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 non-directory suffix.
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 * od: (coreutils)od invocation. Dump files in octal, etc.
88 * paste: (coreutils)paste invocation. Merge lines of files.
89 * pathchk: (coreutils)pathchk invocation. Check file name portability.
90 * pr: (coreutils)pr invocation. Paginate or columnate files.
91 * printenv: (coreutils)printenv invocation. Print environment variables.
92 * printf: (coreutils)printf invocation. Format and print data.
93 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
94 * pwd: (coreutils)pwd invocation. Print working directory.
95 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
96 * rm: (coreutils)rm invocation. Remove files.
97 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
98 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
99 * seq: (coreutils)seq invocation. Print numeric sequences
100 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
101 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
102 * shred: (coreutils)shred invocation. Remove files more securely.
103 * shuf: (coreutils)shuf invocation. Shuffling text files.
104 * sleep: (coreutils)sleep invocation. Delay for a specified time.
105 * sort: (coreutils)sort invocation. Sort text files.
106 * split: (coreutils)split invocation. Split into fixed-size pieces.
107 * stat: (coreutils)stat invocation. Report file(system) status.
108 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
109 * stty: (coreutils)stty invocation. Print/change terminal settings.
110 * su: (coreutils)su invocation. Modify user and group ID.
111 * sum: (coreutils)sum invocation. Print traditional checksum.
112 * sync: (coreutils)sync invocation. Synchronize memory and disk.
113 * tac: (coreutils)tac invocation. Reverse files.
114 * tail: (coreutils)tail invocation. Output the last part of files.
115 * tee: (coreutils)tee invocation. Redirect to multiple files.
116 * test: (coreutils)test invocation. File/string tests.
117 * timeout: (coreutils)timeout invocation. Run with time limit.
118 * touch: (coreutils)touch invocation. Change file timestamps.
119 * tr: (coreutils)tr invocation. Translate characters.
120 * true: (coreutils)true invocation. Do nothing, successfully.
121 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
122 * tsort: (coreutils)tsort invocation. Topological sort.
123 * tty: (coreutils)tty invocation. Print terminal name.
124 * uname: (coreutils)uname invocation. Print system information.
125 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
126 * uniq: (coreutils)uniq invocation. Uniquify files.
127 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
128 * uptime: (coreutils)uptime invocation. Print uptime and load.
129 * users: (coreutils)users invocation. Print current user names.
130 * vdir: (coreutils)vdir invocation. List directories verbosely.
131 * wc: (coreutils)wc invocation. Line, word, and byte counts.
132 * who: (coreutils)who invocation. Print who is logged in.
133 * whoami: (coreutils)whoami invocation. Print effective user ID.
134 * yes: (coreutils)yes invocation. Print a string indefinitely.
138 This manual documents version @value{VERSION} of the @sc{gnu} core
139 utilities, including the standard programs for text and file manipulation.
141 Copyright @copyright{} 1994-1996, 2000-2009 Free Software Foundation, Inc.
144 Permission is granted to copy, distribute and/or modify this document
145 under the terms of the GNU Free Documentation License, Version 1.3 or
146 any later version published by the Free Software Foundation; with no
147 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
148 Texts. A copy of the license is included in the section entitled ``GNU
149 Free Documentation License''.
154 @title @sc{gnu} @code{Coreutils}
155 @subtitle Core GNU utilities
156 @subtitle for version @value{VERSION}, @value{UPDATED}
157 @author David MacKenzie et al.
160 @vskip 0pt plus 1filll
173 @cindex core utilities
174 @cindex text utilities
175 @cindex shell utilities
176 @cindex file utilities
179 * Introduction:: Caveats, overview, and authors
180 * Common options:: Common options
181 * Output of entire files:: cat tac nl od base64
182 * Formatting file contents:: fmt pr fold
183 * Output of parts of files:: head tail split csplit
184 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
185 * Operating on sorted files:: sort shuf uniq comm ptx tsort
186 * Operating on fields:: cut paste join
187 * Operating on characters:: tr expand unexpand
188 * Directory listing:: ls dir vdir dircolors
189 * Basic operations:: cp dd install mv rm shred
190 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
191 * Changing file attributes:: chgrp chmod chown touch
192 * Disk usage:: df du stat sync truncate
193 * Printing text:: echo printf yes
194 * Conditions:: false true test expr
196 * File name manipulation:: dirname basename pathchk mktemp
197 * Working context:: pwd stty printenv tty
198 * User information:: id logname whoami groups users who
199 * System context:: date arch uname hostname hostid uptime
200 * SELinux context:: chcon runcon
201 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
202 * Process control:: kill
204 * Numeric operations:: factor seq
205 * File permissions:: Access modes
206 * Date input formats:: Specifying date strings
207 * Opening the software toolbox:: The software tools philosophy
208 * GNU Free Documentation License:: Copying and sharing this manual
209 * Concept index:: General index
212 --- The Detailed Node Listing ---
216 * Exit status:: Indicating program success or failure
217 * Backup options:: Backup options
218 * Block size:: Block size
219 * Signal specifications:: Specifying signals
220 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
221 * Random sources:: Sources of random data
222 * Target directory:: Target directory
223 * Trailing slashes:: Trailing slashes
224 * Traversing symlinks:: Traversing symlinks to directories
225 * Treating / specially:: Treating / specially
226 * Standards conformance:: Standards conformance
228 Output of entire files
230 * cat invocation:: Concatenate and write files
231 * tac invocation:: Concatenate and write files in reverse
232 * nl invocation:: Number lines and write files
233 * od invocation:: Write files in octal or other formats
234 * base64 invocation:: Transform data into printable data
236 Formatting file contents
238 * fmt invocation:: Reformat paragraph text
239 * pr invocation:: Paginate or columnate files for printing
240 * fold invocation:: Wrap input lines to fit in specified width
242 Output of parts of files
244 * head invocation:: Output the first part of files
245 * tail invocation:: Output the last part of files
246 * split invocation:: Split a file into fixed-size pieces
247 * csplit invocation:: Split a file into context-determined pieces
251 * wc invocation:: Print newline, word, and byte counts
252 * sum invocation:: Print checksum and block counts
253 * cksum invocation:: Print CRC checksum and byte counts
254 * md5sum invocation:: Print or check MD5 digests
255 * sha1sum invocation:: Print or check SHA-1 digests
256 * sha2 utilities:: Print or check SHA-2 digests
258 Operating on sorted files
260 * sort invocation:: Sort text files
261 * shuf invocation:: Shuffle text files
262 * uniq invocation:: Uniquify files
263 * comm invocation:: Compare two sorted files line by line
264 * ptx invocation:: Produce a permuted index of file contents
265 * tsort invocation:: Topological sort
267 @command{ptx}: Produce permuted indexes
269 * General options in ptx:: Options which affect general program behavior
270 * Charset selection in ptx:: Underlying character set considerations
271 * Input processing in ptx:: Input fields, contexts, and keyword selection
272 * Output formatting in ptx:: Types of output format, and sizing the fields
273 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
277 * cut invocation:: Print selected parts of lines
278 * paste invocation:: Merge lines of files
279 * join invocation:: Join lines on a common field
281 Operating on characters
283 * tr invocation:: Translate, squeeze, and/or delete characters
284 * expand invocation:: Convert tabs to spaces
285 * unexpand invocation:: Convert spaces to tabs
287 @command{tr}: Translate, squeeze, and/or delete characters
289 * Character sets:: Specifying sets of characters
290 * Translating:: Changing one set of characters to another
291 * Squeezing:: Squeezing repeats and deleting
295 * ls invocation:: List directory contents
296 * dir invocation:: Briefly list directory contents
297 * vdir invocation:: Verbosely list directory contents
298 * dircolors invocation:: Color setup for @command{ls}
300 @command{ls}: List directory contents
302 * Which files are listed:: Which files are listed
303 * What information is listed:: What information is listed
304 * Sorting the output:: Sorting the output
305 * Details about version sort:: More details about version sort
306 * General output formatting:: General output formatting
307 * Formatting the file names:: Formatting the file names
311 * cp invocation:: Copy files and directories
312 * dd invocation:: Convert and copy a file
313 * install invocation:: Copy files and set attributes
314 * mv invocation:: Move (rename) files
315 * rm invocation:: Remove files or directories
316 * shred invocation:: Remove files more securely
320 * link invocation:: Make a hard link via the link syscall
321 * ln invocation:: Make links between files
322 * mkdir invocation:: Make directories
323 * mkfifo invocation:: Make FIFOs (named pipes)
324 * mknod invocation:: Make block or character special files
325 * readlink invocation:: Print value of a symlink or canonical file name
326 * rmdir invocation:: Remove empty directories
327 * unlink invocation:: Remove files via unlink syscall
329 Changing file attributes
331 * chown invocation:: Change file owner and group
332 * chgrp invocation:: Change group ownership
333 * chmod invocation:: Change access permissions
334 * touch invocation:: Change file timestamps
338 * df invocation:: Report file system disk space usage
339 * du invocation:: Estimate file space usage
340 * stat invocation:: Report file or file system status
341 * sync invocation:: Synchronize data on disk with memory
342 * truncate invocation:: Shrink or extend the size of a file
346 * echo invocation:: Print a line of text
347 * printf invocation:: Format and print data
348 * yes invocation:: Print a string until interrupted
352 * false invocation:: Do nothing, unsuccessfully
353 * true invocation:: Do nothing, successfully
354 * test invocation:: Check file types and compare values
355 * expr invocation:: Evaluate expressions
357 @command{test}: Check file types and compare values
359 * File type tests:: File type tests
360 * Access permission tests:: Access permission tests
361 * File characteristic tests:: File characteristic tests
362 * String tests:: String tests
363 * Numeric tests:: Numeric tests
365 @command{expr}: Evaluate expression
367 * String expressions:: + : match substr index length
368 * Numeric expressions:: + - * / %
369 * Relations for expr:: | & < <= = == != >= >
370 * Examples of expr:: Examples of using @command{expr}
374 * tee invocation:: Redirect output to multiple files or processes
376 File name manipulation
378 * basename invocation:: Strip directory and suffix from a file name
379 * dirname invocation:: Strip non-directory suffix from a file name
380 * pathchk invocation:: Check file name validity and portability
381 * mktemp invocation:: Create temporary file or directory
385 * pwd invocation:: Print working directory
386 * stty invocation:: Print or change terminal characteristics
387 * printenv invocation:: Print all or some environment variables
388 * tty invocation:: Print file name of terminal on standard input
390 @command{stty}: Print or change terminal characteristics
392 * Control:: Control settings
393 * Input:: Input settings
394 * Output:: Output settings
395 * Local:: Local settings
396 * Combination:: Combination settings
397 * Characters:: Special characters
398 * Special:: Special settings
402 * id invocation:: Print user identity
403 * logname invocation:: Print current login name
404 * whoami invocation:: Print effective user ID
405 * groups invocation:: Print group names a user is in
406 * users invocation:: Print login names of users currently logged in
407 * who invocation:: Print who is currently logged in
411 * arch invocation:: Print machine hardware name
412 * date invocation:: Print or set system date and time
413 * uname invocation:: Print system information
414 * hostname invocation:: Print or set system name
415 * hostid invocation:: Print numeric host identifier
416 * uptime invocation:: Print system uptime and load
418 @command{date}: Print or set system date and time
420 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
421 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
422 * Literal conversion specifiers:: %[%nt]
423 * Padding and other flags:: Pad with zeros, spaces, etc.
424 * Setting the time:: Changing the system clock
425 * Options for date:: Instead of the current time
426 * Date input formats:: Specifying date strings
427 * Examples of date:: Examples
431 * chcon invocation:: Change SELinux context of file
432 * runcon invocation:: Run a command in specified SELinux context
434 Modified command invocation
436 * chroot invocation:: Run a command with a different root directory
437 * env invocation:: Run a command in a modified environment
438 * nice invocation:: Run a command with modified niceness
439 * nohup invocation:: Run a command immune to hangups
440 * stdbuf invocation:: Run a command with modified I/O buffering
441 * su invocation:: Run a command with substitute user and group ID
442 * timeout invocation:: Run a command with a time limit
446 * kill invocation:: Sending a signal to processes.
450 * sleep invocation:: Delay for a specified time
454 * factor invocation:: Print prime factors
455 * seq invocation:: Print numeric sequences
459 * Mode Structure:: Structure of file mode bits
460 * Symbolic Modes:: Mnemonic representation of file mode bits
461 * Numeric Modes:: File mode bits as octal numbers
462 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
466 * General date syntax:: Common rules
467 * Calendar date items:: 19 Dec 1994
468 * Time of day items:: 9:20pm
469 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
470 * Day of week items:: Monday and others
471 * Relative items in date strings:: next tuesday, 2 years ago
472 * Pure numbers in date strings:: 19931219, 1440
473 * Seconds since the Epoch:: @@1078100502
474 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
475 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al
477 Opening the software toolbox
479 * Toolbox introduction:: Toolbox introduction
480 * I/O redirection:: I/O redirection
481 * The who command:: The @command{who} command
482 * The cut command:: The @command{cut} command
483 * The sort command:: The @command{sort} command
484 * The uniq command:: The @command{uniq} command
485 * Putting the tools together:: Putting the tools together
489 * GNU Free Documentation License:: Copying and sharing this manual
496 @chapter Introduction
498 This manual is a work in progress: many sections make no attempt to explain
499 basic concepts in a way suitable for novices. Thus, if you are interested,
500 please get involved in improving this manual. The entire @sc{gnu} community
503 @cindex @acronym{POSIX}
504 The @sc{gnu} utilities documented here are mostly compatible with the
505 @acronym{POSIX} standard.
506 @cindex bugs, reporting
507 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
508 to include the version number, machine architecture, input files, and
509 any other information needed to reproduce the bug: your input, what you
510 expected, what you got, and why it is wrong. Diffs are welcome, but
511 please include a description of the problem as well, since this is
512 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
518 @cindex MacKenzie, D.
521 This manual was originally derived from the Unix man pages in the
522 distributions, which were written by David MacKenzie and updated by Jim
523 Meyering. What you are reading now is the authoritative documentation
524 for these utilities; the man pages are no longer being maintained. The
525 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
526 Pinard did the initial conversion to Texinfo format. Karl Berry did the
527 indexing, some reorganization, and editing of the results. Brian
528 Youmans of the Free Software Foundation office staff combined the
529 manuals for textutils, fileutils, and sh-utils to produce the present
530 omnibus manual. Richard Stallman contributed his usual invaluable
531 insights to the overall process.
534 @chapter Common options
538 @itemx @w{@kbd{--backup}[=@var{method}]}
541 @vindex VERSION_CONTROL
542 @cindex backups, making
543 @xref{Backup options}.
544 Make a backup of each file that would otherwise be overwritten or removed.
547 @macro optBackupSuffix
548 @item -S @var{suffix}
549 @itemx --suffix=@var{suffix}
552 Append @var{suffix} to each backup file made with @option{-b}.
553 @xref{Backup options}.
556 @macro optTargetDirectory
557 @item -t @var{directory}
558 @itemx @w{@kbd{--target-directory}=@var{directory}}
560 @opindex --target-directory
561 @cindex target directory
562 @cindex destination directory
563 Specify the destination @var{directory}.
564 @xref{Target directory}.
567 @macro optNoTargetDirectory
569 @itemx --no-target-directory
571 @opindex --no-target-directory
572 @cindex target directory
573 @cindex destination directory
574 Do not treat the last operand specially when it is a directory or a
575 symbolic link to a directory. @xref{Target directory}.
583 @cindex output @sc{nul}-byte-terminated lines
584 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
585 rather than a newline. This option enables other programs to parse the
586 output of @command{\cmd\} even when that output would contain data
587 with embedded newlines.
594 Append an SI-style abbreviation to each size, such as @samp{M} for
595 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
596 1,000,000 bytes. This option is equivalent to
597 @option{--block-size=si}. Use the @option{-h} or
598 @option{--human-readable} option if
599 you prefer powers of 1024.
602 @macro optHumanReadable
604 @itemx --human-readable
606 @opindex --human-readable
607 @cindex human-readable output
608 Append a size letter to each size, such as @samp{M} for mebibytes.
609 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
610 This option is equivalent to @option{--block-size=human-readable}.
611 Use the @option{--si} option if you prefer powers of 1000.
614 @macro optStripTrailingSlashes
615 @itemx @w{@kbd{--strip-trailing-slashes}}
616 @opindex --strip-trailing-slashes
617 @cindex stripping trailing slashes
618 Remove any trailing slashes from each @var{source} argument.
619 @xref{Trailing slashes}.
622 @macro mayConflictWithShellBuiltIn{cmd}
623 @cindex conflicts with shell built-ins
624 @cindex built-in shell commands, conflicts with
625 Due to shell aliases and built-in @command{\cmd\} command, using an
626 unadorned @command{\cmd\} interactively or in a script may get you
627 different functionality than that described here. Invoke it via
628 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
633 @macro multiplierSuffixes{varName}
634 @var{\varName\} may be, or may be an integer optionally followed by,
635 one of the following multiplicative suffixes:
637 @samp{b} => 512 ("blocks")
638 @samp{KB} => 1000 (KiloBytes)
639 @samp{K} => 1024 (KibiBytes)
640 @samp{MB} => 1000*1000 (MegaBytes)
641 @samp{M} => 1024*1024 (MebiBytes)
642 @samp{GB} => 1000*1000*1000 (GigaBytes)
643 @samp{G} => 1024*1024*1024 (GibiBytes)
645 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
648 @c FIXME: same as above, but no ``blocks'' line.
649 @macro multiplierSuffixesNoBlocks{varName}
650 @var{\varName\} may be, or may be an integer optionally followed by,
651 one of the following multiplicative suffixes:
653 @samp{KB} => 1000 (KiloBytes)
654 @samp{K} => 1024 (KibiBytes)
655 @samp{MB} => 1000*1000 (MegaBytes)
656 @samp{M} => 1024*1024 (MebiBytes)
657 @samp{GB} => 1000*1000*1000 (GigaBytes)
658 @samp{G} => 1024*1024*1024 (GibiBytes)
660 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
663 @cindex common options
665 Certain options are available in all of these programs. Rather than
666 writing identical descriptions for each of the programs, they are
667 described here. (In fact, every @sc{gnu} program accepts (or should accept)
670 @vindex POSIXLY_CORRECT
671 Normally options and operands can appear in any order, and programs act
672 as if all the options appear before any operands. For example,
673 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
674 @samp{:} is an option-argument of @option{-t}. However, if the
675 @env{POSIXLY_CORRECT} environment variable is set, options must appear
676 before operands, unless otherwise specified for a particular command.
678 A few programs can usefully have trailing operands with leading
679 @samp{-}. With such a program, options must precede operands even if
680 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
681 program description. For example, the @command{env} command's options
682 must appear before its operands, since in some cases the operands
683 specify a command that itself contains options.
685 Most programs that accept long options recognize unambiguous
686 abbreviations of those options. For example, @samp{rmdir
687 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
688 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
689 @samp{ls --h}, are identified as such.
691 Some of these programs recognize the @option{--help} and @option{--version}
692 options only when one of them is the sole command line argument. For
693 these programs, abbreviations of the long options are not always recognized.
700 Print a usage message listing all available options, then exit successfully.
704 @cindex version number, finding
705 Print the version number, then exit successfully.
709 @cindex option delimiter
710 Delimit the option list. Later arguments, if any, are treated as
711 operands even if they begin with @samp{-}. For example, @samp{sort --
712 -r} reads from the file named @file{-r}.
716 @cindex standard input
717 @cindex standard output
718 A single @samp{-} operand is not really an option, though it looks like one. It
719 stands for standard input, or for standard output if that is clear from
720 the context. For example, @samp{sort -} reads from standard input,
721 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
722 extra copy of its input to standard output. Unless otherwise
723 specified, @samp{-} can appear as any operand that requires a file
727 * Exit status:: Indicating program success or failure.
728 * Backup options:: -b -S, in some programs.
729 * Block size:: BLOCK_SIZE and --block-size, in some programs.
730 * Signal specifications:: Specifying signals using the --signal option.
731 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
732 * Random sources:: --random-source, in some programs.
733 * Target directory:: Specifying a target directory, in some programs.
734 * Trailing slashes:: --strip-trailing-slashes, in some programs.
735 * Traversing symlinks:: -H, -L, or -P, in some programs.
736 * Treating / specially:: --preserve-root and --no-preserve-root.
737 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
738 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
746 An exit status of zero indicates success,
747 and a nonzero value indicates failure.
750 Nearly every command invocation yields an integral @dfn{exit status}
751 that can be used to change how other commands work.
752 For the vast majority of commands, an exit status of zero indicates
753 success. Failure is indicated by a nonzero value---typically
754 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
755 requires only that it be nonzero.
757 However, some of the programs documented here do produce
758 other exit status values and a few associate different
759 meanings with the values @samp{0} and @samp{1}.
760 Here are some of the exceptions:
761 @command{chroot}, @command{env}, @command{expr}, @command{nice},
762 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
763 @command{su}, @command{test}, @command{timeout}, @command{tty}.
767 @section Backup options
769 @cindex backup options
771 Some @sc{gnu} programs (at least @command{cp}, @command{install},
772 @command{ln}, and @command{mv}) optionally make backups of files
773 before writing new versions.
774 These options control the details of these backups. The options are also
775 briefly mentioned in the descriptions of the particular programs.
780 @itemx @w{@kbd{--backup}[=@var{method}]}
783 @vindex VERSION_CONTROL
784 @cindex backups, making
785 Make a backup of each file that would otherwise be overwritten or removed.
786 Without this option, the original versions are destroyed.
787 Use @var{method} to determine the type of backups to make.
788 When this option is used but @var{method} is not specified,
789 then the value of the @env{VERSION_CONTROL}
790 environment variable is used. And if @env{VERSION_CONTROL} is not set,
791 the default backup type is @samp{existing}.
793 Note that the short form of this option, @option{-b} does not accept any
794 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
796 @vindex version-control @r{Emacs variable}
797 This option corresponds to the Emacs variable @samp{version-control};
798 the values for @var{method} are the same as those used in Emacs.
799 This option also accepts more descriptive names.
800 The valid @var{method}s are (unique abbreviations are accepted):
805 @opindex none @r{backup method}
810 @opindex numbered @r{backup method}
811 Always make numbered backups.
815 @opindex existing @r{backup method}
816 Make numbered backups of files that already have them, simple backups
821 @opindex simple @r{backup method}
822 Always make simple backups. Please note @samp{never} is not to be
823 confused with @samp{none}.
827 @item -S @var{suffix}
828 @itemx --suffix=@var{suffix}
831 @cindex backup suffix
832 @vindex SIMPLE_BACKUP_SUFFIX
833 Append @var{suffix} to each backup file made with @option{-b}. If this
834 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
835 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
836 set, the default is @samp{~}, just as in Emacs.
845 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
846 @command{ls}) display sizes in ``blocks''. You can adjust the block size
847 and method of display to make sizes easier to read. The block size
848 used for display is independent of any file system block size.
849 Fractional block counts are rounded up to the nearest integer.
851 @opindex --block-size=@var{size}
854 @vindex DF_BLOCK_SIZE
855 @vindex DU_BLOCK_SIZE
856 @vindex LS_BLOCK_SIZE
857 @vindex POSIXLY_CORRECT@r{, and block size}
859 The default block size is chosen by examining the following environment
860 variables in turn; the first one that is set determines the block size.
865 This specifies the default block size for the @command{df} command.
866 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
867 @env{LS_BLOCK_SIZE} for @command{ls}.
870 This specifies the default block size for all three commands, if the
871 above command-specific environment variables are not set.
874 This specifies the default block size for all values that are normally
875 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
876 command-specific environment variables are set. Unlike the other
877 environment variables, @env{BLOCKSIZE} does not affect values that are
878 normally printed as byte counts, e.g., the file sizes contained in
881 @item POSIXLY_CORRECT
882 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
883 @env{BLOCKSIZE} is set, but this variable is set, the block size
888 If none of the above environment variables are set, the block size
889 currently defaults to 1024 bytes in most contexts, but this number may
890 change in the future. For @command{ls} file sizes, the block size
893 @cindex human-readable output
896 A block size specification can be a positive integer specifying the number
897 of bytes per block, or it can be @code{human-readable} or @code{si} to
898 select a human-readable format. Integers may be followed by suffixes
899 that are upward compatible with the
900 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
901 for decimal multiples and with the
902 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
903 prefixes for binary multiples}.
905 With human-readable formats, output sizes are followed by a size letter
906 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
907 powers of 1024; @samp{M} stands for 1,048,576 bytes.
908 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
909 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
912 A block size specification preceded by @samp{'} causes output sizes to
913 be displayed with thousands separators. The @env{LC_NUMERIC} locale
914 specifies the thousands separator and grouping. For example, in an
915 American English locale, @samp{--block-size="'1kB"} would cause a size
916 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
917 locale, there is no thousands separator so a leading @samp{'} has no
920 An integer block size can be followed by a suffix to specify a
921 multiple of that size. A bare size letter,
922 or one followed by @samp{iB}, specifies
923 a multiple using powers of 1024. A size letter followed by @samp{B}
924 specifies powers of 1000 instead. For example, @samp{1M} and
925 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
926 equivalent to @samp{1000000}.
928 A plain suffix without a preceding integer acts as if @samp{1} were
929 prepended, except that it causes a size indication to be appended to
930 the output. For example, @samp{--block-size="kB"} displays 3000 as
933 The following suffixes are defined. Large sizes like @code{1Y}
934 may be rejected by your computer due to limitations of its arithmetic.
938 @cindex kilobyte, definition of
939 kilobyte: @math{10^3 = 1000}.
943 @cindex kibibyte, definition of
944 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
945 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
946 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
948 @cindex megabyte, definition of
949 megabyte: @math{10^6 = 1,000,000}.
952 @cindex mebibyte, definition of
953 mebibyte: @math{2^{20} = 1,048,576}.
955 @cindex gigabyte, definition of
956 gigabyte: @math{10^9 = 1,000,000,000}.
959 @cindex gibibyte, definition of
960 gibibyte: @math{2^{30} = 1,073,741,824}.
962 @cindex terabyte, definition of
963 terabyte: @math{10^{12} = 1,000,000,000,000}.
966 @cindex tebibyte, definition of
967 tebibyte: @math{2^{40} = 1,099,511,627,776}.
969 @cindex petabyte, definition of
970 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
973 @cindex pebibyte, definition of
974 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
976 @cindex exabyte, definition of
977 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
980 @cindex exbibyte, definition of
981 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
983 @cindex zettabyte, definition of
984 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
987 @math{2^{70} = 1,180,591,620,717,411,303,424}.
988 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
990 @cindex yottabyte, definition of
991 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
994 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
995 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
1000 @opindex --block-size
1001 @opindex --human-readable
1004 Block size defaults can be overridden by an explicit
1005 @option{--block-size=@var{size}} option. The @option{-k}
1006 option is equivalent to @option{--block-size=1K}, which
1007 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1008 set. The @option{-h} or @option{--human-readable} option is equivalent to
1009 @option{--block-size=human-readable}. The @option{--si} option is
1010 equivalent to @option{--block-size=si}.
1012 @node Signal specifications
1013 @section Signal specifications
1014 @cindex signals, specifying
1016 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1017 number like @samp{1}, or an exit status of a process terminated by the
1018 signal. A signal name can be given in canonical form or prefixed by
1019 @samp{SIG}. The case of the letters is ignored. The following signal names
1020 and numbers are supported on all @acronym{POSIX} compliant systems:
1026 2. Terminal interrupt.
1032 9. Kill (cannot be caught or ignored).
1040 Other supported signal names have system-dependent corresponding
1041 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1042 support the following signals:
1046 Access to an undefined portion of a memory object.
1048 Child process terminated, stopped, or continued.
1050 Continue executing, if stopped.
1052 Erroneous arithmetic operation.
1054 Illegal Instruction.
1056 Write on a pipe with no one to read it.
1058 Invalid memory reference.
1060 Stop executing (cannot be caught or ignored).
1064 Background process attempting read.
1066 Background process attempting write.
1068 High bandwidth data is available at a socket.
1070 User-defined signal 1.
1072 User-defined signal 2.
1076 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1077 also support the following signals:
1083 Profiling timer expired.
1087 Trace/breakpoint trap.
1089 Virtual timer expired.
1091 CPU time limit exceeded.
1093 File size limit exceeded.
1097 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1098 also support at least eight real-time signals called @samp{RTMIN},
1099 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1101 @node Disambiguating names and IDs
1102 @section chown and chgrp: Disambiguating user names and IDs
1103 @cindex user names, disambiguating
1104 @cindex user IDs, disambiguating
1105 @cindex group names, disambiguating
1106 @cindex group IDs, disambiguating
1107 @cindex disambiguating group names and IDs
1109 Since the @var{owner} and @var{group} arguments to @command{chown} and
1110 @command{chgrp} may be specified as names or numeric IDs, there is an
1112 What if a user or group @emph{name} is a string of digits?
1113 @footnote{Using a number as a user name is common in some environments.}
1114 Should the command interpret it as a user name or as an ID?
1115 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1116 first attempt to resolve the specified string as a name, and
1117 only once that fails, then try to interpret it as an ID.
1118 This is troublesome when you want to specify a numeric ID, say 42,
1119 and it must work even in a pathological situation where
1120 @samp{42} is a user name that maps to some other user ID, say 1000.
1121 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1122 1000---not what you intended.
1124 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1125 that at the same time may result in a significant performance improvement
1126 by eliminating a database look-up.
1127 Simply precede each numeric user ID and/or group ID with a @samp{+},
1128 in order to force its interpretation as an integer:
1132 chgrp +$numeric_group_id another-file
1136 GNU @command{chown} and @command{chgrp}
1137 skip the name look-up process for each @samp{+}-prefixed string,
1138 because a string containing @samp{+} is never a valid user or group name.
1139 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1141 @node Random sources
1142 @section Sources of random data
1144 @cindex random sources
1146 The @command{shuf}, @command{shred}, and @command{sort} commands
1147 sometimes need random data to do their work. For example, @samp{sort
1148 -R} must choose a hash function at random, and it needs random data to
1149 make this selection.
1151 By default these commands use an internal pseudorandom generator
1152 initialized by a small amount of entropy, but can be directed to use
1153 an external source with the @option{--random-source=@var{file}} option.
1154 An error is reported if @var{file} does not contain enough bytes.
1156 For example, the device file @file{/dev/urandom} could be used as the
1157 source of random data. Typically, this device gathers environmental
1158 noise from device drivers and other sources into an entropy pool, and
1159 uses the pool to generate random bits. If the pool is short of data,
1160 the device reuses the internal pool to produce more bits, using a
1161 cryptographically secure pseudorandom number generator. But be aware
1162 that this device is not designed for bulk random data generation
1163 and is relatively slow.
1165 @file{/dev/urandom} suffices for most practical uses, but applications
1166 requiring high-value or long-term protection of private data may
1167 require an alternate data source like @file{/dev/random} or
1168 @file{/dev/arandom}. The set of available sources depends on your
1171 To reproduce the results of an earlier invocation of a command, you
1172 can save some random data into a file and then use that file as the
1173 random source in earlier and later invocations of the command.
1175 @node Target directory
1176 @section Target directory
1178 @cindex target directory
1180 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1181 commands normally treat the last operand specially when it is a
1182 directory or a symbolic link to a directory. For example, @samp{cp
1183 source dest} is equivalent to @samp{cp source dest/source} if
1184 @file{dest} is a directory. Sometimes this behavior is not exactly
1185 what is wanted, so these commands support the following options to
1186 allow more fine-grained control:
1191 @itemx --no-target-directory
1192 @opindex --no-target-directory
1193 @cindex target directory
1194 @cindex destination directory
1195 Do not treat the last operand specially when it is a directory or a
1196 symbolic link to a directory. This can help avoid race conditions in
1197 programs that operate in a shared area. For example, when the command
1198 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1199 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1200 renamed to @file{/tmp/dest/source} instead, if some other process
1201 created @file{/tmp/dest} as a directory. However, if @file{mv
1202 -T /tmp/source /tmp/dest} succeeds, there is no
1203 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1205 In the opposite situation, where you want the last operand to be
1206 treated as a directory and want a diagnostic otherwise, you can use
1207 the @option{--target-directory} (@option{-t}) option.
1209 @item -t @var{directory}
1210 @itemx @w{@kbd{--target-directory}=@var{directory}}
1211 @opindex --target-directory
1212 @cindex target directory
1213 @cindex destination directory
1214 Use @var{directory} as the directory component of each destination
1217 The interface for most programs is that after processing options and a
1218 finite (possibly zero) number of fixed-position arguments, the remaining
1219 argument list is either expected to be empty, or is a list of items
1220 (usually files) that will all be handled identically. The @command{xargs}
1221 program is designed to work well with this convention.
1223 The commands in the @command{mv}-family are unusual in that they take
1224 a variable number of arguments with a special case at the @emph{end}
1225 (namely, the target directory). This makes it nontrivial to perform some
1226 operations, e.g., ``move all files from here to ../d/'', because
1227 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1228 doesn't have a clean way to specify an extra final argument for each
1229 invocation of the subject command. (It can be done by going through a
1230 shell command, but that requires more human labor and brain power than
1233 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1234 @command{install}, @command{ln}, and @command{mv} programs to be used
1235 conveniently with @command{xargs}. For example, you can move the files
1236 from the current directory to a sibling directory, @code{d} like this:
1239 ls | xargs mv -t ../d --
1242 However, this doesn't move files whose names begin with @samp{.}.
1243 If you use the @sc{gnu} @command{find} program, you can move those
1244 files too, with this command:
1247 find . -mindepth 1 -maxdepth 1 \
1251 But both of the above approaches fail if there are no files in the
1252 current directory, or if any file has a name containing a blank or
1253 some other special characters.
1254 The following example removes those limitations and requires both
1255 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1258 find . -mindepth 1 -maxdepth 1 -print0 \
1259 | xargs --null --no-run-if-empty \
1266 The @option{--target-directory} (@option{-t}) and
1267 @option{--no-target-directory} (@option{-T})
1268 options cannot be combined.
1270 @node Trailing slashes
1271 @section Trailing slashes
1273 @cindex trailing slashes
1275 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1276 remove any trailing slashes from each @var{source} argument before
1277 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1280 This is useful when a @var{source} argument may have a trailing slash and
1281 @c FIXME: mv's behavior in this case is system-dependent
1282 specify a symbolic link to a directory. This scenario is in fact rather
1283 common because some shells can automatically append a trailing slash when
1284 performing file name completion on such symbolic links. Without this
1285 option, @command{mv}, for example, (via the system's rename function) must
1286 interpret a trailing slash as a request to dereference the symbolic link
1287 and so must rename the indirectly referenced @emph{directory} and not
1288 the symbolic link. Although it may seem surprising that such behavior
1289 be the default, it is required by @acronym{POSIX} and is consistent with
1290 other parts of that standard.
1292 @node Traversing symlinks
1293 @section Traversing symlinks
1295 @cindex symbolic link to directory, controlling traversal of
1297 The following options modify how @command{chown} and @command{chgrp}
1298 @c FIXME: note that `du' has these options, too, but they have slightly
1299 @c different meaning.
1300 traverse a hierarchy when the @option{--recursive} (@option{-R})
1301 option is also specified.
1302 If more than one of the following options is specified, only the final
1304 These options specify whether processing a symbolic link to a directory
1305 entails operating on just the symbolic link or on all files in the
1306 hierarchy rooted at that directory.
1308 These options are independent of @option{--dereference} and
1309 @option{--no-dereference} (@option{-h}), which control whether to modify
1310 a symlink or its referent.
1317 @cindex symbolic link to directory, traverse each that is specified on the command line
1318 If @option{--recursive} (@option{-R}) is specified and
1319 a command line argument is a symbolic link to a directory, traverse it.
1326 @cindex symbolic link to directory, traverse each that is encountered
1327 In a recursive traversal, traverse every symbolic link to a directory
1328 that is encountered.
1335 @cindex symbolic link to directory, never traverse
1336 Do not traverse any symbolic links.
1337 This is the default if none of @option{-H}, @option{-L},
1338 or @option{-P} is specified.
1345 @node Treating / specially
1346 @section Treating @file{/} specially
1348 Certain commands can operate destructively on entire hierarchies.
1349 For example, if a user with appropriate privileges mistakenly runs
1350 @samp{rm -rf / tmp/junk}, that may remove
1351 all files on the entire system. Since there are so few
1352 legitimate uses for such a command,
1353 @sc{gnu} @command{rm} normally declines to operate on any directory
1354 that resolves to @file{/}. If you really want to try to remove all
1355 the files on your system, you can use the @option{--no-preserve-root}
1356 option, but the default behavior, specified by the
1357 @option{--preserve-option}, is safer for most purposes.
1359 The commands @command{chgrp}, @command{chmod} and @command{chown}
1360 can also operate destructively on entire hierarchies, so they too
1361 support these options. Although, unlike @command{rm}, they don't
1362 actually unlink files, these commands are arguably more dangerous
1363 when operating recursively on @file{/}, since they often work much
1364 more quickly, and hence damage more files before an alert user can
1365 interrupt them. Tradition and @acronym{POSIX} require these commands
1366 to operate recursively on @file{/}, so they default to
1367 @option{--no-preserve-root}, but using the @option{--preserve-root}
1368 option makes them safer for most purposes. For convenience you can
1369 specify @option{--preserve-root} in an alias or in a shell function.
1371 Note that the @option{--preserve-root} option also ensures
1372 that @command{chgrp} and @command{chown} do not modify @file{/}
1373 even when dereferencing a symlink pointing to @file{/}.
1375 @node Special built-in utilities
1376 @section Special built-in utilities
1378 Some programs like @command{nice} can invoke other programs; for
1379 example, the command @samp{nice cat file} invokes the program
1380 @command{cat} by executing the command @samp{cat file}. However,
1381 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1382 this way. For example, the command @samp{nice exit} does not have a
1383 well-defined behavior: it may generate an error message instead of
1386 Here is a list of the special built-in utilities that are standardized
1387 by @acronym{POSIX} 1003.1-2004.
1390 @t{.@: : break continue eval exec exit export readonly
1391 return set shift times trap unset}
1394 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1395 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1396 pwd} do not work as you might expect.
1398 Many shells extend this list. For example, Bash has several extra
1399 special built-in utilities like @command{history}, and
1400 @command{suspend}, and with Bash the command @samp{nice suspend}
1401 generates an error message instead of suspending.
1403 @node Standards conformance
1404 @section Standards conformance
1406 @vindex POSIXLY_CORRECT
1407 In a few cases, the @sc{gnu} utilities' default behavior is
1408 incompatible with the @acronym{POSIX} standard. To suppress these
1409 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1410 variable. Unless you are checking for @acronym{POSIX} conformance, you
1411 probably do not need to define @env{POSIXLY_CORRECT}.
1413 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1414 versions. For example, older versions of @acronym{POSIX} required the
1415 command @samp{sort +1} to sort based on the second and succeeding
1416 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1417 the same command is required to sort the file named @file{+1}, and you
1418 must instead use the command @samp{sort -k 2} to get the field-based
1421 @vindex _POSIX2_VERSION
1422 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1423 that is standard for your system. To cause them to conform to a
1424 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1425 environment variable to a value of the form @var{yyyymm} specifying
1426 the year and month the standard was adopted. Two values are currently
1427 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1428 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1429 1003.1-2001. For example, if you have a newer system but are running software
1430 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1431 or @samp{tail +10}, you can work around any compatibility problems by setting
1432 @samp{_POSIX2_VERSION=199209} in your environment.
1434 @node Output of entire files
1435 @chapter Output of entire files
1437 @cindex output of entire files
1438 @cindex entire files, output of
1440 These commands read and write entire files, possibly transforming them
1444 * cat invocation:: Concatenate and write files.
1445 * tac invocation:: Concatenate and write files in reverse.
1446 * nl invocation:: Number lines and write files.
1447 * od invocation:: Write files in octal or other formats.
1448 * base64 invocation:: Transform data into printable data.
1451 @node cat invocation
1452 @section @command{cat}: Concatenate and write files
1455 @cindex concatenate and write files
1456 @cindex copying files
1458 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1459 standard input if none are given, to standard output. Synopsis:
1462 cat [@var{option}] [@var{file}]@dots{}
1465 The program accepts the following options. Also see @ref{Common options}.
1473 Equivalent to @option{-vET}.
1476 @itemx --number-nonblank
1478 @opindex --number-nonblank
1479 Number all nonempty output lines, starting with 1.
1483 Equivalent to @option{-vE}.
1488 @opindex --show-ends
1489 Display a @samp{$} after the end of each line.
1495 Number all output lines, starting with 1.
1498 @itemx --squeeze-blank
1500 @opindex --squeeze-blank
1501 @cindex squeezing empty lines
1502 Suppress repeated adjacent empty lines; output just one empty line
1507 Equivalent to @option{-vT}.
1512 @opindex --show-tabs
1513 Display TAB characters as @samp{^I}.
1517 Ignored; for @acronym{POSIX} compatibility.
1520 @itemx --show-nonprinting
1522 @opindex --show-nonprinting
1523 Display control characters except for LFD and TAB using
1524 @samp{^} notation and precede characters that have the high bit set with
1529 On systems like MS-DOS that distinguish between text and binary files,
1530 @command{cat} normally reads and writes in binary mode. However,
1531 @command{cat} reads in text mode if one of the options
1532 @option{-bensAE} is used or if @command{cat} is reading from standard
1533 input and standard input is a terminal. Similarly, @command{cat}
1534 writes in text mode if one of the options @option{-bensAE} is used or
1535 if standard output is a terminal.
1542 # Output f's contents, then standard input, then g's contents.
1545 # Copy standard input to standard output.
1550 @node tac invocation
1551 @section @command{tac}: Concatenate and write files in reverse
1554 @cindex reversing files
1556 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1557 standard input if none are given, to standard output, reversing the
1558 records (lines by default) in each separately. Synopsis:
1561 tac [@var{option}]@dots{} [@var{file}]@dots{}
1564 @dfn{Records} are separated by instances of a string (newline by
1565 default). By default, this separator string is attached to the end of
1566 the record that it follows in the file.
1568 The program accepts the following options. Also see @ref{Common options}.
1576 The separator is attached to the beginning of the record that it
1577 precedes in the file.
1583 Treat the separator string as a regular expression. Users of @command{tac}
1584 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1585 binary mode, each line of a text file might end with a CR/LF pair
1586 instead of the Unix-style LF.
1588 @item -s @var{separator}
1589 @itemx --separator=@var{separator}
1591 @opindex --separator
1592 Use @var{separator} as the record separator, instead of newline.
1600 @section @command{nl}: Number lines and write files
1603 @cindex numbering lines
1604 @cindex line numbering
1606 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1607 standard input if none are given, to standard output, with line numbers
1608 added to some or all of the lines. Synopsis:
1611 nl [@var{option}]@dots{} [@var{file}]@dots{}
1614 @cindex logical pages, numbering on
1615 @command{nl} decomposes its input into (logical) pages; by default, the
1616 line number is reset to 1 at the top of each logical page. @command{nl}
1617 treats all of the input files as a single document; it does not reset
1618 line numbers or logical pages between files.
1620 @cindex headers, numbering
1621 @cindex body, numbering
1622 @cindex footers, numbering
1623 A logical page consists of three sections: header, body, and footer.
1624 Any of the sections can be empty. Each can be numbered in a different
1625 style from the others.
1627 The beginnings of the sections of logical pages are indicated in the
1628 input file by a line containing exactly one of these delimiter strings:
1639 The two characters from which these strings are made can be changed from
1640 @samp{\} and @samp{:} via options (see below), but the pattern and
1641 length of each string cannot be changed.
1643 A section delimiter is replaced by an empty line on output. Any text
1644 that comes before the first section delimiter string in the input file
1645 is considered to be part of a body section, so @command{nl} treats a
1646 file that contains no section delimiters as a single body section.
1648 The program accepts the following options. Also see @ref{Common options}.
1652 @item -b @var{style}
1653 @itemx --body-numbering=@var{style}
1655 @opindex --body-numbering
1656 Select the numbering style for lines in the body section of each
1657 logical page. When a line is not numbered, the current line number
1658 is not incremented, but the line number separator character is still
1659 prepended to the line. The styles are:
1665 number only nonempty lines (default for body),
1667 do not number lines (default for header and footer),
1669 number only lines that contain a match for the basic regular
1670 expression @var{bre}.
1671 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1675 @itemx --section-delimiter=@var{cd}
1677 @opindex --section-delimiter
1678 @cindex section delimiters of pages
1679 Set the section delimiter characters to @var{cd}; default is
1680 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1681 (Remember to protect @samp{\} or other metacharacters from shell
1682 expansion with quotes or extra backslashes.)
1684 @item -f @var{style}
1685 @itemx --footer-numbering=@var{style}
1687 @opindex --footer-numbering
1688 Analogous to @option{--body-numbering}.
1690 @item -h @var{style}
1691 @itemx --header-numbering=@var{style}
1693 @opindex --header-numbering
1694 Analogous to @option{--body-numbering}.
1696 @item -i @var{number}
1697 @itemx --line-increment=@var{number}
1699 @opindex --line-increment
1700 Increment line numbers by @var{number} (default 1).
1702 @item -l @var{number}
1703 @itemx --join-blank-lines=@var{number}
1705 @opindex --join-blank-lines
1706 @cindex empty lines, numbering
1707 @cindex blank lines, numbering
1708 Consider @var{number} (default 1) consecutive empty lines to be one
1709 logical line for numbering, and only number the last one. Where fewer
1710 than @var{number} consecutive empty lines occur, do not number them.
1711 An empty line is one that contains no characters, not even spaces
1714 @item -n @var{format}
1715 @itemx --number-format=@var{format}
1717 @opindex --number-format
1718 Select the line numbering format (default is @code{rn}):
1722 @opindex ln @r{format for @command{nl}}
1723 left justified, no leading zeros;
1725 @opindex rn @r{format for @command{nl}}
1726 right justified, no leading zeros;
1728 @opindex rz @r{format for @command{nl}}
1729 right justified, leading zeros.
1733 @itemx --no-renumber
1735 @opindex --no-renumber
1736 Do not reset the line number at the start of a logical page.
1738 @item -s @var{string}
1739 @itemx --number-separator=@var{string}
1741 @opindex --number-separator
1742 Separate the line number from the text line in the output with
1743 @var{string} (default is the TAB character).
1745 @item -v @var{number}
1746 @itemx --starting-line-number=@var{number}
1748 @opindex --starting-line-number
1749 Set the initial line number on each logical page to @var{number} (default 1).
1751 @item -w @var{number}
1752 @itemx --number-width=@var{number}
1754 @opindex --number-width
1755 Use @var{number} characters for line numbers (default 6).
1763 @section @command{od}: Write files in octal or other formats
1766 @cindex octal dump of files
1767 @cindex hex dump of files
1768 @cindex ASCII dump of files
1769 @cindex file contents, dumping unambiguously
1771 @command{od} writes an unambiguous representation of each @var{file}
1772 (@samp{-} means standard input), or standard input if none are given.
1776 od [@var{option}]@dots{} [@var{file}]@dots{}
1777 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1778 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1781 Each line of output consists of the offset in the input, followed by
1782 groups of data from the file. By default, @command{od} prints the offset in
1783 octal, and each group of file data is a C @code{short int}'s worth of input
1784 printed as a single octal number.
1786 If @var{offset} is given, it specifies how many input bytes to skip
1787 before formatting and writing. By default, it is interpreted as an
1788 octal number, but the optional trailing decimal point causes it to be
1789 interpreted as decimal. If no decimal is specified and the offset
1790 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1791 number. If there is a trailing @samp{b}, the number of bytes skipped
1792 will be @var{offset} multiplied by 512.
1794 If a command is of both the first and second forms, the second form is
1795 assumed if the last operand begins with @samp{+} or (if there are two
1796 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1797 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1800 The program accepts the following options. Also see @ref{Common options}.
1804 @item -A @var{radix}
1805 @itemx --address-radix=@var{radix}
1807 @opindex --address-radix
1808 @cindex radix for file offsets
1809 @cindex file offset radix
1810 Select the base in which file offsets are printed. @var{radix} can
1811 be one of the following:
1821 none (do not print offsets).
1824 The default is octal.
1826 @item -j @var{bytes}
1827 @itemx --skip-bytes=@var{bytes}
1829 @opindex --skip-bytes
1830 Skip @var{bytes} input bytes before formatting and writing. If
1831 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1832 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1834 @multiplierSuffixes{bytes}
1836 @item -N @var{bytes}
1837 @itemx --read-bytes=@var{bytes}
1839 @opindex --read-bytes
1840 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1841 @code{bytes} are interpreted as for the @option{-j} option.
1843 @item -S @var{bytes}
1844 @itemx --strings[=@var{bytes}]
1847 @cindex string constants, outputting
1848 Instead of the normal output, output only @dfn{string constants}: at
1849 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1850 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1851 Prefixes and suffixes on @code{bytes} are interpreted as for the
1854 If @var{n} is omitted with @option{--strings}, the default is 3.
1857 @itemx --format=@var{type}
1860 Select the format in which to output the file data. @var{type} is a
1861 string of one or more of the below type indicator characters. If you
1862 include more than one type indicator character in a single @var{type}
1863 string, or use this option more than once, @command{od} writes one copy
1864 of each output line using each of the data types that you specified,
1865 in the order that you specified.
1867 Adding a trailing ``z'' to any type specification appends a display
1868 of the @acronym{ASCII} character representation of the printable characters
1869 to the output line generated by the type specification.
1873 named character, ignoring high-order bit
1875 @acronym{ASCII} character or backslash escape,
1888 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1889 newline, and @samp{nul} for a zero byte. Only the least significant
1890 seven bits of each byte is used; the high-order bit is ignored.
1891 Type @code{c} outputs
1892 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1895 Except for types @samp{a} and @samp{c}, you can specify the number
1896 of bytes to use in interpreting each number in the given data type
1897 by following the type indicator character with a decimal integer.
1898 Alternately, you can specify the size of one of the C compiler's
1899 built-in data types by following the type indicator character with
1900 one of the following characters. For integers (@samp{d}, @samp{o},
1901 @samp{u}, @samp{x}):
1914 For floating point (@code{f}):
1926 @itemx --output-duplicates
1928 @opindex --output-duplicates
1929 Output consecutive lines that are identical. By default, when two or
1930 more consecutive output lines would be identical, @command{od} outputs only
1931 the first line, and puts just an asterisk on the following line to
1932 indicate the elision.
1935 @itemx --width[=@var{n}]
1938 Dump @code{n} input bytes per output line. This must be a multiple of
1939 the least common multiple of the sizes associated with the specified
1942 If this option is not given at all, the default is 16. If @var{n} is
1943 omitted, the default is 32.
1947 The next several options are shorthands for format specifications.
1948 @sc{gnu} @command{od} accepts any combination of shorthands and format
1949 specification options. These options accumulate.
1955 Output as named characters. Equivalent to @samp{-t a}.
1959 Output as octal bytes. Equivalent to @samp{-t o1}.
1963 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1968 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1972 Output as floats. Equivalent to @samp{-t fF}.
1976 Output as decimal ints. Equivalent to @samp{-t dI}.
1980 Output as decimal long ints. Equivalent to @samp{-t dL}.
1984 Output as octal two-byte units. Equivalent to @option{-t o2}.
1988 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1992 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1995 @opindex --traditional
1996 Recognize the non-option label argument that traditional @command{od}
1997 accepted. The following syntax:
2000 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2004 can be used to specify at most one file and optional arguments
2005 specifying an offset and a pseudo-start address, @var{label}.
2006 The @var{label} argument is interpreted
2007 just like @var{offset}, but it specifies an initial pseudo-address. The
2008 pseudo-addresses are displayed in parentheses following any normal
2015 @node base64 invocation
2016 @section @command{base64}: Transform data into printable data
2019 @cindex base64 encoding
2021 @command{base64} transforms data read from a file, or standard input,
2022 into (or from) base64 encoded form. The base64 encoded form uses
2023 printable @acronym{ASCII} characters to represent binary data.
2027 base64 [@var{option}]@dots{} [@var{file}]
2028 base64 --decode [@var{option}]@dots{} [@var{file}]
2031 The base64 encoding expands data to roughly 133% of the original.
2032 The format conforms to
2033 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2035 The program accepts the following options. Also see @ref{Common options}.
2040 @itemx --wrap=@var{cols}
2044 @cindex column to wrap data after
2045 During encoding, wrap lines after @var{cols} characters. This must be
2048 The default is to wrap after 76 characters. Use the value 0 to
2049 disable line wrapping altogether.
2055 @cindex Decode base64 data
2056 @cindex Base64 decoding
2057 Change the mode of operation, from the default of encoding data, to
2058 decoding data. Input is expected to be base64 encoded data, and the
2059 output will be the original data.
2062 @itemx --ignore-garbage
2064 @opindex --ignore-garbage
2065 @cindex Ignore garbage in base64 stream
2066 When decoding, newlines are always accepted.
2067 During decoding, ignore unrecognized bytes,
2068 to permit distorted data to be decoded.
2075 @node Formatting file contents
2076 @chapter Formatting file contents
2078 @cindex formatting file contents
2080 These commands reformat the contents of files.
2083 * fmt invocation:: Reformat paragraph text.
2084 * pr invocation:: Paginate or columnate files for printing.
2085 * fold invocation:: Wrap input lines to fit in specified width.
2089 @node fmt invocation
2090 @section @command{fmt}: Reformat paragraph text
2093 @cindex reformatting paragraph text
2094 @cindex paragraphs, reformatting
2095 @cindex text, reformatting
2097 @command{fmt} fills and joins lines to produce output lines of (at most)
2098 a given number of characters (75 by default). Synopsis:
2101 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2104 @command{fmt} reads from the specified @var{file} arguments (or standard
2105 input if none are given), and writes to standard output.
2107 By default, blank lines, spaces between words, and indentation are
2108 preserved in the output; successive input lines with different
2109 indentation are not joined; tabs are expanded on input and introduced on
2112 @cindex line-breaking
2113 @cindex sentences and line-breaking
2114 @cindex Knuth, Donald E.
2115 @cindex Plass, Michael F.
2116 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2117 avoid line breaks after the first word of a sentence or before the last
2118 word of a sentence. A @dfn{sentence break} is defined as either the end
2119 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2120 spaces or end of line, ignoring any intervening parentheses or quotes.
2121 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2122 breaks; the algorithm is a variant of that given by Donald E. Knuth
2123 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2124 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2127 The program accepts the following options. Also see @ref{Common options}.
2132 @itemx --crown-margin
2134 @opindex --crown-margin
2135 @cindex crown margin
2136 @dfn{Crown margin} mode: preserve the indentation of the first two
2137 lines within a paragraph, and align the left margin of each subsequent
2138 line with that of the second line.
2141 @itemx --tagged-paragraph
2143 @opindex --tagged-paragraph
2144 @cindex tagged paragraphs
2145 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2146 indentation of the first line of a paragraph is the same as the
2147 indentation of the second, the first line is treated as a one-line
2153 @opindex --split-only
2154 Split lines only. Do not join short lines to form longer ones. This
2155 prevents sample lines of code, and other such ``formatted'' text from
2156 being unduly combined.
2159 @itemx --uniform-spacing
2161 @opindex --uniform-spacing
2162 Uniform spacing. Reduce spacing between words to one space, and spacing
2163 between sentences to two spaces.
2166 @itemx -w @var{width}
2167 @itemx --width=@var{width}
2168 @opindex -@var{width}
2171 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2172 initially tries to make lines about 7% shorter than this, to give it
2173 room to balance line lengths.
2175 @item -p @var{prefix}
2176 @itemx --prefix=@var{prefix}
2177 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2178 are subject to formatting. The prefix and any preceding whitespace are
2179 stripped for the formatting and then re-attached to each formatted output
2180 line. One use is to format certain kinds of program comments, while
2181 leaving the code unchanged.
2189 @section @command{pr}: Paginate or columnate files for printing
2192 @cindex printing, preparing files for
2193 @cindex multicolumn output, generating
2194 @cindex merging files in parallel
2196 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2197 standard input if none are given, to standard output, paginating and
2198 optionally outputting in multicolumn format; optionally merges all
2199 @var{file}s, printing all in parallel, one per column. Synopsis:
2202 pr [@var{option}]@dots{} [@var{file}]@dots{}
2206 By default, a 5-line header is printed at each page: two blank lines;
2207 a line with the date, the file name, and the page count; and two more
2208 blank lines. A footer of five blank lines is also printed.
2209 The default @var{page_length} is 66
2210 lines. The default number of text lines is therefore 56.
2211 The text line of the header takes the form
2212 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2213 @var{string} so that the line takes up the full @var{page_width}. Here,
2214 @var{date} is the date (see the @option{-D} or @option{--date-format}
2215 option for details), @var{string} is the centered header string, and
2216 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2217 category affects the spelling of @var{page}; in the default C locale, it
2218 is @samp{Page @var{number}} where @var{number} is the decimal page
2221 Form feeds in the input cause page breaks in the output. Multiple form
2222 feeds produce empty pages.
2224 Columns are of equal width, separated by an optional string (default
2225 is @samp{space}). For multicolumn output, lines will always be truncated to
2226 @var{page_width} (default 72), unless you use the @option{-J} option.
2228 column output no line truncation occurs by default. Use @option{-W} option to
2229 truncate lines in that case.
2231 The following changes were made in version 1.22i and apply to later
2232 versions of @command{pr}:
2233 @c FIXME: this whole section here sounds very awkward to me. I
2234 @c made a few small changes, but really it all needs to be redone. - Brian
2235 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2240 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2241 redefined for better @acronym{POSIX} compliance. The output of some further
2242 cases has been adapted to other Unix systems. These changes are not
2243 compatible with earlier versions of the program.
2246 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2247 have been introduced to turn off unexpected interferences of small letter
2248 options. The @option{-N} option and the second argument @var{last_page}
2249 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2250 form feeds set in the input files requires the @option{-T} option.
2253 Capital letter options override small letter ones.
2256 Some of the option-arguments (compare @option{-s}, @option{-e},
2257 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2258 preceding option letter (already stated in the @acronym{POSIX} specification).
2261 The program accepts the following options. Also see @ref{Common options}.
2265 @item +@var{first_page}[:@var{last_page}]
2266 @itemx --pages=@var{first_page}[:@var{last_page}]
2267 @c The two following @opindex lines evoke warnings because they contain `:'
2268 @c The `info' spec does not permit that. If we use those lines, we end
2269 @c up with truncated index entries that don't work.
2270 @c @opindex +@var{first_page}[:@var{last_page}]
2271 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2272 @opindex +@var{page_range}
2273 @opindex --pages=@var{page_range}
2274 Begin printing with page @var{first_page} and stop with @var{last_page}.
2275 Missing @samp{:@var{last_page}} implies end of file. While estimating
2276 the number of skipped pages each form feed in the input file results
2277 in a new page. Page counting with and without @samp{+@var{first_page}}
2278 is identical. By default, counting starts with the first page of input
2279 file (not first page printed). Line numbering may be altered by @option{-N}
2283 @itemx --columns=@var{column}
2284 @opindex -@var{column}
2286 @cindex down columns
2287 With each single @var{file}, produce @var{column} columns of output
2288 (default is 1) and print columns down, unless @option{-a} is used. The
2289 column width is automatically decreased as @var{column} increases; unless
2290 you use the @option{-W/-w} option to increase @var{page_width} as well.
2291 This option might well cause some lines to be truncated. The number of
2292 lines in the columns on each page are balanced. The options @option{-e}
2293 and @option{-i} are on for multiple text-column output. Together with
2294 @option{-J} option column alignment and line truncation is turned off.
2295 Lines of full length are joined in a free field format and @option{-S}
2296 option may set field separators. @option{-@var{column}} may not be used
2297 with @option{-m} option.
2303 @cindex across columns
2304 With each single @var{file}, print columns across rather than down. The
2305 @option{-@var{column}} option must be given with @var{column} greater than one.
2306 If a line is too long to fit in a column, it is truncated.
2309 @itemx --show-control-chars
2311 @opindex --show-control-chars
2312 Print control characters using hat notation (e.g., @samp{^G}); print
2313 other nonprinting characters in octal backslash notation. By default,
2314 nonprinting characters are not changed.
2317 @itemx --double-space
2319 @opindex --double-space
2320 @cindex double spacing
2321 Double space the output.
2323 @item -D @var{format}
2324 @itemx --date-format=@var{format}
2325 @cindex time formats
2326 @cindex formatting times
2327 Format header dates using @var{format}, using the same conventions as
2328 for the command @samp{date +@var{format}}; @xref{date invocation}.
2329 Except for directives, which start with
2330 @samp{%}, characters in @var{format} are printed unchanged. You can use
2331 this option to specify an arbitrary string in place of the header date,
2332 e.g., @option{--date-format="Monday morning"}.
2334 @vindex POSIXLY_CORRECT
2336 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2337 @samp{2001-12-04 23:59});
2338 but if the @env{POSIXLY_CORRECT} environment variable is set
2339 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2340 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2341 @samp{Dec@ @ 4 23:59 2001}.
2344 Time stamps are listed according to the time zone rules specified by
2345 the @env{TZ} environment variable, or by the system default rules if
2346 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2347 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2349 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2350 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2352 @opindex --expand-tabs
2354 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2355 the input tab character (default is the TAB character). Second optional
2356 argument @var{in-tabwidth} is the input tab character's width (default
2364 @opindex --form-feed
2365 Use a form feed instead of newlines to separate output pages. This does
2366 not alter the default page length of 66 lines.
2368 @item -h @var{header}
2369 @itemx --header=@var{header}
2372 Replace the file name in the header with the centered string @var{header}.
2373 When using the shell, @var{header} should be quoted and should be
2374 separated from @option{-h} by a space.
2376 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2377 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2379 @opindex --output-tabs
2381 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2382 is the output tab character (default is the TAB character). Second optional
2383 argument @var{out-tabwidth} is the output tab character's width (default
2389 @opindex --join-lines
2390 Merge lines of full length. Used together with the column options
2391 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2392 @option{-W/-w} line truncation;
2393 no column alignment used; may be used with
2394 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2395 (together with @option{-W} and @option{--sep-string})
2396 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2397 @option{-s} along with the three column options.
2400 @item -l @var{page_length}
2401 @itemx --length=@var{page_length}
2404 Set the page length to @var{page_length} (default 66) lines, including
2405 the lines of the header [and the footer]. If @var{page_length} is less
2406 than or equal to 10, the header and footer are omitted, as if the
2407 @option{-t} option had been given.
2413 Merge and print all @var{file}s in parallel, one in each column. If a
2414 line is too long to fit in a column, it is truncated, unless the @option{-J}
2415 option is used. @option{--sep-string[=@var{string}]} may be used.
2417 some @var{file}s (form feeds set) produce empty columns, still marked
2418 by @var{string}. The result is a continuous line numbering and column
2419 marking throughout the whole merged file. Completely empty merged pages
2420 show no separators or line numbers. The default header becomes
2421 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2422 may be used with the @option{-h} or @option{--header} option to fill up
2423 the middle blank part.
2425 @item -n[@var{number-separator}[@var{digits}]]
2426 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2428 @opindex --number-lines
2429 Provide @var{digits} digit line numbering (default for @var{digits} is
2430 5). With multicolumn output the number occupies the first @var{digits}
2431 column positions of each text column or only each line of @option{-m}
2432 output. With single column output the number precedes each line just as
2433 @option{-m} does. Default counting of the line numbers starts with the
2434 first line of the input file (not the first line printed, compare the
2435 @option{--page} option and @option{-N} option).
2436 Optional argument @var{number-separator} is the character appended to
2437 the line number to separate it from the text followed. The default
2438 separator is the TAB character. In a strict sense a TAB is always
2439 printed with single column output only. The TAB width varies
2440 with the TAB position, e.g., with the left @var{margin} specified
2441 by @option{-o} option. With multicolumn output priority is given to
2442 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2443 The TAB width is fixed to the value of the first column and does
2444 not change with different values of left @var{margin}. That means a
2445 fixed number of spaces is always printed in the place of the
2446 @var{number-separator} TAB. The tabification depends upon the output
2449 @item -N @var{line_number}
2450 @itemx --first-line-number=@var{line_number}
2452 @opindex --first-line-number
2453 Start line counting with the number @var{line_number} at first line of
2454 first page printed (in most cases not the first line of the input file).
2456 @item -o @var{margin}
2457 @itemx --indent=@var{margin}
2460 @cindex indenting lines
2462 Indent each line with a margin @var{margin} spaces wide (default is zero).
2463 The total page width is the size of the margin plus the @var{page_width}
2464 set with the @option{-W/-w} option. A limited overflow may occur with
2465 numbered single column output (compare @option{-n} option).
2468 @itemx --no-file-warnings
2470 @opindex --no-file-warnings
2471 Do not print a warning message when an argument @var{file} cannot be
2472 opened. (The exit status will still be nonzero, however.)
2474 @item -s[@var{char}]
2475 @itemx --separator[=@var{char}]
2477 @opindex --separator
2478 Separate columns by a single character @var{char}. The default for
2479 @var{char} is the TAB character without @option{-w} and @samp{no
2480 character} with @option{-w}. Without @option{-s} the default separator
2481 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2482 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2483 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2486 @item -S@var{string}
2487 @itemx --sep-string[=@var{string}]
2489 @opindex --sep-string
2490 Use @var{string} to separate output columns. The @option{-S} option doesn't
2491 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2492 does not affect line truncation or column alignment.
2493 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2495 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2496 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2497 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2500 @itemx --omit-header
2502 @opindex --omit-header
2503 Do not print the usual header [and footer] on each page, and do not fill
2504 out the bottom of pages (with blank lines or a form feed). No page
2505 structure is produced, but form feeds set in the input files are retained.
2506 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2507 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2508 in the input file to 4 spaces but don't make any other changes. Use of
2509 @option{-t} overrides @option{-h}.
2512 @itemx --omit-pagination
2514 @opindex --omit-pagination
2515 Do not print header [and footer]. In addition eliminate all form feeds
2516 set in the input files.
2519 @itemx --show-nonprinting
2521 @opindex --show-nonprinting
2522 Print nonprinting characters in octal backslash notation.
2524 @item -w @var{page_width}
2525 @itemx --width=@var{page_width}
2528 Set page width to @var{page_width} characters for multiple text-column
2529 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2530 off the default page width and any line truncation and column alignment.
2531 Lines of full length are merged, regardless of the column options
2532 set. No @var{page_width} setting is possible with single column output.
2533 A @acronym{POSIX}-compliant formulation.
2535 @item -W @var{page_width}
2536 @itemx --page_width=@var{page_width}
2538 @opindex --page_width
2539 Set the page width to @var{page_width} characters. That's valid with and
2540 without a column option. Text lines are truncated, unless @option{-J}
2541 is used. Together with one of the three column options
2542 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2543 alignment is always used. The separator options @option{-S} or @option{-s}
2544 don't affect the @option{-W} option. Default is 72 characters. Without
2545 @option{-W @var{page_width}} and without any of the column options NO line
2546 truncation is used (defined to keep downward compatibility and to meet
2547 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2548 line is never truncated.
2555 @node fold invocation
2556 @section @command{fold}: Wrap input lines to fit in specified width
2559 @cindex wrapping long input lines
2560 @cindex folding long input lines
2562 @command{fold} writes each @var{file} (@option{-} means standard input), or
2563 standard input if none are given, to standard output, breaking long
2567 fold [@var{option}]@dots{} [@var{file}]@dots{}
2570 By default, @command{fold} breaks lines wider than 80 columns. The output
2571 is split into as many lines as necessary.
2573 @cindex screen columns
2574 @command{fold} counts screen columns by default; thus, a tab may count more
2575 than one column, backspace decreases the column count, and carriage
2576 return sets the column to zero.
2578 The program accepts the following options. Also see @ref{Common options}.
2586 Count bytes rather than columns, so that tabs, backspaces, and carriage
2587 returns are each counted as taking up one column, just like other
2594 Break at word boundaries: the line is broken after the last blank before
2595 the maximum line length. If the line contains no such blanks, the line
2596 is broken at the maximum line length as usual.
2598 @item -w @var{width}
2599 @itemx --width=@var{width}
2602 Use a maximum line length of @var{width} columns instead of 80.
2604 For compatibility @command{fold} supports an obsolete option syntax
2605 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2613 @node Output of parts of files
2614 @chapter Output of parts of files
2616 @cindex output of parts of files
2617 @cindex parts of files, output of
2619 These commands output pieces of the input.
2622 * head invocation:: Output the first part of files.
2623 * tail invocation:: Output the last part of files.
2624 * split invocation:: Split a file into fixed-size pieces.
2625 * csplit invocation:: Split a file into context-determined pieces.
2628 @node head invocation
2629 @section @command{head}: Output the first part of files
2632 @cindex initial part of files, outputting
2633 @cindex first part of files, outputting
2635 @command{head} prints the first part (10 lines by default) of each
2636 @var{file}; it reads from standard input if no files are given or
2637 when given a @var{file} of @option{-}. Synopsis:
2640 head [@var{option}]@dots{} [@var{file}]@dots{}
2643 If more than one @var{file} is specified, @command{head} prints a
2644 one-line header consisting of:
2647 ==> @var{file name} <==
2651 before the output for each @var{file}.
2653 The program accepts the following options. Also see @ref{Common options}.
2658 @itemx --bytes=@var{k}
2661 Print the first @var{k} bytes, instead of initial lines.
2662 However, if @var{k} starts with a @samp{-},
2663 print all but the last @var{k} bytes of each file.
2664 @multiplierSuffixes{k}
2667 @itemx --lines=@var{k}
2670 Output the first @var{k} lines.
2671 However, if @var{k} starts with a @samp{-},
2672 print all but the last @var{k} lines of each file.
2673 Size multiplier suffixes are the same as with the @option{-c} option.
2681 Never print file name headers.
2687 Always print file name headers.
2691 For compatibility @command{head} also supports an obsolete option syntax
2692 @option{-@var{count}@var{options}}, which is recognized only if it is
2693 specified first. @var{count} is a decimal number optionally followed
2694 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2695 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2696 Scripts intended for standard hosts should use @option{-c @var{count}}
2697 or @option{-n @var{count}} instead. If your script must also run on
2698 hosts that support only the obsolete syntax, it is usually simpler to
2699 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2705 @node tail invocation
2706 @section @command{tail}: Output the last part of files
2709 @cindex last part of files, outputting
2711 @command{tail} prints the last part (10 lines by default) of each
2712 @var{file}; it reads from standard input if no files are given or
2713 when given a @var{file} of @samp{-}. Synopsis:
2716 tail [@var{option}]@dots{} [@var{file}]@dots{}
2719 If more than one @var{file} is specified, @command{tail} prints a
2720 one-line header consisting of:
2723 ==> @var{file name} <==
2727 before the output for each @var{file}.
2729 @cindex BSD @command{tail}
2730 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2731 @command{tail} cannot). It also has no @option{-r} option (print in
2732 reverse), since reversing a file is really a different job from printing
2733 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2734 only reverse files that are at most as large as its buffer, which is
2735 typically 32 KiB@. A more reliable and versatile way to reverse files is
2736 the @sc{gnu} @command{tac} command.
2738 The program accepts the following options. Also see @ref{Common options}.
2743 @itemx --bytes=@var{k}
2746 Output the last @var{k} bytes, instead of final lines.
2747 However, if @var{k} starts with a @samp{+}, start printing with the
2748 @var{k}th byte from the start of each file, instead of from the end.
2749 @multiplierSuffixes{k}
2752 @itemx --follow[=@var{how}]
2755 @cindex growing files
2756 @vindex name @r{follow option}
2757 @vindex descriptor @r{follow option}
2758 Loop forever trying to read more characters at the end of the file,
2759 presumably because the file is growing.
2760 If more than one file is given, @command{tail} prints a header whenever it
2761 gets output from a different file, to indicate which file that output is
2764 There are two ways to specify how you'd like to track files with this option,
2765 but that difference is noticeable only when a followed file is removed or
2767 If you'd like to continue to track the end of a growing file even after
2768 it has been unlinked, use @option{--follow=descriptor}. This is the default
2769 behavior, but it is not useful if you're tracking a log file that may be
2770 rotated (removed or renamed, then reopened). In that case, use
2771 @option{--follow=name} to track the named file by reopening it periodically
2772 to see if it has been removed and recreated by some other program.
2774 No matter which method you use, if the tracked file is determined to have
2775 shrunk, @command{tail} prints a message saying the file has been truncated
2776 and resumes tracking the end of the file from the newly-determined endpoint.
2778 When a file is removed, @command{tail}'s behavior depends on whether it is
2779 following the name or the descriptor. When following by name, tail can
2780 detect that a file has been removed and gives a message to that effect,
2781 and if @option{--retry} has been specified it will continue checking
2782 periodically to see if the file reappears.
2783 When following a descriptor, tail does not detect that the file has
2784 been unlinked or renamed and issues no message; even though the file
2785 may no longer be accessible via its original name, it may still be
2788 The option values @samp{descriptor} and @samp{name} may be specified only
2789 with the long form of the option, not with @option{-f}.
2791 The @option{-f} option is ignored if
2792 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2793 Likewise, the @option{-f} option has no effect for any
2794 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2798 This option is the same as @option{--follow=name --retry}. That is, tail
2799 will attempt to reopen a file when it is removed. Should this fail, tail
2800 will keep trying until it becomes accessible again.
2804 This option is useful mainly when following by name (i.e., with
2805 @option{--follow=name}).
2806 Without this option, when tail encounters a file that doesn't
2807 exist or is otherwise inaccessible, it reports that fact and
2808 never checks it again.
2810 @itemx --sleep-interval=@var{number}
2811 @opindex --sleep-interval
2812 Change the number of seconds to wait between iterations (the default is 1.0).
2813 During one iteration, every specified file is checked to see if it has
2815 Historical implementations of @command{tail} have required that
2816 @var{number} be an integer. However, GNU @command{tail} accepts
2817 an arbitrary floating point number (using a period before any
2820 @itemx --pid=@var{pid}
2822 When following by name or by descriptor, you may specify the process ID,
2823 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2824 after that process terminates, tail will also terminate. This will
2825 work properly only if the writer and the tailing process are running on
2826 the same machine. For example, to save the output of a build in a file
2827 and to watch the file grow, if you invoke @command{make} and @command{tail}
2828 like this then the tail process will stop when your build completes.
2829 Without this option, you would have had to kill the @code{tail -f}
2833 $ make >& makerr & tail --pid=$! -f makerr
2836 If you specify a @var{pid} that is not in use or that does not correspond
2837 to the process that is writing to the tailed files, then @command{tail}
2838 may terminate long before any @var{file}s stop growing or it may not
2839 terminate until long after the real writer has terminated.
2840 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2841 will print a warning if this is the case.
2843 @itemx --max-unchanged-stats=@var{n}
2844 @opindex --max-unchanged-stats
2845 When tailing a file by name, if there have been @var{n} (default
2846 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2847 iterations for which the file has not changed, then
2848 @code{open}/@code{fstat} the file to determine if that file name is
2849 still associated with the same device/inode-number pair as before.
2850 When following a log file that is rotated, this is approximately the
2851 number of seconds between when tail prints the last pre-rotation lines
2852 and when it prints the lines that have accumulated in the new log file.
2853 This option is meaningful only when following by name.
2856 @itemx --lines=@var{k}
2859 Output the last @var{k} lines.
2860 However, if @var{k} starts with a @samp{+}, start printing with the
2861 @var{k}th line from the start of each file, instead of from the end.
2862 Size multiplier suffixes are the same as with the @option{-c} option.
2870 Never print file name headers.
2876 Always print file name headers.
2880 For compatibility @command{tail} also supports an obsolete usage
2881 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2882 only if it does not conflict with the usage described
2883 above. This obsolete form uses exactly one option and at most one
2884 file. In the option, @var{count} is an optional decimal number optionally
2885 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2886 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2887 which has the same meaning as @option{-f}.
2889 @vindex _POSIX2_VERSION
2890 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2891 the obsolete option syntax with the same meaning as in counts, and
2892 obsolete usage overrides normal usage when the two conflict.
2893 This obsolete behavior can be enabled or disabled with the
2894 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2897 Scripts intended for use on standard hosts should avoid obsolete
2898 syntax and should use @option{-c @var{count}[b]}, @option{-n
2899 @var{count}}, and/or @option{-f} instead. If your script must also
2900 run on hosts that support only the obsolete syntax, you can often
2901 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2902 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2903 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2904 then @dots{}} to decide which syntax to use.
2906 Even if your script assumes the standard behavior, you should still
2907 beware usages whose behaviors differ depending on the @acronym{POSIX}
2908 version. For example, avoid @samp{tail - main.c}, since it might be
2909 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2910 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2911 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2912 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2917 @node split invocation
2918 @section @command{split}: Split a file into fixed-size pieces
2921 @cindex splitting a file into pieces
2922 @cindex pieces, splitting a file into
2924 @command{split} creates output files containing consecutive sections of
2925 @var{input} (standard input if none is given or @var{input} is
2926 @samp{-}). Synopsis:
2929 split [@var{option}] [@var{input} [@var{prefix}]]
2932 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2933 left over for the last section), into each output file.
2935 @cindex output file name prefix
2936 The output files' names consist of @var{prefix} (@samp{x} by default)
2937 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2938 default), such that concatenating the output files in traditional
2939 sorted order by file name produces
2940 the original input file. If the output file names are exhausted,
2941 @command{split} reports an error without deleting the output files
2944 The program accepts the following options. Also see @ref{Common options}.
2948 @item -l @var{lines}
2949 @itemx --lines=@var{lines}
2952 Put @var{lines} lines of @var{input} into each output file.
2954 For compatibility @command{split} also supports an obsolete
2955 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2956 @var{lines}} instead.
2959 @itemx --bytes=@var{size}
2962 Put @var{size} bytes of @var{input} into each output file.
2963 @multiplierSuffixes{size}
2966 @itemx --line-bytes=@var{size}
2968 @opindex --line-bytes
2969 Put into each output file as many complete lines of @var{input} as
2970 possible without exceeding @var{size} bytes. Individual lines longer than
2971 @var{size} bytes are broken into multiple files.
2972 @var{size} has the same format as for the @option{--bytes} option.
2974 @item -a @var{length}
2975 @itemx --suffix-length=@var{length}
2977 @opindex --suffix-length
2978 Use suffixes of length @var{length}. The default @var{length} is 2.
2981 @itemx --numeric-suffixes
2983 @opindex --numeric-suffixes
2984 Use digits in suffixes rather than lower-case letters.
2988 Write a diagnostic just before each output file is opened.
2995 @node csplit invocation
2996 @section @command{csplit}: Split a file into context-determined pieces
2999 @cindex context splitting
3000 @cindex splitting a file into pieces by context
3002 @command{csplit} creates zero or more output files containing sections of
3003 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3006 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3009 The contents of the output files are determined by the @var{pattern}
3010 arguments, as detailed below. An error occurs if a @var{pattern}
3011 argument refers to a nonexistent line of the input file (e.g., if no
3012 remaining line matches a given regular expression). After every
3013 @var{pattern} has been matched, any remaining input is copied into one
3016 By default, @command{csplit} prints the number of bytes written to each
3017 output file after it has been created.
3019 The types of pattern arguments are:
3024 Create an output file containing the input up to but not including line
3025 @var{n} (a positive integer). If followed by a repeat count, also
3026 create an output file containing the next @var{n} lines of the input
3027 file once for each repeat.
3029 @item /@var{regexp}/[@var{offset}]
3030 Create an output file containing the current line up to (but not
3031 including) the next line of the input file that contains a match for
3032 @var{regexp}. The optional @var{offset} is an integer.
3033 If it is given, the input up to (but not including) the
3034 matching line plus or minus @var{offset} is put into the output file,
3035 and the line after that begins the next section of input.
3037 @item %@var{regexp}%[@var{offset}]
3038 Like the previous type, except that it does not create an output
3039 file, so that section of the input file is effectively ignored.
3041 @item @{@var{repeat-count}@}
3042 Repeat the previous pattern @var{repeat-count} additional
3043 times. The @var{repeat-count} can either be a positive integer or an
3044 asterisk, meaning repeat as many times as necessary until the input is
3049 The output files' names consist of a prefix (@samp{xx} by default)
3050 followed by a suffix. By default, the suffix is an ascending sequence
3051 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3052 concatenating the output files in sorted order by file name produces the
3053 original input file.
3055 By default, if @command{csplit} encounters an error or receives a hangup,
3056 interrupt, quit, or terminate signal, it removes any output files
3057 that it has created so far before it exits.
3059 The program accepts the following options. Also see @ref{Common options}.
3063 @item -f @var{prefix}
3064 @itemx --prefix=@var{prefix}
3067 @cindex output file name prefix
3068 Use @var{prefix} as the output file name prefix.
3070 @item -b @var{suffix}
3071 @itemx --suffix=@var{suffix}
3074 @cindex output file name suffix
3075 Use @var{suffix} as the output file name suffix. When this option is
3076 specified, the suffix string must include exactly one
3077 @code{printf(3)}-style conversion specification, possibly including
3078 format specification flags, a field width, a precision specifications,
3079 or all of these kinds of modifiers. The format letter must convert a
3080 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3081 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3082 entire @var{suffix} is given (with the current output file number) to
3083 @code{sprintf(3)} to form the file name suffixes for each of the
3084 individual output files in turn. If this option is used, the
3085 @option{--digits} option is ignored.
3087 @item -n @var{digits}
3088 @itemx --digits=@var{digits}
3091 Use output file names containing numbers that are @var{digits} digits
3092 long instead of the default 2.
3097 @opindex --keep-files
3098 Do not remove output files when errors are encountered.
3101 @itemx --elide-empty-files
3103 @opindex --elide-empty-files
3104 Suppress the generation of zero-length output files. (In cases where
3105 the section delimiters of the input file are supposed to mark the first
3106 lines of each of the sections, the first output file will generally be a
3107 zero-length file unless you use this option.) The output file sequence
3108 numbers always run consecutively starting from 0, even when this option
3119 Do not print counts of output file sizes.
3125 Here is an example of its usage.
3126 First, create an empty directory for the exercise,
3133 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3136 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3142 Each number printed above is the size of an output
3143 file that csplit has just created.
3144 List the names of those output files:
3151 Use @command{head} to show their contents:
3176 @node Summarizing files
3177 @chapter Summarizing files
3179 @cindex summarizing files
3181 These commands generate just a few numbers representing entire
3185 * wc invocation:: Print newline, word, and byte counts.
3186 * sum invocation:: Print checksum and block counts.
3187 * cksum invocation:: Print CRC checksum and byte counts.
3188 * md5sum invocation:: Print or check MD5 digests.
3189 * sha1sum invocation:: Print or check SHA-1 digests.
3190 * sha2 utilities:: Print or check SHA-2 digests.
3195 @section @command{wc}: Print newline, word, and byte counts
3199 @cindex character count
3203 @command{wc} counts the number of bytes, characters, whitespace-separated
3204 words, and newlines in each given @var{file}, or standard input if none
3205 are given or for a @var{file} of @samp{-}. Synopsis:
3208 wc [@var{option}]@dots{} [@var{file}]@dots{}
3211 @cindex total counts
3212 @command{wc} prints one line of counts for each file, and if the file was
3213 given as an argument, it prints the file name following the counts. If
3214 more than one @var{file} is given, @command{wc} prints a final line
3215 containing the cumulative counts, with the file name @file{total}. The
3216 counts are printed in this order: newlines, words, characters, bytes,
3217 maximum line length.
3218 Each count is printed right-justified in a field with at least one
3219 space between fields so that the numbers and file names normally line
3220 up nicely in columns. The width of the count fields varies depending
3221 on the inputs, so you should not depend on a particular field width.
3222 However, as a @acronym{GNU} extension, if only one count is printed,
3223 it is guaranteed to be printed without leading spaces.
3225 By default, @command{wc} prints three counts: the newline, words, and byte
3226 counts. Options can specify that only certain counts be printed.
3227 Options do not undo others previously given, so
3234 prints both the byte counts and the word counts.
3236 With the @option{--max-line-length} option, @command{wc} prints the length
3237 of the longest line per file, and if there is more than one file it
3238 prints the maximum (not the sum) of those lengths. The line lengths here
3239 are measured in screen columns, according to the current locale and
3240 assuming tab positions in every 8th column.
3242 The program accepts the following options. Also see @ref{Common options}.
3250 Print only the byte counts.
3256 Print only the character counts.
3262 Print only the word counts.
3268 Print only the newline counts.
3271 @itemx --max-line-length
3273 @opindex --max-line-length
3274 Print only the maximum line lengths.
3276 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3277 @itemx --files0-from=@var{file}
3278 @opindex --files0-from=@var{file}
3279 @c This is commented out to avoid a texi2dvi failure.
3280 @c texi2dvi (GNU Texinfo 4.11) 1.104
3281 @c @cindex including files from @command{\cmd\}
3282 Disallow processing files named on the command line, and instead process
3283 those named in file @var{file}; each name being terminated by a zero byte
3284 (@acronym{ASCII} @sc{nul}).
3285 This is useful \withTotalOption\
3286 when the list of file names is so long that it may exceed a command line
3288 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3289 because it splits the list into pieces and makes @command{\cmd\} print
3290 \subListOutput\ for each sublist rather than for the entire list.
3291 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3292 @command{find}, using its @option{-print0} predicate.
3293 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3294 are read from standard input.
3296 @filesZeroFromOption{wc,,a total}
3298 For example, to find the length of the longest line in any @file{.c} or
3299 @file{.h} file in the current hierarchy, do this:
3302 find . -name '*.[ch]' -print0 |
3303 wc -L --files0-from=- | tail -n1
3311 @node sum invocation
3312 @section @command{sum}: Print checksum and block counts
3315 @cindex 16-bit checksum
3316 @cindex checksum, 16-bit
3318 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3319 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3322 sum [@var{option}]@dots{} [@var{file}]@dots{}
3325 @command{sum} prints the checksum for each @var{file} followed by the
3326 number of blocks in the file (rounded up). If more than one @var{file}
3327 is given, file names are also printed (by default). (With the
3328 @option{--sysv} option, corresponding file names are printed when there is
3329 at least one file argument.)
3331 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3332 compatible with BSD @command{sum} and prints file sizes in units of
3335 The program accepts the following options. Also see @ref{Common options}.
3341 @cindex BSD @command{sum}
3342 Use the default (BSD compatible) algorithm. This option is included for
3343 compatibility with the System V @command{sum}. Unless @option{-s} was also
3344 given, it has no effect.
3350 @cindex System V @command{sum}
3351 Compute checksums using an algorithm compatible with System V
3352 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3356 @command{sum} is provided for compatibility; the @command{cksum} program (see
3357 next section) is preferable in new applications.
3362 @node cksum invocation
3363 @section @command{cksum}: Print CRC checksum and byte counts
3366 @cindex cyclic redundancy check
3367 @cindex CRC checksum
3369 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3370 given @var{file}, or standard input if none are given or for a
3371 @var{file} of @samp{-}. Synopsis:
3374 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3377 @command{cksum} prints the CRC checksum for each file along with the number
3378 of bytes in the file, and the file name unless no arguments were given.
3380 @command{cksum} is typically used to ensure that files
3381 transferred by unreliable means (e.g., netnews) have not been corrupted,
3382 by comparing the @command{cksum} output for the received files with the
3383 @command{cksum} output for the original files (typically given in the
3386 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3387 compatible with the BSD or System V @command{sum} algorithms (see the
3388 previous section); it is more robust.
3390 The only options are @option{--help} and @option{--version}. @xref{Common
3396 @node md5sum invocation
3397 @section @command{md5sum}: Print or check MD5 digests
3401 @cindex 128-bit checksum
3402 @cindex checksum, 128-bit
3403 @cindex fingerprint, 128-bit
3404 @cindex message-digest, 128-bit
3406 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3407 @dfn{message-digest}) for each specified @var{file}.
3409 Note: The MD5 digest is more reliable than a simple CRC (provided by
3410 the @command{cksum} command) for detecting accidental file corruption,
3411 as the chances of accidentally having two files with identical MD5
3412 are vanishingly small. However, it should not be considered truly
3413 secure against malicious tampering: although finding a file with a
3414 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3415 considered infeasible at the moment, it is known how to produce
3416 different files with identical MD5 (a ``collision''), something which
3417 can be a security issue in certain contexts. For more secure hashes,
3418 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3419 @ref{sha2 utilities}.
3421 If a @var{file} is specified as @samp{-} or if no files are given
3422 @command{md5sum} computes the checksum for the standard input.
3423 @command{md5sum} can also determine whether a file and checksum are
3424 consistent. Synopsis:
3427 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3430 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3431 indicating a binary or text input file, and the file name.
3432 If @var{file} contains a backslash or newline, the
3433 line is started with a backslash, and each problematic character in
3434 the file name is escaped with a backslash, making the output
3435 unambiguous even in the presence of arbitrary file names.
3436 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3438 The program accepts the following options. Also see @ref{Common options}.
3446 @cindex binary input files
3447 Treat each input file as binary, by reading it in binary mode and
3448 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3449 On systems like @acronym{GNU} that do not distinguish between binary
3450 and text files, this option merely flags each input file as binary:
3451 the MD5 checksum is unaffected. This option is the default on systems
3452 like MS-DOS that distinguish between binary and text files, except
3453 for reading standard input when standard input is a terminal.
3457 Read file names and checksum information (not data) from each
3458 @var{file} (or from stdin if no @var{file} was specified) and report
3459 whether the checksums match the contents of the named files.
3460 The input to this mode of @command{md5sum} is usually the output of
3461 a prior, checksum-generating run of @samp{md5sum}.
3462 Each valid line of input consists of an MD5 checksum, a binary/text
3463 flag, and then a file name.
3464 Binary files are marked with @samp{*}, text with @samp{ }.
3465 For each such line, @command{md5sum} reads the named file and computes its
3466 MD5 checksum. Then, if the computed message digest does not match the
3467 one on the line with the file name, the file is noted as having
3468 failed the test. Otherwise, the file passes the test.
3469 By default, for each valid line, one line is written to standard
3470 output indicating whether the named file passed the test.
3471 After all checks have been performed, if there were any failures,
3472 a warning is issued to standard error.
3473 Use the @option{--status} option to inhibit that output.
3474 If any listed file cannot be opened or read, if any valid line has
3475 an MD5 checksum inconsistent with the associated file, or if no valid
3476 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3477 it exits successfully.
3481 @cindex verifying MD5 checksums
3482 This option is useful only when verifying checksums.
3483 When verifying checksums, don't generate an 'OK' message per successfully
3484 checked file. Files that fail the verification are reported in the
3485 default one-line-per-file format. If there is any checksum mismatch,
3486 print a warning summarizing the failures to standard error.
3490 @cindex verifying MD5 checksums
3491 This option is useful only when verifying checksums.
3492 When verifying checksums, don't generate the default one-line-per-file
3493 diagnostic and don't output the warning summarizing any failures.
3494 Failures to open or read a file still evoke individual diagnostics to
3496 If all listed files are readable and are consistent with the associated
3497 MD5 checksums, exit successfully. Otherwise exit with a status code
3498 indicating there was a failure.
3504 @cindex text input files
3505 Treat each input file as text, by reading it in text mode and
3506 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3507 This option is the default on systems like @acronym{GNU} that do not
3508 distinguish between binary and text files. On other systems, it is
3509 the default for reading standard input when standard input is a
3516 @cindex verifying MD5 checksums
3517 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3518 This option is useful only if all but a few lines in the checked input
3526 @node sha1sum invocation
3527 @section @command{sha1sum}: Print or check SHA-1 digests
3531 @cindex 160-bit checksum
3532 @cindex checksum, 160-bit
3533 @cindex fingerprint, 160-bit
3534 @cindex message-digest, 160-bit
3536 @command{sha1sum} computes a 160-bit checksum for each specified
3537 @var{file}. The usage and options of this command are precisely the
3538 same as for @command{md5sum}. @xref{md5sum invocation}.
3540 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3541 it are known (different files having the same fingerprint). However,
3542 it is known that they can be produced with considerable, but not
3543 unreasonable, resources. For this reason, it is generally considered
3544 that SHA-1 should be gradually phased out in favor of the more secure
3545 SHA-2 hash algorithms. @xref{sha2 utilities}.
3548 @node sha2 utilities
3549 @section sha2 utilities: Print or check SHA-2 digests
3556 @cindex 224-bit checksum
3557 @cindex 256-bit checksum
3558 @cindex 384-bit checksum
3559 @cindex 512-bit checksum
3560 @cindex checksum, 224-bit
3561 @cindex checksum, 256-bit
3562 @cindex checksum, 384-bit
3563 @cindex checksum, 512-bit
3564 @cindex fingerprint, 224-bit
3565 @cindex fingerprint, 256-bit
3566 @cindex fingerprint, 384-bit
3567 @cindex fingerprint, 512-bit
3568 @cindex message-digest, 224-bit
3569 @cindex message-digest, 256-bit
3570 @cindex message-digest, 384-bit
3571 @cindex message-digest, 512-bit
3573 The commands @command{sha224sum}, @command{sha256sum},
3574 @command{sha384sum} and @command{sha512sum} compute checksums of
3575 various lengths (respectively 224, 256, 384 and 512 bits),
3576 collectively known as the SHA-2 hashes. The usage and options of
3577 these commands are precisely the same as for @command{md5sum}.
3578 @xref{md5sum invocation}.
3580 Note: The SHA384 and SHA512 digests are considerably slower to
3581 compute, especially on 32-bit computers, than SHA224 or SHA256.
3584 @node Operating on sorted files
3585 @chapter Operating on sorted files
3587 @cindex operating on sorted files
3588 @cindex sorted files, operations on
3590 These commands work with (or produce) sorted files.
3593 * sort invocation:: Sort text files.
3594 * shuf invocation:: Shuffle text files.
3595 * uniq invocation:: Uniquify files.
3596 * comm invocation:: Compare two sorted files line by line.
3597 * ptx invocation:: Produce a permuted index of file contents.
3598 * tsort invocation:: Topological sort.
3602 @node sort invocation
3603 @section @command{sort}: Sort text files
3606 @cindex sorting files
3608 @command{sort} sorts, merges, or compares all the lines from the given
3609 files, or standard input if none are given or for a @var{file} of
3610 @samp{-}. By default, @command{sort} writes the results to standard
3614 sort [@var{option}]@dots{} [@var{file}]@dots{}
3617 @command{sort} has three modes of operation: sort (the default), merge,
3618 and check for sortedness. The following options change the operation
3625 @itemx --check=diagnose-first
3628 @cindex checking for sortedness
3629 Check whether the given file is already sorted: if it is not all
3630 sorted, print a diagnostic containing the first out-of-order line and
3631 exit with a status of 1.
3632 Otherwise, exit successfully.
3633 At most one input file can be given.
3636 @itemx --check=quiet
3637 @itemx --check=silent
3640 @cindex checking for sortedness
3641 Exit successfully if the given file is already sorted, and
3642 exit with status 1 otherwise.
3643 At most one input file can be given.
3644 This is like @option{-c}, except it does not print a diagnostic.
3650 @cindex merging sorted files
3651 Merge the given files by sorting them as a group. Each input file must
3652 always be individually sorted. It always works to sort instead of
3653 merge; merging is provided because it is faster, in the case where it
3658 @cindex sort stability
3659 @cindex sort's last-resort comparison
3660 A pair of lines is compared as follows:
3661 @command{sort} compares each pair of fields, in the
3662 order specified on the command line, according to the associated
3663 ordering options, until a difference is found or no fields are left.
3664 If no key fields are specified, @command{sort} uses a default key of
3665 the entire line. Finally, as a last resort when all keys compare
3666 equal, @command{sort} compares entire lines as if no ordering options
3667 other than @option{--reverse} (@option{-r}) were specified. The
3668 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3669 comparison} so that lines in which all fields compare equal are left
3670 in their original relative order. The @option{--unique}
3671 (@option{-u}) option also disables the last-resort comparison.
3675 Unless otherwise specified, all comparisons use the character collating
3676 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3677 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3678 to @samp{en_US}), then @command{sort} may produce output that is sorted
3679 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3680 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3681 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3682 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3683 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3684 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3685 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3687 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3688 limit on input line length or restrictions on bytes allowed within lines.
3689 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3690 @command{sort} silently supplies one. A line's trailing newline is not
3691 part of the line for comparison purposes.
3693 @cindex exit status of @command{sort}
3697 0 if no error occurred
3698 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3699 2 if an error occurred
3703 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3704 value as the directory for temporary files instead of @file{/tmp}. The
3705 @option{--temporary-directory} (@option{-T}) option in turn overrides
3706 the environment variable.
3708 The following options affect the ordering of output lines. They may be
3709 specified globally or as part of a specific key field. If no key
3710 fields are specified, global options apply to comparison of entire
3711 lines; otherwise the global options are inherited by key fields that do
3712 not specify any special options of their own. In pre-@acronym{POSIX}
3713 versions of @command{sort}, global options affect only later key fields,
3714 so portable shell scripts should specify global options first.
3719 @itemx --ignore-leading-blanks
3721 @opindex --ignore-leading-blanks
3722 @cindex blanks, ignoring leading
3724 Ignore leading blanks when finding sort keys in each line.
3725 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3726 can change this. Note blanks may be ignored by your locale's collating
3727 rules, but without this option they will be significant for character
3728 positions specified in keys with the @option{-k} option.
3731 @itemx --dictionary-order
3733 @opindex --dictionary-order
3734 @cindex dictionary order
3735 @cindex phone directory order
3736 @cindex telephone directory order
3738 Sort in @dfn{phone directory} order: ignore all characters except
3739 letters, digits and blanks when sorting.
3740 By default letters and digits are those of @acronym{ASCII} and a blank
3741 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3744 @itemx --ignore-case
3746 @opindex --ignore-case
3747 @cindex ignoring case
3748 @cindex case folding
3750 Fold lowercase characters into the equivalent uppercase characters when
3751 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3752 The @env{LC_CTYPE} locale determines character types.
3753 When used with @option{--unique} those lower case equivalent lines are
3754 thrown away. (There is currently no way to throw away the upper case
3755 equivalent instead. (Any @option{--reverse} given would only affect
3756 the final result, after the throwing away.))
3759 @itemx --general-numeric-sort
3760 @itemx --sort=general-numeric
3762 @opindex --general-numeric-sort
3764 @cindex general numeric sort
3766 Sort numerically, using the standard C function @code{strtod} to convert
3767 a prefix of each line to a double-precision floating point number.
3768 This allows floating point numbers to be specified in scientific notation,
3769 like @code{1.0e-34} and @code{10e100}.
3770 The @env{LC_NUMERIC} locale determines the decimal-point character.
3771 Do not report overflow, underflow, or conversion errors.
3772 Use the following collating sequence:
3776 Lines that do not start with numbers (all considered to be equal).
3778 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3779 in a consistent but machine-dependent order.
3783 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3788 Use this option only if there is no alternative; it is much slower than
3789 @option{--numeric-sort} (@option{-n}) and it can lose information when
3790 converting to floating point.
3793 @itemx --human-numeric-sort
3794 @itemx --sort=human-numeric
3796 @opindex --human-numeric-sort
3798 @cindex human numeric sort
3800 Sort numerically, as per the @option{--numeric-sort} option below, and in
3801 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3802 Note a mixture of IEC and SI suffixes is not supported and will
3803 be flagged as an error. Also the numbers must be abbreviated uniformly.
3804 I.E. values with different precisions like 6000K and 5M will be sorted
3808 @itemx --ignore-nonprinting
3810 @opindex --ignore-nonprinting
3811 @cindex nonprinting characters, ignoring
3812 @cindex unprintable characters, ignoring
3814 Ignore nonprinting characters.
3815 The @env{LC_CTYPE} locale determines character types.
3816 This option has no effect if the stronger @option{--dictionary-order}
3817 (@option{-d}) option is also given.
3823 @opindex --month-sort
3825 @cindex months, sorting by
3827 An initial string, consisting of any amount of blanks, followed
3828 by a month name abbreviation, is folded to UPPER case and
3829 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3830 Invalid names compare low to valid names. The @env{LC_TIME} locale
3831 category determines the month spellings.
3832 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3836 @itemx --numeric-sort
3837 @itemx --sort=numeric
3839 @opindex --numeric-sort
3841 @cindex numeric sort
3843 Sort numerically. The number begins each line and consists
3844 of optional blanks, an optional @samp{-} sign, and zero or more
3845 digits possibly separated by thousands separators, optionally followed
3846 by a decimal-point character and zero or more digits. An empty
3847 number is treated as @samp{0}. The @env{LC_NUMERIC}
3848 locale specifies the decimal-point character and thousands separator.
3849 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3852 Comparison is exact; there is no rounding error.
3854 Neither a leading @samp{+} nor exponential notation is recognized.
3855 To compare such strings numerically, use the
3856 @option{--general-numeric-sort} (@option{-g}) option.
3859 @itemx --version-sort
3861 @opindex --version-sort
3862 @cindex version number sort
3864 Sort per @code{strverscmp(3)}. This is a normal string comparison, except
3865 that embedded decimal numbers are sorted by numeric value
3866 (see @option{--numeric-sort} above).
3872 @cindex reverse sorting
3873 Reverse the result of comparison, so that lines with greater key values
3874 appear earlier in the output instead of later.
3877 @itemx --random-sort
3878 @itemx --sort=random
3880 @opindex --random-sort
3883 Sort by hashing the input keys and then sorting the hash values.
3884 Choose the hash function at random, ensuring that it is free of
3885 collisions so that differing keys have differing hash values. This is
3886 like a random permutation of the inputs (@pxref{shuf invocation}),
3887 except that keys with the same value sort together.
3889 If multiple random sort fields are specified, the same random hash
3890 function is used for all fields. To use different random hash
3891 functions for different fields, you can invoke @command{sort} more
3894 The choice of hash function is affected by the
3895 @option{--random-source} option.
3903 @item --compress-program=@var{prog}
3904 Compress any temporary files with the program @var{prog}.
3906 With no arguments, @var{prog} must compress standard input to standard
3907 output, and when given the @option{-d} option it must decompress
3908 standard input to standard output.
3910 Terminate with an error if @var{prog} exits with nonzero status.
3912 White space and the backslash character should not appear in
3913 @var{prog}; they are reserved for future use.
3915 @filesZeroFromOption{sort,,sorted output}
3917 @item -k @var{pos1}[,@var{pos2}]
3918 @itemx --key=@var{pos1}[,@var{pos2}]
3922 Specify a sort field that consists of the part of the line between
3923 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3924 omitted), @emph{inclusive}.
3926 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3927 where @var{f} is the number of the field to use, and @var{c} is the number
3928 of the first character from the beginning of the field. Fields and character
3929 positions are numbered starting with 1; a character position of zero in
3930 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3931 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3932 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3933 @var{opts} are ordering options, allowing individual keys to be sorted
3934 according to different rules; see below for details. Keys can span
3937 Example: To sort on the second field, use @option{--key=2,2}
3938 (@option{-k 2,2}). See below for more notes on keys and more examples.
3940 @item --batch-size=@var{nmerge}
3941 @opindex --batch-size
3942 @cindex number of inputs to merge, nmerge
3943 Merge at most @var{nmerge} inputs at once.
3945 When @command{sort} has to merge more than @var{nmerge} inputs,
3946 it merges them in groups of @var{nmerge}, saving the result in
3947 a temporary file, which is then used as an input in a subsequent merge.
3949 A large value of @var{nmerge} may improve merge performance and decrease
3950 temporary storage utilization at the expense of increased memory usage
3951 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3952 requirements and I/0 at the expense of temporary storage consumption and
3955 The value of @var{nmerge} must be at least 2. The default value is
3956 currently 16, but this is implementation-dependent and may change in
3959 The value of @var{nmerge} may be bounded by a resource limit for open
3960 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3961 OPEN_MAX} may display limits for your systems; these limits may be
3962 modified further if your program already has some files open, or if
3963 the operating system has other limits on the number of open files. If
3964 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3965 silently uses a smaller value.
3967 @item -o @var{output-file}
3968 @itemx --output=@var{output-file}
3971 @cindex overwriting of input, allowed
3972 Write output to @var{output-file} instead of standard output.
3973 Normally, @command{sort} reads all input before opening
3974 @var{output-file}, so you can safely sort a file in place by using
3975 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3976 However, @command{sort} with @option{--merge} (@option{-m}) can open
3977 the output file before reading all input, so a command like @code{cat
3978 F | sort -m -o F - G} is not safe as @command{sort} might start
3979 writing @file{F} before @command{cat} is done reading it.
3981 @vindex POSIXLY_CORRECT
3982 On newer systems, @option{-o} cannot appear after an input file if
3983 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3984 scripts should specify @option{-o @var{output-file}} before any input
3987 @item --random-source=@var{file}
3988 @opindex --random-source
3989 @cindex random source for sorting
3990 Use @var{file} as a source of random data used to determine which
3991 random hash function to use with the @option{-R} option. @xref{Random
3998 @cindex sort stability
3999 @cindex sort's last-resort comparison
4001 Make @command{sort} stable by disabling its last-resort comparison.
4002 This option has no effect if no fields or global ordering options
4003 other than @option{--reverse} (@option{-r}) are specified.
4006 @itemx --buffer-size=@var{size}
4008 @opindex --buffer-size
4009 @cindex size for main memory sorting
4010 Use a main-memory sort buffer of the given @var{size}. By default,
4011 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4012 @var{size} to be interpreted as a percentage of physical memory.
4013 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4014 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4015 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4016 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4019 This option can improve the performance of @command{sort} by causing it
4020 to start with a larger or smaller sort buffer than the default.
4021 However, this option affects only the initial buffer size. The buffer
4022 grows beyond @var{size} if @command{sort} encounters input lines larger
4025 @item -t @var{separator}
4026 @itemx --field-separator=@var{separator}
4028 @opindex --field-separator
4029 @cindex field separator character
4030 Use character @var{separator} as the field separator when finding the
4031 sort keys in each line. By default, fields are separated by the empty
4032 string between a non-blank character and a blank character.
4033 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4036 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4037 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4038 not considered to be part of either the field preceding or the field
4039 following, so with @samp{sort @w{-t " "}} the same input line has
4040 three fields: an empty field, @samp{foo}, and @samp{bar}.
4041 However, fields that extend to the end of the line,
4042 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4043 retain the field separators present between the endpoints of the range.
4045 To specify @acronym{ASCII} @sc{nul} as the field separator,
4046 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4048 @item -T @var{tempdir}
4049 @itemx --temporary-directory=@var{tempdir}
4051 @opindex --temporary-directory
4052 @cindex temporary directory
4054 Use directory @var{tempdir} to store temporary files, overriding the
4055 @env{TMPDIR} environment variable. If this option is given more than
4056 once, temporary files are stored in all the directories given. If you
4057 have a large sort or merge that is I/O-bound, you can often improve
4058 performance by using this option to specify directories on different
4059 disks and controllers.
4065 @cindex uniquifying output
4067 Normally, output only the first of a sequence of lines that compare
4068 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4069 check that no pair of consecutive lines compares equal.
4071 This option also disables the default last-resort comparison.
4073 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4074 this equivalence does not extend to arbitrary @command{sort} options.
4075 For example, @code{sort -n -u} inspects only the value of the initial
4076 numeric string when checking for uniqueness, whereas @code{sort -n |
4077 uniq} inspects the entire line. @xref{uniq invocation}.
4079 @macro zeroTerminatedOption
4081 @itemx --zero-terminated
4083 @opindex --zero-terminated
4084 @cindex process zero-terminated items
4085 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4086 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4087 and terminate output items with @acronym{ASCII} @sc{nul}.
4088 This option can be useful in conjunction with @samp{perl -0} or
4089 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4090 reliably handle arbitrary file names (even those containing blanks
4091 or other special characters).
4093 @zeroTerminatedOption
4097 Historical (BSD and System V) implementations of @command{sort} have
4098 differed in their interpretation of some options, particularly
4099 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4100 behavior, which is usually (but not always!) like the System V behavior.
4101 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4102 consistency, @option{-M} has been changed in the same way. This may
4103 affect the meaning of character positions in field specifications in
4104 obscure cases. The only fix is to add an explicit @option{-b}.
4106 A position in a sort field specified with @option{-k} may have any
4107 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4108 global ordering options are inherited by that particular field. The
4109 @option{-b} option may be independently attached to either or both of
4110 the start and end positions of a field specification, and if it is
4111 inherited from the global options it will be attached to both.
4112 If input lines can contain leading or adjacent blanks and @option{-t}
4113 is not used, then @option{-k} is typically combined with @option{-b} or
4114 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4115 the varying numbers of leading blanks in fields can cause confusing results.
4117 If the start position in a sort field specifier falls after the end of
4118 the line or after the end field, the field is empty. If the @option{-b}
4119 option was specified, the @samp{.@var{c}} part of a field specification
4120 is counted from the first nonblank character of the field.
4122 @vindex _POSIX2_VERSION
4123 @vindex POSIXLY_CORRECT
4124 On older systems, @command{sort} supports an obsolete origin-zero
4125 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4126 This obsolete behavior can be enabled or disabled with the
4127 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4128 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4129 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4131 Scripts intended for use on standard hosts should avoid obsolete
4132 syntax and should use @option{-k} instead. For example, avoid
4133 @samp{sort +2}, since it might be interpreted as either @samp{sort
4134 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4135 support only the obsolete syntax, it can use a test like @samp{if sort
4136 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4139 Here are some examples to illustrate various combinations of options.
4144 Sort in descending (reverse) numeric order.
4151 Sort alphabetically, omitting the first and second fields
4152 and the blanks at the start of the third field.
4153 This uses a single key composed of the characters beginning
4154 at the start of the first nonblank character in field three
4155 and extending to the end of each line.
4162 Sort numerically on the second field and resolve ties by sorting
4163 alphabetically on the third and fourth characters of field five.
4164 Use @samp{:} as the field delimiter.
4167 sort -t : -k 2,2n -k 5.3,5.4
4170 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4171 @command{sort} would have used all characters beginning in the second field
4172 and extending to the end of the line as the primary @emph{numeric}
4173 key. For the large majority of applications, treating keys spanning
4174 more than one field as numeric will not do what you expect.
4176 Also note that the @samp{n} modifier was applied to the field-end
4177 specifier for the first key. It would have been equivalent to
4178 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4179 @samp{b} apply to the associated @emph{field}, regardless of whether
4180 the modifier character is attached to the field-start and/or the
4181 field-end part of the key specifier.
4184 Sort the password file on the fifth field and ignore any
4185 leading blanks. Sort lines with equal values in field five
4186 on the numeric user ID in field three. Fields are separated
4190 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4191 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4192 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4195 These three commands have equivalent effect. The first specifies that
4196 the first key's start position ignores leading blanks and the second
4197 key is sorted numerically. The other two commands rely on global
4198 options being inherited by sort keys that lack modifiers. The inheritance
4199 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4200 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4201 character position is not affected by whether initial blanks are
4205 Sort a set of log files, primarily by IPv4 address and secondarily by
4206 time stamp. If two lines' primary and secondary keys are identical,
4207 output the lines in the same order that they were input. The log
4208 files contain lines that look like this:
4211 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4212 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4215 Fields are separated by exactly one space. Sort IPv4 addresses
4216 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4217 because 61 is less than 129.
4220 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4221 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4224 This example cannot be done with a single @command{sort} invocation,
4225 since IPv4 address components are separated by @samp{.} while dates
4226 come just after a space. So it is broken down into two invocations of
4227 @command{sort}: the first sorts by time stamp and the second by IPv4
4228 address. The time stamp is sorted by year, then month, then day, and
4229 finally by hour-minute-second field, using @option{-k} to isolate each
4230 field. Except for hour-minute-second there's no need to specify the
4231 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4232 based on leading prefixes that cannot cross field boundaries. The
4233 IPv4 addresses are sorted lexicographically. The second sort uses
4234 @samp{-s} so that ties in the primary key are broken by the secondary
4235 key; the first sort uses @samp{-s} so that the combination of the two
4239 Generate a tags file in case-insensitive sorted order.
4242 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4245 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4246 that file names that contain blanks or other special characters are
4248 by the sort operation.
4250 @c This example is a bit contrived and needs more explanation.
4252 @c Sort records separated by an arbitrary string by using a pipe to convert
4253 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4254 @c and converting each @samp{\0} back to the original record delimiter.
4257 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4261 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4262 sort lines according to their length.
4265 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4268 In general this technique can be used to sort data that the @command{sort}
4269 command does not support, or is inefficient at, sorting directly.
4272 Shuffle a list of directories, but preserve the order of files within
4273 each directory. For instance, one could use this to generate a music
4274 playlist in which albums are shuffled but the songs of each album are
4278 ls */* | sort -t / -k 1,1R -k 2,2
4284 @node shuf invocation
4285 @section @command{shuf}: Shuffling text
4288 @cindex shuffling files
4290 @command{shuf} shuffles its input by outputting a random permutation
4291 of its input lines. Each output permutation is equally likely.
4295 shuf [@var{option}]@dots{} [@var{file}]
4296 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4297 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4300 @command{shuf} has three modes of operation that affect where it
4301 obtains its input lines. By default, it reads lines from standard
4302 input. The following options change the operation mode:
4310 @cindex command-line operands to shuffle
4311 Treat each command-line operand as an input line.
4313 @item -i @var{lo}-@var{hi}
4314 @itemx --input-range=@var{lo}-@var{hi}
4316 @opindex --input-range
4317 @cindex input range to shuffle
4318 Act as if input came from a file containing the range of unsigned
4319 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4323 @command{shuf}'s other options can affect its behavior in all
4328 @item -n @var{lines}
4329 @itemx --head-count=@var{count}
4331 @opindex --head-count
4332 @cindex head of output
4333 Output at most @var{count} lines. By default, all input lines are
4336 @item -o @var{output-file}
4337 @itemx --output=@var{output-file}
4340 @cindex overwriting of input, allowed
4341 Write output to @var{output-file} instead of standard output.
4342 @command{shuf} reads all input before opening
4343 @var{output-file}, so you can safely shuffle a file in place by using
4344 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4346 @item --random-source=@var{file}
4347 @opindex --random-source
4348 @cindex random source for shuffling
4349 Use @var{file} as a source of random data used to determine which
4350 permutation to generate. @xref{Random sources}.
4352 @zeroTerminatedOption
4368 might produce the output
4378 Similarly, the command:
4381 shuf -e clubs hearts diamonds spades
4395 and the command @samp{shuf -i 1-4} might output:
4405 These examples all have four input lines, so @command{shuf} might
4406 produce any of the twenty-four possible permutations of the input. In
4407 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4408 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4409 output permutations.
4414 @node uniq invocation
4415 @section @command{uniq}: Uniquify files
4418 @cindex uniquify files
4420 @command{uniq} writes the unique lines in the given @file{input}, or
4421 standard input if nothing is given or for an @var{input} name of
4425 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4428 By default, @command{uniq} prints its input lines, except that
4429 it discards all but the first of adjacent repeated lines, so that
4430 no output lines are repeated. Optionally, it can instead discard
4431 lines that are not repeated, or all repeated lines.
4433 The input need not be sorted, but repeated input lines are detected
4434 only if they are adjacent. If you want to discard non-adjacent
4435 duplicate lines, perhaps you want to use @code{sort -u}.
4436 @xref{sort invocation}.
4439 Comparisons honor the rules specified by the @env{LC_COLLATE}
4442 If no @var{output} file is specified, @command{uniq} writes to standard
4445 The program accepts the following options. Also see @ref{Common options}.
4450 @itemx --skip-fields=@var{n}
4452 @opindex --skip-fields
4453 Skip @var{n} fields on each line before checking for uniqueness. Use
4454 a null string for comparison if a line has fewer than @var{n} fields. Fields
4455 are sequences of non-space non-tab characters that are separated from
4456 each other by at least one space or tab.
4458 For compatibility @command{uniq} supports an obsolete option syntax
4459 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4462 @itemx --skip-chars=@var{n}
4464 @opindex --skip-chars
4465 Skip @var{n} characters before checking for uniqueness. Use a null string
4466 for comparison if a line has fewer than @var{n} characters. If you use both
4467 the field and character skipping options, fields are skipped over first.
4469 @vindex _POSIX2_VERSION
4470 On older systems, @command{uniq} supports an obsolete option syntax
4472 This obsolete behavior can be enabled or disabled with the
4473 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4474 conformance}), but portable scripts should avoid commands whose
4475 behavior depends on this variable.
4476 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4477 the ambiguous @samp{uniq +10}.
4483 Print the number of times each line occurred along with the line.
4486 @itemx --ignore-case
4488 @opindex --ignore-case
4489 Ignore differences in case when comparing lines.
4495 @cindex repeated lines, outputting
4496 Discard lines that are not repeated. When used by itself, this option
4497 causes @command{uniq} to print the first copy of each repeated line,
4501 @itemx --all-repeated[=@var{delimit-method}]
4503 @opindex --all-repeated
4504 @cindex all repeated lines, outputting
4505 Do not discard the second and subsequent repeated input lines,
4506 but discard lines that are not repeated.
4507 This option is useful mainly in conjunction with other options e.g.,
4508 to ignore case or to compare only selected fields.
4509 The optional @var{delimit-method} tells how to delimit
4510 groups of repeated lines, and must be one of the following:
4515 Do not delimit groups of repeated lines.
4516 This is equivalent to @option{--all-repeated} (@option{-D}).
4519 Output a newline before each group of repeated lines.
4520 With @option{--zero-terminated} (@option{-z}), use a zero
4521 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4524 Separate groups of repeated lines with a single newline.
4525 With @option{--zero-terminated} (@option{-z}), use a zero
4526 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4527 This is the same as using @samp{prepend}, except that
4528 no delimiter is inserted before the first group, and hence
4529 may be better suited for output direct to users.
4532 Note that when groups are delimited and the input stream contains
4533 two or more consecutive blank lines, then the output is ambiguous.
4534 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4535 each sequence of consecutive newlines with a single newline.
4537 This is a @sc{gnu} extension.
4538 @c FIXME: give an example showing *how* it's useful
4544 @cindex unique lines, outputting
4545 Discard the first repeated line. When used by itself, this option
4546 causes @command{uniq} to print unique lines, and nothing else.
4549 @itemx --check-chars=@var{n}
4551 @opindex --check-chars
4552 Compare at most @var{n} characters on each line (after skipping any specified
4553 fields and characters). By default the entire rest of the lines are
4556 @zeroTerminatedOption
4563 @node comm invocation
4564 @section @command{comm}: Compare two sorted files line by line
4567 @cindex line-by-line comparison
4568 @cindex comparing sorted files
4570 @command{comm} writes to standard output lines that are common, and lines
4571 that are unique, to two input files; a file name of @samp{-} means
4572 standard input. Synopsis:
4575 comm [@var{option}]@dots{} @var{file1} @var{file2}
4579 Before @command{comm} can be used, the input files must be sorted using the
4580 collating sequence specified by the @env{LC_COLLATE} locale.
4581 If an input file ends in a non-newline
4582 character, a newline is silently appended. The @command{sort} command with
4583 no options always outputs a file that is suitable input to @command{comm}.
4585 @cindex differing lines
4586 @cindex common lines
4587 With no options, @command{comm} produces three-column output. Column one
4588 contains lines unique to @var{file1}, column two contains lines unique
4589 to @var{file2}, and column three contains lines common to both files.
4590 Columns are separated by a single TAB character.
4591 @c FIXME: when there's an option to supply an alternative separator
4592 @c string, append `by default' to the above sentence.
4597 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4598 the corresponding columns (and separators). Also see @ref{Common options}.
4600 Unlike some other comparison utilities, @command{comm} has an exit
4601 status that does not depend on the result of the comparison.
4602 Upon normal completion @command{comm} produces an exit code of zero.
4603 If there is an error it exits with nonzero status.
4605 @macro checkOrderOption{cmd}
4606 If the @option{--check-order} option is given, unsorted inputs will
4607 cause a fatal error message. If the option @option{--nocheck-order}
4608 is given, unsorted inputs will never cause an error message. If
4609 neither of these options is given, wrongly sorted inputs are diagnosed
4610 only if an input file is found to contain unpairable lines. If an
4611 input file is diagnosed as being unsorted, the @command{\cmd\} command
4612 will exit with a nonzero status (and the output should not be used).
4614 Forcing @command{\cmd\} to process wrongly sorted input files
4615 containing unpairable lines by specifying @option{--nocheck-order} is
4616 not guaranteed to produce any particular output. The output will
4617 probably not correspond with whatever you hoped it would be.
4619 @checkOrderOption{comm}
4624 Fail with an error message if either input file is wrongly ordered.
4626 @item --nocheck-order
4627 Do not check that both input files are in sorted order.
4631 @item --output-delimiter=@var{str}
4632 Print @var{str} between adjacent output columns,
4633 rather than the default of a single TAB character.
4635 The delimiter @var{str} may not be empty.
4639 @node ptx invocation
4640 @section @command{ptx}: Produce permuted indexes
4644 @command{ptx} reads a text file and essentially produces a permuted index, with
4645 each keyword in its context. The calling sketch is either one of:
4648 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4649 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4652 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4653 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4654 limitations and changing several of the program's default option values.
4655 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4656 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4657 document. For the full list, see @xref{Compatibility in ptx}.
4659 Individual options are explained in the following sections.
4661 When @sc{gnu} extensions are enabled, there may be zero, one or several
4662 @var{file}s after the options. If there is no @var{file}, the program
4663 reads the standard input. If there is one or several @var{file}s, they
4664 give the name of input files which are all read in turn, as if all the
4665 input files were concatenated. However, there is a full contextual
4666 break between each file and, when automatic referencing is requested,
4667 file names and line numbers refer to individual text input files. In
4668 all cases, the program outputs the permuted index to the standard
4671 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4672 operates in traditional mode, there may be zero, one or two parameters
4673 besides the options. If there are no parameters, the program reads the
4674 standard input and outputs the permuted index to the standard output.
4675 If there is only one parameter, it names the text @var{input} to be read
4676 instead of the standard input. If two parameters are given, they give
4677 respectively the name of the @var{input} file to read and the name of
4678 the @var{output} file to produce. @emph{Be very careful} to note that,
4679 in this case, the contents of file given by the second parameter is
4680 destroyed. This behavior is dictated by System V @command{ptx}
4681 compatibility; @sc{gnu} Standards normally discourage output parameters not
4682 introduced by an option.
4684 Note that for @emph{any} file named as the value of an option or as an
4685 input text file, a single dash @kbd{-} may be used, in which case
4686 standard input is assumed. However, it would not make sense to use this
4687 convention more than once per program invocation.
4690 * General options in ptx:: Options which affect general program behavior.
4691 * Charset selection in ptx:: Underlying character set considerations.
4692 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4693 * Output formatting in ptx:: Types of output format, and sizing the fields.
4694 * Compatibility in ptx::
4698 @node General options in ptx
4699 @subsection General options
4704 @itemx --traditional
4705 As already explained, this option disables all @sc{gnu} extensions to
4706 @command{ptx} and switches to traditional mode.
4709 Print a short help on standard output, then exit without further
4713 Print the program version on standard output, then exit without further
4721 @node Charset selection in ptx
4722 @subsection Charset selection
4724 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4725 As it is set up now, the program assumes that the input file is coded
4726 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4727 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4728 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4729 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4730 of characters which are letters is different; this alters the behavior
4731 of regular expression matching. Thus, the default regular expression
4732 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4733 however, is still crude; it obeys the underlying character set ordering
4739 @itemx --ignore-case
4740 Fold lower case letters to upper case for sorting.
4745 @node Input processing in ptx
4746 @subsection Word selection and input processing
4751 @itemx --break-file=@var{file}
4753 This option provides an alternative (to @option{-W}) method of describing
4754 which characters make up words. It introduces the name of a
4755 file which contains a list of characters which can@emph{not} be part of
4756 one word; this file is called the @dfn{Break file}. Any character which
4757 is not part of the Break file is a word constituent. If both options
4758 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4759 @option{-b} is ignored.
4761 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4762 break character is to write all the break characters in the file with no
4763 newline at all, not even at the end of the file. When @sc{gnu} extensions
4764 are disabled, spaces, tabs and newlines are always considered as break
4765 characters even if not included in the Break file.
4768 @itemx --ignore-file=@var{file}
4770 The file associated with this option contains a list of words which will
4771 never be taken as keywords in concordance output. It is called the
4772 @dfn{Ignore file}. The file contains exactly one word in each line; the
4773 end of line separation of words is not subject to the value of the
4777 @itemx --only-file=@var{file}
4779 The file associated with this option contains a list of words which will
4780 be retained in concordance output; any word not mentioned in this file
4781 is ignored. The file is called the @dfn{Only file}. The file contains
4782 exactly one word in each line; the end of line separation of words is
4783 not subject to the value of the @option{-S} option.
4785 There is no default for the Only file. When both an Only file and an
4786 Ignore file are specified, a word is considered a keyword only
4787 if it is listed in the Only file and not in the Ignore file.
4792 On each input line, the leading sequence of non-white space characters will be
4793 taken to be a reference that has the purpose of identifying this input
4794 line in the resulting permuted index. For more information about reference
4795 production, see @xref{Output formatting in ptx}.
4796 Using this option changes the default value for option @option{-S}.
4798 Using this option, the program does not try very hard to remove
4799 references from contexts in output, but it succeeds in doing so
4800 @emph{when} the context ends exactly at the newline. If option
4801 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4802 are disabled, this condition is always met and references are completely
4803 excluded from the output contexts.
4805 @item -S @var{regexp}
4806 @itemx --sentence-regexp=@var{regexp}
4808 This option selects which regular expression will describe the end of a
4809 line or the end of a sentence. In fact, this regular expression is not
4810 the only distinction between end of lines or end of sentences, and input
4811 line boundaries have no special significance outside this option. By
4812 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4813 used, end of sentences are used. In this case, this @var{regex} is
4814 imported from @sc{gnu} Emacs:
4817 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4820 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4821 of lines are used; in this case, the default @var{regexp} is just:
4827 Using an empty @var{regexp} is equivalent to completely disabling end of
4828 line or end of sentence recognition. In this case, the whole file is
4829 considered to be a single big line or sentence. The user might want to
4830 disallow all truncation flag generation as well, through option @option{-F
4831 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4834 When the keywords happen to be near the beginning of the input line or
4835 sentence, this often creates an unused area at the beginning of the
4836 output context line; when the keywords happen to be near the end of the
4837 input line or sentence, this often creates an unused area at the end of
4838 the output context line. The program tries to fill those unused areas
4839 by wrapping around context in them; the tail of the input line or
4840 sentence is used to fill the unused area on the left of the output line;
4841 the head of the input line or sentence is used to fill the unused area
4842 on the right of the output line.
4844 As a matter of convenience to the user, many usual backslashed escape
4845 sequences from the C language are recognized and converted to the
4846 corresponding characters by @command{ptx} itself.
4848 @item -W @var{regexp}
4849 @itemx --word-regexp=@var{regexp}
4851 This option selects which regular expression will describe each keyword.
4852 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4853 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4854 disabled, a word is by default anything which ends with a space, a tab
4855 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4857 An empty @var{regexp} is equivalent to not using this option.
4858 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4861 As a matter of convenience to the user, many usual backslashed escape
4862 sequences, as found in the C language, are recognized and converted to
4863 the corresponding characters by @command{ptx} itself.
4868 @node Output formatting in ptx
4869 @subsection Output formatting
4871 Output format is mainly controlled by the @option{-O} and @option{-T} options
4872 described in the table below. When neither @option{-O} nor @option{-T} are
4873 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4874 output format suitable for a dumb terminal. Each keyword occurrence is
4875 output to the center of one line, surrounded by its left and right
4876 contexts. Each field is properly justified, so the concordance output
4877 can be readily observed. As a special feature, if automatic
4878 references are selected by option @option{-A} and are output before the
4879 left context, that is, if option @option{-R} is @emph{not} selected, then
4880 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4881 Emacs @code{next-error} processing. In this default output format, each
4882 white space character, like newline and tab, is merely changed to
4883 exactly one space, with no special attempt to compress consecutive
4884 spaces. This might change in the future. Except for those white space
4885 characters, every other character of the underlying set of 256
4886 characters is transmitted verbatim.
4888 Output format is further controlled by the following options.
4892 @item -g @var{number}
4893 @itemx --gap-size=@var{number}
4895 Select the size of the minimum white space gap between the fields on the
4898 @item -w @var{number}
4899 @itemx --width=@var{number}
4901 Select the maximum output width of each final line. If references are
4902 used, they are included or excluded from the maximum output width
4903 depending on the value of option @option{-R}. If this option is not
4904 selected, that is, when references are output before the left context,
4905 the maximum output width takes into account the maximum length of all
4906 references. If this option is selected, that is, when references are
4907 output after the right context, the maximum output width does not take
4908 into account the space taken by references, nor the gap that precedes
4912 @itemx --auto-reference
4914 Select automatic references. Each input line will have an automatic
4915 reference made up of the file name and the line ordinal, with a single
4916 colon between them. However, the file name will be empty when standard
4917 input is being read. If both @option{-A} and @option{-r} are selected, then
4918 the input reference is still read and skipped, but the automatic
4919 reference is used at output time, overriding the input reference.
4922 @itemx --right-side-refs
4924 In the default output format, when option @option{-R} is not used, any
4925 references produced by the effect of options @option{-r} or @option{-A} are
4926 placed to the far right of output lines, after the right context. With
4927 default output format, when the @option{-R} option is specified, references
4928 are rather placed at the beginning of each output line, before the left
4929 context. For any other output format, option @option{-R} is
4930 ignored, with one exception: with @option{-R} the width of references
4931 is @emph{not} taken into account in total output width given by @option{-w}.
4933 This option is automatically selected whenever @sc{gnu} extensions are
4936 @item -F @var{string}
4937 @itemx --flac-truncation=@var{string}
4939 This option will request that any truncation in the output be reported
4940 using the string @var{string}. Most output fields theoretically extend
4941 towards the beginning or the end of the current line, or current
4942 sentence, as selected with option @option{-S}. But there is a maximum
4943 allowed output line width, changeable through option @option{-w}, which is
4944 further divided into space for various output fields. When a field has
4945 to be truncated because it cannot extend beyond the beginning or the end of
4946 the current line to fit in, then a truncation occurs. By default,
4947 the string used is a single slash, as in @option{-F /}.
4949 @var{string} may have more than one character, as in @option{-F ...}.
4950 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4951 truncation flagging is disabled, and no truncation marks are appended in
4954 As a matter of convenience to the user, many usual backslashed escape
4955 sequences, as found in the C language, are recognized and converted to
4956 the corresponding characters by @command{ptx} itself.
4958 @item -M @var{string}
4959 @itemx --macro-name=@var{string}
4961 Select another @var{string} to be used instead of @samp{xx}, while
4962 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4965 @itemx --format=roff
4967 Choose an output format suitable for @command{nroff} or @command{troff}
4968 processing. Each output line will look like:
4971 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4974 so it will be possible to write a @samp{.xx} roff macro to take care of
4975 the output typesetting. This is the default output format when @sc{gnu}
4976 extensions are disabled. Option @option{-M} can be used to change
4977 @samp{xx} to another macro name.
4979 In this output format, each non-graphical character, like newline and
4980 tab, is merely changed to exactly one space, with no special attempt to
4981 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4982 so it will be correctly processed by @command{nroff} or @command{troff}.
4987 Choose an output format suitable for @TeX{} processing. Each output
4988 line will look like:
4991 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4995 so it will be possible to write a @code{\xx} definition to take care of
4996 the output typesetting. Note that when references are not being
4997 produced, that is, neither option @option{-A} nor option @option{-r} is
4998 selected, the last parameter of each @code{\xx} call is inhibited.
4999 Option @option{-M} can be used to change @samp{xx} to another macro
5002 In this output format, some special characters, like @kbd{$}, @kbd{%},
5003 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5004 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5005 backslash and a pair of dollar signs (to force mathematical mode). The
5006 backslash itself produces the sequence @code{\backslash@{@}}.
5007 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5008 @code{~\@{ @}} respectively. Other diacriticized characters of the
5009 underlying character set produce an appropriate @TeX{} sequence as far
5010 as possible. The other non-graphical characters, like newline and tab,
5011 and all other characters which are not part of @acronym{ASCII}, are merely
5012 changed to exactly one space, with no special attempt to compress
5013 consecutive spaces. Let me know how to improve this special character
5014 processing for @TeX{}.
5019 @node Compatibility in ptx
5020 @subsection The @sc{gnu} extensions to @command{ptx}
5022 This version of @command{ptx} contains a few features which do not exist in
5023 System V @command{ptx}. These extra features are suppressed by using the
5024 @option{-G} command line option, unless overridden by other command line
5025 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5026 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5027 Here are the differences between this program and System V @command{ptx}.
5032 This program can read many input files at once, it always writes the
5033 resulting concordance on standard output. On the other hand, System V
5034 @command{ptx} reads only one file and sends the result to standard output
5035 or, if a second @var{file} parameter is given on the command, to that
5038 Having output parameters not introduced by options is a dangerous
5039 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5040 portably between @sc{gnu} and System V, you should always use it with a
5041 single input file, and always expect the result on standard output. You
5042 might also want to automatically configure in a @option{-G} option to
5043 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5044 that the installed @command{ptx} accepts @option{-G}.
5047 The only options available in System V @command{ptx} are options @option{-b},
5048 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5049 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5050 this enumeration. Moreover, some options have a slightly different
5051 meaning when @sc{gnu} extensions are enabled, as explained below.
5054 By default, concordance output is not formatted for @command{troff} or
5055 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5056 or @command{nroff} output may still be selected through option @option{-O}.
5059 Unless @option{-R} option is used, the maximum reference width is
5060 subtracted from the total output line width. With @sc{gnu} extensions
5061 disabled, width of references is not taken into account in the output
5062 line width computations.
5065 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5066 processed from input file with no adverse effect, even if @sc{gnu} extensions
5067 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5068 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5071 Input line length is only limited by available memory, even if @sc{gnu}
5072 extensions are disabled. However, System V @command{ptx} processes only
5073 the first 200 characters in each line.
5076 The break (non-word) characters default to be every character except all
5077 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5078 extensions are disabled, the break characters default to space, tab and
5082 The program makes better use of output line width. If @sc{gnu} extensions
5083 are disabled, the program rather tries to imitate System V @command{ptx},
5084 but still, there are some slight disposition glitches this program does
5085 not completely reproduce.
5088 The user can specify both an Ignore file and an Only file. This is not
5089 allowed with System V @command{ptx}.
5094 @node tsort invocation
5095 @section @command{tsort}: Topological sort
5098 @cindex topological sort
5100 @command{tsort} performs a topological sort on the given @var{file}, or
5101 standard input if no input file is given or for a @var{file} of
5102 @samp{-}. For more details and some history, see @ref{tsort background}.
5106 tsort [@var{option}] [@var{file}]
5109 @command{tsort} reads its input as pairs of strings, separated by blanks,
5110 indicating a partial ordering. The output is a total ordering that
5111 corresponds to the given partial ordering.
5125 will produce the output
5136 Consider a more realistic example.
5137 You have a large set of functions all in one file, and they may all be
5138 declared static except one. Currently that one (say @code{main}) is the
5139 first function defined in the file, and the ones it calls directly follow
5140 it, followed by those they call, etc. Let's say that you are determined
5141 to take advantage of prototypes, so you have to choose between declaring
5142 all of those functions (which means duplicating a lot of information from
5143 the definitions) and rearranging the functions so that as many as possible
5144 are defined before they are used. One way to automate the latter process
5145 is to get a list for each function of the functions it calls directly.
5146 Many programs can generate such lists. They describe a call graph.
5147 Consider the following list, in which a given line indicates that the
5148 function on the left calls the one on the right directly.
5154 tail_file pretty_name
5155 tail_file write_header
5157 tail_forever recheck
5158 tail_forever pretty_name
5159 tail_forever write_header
5160 tail_forever dump_remainder
5163 tail_lines start_lines
5164 tail_lines dump_remainder
5165 tail_lines file_lines
5166 tail_lines pipe_lines
5168 tail_bytes start_bytes
5169 tail_bytes dump_remainder
5170 tail_bytes pipe_bytes
5171 file_lines dump_remainder
5175 then you can use @command{tsort} to produce an ordering of those
5176 functions that satisfies your requirement.
5179 example$ tsort call-graph | tac
5199 @command{tsort} detects any cycles in the input and writes the first cycle
5200 encountered to standard error.
5202 Note that for a given partial ordering, generally there is no unique
5203 total ordering. In the context of the call graph above, the function
5204 @code{parse_options} may be placed anywhere in the list as long as it
5205 precedes @code{main}.
5207 The only options are @option{--help} and @option{--version}. @xref{Common
5213 * tsort background:: Where tsort came from.
5216 @node tsort background
5217 @subsection @command{tsort}: Background
5219 @command{tsort} exists because very early versions of the Unix linker processed
5220 an archive file exactly once, and in order. As @command{ld} read each object
5221 in the archive, it decided whether it was needed in the program based on
5222 whether it defined any symbols which were undefined at that point in
5225 This meant that dependencies within the archive had to be handled
5226 specially. For example, @code{scanf} probably calls @code{read}. That means
5227 that in a single pass through an archive, it was important for @code{scanf.o}
5228 to appear before read.o, because otherwise a program which calls
5229 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5230 reference to @code{read}.
5232 The way to address this problem was to first generate a set of
5233 dependencies of one object file on another. This was done by a shell
5234 script called @command{lorder}. The GNU tools don't provide a version of
5235 lorder, as far as I know, but you can still find it in BSD
5238 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5239 resulting sort to define the order in which you added objects to the archive.
5241 This whole procedure has been obsolete since about 1980, because
5242 Unix archives now contain a symbol table (traditionally built by
5243 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5244 linker uses the symbol table to effectively make multiple passes over
5247 Anyhow, that's where tsort came from. To solve an old problem with
5248 the way the linker handled archive files, which has since been solved
5252 @node Operating on fields
5253 @chapter Operating on fields
5256 * cut invocation:: Print selected parts of lines.
5257 * paste invocation:: Merge lines of files.
5258 * join invocation:: Join lines on a common field.
5262 @node cut invocation
5263 @section @command{cut}: Print selected parts of lines
5266 @command{cut} writes to standard output selected parts of each line of each
5267 input file, or standard input if no files are given or for a file name of
5271 cut @var{option}@dots{} [@var{file}]@dots{}
5274 In the table which follows, the @var{byte-list}, @var{character-list},
5275 and @var{field-list} are one or more numbers or ranges (two numbers
5276 separated by a dash) separated by commas. Bytes, characters, and
5277 fields are numbered starting at 1. Incomplete ranges may be
5278 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5279 @samp{@var{n}} through end of line or last field. The list elements
5280 can be repeated, can overlap, and can be specified in any order; but
5281 the selected input is written in the same order that it is read, and
5282 is written exactly once.
5284 The program accepts the following options. Also see @ref{Common
5289 @item -b @var{byte-list}
5290 @itemx --bytes=@var{byte-list}
5293 Select for printing only the bytes in positions listed in
5294 @var{byte-list}. Tabs and backspaces are treated like any other
5295 character; they take up 1 byte. If an output delimiter is specified,
5296 (see the description of @option{--output-delimiter}), then output that
5297 string between ranges of selected bytes.
5299 @item -c @var{character-list}
5300 @itemx --characters=@var{character-list}
5302 @opindex --characters
5303 Select for printing only the characters in positions listed in
5304 @var{character-list}. The same as @option{-b} for now, but
5305 internationalization will change that. Tabs and backspaces are
5306 treated like any other character; they take up 1 character. If an
5307 output delimiter is specified, (see the description of
5308 @option{--output-delimiter}), then output that string between ranges
5311 @item -f @var{field-list}
5312 @itemx --fields=@var{field-list}
5315 Select for printing only the fields listed in @var{field-list}.
5316 Fields are separated by a TAB character by default. Also print any
5317 line that contains no delimiter character, unless the
5318 @option{--only-delimited} (@option{-s}) option is specified
5320 @item -d @var{input_delim_byte}
5321 @itemx --delimiter=@var{input_delim_byte}
5323 @opindex --delimiter
5324 With @option{-f}, use the first byte of @var{input_delim_byte} as
5325 the input fields separator (default is TAB).
5329 Do not split multi-byte characters (no-op for now).
5332 @itemx --only-delimited
5334 @opindex --only-delimited
5335 For @option{-f}, do not print lines that do not contain the field separator
5336 character. Normally, any line without a field separator is printed verbatim.
5338 @item --output-delimiter=@var{output_delim_string}
5339 @opindex --output-delimiter
5340 With @option{-f}, output fields are separated by @var{output_delim_string}.
5341 The default with @option{-f} is to use the input delimiter.
5342 When using @option{-b} or @option{-c} to select ranges of byte or
5343 character offsets (as opposed to ranges of fields),
5344 output @var{output_delim_string} between non-overlapping
5345 ranges of selected bytes.
5348 @opindex --complement
5349 This option is a @acronym{GNU} extension.
5350 Select for printing the complement of the bytes, characters or fields
5351 selected with the @option{-b}, @option{-c} or @option{-f} options.
5352 In other words, do @emph{not} print the bytes, characters or fields
5353 specified via those options. This option is useful when you have
5354 many fields and want to print all but a few of them.
5361 @node paste invocation
5362 @section @command{paste}: Merge lines of files
5365 @cindex merging files
5367 @command{paste} writes to standard output lines consisting of sequentially
5368 corresponding lines of each given file, separated by a TAB character.
5369 Standard input is used for a file name of @samp{-} or if no input files
5391 paste [@var{option}]@dots{} [@var{file}]@dots{}
5394 The program accepts the following options. Also see @ref{Common options}.
5402 Paste the lines of one file at a time rather than one line from each
5403 file. Using the above example data:
5406 $ paste -s num2 let3
5411 @item -d @var{delim-list}
5412 @itemx --delimiters=@var{delim-list}
5414 @opindex --delimiters
5415 Consecutively use the characters in @var{delim-list} instead of
5416 TAB to separate merged lines. When @var{delim-list} is
5417 exhausted, start again at its beginning. Using the above example data:
5420 $ paste -d '%_' num2 let3 num2
5431 @node join invocation
5432 @section @command{join}: Join lines on a common field
5435 @cindex common field, joining on
5437 @command{join} writes to standard output a line for each pair of input
5438 lines that have identical join fields. Synopsis:
5441 join [@var{option}]@dots{} @var{file1} @var{file2}
5444 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5445 meaning standard input. @var{file1} and @var{file2} should be
5446 sorted on the join fields.
5449 Normally, the sort order is that of the
5450 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5451 the @option{-t} option is given, the sort comparison ignores blanks at
5452 the start of the join field, as in @code{sort -b}. If the
5453 @option{--ignore-case} option is given, the sort comparison ignores
5454 the case of characters in the join field, as in @code{sort -f}.
5456 The @command{sort} and @command{join} commands should use consistent
5457 locales and options if the output of @command{sort} is fed to
5458 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5459 sort a file on its default join field, but if you select a non-default
5460 locale, join field, separator, or comparison options, then you should
5461 do so consistently between @command{join} and @command{sort}.
5463 If the input has no unpairable lines, a @acronym{GNU} extension is
5464 available; the sort order can be any order that considers two fields
5465 to be equal if and only if the sort comparison described above
5466 considers them to be equal. For example:
5483 @checkOrderOption{join}
5487 @item the join field is the first field in each line;
5488 @item fields in the input are separated by one or more blanks, with leading
5489 blanks on the line ignored;
5490 @item fields in the output are separated by a space;
5491 @item each output line consists of the join field, the remaining
5492 fields from @var{file1}, then the remaining fields from @var{file2}.
5495 The program accepts the following options. Also see @ref{Common options}.
5499 @item -a @var{file-number}
5501 Print a line for each unpairable line in file @var{file-number} (either
5502 @samp{1} or @samp{2}), in addition to the normal output.
5505 Fail with an error message if either input file is wrongly ordered.
5507 @item --nocheck-order
5508 Do not check that both input files are in sorted order. This is the default.
5510 @item -e @var{string}
5512 Replace those output fields that are missing in the input with
5516 @itemx --ignore-case
5518 @opindex --ignore-case
5519 Ignore differences in case when comparing keys.
5520 With this option, the lines of the input files must be ordered in the same way.
5521 Use @samp{sort -f} to produce this ordering.
5523 @item -1 @var{field}
5525 Join on field @var{field} (a positive integer) of file 1.
5527 @item -2 @var{field}
5529 Join on field @var{field} (a positive integer) of file 2.
5531 @item -j @var{field}
5532 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5534 @item -o @var{field-list}
5535 Construct each output line according to the format in @var{field-list}.
5536 Each element in @var{field-list} is either the single character @samp{0} or
5537 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5538 @samp{2} and @var{n} is a positive field number.
5540 A field specification of @samp{0} denotes the join field.
5541 In most cases, the functionality of the @samp{0} field spec
5542 may be reproduced using the explicit @var{m.n} that corresponds
5543 to the join field. However, when printing unpairable lines
5544 (using either of the @option{-a} or @option{-v} options), there is no way
5545 to specify the join field using @var{m.n} in @var{field-list}
5546 if there are unpairable lines in both files.
5547 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5548 field specification notation.
5550 The elements in @var{field-list}
5551 are separated by commas or blanks.
5552 Blank separators typically need to be quoted for the shell. For
5553 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5554 2.2'} are equivalent.
5556 All output lines---including those printed because of any -a or -v
5557 option---are subject to the specified @var{field-list}.
5560 Use character @var{char} as the input and output field separator.
5561 Treat as significant each occurrence of @var{char} in the input file.
5562 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5563 @samp{sort}, to produce this ordering.
5565 @item -v @var{file-number}
5566 Print a line for each unpairable line in file @var{file-number}
5567 (either @samp{1} or @samp{2}), instead of the normal output.
5574 @node Operating on characters
5575 @chapter Operating on characters
5577 @cindex operating on characters
5579 This commands operate on individual characters.
5582 * tr invocation:: Translate, squeeze, and/or delete characters.
5583 * expand invocation:: Convert tabs to spaces.
5584 * unexpand invocation:: Convert spaces to tabs.
5589 @section @command{tr}: Translate, squeeze, and/or delete characters
5596 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5599 @command{tr} copies standard input to standard output, performing
5600 one of the following operations:
5604 translate, and optionally squeeze repeated characters in the result,
5606 squeeze repeated characters,
5610 delete characters, then squeeze repeated characters from the result.
5613 The @var{set1} and (if given) @var{set2} arguments define ordered
5614 sets of characters, referred to below as @var{set1} and @var{set2}. These
5615 sets are the characters of the input that @command{tr} operates on.
5616 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5618 complement (all of the characters that are not in @var{set1}).
5620 Currently @command{tr} fully supports only single-byte characters.
5621 Eventually it will support multibyte characters; when it does, the
5622 @option{-C} option will cause it to complement the set of characters,
5623 whereas @option{-c} will cause it to complement the set of values.
5624 This distinction will matter only when some values are not characters,
5625 and this is possible only in locales using multibyte encodings when
5626 the input contains encoding errors.
5628 The program accepts the @option{--help} and @option{--version}
5629 options. @xref{Common options}. Options must precede operands.
5634 * Character sets:: Specifying sets of characters.
5635 * Translating:: Changing one set of characters to another.
5636 * Squeezing:: Squeezing repeats and deleting.
5640 @node Character sets
5641 @subsection Specifying sets of characters
5643 @cindex specifying sets of characters
5645 The format of the @var{set1} and @var{set2} arguments resembles
5646 the format of regular expressions; however, they are not regular
5647 expressions, only lists of characters. Most characters simply
5648 represent themselves in these strings, but the strings can contain
5649 the shorthands listed below, for convenience. Some of them can be
5650 used only in @var{set1} or @var{set2}, as noted below.
5654 @item Backslash escapes
5655 @cindex backslash escapes
5657 The following backslash escape sequences are recognized:
5675 The character with the value given by @var{ooo}, which is 1 to 3
5681 While a backslash followed by a character not listed above is
5682 interpreted as that character, the backslash also effectively
5683 removes any special significance, so it is useful to escape
5684 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5689 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5690 from @var{m} through @var{n}, in ascending order. @var{m} should
5691 collate before @var{n}; if it doesn't, an error results. As an example,
5692 @samp{0-9} is the same as @samp{0123456789}.
5694 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5695 brackets to enclose ranges. Translations specified in that format
5696 sometimes work as expected, since the brackets are often transliterated
5697 to themselves. However, they should be avoided because they sometimes
5698 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5701 Many historically common and even accepted uses of ranges are not
5702 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5703 range will not do what most would expect because @samp{A} through @samp{Z}
5704 are not contiguous as they are in @acronym{ASCII}.
5705 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5706 the best way to work around this is to use character classes (see below).
5707 Otherwise, it is most portable (and most ugly) to enumerate the members
5710 @item Repeated characters
5711 @cindex repeated characters
5713 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5714 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5715 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5716 to as many copies of @var{c} as are needed to make @var{set2} as long as
5717 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5718 octal, otherwise in decimal.
5720 @item Character classes
5721 @cindex character classes
5723 The notation @samp{[:@var{class}:]} expands to all of the characters in
5724 the (predefined) class @var{class}. The characters expand in no
5725 particular order, except for the @code{upper} and @code{lower} classes,
5726 which expand in ascending order. When the @option{--delete} (@option{-d})
5727 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5728 character class can be used in @var{set2}. Otherwise, only the
5729 character classes @code{lower} and @code{upper} are accepted in
5730 @var{set2}, and then only if the corresponding character class
5731 (@code{upper} and @code{lower}, respectively) is specified in the same
5732 relative position in @var{set1}. Doing this specifies case conversion.
5733 The class names are given below; an error results when an invalid class
5745 Horizontal whitespace.
5754 Printable characters, not including space.
5760 Printable characters, including space.
5763 Punctuation characters.
5766 Horizontal or vertical whitespace.
5775 @item Equivalence classes
5776 @cindex equivalence classes
5778 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5779 equivalent to @var{c}, in no particular order. Equivalence classes are
5780 a relatively recent invention intended to support non-English alphabets.
5781 But there seems to be no standard way to define them or determine their
5782 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5783 each character's equivalence class consists only of that character,
5784 which is of no particular use.
5790 @subsection Translating
5792 @cindex translating characters
5794 @command{tr} performs translation when @var{set1} and @var{set2} are
5795 both given and the @option{--delete} (@option{-d}) option is not given.
5796 @command{tr} translates each character of its input that is in @var{set1}
5797 to the corresponding character in @var{set2}. Characters not in
5798 @var{set1} are passed through unchanged. When a character appears more
5799 than once in @var{set1} and the corresponding characters in @var{set2}
5800 are not all the same, only the final one is used. For example, these
5801 two commands are equivalent:
5808 A common use of @command{tr} is to convert lowercase characters to
5809 uppercase. This can be done in many ways. Here are three of them:
5812 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5814 tr '[:lower:]' '[:upper:]'
5818 But note that using ranges like @code{a-z} above is not portable.
5820 When @command{tr} is performing translation, @var{set1} and @var{set2}
5821 typically have the same length. If @var{set1} is shorter than
5822 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5824 On the other hand, making @var{set1} longer than @var{set2} is not
5825 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5826 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5827 the last character of @var{set2} as many times as necessary. System V
5828 @command{tr} truncates @var{set1} to the length of @var{set2}.
5830 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5831 When the @option{--truncate-set1} (@option{-t}) option is given,
5832 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5833 instead. This option is ignored for operations other than translation.
5835 Acting like System V @command{tr} in this case breaks the relatively common
5839 tr -cs A-Za-z0-9 '\012'
5843 because it converts only zero bytes (the first element in the
5844 complement of @var{set1}), rather than all non-alphanumerics, to
5848 By the way, the above idiom is not portable because it uses ranges, and
5849 it assumes that the octal code for newline is 012.
5850 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5853 tr -cs '[:alnum:]' '[\n*]'
5858 @subsection Squeezing repeats and deleting
5860 @cindex squeezing repeat characters
5861 @cindex deleting characters
5863 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5864 removes any input characters that are in @var{set1}.
5866 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5867 @command{tr} replaces each input sequence of a repeated character that
5868 is in @var{set1} with a single occurrence of that character.
5870 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5871 first performs any deletions using @var{set1}, then squeezes repeats
5872 from any remaining characters using @var{set2}.
5874 The @option{--squeeze-repeats} option may also be used when translating,
5875 in which case @command{tr} first performs translation, then squeezes
5876 repeats from any remaining characters using @var{set2}.
5878 Here are some examples to illustrate various combinations of options:
5883 Remove all zero bytes:
5890 Put all words on lines by themselves. This converts all
5891 non-alphanumeric characters to newlines, then squeezes each string
5892 of repeated newlines into a single newline:
5895 tr -cs '[:alnum:]' '[\n*]'
5899 Convert each sequence of repeated newlines to a single newline:
5906 Find doubled occurrences of words in a document.
5907 @c Separate the following two "the"s, so typo checkers don't complain.
5908 For example, people often write ``the @w{}the'' with the repeated words
5909 separated by a newline. The Bourne shell script below works first
5910 by converting each sequence of punctuation and blank characters to a
5911 single newline. That puts each ``word'' on a line by itself.
5912 Next it maps all uppercase characters to lower case, and finally it
5913 runs @command{uniq} with the @option{-d} option to print out only the words
5919 | tr -s '[:punct:][:blank:]' '[\n*]' \
5920 | tr '[:upper:]' '[:lower:]' \
5925 Deleting a small set of characters is usually straightforward. For example,
5926 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5932 However, when @samp{-} is one of those characters, it can be tricky because
5933 @samp{-} has special meanings. Performing the same task as above but also
5934 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5935 that would fail because @command{tr} would try to interpret @option{-a} as
5936 a command-line option. Alternatively, we could try putting the hyphen
5937 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5938 it would make @command{tr} interpret @code{a-x} as the range of characters
5939 @samp{a}@dots{}@samp{x} rather than the three.
5940 One way to solve the problem is to put the hyphen at the end of the list
5947 Or you can use @samp{--} to terminate option processing:
5953 More generally, use the character class notation @code{[=c=]}
5954 with @samp{-} (or any other character) in place of the @samp{c}:
5960 Note how single quotes are used in the above example to protect the
5961 square brackets from interpretation by a shell.
5966 @node expand invocation
5967 @section @command{expand}: Convert tabs to spaces
5970 @cindex tabs to spaces, converting
5971 @cindex converting tabs to spaces
5973 @command{expand} writes the contents of each given @var{file}, or standard
5974 input if none are given or for a @var{file} of @samp{-}, to standard
5975 output, with tab characters converted to the appropriate number of
5979 expand [@var{option}]@dots{} [@var{file}]@dots{}
5982 By default, @command{expand} converts all tabs to spaces. It preserves
5983 backspace characters in the output; they decrement the column count for
5984 tab calculations. The default action is equivalent to @option{-t 8} (set
5985 tabs every 8 columns).
5987 The program accepts the following options. Also see @ref{Common options}.
5991 @item -t @var{tab1}[,@var{tab2}]@dots{}
5992 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
5995 @cindex tab stops, setting
5996 If only one tab stop is given, set the tabs @var{tab1} spaces apart
5997 (default is 8). Otherwise, set the tabs at columns @var{tab1},
5998 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
5999 last tab stop given with single spaces. Tab stops can be separated by
6000 blanks as well as by commas.
6002 For compatibility, GNU @command{expand} also accepts the obsolete
6003 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6004 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6010 @cindex initial tabs, converting
6011 Only convert initial tabs (those that precede all non-space or non-tab
6012 characters) on each line to spaces.
6019 @node unexpand invocation
6020 @section @command{unexpand}: Convert spaces to tabs
6024 @command{unexpand} writes the contents of each given @var{file}, or
6025 standard input if none are given or for a @var{file} of @samp{-}, to
6026 standard output, converting blanks at the beginning of each line into
6027 as many tab characters as needed. In the default @acronym{POSIX}
6028 locale, a @dfn{blank} is a space or a tab; other locales may specify
6029 additional blank characters. Synopsis:
6032 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6035 By default, @command{unexpand} converts only initial blanks (those
6036 that precede all non-blank characters) on each line. It
6037 preserves backspace characters in the output; they decrement the column
6038 count for tab calculations. By default, tabs are set at every 8th
6041 The program accepts the following options. Also see @ref{Common options}.
6045 @item -t @var{tab1}[,@var{tab2}]@dots{}
6046 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6049 If only one tab stop is given, set the tabs @var{tab1} columns apart
6050 instead of the default 8. Otherwise, set the tabs at columns
6051 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6052 beyond the tab stops given unchanged. Tab stops can be separated by
6053 blanks as well as by commas. This option implies the @option{-a} option.
6055 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6056 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6057 separated by commas. (Unlike @option{-t}, this obsolete option does
6058 not imply @option{-a}.) New scripts should use @option{--first-only -t
6059 @var{tab1}[,@var{tab2}]@dots{}} instead.
6065 Also convert all sequences of two or more blanks just before a tab stop,
6066 even if they occur after non-blank characters in a line.
6073 @node Directory listing
6074 @chapter Directory listing
6076 This chapter describes the @command{ls} command and its variants @command{dir}
6077 and @command{vdir}, which list information about files.
6080 * ls invocation:: List directory contents.
6081 * dir invocation:: Briefly ls.
6082 * vdir invocation:: Verbosely ls.
6083 * dircolors invocation:: Color setup for ls, etc.
6088 @section @command{ls}: List directory contents
6091 @cindex directory listing
6093 The @command{ls} program lists information about files (of any type,
6094 including directories). Options and file arguments can be intermixed
6095 arbitrarily, as usual.
6097 For non-option command-line arguments that are directories, by default
6098 @command{ls} lists the contents of directories, not recursively, and
6099 omitting files with names beginning with @samp{.}. For other non-option
6100 arguments, by default @command{ls} lists just the file name. If no
6101 non-option argument is specified, @command{ls} operates on the current
6102 directory, acting as if it had been invoked with a single argument of @samp{.}.
6105 By default, the output is sorted alphabetically, according to the locale
6106 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6107 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6108 produce output that is sorted differently than you're accustomed to.
6109 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6110 If standard output is
6111 a terminal, the output is in columns (sorted vertically) and control
6112 characters are output as question marks; otherwise, the output is listed
6113 one per line and control characters are output as-is.
6115 Because @command{ls} is such a fundamental program, it has accumulated many
6116 options over the years. They are described in the subsections below;
6117 within each section, options are listed alphabetically (ignoring case).
6118 The division of options into the subsections is not absolute, since some
6119 options affect more than one aspect of @command{ls}'s operation.
6121 @cindex exit status of @command{ls}
6126 1 minor problems (e.g., failure to access a file or directory not
6127 specified as a command line argument. This happens when listing a
6128 directory in which entries are actively being removed or renamed.)
6129 2 serious trouble (e.g., memory exhausted, invalid option, failure
6130 to access a file or directory specified as a command line argument
6131 or a directory loop)
6134 Also see @ref{Common options}.
6137 * Which files are listed::
6138 * What information is listed::
6139 * Sorting the output::
6140 * Details about version sort::
6141 * General output formatting::
6142 * Formatting file timestamps::
6143 * Formatting the file names::
6147 @node Which files are listed
6148 @subsection Which files are listed
6150 These options determine which files @command{ls} lists information for.
6151 By default, @command{ls} lists files and the contents of any
6152 directories on the command line, except that in directories it ignores
6153 files whose names start with @samp{.}.
6161 In directories, do not ignore file names that start with @samp{.}.
6166 @opindex --almost-all
6167 In directories, do not ignore all file names that start with @samp{.};
6168 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6169 option overrides this option.
6172 @itemx --ignore-backups
6174 @opindex --ignore-backups
6175 @cindex backup files, ignoring
6176 In directories, ignore files that end with @samp{~}. This option is
6177 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6182 @opindex --directory
6183 List just the names of directories, as with other types of files, rather
6184 than listing their contents.
6185 @c The following sentence is the same as the one for -F.
6186 Do not follow symbolic links listed on the
6187 command line unless the @option{--dereference-command-line} (@option{-H}),
6188 @option{--dereference} (@option{-L}), or
6189 @option{--dereference-command-line-symlink-to-dir} options are specified.
6192 @itemx --dereference-command-line
6194 @opindex --dereference-command-line
6195 @cindex symbolic links, dereferencing
6196 If a command line argument specifies a symbolic link, show information
6197 for the file the link references rather than for the link itself.
6199 @itemx --dereference-command-line-symlink-to-dir
6200 @opindex --dereference-command-line-symlink-to-dir
6201 @cindex symbolic links, dereferencing
6202 Do not dereference symbolic links, with one exception:
6203 if a command line argument specifies a symbolic link that refers to
6204 a directory, show information for that directory rather than for the
6206 This is the default behavior when no other dereferencing-related
6207 option has been specified (@option{--classify} (@option{-F}),
6208 @option{--directory} (@option{-d}),
6210 @option{--dereference} (@option{-L}), or
6211 @option{--dereference-command-line} (@option{-H})).
6213 @item --group-directories-first
6214 @opindex --group-directories-first
6215 Group all the directories before the files and then sort the
6216 directories and the files separately using the selected sort key
6217 (see --sort option).
6218 That is, this option specifies a primary sort key,
6219 and the --sort option specifies a secondary key.
6220 However, any use of @option{--sort=none}
6221 (@option{-U}) disables this option altogether.
6223 @item --hide=PATTERN
6224 @opindex --hide=@var{pattern}
6225 In directories, ignore files whose names match the shell pattern
6226 @var{pattern}, unless the @option{--all} (@option{-a}) or
6227 @option{--almost-all} (@option{-A}) is also given. This
6228 option acts like @option{--ignore=@var{pattern}} except that it has no
6229 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6230 (@option{-A}) is also given.
6232 This option can be useful in shell aliases. For example, if
6233 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6234 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6235 lists the file @file{README~} even though @samp{ly -A} would not.
6237 @item -I @var{pattern}
6238 @itemx --ignore=@var{pattern}
6240 @opindex --ignore=@var{pattern}
6241 In directories, ignore files whose names match the shell pattern
6242 (not regular expression) @var{pattern}. As
6243 in the shell, an initial @samp{.} in a file name does not match a
6244 wildcard at the start of @var{pattern}. Sometimes it is useful
6245 to give this option several times. For example,
6248 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6251 The first option ignores names of length 3 or more that start with @samp{.},
6252 the second ignores all two-character names that start with @samp{.}
6253 except @samp{..}, and the third ignores names that start with @samp{#}.
6256 @itemx --dereference
6258 @opindex --dereference
6259 @cindex symbolic links, dereferencing
6260 When showing file information for a symbolic link, show information
6261 for the file the link references rather than the link itself.
6262 However, even with this option, @command{ls} still prints the name
6263 of the link itself, not the name of the file that the link points to.
6268 @opindex --recursive
6269 @cindex recursive directory listing
6270 @cindex directory listing, recursive
6271 List the contents of all directories recursively.
6276 @node What information is listed
6277 @subsection What information is listed
6279 These options affect the information that @command{ls} displays. By
6280 default, only file names are shown.
6286 @cindex hurd, author, printing
6287 List each file's author when producing long format directory listings.
6288 In GNU/Hurd, file authors can differ from their owners, but in other
6289 operating systems the two are the same.
6295 @cindex dired Emacs mode support
6296 With the long listing (@option{-l}) format, print an additional line after
6300 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6304 The @var{begn} and @var{endn} are unsigned integers that record the
6305 byte position of the beginning and end of each file name in the output.
6306 This makes it easy for Emacs to find the names, even when they contain
6307 unusual characters such as space or newline, without fancy searching.
6309 If directories are being listed recursively (@option{-R}), output a similar
6310 line with offsets for each subdirectory name:
6313 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6316 Finally, output a line of the form:
6319 //DIRED-OPTIONS// --quoting-style=@var{word}
6323 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6325 Here is an actual example:
6328 $ mkdir -p a/sub/deeper a/sub2
6330 $ touch a/sub/deeper/file
6331 $ ls -gloRF --dired a
6334 -rw-r--r-- 1 0 Jun 10 12:27 f1
6335 -rw-r--r-- 1 0 Jun 10 12:27 f2
6336 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6337 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6341 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6345 -rw-r--r-- 1 0 Jun 10 12:27 file
6349 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6350 //SUBDIRED// 2 3 167 172 228 240 290 296
6351 //DIRED-OPTIONS// --quoting-style=literal
6354 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6355 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6357 The offsets on the @samp{//SUBDIRED//} line delimit the following
6358 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6360 Here is an example of how to extract the fifth entry name, @samp{deeper},
6361 corresponding to the pair of offsets, 222 and 228:
6364 $ ls -gloRF --dired a > out
6365 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6369 Note that although the listing above includes a trailing slash
6370 for the @samp{deeper} entry, the offsets select the name without
6371 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6372 along with an option like @option{--escape} (aka @option{-b}) and operate
6373 on a file whose name contains special characters, notice that the backslash
6378 $ ls -blog --dired 'a b'
6379 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6381 //DIRED-OPTIONS// --quoting-style=escape
6384 If you use a quoting style that adds quote marks
6385 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6386 So beware that the user may select the quoting style via the environment
6387 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6388 should either specify an explicit @option{--quoting-style=literal} option
6389 (aka @option{-N} or @option{--literal}) on the command line, or else be
6390 prepared to parse the escaped names.
6393 @opindex --full-time
6394 Produce long format directory listings, and list times in full. It is
6395 equivalent to using @option{--format=long} with
6396 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6400 Produce long format directory listings, but don't display owner information.
6406 Inhibit display of group information in a long format directory listing.
6407 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6408 provide this option for compatibility.)
6416 @cindex inode number, printing
6417 Print the inode number (also called the file serial number and index
6418 number) of each file to the left of the file name. (This number
6419 uniquely identifies each file within a particular file system.)
6422 @itemx --format=long
6423 @itemx --format=verbose
6426 @opindex long ls @r{format}
6427 @opindex verbose ls @r{format}
6428 In addition to the name of each file, print the file type, file mode bits,
6429 number of hard links, owner name, group name, size, and
6430 timestamp (@pxref{Formatting file timestamps}), normally
6431 the modification time. Print question marks for information that
6432 cannot be determined.
6434 Normally the size is printed as a byte count without punctuation, but
6435 this can be overridden (@pxref{Block size}). For example, @option{-h}
6436 prints an abbreviated, human-readable count, and
6437 @samp{--block-size="'1"} prints a byte count with the thousands
6438 separator of the current locale.
6440 For each directory that is listed, preface the files with a line
6441 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6442 for all files in that directory. The block size currently defaults to 1024
6443 bytes, but this can be overridden (@pxref{Block size}).
6444 The @var{blocks} computed counts each hard link separately;
6445 this is arguably a deficiency.
6447 The file type is one of the following characters:
6449 @c The commented-out entries are ones we're not sure about.
6457 character special file
6459 high performance (``contiguous data'') file
6463 door (Solaris 2.5 and up)
6465 @c semaphore, if this is a distinct file type
6469 @c multiplexed file (7th edition Unix; obsolete)
6471 off-line (``migrated'') file (Cray DMF)
6473 network special file (HP-UX)
6477 port (Solaris 10 and up)
6479 @c message queue, if this is a distinct file type
6483 @c shared memory object, if this is a distinct file type
6485 @c typed memory object, if this is a distinct file type
6487 @c whiteout (4.4BSD; not implemented)
6489 some other file type
6492 @cindex permissions, output by @command{ls}
6493 The file mode bits listed are similar to symbolic mode specifications
6494 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6495 third character of each set of permissions as follows:
6499 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6503 If the set-user-ID or set-group-ID bit is set but the corresponding
6504 executable bit is not set.
6507 If the restricted deletion flag or sticky bit, and the
6508 other-executable bit, are both set. The restricted deletion flag is
6509 another name for the sticky bit. @xref{Mode Structure}.
6512 If the restricted deletion flag or sticky bit is set but the
6513 other-executable bit is not set.
6516 If the executable bit is set and none of the above apply.
6522 Following the file mode bits is a single character that specifies
6523 whether an alternate access method such as an access control list
6524 applies to the file. When the character following the file mode bits is a
6525 space, there is no alternate access method. When it is a printing
6526 character, then there is such a method.
6528 GNU @command{ls} uses a @samp{.} character to indicate a file
6529 with an SELinux security context, but no other alternate access method.
6531 A file with any other combination of alternate access methods
6532 is marked with a @samp{+} character.
6535 @itemx --numeric-uid-gid
6537 @opindex --numeric-uid-gid
6538 @cindex numeric uid and gid
6539 @cindex numeric user and group IDs
6540 Produce long format directory listings, but
6541 display numeric user and group IDs instead of the owner and group names.
6545 Produce long format directory listings, but don't display group information.
6546 It is equivalent to using @option{--format=long} with @option{--no-group} .
6552 @cindex disk allocation
6553 @cindex size of files, reporting
6554 Print the disk allocation of each file to the left of the file name.
6555 This is the amount of disk space used by the file, which is usually a
6556 bit more than the file's size, but it can be less if the file has holes.
6558 Normally the disk allocation is printed in units of
6559 1024 bytes, but this can be overridden (@pxref{Block size}).
6561 @cindex NFS mounts from BSD to HP-UX
6562 For files that are NFS-mounted from an HP-UX system to a BSD system,
6563 this option reports sizes that are half the correct values. On HP-UX
6564 systems, it reports sizes that are twice the correct values for files
6565 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6566 it also affects the HP-UX @command{ls} program.
6575 @cindex security context
6576 Display the SELinux security context or @samp{?} if none is found.
6577 When used with the @option{-l} option, print the security context
6578 to the left of the size column.
6583 @node Sorting the output
6584 @subsection Sorting the output
6586 @cindex sorting @command{ls} output
6587 These options change the order in which @command{ls} sorts the information
6588 it outputs. By default, sorting is done by character code
6589 (e.g., @acronym{ASCII} order).
6595 @itemx --time=status
6598 @opindex ctime@r{, printing or sorting by}
6599 @opindex status time@r{, printing or sorting by}
6600 @opindex use time@r{, printing or sorting files by}
6601 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6602 print the status change time (the @samp{ctime} in the inode) instead of
6603 the modification time.
6604 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6605 or when not using a long listing format,
6606 sort according to the status change time.
6610 @cindex unsorted directory listing
6611 @cindex directory order, listing by
6612 Primarily, like @option{-U}---do not sort; list the files in whatever
6613 order they are stored in the directory. But also enable @option{-a} (list
6614 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6615 were specified before the @option{-f}).
6621 @cindex reverse sorting
6622 Reverse whatever the sorting method is---e.g., list files in reverse
6623 alphabetical order, youngest first, smallest first, or whatever.
6629 @opindex size of files@r{, sorting files by}
6630 Sort by file size, largest first.
6636 @opindex modification time@r{, sorting files by}
6637 Sort by modification time (the @samp{mtime} in the inode), newest first.
6641 @itemx --time=access
6645 @opindex use time@r{, printing or sorting files by}
6646 @opindex atime@r{, printing or sorting files by}
6647 @opindex access time@r{, printing or sorting files by}
6648 If the long listing format (e.g., @option{--format=long}) is being used,
6649 print the last access time (the @samp{atime} in the inode).
6650 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6651 or when not using a long listing format, sort according to the access time.
6657 @opindex none@r{, sorting option for @command{ls}}
6658 Do not sort; list the files in whatever order they are
6659 stored in the directory. (Do not do any of the other unrelated things
6660 that @option{-f} does.) This is especially useful when listing very large
6661 directories, since not doing any sorting can be noticeably faster.
6664 @itemx --sort=version
6667 @opindex version@r{, sorting option for @command{ls}}
6668 Sort by version name and number, lowest first. It behaves like a default
6669 sort, except that each sequence of decimal digits is treated numerically
6670 as an index/version number. (@xref{Details about version sort}.)
6673 @itemx --sort=extension
6676 @opindex extension@r{, sorting files by}
6677 Sort directory contents alphabetically by file extension (characters
6678 after the last @samp{.}); files with no extension are sorted first.
6683 @node Details about version sort
6684 @subsection Details about version sort
6686 The version sort takes into account the fact that file names frequently include
6687 indices or version numbers. Standard sorting functions usually do not produce
6688 the ordering that people expect because comparisons are made on a
6689 character-by-character basis. The version
6690 sort addresses this problem, and is especially useful when browsing
6691 directories that contain many files with indices/version numbers in their
6696 foo.zml-1.gz foo.zml-1.gz
6697 foo.zml-100.gz foo.zml-2.gz
6698 foo.zml-12.gz foo.zml-6.gz
6699 foo.zml-13.gz foo.zml-12.gz
6700 foo.zml-2.gz foo.zml-13.gz
6701 foo.zml-25.gz foo.zml-25.gz
6702 foo.zml-6.gz foo.zml-100.gz
6705 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6706 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6707 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6708 @var{ver1} < @var{ver2} implies that the name composed of
6709 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6710 ``@var{prefix} @var{ver2} @var{suffix}''.
6712 Note also that leading zeros of numeric parts are ignored:
6716 abc-1.007.tgz abc-1.01a.tgz
6717 abc-1.012b.tgz abc-1.007.tgz
6718 abc-1.01a.tgz abc-1.012b.tgz
6721 This functionality is implemented using gnulib's @code{filevercmp} function.
6722 One result of that implementation decision is that @samp{ls -v}
6723 and @samp{sort -V} do not use the locale category, @env{LC_COLLATE},
6724 which means non-numeric prefixes are sorted as if @env{LC_COLLATE} were set
6727 @node General output formatting
6728 @subsection General output formatting
6730 These options affect the appearance of the overall output.
6735 @itemx --format=single-column
6738 @opindex single-column @r{output of files}
6739 List one file per line. This is the default for @command{ls} when standard
6740 output is not a terminal.
6743 @itemx --format=vertical
6746 @opindex vertical @r{sorted files in columns}
6747 List files in columns, sorted vertically. This is the default for
6748 @command{ls} if standard output is a terminal. It is always the default
6749 for the @command{dir} program.
6750 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6751 possible in the fewest lines.
6753 @item --color [=@var{when}]
6755 @cindex color, distinguishing file types with
6756 Specify whether to use color for distinguishing file types. @var{when}
6757 may be omitted, or one of:
6760 @vindex none @r{color option}
6761 - Do not use color at all. This is the default.
6763 @vindex auto @r{color option}
6764 @cindex terminal, using color iff
6765 - Only use color if standard output is a terminal.
6767 @vindex always @r{color option}
6770 Specifying @option{--color} and no @var{when} is equivalent to
6771 @option{--color=always}.
6772 Piping a colorized listing through a pager like @command{more} or
6773 @command{less} usually produces unreadable results. However, using
6774 @code{more -f} does seem to work.
6778 @itemx --indicator-style=classify
6781 @opindex --indicator-style
6782 @cindex file type and executables, marking
6783 @cindex executables and file type, marking
6784 Append a character to each file name indicating the file type. Also,
6785 for regular files that are executable, append @samp{*}. The file type
6786 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6787 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6788 and nothing for regular files.
6789 @c The following sentence is the same as the one for -d.
6790 Do not follow symbolic links listed on the
6791 command line unless the @option{--dereference-command-line} (@option{-H}),
6792 @option{--dereference} (@option{-L}), or
6793 @option{--dereference-command-line-symlink-to-dir} options are specified.
6796 @itemx --indicator-style=file-type
6797 @opindex --file-type
6798 @opindex --indicator-style
6799 @cindex file type, marking
6800 Append a character to each file name indicating the file type. This is
6801 like @option{-F}, except that executables are not marked.
6803 @item --indicator-style=@var{word}
6804 @opindex --indicator-style
6805 Append a character indicator with style @var{word} to entry names,
6810 Do not append any character indicator; this is the default.
6812 Append @samp{/} for directories. This is the same as the @option{-p}
6815 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6816 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6817 the same as the @option{--file-type} option.
6819 Append @samp{*} for executable regular files, otherwise behave as for
6820 @samp{file-type}. This is the same as the @option{-F} or
6821 @option{--classify} option.
6826 Print file sizes in 1024-byte blocks, overriding the default block
6827 size (@pxref{Block size}).
6828 This option is equivalent to @option{--block-size=1K}.
6831 @itemx --format=commas
6834 @opindex commas@r{, outputting between files}
6835 List files horizontally, with as many as will fit on each line,
6836 separated by @samp{, } (a comma and a space).
6839 @itemx --indicator-style=slash
6841 @opindex --indicator-style
6842 @cindex file type, marking
6843 Append a @samp{/} to directory names.
6846 @itemx --format=across
6847 @itemx --format=horizontal
6850 @opindex across@r{, listing files}
6851 @opindex horizontal@r{, listing files}
6852 List the files in columns, sorted horizontally.
6855 @itemx --tabsize=@var{cols}
6858 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6859 @command{ls} uses tabs where possible in the output, for efficiency. If
6860 @var{cols} is zero, do not use tabs at all.
6862 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6863 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6864 do not properly align columns to the right of a TAB following a
6865 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6866 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6867 @command{ls} to align using spaces, not tabs.
6870 @itemx --width=@var{cols}
6874 Assume the screen is @var{cols} columns wide. The default is taken
6875 from the terminal settings if possible; otherwise the environment
6876 variable @env{COLUMNS} is used if it is set; otherwise the default
6882 @node Formatting file timestamps
6883 @subsection Formatting file timestamps
6885 By default, file timestamps are listed in abbreviated form. Most
6886 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6887 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6888 for non-recent timestamps, and a date-without-year and time like
6889 @samp{Mar 30 23:45} for recent timestamps.
6891 A timestamp is considered to be @dfn{recent} if it is less than six
6892 months old, and is not dated in the future. If a timestamp dated
6893 today is not listed in recent form, the timestamp is in the future,
6894 which means you probably have clock skew problems which may break
6895 programs like @command{make} that rely on file timestamps.
6898 Time stamps are listed according to the time zone rules specified by
6899 the @env{TZ} environment variable, or by the system default rules if
6900 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6901 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6903 The following option changes how file timestamps are printed.
6906 @item --time-style=@var{style}
6907 @opindex --time-style
6909 List timestamps in style @var{style}. The @var{style} should
6910 be one of the following:
6915 List timestamps using @var{format}, where @var{format} is interpreted
6916 like the format argument of @command{date} (@pxref{date invocation}).
6917 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6918 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6919 with @command{date}, @var{format}'s interpretation is affected by the
6920 @env{LC_TIME} locale category.
6922 If @var{format} contains two format strings separated by a newline,
6923 the former is used for non-recent files and the latter for recent
6924 files; if you want output columns to line up, you may need to insert
6925 spaces in one of the two formats.
6928 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6929 format with nanosecond precision, e.g., @samp{2002-03-30
6930 23:45:56.477817180 -0700}. This style is equivalent to
6931 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6933 This is useful because the time output includes all the information that
6934 is available from the operating system. For example, this can help
6935 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6936 uses the full timestamp to determine whether a file is out of date.
6939 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6940 @samp{2002-03-30 23:45}. These timestamps are shorter than
6941 @samp{full-iso} timestamps, and are usually good enough for everyday
6942 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6945 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6946 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6947 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6948 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6949 nearly the same information in a smaller space and their brevity helps
6950 @command{ls} output fit within traditional 80-column output lines.
6951 The following two @command{ls} invocations are equivalent:
6956 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6957 ls -l --time-style="iso"
6962 List timestamps in a locale-dependent form. For example, a Finnish
6963 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6964 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6965 timestamps typically consume more space than @samp{iso} timestamps and
6966 are harder for programs to parse because locale conventions vary so
6967 widely, but they are easier for many people to read.
6969 The @env{LC_TIME} locale category specifies the timestamp format. The
6970 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
6971 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
6972 @command{ls} invocations are equivalent:
6977 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
6978 ls -l --time-style="locale"
6981 Other locales behave differently. For example, in a German locale,
6982 @option{--time-style="locale"} might be equivalent to
6983 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
6984 and might generate timestamps like @samp{30. M@"ar 2002@ } and
6985 @samp{30. M@"ar 23:45}.
6987 @item posix-@var{style}
6989 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
6990 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
6991 example, the @samp{posix-long-iso} style lists
6992 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
6993 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
6998 You can specify the default value of the @option{--time-style} option
6999 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7000 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7001 later use the @option{--dired} option and therefore can parse any date
7002 format, but if you are using Emacs 21.1 or 21.2 and specify a
7003 non-@acronym{POSIX} locale you may need to set
7004 @samp{TIME_STYLE="posix-long-iso"}.
7006 To avoid certain denial-of-service attacks, timestamps that would be
7007 longer than 1000 bytes may be treated as errors.
7010 @node Formatting the file names
7011 @subsection Formatting the file names
7013 These options change how file names themselves are printed.
7019 @itemx --quoting-style=escape
7022 @opindex --quoting-style
7023 @cindex backslash sequences for file names
7024 Quote nongraphic characters in file names using alphabetic and octal
7025 backslash sequences like those used in C.
7029 @itemx --quoting-style=literal
7032 @opindex --quoting-style
7033 Do not quote file names. However, with @command{ls} nongraphic
7034 characters are still printed as question marks if the output is a
7035 terminal and you do not specify the @option{--show-control-chars}
7039 @itemx --hide-control-chars
7041 @opindex --hide-control-chars
7042 Print question marks instead of nongraphic characters in file names.
7043 This is the default if the output is a terminal and the program is
7048 @itemx --quoting-style=c
7050 @opindex --quote-name
7051 @opindex --quoting-style
7052 Enclose file names in double quotes and quote nongraphic characters as
7055 @item --quoting-style=@var{word}
7056 @opindex --quoting-style
7057 @cindex quoting style
7058 Use style @var{word} to quote file names and other strings that may
7059 contain arbitrary characters. The @var{word} should
7060 be one of the following:
7064 Output strings as-is; this is the same as the @option{-N} or
7065 @option{--literal} option.
7067 Quote strings for the shell if they contain shell metacharacters or would
7068 cause ambiguous output.
7069 The quoting is suitable for @acronym{POSIX}-compatible shells like
7070 @command{bash}, but it does not always work for incompatible shells
7073 Quote strings for the shell, even if they would normally not require quoting.
7075 Quote strings as for C character string literals, including the
7076 surrounding double-quote characters; this is the same as the
7077 @option{-Q} or @option{--quote-name} option.
7079 Quote strings as for C character string literals, except omit the
7080 surrounding double-quote
7081 characters; this is the same as the @option{-b} or @option{--escape} option.
7083 Quote strings as for C character string literals, except use
7084 surrounding quotation marks appropriate for the
7087 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7088 Quote strings as for C character string literals, except use
7089 surrounding quotation marks appropriate for the locale, and quote
7090 @t{`like this'} instead of @t{"like
7091 this"} in the default C locale. This looks nicer on many displays.
7094 You can specify the default value of the @option{--quoting-style} option
7095 with the environment variable @env{QUOTING_STYLE}. If that environment
7096 variable is not set, the default value is @samp{literal}, but this
7097 default may change to @samp{shell} in a future version of this package.
7099 @item --show-control-chars
7100 @opindex --show-control-chars
7101 Print nongraphic characters as-is in file names.
7102 This is the default unless the output is a terminal and the program is
7108 @node dir invocation
7109 @section @command{dir}: Briefly list directory contents
7112 @cindex directory listing, brief
7114 @command{dir} is equivalent to @code{ls -C
7115 -b}; that is, by default files are listed in columns, sorted vertically,
7116 and special characters are represented by backslash escape sequences.
7118 @xref{ls invocation, @command{ls}}.
7121 @node vdir invocation
7122 @section @command{vdir}: Verbosely list directory contents
7125 @cindex directory listing, verbose
7127 @command{vdir} is equivalent to @code{ls -l
7128 -b}; that is, by default files are listed in long format and special
7129 characters are represented by backslash escape sequences.
7131 @node dircolors invocation
7132 @section @command{dircolors}: Color setup for @command{ls}
7136 @cindex setup for color
7138 @command{dircolors} outputs a sequence of shell commands to set up the
7139 terminal for color output from @command{ls} (and @command{dir}, etc.).
7143 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7146 If @var{file} is specified, @command{dircolors} reads it to determine which
7147 colors to use for which file types and extensions. Otherwise, a
7148 precompiled database is used. For details on the format of these files,
7149 run @samp{dircolors --print-database}.
7151 To make @command{dircolors} read a @file{~/.dircolors} file if it
7152 exists, you can put the following lines in your @file{~/.bashrc} (or
7153 adapt them to your favorite shell):
7157 test -r $d && eval "$(dircolors $d)"
7161 @vindex SHELL @r{environment variable, and color}
7162 The output is a shell command to set the @env{LS_COLORS} environment
7163 variable. You can specify the shell syntax to use on the command line,
7164 or @command{dircolors} will guess it from the value of the @env{SHELL}
7165 environment variable.
7167 The program accepts the following options. Also see @ref{Common options}.
7172 @itemx --bourne-shell
7175 @opindex --bourne-shell
7176 @cindex Bourne shell syntax for color setup
7177 @cindex @command{sh} syntax for color setup
7178 Output Bourne shell commands. This is the default if the @env{SHELL}
7179 environment variable is set and does not end with @samp{csh} or
7188 @cindex C shell syntax for color setup
7189 @cindex @command{csh} syntax for color setup
7190 Output C shell commands. This is the default if @code{SHELL} ends with
7191 @command{csh} or @command{tcsh}.
7194 @itemx --print-database
7196 @opindex --print-database
7197 @cindex color database, printing
7198 @cindex database for color setup, printing
7199 @cindex printing color database
7200 Print the (compiled-in) default color configuration database. This
7201 output is itself a valid configuration file, and is fairly descriptive
7202 of the possibilities.
7209 @node Basic operations
7210 @chapter Basic operations
7212 @cindex manipulating files
7214 This chapter describes the commands for basic file manipulation:
7215 copying, moving (renaming), and deleting (removing).
7218 * cp invocation:: Copy files.
7219 * dd invocation:: Convert and copy a file.
7220 * install invocation:: Copy files and set attributes.
7221 * mv invocation:: Move (rename) files.
7222 * rm invocation:: Remove files or directories.
7223 * shred invocation:: Remove files more securely.
7228 @section @command{cp}: Copy files and directories
7231 @cindex copying files and directories
7232 @cindex files, copying
7233 @cindex directories, copying
7235 @command{cp} copies files (or, optionally, directories). The copy is
7236 completely independent of the original. You can either copy one file to
7237 another, or copy arbitrarily many files to a destination directory.
7241 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7242 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7243 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7248 If two file names are given, @command{cp} copies the first file to the
7252 If the @option{--target-directory} (@option{-t}) option is given, or
7253 failing that if the last file is a directory and the
7254 @option{--no-target-directory} (@option{-T}) option is not given,
7255 @command{cp} copies each @var{source} file to the specified directory,
7256 using the @var{source}s' names.
7259 Generally, files are written just as they are read. For exceptions,
7260 see the @option{--sparse} option below.
7262 By default, @command{cp} does not copy directories. However, the
7263 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7264 copy recursively by descending into source directories and copying files
7265 to corresponding destination directories.
7267 When copying from a symbolic link, @command{cp} normally follows the
7268 link only when not copying
7269 recursively. This default can be overridden with the
7270 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7271 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7272 @option{-H} options. If more than one of these options is specified,
7273 the last one silently overrides the others.
7275 When copying to a symbolic link, @command{cp} follows the
7276 link only when it refers to an existing regular file.
7277 However, when copying to a dangling symbolic link, @command{cp}
7278 refuses by default, and fails with a diagnostic, since the operation
7279 is inherently dangerous. This behavior is contrary to historical
7280 practice and to @acronym{POSIX}.
7281 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7282 the target of a dangling destination symlink, in spite of the possible risk.
7283 Also, when an option like
7284 @option{--backup} or @option{--link} acts to rename or remove the
7285 destination before copying, @command{cp} renames or removes the
7286 symbolic link rather than the file it points to.
7288 By default, @command{cp} copies the contents of special files only
7289 when not copying recursively. This default can be overridden with the
7290 @option{--copy-contents} option.
7292 @cindex self-backups
7293 @cindex backups, making only
7294 @command{cp} generally refuses to copy a file onto itself, with the
7295 following exception: if @option{--force --backup} is specified with
7296 @var{source} and @var{dest} identical, and referring to a regular file,
7297 @command{cp} will make a backup file, either regular or numbered, as
7298 specified in the usual ways (@pxref{Backup options}). This is useful when
7299 you simply want to make a backup of an existing file before changing it.
7301 The program accepts the following options. Also see @ref{Common options}.
7308 Preserve as much as possible of the structure and attributes of the
7309 original files in the copy (but do not attempt to preserve internal
7310 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7311 directory in a different order).
7312 Try to preserve SELinux security context and extended attributes (xattr),
7313 but ignore any failure to do that and print no corresponding diagnostic.
7314 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7317 @itemx @w{@kbd{--backup}[=@var{method}]}
7320 @vindex VERSION_CONTROL
7321 @cindex backups, making
7322 @xref{Backup options}.
7323 Make a backup of each file that would otherwise be overwritten or removed.
7324 As a special case, @command{cp} makes a backup of @var{source} when the force
7325 and backup options are given and @var{source} and @var{dest} are the same
7326 name for an existing, regular file. One useful application of this
7327 combination of options is this tiny Bourne shell script:
7331 # Usage: backup FILE...
7332 # Create a @sc{gnu}-style backup of each listed FILE.
7334 cp --backup --force -- "$i" "$i"
7338 @item --copy-contents
7339 @cindex directories, copying recursively
7340 @cindex copying directories recursively
7341 @cindex recursively copying directories
7342 @cindex non-directories, copying as special files
7343 If copying recursively, copy the contents of any special files (e.g.,
7344 FIFOs and device files) as if they were regular files. This means
7345 trying to read the data in each source file and writing it to the
7346 destination. It is usually a mistake to use this option, as it
7347 normally has undesirable effects on special files like FIFOs and the
7348 ones typically found in the @file{/dev} directory. In most cases,
7349 @code{cp -R --copy-contents} will hang indefinitely trying to read
7350 from FIFOs and special files like @file{/dev/console}, and it will
7351 fill up your destination disk if you use it to copy @file{/dev/zero}.
7352 This option has no effect unless copying recursively, and it does not
7353 affect the copying of symbolic links.
7357 @cindex symbolic links, copying
7358 @cindex hard links, preserving
7359 Copy symbolic links as symbolic links rather than copying the files that
7360 they point to, and preserve hard links between source files in the copies.
7361 Equivalent to @option{--no-dereference --preserve=links}.
7367 When copying without this option and an existing destination file cannot
7368 be opened for writing, the copy fails. However, with @option{--force}),
7369 when a destination file cannot be opened, @command{cp} then removes it and
7370 tries to open it again. Contrast this behavior with that enabled by
7371 @option{--link} and @option{--symbolic-link}, whereby the destination file
7372 is never opened but rather is removed unconditionally. Also see the
7373 description of @option{--remove-destination}.
7375 This option is independent of the @option{--interactive} or
7376 @option{-i} option: neither cancels the effect of the other.
7378 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7383 If a command line argument specifies a symbolic link, then copy the
7384 file it points to rather than the symbolic link itself. However,
7385 copy (preserving its nature) any symbolic link that is encountered
7386 via recursive traversal.
7389 @itemx --interactive
7391 @opindex --interactive
7392 When copying a file other than a directory, prompt whether to
7393 overwrite an existing destination file. The @option{-i} option overrides
7394 a previous @option{-n} option.
7400 Make hard links instead of copies of non-directories.
7403 @itemx --dereference
7405 @opindex --dereference
7406 Follow symbolic links when copying from them.
7407 With this option, @command{cp} cannot create a symbolic link.
7408 For example, a symlink (to regular file) in the source tree will be copied to
7409 a regular file in the destination tree.
7414 @opindex --no-clobber
7415 Do not overwrite an existing file. The @option{-n} option overrides a previous
7416 @option{-i} option. This option is mutually exclusive with @option{-b} or
7417 @option{--backup} option.
7420 @itemx --no-dereference
7422 @opindex --no-dereference
7423 @cindex symbolic links, copying
7424 Copy symbolic links as symbolic links rather than copying the files that
7425 they point to. This option affects only symbolic links in the source;
7426 symbolic links in the destination are always followed if possible.
7429 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7432 @cindex file information, preserving, extended attributes, xattr
7433 Preserve the specified attributes of the original files.
7434 If specified, the @var{attribute_list} must be a comma-separated list
7435 of one or more of the following strings:
7439 Preserve the file mode bits and access control lists.
7441 Preserve the owner and group. On most modern systems,
7442 only users with appropriate privileges may change the owner of a file,
7444 may preserve the group ownership of a file only if they happen to be
7445 a member of the desired group.
7447 Preserve the times of last access and last modification, when possible.
7448 On older systems, it is not possible to preserve these attributes
7449 when the affected file is a symbolic link.
7450 However, many systems now provide the @code{utimensat} function,
7451 which makes it possible even for symbolic links.
7453 Preserve in the destination files
7454 any links between corresponding source files.
7455 Note that with @option{-L} or @option{-H}, this option can convert
7456 symbolic links to hard links. For example,
7458 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7463 Note the inputs: @file{b} is a symlink to regular file @file{a},
7464 yet the files in destination directory, @file{c/}, are hard-linked.
7465 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7466 tells @command{cp} to dereference command line arguments, it sees two files
7467 with the same inode number, and preserves the perceived hard link.
7469 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7471 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7477 Preserve SELinux security context of the file. @command{cp} will fail
7478 if the preserving of SELinux security context is not succesful.
7480 Preserve extended attributes if @command{cp} is built with xattr support,
7481 and xattrs are supported and enabled on your file system.
7482 If SELinux context and/or ACLs are implemented using xattrs,
7483 they are preserved by this option as well.
7485 Preserve all file attributes.
7486 Equivalent to specifying all of the above, but with the difference
7487 that failure to preserve SELinux security context or extended attributes
7488 does not change @command{cp}'s exit status.
7489 @command{cp} does diagnose such failures.
7492 Using @option{--preserve} with no @var{attribute_list} is equivalent
7493 to @option{--preserve=mode,ownership,timestamps}.
7495 In the absence of this option, each destination file is created with the
7496 mode bits of the corresponding source file, minus the bits set in the
7497 umask and minus the set-user-ID and set-group-ID bits.
7498 @xref{File permissions}.
7500 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7501 @cindex file information, preserving
7502 Do not preserve the specified attributes. The @var{attribute_list}
7503 has the same form as for @option{--preserve}.
7507 @cindex parent directories and @command{cp}
7508 Form the name of each destination file by appending to the target
7509 directory a slash and the specified name of the source file. The last
7510 argument given to @command{cp} must be the name of an existing directory.
7511 For example, the command:
7514 cp --parents a/b/c existing_dir
7518 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7519 any missing intermediate directories.
7526 @opindex --recursive
7527 @cindex directories, copying recursively
7528 @cindex copying directories recursively
7529 @cindex recursively copying directories
7530 @cindex non-directories, copying as special files
7531 Copy directories recursively. By default, do not follow symbolic
7532 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7533 @option{--dereference} (@option{-L}), @option{--no-dereference}
7534 (@option{-P}), and @option{-H} options. Special files are copied by
7535 creating a destination file of the same type as the source; see the
7536 @option{--copy-contents} option. It is not portable to use
7537 @option{-r} to copy symbolic links or special files. On some
7538 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7539 @option{-L} and @option{--copy-contents} for historical reasons.
7540 Also, it is not portable to use @option{-R} to copy symbolic links
7541 unless you also specify @option{-P}, as @acronym{POSIX} allows
7542 implementations that dereference symbolic links by default.
7544 @item --reflink[=@var{when}]
7545 @opindex --reflink[=@var{when}]
7548 @cindex copy on write
7549 Perform a lightweight, copy-on-write (COW) copy.
7550 Copying with this option can succeed only on some file systems.
7551 Once it has succeeded, beware that the source and destination files
7552 share the same disk data blocks as long as they remain unmodified.
7553 Thus, if a disk I/O error affects data blocks of one of the files,
7554 the other suffers the exact same fate.
7556 The @var{when} value can be one of the following:
7560 The default behavior: if the copy-on-write operation is not supported
7561 then report the failure for each file and exit with a failure status.
7564 If the copy-on-write operation is not supported then fall back
7565 to the standard copy behaviour.
7569 @item --remove-destination
7570 @opindex --remove-destination
7571 Remove each existing destination file before attempting to open it
7572 (contrast with @option{-f} above).
7574 @item --sparse=@var{when}
7575 @opindex --sparse=@var{when}
7576 @cindex sparse files, copying
7577 @cindex holes, copying files with
7578 @findex read @r{system call, and holes}
7579 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7580 does not occupy any physical disk blocks; the @samp{read} system call
7581 reads these as zeros. This can both save considerable disk space and
7582 increase speed, since many binary files contain lots of consecutive zero
7583 bytes. By default, @command{cp} detects holes in input source files via a crude
7584 heuristic and makes the corresponding output file sparse as well.
7585 Only regular files may be sparse.
7587 The @var{when} value can be one of the following:
7591 The default behavior: if the input file is sparse, attempt to make
7592 the output file sparse, too. However, if an output file exists but
7593 refers to a non-regular file, then do not attempt to make it sparse.
7596 For each sufficiently long sequence of zero bytes in the input file,
7597 attempt to create a corresponding hole in the output file, even if the
7598 input file does not appear to be sparse.
7599 This is useful when the input file resides on a file system
7600 that does not support sparse files
7601 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7602 but the output file is on a type of file system that does support them.
7603 Holes may be created only in regular files, so if the destination file
7604 is of some other type, @command{cp} does not even try to make it sparse.
7607 Never make the output file sparse.
7608 This is useful in creating a file for use with the @command{mkswap} command,
7609 since such a file must not have any holes.
7612 @optStripTrailingSlashes
7615 @itemx --symbolic-link
7617 @opindex --symbolic-link
7618 @cindex symbolic links, copying with
7619 Make symbolic links instead of copies of non-directories. All source
7620 file names must be absolute (starting with @samp{/}) unless the
7621 destination files are in the current directory. This option merely
7622 results in an error message on systems that do not support symbolic links.
7628 @optNoTargetDirectory
7634 @cindex newer files, copying only
7635 Do not copy a non-directory that has an existing destination with the
7636 same or newer modification time. If time stamps are being preserved,
7637 the comparison is to the source time stamp truncated to the
7638 resolutions of the destination file system and of the system calls
7639 used to update time stamps; this avoids duplicate work if several
7640 @samp{cp -pu} commands are executed with the same source and
7647 Print the name of each file before copying it.
7650 @itemx --one-file-system
7652 @opindex --one-file-system
7653 @cindex file systems, omitting copying to different
7654 Skip subdirectories that are on different file systems from the one that
7655 the copy started on.
7656 However, mount point directories @emph{are} copied.
7664 @section @command{dd}: Convert and copy a file
7667 @cindex converting while copying a file
7669 @command{dd} copies a file (from standard input to standard output, by
7670 default) with a changeable I/O block size, while optionally performing
7671 conversions on it. Synopses:
7674 dd [@var{operand}]@dots{}
7678 The only options are @option{--help} and @option{--version}.
7679 @xref{Common options}. @command{dd} accepts the following operands.
7685 Read from @var{file} instead of standard input.
7689 Write to @var{file} instead of standard output. Unless
7690 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7691 bytes (or the size specified with @samp{seek=}).
7693 @item ibs=@var{bytes}
7695 @cindex block size of input
7696 @cindex input block size
7697 Set the input block size to @var{bytes}.
7698 This makes @command{dd} read @var{bytes} per block.
7699 The default is 512 bytes.
7701 @item obs=@var{bytes}
7703 @cindex block size of output
7704 @cindex output block size
7705 Set the output block size to @var{bytes}.
7706 This makes @command{dd} write @var{bytes} per block.
7707 The default is 512 bytes.
7709 @item bs=@var{bytes}
7712 Set both input and output block sizes to @var{bytes}.
7713 This makes @command{dd} read and write @var{bytes} per block,
7714 overriding any @samp{ibs} and @samp{obs} settings.
7715 In addition, if no data-transforming @option{conv} option is specified,
7716 each input block is copied to the output as a single block,
7717 without aggregating short reads.
7719 @item cbs=@var{bytes}
7721 @cindex block size of conversion
7722 @cindex conversion block size
7723 @cindex fixed-length records, converting to variable-length
7724 @cindex variable-length records, converting to fixed-length
7725 Set the conversion block size to @var{bytes}.
7726 When converting variable-length records to fixed-length ones
7727 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7728 use @var{bytes} as the fixed record length.
7730 @item skip=@var{blocks}
7732 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7734 @item seek=@var{blocks}
7736 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7738 @item count=@var{blocks}
7740 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7741 of everything until the end of the file.
7745 Do not print the overall transfer rate and volume statistics
7746 that normally make up the third status line when @command{dd} exits.
7748 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7750 Convert the file as specified by the @var{conversion} argument(s).
7751 (No spaces around any comma(s).)
7758 @opindex ascii@r{, converting to}
7759 Convert @acronym{EBCDIC} to @acronym{ASCII},
7760 using the conversion table specified by @acronym{POSIX}.
7761 This provides a 1:1 translation for all 256 bytes.
7764 @opindex ebcdic@r{, converting to}
7765 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7766 This is the inverse of the @samp{ascii} conversion.
7769 @opindex alternate ebcdic@r{, converting to}
7770 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7771 using the alternate conversion table specified by @acronym{POSIX}.
7772 This is not a 1:1 translation, but reflects common historical practice
7773 for @samp{~}, @samp{[}, and @samp{]}.
7775 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7779 @opindex block @r{(space-padding)}
7780 For each line in the input, output @samp{cbs} bytes, replacing the
7781 input newline with a space and padding with spaces as necessary.
7785 Remove any trailing spaces in each @samp{cbs}-sized input block,
7786 and append a newline.
7788 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7791 @opindex lcase@r{, converting to}
7792 Change uppercase letters to lowercase.
7795 @opindex ucase@r{, converting to}
7796 Change lowercase letters to uppercase.
7798 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7801 @opindex swab @r{(byte-swapping)}
7802 @cindex byte-swapping
7803 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7804 when an odd number of bytes are read---the last byte is simply copied
7805 (since there is nothing to swap it with).
7809 @cindex read errors, ignoring
7810 Continue after read errors.
7814 @cindex creating output file, avoiding
7815 Do not create the output file; the output file must already exist.
7819 @cindex creating output file, requiring
7820 Fail if the output file already exists; @command{dd} must create the
7823 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7827 @cindex truncating output file, avoiding
7828 Do not truncate the output file.
7831 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7832 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7833 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7838 @cindex synchronized data writes, before finishing
7839 Synchronize output data just before finishing. This forces a physical
7840 write of output data.
7844 @cindex synchronized data and metadata writes, before finishing
7845 Synchronize output data and metadata just before finishing. This
7846 forces a physical write of output data and metadata.
7850 @item iflag=@var{flag}[,@var{flag}]@dots{}
7852 Access the input file using the flags specified by the @var{flag}
7853 argument(s). (No spaces around any comma(s).)
7855 @item oflag=@var{flag}[,@var{flag}]@dots{}
7857 Access the output file using the flags specified by the @var{flag}
7858 argument(s). (No spaces around any comma(s).)
7860 Here are the flags. Not every flag is supported on every operating
7867 @cindex appending to the output file
7868 Write in append mode, so that even if some other process is writing to
7869 this file, every @command{dd} write will append to the current
7870 contents of the file. This flag makes sense only for output.
7871 If you combine this flag with the @samp{of=@var{file}} operand,
7872 you should also specify @samp{conv=notrunc} unless you want the
7873 output file to be truncated before being appended to.
7877 @cindex concurrent I/O
7878 Use concurrent I/O mode for data. This mode performs direct I/O
7879 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7880 A file cannot be opened in CIO mode and with a standard open at the
7886 Use direct I/O for data, avoiding the buffer cache.
7887 Note that the kernel may impose restrictions on read or write buffer sizes.
7888 For example, with an ext4 destination file system and a linux-based kernel,
7889 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7890 output buffer size is not a multiple of 512.
7894 @cindex directory I/O
7896 Fail unless the file is a directory. Most operating systems do not
7897 allow I/O to a directory, so this flag has limited utility.
7901 @cindex synchronized data reads
7902 Use synchronized I/O for data. For the output file, this forces a
7903 physical write of output data on each write. For the input file,
7904 this flag can matter when reading from a remote file that has been
7905 written to synchronously by some other process. Metadata (e.g.,
7906 last-access and last-modified time) is not necessarily synchronized.
7910 @cindex synchronized data and metadata I/O
7911 Use synchronized I/O for both data and metadata.
7915 @cindex nonblocking I/O
7916 Use non-blocking I/O.
7921 Do not update the file's access time.
7922 Some older file systems silently ignore this flag, so it is a good
7923 idea to test it on your files before relying on it.
7927 @cindex controlling terminal
7928 Do not assign the file to be a controlling terminal for @command{dd}.
7929 This has no effect when the file is not a terminal.
7930 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7935 @cindex symbolic links, following
7936 Do not follow symbolic links.
7941 Fail if the file has multiple hard links.
7946 Use binary I/O. This option has an effect only on nonstandard
7947 platforms that distinguish binary from text I/O.
7952 Use text I/O. Like @samp{binary}, this option has no effect on
7957 Accumulate full blocks from input. The @code{read} system call
7958 may return early if a full block is not available.
7959 When that happens, continue calling @code{read} to fill the remainder
7961 This flag can be used only with @code{iflag}.
7965 These flags are not supported on all systems, and @samp{dd} rejects
7966 attempts to use them when they are not supported. When reading from
7967 standard input or writing to standard output, the @samp{nofollow} and
7968 @samp{noctty} flags should not be specified, and the other flags
7969 (e.g., @samp{nonblock}) can affect how other processes behave with the
7970 affected file descriptors, even after @command{dd} exits.
7974 @cindex multipliers after numbers
7975 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
7976 followed by a multiplier: @samp{b}=512, @samp{c}=1,
7977 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
7978 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
7980 Use different @command{dd} invocations to use different block sizes for
7981 skipping and I/O@. For example, the following shell commands copy data
7982 in 512 KiB blocks between a disk and a tape, but do not save or restore a
7983 4 KiB label at the start of the disk:
7986 disk=/dev/rdsk/c0t1d0s2
7989 # Copy all but the label from disk to tape.
7990 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
7992 # Copy from tape back to disk, but leave the disk label alone.
7993 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
7996 Sending an @samp{INFO} signal to a running @command{dd}
7997 process makes it print I/O statistics to standard error
7998 and then resume copying. In the example below,
7999 @command{dd} is run in the background to copy 10 million blocks.
8000 The @command{kill} command makes it output intermediate I/O statistics,
8001 and when @command{dd} completes normally or is killed by the
8002 @code{SIGINT} signal, it outputs the final statistics.
8005 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8006 $ kill -s INFO $pid; wait $pid
8007 3385223+0 records in
8008 3385223+0 records out
8009 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8010 10000000+0 records in
8011 10000000+0 records out
8012 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8015 @vindex POSIXLY_CORRECT
8016 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8017 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8018 environment variable is set.
8023 @node install invocation
8024 @section @command{install}: Copy files and set attributes
8027 @cindex copying files and setting attributes
8029 @command{install} copies files while setting their file mode bits and, if
8030 possible, their owner and group. Synopses:
8033 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8034 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8035 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8036 install [@var{option}]@dots{} -d @var{directory}@dots{}
8041 If two file names are given, @command{install} copies the first file to the
8045 If the @option{--target-directory} (@option{-t}) option is given, or
8046 failing that if the last file is a directory and the
8047 @option{--no-target-directory} (@option{-T}) option is not given,
8048 @command{install} copies each @var{source} file to the specified
8049 directory, using the @var{source}s' names.
8052 If the @option{--directory} (@option{-d}) option is given,
8053 @command{install} creates each @var{directory} and any missing parent
8054 directories. Parent directories are created with mode
8055 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8056 current umask. @xref{Directory Setuid and Setgid}, for how the
8057 set-user-ID and set-group-ID bits of parent directories are inherited.
8060 @cindex Makefiles, installing programs in
8061 @command{install} is similar to @command{cp}, but allows you to control the
8062 attributes of destination files. It is typically used in Makefiles to
8063 copy programs into their destination directories. It refuses to copy
8064 files onto themselves.
8066 @cindex extended attributes, xattr
8067 @command{install} never preserves extended attributes (xattr).
8069 The program accepts the following options. Also see @ref{Common options}.
8079 Compare each pair of source and destination files, and if the destination has
8080 identical content and any specified owner, group, permissions, and possibly
8081 SELinux context, then do not modify the destination at all.
8085 Ignored; for compatibility with old Unix versions of @command{install}.
8089 Create any missing parent directories of @var{dest},
8090 then copy @var{source} to @var{dest}.
8091 This option is ignored if a destination directory is specified
8092 via @option{--target-directory=DIR}.
8097 @opindex --directory
8098 @cindex directories, creating with given attributes
8099 @cindex parent directories, creating missing
8100 @cindex leading directories, creating missing
8101 Create any missing parent directories, giving them the default
8102 attributes. Then create each given directory, setting their owner,
8103 group and mode as given on the command line or to the defaults.
8105 @item -g @var{group}
8106 @itemx --group=@var{group}
8109 @cindex group ownership of installed files, setting
8110 Set the group ownership of installed files or directories to
8111 @var{group}. The default is the process's current group. @var{group}
8112 may be either a group name or a numeric group ID.
8115 @itemx --mode=@var{mode}
8118 @cindex permissions of installed files, setting
8119 Set the file mode bits for the installed file or directory to @var{mode},
8120 which can be either an octal number, or a symbolic mode as in
8121 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8122 point of departure (@pxref{File permissions}).
8123 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8124 execute for the owner, read and execute for group and other, and with
8125 set-user-ID and set-group-ID disabled.
8126 This default is not quite the same as @samp{755}, since it disables
8127 instead of preserving set-user-ID and set-group-ID on directories.
8128 @xref{Directory Setuid and Setgid}.
8130 @item -o @var{owner}
8131 @itemx --owner=@var{owner}
8134 @cindex ownership of installed files, setting
8135 @cindex appropriate privileges
8136 @vindex root @r{as default owner}
8137 If @command{install} has appropriate privileges (is run as root), set the
8138 ownership of installed files or directories to @var{owner}. The default
8139 is @code{root}. @var{owner} may be either a user name or a numeric user
8142 @item --preserve-context
8143 @opindex --preserve-context
8145 @cindex security context
8146 Preserve the SELinux security context of files and directories.
8147 Failure to preserve the context in all of the files or directories
8148 will result in an exit status of 1. If SELinux is disabled then
8149 print a warning and ignore the option.
8152 @itemx --preserve-timestamps
8154 @opindex --preserve-timestamps
8155 @cindex timestamps of installed files, preserving
8156 Set the time of last access and the time of last modification of each
8157 installed file to match those of each corresponding original file.
8158 When a file is installed without this option, its last access and
8159 last modification times are both set to the time of installation.
8160 This option is useful if you want to use the last modification times
8161 of installed files to keep track of when they were last built as opposed
8162 to when they were last installed.
8168 @cindex symbol table information, stripping
8169 @cindex stripping symbol table information
8170 Strip the symbol tables from installed binary executables.
8172 @itemx --strip-program=@var{program}
8173 @opindex --strip-program
8174 @cindex symbol table information, stripping, program
8175 Program used to strip binaries.
8181 @optNoTargetDirectory
8187 Print the name of each file before copying it.
8189 @item -Z @var{context}
8190 @itemx --context=@var{context}
8194 @cindex security context
8195 Set the default SELinux security context to be used for any
8196 created files and directories. If SELinux is disabled then
8197 print a warning and ignore the option.
8205 @section @command{mv}: Move (rename) files
8209 @command{mv} moves or renames files (or directories). Synopses:
8212 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8213 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8214 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8219 If two file names are given, @command{mv} moves the first file to the
8223 If the @option{--target-directory} (@option{-t}) option is given, or
8224 failing that if the last file is a directory and the
8225 @option{--no-target-directory} (@option{-T}) option is not given,
8226 @command{mv} moves each @var{source} file to the specified
8227 directory, using the @var{source}s' names.
8230 @command{mv} can move any type of file from one file system to another.
8231 Prior to version @code{4.0} of the fileutils,
8232 @command{mv} could move only regular files between file systems.
8233 For example, now @command{mv} can move an entire directory hierarchy
8234 including special device files from one partition to another. It first
8235 uses some of the same code that's used by @code{cp -a} to copy the
8236 requested directories and files, then (assuming the copy succeeded)
8237 it removes the originals. If the copy fails, then the part that was
8238 copied to the destination partition is removed. If you were to copy
8239 three directories from one partition to another and the copy of the first
8240 directory succeeded, but the second didn't, the first would be left on
8241 the destination partition and the second and third would be left on the
8244 @cindex extended attributes, xattr
8245 @command{mv} always tries to copy extended attributes (xattr).
8247 @cindex prompting, and @command{mv}
8248 If a destination file exists but is normally unwritable, standard input
8249 is a terminal, and the @option{-f} or @option{--force} option is not given,
8250 @command{mv} prompts the user for whether to replace the file. (You might
8251 own the file, or have write permission on its directory.) If the
8252 response is not affirmative, the file is skipped.
8254 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8255 when it might be a symlink to a directory.
8256 Otherwise, @command{mv} may do something very surprising, since
8257 its behavior depends on the underlying rename system call.
8258 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8259 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8260 renames not the symlink but rather the directory referenced by the symlink.
8261 @xref{Trailing slashes}.
8263 The program accepts the following options. Also see @ref{Common options}.
8273 @cindex prompts, omitting
8274 Do not prompt the user before removing a destination file.
8276 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8277 options, only the final one takes effect.
8282 @itemx --interactive
8284 @opindex --interactive
8285 @cindex prompts, forcing
8286 Prompt whether to overwrite each existing destination file, regardless
8288 If the response is not affirmative, the file is skipped.
8294 @opindex --no-clobber
8295 @cindex prompts, omitting
8296 Do not overwrite an existing file.
8298 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8304 @cindex newer files, moving only
8305 Do not move a non-directory that has an existing destination with the
8306 same or newer modification time.
8307 If the move is across file system boundaries, the comparison is to the
8308 source time stamp truncated to the resolutions of the destination file
8309 system and of the system calls used to update time stamps; this avoids
8310 duplicate work if several @samp{mv -u} commands are executed with the
8311 same source and destination.
8317 Print the name of each file before moving it.
8319 @optStripTrailingSlashes
8325 @optNoTargetDirectory
8333 @section @command{rm}: Remove files or directories
8336 @cindex removing files or directories
8338 @command{rm} removes each given @var{file}. By default, it does not remove
8339 directories. Synopsis:
8342 rm [@var{option}]@dots{} [@var{file}]@dots{}
8345 @cindex prompting, and @command{rm}
8346 If the @option{-I} or @option{--interactive=once} option is given,
8347 and there are more than three files or the @option{-r}, @option{-R},
8348 or @option{--recursive} are given, then @command{rm} prompts the user
8349 for whether to proceed with the entire operation. If the response is
8350 not affirmative, the entire command is aborted.
8352 Otherwise, if a file is unwritable, standard input is a terminal, and
8353 the @option{-f} or @option{--force} option is not given, or the
8354 @option{-i} or @option{--interactive=always} option @emph{is} given,
8355 @command{rm} prompts the user for whether to remove the file.
8356 If the response is not affirmative, the file is skipped.
8358 Any attempt to remove a file whose last file name component is
8359 @file{.} or @file{..} is rejected without any prompting.
8361 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8362 possible to recover the contents of that file. If you want more assurance
8363 that the contents are truly unrecoverable, consider using @command{shred}.
8365 The program accepts the following options. Also see @ref{Common options}.
8373 Ignore nonexistent files and never prompt the user.
8374 Ignore any previous @option{--interactive} (@option{-i}) option.
8378 Prompt whether to remove each file.
8379 If the response is not affirmative, the file is skipped.
8380 Ignore any previous @option{--force} (@option{-f}) option.
8381 Equivalent to @option{--interactive=always}.
8385 Prompt once whether to proceed with the command, if more than three
8386 files are named or if a recursive removal is requested. Ignore any
8387 previous @option{--force} (@option{-f}) option. Equivalent to
8388 @option{--interactive=once}.
8390 @itemx --interactive [=@var{when}]
8391 @opindex --interactive
8392 Specify when to issue an interactive prompt. @var{when} may be
8396 @vindex never @r{interactive option}
8397 - Do not prompt at all.
8399 @vindex once @r{interactive option}
8400 - Prompt once if more than three files are named or if a recursive
8401 removal is requested. Equivalent to @option{-I}.
8403 @vindex always @r{interactive option}
8404 - Prompt for every file being removed. Equivalent to @option{-i}.
8406 @option{--interactive} with no @var{when} is equivalent to
8407 @option{--interactive=always}.
8409 @itemx --one-file-system
8410 @opindex --one-file-system
8411 @cindex one file system, restricting @command{rm} to
8412 When removing a hierarchy recursively, skip any directory that is on a
8413 file system different from that of the corresponding command line argument.
8415 This option is useful when removing a build ``chroot'' hierarchy,
8416 which normally contains no valuable data. However, it is not uncommon
8417 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8418 use one's start-up file. The catch is that it's easy to forget to
8419 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8420 your normally throw-away chroot, that command will remove everything
8421 under @file{/home}, too.
8422 Use the @option{--one-file-system} option, and it will
8423 warn about and skip directories on other file systems.
8424 Of course, this will not save your @file{/home} if it and your
8425 chroot happen to be on the same file system.
8427 @itemx --preserve-root
8428 @opindex --preserve-root
8429 @cindex root directory, disallow recursive destruction
8430 Fail upon any attempt to remove the root directory, @file{/},
8431 when used with the @option{--recursive} option.
8432 This is the default behavior.
8433 @xref{Treating / specially}.
8435 @itemx --no-preserve-root
8436 @opindex --no-preserve-root
8437 @cindex root directory, allow recursive destruction
8438 Do not treat @file{/} specially when removing recursively.
8439 This option is not recommended unless you really want to
8440 remove all the files on your computer.
8441 @xref{Treating / specially}.
8448 @opindex --recursive
8449 @cindex directories, removing (recursively)
8450 Remove the listed directories and their contents recursively.
8456 Print the name of each file before removing it.
8460 @cindex files beginning with @samp{-}, removing
8461 @cindex @samp{-}, removing files beginning with
8462 One common question is how to remove files whose names begin with a
8463 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8464 function to parse its arguments, lets you use the @samp{--} option to
8465 indicate that all following arguments are non-options. To remove a file
8466 called @file{-f} in the current directory, you could type either:
8479 @opindex - @r{and Unix @command{rm}}
8480 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8481 predates the development of the getopt standard syntax.
8486 @node shred invocation
8487 @section @command{shred}: Remove files more securely
8490 @cindex data, erasing
8491 @cindex erasing data
8493 @command{shred} overwrites devices or files, to help prevent even
8494 very expensive hardware from recovering the data.
8496 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8497 not actually destroyed. Only the index listing where the file is
8498 stored is destroyed, and the storage is made available for reuse.
8499 There are undelete utilities that will attempt to reconstruct the index
8500 and can bring the file back if the parts were not reused.
8502 On a busy system with a nearly-full drive, space can get reused in a few
8503 seconds. But there is no way to know for sure. If you have sensitive
8504 data, you may want to be sure that recovery is not possible by actually
8505 overwriting the file with non-sensitive data.
8507 However, even after doing that, it is possible to take the disk back
8508 to a laboratory and use a lot of sensitive (and expensive) equipment
8509 to look for the faint ``echoes'' of the original data underneath the
8510 overwritten data. If the data has only been overwritten once, it's not
8513 The best way to remove something irretrievably is to destroy the media
8514 it's on with acid, melt it down, or the like. For cheap removable media
8515 like floppy disks, this is the preferred method. However, hard drives
8516 are expensive and hard to melt, so the @command{shred} utility tries
8517 to achieve a similar effect non-destructively.
8519 This uses many overwrite passes, with the data patterns chosen to
8520 maximize the damage they do to the old data. While this will work on
8521 floppies, the patterns are designed for best effect on hard drives.
8522 For more details, see the source code and Peter Gutmann's paper
8523 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8524 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8525 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8526 California, July 22--25, 1996).
8528 @strong{Please note} that @command{shred} relies on a very important assumption:
8529 that the file system overwrites data in place. This is the traditional
8530 way to do things, but many modern file system designs do not satisfy this
8531 assumption. Exceptions include:
8536 Log-structured or journaled file systems, such as those supplied with
8537 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8538 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8541 File systems that write redundant data and carry on even if some writes
8542 fail, such as RAID-based file systems.
8545 File systems that make snapshots, such as Network Appliance's NFS server.
8548 File systems that cache in temporary locations, such as NFS version 3
8552 Compressed file systems.
8555 In the particular case of ext3 file systems, the above disclaimer applies (and
8556 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8557 mode, which journals file data in addition to just metadata. In both
8558 the @code{data=ordered} (default) and @code{data=writeback} modes,
8559 @command{shred} works as usual. Ext3 journaling modes can be changed
8560 by adding the @code{data=something} option to the mount options for a
8561 particular file system in the @file{/etc/fstab} file, as documented in
8562 the mount man page (man mount).
8564 If you are not sure how your file system operates, then you should assume
8565 that it does not overwrite data in place, which means that shred cannot
8566 reliably operate on regular files in your file system.
8568 Generally speaking, it is more reliable to shred a device than a file,
8569 since this bypasses the problem of file system design mentioned above.
8570 However, even shredding devices is not always completely reliable. For
8571 example, most disks map out bad sectors invisibly to the application; if
8572 the bad sectors contain sensitive data, @command{shred} won't be able to
8575 @command{shred} makes no attempt to detect or report this problem, just as
8576 it makes no attempt to do anything about backups. However, since it is
8577 more reliable to shred devices than files, @command{shred} by default does
8578 not truncate or remove the output file. This default is more suitable
8579 for devices, which typically cannot be truncated and should not be
8582 Finally, consider the risk of backups and mirrors.
8583 File system backups and remote mirrors may contain copies of the
8584 file that cannot be removed, and that will allow a shredded file
8585 to be recovered later. So if you keep any data you may later want
8586 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8589 shred [@var{option}]@dots{} @var{file}[@dots{}]
8592 The program accepts the following options. Also see @ref{Common options}.
8600 @cindex force deletion
8601 Override file permissions if necessary to allow overwriting.
8604 @itemx -n @var{number}
8605 @itemx --iterations=@var{number}
8606 @opindex -n @var{number}
8607 @opindex --iterations=@var{number}
8608 @cindex iterations, selecting the number of
8609 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8610 overwrite. You can reduce this to save time, or increase it if you think it's
8611 appropriate. After 25 passes all of the internal overwrite patterns will have
8612 been used at least once.
8614 @item --random-source=@var{file}
8615 @opindex --random-source
8616 @cindex random source for shredding
8617 Use @var{file} as a source of random data used to overwrite and to
8618 choose pass ordering. @xref{Random sources}.
8620 @item -s @var{bytes}
8621 @itemx --size=@var{bytes}
8622 @opindex -s @var{bytes}
8623 @opindex --size=@var{bytes}
8624 @cindex size of file to shred
8625 Shred the first @var{bytes} bytes of the file. The default is to shred
8626 the whole file. @var{bytes} can be followed by a size specification like
8627 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8633 @cindex removing files after shredding
8634 After shredding a file, truncate it (if possible) and then remove it.
8635 If a file has multiple links, only the named links will be removed.
8641 Display to standard error all status updates as sterilization proceeds.
8647 By default, @command{shred} rounds the size of a regular file up to the next
8648 multiple of the file system block size to fully erase the last block of the file.
8649 Use @option{--exact} to suppress that behavior.
8650 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8651 blocks, the resulting file will be 512 bytes long. With this option,
8652 shred does not increase the apparent size of the file.
8658 Normally, the last pass that @command{shred} writes is made up of
8659 random data. If this would be conspicuous on your hard drive (for
8660 example, because it looks like encrypted data), or you just think
8661 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8662 all zero bits. This is in addition to the number of passes specified
8663 by the @option{--iterations} option.
8667 You might use the following command to erase all trace of the
8668 file system you'd created on the floppy disk in your first drive.
8669 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8673 shred --verbose /dev/fd0
8676 Similarly, to erase all data on a selected partition of
8677 your hard disk, you could give a command like this:
8680 shred --verbose /dev/sda5
8683 A @var{file} of @samp{-} denotes standard output.
8684 The intended use of this is to shred a removed temporary file.
8688 i=`tempfile -m 0600`
8691 echo "Hello, world" >&3
8696 However, the command @samp{shred - >file} does not shred the contents
8697 of @var{file}, since the shell truncates @var{file} before invoking
8698 @command{shred}. Use the command @samp{shred file} or (if using a
8699 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8704 @node Special file types
8705 @chapter Special file types
8707 @cindex special file types
8708 @cindex file types, special
8710 This chapter describes commands which create special types of files (and
8711 @command{rmdir}, which removes directories, one special file type).
8713 @cindex special file types
8715 Although Unix-like operating systems have markedly fewer special file
8716 types than others, not @emph{everything} can be treated only as the
8717 undifferentiated byte stream of @dfn{normal files}. For example, when a
8718 file is created or removed, the system must record this information,
8719 which it does in a @dfn{directory}---a special type of file. Although
8720 you can read directories as normal files, if you're curious, in order
8721 for the system to do its job it must impose a structure, a certain
8722 order, on the bytes of the file. Thus it is a ``special'' type of file.
8724 Besides directories, other special file types include named pipes
8725 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8728 * link invocation:: Make a hard link via the link syscall
8729 * ln invocation:: Make links between files.
8730 * mkdir invocation:: Make directories.
8731 * mkfifo invocation:: Make FIFOs (named pipes).
8732 * mknod invocation:: Make block or character special files.
8733 * readlink invocation:: Print value of a symlink or canonical file name.
8734 * rmdir invocation:: Remove empty directories.
8735 * unlink invocation:: Remove files via the unlink syscall
8739 @node link invocation
8740 @section @command{link}: Make a hard link via the link syscall
8743 @cindex links, creating
8744 @cindex hard links, creating
8745 @cindex creating links (hard only)
8747 @command{link} creates a single hard link at a time.
8748 It is a minimalist interface to the system-provided
8749 @code{link} function. @xref{Hard Links, , , libc,
8750 The GNU C Library Reference Manual}.
8751 It avoids the bells and whistles of the more commonly-used
8752 @command{ln} command (@pxref{ln invocation}).
8756 link @var{filename} @var{linkname}
8759 @var{filename} must specify an existing file, and @var{linkname}
8760 must specify a nonexistent entry in an existing directory.
8761 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8764 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8765 --no-target-directory @var{filename} @var{linkname}}. However, the
8766 @option{--directory} and @option{--no-target-directory} options are
8767 not specified by @acronym{POSIX}, and the @command{link} command is
8768 more portable in practice.
8770 If @var{filename} is a symbolic link, it is unspecified whether
8771 @var{linkname} will be a hard link to the symbolic link or to the
8772 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8773 to specify which behavior is desired.
8779 @section @command{ln}: Make links between files
8782 @cindex links, creating
8783 @cindex hard links, creating
8784 @cindex symbolic (soft) links, creating
8785 @cindex creating links (hard or soft)
8787 @cindex file systems and hard links
8788 @command{ln} makes links between files. By default, it makes hard links;
8789 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8793 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8794 ln [@var{option}]@dots{} @var{target}
8795 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8796 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8802 If two file names are given, @command{ln} creates a link to the first
8803 file from the second.
8806 If one @var{target} is given, @command{ln} creates a link to that file
8807 in the current directory.
8810 If the @option{--target-directory} (@option{-t}) option is given, or
8811 failing that if the last file is a directory and the
8812 @option{--no-target-directory} (@option{-T}) option is not given,
8813 @command{ln} creates a link to each @var{target} file in the specified
8814 directory, using the @var{target}s' names.
8818 Normally @command{ln} does not remove existing files. Use the
8819 @option{--force} (@option{-f}) option to remove them unconditionally,
8820 the @option{--interactive} (@option{-i}) option to remove them
8821 conditionally, and the @option{--backup} (@option{-b}) option to
8824 @cindex hard link, defined
8825 @cindex inode, and hard links
8826 A @dfn{hard link} is another name for an existing file; the link and the
8827 original are indistinguishable. Technically speaking, they share the
8828 same inode, and the inode contains all the information about a
8829 file---indeed, it is not incorrect to say that the inode @emph{is} the
8830 file. Most systems prohibit making a hard link to
8831 a directory; on those where it is allowed, only the super-user can do
8832 so (and with caution, since creating a cycle will cause problems to many
8833 other utilities). Hard links cannot cross file system boundaries. (These
8834 restrictions are not mandated by @acronym{POSIX}, however.)
8836 @cindex dereferencing symbolic links
8837 @cindex symbolic link, defined
8838 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8839 a special file type (which not all kernels support: System V release 3
8840 (and older) systems lack symlinks) in which the link file actually
8841 refers to a different file, by name. When most operations (opening,
8842 reading, writing, and so on) are passed the symbolic link file, the
8843 kernel automatically @dfn{dereferences} the link and operates on the
8844 target of the link. But some operations (e.g., removing) work on the
8845 link file itself, rather than on its target. The owner and group of a
8846 symlink are not significant to file access performed through
8847 the link, but do have implications on deleting a symbolic link from a
8848 directory with the restricted deletion bit set. On the GNU system,
8849 the mode of a symlink has no significance and cannot be changed, but
8850 on some BSD systems, the mode can be changed and will affect whether
8851 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8852 libc, The GNU C Library Reference Manual}.
8854 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8855 occurs when the string in the symlink does not resolve to a file.
8856 There are no restrictions against creating dangling symbolic links.
8857 There are trade-offs to using absolute or relative symlinks. An
8858 absolute symlink always points to the same file, even if the directory
8859 containing the link is moved. However, if the symlink is visible from
8860 more than one machine (such as on a networked file system), the file
8861 pointed to might not always be the same. A relative symbolic link is
8862 resolved in relation to the directory that contains the link, and is
8863 often useful in referring to files on the same device without regards
8864 to what name that device is mounted on when accessed via networked
8867 When creating a relative symlink in a different location than the
8868 current directory, the resolution of the symlink will be different
8869 than the resolution of the same string from the current directory.
8870 Therefore, many users prefer to first change directories to the
8871 location where the relative symlink will be created, so that
8872 tab-completion or other file resolution will find the same target as
8873 what will be placed in the symlink.
8875 The program accepts the following options. Also see @ref{Common options}.
8886 @opindex --directory
8887 @cindex hard links to directories
8888 Allow users with appropriate privileges to attempt to make hard links
8890 However, note that this will probably fail due to
8891 system restrictions, even for the super-user.
8897 Remove existing destination files.
8900 @itemx --interactive
8902 @opindex --interactive
8903 @cindex prompting, and @command{ln}
8904 Prompt whether to remove existing destination files.
8910 If @option{-s} is not in effect, and the source file is a symbolic
8911 link, create the hard link to the file referred to by the symbolic
8912 link, rather than the symbolic link itself.
8915 @itemx --no-dereference
8917 @opindex --no-dereference
8918 Do not treat the last operand specially when it is a symbolic link to
8919 a directory. Instead, treat it as if it were a normal file.
8921 When the destination is an actual directory (not a symlink to one),
8922 there is no ambiguity. The link is created in that directory.
8923 But when the specified destination is a symlink to a directory,
8924 there are two ways to treat the user's request. @command{ln} can
8925 treat the destination just as it would a normal directory and create
8926 the link in it. On the other hand, the destination can be viewed as a
8927 non-directory---as the symlink itself. In that case, @command{ln}
8928 must delete or backup that symlink before creating the new link.
8929 The default is to treat a destination that is a symlink to a directory
8930 just like a directory.
8932 This option is weaker than the @option{--no-target-directory}
8933 (@option{-T}) option, so it has no effect if both options are given.
8939 If @option{-s} is not in effect, and the source file is a symbolic
8940 link, create the hard link to the symbolic link itself. On platforms
8941 where this is not supported by the kernel, this option creates a
8942 symbolic link with identical contents; since symbolic link contents
8943 cannot be edited, any file name resolution performed through either
8944 link will be the same as if a hard link had been created.
8950 Make symbolic links instead of hard links. This option merely produces
8951 an error message on systems that do not support symbolic links.
8957 @optNoTargetDirectory
8963 Print the name of each file after linking it successfully.
8967 @cindex hard links to symbolic links
8968 @cindex symbolic links and @command{ln}
8969 If @option{-L} and @option{-P} are both given, the last one takes
8970 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
8971 are silently ignored. If neither option is given, then this
8972 implementation defaults to @option{-P} if the system @code{link} supports
8973 hard links to symbolic links (such as the GNU system), and @option{-L}
8974 if @code{link} follows symbolic links (such as on BSD).
8983 # Create link ../a pointing to a in that directory.
8984 # Not really useful because it points to itself.
8989 # Change to the target before creating symlinks to avoid being confused.
8995 # Hard coded file names don't move well.
8996 ln -s $(pwd)/a /some/dir/
9000 # Relative file names survive directory moves and also
9001 # work across networked file systems.
9002 ln -s afile anotherfile
9003 ln -s ../adir/afile yetanotherfile
9007 @node mkdir invocation
9008 @section @command{mkdir}: Make directories
9011 @cindex directories, creating
9012 @cindex creating directories
9014 @command{mkdir} creates directories with the specified names. Synopsis:
9017 mkdir [@var{option}]@dots{} @var{name}@dots{}
9020 @command{mkdir} creates each directory @var{name} in the order given.
9021 It reports an error if @var{name} already exists, unless the
9022 @option{-p} option is given and @var{name} is a directory.
9024 The program accepts the following options. Also see @ref{Common options}.
9029 @itemx --mode=@var{mode}
9032 @cindex modes of created directories, setting
9033 Set the file permission bits of created directories to @var{mode},
9034 which uses the same syntax as
9035 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9036 everyone) for the point of the departure. @xref{File permissions}.
9038 Normally the directory has the desired file mode bits at the moment it
9039 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9040 special mode bits, but in this case there may be a temporary window
9041 during which the directory exists but its special mode bits are
9042 incorrect. @xref{Directory Setuid and Setgid}, for how the
9043 set-user-ID and set-group-ID bits of directories are inherited unless
9044 overridden in this way.
9050 @cindex parent directories, creating
9051 Make any missing parent directories for each argument, setting their
9052 file permission bits to the umask modified by @samp{u+wx}. Ignore
9053 existing parent directories, and do not change their file permission
9056 To set the file permission bits of any newly-created parent
9057 directories to a value that includes @samp{u+wx}, you can set the
9058 umask before invoking @command{mkdir}. For example, if the shell
9059 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9060 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9061 To set a parent's special mode bits as well, you can invoke
9062 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9063 Setgid}, for how the set-user-ID and set-group-ID bits of
9064 newly-created parent directories are inherited.
9070 Print a message for each created directory. This is most useful with
9073 @item -Z @var{context}
9074 @itemx --context=@var{context}
9078 @cindex security context
9079 Set the default SELinux security context to be used for created directories.
9086 @node mkfifo invocation
9087 @section @command{mkfifo}: Make FIFOs (named pipes)
9090 @cindex FIFOs, creating
9091 @cindex named pipes, creating
9092 @cindex creating FIFOs (named pipes)
9094 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9095 specified names. Synopsis:
9098 mkfifo [@var{option}] @var{name}@dots{}
9101 A @dfn{FIFO} is a special file type that permits independent processes
9102 to communicate. One process opens the FIFO file for writing, and
9103 another for reading, after which data can flow as with the usual
9104 anonymous pipe in shells or elsewhere.
9106 The program accepts the following option. Also see @ref{Common options}.
9111 @itemx --mode=@var{mode}
9114 @cindex modes of created FIFOs, setting
9115 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9116 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9117 for the point of departure. @var{mode} should specify only file
9118 permission bits. @xref{File permissions}.
9120 @item -Z @var{context}
9121 @itemx --context=@var{context}
9125 @cindex security context
9126 Set the default SELinux security context to be used for created FIFOs.
9133 @node mknod invocation
9134 @section @command{mknod}: Make block or character special files
9137 @cindex block special files, creating
9138 @cindex character special files, creating
9140 @command{mknod} creates a FIFO, character special file, or block special
9141 file with the specified name. Synopsis:
9144 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9147 @cindex special files
9148 @cindex block special files
9149 @cindex character special files
9150 Unlike the phrase ``special file type'' above, the term @dfn{special
9151 file} has a technical meaning on Unix: something that can generate or
9152 receive data. Usually this corresponds to a physical piece of hardware,
9153 e.g., a printer or a disk. (These files are typically created at
9154 system-configuration time.) The @command{mknod} command is what creates
9155 files of this type. Such devices can be read either a character at a
9156 time or a ``block'' (many characters) at a time, hence we say there are
9157 @dfn{block special} files and @dfn{character special} files.
9159 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9160 @mayConflictWithShellBuiltIn{mknod}
9162 The arguments after @var{name} specify the type of file to make:
9167 @opindex p @r{for FIFO file}
9171 @opindex b @r{for block special file}
9172 for a block special file
9175 @c Don't document the `u' option -- it's just a synonym for `c'.
9176 @c Do *any* versions of mknod still use it?
9178 @opindex c @r{for character special file}
9179 @c @opindex u @r{for character special file}
9180 for a character special file
9184 When making a block or character special file, the major and minor
9185 device numbers must be given after the file type.
9186 If a major or minor device number begins with @samp{0x} or @samp{0X},
9187 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9188 as octal; otherwise, as decimal.
9190 The program accepts the following option. Also see @ref{Common options}.
9195 @itemx --mode=@var{mode}
9198 Set the mode of created files to @var{mode}, which is symbolic as in
9199 @command{chmod} and uses @samp{a=rw} as the point of departure.
9200 @var{mode} should specify only file permission bits.
9201 @xref{File permissions}.
9203 @item -Z @var{context}
9204 @itemx --context=@var{context}
9208 @cindex security context
9209 Set the default SELinux security context to be used for created files.
9216 @node readlink invocation
9217 @section @command{readlink}: Print value of a symlink or canonical file name
9220 @cindex displaying value of a symbolic link
9221 @cindex canonical file name
9222 @cindex canonicalize a file name
9226 @command{readlink} may work in one of two supported modes:
9232 @command{readlink} outputs the value of the given symbolic link.
9233 If @command{readlink} is invoked with an argument other than the name
9234 of a symbolic link, it produces no output and exits with a nonzero exit code.
9236 @item Canonicalize mode
9238 @command{readlink} outputs the absolute name of the given file which contains
9239 no @file{.}, @file{..} components nor any repeated separators
9240 (@file{/}) or symbolic links.
9245 readlink [@var{option}] @var{file}
9248 By default, @command{readlink} operates in readlink mode.
9250 The program accepts the following options. Also see @ref{Common options}.
9255 @itemx --canonicalize
9257 @opindex --canonicalize
9258 Activate canonicalize mode.
9259 If any component of the file name except the last one is missing or unavailable,
9260 @command{readlink} produces no output and exits with a nonzero exit
9261 code. A trailing slash is ignored.
9264 @itemx --canonicalize-existing
9266 @opindex --canonicalize-existing
9267 Activate canonicalize mode.
9268 If any component is missing or unavailable, @command{readlink} produces
9269 no output and exits with a nonzero exit code. A trailing slash
9270 requires that the name resolve to a directory.
9273 @itemx --canonicalize-missing
9275 @opindex --canonicalize-missing
9276 Activate canonicalize mode.
9277 If any component is missing or unavailable, @command{readlink} treats it
9283 @opindex --no-newline
9284 Do not output the trailing newline.
9294 Suppress most error messages.
9300 Report error messages.
9304 The @command{readlink} utility first appeared in OpenBSD 2.1.
9306 There is a @command{realpath} command on some systems
9307 which operates like @command{readlink} in canonicalize mode.
9312 @node rmdir invocation
9313 @section @command{rmdir}: Remove empty directories
9316 @cindex removing empty directories
9317 @cindex directories, removing empty
9319 @command{rmdir} removes empty directories. Synopsis:
9322 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9325 If any @var{directory} argument does not refer to an existing empty
9326 directory, it is an error.
9328 The program accepts the following options. Also see @ref{Common options}.
9332 @item --ignore-fail-on-non-empty
9333 @opindex --ignore-fail-on-non-empty
9334 @cindex directory deletion, ignoring failures
9335 Ignore each failure to remove a directory that is solely because
9336 the directory is non-empty.
9342 @cindex parent directories, removing
9343 Remove @var{directory}, then try to remove each component of @var{directory}.
9344 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9345 As such, it fails if any of those directories turns out not to be empty.
9346 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9347 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9348 exit unsuccessfully.
9354 @cindex directory deletion, reporting
9355 Give a diagnostic for each successful removal.
9356 @var{directory} is removed.
9360 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9365 @node unlink invocation
9366 @section @command{unlink}: Remove files via the unlink syscall
9369 @cindex removing files or directories (via the unlink syscall)
9371 @command{unlink} deletes a single specified file name.
9372 It is a minimalist interface to the system-provided
9373 @code{unlink} function. @xref{Deleting Files, , , libc,
9374 The GNU C Library Reference Manual}. Synopsis:
9375 It avoids the bells and whistles of the more commonly-used
9376 @command{rm} command (@pxref{rm invocation}).
9379 unlink @var{filename}
9382 On some systems @code{unlink} can be used to delete the name of a
9383 directory. On others, it can be used that way only by a privileged user.
9384 In the GNU system @code{unlink} can never delete the name of a directory.
9386 The @command{unlink} command honors the @option{--help} and
9387 @option{--version} options. To remove a file whose name begins with
9388 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9393 @node Changing file attributes
9394 @chapter Changing file attributes
9396 @cindex changing file attributes
9397 @cindex file attributes, changing
9398 @cindex attributes, file
9400 A file is not merely its contents, a name, and a file type
9401 (@pxref{Special file types}). A file also has an owner (a user ID), a
9402 group (a group ID), permissions (what the owner can do with the file,
9403 what people in the group can do, and what everyone else can do), various
9404 timestamps, and other information. Collectively, we call these a file's
9407 These commands change file attributes.
9410 * chgrp invocation:: Change file groups.
9411 * chmod invocation:: Change access permissions.
9412 * chown invocation:: Change file owners and groups.
9413 * touch invocation:: Change file timestamps.
9417 @node chown invocation
9418 @section @command{chown}: Change file owner and group
9421 @cindex file ownership, changing
9422 @cindex group ownership, changing
9423 @cindex changing file ownership
9424 @cindex changing group ownership
9426 @command{chown} changes the user and/or group ownership of each given @var{file}
9427 to @var{new-owner} or to the user and group of an existing reference file.
9431 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9434 If used, @var{new-owner} specifies the new owner and/or group as follows
9435 (with no embedded white space):
9438 [@var{owner}] [ : [@var{group}] ]
9445 If only an @var{owner} (a user name or numeric user ID) is given, that
9446 user is made the owner of each given file, and the files' group is not
9449 @item owner@samp{:}group
9450 If the @var{owner} is followed by a colon and a @var{group} (a
9451 group name or numeric group ID), with no spaces between them, the group
9452 ownership of the files is changed as well (to @var{group}).
9455 If a colon but no group name follows @var{owner}, that user is
9456 made the owner of the files and the group of the files is changed to
9457 @var{owner}'s login group.
9460 If the colon and following @var{group} are given, but the owner
9461 is omitted, only the group of the files is changed; in this case,
9462 @command{chown} performs the same function as @command{chgrp}.
9465 If only a colon is given, or if @var{new-owner} is empty, neither the
9466 owner nor the group is changed.
9470 If @var{owner} or @var{group} is intended to represent a numeric user
9471 or group ID, then you may specify it with a leading @samp{+}.
9472 @xref{Disambiguating names and IDs}.
9474 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9475 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9476 require support for that, but for backward compatibility @acronym{GNU}
9477 @command{chown} supports @samp{.} so long as no ambiguity results.
9478 New scripts should avoid the use of @samp{.} because it is not
9479 portable, and because it has undesirable results if the entire
9480 @var{owner@samp{.}group} happens to identify a user whose name
9483 The @command{chown} command sometimes clears the set-user-ID or
9484 set-group-ID permission bits. This behavior depends on the policy and
9485 functionality of the underlying @code{chown} system call, which may
9486 make system-dependent file mode modifications outside the control of
9487 the @command{chown} command. For example, the @command{chown} command
9488 might not affect those bits when invoked by a user with appropriate
9489 privileges, or when the
9490 bits signify some function other than executable permission (e.g.,
9492 When in doubt, check the underlying system behavior.
9494 The program accepts the following options. Also see @ref{Common options}.
9502 @cindex changed owners, verbosely describing
9503 Verbosely describe the action for each @var{file} whose ownership
9512 @cindex error messages, omitting
9513 Do not print error messages about files whose ownership cannot be
9516 @itemx @w{@kbd{--from}=@var{old-owner}}
9518 @cindex symbolic links, changing owner
9519 Change a @var{file}'s ownership only if it has current attributes specified
9520 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9522 This option is useful primarily from a security standpoint in that
9523 it narrows considerably the window of potential abuse.
9524 For example, to reflect a user ID numbering change for one user's files
9525 without an option like this, @code{root} might run
9528 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9531 But that is dangerous because the interval between when the @command{find}
9532 tests the existing file's owner and when the @command{chown} is actually run
9534 One way to narrow the gap would be to invoke chown for each file
9538 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9541 But that is very slow if there are many affected files.
9542 With this option, it is safer (the gap is narrower still)
9543 though still not perfect:
9546 chown -h -R --from=OLDUSER NEWUSER /
9550 @opindex --dereference
9551 @cindex symbolic links, changing owner
9553 Do not act on symbolic links themselves but rather on what they point to.
9554 This is the default.
9557 @itemx --no-dereference
9559 @opindex --no-dereference
9560 @cindex symbolic links, changing owner
9562 Act on symbolic links themselves instead of what they point to.
9563 This mode relies on the @code{lchown} system call.
9564 On systems that do not provide the @code{lchown} system call,
9565 @command{chown} fails when a file specified on the command line
9567 By default, no diagnostic is issued for symbolic links encountered
9568 during a recursive traversal, but see @option{--verbose}.
9570 @itemx --preserve-root
9571 @opindex --preserve-root
9572 @cindex root directory, disallow recursive modification
9573 Fail upon any attempt to recursively change the root directory, @file{/}.
9574 Without @option{--recursive}, this option has no effect.
9575 @xref{Treating / specially}.
9577 @itemx --no-preserve-root
9578 @opindex --no-preserve-root
9579 @cindex root directory, allow recursive modification
9580 Cancel the effect of any preceding @option{--preserve-root} option.
9581 @xref{Treating / specially}.
9583 @item --reference=@var{ref_file}
9584 @opindex --reference
9585 Change the user and group of each @var{file} to be the same as those of
9586 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9587 user and group of the symbolic link, but rather those of the file it
9594 Output a diagnostic for every file processed.
9595 If a symbolic link is encountered during a recursive traversal
9596 on a system without the @code{lchown} system call, and @option{--no-dereference}
9597 is in effect, then issue a diagnostic saying neither the symbolic link nor
9598 its referent is being changed.
9603 @opindex --recursive
9604 @cindex recursively changing file ownership
9605 Recursively change ownership of directories and their contents.
9608 @xref{Traversing symlinks}.
9611 @xref{Traversing symlinks}.
9614 @xref{Traversing symlinks}.
9623 # Change the owner of /u to "root".
9626 # Likewise, but also change its group to "staff".
9629 # Change the owner of /u and subfiles to "root".
9634 @node chgrp invocation
9635 @section @command{chgrp}: Change group ownership
9638 @cindex group ownership, changing
9639 @cindex changing group ownership
9641 @command{chgrp} changes the group ownership of each given @var{file}
9642 to @var{group} (which can be either a group name or a numeric group ID)
9643 or to the group of an existing reference file. Synopsis:
9646 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9649 If @var{group} is intended to represent a
9650 numeric group ID, then you may specify it with a leading @samp{+}.
9651 @xref{Disambiguating names and IDs}.
9653 The program accepts the following options. Also see @ref{Common options}.
9661 @cindex changed files, verbosely describing
9662 Verbosely describe the action for each @var{file} whose group actually
9671 @cindex error messages, omitting
9672 Do not print error messages about files whose group cannot be
9676 @opindex --dereference
9677 @cindex symbolic links, changing owner
9679 Do not act on symbolic links themselves but rather on what they point to.
9680 This is the default.
9683 @itemx --no-dereference
9685 @opindex --no-dereference
9686 @cindex symbolic links, changing group
9688 Act on symbolic links themselves instead of what they point to.
9689 This mode relies on the @code{lchown} system call.
9690 On systems that do not provide the @code{lchown} system call,
9691 @command{chgrp} fails when a file specified on the command line
9693 By default, no diagnostic is issued for symbolic links encountered
9694 during a recursive traversal, but see @option{--verbose}.
9696 @itemx --preserve-root
9697 @opindex --preserve-root
9698 @cindex root directory, disallow recursive modification
9699 Fail upon any attempt to recursively change the root directory, @file{/}.
9700 Without @option{--recursive}, this option has no effect.
9701 @xref{Treating / specially}.
9703 @itemx --no-preserve-root
9704 @opindex --no-preserve-root
9705 @cindex root directory, allow recursive modification
9706 Cancel the effect of any preceding @option{--preserve-root} option.
9707 @xref{Treating / specially}.
9709 @item --reference=@var{ref_file}
9710 @opindex --reference
9711 Change the group of each @var{file} to be the same as that of
9712 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9713 group of the symbolic link, but rather that of the file it refers to.
9719 Output a diagnostic for every file processed.
9720 If a symbolic link is encountered during a recursive traversal
9721 on a system without the @code{lchown} system call, and @option{--no-dereference}
9722 is in effect, then issue a diagnostic saying neither the symbolic link nor
9723 its referent is being changed.
9728 @opindex --recursive
9729 @cindex recursively changing group ownership
9730 Recursively change the group ownership of directories and their contents.
9733 @xref{Traversing symlinks}.
9736 @xref{Traversing symlinks}.
9739 @xref{Traversing symlinks}.
9748 # Change the group of /u to "staff".
9751 # Change the group of /u and subfiles to "staff".
9756 @node chmod invocation
9757 @section @command{chmod}: Change access permissions
9760 @cindex changing access permissions
9761 @cindex access permissions, changing
9762 @cindex permissions, changing access
9764 @command{chmod} changes the access permissions of the named files. Synopsis:
9767 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9770 @cindex symbolic links, permissions of
9771 @command{chmod} never changes the permissions of symbolic links, since
9772 the @command{chmod} system call cannot change their permissions.
9773 This is not a problem since the permissions of symbolic links are
9774 never used. However, for each symbolic link listed on the command
9775 line, @command{chmod} changes the permissions of the pointed-to file.
9776 In contrast, @command{chmod} ignores symbolic links encountered during
9777 recursive directory traversals.
9779 A successful use of @command{chmod} clears the set-group-ID bit of a
9780 regular file if the file's group ID does not match the user's
9781 effective group ID or one of the user's supplementary group IDs,
9782 unless the user has appropriate privileges. Additional restrictions
9783 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9784 @var{ref_file} to be ignored. This behavior depends on the policy and
9785 functionality of the underlying @code{chmod} system call. When in
9786 doubt, check the underlying system behavior.
9788 If used, @var{mode} specifies the new file mode bits.
9789 For details, see the section on @ref{File permissions}.
9790 If you really want @var{mode} to have a leading @samp{-}, you should
9791 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9792 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9793 file} (without the @option{--}) complains if it behaves differently
9794 from what @samp{chmod a-w file} would do.
9796 The program accepts the following options. Also see @ref{Common options}.
9804 Verbosely describe the action for each @var{file} whose permissions
9813 @cindex error messages, omitting
9814 Do not print error messages about files whose permissions cannot be
9817 @itemx --preserve-root
9818 @opindex --preserve-root
9819 @cindex root directory, disallow recursive modification
9820 Fail upon any attempt to recursively change the root directory, @file{/}.
9821 Without @option{--recursive}, this option has no effect.
9822 @xref{Treating / specially}.
9824 @itemx --no-preserve-root
9825 @opindex --no-preserve-root
9826 @cindex root directory, allow recursive modification
9827 Cancel the effect of any preceding @option{--preserve-root} option.
9828 @xref{Treating / specially}.
9834 Verbosely describe the action or non-action taken for every @var{file}.
9836 @item --reference=@var{ref_file}
9837 @opindex --reference
9838 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9839 @xref{File permissions}.
9840 If @var{ref_file} is a symbolic link, do not use the mode
9841 of the symbolic link, but rather that of the file it refers to.
9846 @opindex --recursive
9847 @cindex recursively changing access permissions
9848 Recursively change permissions of directories and their contents.
9855 @node touch invocation
9856 @section @command{touch}: Change file timestamps
9859 @cindex changing file timestamps
9860 @cindex file timestamps, changing
9861 @cindex timestamps, changing file
9863 @command{touch} changes the access and/or modification times of the
9864 specified files. Synopsis:
9867 touch [@var{option}]@dots{} @var{file}@dots{}
9870 @cindex empty files, creating
9871 Any @var{file} argument that does not exist is created empty, unless
9872 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9873 (@option{-h}) was in effect.
9875 A @var{file} argument string of @samp{-} is handled specially and
9876 causes @command{touch} to change the times of the file associated with
9879 @cindex permissions, for changing file timestamps
9880 If changing both the access and modification times to the current
9881 time, @command{touch} can change the timestamps for files that the user
9882 running it does not own but has write permission for. Otherwise, the
9883 user must own the files.
9885 Although @command{touch} provides options for changing two of the times---the
9886 times of last access and modification---of a file, there is actually
9887 a standard third one as well: the inode change time. This is often
9888 referred to as a file's @code{ctime}.
9889 The inode change time represents the time when the file's meta-information
9890 last changed. One common example of this is when the permissions of a
9891 file change. Changing the permissions doesn't access the file, so
9892 the atime doesn't change, nor does it modify the file, so the mtime
9893 doesn't change. Yet, something about the file itself has changed,
9894 and this must be noted somewhere. This is the job of the ctime field.
9895 This is necessary, so that, for example, a backup program can make a
9896 fresh copy of the file, including the new permissions value.
9897 Another operation that modifies a file's ctime without affecting
9898 the others is renaming. In any case, it is not possible, in normal
9899 operations, for a user to change the ctime field to a user-specified value.
9900 Some operating systems and file systems support a fourth time: the
9901 birth time, when the file was first created; by definition, this
9902 timestamp never changes.
9905 Time stamps assume the time zone rules specified by the @env{TZ}
9906 environment variable, or by the system default rules if @env{TZ} is
9907 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9908 libc, The GNU C Library Reference Manual}.
9909 You can avoid ambiguities during
9910 daylight saving transitions by using @sc{utc} time stamps.
9912 The program accepts the following options. Also see @ref{Common options}.
9918 @itemx --time=access
9922 @opindex atime@r{, changing}
9923 @opindex access @r{time, changing}
9924 @opindex use @r{time, changing}
9925 Change the access time only.
9930 @opindex --no-create
9931 Do not warn about or create files that do not exist.
9934 @itemx --date=@var{time}
9938 Use @var{time} instead of the current time. It can contain month names,
9939 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9940 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9941 specifies the instant of time that is 489,392,193 nanoseconds after
9942 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9943 minutes east of @acronym{UTC}. @xref{Date input formats}.
9944 File systems that do not support high-resolution time stamps
9945 silently ignore any excess precision here.
9949 @cindex BSD @command{touch} compatibility
9950 Ignored; for compatibility with BSD versions of @command{touch}.
9953 @itemx --no-dereference
9955 @opindex --no-dereference
9956 @cindex symbolic links, changing time
9958 Attempt to change the timestamps of a symbolic link, rather than what
9959 the link refers to. When using this option, empty files are not
9960 created, but option @option{-c} must also be used to avoid warning
9961 about files that do not exist. Not all systems support changing the
9962 timestamps of symlinks, since underlying system support for this
9963 action was not required until @acronym{POSIX} 2008. Also, on some
9964 systems, the mere act of examining a symbolic link changes the access
9965 time, such that only changes to the modification time will persist
9966 long enough to be observable. When coupled with option @option{-r}, a
9967 reference timestamp is taken from a symbolic link rather than the file
9972 @itemx --time=modify
9975 @opindex mtime@r{, changing}
9976 @opindex modify @r{time, changing}
9977 Change the modification time only.
9980 @itemx --reference=@var{file}
9982 @opindex --reference
9983 Use the times of the reference @var{file} instead of the current time.
9984 If this option is combined with the @option{--date=@var{time}}
9985 (@option{-d @var{time}}) option, the reference @var{file}'s time is
9986 the origin for any relative @var{time}s given, but is otherwise ignored.
9987 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
9988 equal to five seconds before the corresponding time stamp for @file{foo}.
9989 If @var{file} is a symbolic link, the reference timestamp is taken
9990 from the target of the symlink, unless @option{-h} was also in effect.
9992 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
9993 Use the argument (optional four-digit or two-digit years, months,
9994 days, hours, minutes, optional seconds) instead of the current time.
9995 If the year is specified with only two digits, then @var{cc}
9996 is 20 for years in the range 0 @dots{} 68, and 19 for years in
9997 69 @dots{} 99. If no digits of the year are specified,
9998 the argument is interpreted as a date in the current year.
9999 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10003 @vindex _POSIX2_VERSION
10004 On older systems, @command{touch} supports an obsolete syntax, as follows.
10005 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10006 @option{-t} options, and if there are two or more @var{file}s and the
10007 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10008 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10009 any, were moved to the front), and if the represented year
10010 is in the range 1969--1999, that argument is interpreted as the time
10011 for the other files instead of as a file name.
10012 This obsolete behavior can be enabled or disabled with the
10013 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10014 conformance}), but portable scripts should avoid commands whose
10015 behavior depends on this variable.
10016 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10017 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10023 @chapter Disk usage
10027 No disk can hold an infinite amount of data. These commands report
10028 how much disk storage is in use or available, report other file and
10029 file status information, and write buffers to disk.
10032 * df invocation:: Report file system disk space usage.
10033 * du invocation:: Estimate file space usage.
10034 * stat invocation:: Report file or file system status.
10035 * sync invocation:: Synchronize memory and disk.
10036 * truncate invocation:: Shrink or extend the size of a file.
10040 @node df invocation
10041 @section @command{df}: Report file system disk space usage
10044 @cindex file system disk usage
10045 @cindex disk usage by file system
10047 @command{df} reports the amount of disk space used and available on
10048 file systems. Synopsis:
10051 df [@var{option}]@dots{} [@var{file}]@dots{}
10054 With no arguments, @command{df} reports the space used and available on all
10055 currently mounted file systems (of all types). Otherwise, @command{df}
10056 reports on the file system containing each argument @var{file}.
10058 Normally the disk space is printed in units of
10059 1024 bytes, but this can be overridden (@pxref{Block size}).
10060 Non-integer quantities are rounded up to the next higher unit.
10062 @cindex disk device file
10063 @cindex device file, disk
10064 If an argument @var{file} is a disk device file containing a mounted
10065 file system, @command{df} shows the space available on that file system
10066 rather than on the file system containing the device node (i.e., the root
10067 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10068 on unmounted file systems, because on most kinds of systems doing so
10069 requires extremely nonportable intimate knowledge of file system
10072 The program accepts the following options. Also see @ref{Common options}.
10080 @cindex automounter file systems
10081 @cindex ignore file systems
10082 Include in the listing dummy file systems, which
10083 are omitted by default. Such file systems are typically special-purpose
10084 pseudo-file-systems, such as automounter entries.
10086 @item -B @var{size}
10087 @itemx --block-size=@var{size}
10089 @opindex --block-size
10090 @cindex file system sizes
10091 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10092 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10096 @cindex grand total of disk size, usage and available space
10097 Print a grand total of all arguments after all arguments have
10098 been processed. This can be used to find out the total disk size, usage
10099 and available space of all listed devices.
10105 Equivalent to @option{--si}.
10111 @cindex inode usage
10112 List inode usage information instead of block usage. An inode (short
10113 for index node) contains information about a file such as its owner,
10114 permissions, timestamps, and location on the disk.
10118 @cindex kibibytes for file system sizes
10119 Print sizes in 1024-byte blocks, overriding the default block size
10120 (@pxref{Block size}).
10121 This option is equivalent to @option{--block-size=1K}.
10127 @cindex file system types, limiting output to certain
10128 Limit the listing to local file systems. By default, remote file systems
10133 @cindex file system space, retrieving old data more quickly
10134 Do not invoke the @code{sync} system call before getting any usage data.
10135 This may make @command{df} run significantly faster on systems with many
10136 disks, but on some systems (notably SunOS) the results may be slightly
10137 out of date. This is the default.
10140 @itemx --portability
10142 @opindex --portability
10143 @cindex one-line output format
10144 @cindex @acronym{POSIX} output format
10145 @cindex portable output format
10146 @cindex output format, portable
10147 Use the @acronym{POSIX} output format. This is like the default format except
10152 The information about each file system is always printed on exactly
10153 one line; a mount device is never put on a line by itself. This means
10154 that if the mount device name is more than 20 characters long (e.g., for
10155 some network mounts), the columns are misaligned.
10158 The labels in the header output line are changed to conform to @acronym{POSIX}.
10161 The default block size and output format are unaffected by the
10162 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10163 variables. However, the default block size is still affected by
10164 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10165 otherwise. @xref{Block size}.
10172 @cindex file system space, retrieving current data more slowly
10173 Invoke the @code{sync} system call before getting any usage data. On
10174 some systems (notably SunOS), doing this yields more up to date results,
10175 but in general this option makes @command{df} much slower, especially when
10176 there are many or very busy file systems.
10178 @item -t @var{fstype}
10179 @itemx --type=@var{fstype}
10182 @cindex file system types, limiting output to certain
10183 Limit the listing to file systems of type @var{fstype}. Multiple
10184 file system types can be specified by giving multiple @option{-t} options.
10185 By default, nothing is omitted.
10188 @itemx --print-type
10190 @opindex --print-type
10191 @cindex file system types, printing
10192 Print each file system's type. The types printed here are the same ones
10193 you can include or exclude with @option{-t} and @option{-x}. The particular
10194 types printed are whatever is supported by the system. Here are some of
10195 the common names (this list is certainly not exhaustive):
10200 @cindex @acronym{NFS} file system type
10201 An @acronym{NFS} file system, i.e., one mounted over a network from another
10202 machine. This is the one type name which seems to be used uniformly by
10205 @item 4.2@r{, }ufs@r{, }efs@dots{}
10206 @cindex Linux file system types
10207 @cindex local file system types
10208 @opindex 4.2 @r{file system type}
10209 @opindex ufs @r{file system type}
10210 @opindex efs @r{file system type}
10211 A file system on a locally-mounted hard disk. (The system might even
10212 support more than one type here; Linux does.)
10214 @item hsfs@r{, }cdfs
10215 @cindex CD-ROM file system type
10216 @cindex High Sierra file system
10217 @opindex hsfs @r{file system type}
10218 @opindex cdfs @r{file system type}
10219 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10220 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10223 @cindex PC file system
10224 @cindex DOS file system
10225 @cindex MS-DOS file system
10226 @cindex diskette file system
10228 An MS-DOS file system, usually on a diskette.
10232 @item -x @var{fstype}
10233 @itemx --exclude-type=@var{fstype}
10235 @opindex --exclude-type
10236 Limit the listing to file systems not of type @var{fstype}.
10237 Multiple file system types can be eliminated by giving multiple
10238 @option{-x} options. By default, no file system types are omitted.
10241 Ignored; for compatibility with System V versions of @command{df}.
10246 Failure includes the case where no output is generated, so you can
10247 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10248 @var{dir}} to test whether @var{dir} is on a file system of type
10249 @samp{ext3} or @samp{reiserfs}.
10252 @node du invocation
10253 @section @command{du}: Estimate file space usage
10256 @cindex file space usage
10257 @cindex disk usage for files
10259 @command{du} reports the amount of disk space used by the specified files
10260 and for each subdirectory (of directory arguments). Synopsis:
10263 du [@var{option}]@dots{} [@var{file}]@dots{}
10266 With no arguments, @command{du} reports the disk space for the current
10267 directory. Normally the disk space is printed in units of
10268 1024 bytes, but this can be overridden (@pxref{Block size}).
10269 Non-integer quantities are rounded up to the next higher unit.
10271 If two or more hard links point to the same file, only one of the hard
10272 links is counted. The @var{file} argument order affects which links
10273 are counted, and changing the argument order may change the numbers
10274 that @command{du} outputs.
10276 The program accepts the following options. Also see @ref{Common options}.
10284 Show counts for all files, not just directories.
10286 @itemx --apparent-size
10287 @opindex --apparent-size
10288 Print apparent sizes, rather than disk usage. The apparent size of a
10289 file is the number of bytes reported by @code{wc -c} on regular files,
10290 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10291 For example, a file containing the word @samp{zoo} with no newline would,
10292 of course, have an apparent size of 3. Such a small file may require
10293 anywhere from 0 to 16 KiB or more of disk space, depending on
10294 the type and configuration of the file system on which the file resides.
10295 However, a sparse file created with this command:
10298 dd bs=1 seek=2GiB if=/dev/null of=big
10302 has an apparent size of 2 GiB, yet on most modern
10303 systems, it actually uses almost no disk space.
10309 Equivalent to @code{--apparent-size --block-size=1}.
10311 @item -B @var{size}
10312 @itemx --block-size=@var{size}
10314 @opindex --block-size
10316 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10317 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10323 @cindex grand total of disk space
10324 Print a grand total of all arguments after all arguments have
10325 been processed. This can be used to find out the total disk usage of
10326 a given set of files or directories.
10329 @itemx --dereference-args
10331 @opindex --dereference-args
10332 Dereference symbolic links that are command line arguments.
10333 Does not affect other symbolic links. This is helpful for finding
10334 out the disk usage of directories, such as @file{/usr/tmp}, which
10335 are often symbolic links.
10337 @c --files0-from=FILE
10338 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10344 Equivalent to @option{--dereference-args} (@option{-D}).
10348 @cindex kibibytes for file sizes
10349 Print sizes in 1024-byte blocks, overriding the default block size
10350 (@pxref{Block size}).
10351 This option is equivalent to @option{--block-size=1K}.
10354 @itemx --count-links
10356 @opindex --count-links
10357 @cindex hard links, counting in @command{du}
10358 Count the size of all files, even if they have appeared already (as a
10362 @itemx --dereference
10364 @opindex --dereference
10365 @cindex symbolic links, dereferencing in @command{du}
10366 Dereference symbolic links (show the disk space used by the file
10367 or directory that the link points to instead of the space used by
10372 @cindex mebibytes for file sizes
10373 Print sizes in 1,048,576-byte blocks, overriding the default block size
10374 (@pxref{Block size}).
10375 This option is equivalent to @option{--block-size=1M}.
10378 @itemx --no-dereference
10380 @opindex --no-dereference
10381 @cindex symbolic links, dereferencing in @command{du}
10382 For each symbolic links encountered by @command{du},
10383 consider the disk space used by the symbolic link.
10385 @item --max-depth=@var{depth}
10386 @opindex --max-depth=@var{depth}
10387 @cindex limiting output of @command{du}
10388 Show the total for each directory (and file if --all) that is at
10389 most MAX_DEPTH levels down from the root of the hierarchy. The root
10390 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10399 @opindex --summarize
10400 Display only a total for each argument.
10403 @itemx --separate-dirs
10405 @opindex --separate-dirs
10406 Normally, in the output of @command{du} (when not using @option{--summarize}),
10407 the size listed next to a directory name, @var{d}, represents the sum
10408 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10409 With @option{--separate-dirs}, the size reported for a directory name,
10410 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10415 @cindex last modified dates, displaying in @command{du}
10416 Show time of the most recent modification of any file in the directory,
10417 or any of its subdirectories.
10419 @itemx --time=ctime
10420 @itemx --time=status
10423 @opindex ctime@r{, show the most recent}
10424 @opindex status time@r{, show the most recent}
10425 @opindex use time@r{, show the most recent}
10426 Show the most recent status change time (the @samp{ctime} in the inode) of
10427 any file in the directory, instead of the modification time.
10429 @itemx --time=atime
10430 @itemx --time=access
10432 @opindex atime@r{, show the most recent}
10433 @opindex access time@r{, show the most recent}
10434 Show the most recent access time (the @samp{atime} in the inode) of
10435 any file in the directory, instead of the modification time.
10437 @item --time-style=@var{style}
10438 @opindex --time-style
10440 List timestamps in style @var{style}. This option has an effect only if
10441 the @option{--time} option is also specified. The @var{style} should
10442 be one of the following:
10445 @item +@var{format}
10447 List timestamps using @var{format}, where @var{format} is interpreted
10448 like the format argument of @command{date} (@pxref{date invocation}).
10449 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10450 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10451 with @command{date}, @var{format}'s interpretation is affected by the
10452 @env{LC_TIME} locale category.
10455 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10456 format with nanosecond precision, e.g., @samp{2002-03-30
10457 23:45:56.477817180 -0700}. This style is equivalent to
10458 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10461 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10462 @samp{2002-03-30 23:45}. These timestamps are shorter than
10463 @samp{full-iso} timestamps, and are usually good enough for everyday
10464 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10467 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10468 This style is equivalent to @samp{+%Y-%m-%d}.
10472 You can specify the default value of the @option{--time-style} option
10473 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10474 the default style is @samp{long-iso}. For compatibility with @command{ls},
10475 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10476 the newline and any later characters are ignored; if @env{TIME_STYLE}
10477 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10478 @env{TIME_STYLE} is @samp{locale} it is ignored.
10481 @itemx --one-file-system
10483 @opindex --one-file-system
10484 @cindex one file system, restricting @command{du} to
10485 Skip directories that are on different file systems from the one that
10486 the argument being processed is on.
10488 @item --exclude=@var{pattern}
10489 @opindex --exclude=@var{pattern}
10490 @cindex excluding files from @command{du}
10491 When recursing, skip subdirectories or files matching @var{pattern}.
10492 For example, @code{du --exclude='*.o'} excludes files whose names
10495 @item -X @var{file}
10496 @itemx --exclude-from=@var{file}
10497 @opindex -X @var{file}
10498 @opindex --exclude-from=@var{file}
10499 @cindex excluding files from @command{du}
10500 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10501 one per line. If @var{file} is @samp{-}, take the patterns from standard
10506 @cindex NFS mounts from BSD to HP-UX
10507 On BSD systems, @command{du} reports sizes that are half the correct
10508 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10509 systems, it reports sizes that are twice the correct values for
10510 files that are NFS-mounted from BSD systems. This is due to a flaw
10511 in HP-UX; it also affects the HP-UX @command{du} program.
10516 @node stat invocation
10517 @section @command{stat}: Report file or file system status
10520 @cindex file status
10521 @cindex file system status
10523 @command{stat} displays information about the specified file(s). Synopsis:
10526 stat [@var{option}]@dots{} [@var{file}]@dots{}
10529 With no option, @command{stat} reports all information about the given files.
10530 But it also can be used to report the information of the file systems the
10531 given files are located on. If the files are links, @command{stat} can
10532 also give information about the files the links point to.
10534 @mayConflictWithShellBuiltIn{stat}
10539 @itemx --dereference
10541 @opindex --dereference
10542 @cindex symbolic links, dereferencing in @command{stat}
10543 Change how @command{stat} treats symbolic links.
10544 With this option, @command{stat} acts on the file referenced
10545 by each symbolic link argument.
10546 Without it, @command{stat} acts on any symbolic link argument directly.
10549 @itemx --file-system
10551 @opindex --file-system
10552 @cindex file systems
10553 Report information about the file systems where the given files are located
10554 instead of information about the files themselves.
10557 @itemx --format=@var{format}
10559 @opindex --format=@var{format}
10560 @cindex output format
10561 Use @var{format} rather than the default format.
10562 @var{format} is automatically newline-terminated, so
10563 running a command like the following with two or more @var{file}
10564 operands produces a line of output for each operand:
10566 $ stat --format=%d:%i / /usr
10571 @itemx --printf=@var{format}
10572 @opindex --printf=@var{format}
10573 @cindex output format
10574 Use @var{format} rather than the default format.
10575 Like @option{--format}, but interpret backslash escapes,
10576 and do not output a mandatory trailing newline.
10577 If you want a newline, include @samp{\n} in the @var{format}.
10578 Here's how you would use @option{--printf} to print the device
10579 and inode numbers of @file{/} and @file{/usr}:
10581 $ stat --printf='%d:%i\n' / /usr
10590 @cindex terse output
10591 Print the information in terse form, suitable for parsing by other programs.
10595 The valid @var{format} directives for files with @option{--format} and
10596 @option{--printf} are:
10599 @item %a - Access rights in octal
10600 @item %A - Access rights in human readable form
10601 @item %b - Number of blocks allocated (see @samp{%B})
10602 @item %B - The size in bytes of each block reported by @samp{%b}
10603 @item %d - Device number in decimal
10604 @item %D - Device number in hex
10605 @item %f - Raw mode in hex
10606 @item %F - File type
10607 @item %g - Group ID of owner
10608 @item %G - Group name of owner
10609 @item %h - Number of hard links
10610 @item %i - Inode number
10611 @item %n - File name
10612 @item %N - Quoted file name with dereference if symbolic link
10613 @item %o - I/O block size
10614 @item %s - Total size, in bytes
10615 @item %t - Major device type in hex
10616 @item %T - Minor device type in hex
10617 @item %u - User ID of owner
10618 @item %U - User name of owner
10619 @item %x - Time of last access
10620 @item %X - Time of last access as seconds since Epoch
10621 @item %y - Time of last modification
10622 @item %Y - Time of last modification as seconds since Epoch
10623 @item %z - Time of last change
10624 @item %Z - Time of last change as seconds since Epoch
10627 When listing file system information (@option{--file-system} (@option{-f})),
10628 you must use a different set of @var{format} directives:
10631 @item %a - Free blocks available to non-super-user
10632 @item %b - Total data blocks in file system
10633 @item %c - Total file nodes in file system
10634 @item %d - Free file nodes in file system
10635 @item %f - Free blocks in file system
10636 @item %i - File System ID in hex
10637 @item %l - Maximum length of file names
10638 @item %n - File name
10639 @item %s - Block size (for faster transfers)
10640 @item %S - Fundamental block size (for block counts)
10641 @item %t - Type in hex
10642 @item %T - Type in human readable form
10646 Time stamps are listed according to the time zone rules specified by
10647 the @env{TZ} environment variable, or by the system default rules if
10648 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10649 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10654 @node sync invocation
10655 @section @command{sync}: Synchronize data on disk with memory
10658 @cindex synchronize disk and memory
10660 @cindex superblock, writing
10661 @cindex inodes, written buffered
10662 @command{sync} writes any data buffered in memory out to disk. This can
10663 include (but is not limited to) modified superblocks, modified inodes,
10664 and delayed reads and writes. This must be implemented by the kernel;
10665 The @command{sync} program does nothing but exercise the @code{sync} system
10668 @cindex crashes and corruption
10669 The kernel keeps data in memory to avoid doing (relatively slow) disk
10670 reads and writes. This improves performance, but if the computer
10671 crashes, data may be lost or the file system corrupted as a
10672 result. The @command{sync} command ensures everything in memory
10673 is written to disk.
10675 Any arguments are ignored, except for a lone @option{--help} or
10676 @option{--version} (@pxref{Common options}).
10681 @node truncate invocation
10682 @section @command{truncate}: Shrink or extend the size of a file
10685 @cindex truncating, file sizes
10687 @command{truncate} shrinks or extends the size of each @var{file} to the
10688 specified size. Synopsis:
10691 truncate @var{option}@dots{} @var{file}@dots{}
10694 @cindex files, creating
10695 Any @var{file} that does not exist is created.
10697 @cindex sparse files, creating
10698 @cindex holes, creating files with
10699 If a @var{file} is larger than the specified size, the extra data is lost.
10700 If a @var{file} is shorter, it is extended and the extended part (or hole)
10701 reads as zero bytes.
10703 The program accepts the following options. Also see @ref{Common options}.
10710 @opindex --no-create
10711 Do not create files that do not exist.
10716 @opindex --io-blocks
10717 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10719 @item -r @var{rfile}
10720 @itemx --reference=@var{rfile}
10722 @opindex --reference
10723 Set the size of each @var{file} to the same size as @var{rfile}.
10725 @item -s @var{size}
10726 @itemx --size=@var{size}
10729 Set the size of each @var{file} to this @var{size}.
10730 @multiplierSuffixesNoBlocks{size}
10732 @var{size} may also be prefixed by one of the following to adjust
10733 the size of each @var{file} based on their current size:
10735 @samp{+} => extend by
10736 @samp{-} => reduce by
10737 @samp{<} => at most
10738 @samp{>} => at least
10739 @samp{/} => round down to multiple of
10740 @samp{%} => round up to multiple of
10748 @node Printing text
10749 @chapter Printing text
10751 @cindex printing text, commands for
10752 @cindex commands for printing text
10754 This section describes commands that display text strings.
10757 * echo invocation:: Print a line of text.
10758 * printf invocation:: Format and print data.
10759 * yes invocation:: Print a string until interrupted.
10763 @node echo invocation
10764 @section @command{echo}: Print a line of text
10767 @cindex displaying text
10768 @cindex printing text
10769 @cindex text, displaying
10770 @cindex arbitrary text, displaying
10772 @command{echo} writes each given @var{string} to standard output, with a
10773 space between each and a newline after the last one. Synopsis:
10776 echo [@var{option}]@dots{} [@var{string}]@dots{}
10779 @mayConflictWithShellBuiltIn{echo}
10781 The program accepts the following options. Also see @ref{Common options}.
10782 Options must precede operands, and the normally-special argument
10783 @samp{--} has no special meaning and is treated like any other
10789 Do not output the trailing newline.
10793 @cindex backslash escapes
10794 Enable interpretation of the following backslash-escaped characters in
10803 produce no further output
10819 the eight-bit value that is the octal number @var{nnn}
10820 (zero to three octal digits)
10822 the eight-bit value that is the octal number @var{nnn}
10823 (one to three octal digits)
10825 the eight-bit value that is the hexadecimal number @var{hh}
10826 (one or two hexadecimal digits)
10831 @cindex backslash escapes
10832 Disable interpretation of backslash escapes in each @var{string}.
10833 This is the default. If @option{-e} and @option{-E} are both
10834 specified, the last one given takes effect.
10838 @vindex POSIXLY_CORRECT
10839 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10840 @command{echo}'s first argument is not @option{-n} it outputs
10841 option-like arguments instead of treating them as options. For
10842 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10843 plain @samp{hello}.
10845 @acronym{POSIX} does not require support for any options, and says
10846 that the behavior of @command{echo} is implementation-defined if any
10847 @var{string} contains a backslash or if the first argument is
10848 @option{-n}. Portable programs can use the @command{printf} command
10849 if they need to omit trailing newlines or output control characters or
10850 backslashes. @xref{printf invocation}.
10855 @node printf invocation
10856 @section @command{printf}: Format and print data
10859 @command{printf} does formatted printing of text. Synopsis:
10862 printf @var{format} [@var{argument}]@dots{}
10865 @command{printf} prints the @var{format} string, interpreting @samp{%}
10866 directives and @samp{\} escapes to format numeric and string arguments
10867 in a way that is mostly similar to the C @samp{printf} function.
10868 @xref{Output Conversion Syntax,, @command{printf} format directives,
10869 libc, The GNU C Library Reference Manual}, for details.
10870 The differences are listed below.
10872 @mayConflictWithShellBuiltIn{printf}
10877 The @var{format} argument is reused as necessary to convert all the
10878 given @var{argument}s. For example, the command @samp{printf %s a b}
10882 Missing @var{argument}s are treated as null strings or as zeros,
10883 depending on whether the context expects a string or a number. For
10884 example, the command @samp{printf %sx%d} prints @samp{x0}.
10888 An additional escape, @samp{\c}, causes @command{printf} to produce no
10889 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10890 E} prints @samp{ABC}.
10893 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10894 digits, as opposed to C where it can have an unlimited number of
10895 digits. For example, the command @samp{printf '\x07e'} prints two
10896 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10901 @command{printf} has an additional directive, @samp{%b}, which prints its
10902 argument string with @samp{\} escapes interpreted in the same way as in
10903 the @var{format} string, except that octal escapes are of the form
10904 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10905 If a precision is also given, it limits the number of bytes printed
10906 from the converted string.
10909 Numeric arguments must be single C constants, possibly with leading
10910 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10914 @vindex POSIXLY_CORRECT
10915 If the leading character of a numeric argument is @samp{"} or @samp{'}
10916 then its value is the numeric value of the immediately following
10917 character. Any remaining characters are silently ignored if the
10918 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10919 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10920 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10921 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10926 A floating-point argument must use a period before any fractional
10927 digits, but is printed according to the @env{LC_NUMERIC} category of the
10928 current locale. For example, in a locale whose radix character is a
10929 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10930 the command @samp{printf %g 3,14} is an error.
10934 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10935 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10936 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10937 digits) specifying a character to print.
10942 @cindex ISO/IEC 10646
10944 @command{printf} interprets two character syntaxes introduced in
10945 @acronym{ISO} C 99:
10946 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10947 characters, specified as
10948 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10949 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10950 @command{printf} outputs the Unicode characters
10951 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10952 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10953 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10955 The processing of @samp{\u} and @samp{\U} requires a full-featured
10956 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10957 or when @code{libiconv} is installed prior to this package. Otherwise
10958 @samp{\u} and @samp{\U} will print as-is.
10960 The only options are a lone @option{--help} or
10961 @option{--version}. @xref{Common options}.
10962 Options must precede operands.
10964 The Unicode character syntaxes are useful for writing strings in a locale
10965 independent way. For example, a string containing the Euro currency symbol
10968 $ env printf '\u20AC 14.95'
10972 will be output correctly in all locales supporting the Euro symbol
10973 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
10976 $ env printf '\u4e2d\u6587'
10980 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
10982 Note that in these examples, the @command{printf} command has been
10983 invoked via @command{env} to ensure that we run the program found via
10984 your shell's search path, and not a shell alias or a built-in function.
10986 For larger strings, you don't need to look up the hexadecimal code
10987 values of each character one by one. @acronym{ASCII} characters mixed with \u
10988 escape sequences is also known as the JAVA source file encoding. You can
10989 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
10990 is how to convert a piece of text into a shell script which will output
10991 this text in a locale-independent way:
10994 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
10995 '\u4e2d\u6587\n' > sample.txt
10996 $ recode BIG5..JAVA < sample.txt \
10997 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11004 @node yes invocation
11005 @section @command{yes}: Print a string until interrupted
11008 @cindex repeated output of a string
11010 @command{yes} prints the command line arguments, separated by spaces and
11011 followed by a newline, forever until it is killed. If no arguments are
11012 given, it prints @samp{y} followed by a newline forever until killed.
11014 Upon a write error, @command{yes} exits with status @samp{1}.
11016 The only options are a lone @option{--help} or @option{--version}.
11017 To output an argument that begins with
11018 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11019 @xref{Common options}.
11023 @chapter Conditions
11026 @cindex commands for exit status
11027 @cindex exit status commands
11029 This section describes commands that are primarily useful for their exit
11030 status, rather than their output. Thus, they are often used as the
11031 condition of shell @code{if} statements, or as the last command in a
11035 * false invocation:: Do nothing, unsuccessfully.
11036 * true invocation:: Do nothing, successfully.
11037 * test invocation:: Check file types and compare values.
11038 * expr invocation:: Evaluate expressions.
11042 @node false invocation
11043 @section @command{false}: Do nothing, unsuccessfully
11046 @cindex do nothing, unsuccessfully
11047 @cindex failure exit status
11048 @cindex exit status of @command{false}
11050 @command{false} does nothing except return an exit status of 1, meaning
11051 @dfn{failure}. It can be used as a place holder in shell scripts
11052 where an unsuccessful command is needed.
11053 In most modern shells, @command{false} is a built-in command, so when
11054 you use @samp{false} in a script, you're probably using the built-in
11055 command, not the one documented here.
11057 @command{false} honors the @option{--help} and @option{--version} options.
11059 This version of @command{false} is implemented as a C program, and is thus
11060 more secure and faster than a shell script implementation, and may safely
11061 be used as a dummy shell for the purpose of disabling accounts.
11063 Note that @command{false} (unlike all other programs documented herein)
11064 exits unsuccessfully, even when invoked with
11065 @option{--help} or @option{--version}.
11067 Portable programs should not assume that the exit status of
11068 @command{false} is 1, as it is greater than 1 on some
11069 non-@acronym{GNU} hosts.
11072 @node true invocation
11073 @section @command{true}: Do nothing, successfully
11076 @cindex do nothing, successfully
11078 @cindex successful exit
11079 @cindex exit status of @command{true}
11081 @command{true} does nothing except return an exit status of 0, meaning
11082 @dfn{success}. It can be used as a place holder in shell scripts
11083 where a successful command is needed, although the shell built-in
11084 command @code{:} (colon) may do the same thing faster.
11085 In most modern shells, @command{true} is a built-in command, so when
11086 you use @samp{true} in a script, you're probably using the built-in
11087 command, not the one documented here.
11089 @command{true} honors the @option{--help} and @option{--version} options.
11091 Note, however, that it is possible to cause @command{true}
11092 to exit with nonzero status: with the @option{--help} or @option{--version}
11093 option, and with standard
11094 output already closed or redirected to a file that evokes an I/O error.
11095 For example, using a Bourne-compatible shell:
11098 $ ./true --version >&-
11099 ./true: write error: Bad file number
11100 $ ./true --version > /dev/full
11101 ./true: write error: No space left on device
11104 This version of @command{true} is implemented as a C program, and is thus
11105 more secure and faster than a shell script implementation, and may safely
11106 be used as a dummy shell for the purpose of disabling accounts.
11108 @node test invocation
11109 @section @command{test}: Check file types and compare values
11112 @cindex check file types
11113 @cindex compare values
11114 @cindex expression evaluation
11116 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11117 evaluation of the conditional expression @var{expr}. Each part of the
11118 expression must be a separate argument.
11120 @command{test} has file status checks, string operators, and numeric
11121 comparison operators.
11123 @command{test} has an alternate form that uses opening and closing
11124 square brackets instead a leading @samp{test}. For example, instead
11125 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11126 brackets must be separate arguments; for example, @samp{[-d /]} does
11127 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11128 @var{expr} ]} have the same meaning, only the former form is discussed
11134 test @var{expression}
11136 [ @var{expression} ]
11141 @mayConflictWithShellBuiltIn{test}
11143 If @var{expression} is omitted, @command{test} returns false.
11144 If @var{expression} is a single argument,
11145 @command{test} returns false if the argument is null and true otherwise. The argument
11146 can be any string, including strings like @samp{-d}, @samp{-1},
11147 @samp{--}, @samp{--help}, and @samp{--version} that most other
11148 programs would treat as options. To get help and version information,
11149 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11150 the usual closing brackets. @xref{Common options}.
11152 @cindex exit status of @command{test}
11156 0 if the expression is true,
11157 1 if the expression is false,
11158 2 if an error occurred.
11162 * File type tests:: -[bcdfhLpSt]
11163 * Access permission tests:: -[gkruwxOG]
11164 * File characteristic tests:: -e -s -nt -ot -ef
11165 * String tests:: -z -n = !=
11166 * Numeric tests:: -eq -ne -lt -le -gt -ge
11167 * Connectives for test:: ! -a -o
11171 @node File type tests
11172 @subsection File type tests
11174 @cindex file type tests
11176 These options test for particular types of files. (Everything's a file,
11177 but not all files are the same!)
11181 @item -b @var{file}
11183 @cindex block special check
11184 True if @var{file} exists and is a block special device.
11186 @item -c @var{file}
11188 @cindex character special check
11189 True if @var{file} exists and is a character special device.
11191 @item -d @var{file}
11193 @cindex directory check
11194 True if @var{file} exists and is a directory.
11196 @item -f @var{file}
11198 @cindex regular file check
11199 True if @var{file} exists and is a regular file.
11201 @item -h @var{file}
11202 @itemx -L @var{file}
11205 @cindex symbolic link check
11206 True if @var{file} exists and is a symbolic link.
11207 Unlike all other file-related tests, this test does not dereference
11208 @var{file} if it is a symbolic link.
11210 @item -p @var{file}
11212 @cindex named pipe check
11213 True if @var{file} exists and is a named pipe.
11215 @item -S @var{file}
11217 @cindex socket check
11218 True if @var{file} exists and is a socket.
11222 @cindex terminal check
11223 True if @var{fd} is a file descriptor that is associated with a
11229 @node Access permission tests
11230 @subsection Access permission tests
11232 @cindex access permission tests
11233 @cindex permission tests
11235 These options test for particular access permissions.
11239 @item -g @var{file}
11241 @cindex set-group-ID check
11242 True if @var{file} exists and has its set-group-ID bit set.
11244 @item -k @var{file}
11246 @cindex sticky bit check
11247 True if @var{file} exists and has its @dfn{sticky} bit set.
11249 @item -r @var{file}
11251 @cindex readable file check
11252 True if @var{file} exists and read permission is granted.
11254 @item -u @var{file}
11256 @cindex set-user-ID check
11257 True if @var{file} exists and has its set-user-ID bit set.
11259 @item -w @var{file}
11261 @cindex writable file check
11262 True if @var{file} exists and write permission is granted.
11264 @item -x @var{file}
11266 @cindex executable file check
11267 True if @var{file} exists and execute permission is granted
11268 (or search permission, if it is a directory).
11270 @item -O @var{file}
11272 @cindex owned by effective user ID check
11273 True if @var{file} exists and is owned by the current effective user ID.
11275 @item -G @var{file}
11277 @cindex owned by effective group ID check
11278 True if @var{file} exists and is owned by the current effective group ID.
11282 @node File characteristic tests
11283 @subsection File characteristic tests
11285 @cindex file characteristic tests
11287 These options test other file characteristics.
11291 @item -e @var{file}
11293 @cindex existence-of-file check
11294 True if @var{file} exists.
11296 @item -s @var{file}
11298 @cindex nonempty file check
11299 True if @var{file} exists and has a size greater than zero.
11301 @item @var{file1} -nt @var{file2}
11303 @cindex newer-than file check
11304 True if @var{file1} is newer (according to modification date) than
11305 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11307 @item @var{file1} -ot @var{file2}
11309 @cindex older-than file check
11310 True if @var{file1} is older (according to modification date) than
11311 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11313 @item @var{file1} -ef @var{file2}
11315 @cindex same file check
11316 @cindex hard link check
11317 True if @var{file1} and @var{file2} have the same device and inode
11318 numbers, i.e., if they are hard links to each other.
11324 @subsection String tests
11326 @cindex string tests
11328 These options test string characteristics. You may need to quote
11329 @var{string} arguments for the shell. For example:
11335 The quotes here prevent the wrong arguments from being passed to
11336 @command{test} if @samp{$V} is empty or contains special characters.
11340 @item -z @var{string}
11342 @cindex zero-length string check
11343 True if the length of @var{string} is zero.
11345 @item -n @var{string}
11346 @itemx @var{string}
11348 @cindex nonzero-length string check
11349 True if the length of @var{string} is nonzero.
11351 @item @var{string1} = @var{string2}
11353 @cindex equal string check
11354 True if the strings are equal.
11356 @item @var{string1} != @var{string2}
11358 @cindex not-equal string check
11359 True if the strings are not equal.
11364 @node Numeric tests
11365 @subsection Numeric tests
11367 @cindex numeric tests
11368 @cindex arithmetic tests
11370 Numeric relational operators. The arguments must be entirely numeric
11371 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11372 which evaluates to the length of @var{string}.
11376 @item @var{arg1} -eq @var{arg2}
11377 @itemx @var{arg1} -ne @var{arg2}
11378 @itemx @var{arg1} -lt @var{arg2}
11379 @itemx @var{arg1} -le @var{arg2}
11380 @itemx @var{arg1} -gt @var{arg2}
11381 @itemx @var{arg1} -ge @var{arg2}
11388 These arithmetic binary operators return true if @var{arg1} is equal,
11389 not-equal, less-than, less-than-or-equal, greater-than, or
11390 greater-than-or-equal than @var{arg2}, respectively.
11397 test -1 -gt -2 && echo yes
11399 test -l abc -gt 1 && echo yes
11402 @error{} test: integer expression expected before -eq
11406 @node Connectives for test
11407 @subsection Connectives for @command{test}
11409 @cindex logical connectives
11410 @cindex connectives, logical
11412 The usual logical connectives.
11418 True if @var{expr} is false.
11420 @item @var{expr1} -a @var{expr2}
11422 @cindex logical and operator
11423 @cindex and operator
11424 True if both @var{expr1} and @var{expr2} are true.
11426 @item @var{expr1} -o @var{expr2}
11428 @cindex logical or operator
11429 @cindex or operator
11430 True if either @var{expr1} or @var{expr2} is true.
11435 @node expr invocation
11436 @section @command{expr}: Evaluate expressions
11439 @cindex expression evaluation
11440 @cindex evaluation of expressions
11442 @command{expr} evaluates an expression and writes the result on standard
11443 output. Each token of the expression must be a separate argument.
11445 Operands are either integers or strings. Integers consist of one or
11446 more decimal digits, with an optional leading @samp{-}.
11447 @command{expr} converts
11448 anything appearing in an operand position to an integer or a string
11449 depending on the operation being applied to it.
11451 Strings are not quoted for @command{expr} itself, though you may need to
11452 quote them to protect characters with special meaning to the shell,
11453 e.g., spaces. However, regardless of whether it is quoted, a string
11454 operand should not be a parenthesis or any of @command{expr}'s
11455 operators like @code{+}, so you cannot safely pass an arbitrary string
11456 @code{$str} to expr merely by quoting it to the shell. One way to
11457 work around this is to use the @sc{gnu} extension @code{+},
11458 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11459 @code{@w{" $str"}} and to adjust the rest of the expression to take
11460 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11462 You should not pass a negative integer or a string with leading
11463 @samp{-} as @command{expr}'s first argument, as it might be
11464 misinterpreted as an option; this can be avoided by parenthesization.
11465 Also, portable scripts should not use a string operand that happens to
11466 take the form of an integer; this can be worked around by inserting
11467 leading spaces as mentioned above.
11469 @cindex parentheses for grouping
11470 Operators may be given as infix symbols or prefix keywords. Parentheses
11471 may be used for grouping in the usual manner. You must quote
11472 parentheses and many operators to avoid the shell evaluating them,
11475 When built with support for the GNU MP library, @command{expr} uses
11476 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11477 types and may fail due to arithmetic overflow.
11479 The only options are @option{--help} and @option{--version}. @xref{Common
11480 options}. Options must precede operands.
11482 @cindex exit status of @command{expr}
11486 0 if the expression is neither null nor 0,
11487 1 if the expression is null or 0,
11488 2 if the expression is invalid,
11489 3 if an internal error occurred (e.g., arithmetic overflow).
11493 * String expressions:: + : match substr index length
11494 * Numeric expressions:: + - * / %
11495 * Relations for expr:: | & < <= = == != >= >
11496 * Examples of expr:: Examples.
11500 @node String expressions
11501 @subsection String expressions
11503 @cindex string expressions
11504 @cindex expressions, string
11506 @command{expr} supports pattern matching and other string operators. These
11507 have higher precedence than both the numeric and relational operators (in
11508 the next sections).
11512 @item @var{string} : @var{regex}
11513 @cindex pattern matching
11514 @cindex regular expression matching
11515 @cindex matching patterns
11516 Perform pattern matching. The arguments are converted to strings and the
11517 second is considered to be a (basic, a la GNU @code{grep}) regular
11518 expression, with a @code{^} implicitly prepended. The first argument is
11519 then matched against this regular expression.
11521 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11522 @code{:} expression returns the part of @var{string} that matched the
11523 subexpression; otherwise, it returns the number of characters matched.
11525 If the match fails, the @code{:} operator returns the null string if
11526 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11528 @kindex \( @r{regexp operator}
11529 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11530 value; additional pairs are meaningful only for grouping the regular
11531 expression operators.
11533 @kindex \+ @r{regexp operator}
11534 @kindex \? @r{regexp operator}
11535 @kindex \| @r{regexp operator}
11536 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11537 operators which respectively match one or more, zero or one, or separate
11538 alternatives. SunOS and other @command{expr}'s treat these as regular
11539 characters. (@acronym{POSIX} allows either behavior.)
11540 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11541 regular expression syntax. Some examples are in @ref{Examples of expr}.
11543 @item match @var{string} @var{regex}
11545 An alternative way to do pattern matching. This is the same as
11546 @w{@samp{@var{string} : @var{regex}}}.
11548 @item substr @var{string} @var{position} @var{length}
11550 Returns the substring of @var{string} beginning at @var{position}
11551 with length at most @var{length}. If either @var{position} or
11552 @var{length} is negative, zero, or non-numeric, returns the null string.
11554 @item index @var{string} @var{charset}
11556 Returns the first position in @var{string} where the first character in
11557 @var{charset} was found. If no character in @var{charset} is found in
11558 @var{string}, return 0.
11560 @item length @var{string}
11562 Returns the length of @var{string}.
11564 @item + @var{token}
11566 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11567 or an operator like @code{/}.
11568 This makes it possible to test @code{expr length + "$x"} or
11569 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11570 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11571 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11572 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11576 To make @command{expr} interpret keywords as strings, you must use the
11577 @code{quote} operator.
11580 @node Numeric expressions
11581 @subsection Numeric expressions
11583 @cindex numeric expressions
11584 @cindex expressions, numeric
11586 @command{expr} supports the usual numeric operators, in order of increasing
11587 precedence. These numeric operators have lower precedence than the
11588 string operators described in the previous section, and higher precedence
11589 than the connectives (next section).
11597 @cindex subtraction
11598 Addition and subtraction. Both arguments are converted to integers;
11599 an error occurs if this cannot be done.
11605 @cindex multiplication
11608 Multiplication, division, remainder. Both arguments are converted to
11609 integers; an error occurs if this cannot be done.
11614 @node Relations for expr
11615 @subsection Relations for @command{expr}
11617 @cindex connectives, logical
11618 @cindex logical connectives
11619 @cindex relations, numeric or string
11621 @command{expr} supports the usual logical connectives and relations. These
11622 have lower precedence than the string and numeric operators
11623 (previous sections). Here is the list, lowest-precedence operator first.
11629 @cindex logical or operator
11630 @cindex or operator
11631 Returns its first argument if that is neither null nor zero, otherwise
11632 its second argument if it is neither null nor zero, otherwise 0. It
11633 does not evaluate its second argument if its first argument is neither
11638 @cindex logical and operator
11639 @cindex and operator
11640 Return its first argument if neither argument is null or zero, otherwise
11641 0. It does not evaluate its second argument if its first argument is
11644 @item < <= = == != >= >
11651 @cindex comparison operators
11653 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11654 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11655 both arguments to integers and do a numeric comparison; if either
11656 conversion fails, it does a lexicographic comparison using the character
11657 collating sequence specified by the @env{LC_COLLATE} locale.
11662 @node Examples of expr
11663 @subsection Examples of using @command{expr}
11665 @cindex examples of @command{expr}
11666 Here are a few examples, including quoting for shell metacharacters.
11668 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11671 foo=`expr $foo + 1`
11674 To print the non-directory part of the file name stored in
11675 @code{$fname}, which need not contain a @code{/}:
11678 expr $fname : '.*/\(.*\)' '|' $fname
11681 An example showing that @code{\+} is an operator:
11689 expr abc : 'a\(.\)c'
11691 expr index abcdef cz
11694 @error{} expr: syntax error
11695 expr index + index a
11701 @chapter Redirection
11703 @cindex redirection
11704 @cindex commands for redirection
11706 Unix shells commonly provide several forms of @dfn{redirection}---ways
11707 to change the input source or output destination of a command. But one
11708 useful redirection is performed by a separate command, not by the shell;
11709 it's described here.
11712 * tee invocation:: Redirect output to multiple files or processes.
11716 @node tee invocation
11717 @section @command{tee}: Redirect output to multiple files or processes
11720 @cindex pipe fitting
11721 @cindex destinations, multiple output
11722 @cindex read from stdin and write to stdout and files
11724 The @command{tee} command copies standard input to standard output and also
11725 to any files given as arguments. This is useful when you want not only
11726 to send some data down a pipe, but also to save a copy. Synopsis:
11729 tee [@var{option}]@dots{} [@var{file}]@dots{}
11732 If a file being written to does not already exist, it is created. If a
11733 file being written to already exists, the data it previously contained
11734 is overwritten unless the @option{-a} option is used.
11736 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11737 input to standard output, but this is typically not that useful as the
11738 copies are interleaved.
11740 The program accepts the following options. Also see @ref{Common options}.
11747 Append standard input to the given files rather than overwriting
11751 @itemx --ignore-interrupts
11753 @opindex --ignore-interrupts
11754 Ignore interrupt signals.
11758 The @command{tee} command is useful when you happen to be transferring a large
11759 amount of data and also want to summarize that data without reading
11760 it a second time. For example, when you are downloading a DVD image,
11761 you often want to verify its signature or checksum right away.
11762 The inefficient way to do it is simply:
11765 wget http://example.com/some.iso && sha1sum some.iso
11768 One problem with the above is that it makes you wait for the
11769 download to complete before starting the time-consuming SHA1 computation.
11770 Perhaps even more importantly, the above requires reading
11771 the DVD image a second time (the first was from the network).
11773 The efficient way to do it is to interleave the download
11774 and SHA1 computation. Then, you'll get the checksum for
11775 free, because the entire process parallelizes so well:
11778 # slightly contrived, to demonstrate process substitution
11779 wget -O - http://example.com/dvd.iso \
11780 | tee >(sha1sum > dvd.sha1) > dvd.iso
11783 That makes @command{tee} write not just to the expected output file,
11784 but also to a pipe running @command{sha1sum} and saving the final
11785 checksum in a file named @file{dvd.sha1}.
11787 Note, however, that this example relies on a feature of modern shells
11788 called @dfn{process substitution}
11789 (the @samp{>(command)} syntax, above;
11790 @xref{Process Substitution,,Process Substitution, bashref,
11791 The Bash Reference Manual}.),
11792 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11793 but not with @command{/bin/sh}. So if you write code like this
11794 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11796 Since the above example writes to one file and one process,
11797 a more conventional and portable use of @command{tee} is even better:
11800 wget -O - http://example.com/dvd.iso \
11801 | tee dvd.iso | sha1sum > dvd.sha1
11804 You can extend this example to make @command{tee} write to two processes,
11805 computing MD5 and SHA1 checksums in parallel. In this case,
11806 process substitution is required:
11809 wget -O - http://example.com/dvd.iso \
11810 | tee >(sha1sum > dvd.sha1) \
11811 >(md5sum > dvd.md5) \
11815 This technique is also useful when you want to make a @emph{compressed}
11816 copy of the contents of a pipe.
11817 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11818 For a large hierarchy, @samp{du -ak} can run for a long time,
11819 and can easily produce terabytes of data, so you won't want to
11820 rerun the command unnecessarily. Nor will you want to save
11821 the uncompressed output.
11823 Doing it the inefficient way, you can't even start the GUI
11824 until after you've compressed all of the @command{du} output:
11827 du -ak | gzip -9 > /tmp/du.gz
11828 gzip -d /tmp/du.gz | xdiskusage -a
11831 With @command{tee} and process substitution, you start the GUI
11832 right away and eliminate the decompression completely:
11835 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11838 Finally, if you regularly create more than one type of
11839 compressed tarball at once, for example when @code{make dist} creates
11840 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11841 there may be a better way.
11842 Typical @command{automake}-generated @file{Makefile} rules create
11843 the two compressed tar archives with commands in sequence, like this
11844 (slightly simplified):
11847 tardir=your-pkg-M.N
11848 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11849 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11852 However, if the hierarchy you are archiving and compressing is larger
11853 than a couple megabytes, and especially if you are using a multi-processor
11854 system with plenty of memory, then you can do much better by reading the
11855 directory contents only once and running the compression programs in parallel:
11858 tardir=your-pkg-M.N
11859 tar chof - "$tardir" \
11860 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11861 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11867 @node File name manipulation
11868 @chapter File name manipulation
11870 @cindex file name manipulation
11871 @cindex manipulation of file names
11872 @cindex commands for file name manipulation
11874 This section describes commands that manipulate file names.
11877 * basename invocation:: Strip directory and suffix from a file name.
11878 * dirname invocation:: Strip non-directory suffix from a file name.
11879 * pathchk invocation:: Check file name validity and portability.
11880 * mktemp invocation:: Create temporary file or directory.
11884 @node basename invocation
11885 @section @command{basename}: Strip directory and suffix from a file name
11888 @cindex strip directory and suffix from file names
11889 @cindex directory, stripping from file names
11890 @cindex suffix, stripping from file names
11891 @cindex file names, stripping directory and suffix
11892 @cindex leading directory components, stripping
11894 @command{basename} removes any leading directory components from
11895 @var{name}. Synopsis:
11898 basename @var{name} [@var{suffix}]
11901 If @var{suffix} is specified and is identical to the end of @var{name},
11902 it is removed from @var{name} as well. Note that since trailing slashes
11903 are removed prior to suffix matching, @var{suffix} will do nothing if it
11904 contains slashes. @command{basename} prints the result on standard
11907 @c This test is used both here and in the section on dirname.
11908 @macro basenameAndDirname
11909 Together, @command{basename} and @command{dirname} are designed such
11910 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11911 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11912 for everything except file names containing a trailing newline.
11914 @basenameAndDirname
11916 @acronym{POSIX} allows the implementation to define the results if
11917 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11918 @command{basename} returns the empty string. In the latter case, the
11919 result is @samp{//} on platforms where @var{//} is distinct from
11920 @var{/}, and @samp{/} on platforms where there is no difference.
11922 The only options are @option{--help} and @option{--version}. @xref{Common
11923 options}. Options must precede operands.
11931 basename /usr/bin/sort
11934 basename include/stdio.h .h
11938 @node dirname invocation
11939 @section @command{dirname}: Strip non-directory suffix from a file name
11942 @cindex directory components, printing
11943 @cindex stripping non-directory suffix
11944 @cindex non-directory suffix, stripping
11946 @command{dirname} prints all but the final slash-delimited component of
11947 a string (presumably a file name). Synopsis:
11953 If @var{name} is a single component, @command{dirname} prints @samp{.}
11954 (meaning the current directory).
11956 @basenameAndDirname
11958 @acronym{POSIX} allows the implementation to define the results if
11959 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11960 result is @samp{//} on platforms where @var{//} is distinct from
11961 @var{/}, and @samp{/} on platforms where there is no difference.
11963 The only options are @option{--help} and @option{--version}. @xref{Common
11971 # Output "/usr/bin".
11972 dirname /usr/bin/sort
11979 @node pathchk invocation
11980 @section @command{pathchk}: Check file name validity and portability
11983 @cindex file names, checking validity and portability
11984 @cindex valid file names, checking for
11985 @cindex portable file names, checking for
11987 @command{pathchk} checks validity and portability of file names. Synopsis:
11990 pathchk [@var{option}]@dots{} @var{name}@dots{}
11993 For each @var{name}, @command{pathchk} prints an error message if any of
11994 these conditions is true:
11998 One of the existing directories in @var{name} does not have search
11999 (execute) permission,
12001 The length of @var{name} is larger than the maximum supported by the
12004 The length of one component of @var{name} is longer than
12005 its file system's maximum.
12008 A nonexistent @var{name} is not an error, so long a file with that
12009 name could be created under the above conditions.
12011 The program accepts the following options. Also see @ref{Common options}.
12012 Options must precede operands.
12018 Instead of performing checks based on the underlying file system,
12019 print an error message if any of these conditions is true:
12023 A file name is empty.
12026 A file name contains a character outside the @acronym{POSIX} portable file
12027 name character set, namely, the ASCII letters and digits, @samp{.},
12028 @samp{_}, @samp{-}, and @samp{/}.
12031 The length of a file name or one of its components exceeds the
12032 @acronym{POSIX} minimum limits for portability.
12037 Print an error message if a file name is empty, or if it contains a component
12038 that begins with @samp{-}.
12040 @item --portability
12041 @opindex --portability
12042 Print an error message if a file name is not portable to all @acronym{POSIX}
12043 hosts. This option is equivalent to @samp{-p -P}.
12047 @cindex exit status of @command{pathchk}
12051 0 if all specified file names passed all checks,
12055 @node mktemp invocation
12056 @section @command{mktemp}: Create temporary file or directory
12059 @cindex file names, creating temporary
12060 @cindex directory, creating temporary
12061 @cindex temporary files and directories
12063 @command{mktemp} manages the creation of temporary files and
12064 directories. Synopsis:
12067 mktemp [@var{option}]@dots{} [@var{template}]
12070 Safely create a temporary file or directory based on @var{template},
12071 and print its name. If given, @var{template} must end in at least
12072 three consecutive @samp{X}s. If omitted, the template
12073 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12074 implied. The trailing @samp{X}s in the @var{template} will be replaced
12075 by alpha-numeric characters; thus, on a case-sensitive file system,
12076 and with a @var{template} ending in @var{n} instances of @samp{X},
12077 there are @samp{62**@var{n}} potential file names.
12079 Older scripts used to create temporary files by simply joining the
12080 name of the program with the process id (@samp{$$}) as a suffix.
12081 However, that naming scheme is easily predictable, and suffers from a
12082 race condition where the attacker can create an appropriately named
12083 symbolic link, such that when the script then opens a handle to what
12084 it thought was an unused file, it is instead modifying an existing
12085 file. Using the same scheme to create a directory is slightly safer,
12086 since the @command{mkdir} will fail if the target already exists, but
12087 it is still inferior because it allows for denial of service attacks.
12088 Therefore, modern scripts should use the @command{mktemp} command to
12089 guarantee that the generated name will be unpredictable, and that
12090 knowledge of the temporary file name implies that the file was created
12091 by the current script and cannot be modified by other users.
12093 When creating a file, the resulting file has read and write
12094 permissions for the current user, but no permissions for the group or
12095 others; these permissions are reduced if the current umask is more
12098 Here are some examples (although note that if you repeat them, you
12099 will most likely get different file names):
12104 Create a temporary file in the current directory.
12111 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12112 but falling back to the current directory rather than @file{/tmp}.
12113 Note that @command{mktemp} does not create fifos, but can create a
12114 secure directory in which the fifo can live. Exit the shell if the
12115 directory or fifo could not be created.
12117 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12119 $ mkfifo "$fifo" || @{ rmdir $dir; exit 1; @}
12123 Create and use a temporary file if possible, but ignore failure. The
12124 file will reside in the directory named by @env{TMPDIR}, if specified,
12125 or else in @file{/tmp}.
12127 $ file=$(mktemp -q) && @{
12128 > # Safe to use $file only within this block
12135 Act as a semi-random character generator (it is not fully random,
12136 since it is impacted by the contents of the current directory). To
12137 avoid security holes, do not use the resulting names to create a file.
12147 The program accepts the following options. Also see @ref{Common options}.
12154 @opindex --directory
12155 Create a directory rather than a file. The directory will have read,
12156 write, and search permissions for the current user, but no permissions
12157 for the group or others; these permissions are reduced if the current
12158 umask is more restrictive.
12164 Suppress diagnostics about failure to create a file or directory. The
12165 exit status will still reflect whether a file was created.
12171 Generate a temporary name that does not name an existing file, without
12172 changing the file system contents. Using the output of this command
12173 to create a new file is inherently unsafe, as there is a window of
12174 time between generating the name and using it where another process
12175 can create an object by the same name.
12178 @itemx --tempdir[=@var{dir}]
12181 Treat @var{template} relative to the directory @var{dir}. If
12182 @var{dir} is not specified (only possible with the long option
12183 @option{--tempdir}) or is the empty string, use the value of
12184 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12185 specified, @var{template} must not be absolute. However,
12186 @var{template} can still contain slashes, although intermediate
12187 directories must already exist.
12191 Treat @var{template} as a single file relative to the value of
12192 @env{TMPDIR} if available, or to the directory specified by
12193 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12194 contain slashes. This option is deprecated; the use of @option{-p}
12195 without @option{-t} offers better defaults (by favoring the command
12196 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12201 @cindex exit status of @command{mktemp}
12205 0 if the file was created,
12210 @node Working context
12211 @chapter Working context
12213 @cindex working context
12214 @cindex commands for printing the working context
12216 This section describes commands that display or alter the context in
12217 which you are working: the current directory, the terminal settings, and
12218 so forth. See also the user-related commands in the next section.
12221 * pwd invocation:: Print working directory.
12222 * stty invocation:: Print or change terminal characteristics.
12223 * printenv invocation:: Print environment variables.
12224 * tty invocation:: Print file name of terminal on standard input.
12228 @node pwd invocation
12229 @section @command{pwd}: Print working directory
12232 @cindex print name of current directory
12233 @cindex current working directory, printing
12234 @cindex working directory, printing
12237 @command{pwd} prints the name of the current directory. Synopsis:
12240 pwd [@var{option}]@dots{}
12243 The program accepts the following options. Also see @ref{Common options}.
12250 If the contents of the environment variable @env{PWD} provide an
12251 absolute name of the current directory with no @samp{.} or @samp{..}
12252 components, but possibly with symbolic links, then output those
12253 contents. Otherwise, fall back to default @option{-P} handling.
12258 @opindex --physical
12259 Print a fully resolved name for the current directory. That is, all
12260 components of the printed name will be actual directory names---none
12261 will be symbolic links.
12264 @cindex symbolic links and @command{pwd}
12265 If @option{-L} and @option{-P} are both given, the last one takes
12266 precedence. If neither option is given, then this implementation uses
12267 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12268 environment variable is set.
12270 @mayConflictWithShellBuiltIn{pwd}
12275 @node stty invocation
12276 @section @command{stty}: Print or change terminal characteristics
12279 @cindex change or print terminal settings
12280 @cindex terminal settings
12281 @cindex line settings of terminal
12283 @command{stty} prints or changes terminal characteristics, such as baud rate.
12287 stty [@var{option}] [@var{setting}]@dots{}
12288 stty [@var{option}]
12291 If given no line settings, @command{stty} prints the baud rate, line
12292 discipline number (on systems that support it), and line settings
12293 that have been changed from the values set by @samp{stty sane}.
12294 By default, mode reading and setting are performed on the tty line
12295 connected to standard input, although this can be modified by the
12296 @option{--file} option.
12298 @command{stty} accepts many non-option arguments that change aspects of
12299 the terminal line operation, as described below.
12301 The program accepts the following options. Also see @ref{Common options}.
12308 Print all current settings in human-readable form. This option may not
12309 be used in combination with any line settings.
12311 @item -F @var{device}
12312 @itemx --file=@var{device}
12315 Set the line opened by the file name specified in @var{device} instead of
12316 the tty line connected to standard input. This option is necessary
12317 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12318 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12319 the @code{clocal} flag is not set. Hence, it is not always possible
12320 to allow the shell to open the device in the traditional manner.
12326 @cindex machine-readable @command{stty} output
12327 Print all current settings in a form that can be used as an argument to
12328 another @command{stty} command to restore the current settings. This option
12329 may not be used in combination with any line settings.
12333 Many settings can be turned off by preceding them with a @samp{-}.
12334 Such arguments are marked below with ``May be negated'' in their
12335 description. The descriptions themselves refer to the positive
12336 case, that is, when @emph{not} negated (unless stated otherwise,
12339 Some settings are not available on all @acronym{POSIX} systems, since they use
12340 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12341 description. On non-@acronym{POSIX} systems, those or other settings also may not
12342 be available, but it's not feasible to document all the variations: just
12348 * Control:: Control settings
12349 * Input:: Input settings
12350 * Output:: Output settings
12351 * Local:: Local settings
12352 * Combination:: Combination settings
12353 * Characters:: Special characters
12354 * Special:: Special settings
12359 @subsection Control settings
12361 @cindex control settings
12367 @cindex two-way parity
12368 Generate parity bit in output and expect parity bit in input.
12374 @cindex even parity
12375 Set odd parity (even if negated). May be negated.
12382 @cindex character size
12383 @cindex eight-bit characters
12384 Set character size to 5, 6, 7, or 8 bits.
12389 Send a hangup signal when the last process closes the tty. May be
12395 Use two stop bits per character (one if negated). May be negated.
12399 Allow input to be received. May be negated.
12403 @cindex modem control
12404 Disable modem control signals. May be negated.
12408 @cindex hardware flow control
12409 @cindex flow control, hardware
12410 @cindex RTS/CTS flow control
12411 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12416 @subsection Input settings
12418 @cindex input settings
12419 These settings control operations on data received from the terminal.
12424 @cindex breaks, ignoring
12425 Ignore break characters. May be negated.
12429 @cindex breaks, cause interrupts
12430 Make breaks cause an interrupt signal. May be negated.
12434 @cindex parity, ignoring
12435 Ignore characters with parity errors. May be negated.
12439 @cindex parity errors, marking
12440 Mark parity errors (with a 255-0-character sequence). May be negated.
12444 Enable input parity checking. May be negated.
12448 @cindex eight-bit input
12449 Clear high (8th) bit of input characters. May be negated.
12453 @cindex newline, translating to return
12454 Translate newline to carriage return. May be negated.
12458 @cindex return, ignoring
12459 Ignore carriage return. May be negated.
12463 @cindex return, translating to newline
12464 Translate carriage return to newline. May be negated.
12468 @cindex input encoding, UTF-8
12469 Assume input characters are UTF-8 encoded. May be negated.
12473 @kindex C-s/C-q flow control
12474 @cindex XON/XOFF flow control
12475 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12482 @cindex software flow control
12483 @cindex flow control, software
12484 Enable sending of @code{stop} character when the system input buffer
12485 is almost full, and @code{start} character when it becomes almost
12486 empty again. May be negated.
12490 @cindex uppercase, translating to lowercase
12491 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12492 negated. Note ilcuc is not implemented, as one would not be able to issue
12493 almost any (lowercase) Unix command, after invoking it.
12497 Allow any character to restart output (only the start character
12498 if negated). Non-@acronym{POSIX}. May be negated.
12502 @cindex beeping at input buffer full
12503 Enable beeping and not flushing input buffer if a character arrives
12504 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12509 @subsection Output settings
12511 @cindex output settings
12512 These settings control operations on data sent to the terminal.
12517 Postprocess output. May be negated.
12521 @cindex lowercase, translating to output
12522 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12523 negated. (Note ouclc is not currently implemented.)
12527 @cindex return, translating to newline
12528 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12532 @cindex newline, translating to crlf
12533 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12538 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12543 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12547 @cindex pad instead of timing for delaying
12548 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12553 @cindex pad character
12554 Use @acronym{ASCII} @sc{del} characters for fill instead of
12555 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12561 Newline delay style. Non-@acronym{POSIX}.
12568 Carriage return delay style. Non-@acronym{POSIX}.
12574 @opindex tab@var{n}
12575 Horizontal tab delay style. Non-@acronym{POSIX}.
12580 Backspace delay style. Non-@acronym{POSIX}.
12585 Vertical tab delay style. Non-@acronym{POSIX}.
12590 Form feed delay style. Non-@acronym{POSIX}.
12595 @subsection Local settings
12597 @cindex local settings
12602 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12603 characters. May be negated.
12607 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12608 special characters. May be negated.
12612 Enable non-@acronym{POSIX} special characters. May be negated.
12616 Echo input characters. May be negated.
12622 Echo @code{erase} characters as backspace-space-backspace. May be
12627 @cindex newline echoing after @code{kill}
12628 Echo a newline after a @code{kill} character. May be negated.
12632 @cindex newline, echoing
12633 Echo newline even if not echoing other characters. May be negated.
12637 @cindex flushing, disabling
12638 Disable flushing after @code{interrupt} and @code{quit} special
12639 characters. May be negated.
12643 @cindex case translation
12644 Enable input and output of uppercase characters by preceding their
12645 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12646 Non-@acronym{POSIX}. May be negated.
12650 @cindex background jobs, stopping at terminal write
12651 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12658 Echo erased characters backward, between @samp{\} and @samp{/}.
12659 Non-@acronym{POSIX}. May be negated.
12665 @cindex control characters, using @samp{^@var{c}}
12666 @cindex hat notation for control characters
12667 Echo control characters in hat notation (@samp{^@var{c}}) instead
12668 of literally. Non-@acronym{POSIX}. May be negated.
12674 Echo the @code{kill} special character by erasing each character on
12675 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12676 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12682 @subsection Combination settings
12684 @cindex combination settings
12685 Combination settings:
12692 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12693 as @code{-parenb cs8}.
12697 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12698 as @code{-parenb cs8}.
12702 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12703 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12707 Reset the @code{erase} and @code{kill} special characters to their default
12714 @c This is too long to write inline.
12716 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12717 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12718 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12719 ff0 isig icanon iexten echo echoe echok -echonl
12720 -noflsh -xcase -tostop -echoprt echoctl echoke
12724 and also sets all special characters to their default values.
12728 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12729 sets the @code{eof} and @code{eol} characters to their default values
12730 if they are the same as the @code{min} and @code{time} characters.
12731 May be negated. If negated, same as @code{raw}.
12738 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12739 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12740 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12744 May be negated. If negated, same as @code{cooked}.
12748 Same as @option{-icanon}. May be negated. If negated, same as
12753 @cindex eight-bit characters
12754 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12755 same as @code{parenb istrip cs7}.
12759 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12760 If negated, same as @code{parenb istrip opost cs7}.
12764 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12768 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12775 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12776 (Used for terminals with uppercase characters only.)
12780 Same as @code{echoe echoctl echoke}.
12784 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12789 @subsection Special characters
12791 @cindex special characters
12792 @cindex characters, special
12794 The special characters' default values vary from system to system.
12795 They are set with the syntax @samp{name value}, where the names are
12796 listed below and the value can be given either literally, in hat
12797 notation (@samp{^@var{c}}), or as an integer which may start with
12798 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12799 any other digit to indicate decimal.
12801 @cindex disabling special characters
12802 @kindex u@r{, and disabling special characters}
12803 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12804 special character. (This is incompatible with Ultrix @command{stty},
12805 which uses a value of @samp{u} to disable a special character. GNU
12806 @command{stty} treats a value @samp{u} like any other, namely to set that
12807 special character to @key{U}.)
12813 Send an interrupt signal.
12817 Send a quit signal.
12821 Erase the last character typed.
12825 Erase the current line.
12829 Send an end of file (terminate the input).
12837 Alternate character to end the line. Non-@acronym{POSIX}.
12841 Switch to a different shell layer. Non-@acronym{POSIX}.
12845 Restart the output after stopping it.
12853 Send a terminal stop signal.
12857 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12861 Redraw the current line. Non-@acronym{POSIX}.
12865 Erase the last word typed. Non-@acronym{POSIX}.
12869 Enter the next character typed literally, even if it is a special
12870 character. Non-@acronym{POSIX}.
12875 @subsection Special settings
12877 @cindex special settings
12882 Set the minimum number of characters that will satisfy a read until
12883 the time value has expired, when @option{-icanon} is set.
12887 Set the number of tenths of a second before reads time out if the minimum
12888 number of characters have not been read, when @option{-icanon} is set.
12890 @item ispeed @var{n}
12892 Set the input speed to @var{n}.
12894 @item ospeed @var{n}
12896 Set the output speed to @var{n}.
12900 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12903 @itemx columns @var{n}
12906 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12912 Print the number of rows and columns that the kernel thinks the
12913 terminal has. (Systems that don't support rows and columns in the kernel
12914 typically use the environment variables @env{LINES} and @env{COLUMNS}
12915 instead; however, GNU @command{stty} does not know anything about them.)
12916 Non-@acronym{POSIX}.
12920 Use line discipline @var{n}. Non-@acronym{POSIX}.
12924 Print the terminal speed.
12927 @cindex baud rate, setting
12928 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12929 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12930 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12931 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12932 support higher speeds. The @command{stty} command includes support
12949 4000000 where the system supports these.
12950 0 hangs up the line if @option{-clocal} is set.
12954 @node printenv invocation
12955 @section @command{printenv}: Print all or some environment variables
12958 @cindex printing all or some environment variables
12959 @cindex environment variables, printing
12961 @command{printenv} prints environment variable values. Synopsis:
12964 printenv [@var{option}] [@var{variable}]@dots{}
12967 If no @var{variable}s are specified, @command{printenv} prints the value of
12968 every environment variable. Otherwise, it prints the value of each
12969 @var{variable} that is set, and nothing for those that are not set.
12971 The program accepts the following option. Also see @ref{Common options}.
12979 @cindex exit status of @command{printenv}
12983 0 if all variables specified were found
12984 1 if at least one specified variable was not found
12985 2 if a write error occurred
12989 @node tty invocation
12990 @section @command{tty}: Print file name of terminal on standard input
12993 @cindex print terminal file name
12994 @cindex terminal file name, printing
12996 @command{tty} prints the file name of the terminal connected to its standard
12997 input. It prints @samp{not a tty} if standard input is not a terminal.
13001 tty [@var{option}]@dots{}
13004 The program accepts the following option. Also see @ref{Common options}.
13014 Print nothing; only return an exit status.
13018 @cindex exit status of @command{tty}
13022 0 if standard input is a terminal
13023 1 if standard input is not a terminal
13024 2 if given incorrect arguments
13025 3 if a write error occurs
13029 @node User information
13030 @chapter User information
13032 @cindex user information, commands for
13033 @cindex commands for printing user information
13035 This section describes commands that print user-related information:
13036 logins, groups, and so forth.
13039 * id invocation:: Print user identity.
13040 * logname invocation:: Print current login name.
13041 * whoami invocation:: Print effective user ID.
13042 * groups invocation:: Print group names a user is in.
13043 * users invocation:: Print login names of users currently logged in.
13044 * who invocation:: Print who is currently logged in.
13048 @node id invocation
13049 @section @command{id}: Print user identity
13052 @cindex real user and group IDs, printing
13053 @cindex effective user and group IDs, printing
13054 @cindex printing real and effective user and group IDs
13056 @command{id} prints information about the given user, or the process
13057 running it if no user is specified. Synopsis:
13060 id [@var{option}]@dots{} [@var{username}]
13063 @vindex POSIXLY_CORRECT
13064 By default, it prints the real user ID, real group ID, effective user ID
13065 if different from the real user ID, effective group ID if different from
13066 the real group ID, and supplemental group IDs.
13067 In addition, if SELinux
13068 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13069 then print @samp{context=@var{c}}, where @var{c} is the security context.
13071 Each of these numeric values is preceded by an identifying string and
13072 followed by the corresponding user or group name in parentheses.
13074 The options cause @command{id} to print only part of the above information.
13075 Also see @ref{Common options}.
13082 Print only the group ID.
13088 Print only the group ID and the supplementary groups.
13094 Print the user or group name instead of the ID number. Requires
13095 @option{-u}, @option{-g}, or @option{-G}.
13101 Print the real, instead of effective, user or group ID. Requires
13102 @option{-u}, @option{-g}, or @option{-G}.
13108 Print only the user ID.
13115 @cindex security context
13116 Print only the security context of the current user.
13117 If SELinux is disabled then print a warning and
13118 set the exit status to 1.
13124 @macro primaryAndSupplementaryGroups{cmd,arg}
13125 Primary and supplementary groups for a process are normally inherited
13126 from its parent and are usually unchanged since login. This means
13127 that if you change the group database after logging in, @command{\cmd\}
13128 will not reflect your changes within your existing login session.
13129 Running @command{\cmd\} with a \arg\ causes the user and group
13130 database to be consulted afresh, and so will give a different result.
13132 @primaryAndSupplementaryGroups{id,user argument}
13134 @node logname invocation
13135 @section @command{logname}: Print current login name
13138 @cindex printing user's login name
13139 @cindex login name, printing
13140 @cindex user name, printing
13143 @command{logname} prints the calling user's name, as found in a
13144 system-maintained file (often @file{/var/run/utmp} or
13145 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13146 for the calling process, @command{logname} prints
13147 an error message and exits with a status of 1.
13149 The only options are @option{--help} and @option{--version}. @xref{Common
13155 @node whoami invocation
13156 @section @command{whoami}: Print effective user ID
13159 @cindex effective user ID, printing
13160 @cindex printing the effective user ID
13162 @command{whoami} prints the user name associated with the current
13163 effective user ID. It is equivalent to the command @samp{id -un}.
13165 The only options are @option{--help} and @option{--version}. @xref{Common
13171 @node groups invocation
13172 @section @command{groups}: Print group names a user is in
13175 @cindex printing groups a user is in
13176 @cindex supplementary groups, printing
13178 @command{groups} prints the names of the primary and any supplementary
13179 groups for each given @var{username}, or the current process if no names
13180 are given. If more than one name is given, the name of each user is
13182 the list of that user's groups and the user name is separated from the
13183 group list by a colon. Synopsis:
13186 groups [@var{username}]@dots{}
13189 The group lists are equivalent to the output of the command @samp{id -Gn}.
13191 @primaryAndSupplementaryGroups{groups,list of users}
13193 The only options are @option{--help} and @option{--version}. @xref{Common
13199 @node users invocation
13200 @section @command{users}: Print login names of users currently logged in
13203 @cindex printing current usernames
13204 @cindex usernames, printing current
13206 @cindex login sessions, printing users with
13207 @command{users} prints on a single line a blank-separated list of user
13208 names of users currently logged in to the current host. Each user name
13209 corresponds to a login session, so if a user has more than one login
13210 session, that user's name will appear the same number of times in the
13219 With no @var{file} argument, @command{users} extracts its information from
13220 a system-maintained file (often @file{/var/run/utmp} or
13221 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13222 that file instead. A common choice is @file{/var/log/wtmp}.
13224 The only options are @option{--help} and @option{--version}. @xref{Common
13230 @node who invocation
13231 @section @command{who}: Print who is currently logged in
13234 @cindex printing current user information
13235 @cindex information, about current users
13237 @command{who} prints information about users who are currently logged on.
13241 @command{who} [@var{option}] [@var{file}] [am i]
13244 @cindex terminal lines, currently used
13246 @cindex remote hostname
13247 If given no non-option arguments, @command{who} prints the following
13248 information for each user currently logged on: login name, terminal
13249 line, login time, and remote hostname or X display.
13253 If given one non-option argument, @command{who} uses that instead of
13254 a default system-maintained file (often @file{/var/run/utmp} or
13255 @file{/etc/utmp}) as the name of the file containing the record of
13256 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13257 to @command{who} to look at who has previously logged on.
13261 If given two non-option arguments, @command{who} prints only the entry
13262 for the user running it (determined from its standard input), preceded
13263 by the hostname. Traditionally, the two arguments given are @samp{am
13264 i}, as in @samp{who am i}.
13267 Time stamps are listed according to the time zone rules specified by
13268 the @env{TZ} environment variable, or by the system default rules if
13269 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13270 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13272 The program accepts the following options. Also see @ref{Common options}.
13280 Same as @samp{-b -d --login -p -r -t -T -u}.
13286 Print the date and time of last system boot.
13292 Print information corresponding to dead processes.
13298 Print a line of column headings.
13304 List only the entries that correspond to processes via which the
13305 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13309 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13310 is not the default because it can cause significant delays on systems with
13311 automatic dial-up internet access.
13315 Same as @samp{who am i}.
13321 List active processes spawned by init.
13327 Print only the login names and the number of users logged on.
13328 Overrides all other options.
13333 @opindex --runlevel
13334 Print the current (and maybe previous) run-level of the init process.
13338 Ignored; for compatibility with other versions of @command{who}.
13344 Print last system clock change.
13349 After the login time, print the number of hours and minutes that the
13350 user has been idle. @samp{.} means the user was active in the last minute.
13351 @samp{old} means the user has been idle for more than 24 hours.
13362 @opindex --writable
13363 @cindex message status
13364 @pindex write@r{, allowed}
13365 After each login name print a character indicating the user's message status:
13368 @samp{+} allowing @code{write} messages
13369 @samp{-} disallowing @code{write} messages
13370 @samp{?} cannot find terminal device
13378 @node System context
13379 @chapter System context
13381 @cindex system context
13382 @cindex context, system
13383 @cindex commands for system context
13385 This section describes commands that print or change system-wide
13389 * date invocation:: Print or set system date and time.
13390 * arch invocation:: Print machine hardware name.
13391 * uname invocation:: Print system information.
13392 * hostname invocation:: Print or set system name.
13393 * hostid invocation:: Print numeric host identifier.
13394 * uptime invocation:: Print system uptime and load.
13397 @node date invocation
13398 @section @command{date}: Print or set system date and time
13401 @cindex time, printing or setting
13402 @cindex printing the current time
13407 date [@var{option}]@dots{} [+@var{format}]
13408 date [-u|--utc|--universal] @c this avoids a newline in the output
13409 [ MMDDhhmm[[CC]YY][.ss] ]
13413 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13414 it with a default format that depends on the @env{LC_TIME} locale category.
13415 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13416 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13419 Normally, @command{date} uses the time zone rules indicated by the
13420 @env{TZ} environment variable, or the system default rules if @env{TZ}
13421 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13422 @env{TZ}, libc, The GNU C Library Reference Manual}.
13424 @findex strftime @r{and @command{date}}
13425 @cindex time formats
13426 @cindex formatting times
13427 If given an argument that starts with a @samp{+}, @command{date} prints the
13428 current date and time (or the date and time specified by the
13429 @option{--date} option, see below) in the format defined by that argument,
13430 which is similar to that of the @code{strftime} function. Except for
13431 conversion specifiers, which start with @samp{%}, characters in the
13432 format string are printed unchanged. The conversion specifiers are
13438 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13439 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13440 * Literal conversion specifiers:: %[%nt]
13441 * Padding and other flags:: Pad with zeros, spaces, etc.
13442 * Setting the time:: Changing the system clock.
13443 * Options for date:: Instead of the current time.
13445 * Date input formats:: Specifying date strings.
13447 * Examples of date:: Examples.
13450 @node Time conversion specifiers
13451 @subsection Time conversion specifiers
13453 @cindex time conversion specifiers
13454 @cindex conversion specifiers, time
13456 @command{date} conversion specifiers related to times.
13460 hour (@samp{00}@dots{}@samp{23})
13462 hour (@samp{01}@dots{}@samp{12})
13464 hour (@samp{ 0}@dots{}@samp{23}).
13465 This is a @acronym{GNU} extension.
13467 hour (@samp{ 1}@dots{}@samp{12}).
13468 This is a @acronym{GNU} extension.
13470 minute (@samp{00}@dots{}@samp{59})
13472 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13473 This is a @acronym{GNU} extension.
13475 locale's equivalent of either @samp{AM} or @samp{PM};
13476 blank in many locales.
13477 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13479 like @samp{%p}, except lower case.
13480 This is a @acronym{GNU} extension.
13482 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13484 24-hour hour and minute. Same as @samp{%H:%M}.
13485 This is a @acronym{GNU} extension.
13487 @cindex epoch, seconds since
13488 @cindex seconds since the epoch
13489 @cindex beginning of time
13490 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13491 Leap seconds are not counted unless leap second support is available.
13492 @xref{%s-examples}, for examples.
13493 This is a @acronym{GNU} extension.
13495 second (@samp{00}@dots{}@samp{60}).
13496 This may be @samp{60} if leap seconds are supported.
13498 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13500 locale's time representation (e.g., @samp{23:13:48})
13502 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13503 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13504 time zone is determinable. This value reflects the numeric time zone
13505 appropriate for the current time, using the time zone rules specified
13506 by the @env{TZ} environment variable.
13507 The time (and optionally, the time zone rules) can be overridden
13508 by the @option{--date} option.
13509 This is a @acronym{GNU} extension.
13511 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13512 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13513 zone is determinable.
13514 This is a @acronym{GNU} extension.
13516 Numeric time zone to the nearest second with @samp{:} (e.g.,
13517 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13519 This is a @acronym{GNU} extension.
13521 Numeric time zone with @samp{:} using the minimum necessary precision
13522 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13523 no time zone is determinable.
13524 This is a @acronym{GNU} extension.
13526 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13527 time zone is determinable. See @samp{%z} for how it is determined.
13531 @node Date conversion specifiers
13532 @subsection Date conversion specifiers
13534 @cindex date conversion specifiers
13535 @cindex conversion specifiers, date
13537 @command{date} conversion specifiers related to dates.
13541 locale's abbreviated weekday name (e.g., @samp{Sun})
13543 locale's full weekday name, variable length (e.g., @samp{Sunday})
13545 locale's abbreviated month name (e.g., @samp{Jan})
13547 locale's full month name, variable length (e.g., @samp{January})
13549 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13551 century. This is like @samp{%Y}, except the last two digits are omitted.
13552 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13553 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13554 It is normally at least two characters, but it may be more.
13556 day of month (e.g., @samp{01})
13558 date; same as @samp{%m/%d/%y}
13560 day of month, space padded; same as @samp{%_d}
13562 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13563 This is a good choice for a date format, as it is standard and
13564 is easy to sort in the usual case where years are in the range
13566 This is a @acronym{GNU} extension.
13568 year corresponding to the @acronym{ISO} week number, but without the century
13569 (range @samp{00} through @samp{99}). This has the same format and value
13570 as @samp{%y}, except that if the @acronym{ISO} week number (see
13572 to the previous or next year, that year is used instead.
13573 This is a @acronym{GNU} extension.
13575 year corresponding to the @acronym{ISO} week number. This has the
13576 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13578 @samp{%V}) belongs to the previous or next year, that year is used
13580 It is normally useful only if @samp{%V} is also used;
13581 for example, the format @samp{%G-%m-%d} is probably a mistake,
13582 since it combines the ISO week number year with the conventional month and day.
13583 This is a @acronym{GNU} extension.
13587 day of year (@samp{001}@dots{}@samp{366})
13589 month (@samp{01}@dots{}@samp{12})
13591 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13593 week number of year, with Sunday as the first day of the week
13594 (@samp{00}@dots{}@samp{53}).
13595 Days in a new year preceding the first Sunday are in week zero.
13597 @acronym{ISO} week number, that is, the
13598 week number of year, with Monday as the first day of the week
13599 (@samp{01}@dots{}@samp{53}).
13600 If the week containing January 1 has four or more days in
13601 the new year, then it is considered week 1; otherwise, it is week 53 of
13602 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13605 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13607 week number of year, with Monday as first day of week
13608 (@samp{00}@dots{}@samp{53}).
13609 Days in a new year preceding the first Monday are in week zero.
13611 locale's date representation (e.g., @samp{12/31/99})
13613 last two digits of year (@samp{00}@dots{}@samp{99})
13615 year. This is normally at least four characters, but it may be more.
13616 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13617 precedes year @samp{0000}.
13621 @node Literal conversion specifiers
13622 @subsection Literal conversion specifiers
13624 @cindex literal conversion specifiers
13625 @cindex conversion specifiers, literal
13627 @command{date} conversion specifiers that produce literal strings.
13639 @node Padding and other flags
13640 @subsection Padding and other flags
13642 @cindex numeric field padding
13643 @cindex padding of numeric fields
13644 @cindex fields, padding numeric
13646 Unless otherwise specified, @command{date} normally pads numeric fields
13647 with zeros, so that, for
13648 example, numeric months are always output as two digits.
13649 Seconds since the epoch are not padded, though,
13650 since there is no natural width for them.
13652 As a @acronym{GNU} extension, @command{date} recognizes any of the
13653 following optional flags after the @samp{%}:
13657 (hyphen) Do not pad the field; useful if the output is intended for
13660 (underscore) Pad with spaces; useful if you need a fixed
13661 number of characters in the output, but zeros are too distracting.
13663 (zero) Pad with zeros even if the conversion specifier
13664 would normally pad with spaces.
13666 Use upper case characters if possible.
13668 Use opposite case characters if possible.
13669 A field that is normally upper case becomes lower case, and vice versa.
13673 Here are some examples of padding:
13676 date +%d/%m -d "Feb 1"
13678 date +%-d/%-m -d "Feb 1"
13680 date +%_d/%_m -d "Feb 1"
13684 As a @acronym{GNU} extension, you can specify the field width
13685 (after any flag, if present) as a decimal number. If the natural size of the
13686 output of the field has less than the specified number of characters,
13687 the result is written right adjusted and padded to the given
13688 size. For example, @samp{%9B} prints the right adjusted month name in
13689 a field of width 9.
13691 An optional modifier can follow the optional flag and width
13692 specification. The modifiers are:
13696 Use the locale's alternate representation for date and time. This
13697 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13698 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13699 example, @samp{%Ex} might yield a date format based on the Japanese
13703 Use the locale's alternate numeric symbols for numbers. This modifier
13704 applies only to numeric conversion specifiers.
13707 If the format supports the modifier but no alternate representation
13708 is available, it is ignored.
13711 @node Setting the time
13712 @subsection Setting the time
13714 @cindex setting the time
13715 @cindex time setting
13716 @cindex appropriate privileges
13718 If given an argument that does not start with @samp{+}, @command{date} sets
13719 the system clock to the date and time specified by that argument (as
13720 described below). You must have appropriate privileges to set the
13721 system clock. The @option{--date} and @option{--set} options may not be
13722 used with such an argument. The @option{--universal} option may be used
13723 with such an argument to indicate that the specified date and time are
13724 relative to Coordinated Universal Time rather than to the local time
13727 The argument must consist entirely of digits, which have the following
13740 first two digits of year (optional)
13742 last two digits of year (optional)
13747 The @option{--set} option also sets the system clock; see the next section.
13750 @node Options for date
13751 @subsection Options for @command{date}
13753 @cindex @command{date} options
13754 @cindex options for @command{date}
13756 The program accepts the following options. Also see @ref{Common options}.
13760 @item -d @var{datestr}
13761 @itemx --date=@var{datestr}
13764 @cindex parsing date strings
13765 @cindex date strings, parsing
13766 @cindex arbitrary date strings, parsing
13769 @opindex next @var{day}
13770 @opindex last @var{day}
13771 Display the date and time specified in @var{datestr} instead of the
13772 current date and time. @var{datestr} can be in almost any common
13773 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13774 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13775 14:19:13.489392193 +0530"} specifies the instant of time that is
13776 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13777 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13778 Note: input currently must be in locale independent format. E.g., the
13779 LC_TIME=C below is needed to print back the correct date in many locales:
13781 date -d "$(LC_TIME=C date)"
13783 @xref{Date input formats}.
13785 @item -f @var{datefile}
13786 @itemx --file=@var{datefile}
13789 Parse each line in @var{datefile} as with @option{-d} and display the
13790 resulting date and time. If @var{datefile} is @samp{-}, use standard
13791 input. This is useful when you have many dates to process, because the
13792 system overhead of starting up the @command{date} executable many times can
13795 @item -r @var{file}
13796 @itemx --reference=@var{file}
13798 @opindex --reference
13799 Display the date and time of the last modification of @var{file},
13800 instead of the current date and time.
13807 @opindex --rfc-2822
13808 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13809 %z}, evaluated in the C locale so abbreviations are always in English.
13813 Fri, 09 Sep 2005 13:51:39 -0700
13816 This format conforms to
13817 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13818 @acronym{RFCs} 2822} and
13819 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13820 current and previous standards for Internet email.
13822 @item --rfc-3339=@var{timespec}
13823 @opindex --rfc-3339=@var{timespec}
13824 Display the date using a format specified by
13825 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13826 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13827 format, except that it also permits applications to use a space rather
13828 than a @samp{T} to separate dates from times. Unlike the other
13829 standard formats, @acronym{RFC} 3339 format is always suitable as
13830 input for the @option{--date} (@option{-d}) and @option{--file}
13831 (@option{-f}) options, regardless of the current locale.
13833 The argument @var{timespec} specifies how much of the time to include.
13834 It can be one of the following:
13838 Print just the full-date, e.g., @samp{2005-09-14}.
13839 This is equivalent to the format @samp{%Y-%m-%d}.
13842 Print the full-date and full-time separated by a space, e.g.,
13843 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13844 time-offset; here the @samp{+05:30} means that local time is five
13845 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13846 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13849 Like @samp{seconds}, but also print nanoseconds, e.g.,
13850 @samp{2005-09-14 00:56:06.998458565+05:30}.
13851 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13855 @item -s @var{datestr}
13856 @itemx --set=@var{datestr}
13859 Set the date and time to @var{datestr}. See @option{-d} above.
13866 @opindex --universal
13867 @cindex Coordinated Universal Time
13869 @cindex Greenwich Mean Time
13872 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13873 @env{TZ} environment variable were set to the string @samp{UTC0}.
13875 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13876 historical reasons.
13880 @node Examples of date
13881 @subsection Examples of @command{date}
13883 @cindex examples of @command{date}
13885 Here are a few examples. Also see the documentation for the @option{-d}
13886 option in the previous section.
13891 To print the date of the day before yesterday:
13894 date --date='2 days ago'
13898 To print the date of the day three months and one day hence:
13901 date --date='3 months 1 day'
13905 To print the day of year of Christmas in the current year:
13908 date --date='25 Dec' +%j
13912 To print the current full month name and the day of the month:
13918 But this may not be what you want because for the first nine days of
13919 the month, the @samp{%d} expands to a zero-padded two-digit field,
13920 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13923 To print a date without the leading zero for one-digit days
13924 of the month, you can use the (@acronym{GNU} extension)
13925 @samp{-} flag to suppress
13926 the padding altogether:
13929 date -d 1may '+%B %-d
13933 To print the current date and time in the format required by many
13934 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13937 date +%m%d%H%M%Y.%S
13941 To set the system clock forward by two minutes:
13944 date --set='+2 minutes'
13948 To print the date in @acronym{RFC} 2822 format,
13949 use @samp{date --rfc-2822}. Here is some example output:
13952 Fri, 09 Sep 2005 13:51:39 -0700
13955 @anchor{%s-examples}
13957 To convert a date string to the number of seconds since the epoch
13958 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
13959 the @samp{%s} format. That can be useful in sorting and/or graphing
13960 and/or comparing data by date. The following command outputs the
13961 number of the seconds since the epoch for the time two minutes after the
13965 date --date='1970-01-01 00:02:00 +0000' +%s
13969 If you do not specify time zone information in the date string,
13970 @command{date} uses your computer's idea of the time zone when
13971 interpreting the string. For example, if your computer's time zone is
13972 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
13973 seconds) behind UTC:
13976 # local time zone used
13977 date --date='1970-01-01 00:02:00' +%s
13982 If you're sorting or graphing dated data, your raw date values may be
13983 represented as seconds since the epoch. But few people can look at
13984 the date @samp{946684800} and casually note ``Oh, that's the first second
13985 of the year 2000 in Greenwich, England.''
13988 date --date='2000-01-01 UTC' +%s
13992 An alternative is to use the @option{--utc} (@option{-u}) option.
13993 Then you may omit @samp{UTC} from the date string. Although this
13994 produces the same result for @samp{%s} and many other format sequences,
13995 with a time zone offset different from zero, it would give a different
13996 result for zone-dependent formats like @samp{%z}.
13999 date -u --date=2000-01-01 +%s
14003 To convert such an unwieldy number of seconds back to
14004 a more readable form, use a command like this:
14007 # local time zone used
14008 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14009 1999-12-31 19:00:00 -0500
14012 Or if you do not mind depending on the @samp{@@} feature present since
14013 coreutils 5.3.0, you could shorten this to:
14016 date -d @@946684800 +"%F %T %z"
14017 1999-12-31 19:00:00 -0500
14020 Often it is better to output UTC-relative date and time:
14023 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14024 2000-01-01 00:00:00 +0000
14030 @node arch invocation
14031 @section @command{arch}: Print machine hardware name
14034 @cindex print machine hardware name
14035 @cindex system information, printing
14037 @command{arch} prints the machine hardware name,
14038 and is equivalent to @samp{uname -m}.
14042 arch [@var{option}]
14045 The program accepts the @ref{Common options} only.
14050 @node uname invocation
14051 @section @command{uname}: Print system information
14054 @cindex print system information
14055 @cindex system information, printing
14057 @command{uname} prints information about the machine and operating system
14058 it is run on. If no options are given, @command{uname} acts as if the
14059 @option{-s} option were given. Synopsis:
14062 uname [@var{option}]@dots{}
14065 If multiple options or @option{-a} are given, the selected information is
14066 printed in this order:
14069 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14070 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14073 The information may contain internal spaces, so such output cannot be
14074 parsed reliably. In the following example, @var{release} is
14075 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14079 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14083 The program accepts the following options. Also see @ref{Common options}.
14091 Print all of the below information, except omit the processor type
14092 and the hardware platform name if they are unknown.
14095 @itemx --hardware-platform
14097 @opindex --hardware-platform
14098 @cindex implementation, hardware
14099 @cindex hardware platform
14100 @cindex platform, hardware
14101 Print the hardware platform name
14102 (sometimes called the hardware implementation).
14103 Print @samp{unknown} if the kernel does not make this information
14104 easily available, as is the case with Linux kernels.
14110 @cindex machine type
14111 @cindex hardware class
14112 @cindex hardware type
14113 Print the machine hardware name (sometimes called the hardware class
14119 @opindex --nodename
14122 @cindex network node name
14123 Print the network node hostname.
14128 @opindex --processor
14129 @cindex host processor type
14130 Print the processor type (sometimes called the instruction set
14131 architecture or ISA).
14132 Print @samp{unknown} if the kernel does not make this information
14133 easily available, as is the case with Linux kernels.
14136 @itemx --operating-system
14138 @opindex --operating-system
14139 @cindex operating system name
14140 Print the name of the operating system.
14143 @itemx --kernel-release
14145 @opindex --kernel-release
14146 @cindex kernel release
14147 @cindex release of kernel
14148 Print the kernel release.
14151 @itemx --kernel-name
14153 @opindex --kernel-name
14154 @cindex kernel name
14155 @cindex name of kernel
14156 Print the kernel name.
14157 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14158 ``the implementation of the operating system'', because the
14159 @acronym{POSIX} specification itself has no notion of ``kernel''.
14160 The kernel name might be the same as the operating system name printed
14161 by the @option{-o} or @option{--operating-system} option, but it might
14162 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14163 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14167 @itemx --kernel-version
14169 @opindex --kernel-version
14170 @cindex kernel version
14171 @cindex version of kernel
14172 Print the kernel version.
14179 @node hostname invocation
14180 @section @command{hostname}: Print or set system name
14183 @cindex setting the hostname
14184 @cindex printing the hostname
14185 @cindex system name, printing
14186 @cindex appropriate privileges
14188 With no arguments, @command{hostname} prints the name of the current host
14189 system. With one argument, it sets the current host name to the
14190 specified string. You must have appropriate privileges to set the host
14194 hostname [@var{name}]
14197 The only options are @option{--help} and @option{--version}. @xref{Common
14203 @node hostid invocation
14204 @section @command{hostid}: Print numeric host identifier
14207 @cindex printing the host identifier
14209 @command{hostid} prints the numeric identifier of the current host
14210 in hexadecimal. This command accepts no arguments.
14211 The only options are @option{--help} and @option{--version}.
14212 @xref{Common options}.
14214 For example, here's what it prints on one system I use:
14221 On that system, the 32-bit quantity happens to be closely
14222 related to the system's Internet address, but that isn't always
14227 @node uptime invocation
14228 @section @command{uptime}: Print system uptime and load
14231 @cindex printing the system uptime and load
14233 @command{uptime} prints the current time, the system's uptime, the
14234 number of logged-in users and the current load average.
14236 If an argument is specified, it is used as the file to be read
14237 to discover how many users are logged in. If no argument is
14238 specified, a system default is used (@command{uptime --help} indicates
14239 the default setting).
14241 The only options are @option{--help} and @option{--version}.
14242 @xref{Common options}.
14244 For example, here's what it prints right now on one system I use:
14248 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14251 The precise method of calculation of load average varies somewhat
14252 between systems. Some systems calculate it as the average number of
14253 runnable processes over the last 1, 5 and 15 minutes, but some systems
14254 also include processes in the uninterruptible sleep state (that is,
14255 those processes which are waiting for disk I/O). The Linux kernel
14256 includes uninterruptible processes.
14258 @node SELinux context
14259 @chapter SELinux context
14261 @cindex SELinux context
14262 @cindex SELinux, context
14263 @cindex commands for SELinux context
14265 This section describes commands for operations with SELinux
14269 * chcon invocation:: Change SELinux context of file
14270 * runcon invocation:: Run a command in specified SELinux context
14273 @node chcon invocation
14274 @section @command{chcon}: Change SELinux context of file
14277 @cindex changing security context
14278 @cindex change SELinux context
14280 @command{chcon} changes the SELinux security context of the selected files.
14284 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14285 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14286 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14289 Change the SELinux security context of each @var{file} to @var{context}.
14290 With @option{--reference}, change the security context of each @var{file}
14291 to that of @var{rfile}.
14293 The program accepts the following options. Also see @ref{Common options}.
14298 @itemx --no-dereference
14300 @opindex --no-dereference
14301 @cindex no dereference
14302 Affect symbolic links instead of any referenced file.
14304 @item --reference=@var{rfile}
14305 @opindex --reference
14306 @cindex reference file
14307 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14312 @opindex --recursive
14313 Operate on files and directories recursively.
14316 @xref{Traversing symlinks}.
14319 @xref{Traversing symlinks}.
14322 @xref{Traversing symlinks}.
14329 Output a diagnostic for every file processed.
14331 @item -u @var{user}
14332 @itemx --user=@var{user}
14335 Set user @var{user} in the target security context.
14337 @item -r @var{role}
14338 @itemx --role=@var{role}
14341 Set role @var{role} in the target security context.
14343 @item -t @var{type}
14344 @itemx --type=@var{type}
14347 Set type @var{type} in the target security context.
14349 @item -l @var{range}
14350 @itemx --range=@var{range}
14353 Set range @var{range} in the target security context.
14359 @node runcon invocation
14360 @section @command{runcon}: Run a command in specified SELinux context
14363 @cindex run with security context
14366 @command{runcon} runs file in specified SELinux security context.
14370 runcon @var{context} @var{command} [@var{args}]
14371 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14374 Run @var{command} with completely-specified @var{context}, or with
14375 current or transitioned security context modified by one or more of @var{level},
14376 @var{role}, @var{type} and @var{user}.
14378 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14379 is specified, the first argument is used as the complete context.
14380 Any additional arguments after @var{command}
14381 are interpreted as arguments to the command.
14383 With neither @var{context} nor @var{command}, print the current security context.
14385 The program accepts the following options. Also see @ref{Common options}.
14393 Compute process transition context before modifying.
14395 @item -u @var{user}
14396 @itemx --user=@var{user}
14399 Set user @var{user} in the target security context.
14401 @item -r @var{role}
14402 @itemx --role=@var{role}
14405 Set role @var{role} in the target security context.
14407 @item -t @var{type}
14408 @itemx --type=@var{type}
14411 Set type @var{type} in the target security context.
14413 @item -l @var{range}
14414 @itemx --range=@var{range}
14417 Set range @var{range} in the target security context.
14421 @cindex exit status of @command{runcon}
14425 126 if @var{command} is found but cannot be invoked
14426 127 if @command{runcon} itself fails or if @var{command} cannot be found
14427 the exit status of @var{command} otherwise
14430 @node Modified command invocation
14431 @chapter Modified command invocation
14433 @cindex modified command invocation
14434 @cindex invocation of commands, modified
14435 @cindex commands for invoking other commands
14437 This section describes commands that run other commands in some context
14438 different than the current one: a modified environment, as a different
14442 * chroot invocation:: Modify the root directory.
14443 * env invocation:: Modify environment variables.
14444 * nice invocation:: Modify niceness.
14445 * nohup invocation:: Immunize to hangups.
14446 * stdbuf invocation:: Modify buffering of standard streams.
14447 * su invocation:: Modify user and group ID.
14448 * timeout invocation:: Run with time limit.
14452 @node chroot invocation
14453 @section @command{chroot}: Run a command with a different root directory
14456 @cindex running a program in a specified root directory
14457 @cindex root directory, running a program in a specified
14459 @command{chroot} runs a command with a specified root directory.
14460 On many systems, only the super-user can do this.@footnote{However,
14461 some systems (e.g., FreeBSD) can be configured to allow certain regular
14462 users to use the @code{chroot} system call, and hence to run this program.
14463 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14464 underlying function is non-privileged due to lack of support in MS-Windows.}
14468 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14469 chroot @var{option}
14472 Ordinarily, file names are looked up starting at the root of the
14473 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14474 the directory @var{newroot} (which must exist) and then runs
14475 @var{command} with optional @var{args}. If @var{command} is not
14476 specified, the default is the value of the @env{SHELL} environment
14477 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14478 @var{command} must not be a special built-in utility
14479 (@pxref{Special built-in utilities}).
14481 The program accepts the following options. Also see @ref{Common options}.
14482 Options must precede operands.
14486 @itemx --userspec=@var{user}[:@var{group}]
14487 @opindex --userspec
14488 By default, @var{command} is run with the same credentials
14489 as the invoking process.
14490 Use this option to run it as a different @var{user} and/or with a
14491 different primary @var{group}.
14493 @itemx --groups=@var{groups}
14495 Use this option to specify the supplementary @var{groups} to be
14496 used by the new process.
14497 The items in the list (names or numeric IDs) must be separated by commas.
14501 Here are a few tips to help avoid common problems in using chroot.
14502 To start with a simple example, make @var{command} refer to a statically
14503 linked binary. If you were to use a dynamically linked executable, then
14504 you'd have to arrange to have the shared libraries in the right place under
14505 your new root directory.
14507 For example, if you create a statically linked @command{ls} executable,
14508 and put it in @file{/tmp/empty}, you can run this command as root:
14511 $ chroot /tmp/empty /ls -Rl /
14514 Then you'll see output like this:
14519 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14522 If you want to use a dynamically linked executable, say @command{bash},
14523 then first run @samp{ldd bash} to see what shared objects it needs.
14524 Then, in addition to copying the actual binary, also copy the listed
14525 files to the required positions under your intended new root directory.
14526 Finally, if the executable requires any other files (e.g., data, state,
14527 device files), copy them into place, too.
14529 @cindex exit status of @command{chroot}
14533 125 if @command{chroot} itself fails
14534 126 if @var{command} is found but cannot be invoked
14535 127 if @var{command} cannot be found
14536 the exit status of @var{command} otherwise
14540 @node env invocation
14541 @section @command{env}: Run a command in a modified environment
14544 @cindex environment, running a program in a modified
14545 @cindex modified environment, running a program in a
14546 @cindex running a program in a modified environment
14548 @command{env} runs a command with a modified environment. Synopses:
14551 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14552 [@var{command} [@var{args}]@dots{}]
14556 Operands of the form @samp{@var{variable}=@var{value}} set
14557 the environment variable @var{variable} to value @var{value}.
14558 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14559 to an empty value is different from unsetting it.
14560 These operands are evaluated left-to-right, so if two operands
14561 mention the same variable the earlier is ignored.
14563 Environment variable names can be empty, and can contain any
14564 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14565 However, it is wise to limit yourself to names that
14566 consist solely of underscores, digits, and @acronym{ASCII} letters,
14567 and that begin with a non-digit, as applications like the shell do not
14568 work well with other names.
14571 The first operand that does not contain the character @samp{=}
14572 specifies the program to invoke; it is
14573 searched for according to the @env{PATH} environment variable. Any
14574 remaining arguments are passed as arguments to that program.
14575 The program should not be a special built-in utility
14576 (@pxref{Special built-in utilities}).
14578 Modifications to @env{PATH} take effect prior to searching for
14579 @var{command}. Use caution when reducing @env{PATH}; behavior is
14580 not portable when @env{PATH} is undefined or omits key directories
14581 such as @file{/bin}.
14583 In the rare case that a utility contains a @samp{=} in the name, the
14584 only way to disambiguate it from a variable assignment is to use an
14585 intermediate command for @var{command}, and pass the problematic
14586 program name via @var{args}. For example, if @file{./prog=} is an
14587 executable in the current @env{PATH}:
14590 env prog= true # runs 'true', with prog= in environment
14591 env ./prog= true # runs 'true', with ./prog= in environment
14592 env -- prog= true # runs 'true', with prog= in environment
14593 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14594 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14597 @cindex environment, printing
14599 If no command name is specified following the environment
14600 specifications, the resulting environment is printed. This is like
14601 specifying the @command{printenv} program.
14603 For some examples, suppose the environment passed to @command{env}
14604 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14605 @samp{PATH=.:/gnubin:/hacks}:
14610 Output the current environment.
14612 $ env | LC_ALL=C sort
14615 PATH=.:/gnubin:/hacks
14619 Run @command{foo} with a reduced environment, preserving only the
14620 original @env{PATH} to avoid problems in locating @command{foo}.
14622 env - PATH="$PATH" foo
14626 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14627 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14628 that @command{foo} was found in the file system rather than as a shell
14635 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14636 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14637 @samp{DISPLAY=gnu:0}.
14639 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14643 Attempt to run the program @command{/energy/--} (as that is the only
14644 possible path search result); if the command exists, the environment
14645 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14646 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14648 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14654 The program accepts the following options. Also see @ref{Common options}.
14655 Options must precede operands.
14661 @item -u @var{name}
14662 @itemx --unset=@var{name}
14665 Remove variable @var{name} from the environment, if it was in the
14670 @itemx --ignore-environment
14673 @opindex --ignore-environment
14674 Start with an empty environment, ignoring the inherited environment.
14678 @cindex exit status of @command{env}
14682 0 if no @var{command} is specified and the environment is output
14683 125 if @command{env} itself fails
14684 126 if @var{command} is found but cannot be invoked
14685 127 if @var{command} cannot be found
14686 the exit status of @var{command} otherwise
14690 @node nice invocation
14691 @section @command{nice}: Run a command with modified niceness
14695 @cindex scheduling, affecting
14696 @cindex appropriate privileges
14698 @command{nice} prints or modifies a process's @dfn{niceness},
14699 a parameter that affects whether the process is scheduled favorably.
14703 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14706 If no arguments are given, @command{nice} prints the current niceness.
14707 Otherwise, @command{nice} runs the given @var{command} with its
14708 niceness adjusted. By default, its niceness is incremented by 10.
14710 Niceness values range at least from @minus{}20 (process has high priority
14711 and gets more resources, thus slowing down other processes) through 19
14712 (process has lower priority and runs slowly itself, but has less impact
14713 on the speed of other running processes). Some systems
14714 may have a wider range of nicenesses; conversely, other systems may
14715 enforce more restrictive limits. An attempt to set the niceness
14716 outside the supported range is treated as an attempt to use the
14717 minimum or maximum supported value.
14719 A niceness should not be confused with a scheduling priority, which
14720 lets applications determine the order in which threads are scheduled
14721 to run. Unlike a priority, a niceness is merely advice to the
14722 scheduler, which the scheduler is free to ignore. Also, as a point of
14723 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14724 terms of a @dfn{nice value}, which is the nonnegative difference
14725 between a niceness and the minimum niceness. Though @command{nice}
14726 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14727 term ``niceness'' for compatibility with historical practice.
14729 @var{command} must not be a special built-in utility (@pxref{Special
14730 built-in utilities}).
14732 @mayConflictWithShellBuiltIn{nice}
14734 The program accepts the following option. Also see @ref{Common options}.
14735 Options must precede operands.
14738 @item -n @var{adjustment}
14739 @itemx --adjustment=@var{adjustment}
14741 @opindex --adjustment
14742 Add @var{adjustment} instead of 10 to the command's niceness. If
14743 @var{adjustment} is negative and you lack appropriate privileges,
14744 @command{nice} issues a warning but otherwise acts as if you specified
14747 For compatibility @command{nice} also supports an obsolete
14748 option syntax @option{-@var{adjustment}}. New scripts should use
14749 @option{-n @var{adjustment}} instead.
14753 @cindex exit status of @command{nice}
14757 0 if no @var{command} is specified and the niceness is output
14758 125 if @command{nice} itself fails
14759 126 if @var{command} is found but cannot be invoked
14760 127 if @var{command} cannot be found
14761 the exit status of @var{command} otherwise
14764 It is sometimes useful to run a non-interactive program with reduced niceness.
14767 $ nice factor 4611686018427387903
14770 Since @command{nice} prints the current niceness,
14771 you can invoke it through itself to demonstrate how it works.
14773 The default behavior is to increase the niceness by @samp{10}:
14784 The @var{adjustment} is relative to the current niceness. In the
14785 next example, the first @command{nice} invocation runs the second one
14786 with niceness 10, and it in turn runs the final one with a niceness
14790 $ nice nice -n 3 nice
14794 Specifying a niceness larger than the supported range
14795 is the same as specifying the maximum supported value:
14798 $ nice -n 10000000000 nice
14802 Only a privileged user may run a process with lower niceness:
14806 nice: cannot set niceness: Permission denied
14808 $ sudo nice -n -1 nice
14813 @node nohup invocation
14814 @section @command{nohup}: Run a command immune to hangups
14817 @cindex hangups, immunity to
14818 @cindex immunity to hangups
14819 @cindex logging out and continuing to run
14822 @command{nohup} runs the given @var{command} with hangup signals ignored,
14823 so that the command can continue running in the background after you log
14827 nohup @var{command} [@var{arg}]@dots{}
14830 If standard input is a terminal, it is redirected from
14831 @file{/dev/null} so that terminal sessions do not mistakenly consider
14832 the terminal to be used by the command. This is a @acronym{GNU}
14833 extension; programs intended to be portable to non-@acronym{GNU} hosts
14834 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14838 If standard output is a terminal, the command's standard output is appended
14839 to the file @file{nohup.out}; if that cannot be written to, it is appended
14840 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14841 command is not run.
14842 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14843 @command{nohup} is made readable and writable only to the user,
14844 regardless of the current umask settings.
14846 If standard error is a terminal, it is normally redirected to the same file
14847 descriptor as the (possibly-redirected) standard output.
14848 However, if standard output is closed, standard error terminal output
14849 is instead appended to the file @file{nohup.out} or
14850 @file{$HOME/nohup.out} as above.
14852 To capture the command's output to a file other than @file{nohup.out}
14853 you can redirect it. For example, to capture the output of
14857 nohup make > make.log
14860 @command{nohup} does not automatically put the command it runs in the
14861 background; you must do that explicitly, by ending the command line
14862 with an @samp{&}. Also, @command{nohup} does not alter the
14863 niceness of @var{command}; use @command{nice} for that,
14864 e.g., @samp{nohup nice @var{command}}.
14866 @var{command} must not be a special built-in utility (@pxref{Special
14867 built-in utilities}).
14869 The only options are @option{--help} and @option{--version}. @xref{Common
14870 options}. Options must precede operands.
14872 @cindex exit status of @command{nohup}
14876 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14877 126 if @var{command} is found but cannot be invoked
14878 127 if @var{command} cannot be found
14879 the exit status of @var{command} otherwise
14882 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
14886 @node stdbuf invocation
14887 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14890 @cindex standard streams, buffering
14891 @cindex line buffered
14893 @command{stdbuf} allows one to modify the buffering operations of the
14894 three standard I/O streams associated with a program. Synopsis:
14897 stdbuf @var{option}@dots{} @var{command}
14900 Any additional @var{arg}s are passed as additional arguments to the
14903 The program accepts the following options. Also see @ref{Common options}.
14907 @item -i @var{mode}
14908 @itemx --input=@var{mode}
14911 Adjust the standard input stream buffering.
14913 @item -o @var{mode}
14914 @itemx --output=@var{mode}
14917 Adjust the standard output stream buffering.
14919 @item -e @var{mode}
14920 @itemx --error=@var{mode}
14923 Adjust the standard error stream buffering.
14927 The @var{mode} can be specified as follows:
14932 Set the stream to line buffered mode.
14933 In this mode data is coalesced until a newline is output or
14934 input is read from any stream attached to a terminal device.
14935 This option is invalid with standard input.
14938 Disable buffering of the selected stream.
14939 In this mode data is output immediately and only the
14940 amount of data requested is read from input.
14943 Specify the size of the buffer to use in fully buffered mode.
14944 @multiplierSuffixesNoBlocks{size}
14948 NOTE: If @var{command} adjusts the buffering of its standard streams
14949 (@command{tee} does for e.g.) then that will override corresponding settings
14950 changed by @command{stdbuf}. Also some filters (like @command{dd} and
14951 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
14952 by @command{stdbuf} settings.
14954 @cindex exit status of @command{stdbuf}
14958 125 if @command{stdbuf} itself fails
14959 126 if @var{command} is found but cannot be invoked
14960 127 if @var{command} cannot be found
14961 the exit status of @var{command} otherwise
14965 @node su invocation
14966 @section @command{su}: Run a command with substitute user and group ID
14969 @cindex substitute user and group IDs
14970 @cindex user ID, switching
14971 @cindex super-user, becoming
14972 @cindex root, becoming
14974 @command{su} allows one user to temporarily become another user. It runs a
14975 command (often an interactive shell) with the real and effective user
14976 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
14979 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
14982 @cindex passwd entry, and @command{su} shell
14984 @flindex /etc/passwd
14985 If no @var{user} is given, the default is @code{root}, the super-user.
14986 The shell to use is taken from @var{user}'s @code{passwd} entry, or
14987 @file{/bin/sh} if none is specified there. If @var{user} has a
14988 password, @command{su} prompts for the password unless run by a user with
14989 effective user ID of zero (the super-user).
14995 @cindex login shell
14996 By default, @command{su} does not change the current directory.
14997 It sets the environment variables @env{HOME} and @env{SHELL}
14998 from the password entry for @var{user}, and if @var{user} is not
14999 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15000 By default, the shell is not a login shell.
15002 Any additional @var{arg}s are passed as additional arguments to the
15005 @cindex @option{-su}
15006 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15007 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15008 to certain shells, etc.).
15011 @command{su} can optionally be compiled to use @code{syslog} to report
15012 failed, and optionally successful, @command{su} attempts. (If the system
15013 supports @code{syslog}.) However, GNU @command{su} does not check if the
15014 user is a member of the @code{wheel} group; see below.
15016 The program accepts the following options. Also see @ref{Common options}.
15019 @item -c @var{command}
15020 @itemx --command=@var{command}
15023 Pass @var{command}, a single command line to run, to the shell with
15024 a @option{-c} option instead of starting an interactive shell.
15031 @cindex file name pattern expansion, disabled
15032 @cindex globbing, disabled
15033 Pass the @option{-f} option to the shell. This probably only makes sense
15034 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15035 option prevents reading the startup file (@file{.cshrc}). With
15036 Bourne-like shells, the @option{-f} option disables file name pattern
15037 expansion (globbing), which is not likely to be useful.
15045 @c other variables already indexed above
15048 @cindex login shell, creating
15049 Make the shell a login shell. This means the following. Unset all
15050 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15051 (which are set as described above), and @env{USER} and @env{LOGNAME}
15052 (which are set, even for the super-user, as described above), and set
15053 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15054 directory. Prepend @samp{-} to the shell's name, intended to make it
15055 read its login startup file(s).
15059 @itemx --preserve-environment
15062 @opindex --preserve-environment
15063 @cindex environment, preserving
15064 @flindex /etc/shells
15065 @cindex restricted shell
15066 Do not change the environment variables @env{HOME}, @env{USER},
15067 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15068 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15069 entry, unless the user running @command{su} is not the super-user and
15070 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15071 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15072 if that file does not exist. Parts of what this option does can be
15073 overridden by @option{--login} and @option{--shell}.
15075 @item -s @var{shell}
15076 @itemx --shell=@var{shell}
15079 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15080 unless the user running @command{su} is not the super-user and @var{user}'s
15081 shell is restricted (see @option{-m} just above).
15085 @cindex exit status of @command{su}
15089 125 if @command{su} itself fails
15090 126 if subshell is found but cannot be invoked
15091 127 if subshell cannot be found
15092 the exit status of the subshell otherwise
15095 @cindex wheel group, not supported
15096 @cindex group wheel, not supported
15098 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15100 (This section is by Richard Stallman.)
15104 Sometimes a few of the users try to hold total power over all the
15105 rest. For example, in 1984, a few users at the MIT AI lab decided to
15106 seize power by changing the operator password on the Twenex system and
15107 keeping it secret from everyone else. (I was able to thwart this coup
15108 and give power back to the users by patching the kernel, but I
15109 wouldn't know how to do that in Unix.)
15111 However, occasionally the rulers do tell someone. Under the usual
15112 @command{su} mechanism, once someone learns the root password who
15113 sympathizes with the ordinary users, he or she can tell the rest. The
15114 ``wheel group'' feature would make this impossible, and thus cement the
15115 power of the rulers.
15117 I'm on the side of the masses, not that of the rulers. If you are
15118 used to supporting the bosses and sysadmins in whatever they do, you
15119 might find this idea strange at first.
15122 @node timeout invocation
15123 @section @command{timeout}: Run a command with a time limit
15127 @cindex run commands with bounded time
15129 @command{timeout} runs the given @var{command} and kills it if it is
15130 still running after the specified time interval. Synopsis:
15133 timeout [@var{option}] @var{number}[smhd] @var{command} [@var{arg}]@dots{}
15137 @var{number} is an integer followed by an optional unit; the default
15138 is seconds. The units are:
15151 @var{command} must not be a special built-in utility (@pxref{Special
15152 built-in utilities}).
15154 The program accepts the following option. Also see @ref{Common options}.
15155 Options must precede operands.
15158 @item -s @var{signal}
15159 @itemx --signal=@var{signal}
15162 Send this @var{signal} to @var{command} on timeout, rather than the
15163 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15164 or a number. Also see @xref{Signal specifications}.
15168 @cindex exit status of @command{timeout}
15172 124 if @var{command} times out
15173 125 if @command{timeout} itself fails
15174 126 if @var{command} is found but cannot be invoked
15175 127 if @var{command} cannot be found
15176 the exit status of @var{command} otherwise
15180 @node Process control
15181 @chapter Process control
15183 @cindex processes, commands for controlling
15184 @cindex commands for controlling processes
15187 * kill invocation:: Sending a signal to processes.
15191 @node kill invocation
15192 @section @command{kill}: Send a signal to processes
15195 @cindex send a signal to processes
15197 The @command{kill} command sends a signal to processes, causing them
15198 to terminate or otherwise act upon receiving the signal in some way.
15199 Alternatively, it lists information about signals. Synopses:
15202 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15203 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15206 @mayConflictWithShellBuiltIn{kill}
15208 The first form of the @command{kill} command sends a signal to all
15209 @var{pid} arguments. The default signal to send if none is specified
15210 is @samp{TERM}. The special signal number @samp{0} does not denote a
15211 valid signal, but can be used to test whether the @var{pid} arguments
15212 specify processes to which a signal could be sent.
15214 If @var{pid} is positive, the signal is sent to the process with the
15215 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15216 processes in the process group of the current process. If @var{pid}
15217 is @minus{}1, the signal is sent to all processes for which the user has
15218 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15219 is sent to all processes in the process group that equals the absolute
15220 value of @var{pid}.
15222 If @var{pid} is not positive, a system-dependent set of system
15223 processes is excluded from the list of processes to which the signal
15226 If a negative @var{pid} argument is desired as the first one, it
15227 should be preceded by @option{--}. However, as a common extension to
15228 @acronym{POSIX}, @option{--} is not required with @samp{kill
15229 -@var{signal} -@var{pid}}. The following commands are equivalent:
15238 The first form of the @command{kill} command succeeds if every @var{pid}
15239 argument specifies at least one process that the signal was sent to.
15241 The second form of the @command{kill} command lists signal information.
15242 Either the @option{-l} or @option{--list} option, or the @option{-t}
15243 or @option{--table} option must be specified. Without any
15244 @var{signal} argument, all supported signals are listed. The output
15245 of @option{-l} or @option{--list} is a list of the signal names, one
15246 per line; if @var{signal} is already a name, the signal number is
15247 printed instead. The output of @option{-t} or @option{--table} is a
15248 table of signal numbers, names, and descriptions. This form of the
15249 @command{kill} command succeeds if all @var{signal} arguments are valid
15250 and if there is no output error.
15252 The @command{kill} command also supports the @option{--help} and
15253 @option{--version} options. @xref{Common options}.
15255 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15256 number like @samp{1}, or an exit status of a process terminated by the
15257 signal. A signal name can be given in canonical form or prefixed by
15258 @samp{SIG}. The case of the letters is ignored, except for the
15259 @option{-@var{signal}} option which must use upper case to avoid
15260 ambiguity with lower case option letters. For a list of supported
15261 signal names and numbers see @xref{Signal specifications}.
15266 @cindex delaying commands
15267 @cindex commands for delaying
15269 @c Perhaps @command{wait} or other commands should be described here also?
15272 * sleep invocation:: Delay for a specified time.
15276 @node sleep invocation
15277 @section @command{sleep}: Delay for a specified time
15280 @cindex delay for a specified time
15282 @command{sleep} pauses for an amount of time specified by the sum of
15283 the values of the command line arguments.
15287 sleep @var{number}[smhd]@dots{}
15291 Each argument is a number followed by an optional unit; the default
15292 is seconds. The units are:
15305 Historical implementations of @command{sleep} have required that
15306 @var{number} be an integer, and only accepted a single argument
15307 without a suffix. However, GNU @command{sleep} accepts
15308 arbitrary floating point numbers (using a period before any fractional
15311 The only options are @option{--help} and @option{--version}. @xref{Common
15314 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15315 @mayConflictWithShellBuiltIn{sleep}
15320 @node Numeric operations
15321 @chapter Numeric operations
15323 @cindex numeric operations
15324 These programs do numerically-related operations.
15327 * factor invocation:: Show factors of numbers.
15328 * seq invocation:: Print sequences of numbers.
15332 @node factor invocation
15333 @section @command{factor}: Print prime factors
15336 @cindex prime factors
15338 @command{factor} prints prime factors. Synopses:
15341 factor [@var{number}]@dots{}
15342 factor @var{option}
15345 If no @var{number} is specified on the command line, @command{factor} reads
15346 numbers from standard input, delimited by newlines, tabs, or spaces.
15348 The @command{factor} command supports only a small number of options:
15352 Print a short help on standard output, then exit without further
15356 Print the program version on standard output, then exit without further
15360 Factoring the product of the eighth and ninth Mersenne primes
15361 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15364 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15365 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15366 4951760154835678088235319297: 2147483647 2305843009213693951
15370 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15371 about 20 seconds on the same machine.
15373 Factoring large prime numbers is, in general, hard. The Pollard Rho
15374 algorithm used by @command{factor} is particularly effective for
15375 numbers with relatively small factors. If you wish to factor large
15376 numbers which do not have small factors (for example, numbers which
15377 are the product of two large primes), other methods are far better.
15379 If @command{factor} is built without using GNU MP, only
15380 single-precision arithmetic is available, and so large numbers
15381 (typically @math{2^{64}} and above) will not be supported. The single-precision
15382 code uses an algorithm which is designed for factoring smaller
15388 @node seq invocation
15389 @section @command{seq}: Print numeric sequences
15392 @cindex numeric sequences
15393 @cindex sequence of numbers
15395 @command{seq} prints a sequence of numbers to standard output. Synopses:
15398 seq [@var{option}]@dots{} @var{last}
15399 seq [@var{option}]@dots{} @var{first} @var{last}
15400 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15403 @command{seq} prints the numbers from @var{first} to @var{last} by
15404 @var{increment}. By default, each number is printed on a separate line.
15405 When @var{increment} is not specified, it defaults to @samp{1},
15406 even when @var{first} is larger than @var{last}.
15407 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15408 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15409 Floating-point numbers
15410 may be specified (using a period before any fractional digits).
15412 The program accepts the following options. Also see @ref{Common options}.
15413 Options must precede operands.
15416 @item -f @var{format}
15417 @itemx --format=@var{format}
15418 @opindex -f @var{format}
15419 @opindex --format=@var{format}
15420 @cindex formatting of numbers in @command{seq}
15421 Print all numbers using @var{format}.
15422 @var{format} must contain exactly one of the @samp{printf}-style
15423 floating point conversion specifications @samp{%a}, @samp{%e},
15424 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15425 The @samp{%} may be followed by zero or more flags taken from the set
15426 @samp{-+#0 '}, then an optional width containing one or more digits,
15427 then an optional precision consisting of a @samp{.} followed by zero
15428 or more digits. @var{format} may also contain any number of @samp{%%}
15429 conversion specifications. All conversion specifications have the
15430 same meaning as with @samp{printf}.
15432 The default format is derived from @var{first}, @var{step}, and
15433 @var{last}. If these all use a fixed point decimal representation,
15434 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15435 precision that can represent the output numbers exactly. Otherwise,
15436 the default format is @samp{%g}.
15438 @item -s @var{string}
15439 @itemx --separator=@var{string}
15440 @cindex separator for numbers in @command{seq}
15441 Separate numbers with @var{string}; default is a newline.
15442 The output always terminates with a newline.
15445 @itemx --equal-width
15446 Print all numbers with the same width, by padding with leading zeros.
15447 @var{first}, @var{step}, and @var{last} should all use a fixed point
15448 decimal representation.
15449 (To have other kinds of padding, use @option{--format}).
15453 You can get finer-grained control over output with @option{-f}:
15456 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15462 If you want hexadecimal integer output, you can use @command{printf}
15463 to perform the conversion:
15466 $ printf '%x\n' `seq 1048575 1024 1050623`
15472 For very long lists of numbers, use xargs to avoid
15473 system limitations on the length of an argument list:
15476 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15482 To generate octal output, use the printf @code{%o} format instead
15485 On most systems, seq can produce whole-number output for values up to
15486 at least @math{2^{53}}. Larger integers are approximated. The details
15487 differ depending on your floating-point implementation, but a common
15488 case is that @command{seq} works with integers through @math{2^{64}},
15489 and larger integers may not be numerically correct:
15492 $ seq 18446744073709551616 1 18446744073709551618
15493 18446744073709551616
15494 18446744073709551616
15495 18446744073709551618
15498 Be careful when using @command{seq} with outlandish values: otherwise
15499 you may see surprising results, as @command{seq} uses floating point
15500 internally. For example, on the x86 platform, where the internal
15501 representation uses a 64-bit fraction, the command:
15504 seq 1 0.0000000000000000001 1.0000000000000000009
15507 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15512 @node File permissions
15513 @chapter File permissions
15516 @include getdate.texi
15520 @node Opening the software toolbox
15521 @chapter Opening the Software Toolbox
15523 An earlier version of this chapter appeared in
15524 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15525 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15526 It was written by Arnold Robbins.
15529 * Toolbox introduction:: Toolbox introduction
15530 * I/O redirection:: I/O redirection
15531 * The who command:: The @command{who} command
15532 * The cut command:: The @command{cut} command
15533 * The sort command:: The @command{sort} command
15534 * The uniq command:: The @command{uniq} command
15535 * Putting the tools together:: Putting the tools together
15539 @node Toolbox introduction
15540 @unnumberedsec Toolbox Introduction
15542 This month's column is only peripherally related to the GNU Project, in
15543 that it describes a number of the GNU tools on your GNU/Linux system and how they
15544 might be used. What it's really about is the ``Software Tools'' philosophy
15545 of program development and usage.
15547 The software tools philosophy was an important and integral concept
15548 in the initial design and development of Unix (of which Linux and GNU are
15549 essentially clones). Unfortunately, in the modern day press of
15550 Internetworking and flashy GUIs, it seems to have fallen by the
15551 wayside. This is a shame, since it provides a powerful mental model
15552 for solving many kinds of problems.
15554 Many people carry a Swiss Army knife around in their pants pockets (or
15555 purse). A Swiss Army knife is a handy tool to have: it has several knife
15556 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15557 a number of other things on it. For the everyday, small miscellaneous jobs
15558 where you need a simple, general purpose tool, it's just the thing.
15560 On the other hand, an experienced carpenter doesn't build a house using
15561 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15562 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15563 exactly when and where to use each tool; you won't catch him hammering nails
15564 with the handle of his screwdriver.
15566 The Unix developers at Bell Labs were all professional programmers and trained
15567 computer scientists. They had found that while a one-size-fits-all program
15568 might appeal to a user because there's only one program to use, in practice
15573 difficult to write,
15576 difficult to maintain and
15580 difficult to extend to meet new situations.
15583 Instead, they felt that programs should be specialized tools. In short, each
15584 program ``should do one thing well.'' No more and no less. Such programs are
15585 simpler to design, write, and get right---they only do one thing.
15587 Furthermore, they found that with the right machinery for hooking programs
15588 together, that the whole was greater than the sum of the parts. By combining
15589 several special purpose programs, you could accomplish a specific task
15590 that none of the programs was designed for, and accomplish it much more
15591 quickly and easily than if you had to write a special purpose program.
15592 We will see some (classic) examples of this further on in the column.
15593 (An important additional point was that, if necessary, take a detour
15594 and build any software tools you may need first, if you don't already
15595 have something appropriate in the toolbox.)
15597 @node I/O redirection
15598 @unnumberedsec I/O Redirection
15600 Hopefully, you are familiar with the basics of I/O redirection in the
15601 shell, in particular the concepts of ``standard input,'' ``standard output,''
15602 and ``standard error''. Briefly, ``standard input'' is a data source, where
15603 data comes from. A program should not need to either know or care if the
15604 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15605 card reader. Similarly, ``standard output'' is a data sink, where data goes
15606 to. The program should neither know nor care where this might be.
15607 Programs that only read their standard input, do something to the data,
15608 and then send it on, are called @dfn{filters}, by analogy to filters in a
15611 With the Unix shell, it's very easy to set up data pipelines:
15614 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15617 We start out by creating the raw data; each filter applies some successive
15618 transformation to the data, until by the time it comes out of the pipeline,
15619 it is in the desired form.
15621 This is fine and good for standard input and standard output. Where does the
15622 standard error come in to play? Well, think about @command{filter1} in
15623 the pipeline above. What happens if it encounters an error in the data it
15624 sees? If it writes an error message to standard output, it will just
15625 disappear down the pipeline into @command{filter2}'s input, and the
15626 user will probably never see it. So programs need a place where they can send
15627 error messages so that the user will notice them. This is standard error,
15628 and it is usually connected to your console or window, even if you have
15629 redirected standard output of your program away from your screen.
15631 For filter programs to work together, the format of the data has to be
15632 agreed upon. The most straightforward and easiest format to use is simply
15633 lines of text. Unix data files are generally just streams of bytes, with
15634 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15635 conventionally called a ``newline'' in the Unix literature. (This is
15636 @code{'\n'} if you're a C programmer.) This is the format used by all
15637 the traditional filtering programs. (Many earlier operating systems
15638 had elaborate facilities and special purpose programs for managing
15639 binary data. Unix has always shied away from such things, under the
15640 philosophy that it's easiest to simply be able to view and edit your
15641 data with a text editor.)
15643 OK, enough introduction. Let's take a look at some of the tools, and then
15644 we'll see how to hook them together in interesting ways. In the following
15645 discussion, we will only present those command line options that interest
15646 us. As you should always do, double check your system documentation
15647 for the full story.
15649 @node The who command
15650 @unnumberedsec The @command{who} Command
15652 The first program is the @command{who} command. By itself, it generates a
15653 list of the users who are currently logged in. Although I'm writing
15654 this on a single-user system, we'll pretend that several people are
15659 @print{} arnold console Jan 22 19:57
15660 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15661 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15662 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15665 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15666 There are three people logged in, and I am logged in twice. On traditional
15667 Unix systems, user names are never more than eight characters long. This
15668 little bit of trivia will be useful later. The output of @command{who} is nice,
15669 but the data is not all that exciting.
15671 @node The cut command
15672 @unnumberedsec The @command{cut} Command
15674 The next program we'll look at is the @command{cut} command. This program
15675 cuts out columns or fields of input data. For example, we can tell it
15676 to print just the login name and full name from the @file{/etc/passwd}
15677 file. The @file{/etc/passwd} file has seven fields, separated by
15681 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15684 To get the first and fifth fields, we would use @command{cut} like this:
15687 $ cut -d: -f1,5 /etc/passwd
15688 @print{} root:Operator
15690 @print{} arnold:Arnold D. Robbins
15691 @print{} miriam:Miriam A. Robbins
15695 With the @option{-c} option, @command{cut} will cut out specific characters
15696 (i.e., columns) in the input lines. This is useful for input data
15697 that has fixed width fields, and does not have a field separator. For
15698 example, list the Monday dates for the current month:
15700 @c Is using cal ok? Looked at gcal, but I don't like it.
15711 @node The sort command
15712 @unnumberedsec The @command{sort} Command
15714 Next we'll look at the @command{sort} command. This is one of the most
15715 powerful commands on a Unix-style system; one that you will often find
15716 yourself using when setting up fancy data plumbing.
15719 command reads and sorts each file named on the command line. It then
15720 merges the sorted data and writes it to standard output. It will read
15721 standard input if no files are given on the command line (thus
15722 making it into a filter). The sort is based on the character collating
15723 sequence or based on user-supplied ordering criteria.
15726 @node The uniq command
15727 @unnumberedsec The @command{uniq} Command
15729 Finally (at least for now), we'll look at the @command{uniq} program. When
15730 sorting data, you will often end up with duplicate lines, lines that
15731 are identical. Usually, all you need is one instance of each line.
15732 This is where @command{uniq} comes in. The @command{uniq} program reads its
15733 standard input. It prints only one
15734 copy of each repeated line. It does have several options. Later on,
15735 we'll use the @option{-c} option, which prints each unique line, preceded
15736 by a count of the number of times that line occurred in the input.
15739 @node Putting the tools together
15740 @unnumberedsec Putting the Tools Together
15742 Now, let's suppose this is a large ISP server system with dozens of users
15743 logged in. The management wants the system administrator to write a program that will
15744 generate a sorted list of logged in users. Furthermore, even if a user
15745 is logged in multiple times, his or her name should only show up in the
15748 The administrator could sit down with the system documentation and write a C
15749 program that did this. It would take perhaps a couple of hundred lines
15750 of code and about two hours to write it, test it, and debug it.
15751 However, knowing the software toolbox, the administrator can instead start out
15752 by generating just a list of logged on users:
15762 Next, sort the list:
15765 $ who | cut -c1-8 | sort
15772 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15775 $ who | cut -c1-8 | sort | uniq
15781 The @command{sort} command actually has a @option{-u} option that does what
15782 @command{uniq} does. However, @command{uniq} has other uses for which one
15783 cannot substitute @samp{sort -u}.
15785 The administrator puts this pipeline into a shell script, and makes it available for
15786 all the users on the system (@samp{#} is the system administrator,
15787 or @code{root}, prompt):
15790 # cat > /usr/local/bin/listusers
15791 who | cut -c1-8 | sort | uniq
15793 # chmod +x /usr/local/bin/listusers
15796 There are four major points to note here. First, with just four
15797 programs, on one command line, the administrator was able to save about two
15798 hours worth of work. Furthermore, the shell pipeline is just about as
15799 efficient as the C program would be, and it is much more efficient in
15800 terms of programmer time. People time is much more expensive than
15801 computer time, and in our modern ``there's never enough time to do
15802 everything'' society, saving two hours of programmer time is no mean
15805 Second, it is also important to emphasize that with the
15806 @emph{combination} of the tools, it is possible to do a special
15807 purpose job never imagined by the authors of the individual programs.
15809 Third, it is also valuable to build up your pipeline in stages, as we did here.
15810 This allows you to view the data at each stage in the pipeline, which helps
15811 you acquire the confidence that you are indeed using these tools correctly.
15813 Finally, by bundling the pipeline in a shell script, other users can use
15814 your command, without having to remember the fancy plumbing you set up for
15815 them. In terms of how you run them, shell scripts and compiled programs are
15818 After the previous warm-up exercise, we'll look at two additional, more
15819 complicated pipelines. For them, we need to introduce two more tools.
15821 The first is the @command{tr} command, which stands for ``transliterate.''
15822 The @command{tr} command works on a character-by-character basis, changing
15823 characters. Normally it is used for things like mapping upper case to
15827 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15828 @print{} this example has mixed case!
15831 There are several options of interest:
15835 work on the complement of the listed characters, i.e.,
15836 operations apply to characters not in the given set
15839 delete characters in the first set from the output
15842 squeeze repeated characters in the output into just one character.
15845 We will be using all three options in a moment.
15847 The other command we'll look at is @command{comm}. The @command{comm}
15848 command takes two sorted input files as input data, and prints out the
15849 files' lines in three columns. The output columns are the data lines
15850 unique to the first file, the data lines unique to the second file, and
15851 the data lines that are common to both. The @option{-1}, @option{-2}, and
15852 @option{-3} command line options @emph{omit} the respective columns. (This is
15853 non-intuitive and takes a little getting used to.) For example:
15875 The file name @file{-} tells @command{comm} to read standard input
15876 instead of a regular file.
15878 Now we're ready to build a fancy pipeline. The first application is a word
15879 frequency counter. This helps an author determine if he or she is over-using
15882 The first step is to change the case of all the letters in our input file
15883 to one case. ``The'' and ``the'' are the same word when doing counting.
15886 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15889 The next step is to get rid of punctuation. Quoted words and unquoted words
15890 should be treated identically; it's easiest to just get the punctuation out of
15894 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15897 The second @command{tr} command operates on the complement of the listed
15898 characters, which are all the letters, the digits, the underscore, and
15899 the blank. The @samp{\n} represents the newline character; it has to
15900 be left alone. (The @acronym{ASCII} tab character should also be included for
15901 good measure in a production script.)
15903 At this point, we have data consisting of words separated by blank space.
15904 The words only contain alphanumeric characters (and the underscore). The
15905 next step is break the data apart so that we have one word per line. This
15906 makes the counting operation much easier, as we will see shortly.
15909 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15910 > tr -s ' ' '\n' | ...
15913 This command turns blanks into newlines. The @option{-s} option squeezes
15914 multiple newline characters in the output into just one. This helps us
15915 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
15916 This is what the shell prints when it notices you haven't finished
15917 typing in all of a command.)
15919 We now have data consisting of one word per line, no punctuation, all one
15920 case. We're ready to count each word:
15923 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15924 > tr -s ' ' '\n' | sort | uniq -c | ...
15927 At this point, the data might look something like this:
15940 The output is sorted by word, not by count! What we want is the most
15941 frequently used words first. Fortunately, this is easy to accomplish,
15942 with the help of two more @command{sort} options:
15946 do a numeric sort, not a textual one
15949 reverse the order of the sort
15952 The final pipeline looks like this:
15955 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15956 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
15965 Whew! That's a lot to digest. Yet, the same principles apply. With six
15966 commands, on two lines (really one long one split for convenience), we've
15967 created a program that does something interesting and useful, in much
15968 less time than we could have written a C program to do the same thing.
15970 A minor modification to the above pipeline can give us a simple spelling
15971 checker! To determine if you've spelled a word correctly, all you have to
15972 do is look it up in a dictionary. If it is not there, then chances are
15973 that your spelling is incorrect. So, we need a dictionary.
15974 The conventional location for a dictionary is @file{/usr/dict/words}.
15975 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
15976 revision of this article.}
15977 this is a sorted, 45,402 word dictionary.
15979 Now, how to compare our file with the dictionary? As before, we generate
15980 a sorted list of words, one per line:
15983 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15984 > tr -s ' ' '\n' | sort -u | ...
15987 Now, all we need is a list of words that are @emph{not} in the
15988 dictionary. Here is where the @command{comm} command comes in.
15991 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
15992 > tr -s ' ' '\n' | sort -u |
15993 > comm -23 - /usr/dict/words
15996 The @option{-2} and @option{-3} options eliminate lines that are only in the
15997 dictionary (the second file), and lines that are in both files. Lines
15998 only in the first file (standard input, our stream of words), are
15999 words that are not in the dictionary. These are likely candidates for
16000 spelling errors. This pipeline was the first cut at a production
16001 spelling checker on Unix.
16003 There are some other tools that deserve brief mention.
16007 search files for text that matches a regular expression
16010 count lines, words, characters
16013 a T-fitting for data pipes, copies data to files and to standard output
16016 the stream editor, an advanced tool
16019 a data manipulation language, another advanced tool
16022 The software tools philosophy also espoused the following bit of
16023 advice: ``Let someone else do the hard part.'' This means, take
16024 something that gives you most of what you need, and then massage it the
16025 rest of the way until it's in the form that you want.
16031 Each program should do one thing well. No more, no less.
16034 Combining programs with appropriate plumbing leads to results where
16035 the whole is greater than the sum of the parts. It also leads to novel
16036 uses of programs that the authors might never have imagined.
16039 Programs should never print extraneous header or trailer data, since these
16040 could get sent on down a pipeline. (A point we didn't mention earlier.)
16043 Let someone else do the hard part.
16046 Know your toolbox! Use each program appropriately. If you don't have an
16047 appropriate tool, build one.
16050 As of this writing, all the programs we've discussed are available via
16051 anonymous @command{ftp} from: @*
16052 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16053 be more recent versions available now.)
16055 None of what I have presented in this column is new. The Software Tools
16056 philosophy was first introduced in the book @cite{Software Tools}, by
16057 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16058 This book showed how to write and use software tools. It was written in
16059 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16060 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16061 was. The last chapter presented a @command{ratfor} to FORTRAN
16062 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16063 lot like C; if you know C, you won't have any problem following the
16066 In 1981, the book was updated and made available as @cite{Software Tools
16067 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16068 still in print and are well worth
16069 reading if you're a programmer. They certainly made a major change in
16070 how I view programming.
16072 The programs in both books are available from
16073 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16074 For a number of years, there was an active
16075 Software Tools Users Group, whose members had ported the original
16076 @command{ratfor} programs to essentially every computer system with a
16077 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16078 as Unix began to spread beyond universities.
16080 With the current proliferation of GNU code and other clones of Unix programs,
16081 these programs now receive little attention; modern C versions are
16082 much more efficient and do more than these programs do. Nevertheless, as
16083 exposition of good programming style, and evangelism for a still-valuable
16084 philosophy, these books are unparalleled, and I recommend them highly.
16086 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16087 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16089 @node GNU Free Documentation License
16090 @appendix GNU Free Documentation License
16094 @node Concept index
16101 @c Local variables:
16102 @c texinfo-column-for-description: 32