if subshell cannot be found
15863 the exit status of the subshell otherwise
15866 @cindex wheel group, not supported
15867 @cindex group wheel, not supported
15869 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15871 (This section is by Richard Stallman.)
15875 Sometimes a few of the users try to hold total power over all the
15876 rest. For example, in 1984, a few users at the MIT AI lab decided to
15877 seize power by changing the operator password on the Twenex system and
15878 keeping it secret from everyone else. (I was able to thwart this coup
15879 and give power back to the users by patching the kernel, but I
15880 wouldn't know how to do that in Unix.)
15882 However, occasionally the rulers do tell someone. Under the usual
15883 @command{su} mechanism, once someone learns the root password who
15884 sympathizes with the ordinary users, he or she can tell the rest. The
15885 ``wheel group'' feature would make this impossible, and thus cement the
15886 power of the rulers.
15888 I'm on the side of the masses, not that of the rulers. If you are
15889 used to supporting the bosses and sysadmins in whatever they do, you
15890 might find this idea strange at first.
15893 @node timeout invocation
15894 @section @command{timeout}: Run a command with a time limit
15898 @cindex run commands with bounded time
15900 @command{timeout} runs the given @var{command} and kills it if it is
15901 still running after the specified time interval. Synopsis:
15904 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15907 @var{command} must not be a special built-in utility (@pxref{Special
15908 built-in utilities}).
15910 The program accepts the following options. Also see @ref{Common options}.
15911 Options must precede operands.
15914 @itemx --foreground
15915 @opindex --foreground
15916 Don't create a separate background program group, so that
15917 the managed @var{command} can use the foreground TTY normally.
15918 This is needed to support timing out commands not started
15919 directly from an interactive shell, in two situations.
15922 @var{command} is interactive and needs to read from the terminal for example
15924 the user wants to support sending signals directly to @var{command}
15925 from the terminal (like Ctrl-C for example)
15928 Note in this mode of operation, any children of @var{command}
15929 will not be timed out.
15931 @item -k @var{duration}
15932 @itemx --kill-after=@var{duration}
15934 @opindex --kill-after
15935 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15936 signal, after the specified @var{duration}. Without this option, if the
15937 selected signal proves not to be fatal, @command{timeout} does not kill
15940 @item -s @var{signal}
15941 @itemx --signal=@var{signal}
15944 Send this @var{signal} to @var{command} on timeout, rather than the
15945 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15946 or a number. Also see @xref{Signal specifications}.
15950 @var{duration} is a floating point number followed by an optional unit:
15952 @samp{s} for seconds (the default)
15953 @samp{m} for minutes
15957 A duration of 0 disables the associated timeout.
15958 Note that the actual timeout duration is dependent on system conditions,
15959 which should be especially considered when specifying sub-second timeouts.
15961 @cindex exit status of @command{timeout}
15965 124 if @var{command} times out
15966 125 if @command{timeout} itself fails
15967 126 if @var{command} is found but cannot be invoked
15968 127 if @var{command} cannot be found
15969 137 if @var{command} is sent the KILL(9) signal (128+9)
15970 the exit status of @var{command} otherwise
15974 @node Process control
15975 @chapter Process control
15977 @cindex processes, commands for controlling
15978 @cindex commands for controlling processes
15981 * kill invocation:: Sending a signal to processes.
15985 @node kill invocation
15986 @section @command{kill}: Send a signal to processes
15989 @cindex send a signal to processes
15991 The @command{kill} command sends a signal to processes, causing them
15992 to terminate or otherwise act upon receiving the signal in some way.
15993 Alternatively, it lists information about signals. Synopses:
15996 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15997 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
16000 @mayConflictWithShellBuiltIn{kill}
16002 The first form of the @command{kill} command sends a signal to all
16003 @var{pid} arguments. The default signal to send if none is specified
16004 is @samp{TERM}. The special signal number @samp{0} does not denote a
16005 valid signal, but can be used to test whether the @var{pid} arguments
16006 specify processes to which a signal could be sent.
16008 If @var{pid} is positive, the signal is sent to the process with the
16009 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
16010 processes in the process group of the current process. If @var{pid}
16011 is @minus{}1, the signal is sent to all processes for which the user has
16012 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
16013 is sent to all processes in the process group that equals the absolute
16014 value of @var{pid}.
16016 If @var{pid} is not positive, a system-dependent set of system
16017 processes is excluded from the list of processes to which the signal
16020 If a negative @var{pid} argument is desired as the first one, it
16021 should be preceded by @option{--}. However, as a common extension to
16022 @acronym{POSIX}, @option{--} is not required with @samp{kill
16023 -@var{signal} -@var{pid}}. The following commands are equivalent:
16032 The first form of the @command{kill} command succeeds if every @var{pid}
16033 argument specifies at least one process that the signal was sent to.
16035 The second form of the @command{kill} command lists signal information.
16036 Either the @option{-l} or @option{--list} option, or the @option{-t}
16037 or @option{--table} option must be specified. Without any
16038 @var{signal} argument, all supported signals are listed. The output
16039 of @option{-l} or @option{--list} is a list of the signal names, one
16040 per line; if @var{signal} is already a name, the signal number is
16041 printed instead. The output of @option{-t} or @option{--table} is a
16042 table of signal numbers, names, and descriptions. This form of the
16043 @command{kill} command succeeds if all @var{signal} arguments are valid
16044 and if there is no output error.
16046 The @command{kill} command also supports the @option{--help} and
16047 @option{--version} options. @xref{Common options}.
16049 A @var{signal} may be a signal name like @samp{HUP}, or a signal
16050 number like @samp{1}, or an exit status of a process terminated by the
16051 signal. A signal name can be given in canonical form or prefixed by
16052 @samp{SIG}. The case of the letters is ignored, except for the
16053 @option{-@var{signal}} option which must use upper case to avoid
16054 ambiguity with lower case option letters. For a list of supported
16055 signal names and numbers see @xref{Signal specifications}.
16060 @cindex delaying commands
16061 @cindex commands for delaying
16063 @c Perhaps @command{wait} or other commands should be described here also?
16066 * sleep invocation:: Delay for a specified time.
16070 @node sleep invocation
16071 @section @command{sleep}: Delay for a specified time
16074 @cindex delay for a specified time
16076 @command{sleep} pauses for an amount of time specified by the sum of
16077 the values of the command line arguments.
16081 sleep @var{number}[smhd]@dots{}
16085 Each argument is a number followed by an optional unit; the default
16086 is seconds. The units are:
16099 Historical implementations of @command{sleep} have required that
16100 @var{number} be an integer, and only accepted a single argument
16101 without a suffix. However, GNU @command{sleep} accepts
16102 arbitrary floating point numbers. @xref{Floating point}.
16104 The only options are @option{--help} and @option{--version}. @xref{Common
16107 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
16108 @mayConflictWithShellBuiltIn{sleep}
16113 @node Numeric operations
16114 @chapter Numeric operations
16116 @cindex numeric operations
16117 These programs do numerically-related operations.
16120 * factor invocation:: Show factors of numbers.
16121 * seq invocation:: Print sequences of numbers.
16125 @node factor invocation
16126 @section @command{factor}: Print prime factors
16129 @cindex prime factors
16131 @command{factor} prints prime factors. Synopses:
16134 factor [@var{number}]@dots{}
16135 factor @var{option}
16138 If no @var{number} is specified on the command line, @command{factor} reads
16139 numbers from standard input, delimited by newlines, tabs, or spaces.
16141 The @command{factor} command supports only a small number of options:
16145 Print a short help on standard output, then exit without further
16149 Print the program version on standard output, then exit without further
16153 Factoring the product of the eighth and ninth Mersenne primes
16154 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
16157 M8=$(echo 2^31-1|bc)
16158 M9=$(echo 2^61-1|bc)
16159 n=$(echo "$M8 * $M9" | bc)
16160 /usr/bin/time -f %U factor $n
16161 4951760154835678088235319297: 2147483647 2305843009213693951
16165 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
16166 about 20 seconds on the same machine.
16168 Factoring large numbers is, in general, hard. The Pollard Rho
16169 algorithm used by @command{factor} is particularly effective for
16170 numbers with relatively small factors. If you wish to factor large
16171 numbers which do not have small factors (for example, numbers which
16172 are the product of two large primes), other methods are far better.
16174 If @command{factor} is built without using GNU MP, only
16175 single-precision arithmetic is available, and so large numbers
16176 (typically @math{2^{64}} and above) will not be supported. The single-precision
16177 code uses an algorithm which is designed for factoring smaller
16183 @node seq invocation
16184 @section @command{seq}: Print numeric sequences
16187 @cindex numeric sequences
16188 @cindex sequence of numbers
16190 @command{seq} prints a sequence of numbers to standard output. Synopses:
16193 seq [@var{option}]@dots{} @var{last}
16194 seq [@var{option}]@dots{} @var{first} @var{last}
16195 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
16198 @command{seq} prints the numbers from @var{first} to @var{last} by
16199 @var{increment}. By default, each number is printed on a separate line.
16200 When @var{increment} is not specified, it defaults to @samp{1},
16201 even when @var{first} is larger than @var{last}.
16202 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
16203 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
16204 Floating-point numbers may be specified. @xref{Floating point}.
16206 The program accepts the following options. Also see @ref{Common options}.
16207 Options must precede operands.
16210 @item -f @var{format}
16211 @itemx --format=@var{format}
16212 @opindex -f @var{format}
16213 @opindex --format=@var{format}
16214 @cindex formatting of numbers in @command{seq}
16215 Print all numbers using @var{format}.
16216 @var{format} must contain exactly one of the @samp{printf}-style
16217 floating point conversion specifications @samp{%a}, @samp{%e},
16218 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
16219 The @samp{%} may be followed by zero or more flags taken from the set
16220 @samp{-+#0 '}, then an optional width containing one or more digits,
16221 then an optional precision consisting of a @samp{.} followed by zero
16222 or more digits. @var{format} may also contain any number of @samp{%%}
16223 conversion specifications. All conversion specifications have the
16224 same meaning as with @samp{printf}.
16226 The default format is derived from @var{first}, @var{step}, and
16227 @var{last}. If these all use a fixed point decimal representation,
16228 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
16229 precision that can represent the output numbers exactly. Otherwise,
16230 the default format is @samp{%g}.
16232 @item -s @var{string}
16233 @itemx --separator=@var{string}
16234 @cindex separator for numbers in @command{seq}
16235 Separate numbers with @var{string}; default is a newline.
16236 The output always terminates with a newline.
16239 @itemx --equal-width
16240 Print all numbers with the same width, by padding with leading zeros.
16241 @var{first}, @var{step}, and @var{last} should all use a fixed point
16242 decimal representation.
16243 (To have other kinds of padding, use @option{--format}).
16247 You can get finer-grained control over output with @option{-f}:
16250 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
16256 If you want hexadecimal integer output, you can use @command{printf}
16257 to perform the conversion:
16260 $ printf '%x\n' `seq 1048575 1024 1050623`
16266 For very long lists of numbers, use xargs to avoid
16267 system limitations on the length of an argument list:
16270 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
16276 To generate octal output, use the printf @code{%o} format instead
16279 On most systems, seq can produce whole-number output for values up to
16280 at least @math{2^{53}}. Larger integers are approximated. The details
16281 differ depending on your floating-point implementation.
16282 @xref{Floating point}. A common
16283 case is that @command{seq} works with integers through @math{2^{64}},
16284 and larger integers may not be numerically correct:
16287 $ seq 18446744073709551616 1 18446744073709551618
16288 18446744073709551616
16289 18446744073709551616
16290 18446744073709551618
16293 Be careful when using @command{seq} with outlandish values: otherwise
16294 you may see surprising results, as @command{seq} uses floating point
16295 internally. For example, on the x86 platform, where the internal
16296 representation uses a 64-bit fraction, the command:
16299 seq 1 0.0000000000000000001 1.0000000000000000009
16302 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
16307 @node File permissions
16308 @chapter File permissions
16311 @include parse-datetime.texi
16315 @node Opening the software toolbox
16316 @chapter Opening the Software Toolbox
16318 An earlier version of this chapter appeared in
16319 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
16320 @cite{What's GNU?} column of the June 1994 @cite{Linux Journal}}.
16321 It was written by Arnold Robbins.
16324 * Toolbox introduction:: Toolbox introduction
16325 * I/O redirection:: I/O redirection
16326 * The who command:: The @command{who} command
16327 * The cut command:: The @command{cut} command
16328 * The sort command:: The @command{sort} command
16329 * The uniq command:: The @command{uniq} command
16330 * Putting the tools together:: Putting the tools together
16334 @node Toolbox introduction
16335 @unnumberedsec Toolbox Introduction
16337 This month's column is only peripherally related to the GNU Project, in
16338 that it describes a number of the GNU tools on your GNU/Linux system
16340 might be used. What it's really about is the ``Software Tools'' philosophy
16341 of program development and usage.
16343 The software tools philosophy was an important and integral concept
16344 in the initial design and development of Unix (of which Linux and GNU are
16345 essentially clones). Unfortunately, in the modern day press of
16346 Internetworking and flashy GUIs, it seems to have fallen by the
16347 wayside. This is a shame, since it provides a powerful mental model
16348 for solving many kinds of problems.
16350 Many people carry a Swiss Army knife around in their pants pockets (or
16351 purse). A Swiss Army knife is a handy tool to have: it has several knife
16352 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
16353 a number of other things on it. For the everyday, small miscellaneous jobs
16354 where you need a simple, general purpose tool, it's just the thing.
16356 On the other hand, an experienced carpenter doesn't build a house using
16357 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
16358 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
16359 exactly when and where to use each tool; you won't catch him hammering nails
16360 with the handle of his screwdriver.
16362 The Unix developers at Bell Labs were all professional programmers and trained
16363 computer scientists. They had found that while a one-size-fits-all program
16364 might appeal to a user because there's only one program to use, in practice
16369 difficult to write,
16372 difficult to maintain and
16376 difficult to extend to meet new situations.
16379 Instead, they felt that programs should be specialized tools. In short, each
16380 program ``should do one thing well.'' No more and no less. Such programs are
16381 simpler to design, write, and get right---they only do one thing.
16383 Furthermore, they found that with the right machinery for hooking programs
16384 together, that the whole was greater than the sum of the parts. By combining
16385 several special purpose programs, you could accomplish a specific task
16386 that none of the programs was designed for, and accomplish it much more
16387 quickly and easily than if you had to write a special purpose program.
16388 We will see some (classic) examples of this further on in the column.
16389 (An important additional point was that, if necessary, take a detour
16390 and build any software tools you may need first, if you don't already
16391 have something appropriate in the toolbox.)
16393 @node I/O redirection
16394 @unnumberedsec I/O Redirection
16396 Hopefully, you are familiar with the basics of I/O redirection in the
16397 shell, in particular the concepts of ``standard input,'' ``standard output,''
16398 and ``standard error''. Briefly, ``standard input'' is a data source, where
16399 data comes from. A program should not need to either know or care if the
16400 data source is a disk file, a keyboard, a magnetic tape, or even a punched
16401 card reader. Similarly, ``standard output'' is a data sink, where data goes
16402 to. The program should neither know nor care where this might be.
16403 Programs that only read their standard input, do something to the data,
16404 and then send it on, are called @dfn{filters}, by analogy to filters in a
16407 With the Unix shell, it's very easy to set up data pipelines:
16410 program_to_create_data | filter1 | ... | filterN > final.pretty.data
16413 We start out by creating the raw data; each filter applies some successive
16414 transformation to the data, until by the time it comes out of the pipeline,
16415 it is in the desired form.
16417 This is fine and good for standard input and standard output. Where does the
16418 standard error come in to play? Well, think about @command{filter1} in
16419 the pipeline above. What happens if it encounters an error in the data it
16420 sees? If it writes an error message to standard output, it will just
16421 disappear down the pipeline into @command{filter2}'s input, and the
16422 user will probably never see it. So programs need a place where they can send
16423 error messages so that the user will notice them. This is standard error,
16424 and it is usually connected to your console or window, even if you have
16425 redirected standard output of your program away from your screen.
16427 For filter programs to work together, the format of the data has to be
16428 agreed upon. The most straightforward and easiest format to use is simply
16429 lines of text. Unix data files are generally just streams of bytes, with
16430 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
16431 conventionally called a ``newline'' in the Unix literature. (This is
16432 @code{'\n'} if you're a C programmer.) This is the format used by all
16433 the traditional filtering programs. (Many earlier operating systems
16434 had elaborate facilities and special purpose programs for managing
16435 binary data. Unix has always shied away from such things, under the
16436 philosophy that it's easiest to simply be able to view and edit your
16437 data with a text editor.)
16439 OK, enough introduction. Let's take a look at some of the tools, and then
16440 we'll see how to hook them together in interesting ways. In the following
16441 discussion, we will only present those command line options that interest
16442 us. As you should always do, double check your system documentation
16443 for the full story.
16445 @node The who command
16446 @unnumberedsec The @command{who} Command
16448 The first program is the @command{who} command. By itself, it generates a
16449 list of the users who are currently logged in. Although I'm writing
16450 this on a single-user system, we'll pretend that several people are
16455 @print{} arnold console Jan 22 19:57
16456 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
16457 @print{} bill ttyp1 Jan 21 09:32(:0.0)
16458 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
16461 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
16462 There are three people logged in, and I am logged in twice. On traditional
16463 Unix systems, user names are never more than eight characters long. This
16464 little bit of trivia will be useful later. The output of @command{who} is nice,
16465 but the data is not all that exciting.
16467 @node The cut command
16468 @unnumberedsec The @command{cut} Command
16470 The next program we'll look at is the @command{cut} command. This program
16471 cuts out columns or fields of input data. For example, we can tell it
16472 to print just the login name and full name from the @file{/etc/passwd}
16473 file. The @file{/etc/passwd} file has seven fields, separated by
16477 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
16480 To get the first and fifth fields, we would use @command{cut} like this:
16483 $ cut -d: -f1,5 /etc/passwd
16484 @print{} root:Operator
16486 @print{} arnold:Arnold D. Robbins
16487 @print{} miriam:Miriam A. Robbins
16491 With the @option{-c} option, @command{cut} will cut out specific characters
16492 (i.e., columns) in the input lines. This is useful for input data
16493 that has fixed width fields, and does not have a field separator. For
16494 example, list the Monday dates for the current month:
16496 @c Is using cal ok? Looked at gcal, but I don't like it.
16507 @node The sort command
16508 @unnumberedsec The @command{sort} Command
16510 Next we'll look at the @command{sort} command. This is one of the most
16511 powerful commands on a Unix-style system; one that you will often find
16512 yourself using when setting up fancy data plumbing.
16515 command reads and sorts each file named on the command line. It then
16516 merges the sorted data and writes it to standard output. It will read
16517 standard input if no files are given on the command line (thus
16518 making it into a filter). The sort is based on the character collating
16519 sequence or based on user-supplied ordering criteria.
16522 @node The uniq command
16523 @unnumberedsec The @command{uniq} Command
16525 Finally (at least for now), we'll look at the @command{uniq} program. When
16526 sorting data, you will often end up with duplicate lines, lines that
16527 are identical. Usually, all you need is one instance of each line.
16528 This is where @command{uniq} comes in. The @command{uniq} program reads its
16529 standard input. It prints only one
16530 copy of each repeated line. It does have several options. Later on,
16531 we'll use the @option{-c} option, which prints each unique line, preceded
16532 by a count of the number of times that line occurred in the input.
16535 @node Putting the tools together
16536 @unnumberedsec Putting the Tools Together
16538 Now, let's suppose this is a large ISP server system with dozens of users
16539 logged in. The management wants the system administrator to write a
16541 generate a sorted list of logged in users. Furthermore, even if a user
16542 is logged in multiple times, his or her name should only show up in the
16545 The administrator could sit down with the system documentation and write a C
16546 program that did this. It would take perhaps a couple of hundred lines
16547 of code and about two hours to write it, test it, and debug it.
16548 However, knowing the software toolbox, the administrator can instead start out
16549 by generating just a list of logged on users:
16559 Next, sort the list:
16562 $ who | cut -c1-8 | sort
16569 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
16572 $ who | cut -c1-8 | sort | uniq
16578 The @command{sort} command actually has a @option{-u} option that does what
16579 @command{uniq} does. However, @command{uniq} has other uses for which one
16580 cannot substitute @samp{sort -u}.
16582 The administrator puts this pipeline into a shell script, and makes it
16584 all the users on the system (@samp{#} is the system administrator,
16585 or @code{root}, prompt):
16588 # cat > /usr/local/bin/listusers
16589 who | cut -c1-8 | sort | uniq
16591 # chmod +x /usr/local/bin/listusers
16594 There are four major points to note here. First, with just four
16595 programs, on one command line, the administrator was able to save about two
16596 hours worth of work. Furthermore, the shell pipeline is just about as
16597 efficient as the C program would be, and it is much more efficient in
16598 terms of programmer time. People time is much more expensive than
16599 computer time, and in our modern ``there's never enough time to do
16600 everything'' society, saving two hours of programmer time is no mean
16603 Second, it is also important to emphasize that with the
16604 @emph{combination} of the tools, it is possible to do a special
16605 purpose job never imagined by the authors of the individual programs.
16607 Third, it is also valuable to build up your pipeline in stages, as we did here.
16608 This allows you to view the data at each stage in the pipeline, which helps
16609 you acquire the confidence that you are indeed using these tools correctly.
16611 Finally, by bundling the pipeline in a shell script, other users can use
16612 your command, without having to remember the fancy plumbing you set up for
16613 them. In terms of how you run them, shell scripts and compiled programs are
16616 After the previous warm-up exercise, we'll look at two additional, more
16617 complicated pipelines. For them, we need to introduce two more tools.
16619 The first is the @command{tr} command, which stands for ``transliterate.''
16620 The @command{tr} command works on a character-by-character basis, changing
16621 characters. Normally it is used for things like mapping upper case to
16625 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
16626 @print{} this example has mixed case!
16629 There are several options of interest:
16633 work on the complement of the listed characters, i.e.,
16634 operations apply to characters not in the given set
16637 delete characters in the first set from the output
16640 squeeze repeated characters in the output into just one character.
16643 We will be using all three options in a moment.
16645 The other command we'll look at is @command{comm}. The @command{comm}
16646 command takes two sorted input files as input data, and prints out the
16647 files' lines in three columns. The output columns are the data lines
16648 unique to the first file, the data lines unique to the second file, and
16649 the data lines that are common to both. The @option{-1}, @option{-2}, and
16650 @option{-3} command line options @emph{omit} the respective columns. (This is
16651 non-intuitive and takes a little getting used to.) For example:
16673 The file name @file{-} tells @command{comm} to read standard input
16674 instead of a regular file.
16676 Now we're ready to build a fancy pipeline. The first application is a word
16677 frequency counter. This helps an author determine if he or she is over-using
16680 The first step is to change the case of all the letters in our input file
16681 to one case. ``The'' and ``the'' are the same word when doing counting.
16684 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16687 The next step is to get rid of punctuation. Quoted words and unquoted words
16688 should be treated identically; it's easiest to just get the punctuation out of
16692 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16695 The second @command{tr} command operates on the complement of the listed
16696 characters, which are all the letters, the digits, the underscore, and
16697 the blank. The @samp{\n} represents the newline character; it has to
16698 be left alone. (The @acronym{ASCII} tab character should also be included for
16699 good measure in a production script.)
16701 At this point, we have data consisting of words separated by blank space.
16702 The words only contain alphanumeric characters (and the underscore). The
16703 next step is break the data apart so that we have one word per line. This
16704 makes the counting operation much easier, as we will see shortly.
16707 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16708 > tr -s ' ' '\n' | ...
16711 This command turns blanks into newlines. The @option{-s} option squeezes
16712 multiple newline characters in the output into just one. This helps us
16713 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16714 This is what the shell prints when it notices you haven't finished
16715 typing in all of a command.)
16717 We now have data consisting of one word per line, no punctuation, all one
16718 case. We're ready to count each word:
16721 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16722 > tr -s ' ' '\n' | sort | uniq -c | ...
16725 At this point, the data might look something like this:
16738 The output is sorted by word, not by count! What we want is the most
16739 frequently used words first. Fortunately, this is easy to accomplish,
16740 with the help of two more @command{sort} options:
16744 do a numeric sort, not a textual one
16747 reverse the order of the sort
16750 The final pipeline looks like this:
16753 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16754 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16763 Whew! That's a lot to digest. Yet, the same principles apply. With six
16764 commands, on two lines (really one long one split for convenience), we've
16765 created a program that does something interesting and useful, in much
16766 less time than we could have written a C program to do the same thing.
16768 A minor modification to the above pipeline can give us a simple spelling
16769 checker! To determine if you've spelled a word correctly, all you have to
16770 do is look it up in a dictionary. If it is not there, then chances are
16771 that your spelling is incorrect. So, we need a dictionary.
16772 The conventional location for a dictionary is @file{/usr/dict/words}.
16773 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16774 revision of this article.}
16775 this is a sorted, 45,402 word dictionary.
16777 Now, how to compare our file with the dictionary? As before, we generate
16778 a sorted list of words, one per line:
16781 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16782 > tr -s ' ' '\n' | sort -u | ...
16785 Now, all we need is a list of words that are @emph{not} in the
16786 dictionary. Here is where the @command{comm} command comes in.
16789 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16790 > tr -s ' ' '\n' | sort -u |
16791 > comm -23 - /usr/dict/words
16794 The @option{-2} and @option{-3} options eliminate lines that are only in the
16795 dictionary (the second file), and lines that are in both files. Lines
16796 only in the first file (standard input, our stream of words), are
16797 words that are not in the dictionary. These are likely candidates for
16798 spelling errors. This pipeline was the first cut at a production
16799 spelling checker on Unix.
16801 There are some other tools that deserve brief mention.
16805 search files for text that matches a regular expression
16808 count lines, words, characters
16811 a T-fitting for data pipes, copies data to files and to standard output
16814 the stream editor, an advanced tool
16817 a data manipulation language, another advanced tool
16820 The software tools philosophy also espoused the following bit of
16821 advice: ``Let someone else do the hard part.'' This means, take
16822 something that gives you most of what you need, and then massage it the
16823 rest of the way until it's in the form that you want.
16829 Each program should do one thing well. No more, no less.
16832 Combining programs with appropriate plumbing leads to results where
16833 the whole is greater than the sum of the parts. It also leads to novel
16834 uses of programs that the authors might never have imagined.
16837 Programs should never print extraneous header or trailer data, since these
16838 could get sent on down a pipeline. (A point we didn't mention earlier.)
16841 Let someone else do the hard part.
16844 Know your toolbox! Use each program appropriately. If you don't have an
16845 appropriate tool, build one.
16848 As of this writing, all the programs we've discussed are available via
16849 anonymous @command{ftp} from: @*
16850 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16851 be more recent versions available now.)
16853 None of what I have presented in this column is new. The Software Tools
16854 philosophy was first introduced in the book @cite{Software Tools}, by
16855 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16856 This book showed how to write and use software tools. It was written in
16857 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16858 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16859 was. The last chapter presented a @command{ratfor} to FORTRAN
16860 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16861 lot like C; if you know C, you won't have any problem following the
16864 In 1981, the book was updated and made available as @cite{Software Tools
16865 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16866 still in print and are well worth
16867 reading if you're a programmer. They certainly made a major change in
16868 how I view programming.
16870 The programs in both books are available from
16871 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16872 For a number of years, there was an active
16873 Software Tools Users Group, whose members had ported the original
16874 @command{ratfor} programs to essentially every computer system with a
16875 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16876 as Unix began to spread beyond universities.
16878 With the current proliferation of GNU code and other clones of Unix programs,
16879 these programs now receive little attention; modern C versions are
16880 much more efficient and do more than these programs do. Nevertheless, as
16881 exposition of good programming style, and evangelism for a still-valuable
16882 philosophy, these books are unparalleled, and I recommend them highly.
16884 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16885 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16887 @node GNU Free Documentation License
16888 @appendix GNU Free Documentation License
16892 @node Concept index
16899 @c Local variables:
16900 @c texinfo-column-for-description: 32