3 @setfilename coreutils.info
4 @settitle @sc{gnu} Coreutils
9 @include constants.texi
11 @c Define new indices.
15 @c Put everything in one index (arbitrarily chosen to be the concept index).
25 * Coreutils: (coreutils). Core GNU (file, text, shell) utilities.
26 * Common options: (coreutils)Common options. Common options.
27 * File permissions: (coreutils)File permissions. Access modes.
28 * Date input formats: (coreutils)Date input formats.
31 @c FIXME: the following need documentation
32 @c * [: (coreutils)[ invocation. File/string tests.
33 @c * pinky: (coreutils)pinky invocation. FIXME.
35 @dircategory Individual utilities
37 * arch: (coreutils)arch invocation. Print machine hardware name.
38 * base64: (coreutils)base64 invocation. Base64 encode/decode data.
39 * basename: (coreutils)basename invocation. Strip directory and suffix.
40 * cat: (coreutils)cat invocation. Concatenate and write files.
41 * chcon: (coreutils)chcon invocation. Change SELinux CTX of files.
42 * chgrp: (coreutils)chgrp invocation. Change file groups.
43 * chmod: (coreutils)chmod invocation. Change file permissions.
44 * chown: (coreutils)chown invocation. Change file owners/groups.
45 * chroot: (coreutils)chroot invocation. Specify the root directory.
46 * cksum: (coreutils)cksum invocation. Print POSIX CRC checksum.
47 * comm: (coreutils)comm invocation. Compare sorted files by line.
48 * cp: (coreutils)cp invocation. Copy files.
49 * csplit: (coreutils)csplit invocation. Split by context.
50 * cut: (coreutils)cut invocation. Print selected parts of lines.
51 * date: (coreutils)date invocation. Print/set system date and time.
52 * dd: (coreutils)dd invocation. Copy and convert a file.
53 * df: (coreutils)df invocation. Report file system disk usage.
54 * dir: (coreutils)dir invocation. List directories briefly.
55 * dircolors: (coreutils)dircolors invocation. Color setup for ls.
56 * dirname: (coreutils)dirname invocation. Strip last file name component.
57 * du: (coreutils)du invocation. Report on disk usage.
58 * echo: (coreutils)echo invocation. Print a line of text.
59 * env: (coreutils)env invocation. Modify the environment.
60 * expand: (coreutils)expand invocation. Convert tabs to spaces.
61 * expr: (coreutils)expr invocation. Evaluate expressions.
62 * factor: (coreutils)factor invocation. Print prime factors
63 * false: (coreutils)false invocation. Do nothing, unsuccessfully.
64 * fmt: (coreutils)fmt invocation. Reformat paragraph text.
65 * fold: (coreutils)fold invocation. Wrap long input lines.
66 * groups: (coreutils)groups invocation. Print group names a user is in.
67 * head: (coreutils)head invocation. Output the first part of files.
68 * hostid: (coreutils)hostid invocation. Print numeric host identifier.
69 * hostname: (coreutils)hostname invocation. Print or set system name.
70 * id: (coreutils)id invocation. Print user identity.
71 * install: (coreutils)install invocation. Copy and change attributes.
72 * join: (coreutils)join invocation. Join lines on a common field.
73 * kill: (coreutils)kill invocation. Send a signal to processes.
74 * link: (coreutils)link invocation. Make hard links between files.
75 * ln: (coreutils)ln invocation. Make links between files.
76 * logname: (coreutils)logname invocation. Print current login name.
77 * ls: (coreutils)ls invocation. List directory contents.
78 * md5sum: (coreutils)md5sum invocation. Print or check MD5 digests.
79 * mkdir: (coreutils)mkdir invocation. Create directories.
80 * mkfifo: (coreutils)mkfifo invocation. Create FIFOs (named pipes).
81 * mknod: (coreutils)mknod invocation. Create special files.
82 * mktemp: (coreutils)mktemp invocation. Create temporary files.
83 * mv: (coreutils)mv invocation. Rename files.
84 * nice: (coreutils)nice invocation. Modify niceness.
85 * nl: (coreutils)nl invocation. Number lines and write files.
86 * nohup: (coreutils)nohup invocation. Immunize to hangups.
87 * nproc: (coreutils)nproc invocation. Print the number of processors.
88 * od: (coreutils)od invocation. Dump files in octal, etc.
89 * paste: (coreutils)paste invocation. Merge lines of files.
90 * pathchk: (coreutils)pathchk invocation. Check file name portability.
91 * pr: (coreutils)pr invocation. Paginate or columnate files.
92 * printenv: (coreutils)printenv invocation. Print environment variables.
93 * printf: (coreutils)printf invocation. Format and print data.
94 * ptx: (coreutils)ptx invocation. Produce permuted indexes.
95 * pwd: (coreutils)pwd invocation. Print working directory.
96 * readlink: (coreutils)readlink invocation. Print referent of a symlink.
97 * rm: (coreutils)rm invocation. Remove files.
98 * rmdir: (coreutils)rmdir invocation. Remove empty directories.
99 * runcon: (coreutils)runcon invocation. Run in specified SELinux CTX.
100 * seq: (coreutils)seq invocation. Print numeric sequences
101 * sha1sum: (coreutils)sha1sum invocation. Print or check SHA-1 digests.
102 * sha2: (coreutils)sha2 utilities. Print or check SHA-2 digests.
103 * shred: (coreutils)shred invocation. Remove files more securely.
104 * shuf: (coreutils)shuf invocation. Shuffling text files.
105 * sleep: (coreutils)sleep invocation. Delay for a specified time.
106 * sort: (coreutils)sort invocation. Sort text files.
107 * split: (coreutils)split invocation. Split into fixed-size pieces.
108 * stat: (coreutils)stat invocation. Report file(system) status.
109 * stdbuf: (coreutils)stdbuf invocation. Modify stdio buffering.
110 * stty: (coreutils)stty invocation. Print/change terminal settings.
111 * su: (coreutils)su invocation. Modify user and group ID.
112 * sum: (coreutils)sum invocation. Print traditional checksum.
113 * sync: (coreutils)sync invocation. Synchronize memory and disk.
114 * tac: (coreutils)tac invocation. Reverse files.
115 * tail: (coreutils)tail invocation. Output the last part of files.
116 * tee: (coreutils)tee invocation. Redirect to multiple files.
117 * test: (coreutils)test invocation. File/string tests.
118 * timeout: (coreutils)timeout invocation. Run with time limit.
119 * touch: (coreutils)touch invocation. Change file timestamps.
120 * tr: (coreutils)tr invocation. Translate characters.
121 * true: (coreutils)true invocation. Do nothing, successfully.
122 * truncate: (coreutils)truncate invocation. Shrink/extend size of a file.
123 * tsort: (coreutils)tsort invocation. Topological sort.
124 * tty: (coreutils)tty invocation. Print terminal name.
125 * uname: (coreutils)uname invocation. Print system information.
126 * unexpand: (coreutils)unexpand invocation. Convert spaces to tabs.
127 * uniq: (coreutils)uniq invocation. Uniquify files.
128 * unlink: (coreutils)unlink invocation. Removal via unlink(2).
129 * uptime: (coreutils)uptime invocation. Print uptime and load.
130 * users: (coreutils)users invocation. Print current user names.
131 * vdir: (coreutils)vdir invocation. List directories verbosely.
132 * wc: (coreutils)wc invocation. Line, word, and byte counts.
133 * who: (coreutils)who invocation. Print who is logged in.
134 * whoami: (coreutils)whoami invocation. Print effective user ID.
135 * yes: (coreutils)yes invocation. Print a string indefinitely.
139 This manual documents version @value{VERSION} of the @sc{gnu} core
140 utilities, including the standard programs for text and file manipulation.
142 Copyright @copyright{} 1994-1996, 2000-2010 Free Software Foundation, Inc.
145 Permission is granted to copy, distribute and/or modify this document
146 under the terms of the GNU Free Documentation License, Version 1.3 or
147 any later version published by the Free Software Foundation; with no
148 Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
149 Texts. A copy of the license is included in the section entitled ``GNU
150 Free Documentation License''.
155 @title @sc{gnu} @code{Coreutils}
156 @subtitle Core GNU utilities
157 @subtitle for version @value{VERSION}, @value{UPDATED}
158 @author David MacKenzie et al.
161 @vskip 0pt plus 1filll
174 @cindex core utilities
175 @cindex text utilities
176 @cindex shell utilities
177 @cindex file utilities
180 * Introduction:: Caveats, overview, and authors
181 * Common options:: Common options
182 * Output of entire files:: cat tac nl od base64
183 * Formatting file contents:: fmt pr fold
184 * Output of parts of files:: head tail split csplit
185 * Summarizing files:: wc sum cksum md5sum sha1sum sha2
186 * Operating on sorted files:: sort shuf uniq comm ptx tsort
187 * Operating on fields:: cut paste join
188 * Operating on characters:: tr expand unexpand
189 * Directory listing:: ls dir vdir dircolors
190 * Basic operations:: cp dd install mv rm shred
191 * Special file types:: mkdir rmdir unlink mkfifo mknod ln link readlink
192 * Changing file attributes:: chgrp chmod chown touch
193 * Disk usage:: df du stat sync truncate
194 * Printing text:: echo printf yes
195 * Conditions:: false true test expr
197 * File name manipulation:: dirname basename pathchk mktemp
198 * Working context:: pwd stty printenv tty
199 * User information:: id logname whoami groups users who
200 * System context:: date arch nproc uname hostname hostid uptime
201 * SELinux context:: chcon runcon
202 * Modified command invocation:: chroot env nice nohup stdbuf su timeout
203 * Process control:: kill
205 * Numeric operations:: factor seq
206 * File permissions:: Access modes
207 * Date input formats:: Specifying date strings
208 * Opening the software toolbox:: The software tools philosophy
209 * GNU Free Documentation License:: Copying and sharing this manual
210 * Concept index:: General index
213 --- The Detailed Node Listing ---
217 * Exit status:: Indicating program success or failure
218 * Backup options:: Backup options
219 * Block size:: Block size
220 * Signal specifications:: Specifying signals
221 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
222 * Random sources:: Sources of random data
223 * Target directory:: Target directory
224 * Trailing slashes:: Trailing slashes
225 * Traversing symlinks:: Traversing symlinks to directories
226 * Treating / specially:: Treating / specially
227 * Standards conformance:: Standards conformance
229 Output of entire files
231 * cat invocation:: Concatenate and write files
232 * tac invocation:: Concatenate and write files in reverse
233 * nl invocation:: Number lines and write files
234 * od invocation:: Write files in octal or other formats
235 * base64 invocation:: Transform data into printable data
237 Formatting file contents
239 * fmt invocation:: Reformat paragraph text
240 * pr invocation:: Paginate or columnate files for printing
241 * fold invocation:: Wrap input lines to fit in specified width
243 Output of parts of files
245 * head invocation:: Output the first part of files
246 * tail invocation:: Output the last part of files
247 * split invocation:: Split a file into fixed-size pieces
248 * csplit invocation:: Split a file into context-determined pieces
252 * wc invocation:: Print newline, word, and byte counts
253 * sum invocation:: Print checksum and block counts
254 * cksum invocation:: Print CRC checksum and byte counts
255 * md5sum invocation:: Print or check MD5 digests
256 * sha1sum invocation:: Print or check SHA-1 digests
257 * sha2 utilities:: Print or check SHA-2 digests
259 Operating on sorted files
261 * sort invocation:: Sort text files
262 * shuf invocation:: Shuffle text files
263 * uniq invocation:: Uniquify files
264 * comm invocation:: Compare two sorted files line by line
265 * ptx invocation:: Produce a permuted index of file contents
266 * tsort invocation:: Topological sort
268 @command{ptx}: Produce permuted indexes
270 * General options in ptx:: Options which affect general program behavior
271 * Charset selection in ptx:: Underlying character set considerations
272 * Input processing in ptx:: Input fields, contexts, and keyword selection
273 * Output formatting in ptx:: Types of output format, and sizing the fields
274 * Compatibility in ptx:: The @acronym{GNU} extensions to @command{ptx}
278 * cut invocation:: Print selected parts of lines
279 * paste invocation:: Merge lines of files
280 * join invocation:: Join lines on a common field
282 Operating on characters
284 * tr invocation:: Translate, squeeze, and/or delete characters
285 * expand invocation:: Convert tabs to spaces
286 * unexpand invocation:: Convert spaces to tabs
288 @command{tr}: Translate, squeeze, and/or delete characters
290 * Character sets:: Specifying sets of characters
291 * Translating:: Changing one set of characters to another
292 * Squeezing:: Squeezing repeats and deleting
296 * ls invocation:: List directory contents
297 * dir invocation:: Briefly list directory contents
298 * vdir invocation:: Verbosely list directory contents
299 * dircolors invocation:: Color setup for @command{ls}
301 @command{ls}: List directory contents
303 * Which files are listed:: Which files are listed
304 * What information is listed:: What information is listed
305 * Sorting the output:: Sorting the output
306 * Details about version sort:: More details about version sort
307 * General output formatting:: General output formatting
308 * Formatting the file names:: Formatting the file names
312 * cp invocation:: Copy files and directories
313 * dd invocation:: Convert and copy a file
314 * install invocation:: Copy files and set attributes
315 * mv invocation:: Move (rename) files
316 * rm invocation:: Remove files or directories
317 * shred invocation:: Remove files more securely
321 * link invocation:: Make a hard link via the link syscall
322 * ln invocation:: Make links between files
323 * mkdir invocation:: Make directories
324 * mkfifo invocation:: Make FIFOs (named pipes)
325 * mknod invocation:: Make block or character special files
326 * readlink invocation:: Print value of a symlink or canonical file name
327 * rmdir invocation:: Remove empty directories
328 * unlink invocation:: Remove files via unlink syscall
330 Changing file attributes
332 * chown invocation:: Change file owner and group
333 * chgrp invocation:: Change group ownership
334 * chmod invocation:: Change access permissions
335 * touch invocation:: Change file timestamps
339 * df invocation:: Report file system disk space usage
340 * du invocation:: Estimate file space usage
341 * stat invocation:: Report file or file system status
342 * sync invocation:: Synchronize data on disk with memory
343 * truncate invocation:: Shrink or extend the size of a file
347 * echo invocation:: Print a line of text
348 * printf invocation:: Format and print data
349 * yes invocation:: Print a string until interrupted
353 * false invocation:: Do nothing, unsuccessfully
354 * true invocation:: Do nothing, successfully
355 * test invocation:: Check file types and compare values
356 * expr invocation:: Evaluate expressions
358 @command{test}: Check file types and compare values
360 * File type tests:: File type tests
361 * Access permission tests:: Access permission tests
362 * File characteristic tests:: File characteristic tests
363 * String tests:: String tests
364 * Numeric tests:: Numeric tests
366 @command{expr}: Evaluate expression
368 * String expressions:: + : match substr index length
369 * Numeric expressions:: + - * / %
370 * Relations for expr:: | & < <= = == != >= >
371 * Examples of expr:: Examples of using @command{expr}
375 * tee invocation:: Redirect output to multiple files or processes
377 File name manipulation
379 * basename invocation:: Strip directory and suffix from a file name
380 * dirname invocation:: Strip last file name component
381 * pathchk invocation:: Check file name validity and portability
382 * mktemp invocation:: Create temporary file or directory
386 * pwd invocation:: Print working directory
387 * stty invocation:: Print or change terminal characteristics
388 * printenv invocation:: Print all or some environment variables
389 * tty invocation:: Print file name of terminal on standard input
391 @command{stty}: Print or change terminal characteristics
393 * Control:: Control settings
394 * Input:: Input settings
395 * Output:: Output settings
396 * Local:: Local settings
397 * Combination:: Combination settings
398 * Characters:: Special characters
399 * Special:: Special settings
403 * id invocation:: Print user identity
404 * logname invocation:: Print current login name
405 * whoami invocation:: Print effective user ID
406 * groups invocation:: Print group names a user is in
407 * users invocation:: Print login names of users currently logged in
408 * who invocation:: Print who is currently logged in
412 * arch invocation:: Print machine hardware name
413 * date invocation:: Print or set system date and time
414 * nproc invocation:: Print the number of processors
415 * uname invocation:: Print system information
416 * hostname invocation:: Print or set system name
417 * hostid invocation:: Print numeric host identifier
418 * uptime invocation:: Print system uptime and load
420 @command{date}: Print or set system date and time
422 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
423 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
424 * Literal conversion specifiers:: %[%nt]
425 * Padding and other flags:: Pad with zeros, spaces, etc.
426 * Setting the time:: Changing the system clock
427 * Options for date:: Instead of the current time
428 * Date input formats:: Specifying date strings
429 * Examples of date:: Examples
433 * chcon invocation:: Change SELinux context of file
434 * runcon invocation:: Run a command in specified SELinux context
436 Modified command invocation
438 * chroot invocation:: Run a command with a different root directory
439 * env invocation:: Run a command in a modified environment
440 * nice invocation:: Run a command with modified niceness
441 * nohup invocation:: Run a command immune to hangups
442 * stdbuf invocation:: Run a command with modified I/O buffering
443 * su invocation:: Run a command with substitute user and group ID
444 * timeout invocation:: Run a command with a time limit
448 * kill invocation:: Sending a signal to processes.
452 * sleep invocation:: Delay for a specified time
456 * factor invocation:: Print prime factors
457 * seq invocation:: Print numeric sequences
461 * Mode Structure:: Structure of file mode bits
462 * Symbolic Modes:: Mnemonic representation of file mode bits
463 * Numeric Modes:: File mode bits as octal numbers
464 * Directory Setuid and Setgid:: Set-user-ID and set-group-ID on directories
468 * General date syntax:: Common rules
469 * Calendar date items:: 19 Dec 1994
470 * Time of day items:: 9:20pm
471 * Time zone items:: @sc{est}, @sc{pdt}, @sc{gmt}
472 * Day of week items:: Monday and others
473 * Relative items in date strings:: next tuesday, 2 years ago
474 * Pure numbers in date strings:: 19931219, 1440
475 * Seconds since the Epoch:: @@1078100502
476 * Specifying time zone rules:: TZ="America/New_York", TZ="UTC0"
477 * Authors of get_date:: Bellovin, Eggert, Salz, Berets, et al
479 Opening the software toolbox
481 * Toolbox introduction:: Toolbox introduction
482 * I/O redirection:: I/O redirection
483 * The who command:: The @command{who} command
484 * The cut command:: The @command{cut} command
485 * The sort command:: The @command{sort} command
486 * The uniq command:: The @command{uniq} command
487 * Putting the tools together:: Putting the tools together
491 * GNU Free Documentation License:: Copying and sharing this manual
498 @chapter Introduction
500 This manual is a work in progress: many sections make no attempt to explain
501 basic concepts in a way suitable for novices. Thus, if you are interested,
502 please get involved in improving this manual. The entire @sc{gnu} community
505 @cindex @acronym{POSIX}
506 The @sc{gnu} utilities documented here are mostly compatible with the
507 @acronym{POSIX} standard.
508 @cindex bugs, reporting
509 Please report bugs to @email{bug-coreutils@@gnu.org}. Remember
510 to include the version number, machine architecture, input files, and
511 any other information needed to reproduce the bug: your input, what you
512 expected, what you got, and why it is wrong. Diffs are welcome, but
513 please include a description of the problem as well, since this is
514 sometimes difficult to infer. @xref{Bugs, , , gcc, Using and Porting GNU CC}.
520 @cindex MacKenzie, D.
523 This manual was originally derived from the Unix man pages in the
524 distributions, which were written by David MacKenzie and updated by Jim
525 Meyering. What you are reading now is the authoritative documentation
526 for these utilities; the man pages are no longer being maintained. The
527 original @command{fmt} man page was written by Ross Paterson. Fran@,{c}ois
528 Pinard did the initial conversion to Texinfo format. Karl Berry did the
529 indexing, some reorganization, and editing of the results. Brian
530 Youmans of the Free Software Foundation office staff combined the
531 manuals for textutils, fileutils, and sh-utils to produce the present
532 omnibus manual. Richard Stallman contributed his usual invaluable
533 insights to the overall process.
536 @chapter Common options
540 @itemx @w{@kbd{--backup}[=@var{method}]}
543 @vindex VERSION_CONTROL
544 @cindex backups, making
545 @xref{Backup options}.
546 Make a backup of each file that would otherwise be overwritten or removed.
549 @macro optBackupSuffix
550 @item -S @var{suffix}
551 @itemx --suffix=@var{suffix}
554 Append @var{suffix} to each backup file made with @option{-b}.
555 @xref{Backup options}.
558 @macro optTargetDirectory
559 @item -t @var{directory}
560 @itemx @w{@kbd{--target-directory}=@var{directory}}
562 @opindex --target-directory
563 @cindex target directory
564 @cindex destination directory
565 Specify the destination @var{directory}.
566 @xref{Target directory}.
569 @macro optNoTargetDirectory
571 @itemx --no-target-directory
573 @opindex --no-target-directory
574 @cindex target directory
575 @cindex destination directory
576 Do not treat the last operand specially when it is a directory or a
577 symbolic link to a directory. @xref{Target directory}.
585 @cindex output @sc{nul}-byte-terminated lines
586 Output a zero byte (@acronym{ASCII} @sc{nul}) at the end of each line,
587 rather than a newline. This option enables other programs to parse the
588 output of @command{\cmd\} even when that output would contain data
589 with embedded newlines.
596 Append an SI-style abbreviation to each size, such as @samp{M} for
597 megabytes. Powers of 1000 are used, not 1024; @samp{M} stands for
598 1,000,000 bytes. This option is equivalent to
599 @option{--block-size=si}. Use the @option{-h} or
600 @option{--human-readable} option if
601 you prefer powers of 1024.
604 @macro optHumanReadable
606 @itemx --human-readable
608 @opindex --human-readable
609 @cindex human-readable output
610 Append a size letter to each size, such as @samp{M} for mebibytes.
611 Powers of 1024 are used, not 1000; @samp{M} stands for 1,048,576 bytes.
612 This option is equivalent to @option{--block-size=human-readable}.
613 Use the @option{--si} option if you prefer powers of 1000.
616 @macro optStripTrailingSlashes
617 @itemx @w{@kbd{--strip-trailing-slashes}}
618 @opindex --strip-trailing-slashes
619 @cindex stripping trailing slashes
620 Remove any trailing slashes from each @var{source} argument.
621 @xref{Trailing slashes}.
624 @macro mayConflictWithShellBuiltIn{cmd}
625 @cindex conflicts with shell built-ins
626 @cindex built-in shell commands, conflicts with
627 Due to shell aliases and built-in @command{\cmd\} command, using an
628 unadorned @command{\cmd\} interactively or in a script may get you
629 different functionality than that described here. Invoke it via
630 @command{env} (i.e., @code{env \cmd\ @dots{}}) to avoid interference
635 @macro multiplierSuffixes{varName}
636 @var{\varName\} may be, or may be an integer optionally followed by,
637 one of the following multiplicative suffixes:
639 @samp{b} => 512 ("blocks")
640 @samp{KB} => 1000 (KiloBytes)
641 @samp{K} => 1024 (KibiBytes)
642 @samp{MB} => 1000*1000 (MegaBytes)
643 @samp{M} => 1024*1024 (MebiBytes)
644 @samp{GB} => 1000*1000*1000 (GigaBytes)
645 @samp{G} => 1024*1024*1024 (GibiBytes)
647 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
650 @c FIXME: same as above, but no ``blocks'' line.
651 @macro multiplierSuffixesNoBlocks{varName}
652 @var{\varName\} may be, or may be an integer optionally followed by,
653 one of the following multiplicative suffixes:
655 @samp{KB} => 1000 (KiloBytes)
656 @samp{K} => 1024 (KibiBytes)
657 @samp{MB} => 1000*1000 (MegaBytes)
658 @samp{M} => 1024*1024 (MebiBytes)
659 @samp{GB} => 1000*1000*1000 (GigaBytes)
660 @samp{G} => 1024*1024*1024 (GibiBytes)
662 and so on for @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}.
665 @cindex common options
667 Certain options are available in all of these programs. Rather than
668 writing identical descriptions for each of the programs, they are
669 described here. (In fact, every @sc{gnu} program accepts (or should accept)
672 @vindex POSIXLY_CORRECT
673 Normally options and operands can appear in any order, and programs act
674 as if all the options appear before any operands. For example,
675 @samp{sort -r passwd -t :} acts like @samp{sort -r -t : passwd}, since
676 @samp{:} is an option-argument of @option{-t}. However, if the
677 @env{POSIXLY_CORRECT} environment variable is set, options must appear
678 before operands, unless otherwise specified for a particular command.
680 A few programs can usefully have trailing operands with leading
681 @samp{-}. With such a program, options must precede operands even if
682 @env{POSIXLY_CORRECT} is not set, and this fact is noted in the
683 program description. For example, the @command{env} command's options
684 must appear before its operands, since in some cases the operands
685 specify a command that itself contains options.
687 Most programs that accept long options recognize unambiguous
688 abbreviations of those options. For example, @samp{rmdir
689 --ignore-fail-on-non-empty} can be invoked as @samp{rmdir
690 --ignore-fail} or even @samp{rmdir --i}. Ambiguous options, such as
691 @samp{ls --h}, are identified as such.
693 Some of these programs recognize the @option{--help} and @option{--version}
694 options only when one of them is the sole command line argument. For
695 these programs, abbreviations of the long options are not always recognized.
702 Print a usage message listing all available options, then exit successfully.
706 @cindex version number, finding
707 Print the version number, then exit successfully.
711 @cindex option delimiter
712 Delimit the option list. Later arguments, if any, are treated as
713 operands even if they begin with @samp{-}. For example, @samp{sort --
714 -r} reads from the file named @file{-r}.
718 @cindex standard input
719 @cindex standard output
720 A single @samp{-} operand is not really an option, though it looks like one. It
721 stands for standard input, or for standard output if that is clear from
722 the context. For example, @samp{sort -} reads from standard input,
723 and is equivalent to plain @samp{sort}, and @samp{tee -} writes an
724 extra copy of its input to standard output. Unless otherwise
725 specified, @samp{-} can appear as any operand that requires a file
729 * Exit status:: Indicating program success or failure.
730 * Backup options:: -b -S, in some programs.
731 * Block size:: BLOCK_SIZE and --block-size, in some programs.
732 * Signal specifications:: Specifying signals using the --signal option.
733 * Disambiguating names and IDs:: chgrp and chown owner and group syntax
734 * Random sources:: --random-source, in some programs.
735 * Target directory:: Specifying a target directory, in some programs.
736 * Trailing slashes:: --strip-trailing-slashes, in some programs.
737 * Traversing symlinks:: -H, -L, or -P, in some programs.
738 * Treating / specially:: --preserve-root and --no-preserve-root.
739 * Special built-in utilities:: @command{break}, @command{:}, @command{eval}, @dots{}
740 * Standards conformance:: Conformance to the @acronym{POSIX} standard.
748 An exit status of zero indicates success,
749 and a nonzero value indicates failure.
752 Nearly every command invocation yields an integral @dfn{exit status}
753 that can be used to change how other commands work.
754 For the vast majority of commands, an exit status of zero indicates
755 success. Failure is indicated by a nonzero value---typically
756 @samp{1}, though it may differ on unusual platforms as @acronym{POSIX}
757 requires only that it be nonzero.
759 However, some of the programs documented here do produce
760 other exit status values and a few associate different
761 meanings with the values @samp{0} and @samp{1}.
762 Here are some of the exceptions:
763 @command{chroot}, @command{env}, @command{expr}, @command{nice},
764 @command{nohup}, @command{printenv}, @command{sort}, @command{stdbuf},
765 @command{su}, @command{test}, @command{timeout}, @command{tty}.
769 @section Backup options
771 @cindex backup options
773 Some @sc{gnu} programs (at least @command{cp}, @command{install},
774 @command{ln}, and @command{mv}) optionally make backups of files
775 before writing new versions.
776 These options control the details of these backups. The options are also
777 briefly mentioned in the descriptions of the particular programs.
782 @itemx @w{@kbd{--backup}[=@var{method}]}
785 @vindex VERSION_CONTROL
786 @cindex backups, making
787 Make a backup of each file that would otherwise be overwritten or removed.
788 Without this option, the original versions are destroyed.
789 Use @var{method} to determine the type of backups to make.
790 When this option is used but @var{method} is not specified,
791 then the value of the @env{VERSION_CONTROL}
792 environment variable is used. And if @env{VERSION_CONTROL} is not set,
793 the default backup type is @samp{existing}.
795 Note that the short form of this option, @option{-b} does not accept any
796 argument. Using @option{-b} is equivalent to using @option{--backup=existing}.
798 @vindex version-control @r{Emacs variable}
799 This option corresponds to the Emacs variable @samp{version-control};
800 the values for @var{method} are the same as those used in Emacs.
801 This option also accepts more descriptive names.
802 The valid @var{method}s are (unique abbreviations are accepted):
807 @opindex none @r{backup method}
812 @opindex numbered @r{backup method}
813 Always make numbered backups.
817 @opindex existing @r{backup method}
818 Make numbered backups of files that already have them, simple backups
823 @opindex simple @r{backup method}
824 Always make simple backups. Please note @samp{never} is not to be
825 confused with @samp{none}.
829 @item -S @var{suffix}
830 @itemx --suffix=@var{suffix}
833 @cindex backup suffix
834 @vindex SIMPLE_BACKUP_SUFFIX
835 Append @var{suffix} to each backup file made with @option{-b}. If this
836 option is not specified, the value of the @env{SIMPLE_BACKUP_SUFFIX}
837 environment variable is used. And if @env{SIMPLE_BACKUP_SUFFIX} is not
838 set, the default is @samp{~}, just as in Emacs.
847 Some @sc{gnu} programs (at least @command{df}, @command{du}, and
848 @command{ls}) display sizes in ``blocks''. You can adjust the block size
849 and method of display to make sizes easier to read. The block size
850 used for display is independent of any file system block size.
851 Fractional block counts are rounded up to the nearest integer.
853 @opindex --block-size=@var{size}
856 @vindex DF_BLOCK_SIZE
857 @vindex DU_BLOCK_SIZE
858 @vindex LS_BLOCK_SIZE
859 @vindex POSIXLY_CORRECT@r{, and block size}
861 The default block size is chosen by examining the following environment
862 variables in turn; the first one that is set determines the block size.
867 This specifies the default block size for the @command{df} command.
868 Similarly, @env{DU_BLOCK_SIZE} specifies the default for @command{du} and
869 @env{LS_BLOCK_SIZE} for @command{ls}.
872 This specifies the default block size for all three commands, if the
873 above command-specific environment variables are not set.
876 This specifies the default block size for all values that are normally
877 printed as blocks, if neither @env{BLOCK_SIZE} nor the above
878 command-specific environment variables are set. Unlike the other
879 environment variables, @env{BLOCKSIZE} does not affect values that are
880 normally printed as byte counts, e.g., the file sizes contained in
883 @item POSIXLY_CORRECT
884 If neither @env{@var{command}_BLOCK_SIZE}, nor @env{BLOCK_SIZE}, nor
885 @env{BLOCKSIZE} is set, but this variable is set, the block size
890 If none of the above environment variables are set, the block size
891 currently defaults to 1024 bytes in most contexts, but this number may
892 change in the future. For @command{ls} file sizes, the block size
895 @cindex human-readable output
898 A block size specification can be a positive integer specifying the number
899 of bytes per block, or it can be @code{human-readable} or @code{si} to
900 select a human-readable format. Integers may be followed by suffixes
901 that are upward compatible with the
902 @uref{http://www.bipm.fr/enus/3_SI/si-prefixes.html, SI prefixes}
903 for decimal multiples and with the
904 @uref{http://physics.nist.gov/cuu/Units/binary.html, IEC 60027-2
905 prefixes for binary multiples}.
907 With human-readable formats, output sizes are followed by a size letter
908 such as @samp{M} for megabytes. @code{BLOCK_SIZE=human-readable} uses
909 powers of 1024; @samp{M} stands for 1,048,576 bytes.
910 @code{BLOCK_SIZE=si} is similar, but uses powers of 1000 and appends
911 @samp{B}; @samp{MB} stands for 1,000,000 bytes.
914 A block size specification preceded by @samp{'} causes output sizes to
915 be displayed with thousands separators. The @env{LC_NUMERIC} locale
916 specifies the thousands separator and grouping. For example, in an
917 American English locale, @samp{--block-size="'1kB"} would cause a size
918 of 1234000 bytes to be displayed as @samp{1,234}. In the default C
919 locale, there is no thousands separator so a leading @samp{'} has no
922 An integer block size can be followed by a suffix to specify a
923 multiple of that size. A bare size letter,
924 or one followed by @samp{iB}, specifies
925 a multiple using powers of 1024. A size letter followed by @samp{B}
926 specifies powers of 1000 instead. For example, @samp{1M} and
927 @samp{1MiB} are equivalent to @samp{1048576}, whereas @samp{1MB} is
928 equivalent to @samp{1000000}.
930 A plain suffix without a preceding integer acts as if @samp{1} were
931 prepended, except that it causes a size indication to be appended to
932 the output. For example, @samp{--block-size="kB"} displays 3000 as
935 The following suffixes are defined. Large sizes like @code{1Y}
936 may be rejected by your computer due to limitations of its arithmetic.
940 @cindex kilobyte, definition of
941 kilobyte: @math{10^3 = 1000}.
945 @cindex kibibyte, definition of
946 kibibyte: @math{2^{10} = 1024}. @samp{K} is special: the SI prefix is
947 @samp{k} and the IEC 60027-2 prefix is @samp{Ki}, but tradition and
948 @acronym{POSIX} use @samp{k} to mean @samp{KiB}.
950 @cindex megabyte, definition of
951 megabyte: @math{10^6 = 1,000,000}.
954 @cindex mebibyte, definition of
955 mebibyte: @math{2^{20} = 1,048,576}.
957 @cindex gigabyte, definition of
958 gigabyte: @math{10^9 = 1,000,000,000}.
961 @cindex gibibyte, definition of
962 gibibyte: @math{2^{30} = 1,073,741,824}.
964 @cindex terabyte, definition of
965 terabyte: @math{10^{12} = 1,000,000,000,000}.
968 @cindex tebibyte, definition of
969 tebibyte: @math{2^{40} = 1,099,511,627,776}.
971 @cindex petabyte, definition of
972 petabyte: @math{10^{15} = 1,000,000,000,000,000}.
975 @cindex pebibyte, definition of
976 pebibyte: @math{2^{50} = 1,125,899,906,842,624}.
978 @cindex exabyte, definition of
979 exabyte: @math{10^{18} = 1,000,000,000,000,000,000}.
982 @cindex exbibyte, definition of
983 exbibyte: @math{2^{60} = 1,152,921,504,606,846,976}.
985 @cindex zettabyte, definition of
986 zettabyte: @math{10^{21} = 1,000,000,000,000,000,000,000}
989 @math{2^{70} = 1,180,591,620,717,411,303,424}.
990 (@samp{Zi} is a @acronym{GNU} extension to IEC 60027-2.)
992 @cindex yottabyte, definition of
993 yottabyte: @math{10^{24} = 1,000,000,000,000,000,000,000,000}.
996 @math{2^{80} = 1,208,925,819,614,629,174,706,176}.
997 (@samp{Yi} is a @acronym{GNU} extension to IEC 60027-2.)
1002 @opindex --block-size
1003 @opindex --human-readable
1006 Block size defaults can be overridden by an explicit
1007 @option{--block-size=@var{size}} option. The @option{-k}
1008 option is equivalent to @option{--block-size=1K}, which
1009 is the default unless the @env{POSIXLY_CORRECT} environment variable is
1010 set. The @option{-h} or @option{--human-readable} option is equivalent to
1011 @option{--block-size=human-readable}. The @option{--si} option is
1012 equivalent to @option{--block-size=si}.
1014 @node Signal specifications
1015 @section Signal specifications
1016 @cindex signals, specifying
1018 A @var{signal} may be a signal name like @samp{HUP}, or a signal
1019 number like @samp{1}, or an exit status of a process terminated by the
1020 signal. A signal name can be given in canonical form or prefixed by
1021 @samp{SIG}. The case of the letters is ignored. The following signal names
1022 and numbers are supported on all @acronym{POSIX} compliant systems:
1028 2. Terminal interrupt.
1034 9. Kill (cannot be caught or ignored).
1042 Other supported signal names have system-dependent corresponding
1043 numbers. All systems conforming to @acronym{POSIX} 1003.1-2001 also
1044 support the following signals:
1048 Access to an undefined portion of a memory object.
1050 Child process terminated, stopped, or continued.
1052 Continue executing, if stopped.
1054 Erroneous arithmetic operation.
1056 Illegal Instruction.
1058 Write on a pipe with no one to read it.
1060 Invalid memory reference.
1062 Stop executing (cannot be caught or ignored).
1066 Background process attempting read.
1068 Background process attempting write.
1070 High bandwidth data is available at a socket.
1072 User-defined signal 1.
1074 User-defined signal 2.
1078 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XSI} extension
1079 also support the following signals:
1085 Profiling timer expired.
1089 Trace/breakpoint trap.
1091 Virtual timer expired.
1093 CPU time limit exceeded.
1095 File size limit exceeded.
1099 @acronym{POSIX} 1003.1-2001 systems that support the @acronym{XRT} extension
1100 also support at least eight real-time signals called @samp{RTMIN},
1101 @samp{RTMIN+1}, @dots{}, @samp{RTMAX-1}, @samp{RTMAX}.
1103 @node Disambiguating names and IDs
1104 @section chown and chgrp: Disambiguating user names and IDs
1105 @cindex user names, disambiguating
1106 @cindex user IDs, disambiguating
1107 @cindex group names, disambiguating
1108 @cindex group IDs, disambiguating
1109 @cindex disambiguating group names and IDs
1111 Since the @var{owner} and @var{group} arguments to @command{chown} and
1112 @command{chgrp} may be specified as names or numeric IDs, there is an
1114 What if a user or group @emph{name} is a string of digits?
1115 @footnote{Using a number as a user name is common in some environments.}
1116 Should the command interpret it as a user name or as an ID?
1117 @acronym{POSIX} requires that @command{chown} and @command{chgrp}
1118 first attempt to resolve the specified string as a name, and
1119 only once that fails, then try to interpret it as an ID.
1120 This is troublesome when you want to specify a numeric ID, say 42,
1121 and it must work even in a pathological situation where
1122 @samp{42} is a user name that maps to some other user ID, say 1000.
1123 Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
1124 1000---not what you intended.
1126 GNU @command{chown} and @command{chgrp} provide a way to work around this,
1127 that at the same time may result in a significant performance improvement
1128 by eliminating a database look-up.
1129 Simply precede each numeric user ID and/or group ID with a @samp{+},
1130 in order to force its interpretation as an integer:
1134 chgrp +$numeric_group_id another-file
1138 GNU @command{chown} and @command{chgrp}
1139 skip the name look-up process for each @samp{+}-prefixed string,
1140 because a string containing @samp{+} is never a valid user or group name.
1141 This syntax is accepted on most common Unix systems, but not on Solaris 10.
1143 @node Random sources
1144 @section Sources of random data
1146 @cindex random sources
1148 The @command{shuf}, @command{shred}, and @command{sort} commands
1149 sometimes need random data to do their work. For example, @samp{sort
1150 -R} must choose a hash function at random, and it needs random data to
1151 make this selection.
1153 By default these commands use an internal pseudorandom generator
1154 initialized by a small amount of entropy, but can be directed to use
1155 an external source with the @option{--random-source=@var{file}} option.
1156 An error is reported if @var{file} does not contain enough bytes.
1158 For example, the device file @file{/dev/urandom} could be used as the
1159 source of random data. Typically, this device gathers environmental
1160 noise from device drivers and other sources into an entropy pool, and
1161 uses the pool to generate random bits. If the pool is short of data,
1162 the device reuses the internal pool to produce more bits, using a
1163 cryptographically secure pseudorandom number generator. But be aware
1164 that this device is not designed for bulk random data generation
1165 and is relatively slow.
1167 @file{/dev/urandom} suffices for most practical uses, but applications
1168 requiring high-value or long-term protection of private data may
1169 require an alternate data source like @file{/dev/random} or
1170 @file{/dev/arandom}. The set of available sources depends on your
1173 To reproduce the results of an earlier invocation of a command, you
1174 can save some random data into a file and then use that file as the
1175 random source in earlier and later invocations of the command.
1177 @node Target directory
1178 @section Target directory
1180 @cindex target directory
1182 The @command{cp}, @command{install}, @command{ln}, and @command{mv}
1183 commands normally treat the last operand specially when it is a
1184 directory or a symbolic link to a directory. For example, @samp{cp
1185 source dest} is equivalent to @samp{cp source dest/source} if
1186 @file{dest} is a directory. Sometimes this behavior is not exactly
1187 what is wanted, so these commands support the following options to
1188 allow more fine-grained control:
1193 @itemx --no-target-directory
1194 @opindex --no-target-directory
1195 @cindex target directory
1196 @cindex destination directory
1197 Do not treat the last operand specially when it is a directory or a
1198 symbolic link to a directory. This can help avoid race conditions in
1199 programs that operate in a shared area. For example, when the command
1200 @samp{mv /tmp/source /tmp/dest} succeeds, there is no guarantee that
1201 @file{/tmp/source} was renamed to @file{/tmp/dest}: it could have been
1202 renamed to @file{/tmp/dest/source} instead, if some other process
1203 created @file{/tmp/dest} as a directory. However, if @file{mv
1204 -T /tmp/source /tmp/dest} succeeds, there is no
1205 question that @file{/tmp/source} was renamed to @file{/tmp/dest}.
1207 In the opposite situation, where you want the last operand to be
1208 treated as a directory and want a diagnostic otherwise, you can use
1209 the @option{--target-directory} (@option{-t}) option.
1211 @item -t @var{directory}
1212 @itemx @w{@kbd{--target-directory}=@var{directory}}
1213 @opindex --target-directory
1214 @cindex target directory
1215 @cindex destination directory
1216 Use @var{directory} as the directory component of each destination
1219 The interface for most programs is that after processing options and a
1220 finite (possibly zero) number of fixed-position arguments, the remaining
1221 argument list is either expected to be empty, or is a list of items
1222 (usually files) that will all be handled identically. The @command{xargs}
1223 program is designed to work well with this convention.
1225 The commands in the @command{mv}-family are unusual in that they take
1226 a variable number of arguments with a special case at the @emph{end}
1227 (namely, the target directory). This makes it nontrivial to perform some
1228 operations, e.g., ``move all files from here to ../d/'', because
1229 @code{mv * ../d/} might exhaust the argument space, and @code{ls | xargs ...}
1230 doesn't have a clean way to specify an extra final argument for each
1231 invocation of the subject command. (It can be done by going through a
1232 shell command, but that requires more human labor and brain power than
1235 The @w{@kbd{--target-directory}} (@option{-t}) option allows the @command{cp},
1236 @command{install}, @command{ln}, and @command{mv} programs to be used
1237 conveniently with @command{xargs}. For example, you can move the files
1238 from the current directory to a sibling directory, @code{d} like this:
1241 ls | xargs mv -t ../d --
1244 However, this doesn't move files whose names begin with @samp{.}.
1245 If you use the @sc{gnu} @command{find} program, you can move those
1246 files too, with this command:
1249 find . -mindepth 1 -maxdepth 1 \
1253 But both of the above approaches fail if there are no files in the
1254 current directory, or if any file has a name containing a blank or
1255 some other special characters.
1256 The following example removes those limitations and requires both
1257 @sc{gnu} @command{find} and @sc{gnu} @command{xargs}:
1260 find . -mindepth 1 -maxdepth 1 -print0 \
1261 | xargs --null --no-run-if-empty \
1268 The @option{--target-directory} (@option{-t}) and
1269 @option{--no-target-directory} (@option{-T})
1270 options cannot be combined.
1272 @node Trailing slashes
1273 @section Trailing slashes
1275 @cindex trailing slashes
1277 Some @sc{gnu} programs (at least @command{cp} and @command{mv}) allow you to
1278 remove any trailing slashes from each @var{source} argument before
1279 operating on it. The @w{@kbd{--strip-trailing-slashes}} option enables
1282 This is useful when a @var{source} argument may have a trailing slash and
1283 @c FIXME: mv's behavior in this case is system-dependent
1284 specify a symbolic link to a directory. This scenario is in fact rather
1285 common because some shells can automatically append a trailing slash when
1286 performing file name completion on such symbolic links. Without this
1287 option, @command{mv}, for example, (via the system's rename function) must
1288 interpret a trailing slash as a request to dereference the symbolic link
1289 and so must rename the indirectly referenced @emph{directory} and not
1290 the symbolic link. Although it may seem surprising that such behavior
1291 be the default, it is required by @acronym{POSIX} and is consistent with
1292 other parts of that standard.
1294 @node Traversing symlinks
1295 @section Traversing symlinks
1297 @cindex symbolic link to directory, controlling traversal of
1299 The following options modify how @command{chown} and @command{chgrp}
1300 @c FIXME: note that `du' has these options, too, but they have slightly
1301 @c different meaning.
1302 traverse a hierarchy when the @option{--recursive} (@option{-R})
1303 option is also specified.
1304 If more than one of the following options is specified, only the final
1306 These options specify whether processing a symbolic link to a directory
1307 entails operating on just the symbolic link or on all files in the
1308 hierarchy rooted at that directory.
1310 These options are independent of @option{--dereference} and
1311 @option{--no-dereference} (@option{-h}), which control whether to modify
1312 a symlink or its referent.
1319 @cindex symbolic link to directory, traverse each that is specified on the command line
1320 If @option{--recursive} (@option{-R}) is specified and
1321 a command line argument is a symbolic link to a directory, traverse it.
1328 @cindex symbolic link to directory, traverse each that is encountered
1329 In a recursive traversal, traverse every symbolic link to a directory
1330 that is encountered.
1337 @cindex symbolic link to directory, never traverse
1338 Do not traverse any symbolic links.
1339 This is the default if none of @option{-H}, @option{-L},
1340 or @option{-P} is specified.
1347 @node Treating / specially
1348 @section Treating @file{/} specially
1350 Certain commands can operate destructively on entire hierarchies.
1351 For example, if a user with appropriate privileges mistakenly runs
1352 @samp{rm -rf / tmp/junk}, that may remove
1353 all files on the entire system. Since there are so few
1354 legitimate uses for such a command,
1355 @sc{gnu} @command{rm} normally declines to operate on any directory
1356 that resolves to @file{/}. If you really want to try to remove all
1357 the files on your system, you can use the @option{--no-preserve-root}
1358 option, but the default behavior, specified by the
1359 @option{--preserve-option}, is safer for most purposes.
1361 The commands @command{chgrp}, @command{chmod} and @command{chown}
1362 can also operate destructively on entire hierarchies, so they too
1363 support these options. Although, unlike @command{rm}, they don't
1364 actually unlink files, these commands are arguably more dangerous
1365 when operating recursively on @file{/}, since they often work much
1366 more quickly, and hence damage more files before an alert user can
1367 interrupt them. Tradition and @acronym{POSIX} require these commands
1368 to operate recursively on @file{/}, so they default to
1369 @option{--no-preserve-root}, but using the @option{--preserve-root}
1370 option makes them safer for most purposes. For convenience you can
1371 specify @option{--preserve-root} in an alias or in a shell function.
1373 Note that the @option{--preserve-root} option also ensures
1374 that @command{chgrp} and @command{chown} do not modify @file{/}
1375 even when dereferencing a symlink pointing to @file{/}.
1377 @node Special built-in utilities
1378 @section Special built-in utilities
1380 Some programs like @command{nice} can invoke other programs; for
1381 example, the command @samp{nice cat file} invokes the program
1382 @command{cat} by executing the command @samp{cat file}. However,
1383 @dfn{special built-in utilities} like @command{exit} cannot be invoked
1384 this way. For example, the command @samp{nice exit} does not have a
1385 well-defined behavior: it may generate an error message instead of
1388 Here is a list of the special built-in utilities that are standardized
1389 by @acronym{POSIX} 1003.1-2004.
1392 @t{.@: : break continue eval exec exit export readonly
1393 return set shift times trap unset}
1396 For example, because @samp{.}, @samp{:}, and @samp{exec} are special,
1397 the commands @samp{nice . foo.sh}, @samp{nice :}, and @samp{nice exec
1398 pwd} do not work as you might expect.
1400 Many shells extend this list. For example, Bash has several extra
1401 special built-in utilities like @command{history}, and
1402 @command{suspend}, and with Bash the command @samp{nice suspend}
1403 generates an error message instead of suspending.
1405 @node Standards conformance
1406 @section Standards conformance
1408 @vindex POSIXLY_CORRECT
1409 In a few cases, the @sc{gnu} utilities' default behavior is
1410 incompatible with the @acronym{POSIX} standard. To suppress these
1411 incompatibilities, define the @env{POSIXLY_CORRECT} environment
1412 variable. Unless you are checking for @acronym{POSIX} conformance, you
1413 probably do not need to define @env{POSIXLY_CORRECT}.
1415 Newer versions of @acronym{POSIX} are occasionally incompatible with older
1416 versions. For example, older versions of @acronym{POSIX} required the
1417 command @samp{sort +1} to sort based on the second and succeeding
1418 fields in each input line, but starting with @acronym{POSIX} 1003.1-2001
1419 the same command is required to sort the file named @file{+1}, and you
1420 must instead use the command @samp{sort -k 2} to get the field-based
1423 @vindex _POSIX2_VERSION
1424 The @sc{gnu} utilities normally conform to the version of @acronym{POSIX}
1425 that is standard for your system. To cause them to conform to a
1426 different version of @acronym{POSIX}, define the @env{_POSIX2_VERSION}
1427 environment variable to a value of the form @var{yyyymm} specifying
1428 the year and month the standard was adopted. Two values are currently
1429 supported for @env{_POSIX2_VERSION}: @samp{199209} stands for
1430 @acronym{POSIX} 1003.2-1992, and @samp{200112} stands for @acronym{POSIX}
1431 1003.1-2001. For example, if you have a newer system but are running software
1432 that assumes an older version of @acronym{POSIX} and uses @samp{sort +1}
1433 or @samp{tail +10}, you can work around any compatibility problems by setting
1434 @samp{_POSIX2_VERSION=199209} in your environment.
1436 @node Output of entire files
1437 @chapter Output of entire files
1439 @cindex output of entire files
1440 @cindex entire files, output of
1442 These commands read and write entire files, possibly transforming them
1446 * cat invocation:: Concatenate and write files.
1447 * tac invocation:: Concatenate and write files in reverse.
1448 * nl invocation:: Number lines and write files.
1449 * od invocation:: Write files in octal or other formats.
1450 * base64 invocation:: Transform data into printable data.
1453 @node cat invocation
1454 @section @command{cat}: Concatenate and write files
1457 @cindex concatenate and write files
1458 @cindex copying files
1460 @command{cat} copies each @var{file} (@samp{-} means standard input), or
1461 standard input if none are given, to standard output. Synopsis:
1464 cat [@var{option}] [@var{file}]@dots{}
1467 The program accepts the following options. Also see @ref{Common options}.
1475 Equivalent to @option{-vET}.
1478 @itemx --number-nonblank
1480 @opindex --number-nonblank
1481 Number all nonempty output lines, starting with 1.
1485 Equivalent to @option{-vE}.
1490 @opindex --show-ends
1491 Display a @samp{$} after the end of each line.
1497 Number all output lines, starting with 1.
1500 @itemx --squeeze-blank
1502 @opindex --squeeze-blank
1503 @cindex squeezing empty lines
1504 Suppress repeated adjacent empty lines; output just one empty line
1509 Equivalent to @option{-vT}.
1514 @opindex --show-tabs
1515 Display TAB characters as @samp{^I}.
1519 Ignored; for @acronym{POSIX} compatibility.
1522 @itemx --show-nonprinting
1524 @opindex --show-nonprinting
1525 Display control characters except for LFD and TAB using
1526 @samp{^} notation and precede characters that have the high bit set with
1531 On systems like MS-DOS that distinguish between text and binary files,
1532 @command{cat} normally reads and writes in binary mode. However,
1533 @command{cat} reads in text mode if one of the options
1534 @option{-bensAE} is used or if @command{cat} is reading from standard
1535 input and standard input is a terminal. Similarly, @command{cat}
1536 writes in text mode if one of the options @option{-bensAE} is used or
1537 if standard output is a terminal.
1544 # Output f's contents, then standard input, then g's contents.
1547 # Copy standard input to standard output.
1552 @node tac invocation
1553 @section @command{tac}: Concatenate and write files in reverse
1556 @cindex reversing files
1558 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1559 standard input if none are given, to standard output, reversing the
1560 records (lines by default) in each separately. Synopsis:
1563 tac [@var{option}]@dots{} [@var{file}]@dots{}
1566 @dfn{Records} are separated by instances of a string (newline by
1567 default). By default, this separator string is attached to the end of
1568 the record that it follows in the file.
1570 The program accepts the following options. Also see @ref{Common options}.
1578 The separator is attached to the beginning of the record that it
1579 precedes in the file.
1585 Treat the separator string as a regular expression. Users of @command{tac}
1586 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1587 binary mode, each line of a text file might end with a CR/LF pair
1588 instead of the Unix-style LF.
1590 @item -s @var{separator}
1591 @itemx --separator=@var{separator}
1593 @opindex --separator
1594 Use @var{separator} as the record separator, instead of newline.
1602 @section @command{nl}: Number lines and write files
1605 @cindex numbering lines
1606 @cindex line numbering
1608 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1609 standard input if none are given, to standard output, with line numbers
1610 added to some or all of the lines. Synopsis:
1613 nl [@var{option}]@dots{} [@var{file}]@dots{}
1616 @cindex logical pages, numbering on
1617 @command{nl} decomposes its input into (logical) pages; by default, the
1618 line number is reset to 1 at the top of each logical page. @command{nl}
1619 treats all of the input files as a single document; it does not reset
1620 line numbers or logical pages between files.
1622 @cindex headers, numbering
1623 @cindex body, numbering
1624 @cindex footers, numbering
1625 A logical page consists of three sections: header, body, and footer.
1626 Any of the sections can be empty. Each can be numbered in a different
1627 style from the others.
1629 The beginnings of the sections of logical pages are indicated in the
1630 input file by a line containing exactly one of these delimiter strings:
1641 The two characters from which these strings are made can be changed from
1642 @samp{\} and @samp{:} via options (see below), but the pattern and
1643 length of each string cannot be changed.
1645 A section delimiter is replaced by an empty line on output. Any text
1646 that comes before the first section delimiter string in the input file
1647 is considered to be part of a body section, so @command{nl} treats a
1648 file that contains no section delimiters as a single body section.
1650 The program accepts the following options. Also see @ref{Common options}.
1654 @item -b @var{style}
1655 @itemx --body-numbering=@var{style}
1657 @opindex --body-numbering
1658 Select the numbering style for lines in the body section of each
1659 logical page. When a line is not numbered, the current line number
1660 is not incremented, but the line number separator character is still
1661 prepended to the line. The styles are:
1667 number only nonempty lines (default for body),
1669 do not number lines (default for header and footer),
1671 number only lines that contain a match for the basic regular
1672 expression @var{bre}.
1673 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1677 @itemx --section-delimiter=@var{cd}
1679 @opindex --section-delimiter
1680 @cindex section delimiters of pages
1681 Set the section delimiter characters to @var{cd}; default is
1682 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1683 (Remember to protect @samp{\} or other metacharacters from shell
1684 expansion with quotes or extra backslashes.)
1686 @item -f @var{style}
1687 @itemx --footer-numbering=@var{style}
1689 @opindex --footer-numbering
1690 Analogous to @option{--body-numbering}.
1692 @item -h @var{style}
1693 @itemx --header-numbering=@var{style}
1695 @opindex --header-numbering
1696 Analogous to @option{--body-numbering}.
1698 @item -i @var{number}
1699 @itemx --line-increment=@var{number}
1701 @opindex --line-increment
1702 Increment line numbers by @var{number} (default 1).
1704 @item -l @var{number}
1705 @itemx --join-blank-lines=@var{number}
1707 @opindex --join-blank-lines
1708 @cindex empty lines, numbering
1709 @cindex blank lines, numbering
1710 Consider @var{number} (default 1) consecutive empty lines to be one
1711 logical line for numbering, and only number the last one. Where fewer
1712 than @var{number} consecutive empty lines occur, do not number them.
1713 An empty line is one that contains no characters, not even spaces
1716 @item -n @var{format}
1717 @itemx --number-format=@var{format}
1719 @opindex --number-format
1720 Select the line numbering format (default is @code{rn}):
1724 @opindex ln @r{format for @command{nl}}
1725 left justified, no leading zeros;
1727 @opindex rn @r{format for @command{nl}}
1728 right justified, no leading zeros;
1730 @opindex rz @r{format for @command{nl}}
1731 right justified, leading zeros.
1735 @itemx --no-renumber
1737 @opindex --no-renumber
1738 Do not reset the line number at the start of a logical page.
1740 @item -s @var{string}
1741 @itemx --number-separator=@var{string}
1743 @opindex --number-separator
1744 Separate the line number from the text line in the output with
1745 @var{string} (default is the TAB character).
1747 @item -v @var{number}
1748 @itemx --starting-line-number=@var{number}
1750 @opindex --starting-line-number
1751 Set the initial line number on each logical page to @var{number} (default 1).
1753 @item -w @var{number}
1754 @itemx --number-width=@var{number}
1756 @opindex --number-width
1757 Use @var{number} characters for line numbers (default 6).
1765 @section @command{od}: Write files in octal or other formats
1768 @cindex octal dump of files
1769 @cindex hex dump of files
1770 @cindex ASCII dump of files
1771 @cindex file contents, dumping unambiguously
1773 @command{od} writes an unambiguous representation of each @var{file}
1774 (@samp{-} means standard input), or standard input if none are given.
1778 od [@var{option}]@dots{} [@var{file}]@dots{}
1779 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1780 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1783 Each line of output consists of the offset in the input, followed by
1784 groups of data from the file. By default, @command{od} prints the offset in
1785 octal, and each group of file data is a C @code{short int}'s worth of input
1786 printed as a single octal number.
1788 If @var{offset} is given, it specifies how many input bytes to skip
1789 before formatting and writing. By default, it is interpreted as an
1790 octal number, but the optional trailing decimal point causes it to be
1791 interpreted as decimal. If no decimal is specified and the offset
1792 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1793 number. If there is a trailing @samp{b}, the number of bytes skipped
1794 will be @var{offset} multiplied by 512.
1796 If a command is of both the first and second forms, the second form is
1797 assumed if the last operand begins with @samp{+} or (if there are two
1798 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1799 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1802 The program accepts the following options. Also see @ref{Common options}.
1806 @item -A @var{radix}
1807 @itemx --address-radix=@var{radix}
1809 @opindex --address-radix
1810 @cindex radix for file offsets
1811 @cindex file offset radix
1812 Select the base in which file offsets are printed. @var{radix} can
1813 be one of the following:
1823 none (do not print offsets).
1826 The default is octal.
1828 @item -j @var{bytes}
1829 @itemx --skip-bytes=@var{bytes}
1831 @opindex --skip-bytes
1832 Skip @var{bytes} input bytes before formatting and writing. If
1833 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1834 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1836 @multiplierSuffixes{bytes}
1838 @item -N @var{bytes}
1839 @itemx --read-bytes=@var{bytes}
1841 @opindex --read-bytes
1842 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1843 @code{bytes} are interpreted as for the @option{-j} option.
1845 @item -S @var{bytes}
1846 @itemx --strings[=@var{bytes}]
1849 @cindex string constants, outputting
1850 Instead of the normal output, output only @dfn{string constants}: at
1851 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1852 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1853 Prefixes and suffixes on @code{bytes} are interpreted as for the
1856 If @var{n} is omitted with @option{--strings}, the default is 3.
1859 @itemx --format=@var{type}
1862 Select the format in which to output the file data. @var{type} is a
1863 string of one or more of the below type indicator characters. If you
1864 include more than one type indicator character in a single @var{type}
1865 string, or use this option more than once, @command{od} writes one copy
1866 of each output line using each of the data types that you specified,
1867 in the order that you specified.
1869 Adding a trailing ``z'' to any type specification appends a display
1870 of the @acronym{ASCII} character representation of the printable characters
1871 to the output line generated by the type specification.
1875 named character, ignoring high-order bit
1877 @acronym{ASCII} character or backslash escape,
1890 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1891 newline, and @samp{nul} for a zero byte. Only the least significant
1892 seven bits of each byte is used; the high-order bit is ignored.
1893 Type @code{c} outputs
1894 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1897 Except for types @samp{a} and @samp{c}, you can specify the number
1898 of bytes to use in interpreting each number in the given data type
1899 by following the type indicator character with a decimal integer.
1900 Alternately, you can specify the size of one of the C compiler's
1901 built-in data types by following the type indicator character with
1902 one of the following characters. For integers (@samp{d}, @samp{o},
1903 @samp{u}, @samp{x}):
1916 For floating point (@code{f}):
1928 @itemx --output-duplicates
1930 @opindex --output-duplicates
1931 Output consecutive lines that are identical. By default, when two or
1932 more consecutive output lines would be identical, @command{od} outputs only
1933 the first line, and puts just an asterisk on the following line to
1934 indicate the elision.
1937 @itemx --width[=@var{n}]
1940 Dump @code{n} input bytes per output line. This must be a multiple of
1941 the least common multiple of the sizes associated with the specified
1944 If this option is not given at all, the default is 16. If @var{n} is
1945 omitted, the default is 32.
1949 The next several options are shorthands for format specifications.
1950 @sc{gnu} @command{od} accepts any combination of shorthands and format
1951 specification options. These options accumulate.
1957 Output as named characters. Equivalent to @samp{-t a}.
1961 Output as octal bytes. Equivalent to @samp{-t o1}.
1965 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1970 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1974 Output as floats. Equivalent to @samp{-t fF}.
1978 Output as decimal ints. Equivalent to @samp{-t dI}.
1982 Output as decimal long ints. Equivalent to @samp{-t dL}.
1986 Output as octal two-byte units. Equivalent to @option{-t o2}.
1990 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1994 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1997 @opindex --traditional
1998 Recognize the non-option label argument that traditional @command{od}
1999 accepted. The following syntax:
2002 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2006 can be used to specify at most one file and optional arguments
2007 specifying an offset and a pseudo-start address, @var{label}.
2008 The @var{label} argument is interpreted
2009 just like @var{offset}, but it specifies an initial pseudo-address. The
2010 pseudo-addresses are displayed in parentheses following any normal
2017 @node base64 invocation
2018 @section @command{base64}: Transform data into printable data
2021 @cindex base64 encoding
2023 @command{base64} transforms data read from a file, or standard input,
2024 into (or from) base64 encoded form. The base64 encoded form uses
2025 printable @acronym{ASCII} characters to represent binary data.
2029 base64 [@var{option}]@dots{} [@var{file}]
2030 base64 --decode [@var{option}]@dots{} [@var{file}]
2033 The base64 encoding expands data to roughly 133% of the original.
2034 The format conforms to
2035 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2037 The program accepts the following options. Also see @ref{Common options}.
2042 @itemx --wrap=@var{cols}
2046 @cindex column to wrap data after
2047 During encoding, wrap lines after @var{cols} characters. This must be
2050 The default is to wrap after 76 characters. Use the value 0 to
2051 disable line wrapping altogether.
2057 @cindex Decode base64 data
2058 @cindex Base64 decoding
2059 Change the mode of operation, from the default of encoding data, to
2060 decoding data. Input is expected to be base64 encoded data, and the
2061 output will be the original data.
2064 @itemx --ignore-garbage
2066 @opindex --ignore-garbage
2067 @cindex Ignore garbage in base64 stream
2068 When decoding, newlines are always accepted.
2069 During decoding, ignore unrecognized bytes,
2070 to permit distorted data to be decoded.
2077 @node Formatting file contents
2078 @chapter Formatting file contents
2080 @cindex formatting file contents
2082 These commands reformat the contents of files.
2085 * fmt invocation:: Reformat paragraph text.
2086 * pr invocation:: Paginate or columnate files for printing.
2087 * fold invocation:: Wrap input lines to fit in specified width.
2091 @node fmt invocation
2092 @section @command{fmt}: Reformat paragraph text
2095 @cindex reformatting paragraph text
2096 @cindex paragraphs, reformatting
2097 @cindex text, reformatting
2099 @command{fmt} fills and joins lines to produce output lines of (at most)
2100 a given number of characters (75 by default). Synopsis:
2103 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2106 @command{fmt} reads from the specified @var{file} arguments (or standard
2107 input if none are given), and writes to standard output.
2109 By default, blank lines, spaces between words, and indentation are
2110 preserved in the output; successive input lines with different
2111 indentation are not joined; tabs are expanded on input and introduced on
2114 @cindex line-breaking
2115 @cindex sentences and line-breaking
2116 @cindex Knuth, Donald E.
2117 @cindex Plass, Michael F.
2118 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2119 avoid line breaks after the first word of a sentence or before the last
2120 word of a sentence. A @dfn{sentence break} is defined as either the end
2121 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2122 spaces or end of line, ignoring any intervening parentheses or quotes.
2123 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2124 breaks; the algorithm is a variant of that given by Donald E. Knuth
2125 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2126 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2129 The program accepts the following options. Also see @ref{Common options}.
2134 @itemx --crown-margin
2136 @opindex --crown-margin
2137 @cindex crown margin
2138 @dfn{Crown margin} mode: preserve the indentation of the first two
2139 lines within a paragraph, and align the left margin of each subsequent
2140 line with that of the second line.
2143 @itemx --tagged-paragraph
2145 @opindex --tagged-paragraph
2146 @cindex tagged paragraphs
2147 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2148 indentation of the first line of a paragraph is the same as the
2149 indentation of the second, the first line is treated as a one-line
2155 @opindex --split-only
2156 Split lines only. Do not join short lines to form longer ones. This
2157 prevents sample lines of code, and other such ``formatted'' text from
2158 being unduly combined.
2161 @itemx --uniform-spacing
2163 @opindex --uniform-spacing
2164 Uniform spacing. Reduce spacing between words to one space, and spacing
2165 between sentences to two spaces.
2168 @itemx -w @var{width}
2169 @itemx --width=@var{width}
2170 @opindex -@var{width}
2173 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2174 initially tries to make lines about 7% shorter than this, to give it
2175 room to balance line lengths.
2177 @item -p @var{prefix}
2178 @itemx --prefix=@var{prefix}
2179 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2180 are subject to formatting. The prefix and any preceding whitespace are
2181 stripped for the formatting and then re-attached to each formatted output
2182 line. One use is to format certain kinds of program comments, while
2183 leaving the code unchanged.
2191 @section @command{pr}: Paginate or columnate files for printing
2194 @cindex printing, preparing files for
2195 @cindex multicolumn output, generating
2196 @cindex merging files in parallel
2198 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2199 standard input if none are given, to standard output, paginating and
2200 optionally outputting in multicolumn format; optionally merges all
2201 @var{file}s, printing all in parallel, one per column. Synopsis:
2204 pr [@var{option}]@dots{} [@var{file}]@dots{}
2208 By default, a 5-line header is printed at each page: two blank lines;
2209 a line with the date, the file name, and the page count; and two more
2210 blank lines. A footer of five blank lines is also printed.
2211 The default @var{page_length} is 66
2212 lines. The default number of text lines is therefore 56.
2213 The text line of the header takes the form
2214 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2215 @var{string} so that the line takes up the full @var{page_width}. Here,
2216 @var{date} is the date (see the @option{-D} or @option{--date-format}
2217 option for details), @var{string} is the centered header string, and
2218 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2219 category affects the spelling of @var{page}; in the default C locale, it
2220 is @samp{Page @var{number}} where @var{number} is the decimal page
2223 Form feeds in the input cause page breaks in the output. Multiple form
2224 feeds produce empty pages.
2226 Columns are of equal width, separated by an optional string (default
2227 is @samp{space}). For multicolumn output, lines will always be truncated to
2228 @var{page_width} (default 72), unless you use the @option{-J} option.
2230 column output no line truncation occurs by default. Use @option{-W} option to
2231 truncate lines in that case.
2233 The following changes were made in version 1.22i and apply to later
2234 versions of @command{pr}:
2235 @c FIXME: this whole section here sounds very awkward to me. I
2236 @c made a few small changes, but really it all needs to be redone. - Brian
2237 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2242 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2243 redefined for better @acronym{POSIX} compliance. The output of some further
2244 cases has been adapted to other Unix systems. These changes are not
2245 compatible with earlier versions of the program.
2248 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2249 have been introduced to turn off unexpected interferences of small letter
2250 options. The @option{-N} option and the second argument @var{last_page}
2251 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2252 form feeds set in the input files requires the @option{-T} option.
2255 Capital letter options override small letter ones.
2258 Some of the option-arguments (compare @option{-s}, @option{-e},
2259 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2260 preceding option letter (already stated in the @acronym{POSIX} specification).
2263 The program accepts the following options. Also see @ref{Common options}.
2267 @item +@var{first_page}[:@var{last_page}]
2268 @itemx --pages=@var{first_page}[:@var{last_page}]
2269 @c The two following @opindex lines evoke warnings because they contain `:'
2270 @c The `info' spec does not permit that. If we use those lines, we end
2271 @c up with truncated index entries that don't work.
2272 @c @opindex +@var{first_page}[:@var{last_page}]
2273 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2274 @opindex +@var{page_range}
2275 @opindex --pages=@var{page_range}
2276 Begin printing with page @var{first_page} and stop with @var{last_page}.
2277 Missing @samp{:@var{last_page}} implies end of file. While estimating
2278 the number of skipped pages each form feed in the input file results
2279 in a new page. Page counting with and without @samp{+@var{first_page}}
2280 is identical. By default, counting starts with the first page of input
2281 file (not first page printed). Line numbering may be altered by @option{-N}
2285 @itemx --columns=@var{column}
2286 @opindex -@var{column}
2288 @cindex down columns
2289 With each single @var{file}, produce @var{column} columns of output
2290 (default is 1) and print columns down, unless @option{-a} is used. The
2291 column width is automatically decreased as @var{column} increases; unless
2292 you use the @option{-W/-w} option to increase @var{page_width} as well.
2293 This option might well cause some lines to be truncated. The number of
2294 lines in the columns on each page are balanced. The options @option{-e}
2295 and @option{-i} are on for multiple text-column output. Together with
2296 @option{-J} option column alignment and line truncation is turned off.
2297 Lines of full length are joined in a free field format and @option{-S}
2298 option may set field separators. @option{-@var{column}} may not be used
2299 with @option{-m} option.
2305 @cindex across columns
2306 With each single @var{file}, print columns across rather than down. The
2307 @option{-@var{column}} option must be given with @var{column} greater than one.
2308 If a line is too long to fit in a column, it is truncated.
2311 @itemx --show-control-chars
2313 @opindex --show-control-chars
2314 Print control characters using hat notation (e.g., @samp{^G}); print
2315 other nonprinting characters in octal backslash notation. By default,
2316 nonprinting characters are not changed.
2319 @itemx --double-space
2321 @opindex --double-space
2322 @cindex double spacing
2323 Double space the output.
2325 @item -D @var{format}
2326 @itemx --date-format=@var{format}
2327 @cindex time formats
2328 @cindex formatting times
2329 Format header dates using @var{format}, using the same conventions as
2330 for the command @samp{date +@var{format}}; @xref{date invocation}.
2331 Except for directives, which start with
2332 @samp{%}, characters in @var{format} are printed unchanged. You can use
2333 this option to specify an arbitrary string in place of the header date,
2334 e.g., @option{--date-format="Monday morning"}.
2336 @vindex POSIXLY_CORRECT
2338 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2339 @samp{2001-12-04 23:59});
2340 but if the @env{POSIXLY_CORRECT} environment variable is set
2341 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2342 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2343 @samp{Dec@ @ 4 23:59 2001}.
2346 Time stamps are listed according to the time zone rules specified by
2347 the @env{TZ} environment variable, or by the system default rules if
2348 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2349 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2351 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2352 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2354 @opindex --expand-tabs
2356 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2357 the input tab character (default is the TAB character). Second optional
2358 argument @var{in-tabwidth} is the input tab character's width (default
2366 @opindex --form-feed
2367 Use a form feed instead of newlines to separate output pages. This does
2368 not alter the default page length of 66 lines.
2370 @item -h @var{header}
2371 @itemx --header=@var{header}
2374 Replace the file name in the header with the centered string @var{header}.
2375 When using the shell, @var{header} should be quoted and should be
2376 separated from @option{-h} by a space.
2378 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2379 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2381 @opindex --output-tabs
2383 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2384 is the output tab character (default is the TAB character). Second optional
2385 argument @var{out-tabwidth} is the output tab character's width (default
2391 @opindex --join-lines
2392 Merge lines of full length. Used together with the column options
2393 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2394 @option{-W/-w} line truncation;
2395 no column alignment used; may be used with
2396 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2397 (together with @option{-W} and @option{--sep-string})
2398 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2399 @option{-s} along with the three column options.
2402 @item -l @var{page_length}
2403 @itemx --length=@var{page_length}
2406 Set the page length to @var{page_length} (default 66) lines, including
2407 the lines of the header [and the footer]. If @var{page_length} is less
2408 than or equal to 10, the header and footer are omitted, as if the
2409 @option{-t} option had been given.
2415 Merge and print all @var{file}s in parallel, one in each column. If a
2416 line is too long to fit in a column, it is truncated, unless the @option{-J}
2417 option is used. @option{--sep-string[=@var{string}]} may be used.
2419 some @var{file}s (form feeds set) produce empty columns, still marked
2420 by @var{string}. The result is a continuous line numbering and column
2421 marking throughout the whole merged file. Completely empty merged pages
2422 show no separators or line numbers. The default header becomes
2423 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2424 may be used with the @option{-h} or @option{--header} option to fill up
2425 the middle blank part.
2427 @item -n[@var{number-separator}[@var{digits}]]
2428 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2430 @opindex --number-lines
2431 Provide @var{digits} digit line numbering (default for @var{digits} is
2432 5). With multicolumn output the number occupies the first @var{digits}
2433 column positions of each text column or only each line of @option{-m}
2434 output. With single column output the number precedes each line just as
2435 @option{-m} does. Default counting of the line numbers starts with the
2436 first line of the input file (not the first line printed, compare the
2437 @option{--page} option and @option{-N} option).
2438 Optional argument @var{number-separator} is the character appended to
2439 the line number to separate it from the text followed. The default
2440 separator is the TAB character. In a strict sense a TAB is always
2441 printed with single column output only. The TAB width varies
2442 with the TAB position, e.g., with the left @var{margin} specified
2443 by @option{-o} option. With multicolumn output priority is given to
2444 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2445 The TAB width is fixed to the value of the first column and does
2446 not change with different values of left @var{margin}. That means a
2447 fixed number of spaces is always printed in the place of the
2448 @var{number-separator} TAB. The tabification depends upon the output
2451 @item -N @var{line_number}
2452 @itemx --first-line-number=@var{line_number}
2454 @opindex --first-line-number
2455 Start line counting with the number @var{line_number} at first line of
2456 first page printed (in most cases not the first line of the input file).
2458 @item -o @var{margin}
2459 @itemx --indent=@var{margin}
2462 @cindex indenting lines
2464 Indent each line with a margin @var{margin} spaces wide (default is zero).
2465 The total page width is the size of the margin plus the @var{page_width}
2466 set with the @option{-W/-w} option. A limited overflow may occur with
2467 numbered single column output (compare @option{-n} option).
2470 @itemx --no-file-warnings
2472 @opindex --no-file-warnings
2473 Do not print a warning message when an argument @var{file} cannot be
2474 opened. (The exit status will still be nonzero, however.)
2476 @item -s[@var{char}]
2477 @itemx --separator[=@var{char}]
2479 @opindex --separator
2480 Separate columns by a single character @var{char}. The default for
2481 @var{char} is the TAB character without @option{-w} and @samp{no
2482 character} with @option{-w}. Without @option{-s} the default separator
2483 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2484 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2485 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2488 @item -S@var{string}
2489 @itemx --sep-string[=@var{string}]
2491 @opindex --sep-string
2492 Use @var{string} to separate output columns. The @option{-S} option doesn't
2493 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2494 does not affect line truncation or column alignment.
2495 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2497 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2498 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2499 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2502 @itemx --omit-header
2504 @opindex --omit-header
2505 Do not print the usual header [and footer] on each page, and do not fill
2506 out the bottom of pages (with blank lines or a form feed). No page
2507 structure is produced, but form feeds set in the input files are retained.
2508 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2509 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2510 in the input file to 4 spaces but don't make any other changes. Use of
2511 @option{-t} overrides @option{-h}.
2514 @itemx --omit-pagination
2516 @opindex --omit-pagination
2517 Do not print header [and footer]. In addition eliminate all form feeds
2518 set in the input files.
2521 @itemx --show-nonprinting
2523 @opindex --show-nonprinting
2524 Print nonprinting characters in octal backslash notation.
2526 @item -w @var{page_width}
2527 @itemx --width=@var{page_width}
2530 Set page width to @var{page_width} characters for multiple text-column
2531 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2532 off the default page width and any line truncation and column alignment.
2533 Lines of full length are merged, regardless of the column options
2534 set. No @var{page_width} setting is possible with single column output.
2535 A @acronym{POSIX}-compliant formulation.
2537 @item -W @var{page_width}
2538 @itemx --page_width=@var{page_width}
2540 @opindex --page_width
2541 Set the page width to @var{page_width} characters. That's valid with and
2542 without a column option. Text lines are truncated, unless @option{-J}
2543 is used. Together with one of the three column options
2544 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2545 alignment is always used. The separator options @option{-S} or @option{-s}
2546 don't affect the @option{-W} option. Default is 72 characters. Without
2547 @option{-W @var{page_width}} and without any of the column options NO line
2548 truncation is used (defined to keep downward compatibility and to meet
2549 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2550 line is never truncated.
2557 @node fold invocation
2558 @section @command{fold}: Wrap input lines to fit in specified width
2561 @cindex wrapping long input lines
2562 @cindex folding long input lines
2564 @command{fold} writes each @var{file} (@option{-} means standard input), or
2565 standard input if none are given, to standard output, breaking long
2569 fold [@var{option}]@dots{} [@var{file}]@dots{}
2572 By default, @command{fold} breaks lines wider than 80 columns. The output
2573 is split into as many lines as necessary.
2575 @cindex screen columns
2576 @command{fold} counts screen columns by default; thus, a tab may count more
2577 than one column, backspace decreases the column count, and carriage
2578 return sets the column to zero.
2580 The program accepts the following options. Also see @ref{Common options}.
2588 Count bytes rather than columns, so that tabs, backspaces, and carriage
2589 returns are each counted as taking up one column, just like other
2596 Break at word boundaries: the line is broken after the last blank before
2597 the maximum line length. If the line contains no such blanks, the line
2598 is broken at the maximum line length as usual.
2600 @item -w @var{width}
2601 @itemx --width=@var{width}
2604 Use a maximum line length of @var{width} columns instead of 80.
2606 For compatibility @command{fold} supports an obsolete option syntax
2607 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2615 @node Output of parts of files
2616 @chapter Output of parts of files
2618 @cindex output of parts of files
2619 @cindex parts of files, output of
2621 These commands output pieces of the input.
2624 * head invocation:: Output the first part of files.
2625 * tail invocation:: Output the last part of files.
2626 * split invocation:: Split a file into fixed-size pieces.
2627 * csplit invocation:: Split a file into context-determined pieces.
2630 @node head invocation
2631 @section @command{head}: Output the first part of files
2634 @cindex initial part of files, outputting
2635 @cindex first part of files, outputting
2637 @command{head} prints the first part (10 lines by default) of each
2638 @var{file}; it reads from standard input if no files are given or
2639 when given a @var{file} of @option{-}. Synopsis:
2642 head [@var{option}]@dots{} [@var{file}]@dots{}
2645 If more than one @var{file} is specified, @command{head} prints a
2646 one-line header consisting of:
2649 ==> @var{file name} <==
2653 before the output for each @var{file}.
2655 The program accepts the following options. Also see @ref{Common options}.
2660 @itemx --bytes=@var{k}
2663 Print the first @var{k} bytes, instead of initial lines.
2664 However, if @var{k} starts with a @samp{-},
2665 print all but the last @var{k} bytes of each file.
2666 @multiplierSuffixes{k}
2669 @itemx --lines=@var{k}
2672 Output the first @var{k} lines.
2673 However, if @var{k} starts with a @samp{-},
2674 print all but the last @var{k} lines of each file.
2675 Size multiplier suffixes are the same as with the @option{-c} option.
2683 Never print file name headers.
2689 Always print file name headers.
2693 For compatibility @command{head} also supports an obsolete option syntax
2694 @option{-@var{count}@var{options}}, which is recognized only if it is
2695 specified first. @var{count} is a decimal number optionally followed
2696 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2697 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2698 Scripts intended for standard hosts should use @option{-c @var{count}}
2699 or @option{-n @var{count}} instead. If your script must also run on
2700 hosts that support only the obsolete syntax, it is usually simpler to
2701 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2707 @node tail invocation
2708 @section @command{tail}: Output the last part of files
2711 @cindex last part of files, outputting
2713 @command{tail} prints the last part (10 lines by default) of each
2714 @var{file}; it reads from standard input if no files are given or
2715 when given a @var{file} of @samp{-}. Synopsis:
2718 tail [@var{option}]@dots{} [@var{file}]@dots{}
2721 If more than one @var{file} is specified, @command{tail} prints a
2722 one-line header consisting of:
2725 ==> @var{file name} <==
2729 before the output for each @var{file}.
2731 @cindex BSD @command{tail}
2732 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2733 @command{tail} cannot). It also has no @option{-r} option (print in
2734 reverse), since reversing a file is really a different job from printing
2735 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2736 only reverse files that are at most as large as its buffer, which is
2737 typically 32 KiB@. A more reliable and versatile way to reverse files is
2738 the @sc{gnu} @command{tac} command.
2740 The program accepts the following options. Also see @ref{Common options}.
2745 @itemx --bytes=@var{k}
2748 Output the last @var{k} bytes, instead of final lines.
2749 However, if @var{k} starts with a @samp{+}, start printing with the
2750 @var{k}th byte from the start of each file, instead of from the end.
2751 @multiplierSuffixes{k}
2754 @itemx --follow[=@var{how}]
2757 @cindex growing files
2758 @vindex name @r{follow option}
2759 @vindex descriptor @r{follow option}
2760 Loop forever trying to read more characters at the end of the file,
2761 presumably because the file is growing.
2762 If more than one file is given, @command{tail} prints a header whenever it
2763 gets output from a different file, to indicate which file that output is
2766 There are two ways to specify how you'd like to track files with this option,
2767 but that difference is noticeable only when a followed file is removed or
2769 If you'd like to continue to track the end of a growing file even after
2770 it has been unlinked, use @option{--follow=descriptor}. This is the default
2771 behavior, but it is not useful if you're tracking a log file that may be
2772 rotated (removed or renamed, then reopened). In that case, use
2773 @option{--follow=name} to track the named file, perhaps by reopening it
2774 periodically to see if it has been removed and recreated by some other program.
2775 Note that the inotify-based implementation handles this case without
2776 the need for any periodic reopening.
2778 No matter which method you use, if the tracked file is determined to have
2779 shrunk, @command{tail} prints a message saying the file has been truncated
2780 and resumes tracking the end of the file from the newly-determined endpoint.
2782 When a file is removed, @command{tail}'s behavior depends on whether it is
2783 following the name or the descriptor. When following by name, tail can
2784 detect that a file has been removed and gives a message to that effect,
2785 and if @option{--retry} has been specified it will continue checking
2786 periodically to see if the file reappears.
2787 When following a descriptor, tail does not detect that the file has
2788 been unlinked or renamed and issues no message; even though the file
2789 may no longer be accessible via its original name, it may still be
2792 The option values @samp{descriptor} and @samp{name} may be specified only
2793 with the long form of the option, not with @option{-f}.
2795 The @option{-f} option is ignored if
2796 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2797 Likewise, the @option{-f} option has no effect for any
2798 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2802 This option is the same as @option{--follow=name --retry}. That is, tail
2803 will attempt to reopen a file when it is removed. Should this fail, tail
2804 will keep trying until it becomes accessible again.
2808 This option is useful mainly when following by name (i.e., with
2809 @option{--follow=name}).
2810 Without this option, when tail encounters a file that doesn't
2811 exist or is otherwise inaccessible, it reports that fact and
2812 never checks it again.
2814 @itemx --sleep-interval=@var{number}
2815 @opindex --sleep-interval
2816 Change the number of seconds to wait between iterations (the default is 1.0).
2817 During one iteration, every specified file is checked to see if it has
2819 Historical implementations of @command{tail} have required that
2820 @var{number} be an integer. However, GNU @command{tail} accepts
2821 an arbitrary floating point number (using a period before any
2824 @itemx --pid=@var{pid}
2826 When following by name or by descriptor, you may specify the process ID,
2827 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2828 after that process terminates, tail will also terminate. This will
2829 work properly only if the writer and the tailing process are running on
2830 the same machine. For example, to save the output of a build in a file
2831 and to watch the file grow, if you invoke @command{make} and @command{tail}
2832 like this then the tail process will stop when your build completes.
2833 Without this option, you would have had to kill the @code{tail -f}
2837 $ make >& makerr & tail --pid=$! -f makerr
2840 If you specify a @var{pid} that is not in use or that does not correspond
2841 to the process that is writing to the tailed files, then @command{tail}
2842 may terminate long before any @var{file}s stop growing or it may not
2843 terminate until long after the real writer has terminated.
2844 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2845 will print a warning if this is the case.
2847 @itemx --max-unchanged-stats=@var{n}
2848 @opindex --max-unchanged-stats
2849 When tailing a file by name, if there have been @var{n} (default
2850 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2851 iterations for which the file has not changed, then
2852 @code{open}/@code{fstat} the file to determine if that file name is
2853 still associated with the same device/inode-number pair as before.
2854 When following a log file that is rotated, this is approximately the
2855 number of seconds between when tail prints the last pre-rotation lines
2856 and when it prints the lines that have accumulated in the new log file.
2857 This option is meaningful only when following by name.
2860 @itemx --lines=@var{k}
2863 Output the last @var{k} lines.
2864 However, if @var{k} starts with a @samp{+}, start printing with the
2865 @var{k}th line from the start of each file, instead of from the end.
2866 Size multiplier suffixes are the same as with the @option{-c} option.
2874 Never print file name headers.
2880 Always print file name headers.
2884 For compatibility @command{tail} also supports an obsolete usage
2885 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2886 only if it does not conflict with the usage described
2887 above. This obsolete form uses exactly one option and at most one
2888 file. In the option, @var{count} is an optional decimal number optionally
2889 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2890 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2891 which has the same meaning as @option{-f}.
2893 @vindex _POSIX2_VERSION
2894 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2895 the obsolete option syntax with the same meaning as in counts, and
2896 obsolete usage overrides normal usage when the two conflict.
2897 This obsolete behavior can be enabled or disabled with the
2898 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2901 Scripts intended for use on standard hosts should avoid obsolete
2902 syntax and should use @option{-c @var{count}[b]}, @option{-n
2903 @var{count}}, and/or @option{-f} instead. If your script must also
2904 run on hosts that support only the obsolete syntax, you can often
2905 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2906 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2907 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2908 then @dots{}} to decide which syntax to use.
2910 Even if your script assumes the standard behavior, you should still
2911 beware usages whose behaviors differ depending on the @acronym{POSIX}
2912 version. For example, avoid @samp{tail - main.c}, since it might be
2913 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2914 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2915 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2916 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2921 @node split invocation
2922 @section @command{split}: Split a file into fixed-size pieces
2925 @cindex splitting a file into pieces
2926 @cindex pieces, splitting a file into
2928 @command{split} creates output files containing consecutive sections of
2929 @var{input} (standard input if none is given or @var{input} is
2930 @samp{-}). Synopsis:
2933 split [@var{option}] [@var{input} [@var{prefix}]]
2936 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2937 left over for the last section), into each output file.
2939 @cindex output file name prefix
2940 The output files' names consist of @var{prefix} (@samp{x} by default)
2941 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2942 default), such that concatenating the output files in traditional
2943 sorted order by file name produces
2944 the original input file. If the output file names are exhausted,
2945 @command{split} reports an error without deleting the output files
2948 The program accepts the following options. Also see @ref{Common options}.
2952 @item -l @var{lines}
2953 @itemx --lines=@var{lines}
2956 Put @var{lines} lines of @var{input} into each output file.
2958 For compatibility @command{split} also supports an obsolete
2959 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2960 @var{lines}} instead.
2963 @itemx --bytes=@var{size}
2966 Put @var{size} bytes of @var{input} into each output file.
2967 @multiplierSuffixes{size}
2970 @itemx --line-bytes=@var{size}
2972 @opindex --line-bytes
2973 Put into each output file as many complete lines of @var{input} as
2974 possible without exceeding @var{size} bytes. Individual lines longer than
2975 @var{size} bytes are broken into multiple files.
2976 @var{size} has the same format as for the @option{--bytes} option.
2978 @item -a @var{length}
2979 @itemx --suffix-length=@var{length}
2981 @opindex --suffix-length
2982 Use suffixes of length @var{length}. The default @var{length} is 2.
2985 @itemx --numeric-suffixes
2987 @opindex --numeric-suffixes
2988 Use digits in suffixes rather than lower-case letters.
2992 Write a diagnostic just before each output file is opened.
2999 @node csplit invocation
3000 @section @command{csplit}: Split a file into context-determined pieces
3003 @cindex context splitting
3004 @cindex splitting a file into pieces by context
3006 @command{csplit} creates zero or more output files containing sections of
3007 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3010 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3013 The contents of the output files are determined by the @var{pattern}
3014 arguments, as detailed below. An error occurs if a @var{pattern}
3015 argument refers to a nonexistent line of the input file (e.g., if no
3016 remaining line matches a given regular expression). After every
3017 @var{pattern} has been matched, any remaining input is copied into one
3020 By default, @command{csplit} prints the number of bytes written to each
3021 output file after it has been created.
3023 The types of pattern arguments are:
3028 Create an output file containing the input up to but not including line
3029 @var{n} (a positive integer). If followed by a repeat count, also
3030 create an output file containing the next @var{n} lines of the input
3031 file once for each repeat.
3033 @item /@var{regexp}/[@var{offset}]
3034 Create an output file containing the current line up to (but not
3035 including) the next line of the input file that contains a match for
3036 @var{regexp}. The optional @var{offset} is an integer.
3037 If it is given, the input up to (but not including) the
3038 matching line plus or minus @var{offset} is put into the output file,
3039 and the line after that begins the next section of input.
3041 @item %@var{regexp}%[@var{offset}]
3042 Like the previous type, except that it does not create an output
3043 file, so that section of the input file is effectively ignored.
3045 @item @{@var{repeat-count}@}
3046 Repeat the previous pattern @var{repeat-count} additional
3047 times. The @var{repeat-count} can either be a positive integer or an
3048 asterisk, meaning repeat as many times as necessary until the input is
3053 The output files' names consist of a prefix (@samp{xx} by default)
3054 followed by a suffix. By default, the suffix is an ascending sequence
3055 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3056 concatenating the output files in sorted order by file name produces the
3057 original input file.
3059 By default, if @command{csplit} encounters an error or receives a hangup,
3060 interrupt, quit, or terminate signal, it removes any output files
3061 that it has created so far before it exits.
3063 The program accepts the following options. Also see @ref{Common options}.
3067 @item -f @var{prefix}
3068 @itemx --prefix=@var{prefix}
3071 @cindex output file name prefix
3072 Use @var{prefix} as the output file name prefix.
3074 @item -b @var{suffix}
3075 @itemx --suffix=@var{suffix}
3078 @cindex output file name suffix
3079 Use @var{suffix} as the output file name suffix. When this option is
3080 specified, the suffix string must include exactly one
3081 @code{printf(3)}-style conversion specification, possibly including
3082 format specification flags, a field width, a precision specifications,
3083 or all of these kinds of modifiers. The format letter must convert a
3084 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3085 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3086 entire @var{suffix} is given (with the current output file number) to
3087 @code{sprintf(3)} to form the file name suffixes for each of the
3088 individual output files in turn. If this option is used, the
3089 @option{--digits} option is ignored.
3091 @item -n @var{digits}
3092 @itemx --digits=@var{digits}
3095 Use output file names containing numbers that are @var{digits} digits
3096 long instead of the default 2.
3101 @opindex --keep-files
3102 Do not remove output files when errors are encountered.
3105 @itemx --elide-empty-files
3107 @opindex --elide-empty-files
3108 Suppress the generation of zero-length output files. (In cases where
3109 the section delimiters of the input file are supposed to mark the first
3110 lines of each of the sections, the first output file will generally be a
3111 zero-length file unless you use this option.) The output file sequence
3112 numbers always run consecutively starting from 0, even when this option
3123 Do not print counts of output file sizes.
3129 Here is an example of its usage.
3130 First, create an empty directory for the exercise,
3137 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3140 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3146 Each number printed above is the size of an output
3147 file that csplit has just created.
3148 List the names of those output files:
3155 Use @command{head} to show their contents:
3180 @node Summarizing files
3181 @chapter Summarizing files
3183 @cindex summarizing files
3185 These commands generate just a few numbers representing entire
3189 * wc invocation:: Print newline, word, and byte counts.
3190 * sum invocation:: Print checksum and block counts.
3191 * cksum invocation:: Print CRC checksum and byte counts.
3192 * md5sum invocation:: Print or check MD5 digests.
3193 * sha1sum invocation:: Print or check SHA-1 digests.
3194 * sha2 utilities:: Print or check SHA-2 digests.
3199 @section @command{wc}: Print newline, word, and byte counts
3203 @cindex character count
3207 @command{wc} counts the number of bytes, characters, whitespace-separated
3208 words, and newlines in each given @var{file}, or standard input if none
3209 are given or for a @var{file} of @samp{-}. Synopsis:
3212 wc [@var{option}]@dots{} [@var{file}]@dots{}
3215 @cindex total counts
3216 @command{wc} prints one line of counts for each file, and if the file was
3217 given as an argument, it prints the file name following the counts. If
3218 more than one @var{file} is given, @command{wc} prints a final line
3219 containing the cumulative counts, with the file name @file{total}. The
3220 counts are printed in this order: newlines, words, characters, bytes,
3221 maximum line length.
3222 Each count is printed right-justified in a field with at least one
3223 space between fields so that the numbers and file names normally line
3224 up nicely in columns. The width of the count fields varies depending
3225 on the inputs, so you should not depend on a particular field width.
3226 However, as a @acronym{GNU} extension, if only one count is printed,
3227 it is guaranteed to be printed without leading spaces.
3229 By default, @command{wc} prints three counts: the newline, words, and byte
3230 counts. Options can specify that only certain counts be printed.
3231 Options do not undo others previously given, so
3238 prints both the byte counts and the word counts.
3240 With the @option{--max-line-length} option, @command{wc} prints the length
3241 of the longest line per file, and if there is more than one file it
3242 prints the maximum (not the sum) of those lengths. The line lengths here
3243 are measured in screen columns, according to the current locale and
3244 assuming tab positions in every 8th column.
3246 The program accepts the following options. Also see @ref{Common options}.
3254 Print only the byte counts.
3260 Print only the character counts.
3266 Print only the word counts.
3272 Print only the newline counts.
3275 @itemx --max-line-length
3277 @opindex --max-line-length
3278 Print only the maximum line lengths.
3280 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3281 @itemx --files0-from=@var{file}
3282 @opindex --files0-from=@var{file}
3283 @c This is commented out to avoid a texi2dvi failure.
3284 @c texi2dvi (GNU Texinfo 4.11) 1.104
3285 @c @cindex including files from @command{\cmd\}
3286 Disallow processing files named on the command line, and instead process
3287 those named in file @var{file}; each name being terminated by a zero byte
3288 (@acronym{ASCII} @sc{nul}).
3289 This is useful \withTotalOption\
3290 when the list of file names is so long that it may exceed a command line
3292 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3293 because it splits the list into pieces and makes @command{\cmd\} print
3294 \subListOutput\ for each sublist rather than for the entire list.
3295 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3296 @command{find}, using its @option{-print0} predicate.
3297 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3298 are read from standard input.
3300 @filesZeroFromOption{wc,,a total}
3302 For example, to find the length of the longest line in any @file{.c} or
3303 @file{.h} file in the current hierarchy, do this:
3306 find . -name '*.[ch]' -print0 |
3307 wc -L --files0-from=- | tail -n1
3315 @node sum invocation
3316 @section @command{sum}: Print checksum and block counts
3319 @cindex 16-bit checksum
3320 @cindex checksum, 16-bit
3322 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3323 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3326 sum [@var{option}]@dots{} [@var{file}]@dots{}
3329 @command{sum} prints the checksum for each @var{file} followed by the
3330 number of blocks in the file (rounded up). If more than one @var{file}
3331 is given, file names are also printed (by default). (With the
3332 @option{--sysv} option, corresponding file names are printed when there is
3333 at least one file argument.)
3335 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3336 compatible with BSD @command{sum} and prints file sizes in units of
3339 The program accepts the following options. Also see @ref{Common options}.
3345 @cindex BSD @command{sum}
3346 Use the default (BSD compatible) algorithm. This option is included for
3347 compatibility with the System V @command{sum}. Unless @option{-s} was also
3348 given, it has no effect.
3354 @cindex System V @command{sum}
3355 Compute checksums using an algorithm compatible with System V
3356 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3360 @command{sum} is provided for compatibility; the @command{cksum} program (see
3361 next section) is preferable in new applications.
3366 @node cksum invocation
3367 @section @command{cksum}: Print CRC checksum and byte counts
3370 @cindex cyclic redundancy check
3371 @cindex CRC checksum
3373 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3374 given @var{file}, or standard input if none are given or for a
3375 @var{file} of @samp{-}. Synopsis:
3378 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3381 @command{cksum} prints the CRC checksum for each file along with the number
3382 of bytes in the file, and the file name unless no arguments were given.
3384 @command{cksum} is typically used to ensure that files
3385 transferred by unreliable means (e.g., netnews) have not been corrupted,
3386 by comparing the @command{cksum} output for the received files with the
3387 @command{cksum} output for the original files (typically given in the
3390 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3391 compatible with the BSD or System V @command{sum} algorithms (see the
3392 previous section); it is more robust.
3394 The only options are @option{--help} and @option{--version}. @xref{Common
3400 @node md5sum invocation
3401 @section @command{md5sum}: Print or check MD5 digests
3405 @cindex 128-bit checksum
3406 @cindex checksum, 128-bit
3407 @cindex fingerprint, 128-bit
3408 @cindex message-digest, 128-bit
3410 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3411 @dfn{message-digest}) for each specified @var{file}.
3413 Note: The MD5 digest is more reliable than a simple CRC (provided by
3414 the @command{cksum} command) for detecting accidental file corruption,
3415 as the chances of accidentally having two files with identical MD5
3416 are vanishingly small. However, it should not be considered truly
3417 secure against malicious tampering: although finding a file with a
3418 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3419 considered infeasible at the moment, it is known how to produce
3420 different files with identical MD5 (a ``collision''), something which
3421 can be a security issue in certain contexts. For more secure hashes,
3422 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3423 @ref{sha2 utilities}.
3425 If a @var{file} is specified as @samp{-} or if no files are given
3426 @command{md5sum} computes the checksum for the standard input.
3427 @command{md5sum} can also determine whether a file and checksum are
3428 consistent. Synopsis:
3431 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3434 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3435 indicating a binary or text input file, and the file name.
3436 If @var{file} contains a backslash or newline, the
3437 line is started with a backslash, and each problematic character in
3438 the file name is escaped with a backslash, making the output
3439 unambiguous even in the presence of arbitrary file names.
3440 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3442 The program accepts the following options. Also see @ref{Common options}.
3450 @cindex binary input files
3451 Treat each input file as binary, by reading it in binary mode and
3452 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3453 On systems like @acronym{GNU} that do not distinguish between binary
3454 and text files, this option merely flags each input file as binary:
3455 the MD5 checksum is unaffected. This option is the default on systems
3456 like MS-DOS that distinguish between binary and text files, except
3457 for reading standard input when standard input is a terminal.
3461 Read file names and checksum information (not data) from each
3462 @var{file} (or from stdin if no @var{file} was specified) and report
3463 whether the checksums match the contents of the named files.
3464 The input to this mode of @command{md5sum} is usually the output of
3465 a prior, checksum-generating run of @samp{md5sum}.
3466 Each valid line of input consists of an MD5 checksum, a binary/text
3467 flag, and then a file name.
3468 Binary files are marked with @samp{*}, text with @samp{ }.
3469 For each such line, @command{md5sum} reads the named file and computes its
3470 MD5 checksum. Then, if the computed message digest does not match the
3471 one on the line with the file name, the file is noted as having
3472 failed the test. Otherwise, the file passes the test.
3473 By default, for each valid line, one line is written to standard
3474 output indicating whether the named file passed the test.
3475 After all checks have been performed, if there were any failures,
3476 a warning is issued to standard error.
3477 Use the @option{--status} option to inhibit that output.
3478 If any listed file cannot be opened or read, if any valid line has
3479 an MD5 checksum inconsistent with the associated file, or if no valid
3480 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3481 it exits successfully.
3485 @cindex verifying MD5 checksums
3486 This option is useful only when verifying checksums.
3487 When verifying checksums, don't generate an 'OK' message per successfully
3488 checked file. Files that fail the verification are reported in the
3489 default one-line-per-file format. If there is any checksum mismatch,
3490 print a warning summarizing the failures to standard error.
3494 @cindex verifying MD5 checksums
3495 This option is useful only when verifying checksums.
3496 When verifying checksums, don't generate the default one-line-per-file
3497 diagnostic and don't output the warning summarizing any failures.
3498 Failures to open or read a file still evoke individual diagnostics to
3500 If all listed files are readable and are consistent with the associated
3501 MD5 checksums, exit successfully. Otherwise exit with a status code
3502 indicating there was a failure.
3508 @cindex text input files
3509 Treat each input file as text, by reading it in text mode and
3510 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3511 This option is the default on systems like @acronym{GNU} that do not
3512 distinguish between binary and text files. On other systems, it is
3513 the default for reading standard input when standard input is a
3520 @cindex verifying MD5 checksums
3521 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3522 This option is useful only if all but a few lines in the checked input
3530 @node sha1sum invocation
3531 @section @command{sha1sum}: Print or check SHA-1 digests
3535 @cindex 160-bit checksum
3536 @cindex checksum, 160-bit
3537 @cindex fingerprint, 160-bit
3538 @cindex message-digest, 160-bit
3540 @command{sha1sum} computes a 160-bit checksum for each specified
3541 @var{file}. The usage and options of this command are precisely the
3542 same as for @command{md5sum}. @xref{md5sum invocation}.
3544 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3545 it are known (different files having the same fingerprint). However,
3546 it is known that they can be produced with considerable, but not
3547 unreasonable, resources. For this reason, it is generally considered
3548 that SHA-1 should be gradually phased out in favor of the more secure
3549 SHA-2 hash algorithms. @xref{sha2 utilities}.
3552 @node sha2 utilities
3553 @section sha2 utilities: Print or check SHA-2 digests
3560 @cindex 224-bit checksum
3561 @cindex 256-bit checksum
3562 @cindex 384-bit checksum
3563 @cindex 512-bit checksum
3564 @cindex checksum, 224-bit
3565 @cindex checksum, 256-bit
3566 @cindex checksum, 384-bit
3567 @cindex checksum, 512-bit
3568 @cindex fingerprint, 224-bit
3569 @cindex fingerprint, 256-bit
3570 @cindex fingerprint, 384-bit
3571 @cindex fingerprint, 512-bit
3572 @cindex message-digest, 224-bit
3573 @cindex message-digest, 256-bit
3574 @cindex message-digest, 384-bit
3575 @cindex message-digest, 512-bit
3577 The commands @command{sha224sum}, @command{sha256sum},
3578 @command{sha384sum} and @command{sha512sum} compute checksums of
3579 various lengths (respectively 224, 256, 384 and 512 bits),
3580 collectively known as the SHA-2 hashes. The usage and options of
3581 these commands are precisely the same as for @command{md5sum}.
3582 @xref{md5sum invocation}.
3584 Note: The SHA384 and SHA512 digests are considerably slower to
3585 compute, especially on 32-bit computers, than SHA224 or SHA256.
3588 @node Operating on sorted files
3589 @chapter Operating on sorted files
3591 @cindex operating on sorted files
3592 @cindex sorted files, operations on
3594 These commands work with (or produce) sorted files.
3597 * sort invocation:: Sort text files.
3598 * shuf invocation:: Shuffle text files.
3599 * uniq invocation:: Uniquify files.
3600 * comm invocation:: Compare two sorted files line by line.
3601 * ptx invocation:: Produce a permuted index of file contents.
3602 * tsort invocation:: Topological sort.
3606 @node sort invocation
3607 @section @command{sort}: Sort text files
3610 @cindex sorting files
3612 @command{sort} sorts, merges, or compares all the lines from the given
3613 files, or standard input if none are given or for a @var{file} of
3614 @samp{-}. By default, @command{sort} writes the results to standard
3618 sort [@var{option}]@dots{} [@var{file}]@dots{}
3621 @command{sort} has three modes of operation: sort (the default), merge,
3622 and check for sortedness. The following options change the operation
3629 @itemx --check=diagnose-first
3632 @cindex checking for sortedness
3633 Check whether the given file is already sorted: if it is not all
3634 sorted, print a diagnostic containing the first out-of-order line and
3635 exit with a status of 1.
3636 Otherwise, exit successfully.
3637 At most one input file can be given.
3640 @itemx --check=quiet
3641 @itemx --check=silent
3644 @cindex checking for sortedness
3645 Exit successfully if the given file is already sorted, and
3646 exit with status 1 otherwise.
3647 At most one input file can be given.
3648 This is like @option{-c}, except it does not print a diagnostic.
3654 @cindex merging sorted files
3655 Merge the given files by sorting them as a group. Each input file must
3656 always be individually sorted. It always works to sort instead of
3657 merge; merging is provided because it is faster, in the case where it
3662 @cindex sort stability
3663 @cindex sort's last-resort comparison
3664 A pair of lines is compared as follows:
3665 @command{sort} compares each pair of fields, in the
3666 order specified on the command line, according to the associated
3667 ordering options, until a difference is found or no fields are left.
3668 If no key fields are specified, @command{sort} uses a default key of
3669 the entire line. Finally, as a last resort when all keys compare
3670 equal, @command{sort} compares entire lines as if no ordering options
3671 other than @option{--reverse} (@option{-r}) were specified. The
3672 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3673 comparison} so that lines in which all fields compare equal are left
3674 in their original relative order. The @option{--unique}
3675 (@option{-u}) option also disables the last-resort comparison.
3679 Unless otherwise specified, all comparisons use the character collating
3680 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3681 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3682 to @samp{en_US}), then @command{sort} may produce output that is sorted
3683 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3684 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3685 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3686 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3687 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3688 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3689 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3691 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3692 limit on input line length or restrictions on bytes allowed within lines.
3693 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3694 @command{sort} silently supplies one. A line's trailing newline is not
3695 part of the line for comparison purposes.
3697 @cindex exit status of @command{sort}
3701 0 if no error occurred
3702 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3703 2 if an error occurred
3707 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3708 value as the directory for temporary files instead of @file{/tmp}. The
3709 @option{--temporary-directory} (@option{-T}) option in turn overrides
3710 the environment variable.
3712 The following options affect the ordering of output lines. They may be
3713 specified globally or as part of a specific key field. If no key
3714 fields are specified, global options apply to comparison of entire
3715 lines; otherwise the global options are inherited by key fields that do
3716 not specify any special options of their own. In pre-@acronym{POSIX}
3717 versions of @command{sort}, global options affect only later key fields,
3718 so portable shell scripts should specify global options first.
3723 @itemx --ignore-leading-blanks
3725 @opindex --ignore-leading-blanks
3726 @cindex blanks, ignoring leading
3728 Ignore leading blanks when finding sort keys in each line.
3729 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3730 can change this. Note blanks may be ignored by your locale's collating
3731 rules, but without this option they will be significant for character
3732 positions specified in keys with the @option{-k} option.
3735 @itemx --dictionary-order
3737 @opindex --dictionary-order
3738 @cindex dictionary order
3739 @cindex phone directory order
3740 @cindex telephone directory order
3742 Sort in @dfn{phone directory} order: ignore all characters except
3743 letters, digits and blanks when sorting.
3744 By default letters and digits are those of @acronym{ASCII} and a blank
3745 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3748 @itemx --ignore-case
3750 @opindex --ignore-case
3751 @cindex ignoring case
3752 @cindex case folding
3754 Fold lowercase characters into the equivalent uppercase characters when
3755 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3756 The @env{LC_CTYPE} locale determines character types.
3757 When used with @option{--unique} those lower case equivalent lines are
3758 thrown away. (There is currently no way to throw away the upper case
3759 equivalent instead. (Any @option{--reverse} given would only affect
3760 the final result, after the throwing away.))
3763 @itemx --general-numeric-sort
3764 @itemx --sort=general-numeric
3766 @opindex --general-numeric-sort
3768 @cindex general numeric sort
3770 Sort numerically, using the standard C function @code{strtod} to convert
3771 a prefix of each line to a double-precision floating point number.
3772 This allows floating point numbers to be specified in scientific notation,
3773 like @code{1.0e-34} and @code{10e100}.
3774 The @env{LC_NUMERIC} locale determines the decimal-point character.
3775 Do not report overflow, underflow, or conversion errors.
3776 Use the following collating sequence:
3780 Lines that do not start with numbers (all considered to be equal).
3782 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3783 in a consistent but machine-dependent order.
3787 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3792 Use this option only if there is no alternative; it is much slower than
3793 @option{--numeric-sort} (@option{-n}) and it can lose information when
3794 converting to floating point.
3797 @itemx --human-numeric-sort
3798 @itemx --sort=human-numeric
3800 @opindex --human-numeric-sort
3802 @cindex human numeric sort
3804 Sort numerically, as per the @option{--numeric-sort} option below, and in
3805 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3806 Note a mixture of IEC and SI suffixes is not supported and will
3807 be flagged as an error. Also the numbers must be abbreviated uniformly.
3808 I.E. values with different precisions like 6000K and 5M will be sorted
3812 @itemx --ignore-nonprinting
3814 @opindex --ignore-nonprinting
3815 @cindex nonprinting characters, ignoring
3816 @cindex unprintable characters, ignoring
3818 Ignore nonprinting characters.
3819 The @env{LC_CTYPE} locale determines character types.
3820 This option has no effect if the stronger @option{--dictionary-order}
3821 (@option{-d}) option is also given.
3827 @opindex --month-sort
3829 @cindex months, sorting by
3831 An initial string, consisting of any amount of blanks, followed
3832 by a month name abbreviation, is folded to UPPER case and
3833 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3834 Invalid names compare low to valid names. The @env{LC_TIME} locale
3835 category determines the month spellings.
3836 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3840 @itemx --numeric-sort
3841 @itemx --sort=numeric
3843 @opindex --numeric-sort
3845 @cindex numeric sort
3847 Sort numerically. The number begins each line and consists
3848 of optional blanks, an optional @samp{-} sign, and zero or more
3849 digits possibly separated by thousands separators, optionally followed
3850 by a decimal-point character and zero or more digits. An empty
3851 number is treated as @samp{0}. The @env{LC_NUMERIC}
3852 locale specifies the decimal-point character and thousands separator.
3853 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3856 Comparison is exact; there is no rounding error.
3858 Neither a leading @samp{+} nor exponential notation is recognized.
3859 To compare such strings numerically, use the
3860 @option{--general-numeric-sort} (@option{-g}) option.
3863 @itemx --version-sort
3865 @opindex --version-sort
3866 @cindex version number sort
3867 Sort by version name and number. It behaves like a standard sort,
3868 except that each sequence of decimal digits is treated numerically
3869 as an index/version number. (@xref{Details about version sort}.)
3875 @cindex reverse sorting
3876 Reverse the result of comparison, so that lines with greater key values
3877 appear earlier in the output instead of later.
3880 @itemx --random-sort
3881 @itemx --sort=random
3883 @opindex --random-sort
3886 Sort by hashing the input keys and then sorting the hash values.
3887 Choose the hash function at random, ensuring that it is free of
3888 collisions so that differing keys have differing hash values. This is
3889 like a random permutation of the inputs (@pxref{shuf invocation}),
3890 except that keys with the same value sort together.
3892 If multiple random sort fields are specified, the same random hash
3893 function is used for all fields. To use different random hash
3894 functions for different fields, you can invoke @command{sort} more
3897 The choice of hash function is affected by the
3898 @option{--random-source} option.
3906 @item --compress-program=@var{prog}
3907 Compress any temporary files with the program @var{prog}.
3909 With no arguments, @var{prog} must compress standard input to standard
3910 output, and when given the @option{-d} option it must decompress
3911 standard input to standard output.
3913 Terminate with an error if @var{prog} exits with nonzero status.
3915 White space and the backslash character should not appear in
3916 @var{prog}; they are reserved for future use.
3918 @filesZeroFromOption{sort,,sorted output}
3920 @item -k @var{pos1}[,@var{pos2}]
3921 @itemx --key=@var{pos1}[,@var{pos2}]
3925 Specify a sort field that consists of the part of the line between
3926 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3927 omitted), @emph{inclusive}.
3929 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3930 where @var{f} is the number of the field to use, and @var{c} is the number
3931 of the first character from the beginning of the field. Fields and character
3932 positions are numbered starting with 1; a character position of zero in
3933 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3934 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3935 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3936 @var{opts} are ordering options, allowing individual keys to be sorted
3937 according to different rules; see below for details. Keys can span
3940 Example: To sort on the second field, use @option{--key=2,2}
3941 (@option{-k 2,2}). See below for more notes on keys and more examples.
3943 @item --batch-size=@var{nmerge}
3944 @opindex --batch-size
3945 @cindex number of inputs to merge, nmerge
3946 Merge at most @var{nmerge} inputs at once.
3948 When @command{sort} has to merge more than @var{nmerge} inputs,
3949 it merges them in groups of @var{nmerge}, saving the result in
3950 a temporary file, which is then used as an input in a subsequent merge.
3952 A large value of @var{nmerge} may improve merge performance and decrease
3953 temporary storage utilization at the expense of increased memory usage
3954 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3955 requirements and I/0 at the expense of temporary storage consumption and
3958 The value of @var{nmerge} must be at least 2. The default value is
3959 currently 16, but this is implementation-dependent and may change in
3962 The value of @var{nmerge} may be bounded by a resource limit for open
3963 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3964 OPEN_MAX} may display limits for your systems; these limits may be
3965 modified further if your program already has some files open, or if
3966 the operating system has other limits on the number of open files. If
3967 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3968 silently uses a smaller value.
3970 @item -o @var{output-file}
3971 @itemx --output=@var{output-file}
3974 @cindex overwriting of input, allowed
3975 Write output to @var{output-file} instead of standard output.
3976 Normally, @command{sort} reads all input before opening
3977 @var{output-file}, so you can safely sort a file in place by using
3978 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3979 However, @command{sort} with @option{--merge} (@option{-m}) can open
3980 the output file before reading all input, so a command like @code{cat
3981 F | sort -m -o F - G} is not safe as @command{sort} might start
3982 writing @file{F} before @command{cat} is done reading it.
3984 @vindex POSIXLY_CORRECT
3985 On newer systems, @option{-o} cannot appear after an input file if
3986 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3987 scripts should specify @option{-o @var{output-file}} before any input
3990 @item --random-source=@var{file}
3991 @opindex --random-source
3992 @cindex random source for sorting
3993 Use @var{file} as a source of random data used to determine which
3994 random hash function to use with the @option{-R} option. @xref{Random
4001 @cindex sort stability
4002 @cindex sort's last-resort comparison
4004 Make @command{sort} stable by disabling its last-resort comparison.
4005 This option has no effect if no fields or global ordering options
4006 other than @option{--reverse} (@option{-r}) are specified.
4009 @itemx --buffer-size=@var{size}
4011 @opindex --buffer-size
4012 @cindex size for main memory sorting
4013 Use a main-memory sort buffer of the given @var{size}. By default,
4014 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4015 @var{size} to be interpreted as a percentage of physical memory.
4016 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4017 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4018 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4019 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4022 This option can improve the performance of @command{sort} by causing it
4023 to start with a larger or smaller sort buffer than the default.
4024 However, this option affects only the initial buffer size. The buffer
4025 grows beyond @var{size} if @command{sort} encounters input lines larger
4028 @item -t @var{separator}
4029 @itemx --field-separator=@var{separator}
4031 @opindex --field-separator
4032 @cindex field separator character
4033 Use character @var{separator} as the field separator when finding the
4034 sort keys in each line. By default, fields are separated by the empty
4035 string between a non-blank character and a blank character.
4036 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4039 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4040 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4041 not considered to be part of either the field preceding or the field
4042 following, so with @samp{sort @w{-t " "}} the same input line has
4043 three fields: an empty field, @samp{foo}, and @samp{bar}.
4044 However, fields that extend to the end of the line,
4045 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4046 retain the field separators present between the endpoints of the range.
4048 To specify @acronym{ASCII} @sc{nul} as the field separator,
4049 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4051 @item -T @var{tempdir}
4052 @itemx --temporary-directory=@var{tempdir}
4054 @opindex --temporary-directory
4055 @cindex temporary directory
4057 Use directory @var{tempdir} to store temporary files, overriding the
4058 @env{TMPDIR} environment variable. If this option is given more than
4059 once, temporary files are stored in all the directories given. If you
4060 have a large sort or merge that is I/O-bound, you can often improve
4061 performance by using this option to specify directories on different
4062 disks and controllers.
4068 @cindex uniquifying output
4070 Normally, output only the first of a sequence of lines that compare
4071 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4072 check that no pair of consecutive lines compares equal.
4074 This option also disables the default last-resort comparison.
4076 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4077 this equivalence does not extend to arbitrary @command{sort} options.
4078 For example, @code{sort -n -u} inspects only the value of the initial
4079 numeric string when checking for uniqueness, whereas @code{sort -n |
4080 uniq} inspects the entire line. @xref{uniq invocation}.
4082 @macro zeroTerminatedOption
4084 @itemx --zero-terminated
4086 @opindex --zero-terminated
4087 @cindex process zero-terminated items
4088 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4089 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4090 and terminate output items with @acronym{ASCII} @sc{nul}.
4091 This option can be useful in conjunction with @samp{perl -0} or
4092 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4093 reliably handle arbitrary file names (even those containing blanks
4094 or other special characters).
4096 @zeroTerminatedOption
4100 Historical (BSD and System V) implementations of @command{sort} have
4101 differed in their interpretation of some options, particularly
4102 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4103 behavior, which is usually (but not always!) like the System V behavior.
4104 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4105 consistency, @option{-M} has been changed in the same way. This may
4106 affect the meaning of character positions in field specifications in
4107 obscure cases. The only fix is to add an explicit @option{-b}.
4109 A position in a sort field specified with @option{-k} may have any
4110 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4111 global ordering options are inherited by that particular field. The
4112 @option{-b} option may be independently attached to either or both of
4113 the start and end positions of a field specification, and if it is
4114 inherited from the global options it will be attached to both.
4115 If input lines can contain leading or adjacent blanks and @option{-t}
4116 is not used, then @option{-k} is typically combined with @option{-b} or
4117 an option that implicitly ignores leading blanks (@samp{MghnV}) as otherwise
4118 the varying numbers of leading blanks in fields can cause confusing results.
4120 If the start position in a sort field specifier falls after the end of
4121 the line or after the end field, the field is empty. If the @option{-b}
4122 option was specified, the @samp{.@var{c}} part of a field specification
4123 is counted from the first nonblank character of the field.
4125 @vindex _POSIX2_VERSION
4126 @vindex POSIXLY_CORRECT
4127 On older systems, @command{sort} supports an obsolete origin-zero
4128 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4129 This obsolete behavior can be enabled or disabled with the
4130 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4131 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4132 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4134 Scripts intended for use on standard hosts should avoid obsolete
4135 syntax and should use @option{-k} instead. For example, avoid
4136 @samp{sort +2}, since it might be interpreted as either @samp{sort
4137 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4138 support only the obsolete syntax, it can use a test like @samp{if sort
4139 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4142 Here are some examples to illustrate various combinations of options.
4147 Sort in descending (reverse) numeric order.
4154 Sort alphabetically, omitting the first and second fields
4155 and the blanks at the start of the third field.
4156 This uses a single key composed of the characters beginning
4157 at the start of the first nonblank character in field three
4158 and extending to the end of each line.
4165 Sort numerically on the second field and resolve ties by sorting
4166 alphabetically on the third and fourth characters of field five.
4167 Use @samp{:} as the field delimiter.
4170 sort -t : -k 2,2n -k 5.3,5.4
4173 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4174 @command{sort} would have used all characters beginning in the second field
4175 and extending to the end of the line as the primary @emph{numeric}
4176 key. For the large majority of applications, treating keys spanning
4177 more than one field as numeric will not do what you expect.
4179 Also note that the @samp{n} modifier was applied to the field-end
4180 specifier for the first key. It would have been equivalent to
4181 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4182 @samp{b} apply to the associated @emph{field}, regardless of whether
4183 the modifier character is attached to the field-start and/or the
4184 field-end part of the key specifier.
4187 Sort the password file on the fifth field and ignore any
4188 leading blanks. Sort lines with equal values in field five
4189 on the numeric user ID in field three. Fields are separated
4193 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4194 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4195 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4198 These three commands have equivalent effect. The first specifies that
4199 the first key's start position ignores leading blanks and the second
4200 key is sorted numerically. The other two commands rely on global
4201 options being inherited by sort keys that lack modifiers. The inheritance
4202 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4203 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4204 character position is not affected by whether initial blanks are
4208 Sort a set of log files, primarily by IPv4 address and secondarily by
4209 time stamp. If two lines' primary and secondary keys are identical,
4210 output the lines in the same order that they were input. The log
4211 files contain lines that look like this:
4214 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4215 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4218 Fields are separated by exactly one space. Sort IPv4 addresses
4219 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4220 because 61 is less than 129.
4223 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4224 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4227 This example cannot be done with a single @command{sort} invocation,
4228 since IPv4 address components are separated by @samp{.} while dates
4229 come just after a space. So it is broken down into two invocations of
4230 @command{sort}: the first sorts by time stamp and the second by IPv4
4231 address. The time stamp is sorted by year, then month, then day, and
4232 finally by hour-minute-second field, using @option{-k} to isolate each
4233 field. Except for hour-minute-second there's no need to specify the
4234 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4235 based on leading prefixes that cannot cross field boundaries. The
4236 IPv4 addresses are sorted lexicographically. The second sort uses
4237 @samp{-s} so that ties in the primary key are broken by the secondary
4238 key; the first sort uses @samp{-s} so that the combination of the two
4242 Generate a tags file in case-insensitive sorted order.
4245 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4248 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4249 that file names that contain blanks or other special characters are
4251 by the sort operation.
4253 @c This example is a bit contrived and needs more explanation.
4255 @c Sort records separated by an arbitrary string by using a pipe to convert
4256 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4257 @c and converting each @samp{\0} back to the original record delimiter.
4260 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4264 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4265 sort lines according to their length.
4268 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4271 In general this technique can be used to sort data that the @command{sort}
4272 command does not support, or is inefficient at, sorting directly.
4275 Shuffle a list of directories, but preserve the order of files within
4276 each directory. For instance, one could use this to generate a music
4277 playlist in which albums are shuffled but the songs of each album are
4281 ls */* | sort -t / -k 1,1R -k 2,2
4287 @node shuf invocation
4288 @section @command{shuf}: Shuffling text
4291 @cindex shuffling files
4293 @command{shuf} shuffles its input by outputting a random permutation
4294 of its input lines. Each output permutation is equally likely.
4298 shuf [@var{option}]@dots{} [@var{file}]
4299 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4300 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4303 @command{shuf} has three modes of operation that affect where it
4304 obtains its input lines. By default, it reads lines from standard
4305 input. The following options change the operation mode:
4313 @cindex command-line operands to shuffle
4314 Treat each command-line operand as an input line.
4316 @item -i @var{lo}-@var{hi}
4317 @itemx --input-range=@var{lo}-@var{hi}
4319 @opindex --input-range
4320 @cindex input range to shuffle
4321 Act as if input came from a file containing the range of unsigned
4322 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4326 @command{shuf}'s other options can affect its behavior in all
4331 @item -n @var{lines}
4332 @itemx --head-count=@var{count}
4334 @opindex --head-count
4335 @cindex head of output
4336 Output at most @var{count} lines. By default, all input lines are
4339 @item -o @var{output-file}
4340 @itemx --output=@var{output-file}
4343 @cindex overwriting of input, allowed
4344 Write output to @var{output-file} instead of standard output.
4345 @command{shuf} reads all input before opening
4346 @var{output-file}, so you can safely shuffle a file in place by using
4347 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4349 @item --random-source=@var{file}
4350 @opindex --random-source
4351 @cindex random source for shuffling
4352 Use @var{file} as a source of random data used to determine which
4353 permutation to generate. @xref{Random sources}.
4355 @zeroTerminatedOption
4371 might produce the output
4381 Similarly, the command:
4384 shuf -e clubs hearts diamonds spades
4398 and the command @samp{shuf -i 1-4} might output:
4408 These examples all have four input lines, so @command{shuf} might
4409 produce any of the twenty-four possible permutations of the input. In
4410 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4411 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4412 output permutations.
4417 @node uniq invocation
4418 @section @command{uniq}: Uniquify files
4421 @cindex uniquify files
4423 @command{uniq} writes the unique lines in the given @file{input}, or
4424 standard input if nothing is given or for an @var{input} name of
4428 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4431 By default, @command{uniq} prints its input lines, except that
4432 it discards all but the first of adjacent repeated lines, so that
4433 no output lines are repeated. Optionally, it can instead discard
4434 lines that are not repeated, or all repeated lines.
4436 The input need not be sorted, but repeated input lines are detected
4437 only if they are adjacent. If you want to discard non-adjacent
4438 duplicate lines, perhaps you want to use @code{sort -u}.
4439 @xref{sort invocation}.
4442 Comparisons honor the rules specified by the @env{LC_COLLATE}
4445 If no @var{output} file is specified, @command{uniq} writes to standard
4448 The program accepts the following options. Also see @ref{Common options}.
4453 @itemx --skip-fields=@var{n}
4455 @opindex --skip-fields
4456 Skip @var{n} fields on each line before checking for uniqueness. Use
4457 a null string for comparison if a line has fewer than @var{n} fields. Fields
4458 are sequences of non-space non-tab characters that are separated from
4459 each other by at least one space or tab.
4461 For compatibility @command{uniq} supports an obsolete option syntax
4462 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4465 @itemx --skip-chars=@var{n}
4467 @opindex --skip-chars
4468 Skip @var{n} characters before checking for uniqueness. Use a null string
4469 for comparison if a line has fewer than @var{n} characters. If you use both
4470 the field and character skipping options, fields are skipped over first.
4472 @vindex _POSIX2_VERSION
4473 On older systems, @command{uniq} supports an obsolete option syntax
4475 This obsolete behavior can be enabled or disabled with the
4476 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4477 conformance}), but portable scripts should avoid commands whose
4478 behavior depends on this variable.
4479 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4480 the ambiguous @samp{uniq +10}.
4486 Print the number of times each line occurred along with the line.
4489 @itemx --ignore-case
4491 @opindex --ignore-case
4492 Ignore differences in case when comparing lines.
4498 @cindex repeated lines, outputting
4499 Discard lines that are not repeated. When used by itself, this option
4500 causes @command{uniq} to print the first copy of each repeated line,
4504 @itemx --all-repeated[=@var{delimit-method}]
4506 @opindex --all-repeated
4507 @cindex all repeated lines, outputting
4508 Do not discard the second and subsequent repeated input lines,
4509 but discard lines that are not repeated.
4510 This option is useful mainly in conjunction with other options e.g.,
4511 to ignore case or to compare only selected fields.
4512 The optional @var{delimit-method} tells how to delimit
4513 groups of repeated lines, and must be one of the following:
4518 Do not delimit groups of repeated lines.
4519 This is equivalent to @option{--all-repeated} (@option{-D}).
4522 Output a newline before each group of repeated lines.
4523 With @option{--zero-terminated} (@option{-z}), use a zero
4524 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4527 Separate groups of repeated lines with a single newline.
4528 With @option{--zero-terminated} (@option{-z}), use a zero
4529 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4530 This is the same as using @samp{prepend}, except that
4531 no delimiter is inserted before the first group, and hence
4532 may be better suited for output direct to users.
4535 Note that when groups are delimited and the input stream contains
4536 two or more consecutive blank lines, then the output is ambiguous.
4537 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4538 each sequence of consecutive newlines with a single newline.
4540 This is a @sc{gnu} extension.
4541 @c FIXME: give an example showing *how* it's useful
4547 @cindex unique lines, outputting
4548 Discard the first repeated line. When used by itself, this option
4549 causes @command{uniq} to print unique lines, and nothing else.
4552 @itemx --check-chars=@var{n}
4554 @opindex --check-chars
4555 Compare at most @var{n} characters on each line (after skipping any specified
4556 fields and characters). By default the entire rest of the lines are
4559 @zeroTerminatedOption
4566 @node comm invocation
4567 @section @command{comm}: Compare two sorted files line by line
4570 @cindex line-by-line comparison
4571 @cindex comparing sorted files
4573 @command{comm} writes to standard output lines that are common, and lines
4574 that are unique, to two input files; a file name of @samp{-} means
4575 standard input. Synopsis:
4578 comm [@var{option}]@dots{} @var{file1} @var{file2}
4582 Before @command{comm} can be used, the input files must be sorted using the
4583 collating sequence specified by the @env{LC_COLLATE} locale.
4584 If an input file ends in a non-newline
4585 character, a newline is silently appended. The @command{sort} command with
4586 no options always outputs a file that is suitable input to @command{comm}.
4588 @cindex differing lines
4589 @cindex common lines
4590 With no options, @command{comm} produces three-column output. Column one
4591 contains lines unique to @var{file1}, column two contains lines unique
4592 to @var{file2}, and column three contains lines common to both files.
4593 Columns are separated by a single TAB character.
4594 @c FIXME: when there's an option to supply an alternative separator
4595 @c string, append `by default' to the above sentence.
4600 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4601 the corresponding columns (and separators). Also see @ref{Common options}.
4603 Unlike some other comparison utilities, @command{comm} has an exit
4604 status that does not depend on the result of the comparison.
4605 Upon normal completion @command{comm} produces an exit code of zero.
4606 If there is an error it exits with nonzero status.
4608 @macro checkOrderOption{cmd}
4609 If the @option{--check-order} option is given, unsorted inputs will
4610 cause a fatal error message. If the option @option{--nocheck-order}
4611 is given, unsorted inputs will never cause an error message. If
4612 neither of these options is given, wrongly sorted inputs are diagnosed
4613 only if an input file is found to contain unpairable lines. If an
4614 input file is diagnosed as being unsorted, the @command{\cmd\} command
4615 will exit with a nonzero status (and the output should not be used).
4617 Forcing @command{\cmd\} to process wrongly sorted input files
4618 containing unpairable lines by specifying @option{--nocheck-order} is
4619 not guaranteed to produce any particular output. The output will
4620 probably not correspond with whatever you hoped it would be.
4622 @checkOrderOption{comm}
4627 Fail with an error message if either input file is wrongly ordered.
4629 @item --nocheck-order
4630 Do not check that both input files are in sorted order.
4634 @item --output-delimiter=@var{str}
4635 Print @var{str} between adjacent output columns,
4636 rather than the default of a single TAB character.
4638 The delimiter @var{str} may not be empty.
4642 @node ptx invocation
4643 @section @command{ptx}: Produce permuted indexes
4647 @command{ptx} reads a text file and essentially produces a permuted index, with
4648 each keyword in its context. The calling sketch is either one of:
4651 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4652 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4655 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4656 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4657 limitations and changing several of the program's default option values.
4658 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4659 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4660 document. For the full list, see @xref{Compatibility in ptx}.
4662 Individual options are explained in the following sections.
4664 When @sc{gnu} extensions are enabled, there may be zero, one or several
4665 @var{file}s after the options. If there is no @var{file}, the program
4666 reads the standard input. If there is one or several @var{file}s, they
4667 give the name of input files which are all read in turn, as if all the
4668 input files were concatenated. However, there is a full contextual
4669 break between each file and, when automatic referencing is requested,
4670 file names and line numbers refer to individual text input files. In
4671 all cases, the program outputs the permuted index to the standard
4674 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4675 operates in traditional mode, there may be zero, one or two parameters
4676 besides the options. If there are no parameters, the program reads the
4677 standard input and outputs the permuted index to the standard output.
4678 If there is only one parameter, it names the text @var{input} to be read
4679 instead of the standard input. If two parameters are given, they give
4680 respectively the name of the @var{input} file to read and the name of
4681 the @var{output} file to produce. @emph{Be very careful} to note that,
4682 in this case, the contents of file given by the second parameter is
4683 destroyed. This behavior is dictated by System V @command{ptx}
4684 compatibility; @sc{gnu} Standards normally discourage output parameters not
4685 introduced by an option.
4687 Note that for @emph{any} file named as the value of an option or as an
4688 input text file, a single dash @kbd{-} may be used, in which case
4689 standard input is assumed. However, it would not make sense to use this
4690 convention more than once per program invocation.
4693 * General options in ptx:: Options which affect general program behavior.
4694 * Charset selection in ptx:: Underlying character set considerations.
4695 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4696 * Output formatting in ptx:: Types of output format, and sizing the fields.
4697 * Compatibility in ptx::
4701 @node General options in ptx
4702 @subsection General options
4707 @itemx --traditional
4708 As already explained, this option disables all @sc{gnu} extensions to
4709 @command{ptx} and switches to traditional mode.
4712 Print a short help on standard output, then exit without further
4716 Print the program version on standard output, then exit without further
4724 @node Charset selection in ptx
4725 @subsection Charset selection
4727 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4728 As it is set up now, the program assumes that the input file is coded
4729 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4730 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4731 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4732 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4733 of characters which are letters is different; this alters the behavior
4734 of regular expression matching. Thus, the default regular expression
4735 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4736 however, is still crude; it obeys the underlying character set ordering
4742 @itemx --ignore-case
4743 Fold lower case letters to upper case for sorting.
4748 @node Input processing in ptx
4749 @subsection Word selection and input processing
4754 @itemx --break-file=@var{file}
4756 This option provides an alternative (to @option{-W}) method of describing
4757 which characters make up words. It introduces the name of a
4758 file which contains a list of characters which can@emph{not} be part of
4759 one word; this file is called the @dfn{Break file}. Any character which
4760 is not part of the Break file is a word constituent. If both options
4761 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4762 @option{-b} is ignored.
4764 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4765 break character is to write all the break characters in the file with no
4766 newline at all, not even at the end of the file. When @sc{gnu} extensions
4767 are disabled, spaces, tabs and newlines are always considered as break
4768 characters even if not included in the Break file.
4771 @itemx --ignore-file=@var{file}
4773 The file associated with this option contains a list of words which will
4774 never be taken as keywords in concordance output. It is called the
4775 @dfn{Ignore file}. The file contains exactly one word in each line; the
4776 end of line separation of words is not subject to the value of the
4780 @itemx --only-file=@var{file}
4782 The file associated with this option contains a list of words which will
4783 be retained in concordance output; any word not mentioned in this file
4784 is ignored. The file is called the @dfn{Only file}. The file contains
4785 exactly one word in each line; the end of line separation of words is
4786 not subject to the value of the @option{-S} option.
4788 There is no default for the Only file. When both an Only file and an
4789 Ignore file are specified, a word is considered a keyword only
4790 if it is listed in the Only file and not in the Ignore file.
4795 On each input line, the leading sequence of non-white space characters will be
4796 taken to be a reference that has the purpose of identifying this input
4797 line in the resulting permuted index. For more information about reference
4798 production, see @xref{Output formatting in ptx}.
4799 Using this option changes the default value for option @option{-S}.
4801 Using this option, the program does not try very hard to remove
4802 references from contexts in output, but it succeeds in doing so
4803 @emph{when} the context ends exactly at the newline. If option
4804 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4805 are disabled, this condition is always met and references are completely
4806 excluded from the output contexts.
4808 @item -S @var{regexp}
4809 @itemx --sentence-regexp=@var{regexp}
4811 This option selects which regular expression will describe the end of a
4812 line or the end of a sentence. In fact, this regular expression is not
4813 the only distinction between end of lines or end of sentences, and input
4814 line boundaries have no special significance outside this option. By
4815 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4816 used, end of sentences are used. In this case, this @var{regex} is
4817 imported from @sc{gnu} Emacs:
4820 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4823 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4824 of lines are used; in this case, the default @var{regexp} is just:
4830 Using an empty @var{regexp} is equivalent to completely disabling end of
4831 line or end of sentence recognition. In this case, the whole file is
4832 considered to be a single big line or sentence. The user might want to
4833 disallow all truncation flag generation as well, through option @option{-F
4834 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4837 When the keywords happen to be near the beginning of the input line or
4838 sentence, this often creates an unused area at the beginning of the
4839 output context line; when the keywords happen to be near the end of the
4840 input line or sentence, this often creates an unused area at the end of
4841 the output context line. The program tries to fill those unused areas
4842 by wrapping around context in them; the tail of the input line or
4843 sentence is used to fill the unused area on the left of the output line;
4844 the head of the input line or sentence is used to fill the unused area
4845 on the right of the output line.
4847 As a matter of convenience to the user, many usual backslashed escape
4848 sequences from the C language are recognized and converted to the
4849 corresponding characters by @command{ptx} itself.
4851 @item -W @var{regexp}
4852 @itemx --word-regexp=@var{regexp}
4854 This option selects which regular expression will describe each keyword.
4855 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4856 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4857 disabled, a word is by default anything which ends with a space, a tab
4858 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4860 An empty @var{regexp} is equivalent to not using this option.
4861 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4864 As a matter of convenience to the user, many usual backslashed escape
4865 sequences, as found in the C language, are recognized and converted to
4866 the corresponding characters by @command{ptx} itself.
4871 @node Output formatting in ptx
4872 @subsection Output formatting
4874 Output format is mainly controlled by the @option{-O} and @option{-T} options
4875 described in the table below. When neither @option{-O} nor @option{-T} are
4876 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4877 output format suitable for a dumb terminal. Each keyword occurrence is
4878 output to the center of one line, surrounded by its left and right
4879 contexts. Each field is properly justified, so the concordance output
4880 can be readily observed. As a special feature, if automatic
4881 references are selected by option @option{-A} and are output before the
4882 left context, that is, if option @option{-R} is @emph{not} selected, then
4883 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4884 Emacs @code{next-error} processing. In this default output format, each
4885 white space character, like newline and tab, is merely changed to
4886 exactly one space, with no special attempt to compress consecutive
4887 spaces. This might change in the future. Except for those white space
4888 characters, every other character of the underlying set of 256
4889 characters is transmitted verbatim.
4891 Output format is further controlled by the following options.
4895 @item -g @var{number}
4896 @itemx --gap-size=@var{number}
4898 Select the size of the minimum white space gap between the fields on the
4901 @item -w @var{number}
4902 @itemx --width=@var{number}
4904 Select the maximum output width of each final line. If references are
4905 used, they are included or excluded from the maximum output width
4906 depending on the value of option @option{-R}. If this option is not
4907 selected, that is, when references are output before the left context,
4908 the maximum output width takes into account the maximum length of all
4909 references. If this option is selected, that is, when references are
4910 output after the right context, the maximum output width does not take
4911 into account the space taken by references, nor the gap that precedes
4915 @itemx --auto-reference
4917 Select automatic references. Each input line will have an automatic
4918 reference made up of the file name and the line ordinal, with a single
4919 colon between them. However, the file name will be empty when standard
4920 input is being read. If both @option{-A} and @option{-r} are selected, then
4921 the input reference is still read and skipped, but the automatic
4922 reference is used at output time, overriding the input reference.
4925 @itemx --right-side-refs
4927 In the default output format, when option @option{-R} is not used, any
4928 references produced by the effect of options @option{-r} or @option{-A} are
4929 placed to the far right of output lines, after the right context. With
4930 default output format, when the @option{-R} option is specified, references
4931 are rather placed at the beginning of each output line, before the left
4932 context. For any other output format, option @option{-R} is
4933 ignored, with one exception: with @option{-R} the width of references
4934 is @emph{not} taken into account in total output width given by @option{-w}.
4936 This option is automatically selected whenever @sc{gnu} extensions are
4939 @item -F @var{string}
4940 @itemx --flac-truncation=@var{string}
4942 This option will request that any truncation in the output be reported
4943 using the string @var{string}. Most output fields theoretically extend
4944 towards the beginning or the end of the current line, or current
4945 sentence, as selected with option @option{-S}. But there is a maximum
4946 allowed output line width, changeable through option @option{-w}, which is
4947 further divided into space for various output fields. When a field has
4948 to be truncated because it cannot extend beyond the beginning or the end of
4949 the current line to fit in, then a truncation occurs. By default,
4950 the string used is a single slash, as in @option{-F /}.
4952 @var{string} may have more than one character, as in @option{-F ...}.
4953 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4954 truncation flagging is disabled, and no truncation marks are appended in
4957 As a matter of convenience to the user, many usual backslashed escape
4958 sequences, as found in the C language, are recognized and converted to
4959 the corresponding characters by @command{ptx} itself.
4961 @item -M @var{string}
4962 @itemx --macro-name=@var{string}
4964 Select another @var{string} to be used instead of @samp{xx}, while
4965 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4968 @itemx --format=roff
4970 Choose an output format suitable for @command{nroff} or @command{troff}
4971 processing. Each output line will look like:
4974 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4977 so it will be possible to write a @samp{.xx} roff macro to take care of
4978 the output typesetting. This is the default output format when @sc{gnu}
4979 extensions are disabled. Option @option{-M} can be used to change
4980 @samp{xx} to another macro name.
4982 In this output format, each non-graphical character, like newline and
4983 tab, is merely changed to exactly one space, with no special attempt to
4984 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4985 so it will be correctly processed by @command{nroff} or @command{troff}.
4990 Choose an output format suitable for @TeX{} processing. Each output
4991 line will look like:
4994 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
4998 so it will be possible to write a @code{\xx} definition to take care of
4999 the output typesetting. Note that when references are not being
5000 produced, that is, neither option @option{-A} nor option @option{-r} is
5001 selected, the last parameter of each @code{\xx} call is inhibited.
5002 Option @option{-M} can be used to change @samp{xx} to another macro
5005 In this output format, some special characters, like @kbd{$}, @kbd{%},
5006 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5007 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5008 backslash and a pair of dollar signs (to force mathematical mode). The
5009 backslash itself produces the sequence @code{\backslash@{@}}.
5010 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5011 @code{~\@{ @}} respectively. Other diacriticized characters of the
5012 underlying character set produce an appropriate @TeX{} sequence as far
5013 as possible. The other non-graphical characters, like newline and tab,
5014 and all other characters which are not part of @acronym{ASCII}, are merely
5015 changed to exactly one space, with no special attempt to compress
5016 consecutive spaces. Let me know how to improve this special character
5017 processing for @TeX{}.
5022 @node Compatibility in ptx
5023 @subsection The @sc{gnu} extensions to @command{ptx}
5025 This version of @command{ptx} contains a few features which do not exist in
5026 System V @command{ptx}. These extra features are suppressed by using the
5027 @option{-G} command line option, unless overridden by other command line
5028 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5029 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5030 Here are the differences between this program and System V @command{ptx}.
5035 This program can read many input files at once, it always writes the
5036 resulting concordance on standard output. On the other hand, System V
5037 @command{ptx} reads only one file and sends the result to standard output
5038 or, if a second @var{file} parameter is given on the command, to that
5041 Having output parameters not introduced by options is a dangerous
5042 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5043 portably between @sc{gnu} and System V, you should always use it with a
5044 single input file, and always expect the result on standard output. You
5045 might also want to automatically configure in a @option{-G} option to
5046 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5047 that the installed @command{ptx} accepts @option{-G}.
5050 The only options available in System V @command{ptx} are options @option{-b},
5051 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5052 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5053 this enumeration. Moreover, some options have a slightly different
5054 meaning when @sc{gnu} extensions are enabled, as explained below.
5057 By default, concordance output is not formatted for @command{troff} or
5058 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5059 or @command{nroff} output may still be selected through option @option{-O}.
5062 Unless @option{-R} option is used, the maximum reference width is
5063 subtracted from the total output line width. With @sc{gnu} extensions
5064 disabled, width of references is not taken into account in the output
5065 line width computations.
5068 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5069 processed from input file with no adverse effect, even if @sc{gnu} extensions
5070 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5071 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5074 Input line length is only limited by available memory, even if @sc{gnu}
5075 extensions are disabled. However, System V @command{ptx} processes only
5076 the first 200 characters in each line.
5079 The break (non-word) characters default to be every character except all
5080 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5081 extensions are disabled, the break characters default to space, tab and
5085 The program makes better use of output line width. If @sc{gnu} extensions
5086 are disabled, the program rather tries to imitate System V @command{ptx},
5087 but still, there are some slight disposition glitches this program does
5088 not completely reproduce.
5091 The user can specify both an Ignore file and an Only file. This is not
5092 allowed with System V @command{ptx}.
5097 @node tsort invocation
5098 @section @command{tsort}: Topological sort
5101 @cindex topological sort
5103 @command{tsort} performs a topological sort on the given @var{file}, or
5104 standard input if no input file is given or for a @var{file} of
5105 @samp{-}. For more details and some history, see @ref{tsort background}.
5109 tsort [@var{option}] [@var{file}]
5112 @command{tsort} reads its input as pairs of strings, separated by blanks,
5113 indicating a partial ordering. The output is a total ordering that
5114 corresponds to the given partial ordering.
5128 will produce the output
5139 Consider a more realistic example.
5140 You have a large set of functions all in one file, and they may all be
5141 declared static except one. Currently that one (say @code{main}) is the
5142 first function defined in the file, and the ones it calls directly follow
5143 it, followed by those they call, etc. Let's say that you are determined
5144 to take advantage of prototypes, so you have to choose between declaring
5145 all of those functions (which means duplicating a lot of information from
5146 the definitions) and rearranging the functions so that as many as possible
5147 are defined before they are used. One way to automate the latter process
5148 is to get a list for each function of the functions it calls directly.
5149 Many programs can generate such lists. They describe a call graph.
5150 Consider the following list, in which a given line indicates that the
5151 function on the left calls the one on the right directly.
5157 tail_file pretty_name
5158 tail_file write_header
5160 tail_forever recheck
5161 tail_forever pretty_name
5162 tail_forever write_header
5163 tail_forever dump_remainder
5166 tail_lines start_lines
5167 tail_lines dump_remainder
5168 tail_lines file_lines
5169 tail_lines pipe_lines
5171 tail_bytes start_bytes
5172 tail_bytes dump_remainder
5173 tail_bytes pipe_bytes
5174 file_lines dump_remainder
5178 then you can use @command{tsort} to produce an ordering of those
5179 functions that satisfies your requirement.
5182 example$ tsort call-graph | tac
5202 @command{tsort} detects any cycles in the input and writes the first cycle
5203 encountered to standard error.
5205 Note that for a given partial ordering, generally there is no unique
5206 total ordering. In the context of the call graph above, the function
5207 @code{parse_options} may be placed anywhere in the list as long as it
5208 precedes @code{main}.
5210 The only options are @option{--help} and @option{--version}. @xref{Common
5216 * tsort background:: Where tsort came from.
5219 @node tsort background
5220 @subsection @command{tsort}: Background
5222 @command{tsort} exists because very early versions of the Unix linker processed
5223 an archive file exactly once, and in order. As @command{ld} read each object
5224 in the archive, it decided whether it was needed in the program based on
5225 whether it defined any symbols which were undefined at that point in
5228 This meant that dependencies within the archive had to be handled
5229 specially. For example, @code{scanf} probably calls @code{read}. That means
5230 that in a single pass through an archive, it was important for @code{scanf.o}
5231 to appear before read.o, because otherwise a program which calls
5232 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5233 reference to @code{read}.
5235 The way to address this problem was to first generate a set of
5236 dependencies of one object file on another. This was done by a shell
5237 script called @command{lorder}. The GNU tools don't provide a version of
5238 lorder, as far as I know, but you can still find it in BSD
5241 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5242 resulting sort to define the order in which you added objects to the archive.
5244 This whole procedure has been obsolete since about 1980, because
5245 Unix archives now contain a symbol table (traditionally built by
5246 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5247 linker uses the symbol table to effectively make multiple passes over
5250 Anyhow, that's where tsort came from. To solve an old problem with
5251 the way the linker handled archive files, which has since been solved
5255 @node Operating on fields
5256 @chapter Operating on fields
5259 * cut invocation:: Print selected parts of lines.
5260 * paste invocation:: Merge lines of files.
5261 * join invocation:: Join lines on a common field.
5265 @node cut invocation
5266 @section @command{cut}: Print selected parts of lines
5269 @command{cut} writes to standard output selected parts of each line of each
5270 input file, or standard input if no files are given or for a file name of
5274 cut @var{option}@dots{} [@var{file}]@dots{}
5277 In the table which follows, the @var{byte-list}, @var{character-list},
5278 and @var{field-list} are one or more numbers or ranges (two numbers
5279 separated by a dash) separated by commas. Bytes, characters, and
5280 fields are numbered starting at 1. Incomplete ranges may be
5281 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5282 @samp{@var{n}} through end of line or last field. The list elements
5283 can be repeated, can overlap, and can be specified in any order; but
5284 the selected input is written in the same order that it is read, and
5285 is written exactly once.
5287 The program accepts the following options. Also see @ref{Common
5292 @item -b @var{byte-list}
5293 @itemx --bytes=@var{byte-list}
5296 Select for printing only the bytes in positions listed in
5297 @var{byte-list}. Tabs and backspaces are treated like any other
5298 character; they take up 1 byte. If an output delimiter is specified,
5299 (see the description of @option{--output-delimiter}), then output that
5300 string between ranges of selected bytes.
5302 @item -c @var{character-list}
5303 @itemx --characters=@var{character-list}
5305 @opindex --characters
5306 Select for printing only the characters in positions listed in
5307 @var{character-list}. The same as @option{-b} for now, but
5308 internationalization will change that. Tabs and backspaces are
5309 treated like any other character; they take up 1 character. If an
5310 output delimiter is specified, (see the description of
5311 @option{--output-delimiter}), then output that string between ranges
5314 @item -f @var{field-list}
5315 @itemx --fields=@var{field-list}
5318 Select for printing only the fields listed in @var{field-list}.
5319 Fields are separated by a TAB character by default. Also print any
5320 line that contains no delimiter character, unless the
5321 @option{--only-delimited} (@option{-s}) option is specified.
5322 Note @command{cut} does not support specifying runs of whitespace as a
5323 delimiter, so to achieve that common functionality one can pre-process
5324 with @command{tr} like:
5326 tr -s '[:blank:]' '\t' | cut -f@dots{}
5329 @item -d @var{input_delim_byte}
5330 @itemx --delimiter=@var{input_delim_byte}
5332 @opindex --delimiter
5333 With @option{-f}, use the first byte of @var{input_delim_byte} as
5334 the input fields separator (default is TAB).
5338 Do not split multi-byte characters (no-op for now).
5341 @itemx --only-delimited
5343 @opindex --only-delimited
5344 For @option{-f}, do not print lines that do not contain the field separator
5345 character. Normally, any line without a field separator is printed verbatim.
5347 @item --output-delimiter=@var{output_delim_string}
5348 @opindex --output-delimiter
5349 With @option{-f}, output fields are separated by @var{output_delim_string}.
5350 The default with @option{-f} is to use the input delimiter.
5351 When using @option{-b} or @option{-c} to select ranges of byte or
5352 character offsets (as opposed to ranges of fields),
5353 output @var{output_delim_string} between non-overlapping
5354 ranges of selected bytes.
5357 @opindex --complement
5358 This option is a @acronym{GNU} extension.
5359 Select for printing the complement of the bytes, characters or fields
5360 selected with the @option{-b}, @option{-c} or @option{-f} options.
5361 In other words, do @emph{not} print the bytes, characters or fields
5362 specified via those options. This option is useful when you have
5363 many fields and want to print all but a few of them.
5370 @node paste invocation
5371 @section @command{paste}: Merge lines of files
5374 @cindex merging files
5376 @command{paste} writes to standard output lines consisting of sequentially
5377 corresponding lines of each given file, separated by a TAB character.
5378 Standard input is used for a file name of @samp{-} or if no input files
5400 paste [@var{option}]@dots{} [@var{file}]@dots{}
5403 The program accepts the following options. Also see @ref{Common options}.
5411 Paste the lines of one file at a time rather than one line from each
5412 file. Using the above example data:
5415 $ paste -s num2 let3
5420 @item -d @var{delim-list}
5421 @itemx --delimiters=@var{delim-list}
5423 @opindex --delimiters
5424 Consecutively use the characters in @var{delim-list} instead of
5425 TAB to separate merged lines. When @var{delim-list} is
5426 exhausted, start again at its beginning. Using the above example data:
5429 $ paste -d '%_' num2 let3 num2
5440 @node join invocation
5441 @section @command{join}: Join lines on a common field
5444 @cindex common field, joining on
5446 @command{join} writes to standard output a line for each pair of input
5447 lines that have identical join fields. Synopsis:
5450 join [@var{option}]@dots{} @var{file1} @var{file2}
5453 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5454 meaning standard input. @var{file1} and @var{file2} should be
5455 sorted on the join fields.
5458 Normally, the sort order is that of the
5459 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5460 the @option{-t} option is given, the sort comparison ignores blanks at
5461 the start of the join field, as in @code{sort -b}. If the
5462 @option{--ignore-case} option is given, the sort comparison ignores
5463 the case of characters in the join field, as in @code{sort -f}.
5465 The @command{sort} and @command{join} commands should use consistent
5466 locales and options if the output of @command{sort} is fed to
5467 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5468 sort a file on its default join field, but if you select a non-default
5469 locale, join field, separator, or comparison options, then you should
5470 do so consistently between @command{join} and @command{sort}.
5471 If @samp{join -t ''} is specified then the whole line is considered which
5472 matches the default operation of sort.
5474 If the input has no unpairable lines, a @acronym{GNU} extension is
5475 available; the sort order can be any order that considers two fields
5476 to be equal if and only if the sort comparison described above
5477 considers them to be equal. For example:
5494 @checkOrderOption{join}
5498 @item the join field is the first field in each line;
5499 @item fields in the input are separated by one or more blanks, with leading
5500 blanks on the line ignored;
5501 @item fields in the output are separated by a space;
5502 @item each output line consists of the join field, the remaining
5503 fields from @var{file1}, then the remaining fields from @var{file2}.
5506 The program accepts the following options. Also see @ref{Common options}.
5510 @item -a @var{file-number}
5512 Print a line for each unpairable line in file @var{file-number} (either
5513 @samp{1} or @samp{2}), in addition to the normal output.
5516 Fail with an error message if either input file is wrongly ordered.
5518 @item --nocheck-order
5519 Do not check that both input files are in sorted order. This is the default.
5521 @item -e @var{string}
5523 Replace those output fields that are missing in the input with
5528 Treat the first line of each input file as a header line. The header lines will
5529 be joined and printed as the first output line. If @option{-o} is used to
5530 specify output format, the header line will be printed according to the
5531 specified format. The header lines will not be checked for ordering even if
5532 @option{--check-order} is specified. Also if the header lines from each file
5533 do not match, the heading fields from the first file will be used.
5536 @itemx --ignore-case
5538 @opindex --ignore-case
5539 Ignore differences in case when comparing keys.
5540 With this option, the lines of the input files must be ordered in the same way.
5541 Use @samp{sort -f} to produce this ordering.
5543 @item -1 @var{field}
5545 Join on field @var{field} (a positive integer) of file 1.
5547 @item -2 @var{field}
5549 Join on field @var{field} (a positive integer) of file 2.
5551 @item -j @var{field}
5552 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5554 @item -o @var{field-list}
5555 Construct each output line according to the format in @var{field-list}.
5556 Each element in @var{field-list} is either the single character @samp{0} or
5557 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5558 @samp{2} and @var{n} is a positive field number.
5560 A field specification of @samp{0} denotes the join field.
5561 In most cases, the functionality of the @samp{0} field spec
5562 may be reproduced using the explicit @var{m.n} that corresponds
5563 to the join field. However, when printing unpairable lines
5564 (using either of the @option{-a} or @option{-v} options), there is no way
5565 to specify the join field using @var{m.n} in @var{field-list}
5566 if there are unpairable lines in both files.
5567 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5568 field specification notation.
5570 The elements in @var{field-list}
5571 are separated by commas or blanks.
5572 Blank separators typically need to be quoted for the shell. For
5573 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5574 2.2'} are equivalent.
5576 All output lines---including those printed because of any -a or -v
5577 option---are subject to the specified @var{field-list}.
5580 Use character @var{char} as the input and output field separator.
5581 Treat as significant each occurrence of @var{char} in the input file.
5582 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5583 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5584 the whole line is considered, matching the default operation of sort.
5585 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5586 character is used to delimit the fields.
5588 @item -v @var{file-number}
5589 Print a line for each unpairable line in file @var{file-number}
5590 (either @samp{1} or @samp{2}), instead of the normal output.
5597 @node Operating on characters
5598 @chapter Operating on characters
5600 @cindex operating on characters
5602 This commands operate on individual characters.
5605 * tr invocation:: Translate, squeeze, and/or delete characters.
5606 * expand invocation:: Convert tabs to spaces.
5607 * unexpand invocation:: Convert spaces to tabs.
5612 @section @command{tr}: Translate, squeeze, and/or delete characters
5619 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5622 @command{tr} copies standard input to standard output, performing
5623 one of the following operations:
5627 translate, and optionally squeeze repeated characters in the result,
5629 squeeze repeated characters,
5633 delete characters, then squeeze repeated characters from the result.
5636 The @var{set1} and (if given) @var{set2} arguments define ordered
5637 sets of characters, referred to below as @var{set1} and @var{set2}. These
5638 sets are the characters of the input that @command{tr} operates on.
5639 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5641 complement (all of the characters that are not in @var{set1}).
5643 Currently @command{tr} fully supports only single-byte characters.
5644 Eventually it will support multibyte characters; when it does, the
5645 @option{-C} option will cause it to complement the set of characters,
5646 whereas @option{-c} will cause it to complement the set of values.
5647 This distinction will matter only when some values are not characters,
5648 and this is possible only in locales using multibyte encodings when
5649 the input contains encoding errors.
5651 The program accepts the @option{--help} and @option{--version}
5652 options. @xref{Common options}. Options must precede operands.
5657 * Character sets:: Specifying sets of characters.
5658 * Translating:: Changing one set of characters to another.
5659 * Squeezing:: Squeezing repeats and deleting.
5663 @node Character sets
5664 @subsection Specifying sets of characters
5666 @cindex specifying sets of characters
5668 The format of the @var{set1} and @var{set2} arguments resembles
5669 the format of regular expressions; however, they are not regular
5670 expressions, only lists of characters. Most characters simply
5671 represent themselves in these strings, but the strings can contain
5672 the shorthands listed below, for convenience. Some of them can be
5673 used only in @var{set1} or @var{set2}, as noted below.
5677 @item Backslash escapes
5678 @cindex backslash escapes
5680 The following backslash escape sequences are recognized:
5698 The character with the value given by @var{ooo}, which is 1 to 3
5704 While a backslash followed by a character not listed above is
5705 interpreted as that character, the backslash also effectively
5706 removes any special significance, so it is useful to escape
5707 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5712 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5713 from @var{m} through @var{n}, in ascending order. @var{m} should
5714 collate before @var{n}; if it doesn't, an error results. As an example,
5715 @samp{0-9} is the same as @samp{0123456789}.
5717 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5718 brackets to enclose ranges. Translations specified in that format
5719 sometimes work as expected, since the brackets are often transliterated
5720 to themselves. However, they should be avoided because they sometimes
5721 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5724 Many historically common and even accepted uses of ranges are not
5725 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5726 range will not do what most would expect because @samp{A} through @samp{Z}
5727 are not contiguous as they are in @acronym{ASCII}.
5728 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5729 the best way to work around this is to use character classes (see below).
5730 Otherwise, it is most portable (and most ugly) to enumerate the members
5733 @item Repeated characters
5734 @cindex repeated characters
5736 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5737 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5738 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5739 to as many copies of @var{c} as are needed to make @var{set2} as long as
5740 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5741 octal, otherwise in decimal.
5743 @item Character classes
5744 @cindex character classes
5746 The notation @samp{[:@var{class}:]} expands to all of the characters in
5747 the (predefined) class @var{class}. The characters expand in no
5748 particular order, except for the @code{upper} and @code{lower} classes,
5749 which expand in ascending order. When the @option{--delete} (@option{-d})
5750 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5751 character class can be used in @var{set2}. Otherwise, only the
5752 character classes @code{lower} and @code{upper} are accepted in
5753 @var{set2}, and then only if the corresponding character class
5754 (@code{upper} and @code{lower}, respectively) is specified in the same
5755 relative position in @var{set1}. Doing this specifies case conversion.
5756 The class names are given below; an error results when an invalid class
5768 Horizontal whitespace.
5777 Printable characters, not including space.
5783 Printable characters, including space.
5786 Punctuation characters.
5789 Horizontal or vertical whitespace.
5798 @item Equivalence classes
5799 @cindex equivalence classes
5801 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5802 equivalent to @var{c}, in no particular order. Equivalence classes are
5803 a relatively recent invention intended to support non-English alphabets.
5804 But there seems to be no standard way to define them or determine their
5805 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5806 each character's equivalence class consists only of that character,
5807 which is of no particular use.
5813 @subsection Translating
5815 @cindex translating characters
5817 @command{tr} performs translation when @var{set1} and @var{set2} are
5818 both given and the @option{--delete} (@option{-d}) option is not given.
5819 @command{tr} translates each character of its input that is in @var{set1}
5820 to the corresponding character in @var{set2}. Characters not in
5821 @var{set1} are passed through unchanged. When a character appears more
5822 than once in @var{set1} and the corresponding characters in @var{set2}
5823 are not all the same, only the final one is used. For example, these
5824 two commands are equivalent:
5831 A common use of @command{tr} is to convert lowercase characters to
5832 uppercase. This can be done in many ways. Here are three of them:
5835 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5837 tr '[:lower:]' '[:upper:]'
5841 But note that using ranges like @code{a-z} above is not portable.
5843 When @command{tr} is performing translation, @var{set1} and @var{set2}
5844 typically have the same length. If @var{set1} is shorter than
5845 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5847 On the other hand, making @var{set1} longer than @var{set2} is not
5848 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5849 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5850 the last character of @var{set2} as many times as necessary. System V
5851 @command{tr} truncates @var{set1} to the length of @var{set2}.
5853 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5854 When the @option{--truncate-set1} (@option{-t}) option is given,
5855 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5856 instead. This option is ignored for operations other than translation.
5858 Acting like System V @command{tr} in this case breaks the relatively common
5862 tr -cs A-Za-z0-9 '\012'
5866 because it converts only zero bytes (the first element in the
5867 complement of @var{set1}), rather than all non-alphanumerics, to
5871 By the way, the above idiom is not portable because it uses ranges, and
5872 it assumes that the octal code for newline is 012.
5873 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5876 tr -cs '[:alnum:]' '[\n*]'
5881 @subsection Squeezing repeats and deleting
5883 @cindex squeezing repeat characters
5884 @cindex deleting characters
5886 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5887 removes any input characters that are in @var{set1}.
5889 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5890 @command{tr} replaces each input sequence of a repeated character that
5891 is in @var{set1} with a single occurrence of that character.
5893 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5894 first performs any deletions using @var{set1}, then squeezes repeats
5895 from any remaining characters using @var{set2}.
5897 The @option{--squeeze-repeats} option may also be used when translating,
5898 in which case @command{tr} first performs translation, then squeezes
5899 repeats from any remaining characters using @var{set2}.
5901 Here are some examples to illustrate various combinations of options:
5906 Remove all zero bytes:
5913 Put all words on lines by themselves. This converts all
5914 non-alphanumeric characters to newlines, then squeezes each string
5915 of repeated newlines into a single newline:
5918 tr -cs '[:alnum:]' '[\n*]'
5922 Convert each sequence of repeated newlines to a single newline:
5929 Find doubled occurrences of words in a document.
5930 @c Separate the following two "the"s, so typo checkers don't complain.
5931 For example, people often write ``the @w{}the'' with the repeated words
5932 separated by a newline. The Bourne shell script below works first
5933 by converting each sequence of punctuation and blank characters to a
5934 single newline. That puts each ``word'' on a line by itself.
5935 Next it maps all uppercase characters to lower case, and finally it
5936 runs @command{uniq} with the @option{-d} option to print out only the words
5942 | tr -s '[:punct:][:blank:]' '[\n*]' \
5943 | tr '[:upper:]' '[:lower:]' \
5948 Deleting a small set of characters is usually straightforward. For example,
5949 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5955 However, when @samp{-} is one of those characters, it can be tricky because
5956 @samp{-} has special meanings. Performing the same task as above but also
5957 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5958 that would fail because @command{tr} would try to interpret @option{-a} as
5959 a command-line option. Alternatively, we could try putting the hyphen
5960 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5961 it would make @command{tr} interpret @code{a-x} as the range of characters
5962 @samp{a}@dots{}@samp{x} rather than the three.
5963 One way to solve the problem is to put the hyphen at the end of the list
5970 Or you can use @samp{--} to terminate option processing:
5976 More generally, use the character class notation @code{[=c=]}
5977 with @samp{-} (or any other character) in place of the @samp{c}:
5983 Note how single quotes are used in the above example to protect the
5984 square brackets from interpretation by a shell.
5989 @node expand invocation
5990 @section @command{expand}: Convert tabs to spaces
5993 @cindex tabs to spaces, converting
5994 @cindex converting tabs to spaces
5996 @command{expand} writes the contents of each given @var{file}, or standard
5997 input if none are given or for a @var{file} of @samp{-}, to standard
5998 output, with tab characters converted to the appropriate number of
6002 expand [@var{option}]@dots{} [@var{file}]@dots{}
6005 By default, @command{expand} converts all tabs to spaces. It preserves
6006 backspace characters in the output; they decrement the column count for
6007 tab calculations. The default action is equivalent to @option{-t 8} (set
6008 tabs every 8 columns).
6010 The program accepts the following options. Also see @ref{Common options}.
6014 @item -t @var{tab1}[,@var{tab2}]@dots{}
6015 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6018 @cindex tab stops, setting
6019 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6020 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6021 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6022 last tab stop given with single spaces. Tab stops can be separated by
6023 blanks as well as by commas.
6025 For compatibility, GNU @command{expand} also accepts the obsolete
6026 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6027 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6033 @cindex initial tabs, converting
6034 Only convert initial tabs (those that precede all non-space or non-tab
6035 characters) on each line to spaces.
6042 @node unexpand invocation
6043 @section @command{unexpand}: Convert spaces to tabs
6047 @command{unexpand} writes the contents of each given @var{file}, or
6048 standard input if none are given or for a @var{file} of @samp{-}, to
6049 standard output, converting blanks at the beginning of each line into
6050 as many tab characters as needed. In the default @acronym{POSIX}
6051 locale, a @dfn{blank} is a space or a tab; other locales may specify
6052 additional blank characters. Synopsis:
6055 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6058 By default, @command{unexpand} converts only initial blanks (those
6059 that precede all non-blank characters) on each line. It
6060 preserves backspace characters in the output; they decrement the column
6061 count for tab calculations. By default, tabs are set at every 8th
6064 The program accepts the following options. Also see @ref{Common options}.
6068 @item -t @var{tab1}[,@var{tab2}]@dots{}
6069 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6072 If only one tab stop is given, set the tabs @var{tab1} columns apart
6073 instead of the default 8. Otherwise, set the tabs at columns
6074 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6075 beyond the tab stops given unchanged. Tab stops can be separated by
6076 blanks as well as by commas. This option implies the @option{-a} option.
6078 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6079 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6080 separated by commas. (Unlike @option{-t}, this obsolete option does
6081 not imply @option{-a}.) New scripts should use @option{--first-only -t
6082 @var{tab1}[,@var{tab2}]@dots{}} instead.
6088 Also convert all sequences of two or more blanks just before a tab stop,
6089 even if they occur after non-blank characters in a line.
6096 @node Directory listing
6097 @chapter Directory listing
6099 This chapter describes the @command{ls} command and its variants @command{dir}
6100 and @command{vdir}, which list information about files.
6103 * ls invocation:: List directory contents.
6104 * dir invocation:: Briefly ls.
6105 * vdir invocation:: Verbosely ls.
6106 * dircolors invocation:: Color setup for ls, etc.
6111 @section @command{ls}: List directory contents
6114 @cindex directory listing
6116 The @command{ls} program lists information about files (of any type,
6117 including directories). Options and file arguments can be intermixed
6118 arbitrarily, as usual.
6120 For non-option command-line arguments that are directories, by default
6121 @command{ls} lists the contents of directories, not recursively, and
6122 omitting files with names beginning with @samp{.}. For other non-option
6123 arguments, by default @command{ls} lists just the file name. If no
6124 non-option argument is specified, @command{ls} operates on the current
6125 directory, acting as if it had been invoked with a single argument of @samp{.}.
6128 By default, the output is sorted alphabetically, according to the locale
6129 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6130 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6131 produce output that is sorted differently than you're accustomed to.
6132 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6133 If standard output is
6134 a terminal, the output is in columns (sorted vertically) and control
6135 characters are output as question marks; otherwise, the output is listed
6136 one per line and control characters are output as-is.
6138 Because @command{ls} is such a fundamental program, it has accumulated many
6139 options over the years. They are described in the subsections below;
6140 within each section, options are listed alphabetically (ignoring case).
6141 The division of options into the subsections is not absolute, since some
6142 options affect more than one aspect of @command{ls}'s operation.
6144 @cindex exit status of @command{ls}
6149 1 minor problems (e.g., failure to access a file or directory not
6150 specified as a command line argument. This happens when listing a
6151 directory in which entries are actively being removed or renamed.)
6152 2 serious trouble (e.g., memory exhausted, invalid option, failure
6153 to access a file or directory specified as a command line argument
6154 or a directory loop)
6157 Also see @ref{Common options}.
6160 * Which files are listed::
6161 * What information is listed::
6162 * Sorting the output::
6163 * Details about version sort::
6164 * General output formatting::
6165 * Formatting file timestamps::
6166 * Formatting the file names::
6170 @node Which files are listed
6171 @subsection Which files are listed
6173 These options determine which files @command{ls} lists information for.
6174 By default, @command{ls} lists files and the contents of any
6175 directories on the command line, except that in directories it ignores
6176 files whose names start with @samp{.}.
6184 In directories, do not ignore file names that start with @samp{.}.
6189 @opindex --almost-all
6190 In directories, do not ignore all file names that start with @samp{.};
6191 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6192 option overrides this option.
6195 @itemx --ignore-backups
6197 @opindex --ignore-backups
6198 @cindex backup files, ignoring
6199 In directories, ignore files that end with @samp{~}. This option is
6200 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6205 @opindex --directory
6206 List just the names of directories, as with other types of files, rather
6207 than listing their contents.
6208 @c The following sentence is the same as the one for -F.
6209 Do not follow symbolic links listed on the
6210 command line unless the @option{--dereference-command-line} (@option{-H}),
6211 @option{--dereference} (@option{-L}), or
6212 @option{--dereference-command-line-symlink-to-dir} options are specified.
6215 @itemx --dereference-command-line
6217 @opindex --dereference-command-line
6218 @cindex symbolic links, dereferencing
6219 If a command line argument specifies a symbolic link, show information
6220 for the file the link references rather than for the link itself.
6222 @itemx --dereference-command-line-symlink-to-dir
6223 @opindex --dereference-command-line-symlink-to-dir
6224 @cindex symbolic links, dereferencing
6225 Do not dereference symbolic links, with one exception:
6226 if a command line argument specifies a symbolic link that refers to
6227 a directory, show information for that directory rather than for the
6229 This is the default behavior when no other dereferencing-related
6230 option has been specified (@option{--classify} (@option{-F}),
6231 @option{--directory} (@option{-d}),
6233 @option{--dereference} (@option{-L}), or
6234 @option{--dereference-command-line} (@option{-H})).
6236 @item --group-directories-first
6237 @opindex --group-directories-first
6238 Group all the directories before the files and then sort the
6239 directories and the files separately using the selected sort key
6240 (see --sort option).
6241 That is, this option specifies a primary sort key,
6242 and the --sort option specifies a secondary key.
6243 However, any use of @option{--sort=none}
6244 (@option{-U}) disables this option altogether.
6246 @item --hide=PATTERN
6247 @opindex --hide=@var{pattern}
6248 In directories, ignore files whose names match the shell pattern
6249 @var{pattern}, unless the @option{--all} (@option{-a}) or
6250 @option{--almost-all} (@option{-A}) is also given. This
6251 option acts like @option{--ignore=@var{pattern}} except that it has no
6252 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6253 (@option{-A}) is also given.
6255 This option can be useful in shell aliases. For example, if
6256 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6257 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6258 lists the file @file{README~} even though @samp{ly -A} would not.
6260 @item -I @var{pattern}
6261 @itemx --ignore=@var{pattern}
6263 @opindex --ignore=@var{pattern}
6264 In directories, ignore files whose names match the shell pattern
6265 (not regular expression) @var{pattern}. As
6266 in the shell, an initial @samp{.} in a file name does not match a
6267 wildcard at the start of @var{pattern}. Sometimes it is useful
6268 to give this option several times. For example,
6271 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6274 The first option ignores names of length 3 or more that start with @samp{.},
6275 the second ignores all two-character names that start with @samp{.}
6276 except @samp{..}, and the third ignores names that start with @samp{#}.
6279 @itemx --dereference
6281 @opindex --dereference
6282 @cindex symbolic links, dereferencing
6283 When showing file information for a symbolic link, show information
6284 for the file the link references rather than the link itself.
6285 However, even with this option, @command{ls} still prints the name
6286 of the link itself, not the name of the file that the link points to.
6291 @opindex --recursive
6292 @cindex recursive directory listing
6293 @cindex directory listing, recursive
6294 List the contents of all directories recursively.
6299 @node What information is listed
6300 @subsection What information is listed
6302 These options affect the information that @command{ls} displays. By
6303 default, only file names are shown.
6309 @cindex hurd, author, printing
6310 List each file's author when producing long format directory listings.
6311 In GNU/Hurd, file authors can differ from their owners, but in other
6312 operating systems the two are the same.
6318 @cindex dired Emacs mode support
6319 With the long listing (@option{-l}) format, print an additional line after
6323 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6327 The @var{begn} and @var{endn} are unsigned integers that record the
6328 byte position of the beginning and end of each file name in the output.
6329 This makes it easy for Emacs to find the names, even when they contain
6330 unusual characters such as space or newline, without fancy searching.
6332 If directories are being listed recursively (@option{-R}), output a similar
6333 line with offsets for each subdirectory name:
6336 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6339 Finally, output a line of the form:
6342 //DIRED-OPTIONS// --quoting-style=@var{word}
6346 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6348 Here is an actual example:
6351 $ mkdir -p a/sub/deeper a/sub2
6353 $ touch a/sub/deeper/file
6354 $ ls -gloRF --dired a
6357 -rw-r--r-- 1 0 Jun 10 12:27 f1
6358 -rw-r--r-- 1 0 Jun 10 12:27 f2
6359 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6360 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6364 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6368 -rw-r--r-- 1 0 Jun 10 12:27 file
6372 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6373 //SUBDIRED// 2 3 167 172 228 240 290 296
6374 //DIRED-OPTIONS// --quoting-style=literal
6377 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6378 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6380 The offsets on the @samp{//SUBDIRED//} line delimit the following
6381 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6383 Here is an example of how to extract the fifth entry name, @samp{deeper},
6384 corresponding to the pair of offsets, 222 and 228:
6387 $ ls -gloRF --dired a > out
6388 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6392 Note that although the listing above includes a trailing slash
6393 for the @samp{deeper} entry, the offsets select the name without
6394 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6395 along with an option like @option{--escape} (aka @option{-b}) and operate
6396 on a file whose name contains special characters, notice that the backslash
6401 $ ls -blog --dired 'a b'
6402 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6404 //DIRED-OPTIONS// --quoting-style=escape
6407 If you use a quoting style that adds quote marks
6408 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6409 So beware that the user may select the quoting style via the environment
6410 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6411 should either specify an explicit @option{--quoting-style=literal} option
6412 (aka @option{-N} or @option{--literal}) on the command line, or else be
6413 prepared to parse the escaped names.
6416 @opindex --full-time
6417 Produce long format directory listings, and list times in full. It is
6418 equivalent to using @option{--format=long} with
6419 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6423 Produce long format directory listings, but don't display owner information.
6429 Inhibit display of group information in a long format directory listing.
6430 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6431 provide this option for compatibility.)
6439 @cindex inode number, printing
6440 Print the inode number (also called the file serial number and index
6441 number) of each file to the left of the file name. (This number
6442 uniquely identifies each file within a particular file system.)
6445 @itemx --format=long
6446 @itemx --format=verbose
6449 @opindex long ls @r{format}
6450 @opindex verbose ls @r{format}
6451 In addition to the name of each file, print the file type, file mode bits,
6452 number of hard links, owner name, group name, size, and
6453 timestamp (@pxref{Formatting file timestamps}), normally
6454 the modification time. Print question marks for information that
6455 cannot be determined.
6457 Normally the size is printed as a byte count without punctuation, but
6458 this can be overridden (@pxref{Block size}). For example, @option{-h}
6459 prints an abbreviated, human-readable count, and
6460 @samp{--block-size="'1"} prints a byte count with the thousands
6461 separator of the current locale.
6463 For each directory that is listed, preface the files with a line
6464 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6465 for all files in that directory. The block size currently defaults to 1024
6466 bytes, but this can be overridden (@pxref{Block size}).
6467 The @var{blocks} computed counts each hard link separately;
6468 this is arguably a deficiency.
6470 The file type is one of the following characters:
6472 @c The commented-out entries are ones we're not sure about.
6480 character special file
6482 high performance (``contiguous data'') file
6486 door (Solaris 2.5 and up)
6488 @c semaphore, if this is a distinct file type
6492 @c multiplexed file (7th edition Unix; obsolete)
6494 off-line (``migrated'') file (Cray DMF)
6496 network special file (HP-UX)
6500 port (Solaris 10 and up)
6502 @c message queue, if this is a distinct file type
6506 @c shared memory object, if this is a distinct file type
6508 @c typed memory object, if this is a distinct file type
6510 @c whiteout (4.4BSD; not implemented)
6512 some other file type
6515 @cindex permissions, output by @command{ls}
6516 The file mode bits listed are similar to symbolic mode specifications
6517 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6518 third character of each set of permissions as follows:
6522 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6526 If the set-user-ID or set-group-ID bit is set but the corresponding
6527 executable bit is not set.
6530 If the restricted deletion flag or sticky bit, and the
6531 other-executable bit, are both set. The restricted deletion flag is
6532 another name for the sticky bit. @xref{Mode Structure}.
6535 If the restricted deletion flag or sticky bit is set but the
6536 other-executable bit is not set.
6539 If the executable bit is set and none of the above apply.
6545 Following the file mode bits is a single character that specifies
6546 whether an alternate access method such as an access control list
6547 applies to the file. When the character following the file mode bits is a
6548 space, there is no alternate access method. When it is a printing
6549 character, then there is such a method.
6551 GNU @command{ls} uses a @samp{.} character to indicate a file
6552 with an SELinux security context, but no other alternate access method.
6554 A file with any other combination of alternate access methods
6555 is marked with a @samp{+} character.
6558 @itemx --numeric-uid-gid
6560 @opindex --numeric-uid-gid
6561 @cindex numeric uid and gid
6562 @cindex numeric user and group IDs
6563 Produce long format directory listings, but
6564 display numeric user and group IDs instead of the owner and group names.
6568 Produce long format directory listings, but don't display group information.
6569 It is equivalent to using @option{--format=long} with @option{--no-group} .
6575 @cindex disk allocation
6576 @cindex size of files, reporting
6577 Print the disk allocation of each file to the left of the file name.
6578 This is the amount of disk space used by the file, which is usually a
6579 bit more than the file's size, but it can be less if the file has holes.
6581 Normally the disk allocation is printed in units of
6582 1024 bytes, but this can be overridden (@pxref{Block size}).
6584 @cindex NFS mounts from BSD to HP-UX
6585 For files that are NFS-mounted from an HP-UX system to a BSD system,
6586 this option reports sizes that are half the correct values. On HP-UX
6587 systems, it reports sizes that are twice the correct values for files
6588 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6589 it also affects the HP-UX @command{ls} program.
6598 @cindex security context
6599 Display the SELinux security context or @samp{?} if none is found.
6600 When used with the @option{-l} option, print the security context
6601 to the left of the size column.
6606 @node Sorting the output
6607 @subsection Sorting the output
6609 @cindex sorting @command{ls} output
6610 These options change the order in which @command{ls} sorts the information
6611 it outputs. By default, sorting is done by character code
6612 (e.g., @acronym{ASCII} order).
6618 @itemx --time=status
6621 @opindex ctime@r{, printing or sorting by}
6622 @opindex status time@r{, printing or sorting by}
6623 @opindex use time@r{, printing or sorting files by}
6624 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6625 print the status change time (the @samp{ctime} in the inode) instead of
6626 the modification time.
6627 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6628 or when not using a long listing format,
6629 sort according to the status change time.
6633 @cindex unsorted directory listing
6634 @cindex directory order, listing by
6635 Primarily, like @option{-U}---do not sort; list the files in whatever
6636 order they are stored in the directory. But also enable @option{-a} (list
6637 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6638 were specified before the @option{-f}).
6644 @cindex reverse sorting
6645 Reverse whatever the sorting method is---e.g., list files in reverse
6646 alphabetical order, youngest first, smallest first, or whatever.
6652 @opindex size of files@r{, sorting files by}
6653 Sort by file size, largest first.
6659 @opindex modification time@r{, sorting files by}
6660 Sort by modification time (the @samp{mtime} in the inode), newest first.
6664 @itemx --time=access
6668 @opindex use time@r{, printing or sorting files by}
6669 @opindex atime@r{, printing or sorting files by}
6670 @opindex access time@r{, printing or sorting files by}
6671 If the long listing format (e.g., @option{--format=long}) is being used,
6672 print the last access time (the @samp{atime} in the inode).
6673 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6674 or when not using a long listing format, sort according to the access time.
6680 @opindex none@r{, sorting option for @command{ls}}
6681 Do not sort; list the files in whatever order they are
6682 stored in the directory. (Do not do any of the other unrelated things
6683 that @option{-f} does.) This is especially useful when listing very large
6684 directories, since not doing any sorting can be noticeably faster.
6687 @itemx --sort=version
6690 @opindex version@r{, sorting option for @command{ls}}
6691 Sort by version name and number, lowest first. It behaves like a default
6692 sort, except that each sequence of decimal digits is treated numerically
6693 as an index/version number. (@xref{Details about version sort}.)
6696 @itemx --sort=extension
6699 @opindex extension@r{, sorting files by}
6700 Sort directory contents alphabetically by file extension (characters
6701 after the last @samp{.}); files with no extension are sorted first.
6706 @node Details about version sort
6707 @subsection Details about version sort
6709 Version sorting handles the fact that file names frequently include indices or
6710 version numbers. Standard sorting usually does not produce the order that one
6711 expects because comparisons are made on a character-by-character basis.
6712 Version sorting is especially useful when browsing directories that contain
6713 many files with indices/version numbers in their names:
6717 abc.zml-1.gz abc.zml-1.gz
6718 abc.zml-12.gz abc.zml-2.gz
6719 abc.zml-2.gz abc.zml-12.gz
6722 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6723 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6724 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6725 @var{ver1} < @var{ver2} implies that the name composed of
6726 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6727 ``@var{prefix} @var{ver2} @var{suffix}''.
6729 Note also that leading zeros of numeric parts are ignored:
6733 abc-1.007.tgz abc-1.01a.tgz
6734 abc-1.012b.tgz abc-1.007.tgz
6735 abc-1.01a.tgz abc-1.012b.tgz
6738 This functionality is implemented using gnulib's @code{filevercmp} function,
6739 which has some caveats worth noting.
6742 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6743 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6744 was set to @samp{C}.
6745 @item Some suffixes will not be matched by the regular
6746 expression mentioned above. Consequently these examples may
6747 not sort as you expect:
6755 abc-1.2.3.4.x86_64.rpm
6756 abc-1.2.3.x86_64.rpm
6760 @node General output formatting
6761 @subsection General output formatting
6763 These options affect the appearance of the overall output.
6768 @itemx --format=single-column
6771 @opindex single-column @r{output of files}
6772 List one file per line. This is the default for @command{ls} when standard
6773 output is not a terminal.
6776 @itemx --format=vertical
6779 @opindex vertical @r{sorted files in columns}
6780 List files in columns, sorted vertically. This is the default for
6781 @command{ls} if standard output is a terminal. It is always the default
6782 for the @command{dir} program.
6783 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6784 possible in the fewest lines.
6786 @item --color [=@var{when}]
6788 @cindex color, distinguishing file types with
6789 Specify whether to use color for distinguishing file types. @var{when}
6790 may be omitted, or one of:
6793 @vindex none @r{color option}
6794 - Do not use color at all. This is the default.
6796 @vindex auto @r{color option}
6797 @cindex terminal, using color iff
6798 - Only use color if standard output is a terminal.
6800 @vindex always @r{color option}
6803 Specifying @option{--color} and no @var{when} is equivalent to
6804 @option{--color=always}.
6805 Piping a colorized listing through a pager like @command{more} or
6806 @command{less} usually produces unreadable results. However, using
6807 @code{more -f} does seem to work.
6811 @itemx --indicator-style=classify
6814 @opindex --indicator-style
6815 @cindex file type and executables, marking
6816 @cindex executables and file type, marking
6817 Append a character to each file name indicating the file type. Also,
6818 for regular files that are executable, append @samp{*}. The file type
6819 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6820 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6821 and nothing for regular files.
6822 @c The following sentence is the same as the one for -d.
6823 Do not follow symbolic links listed on the
6824 command line unless the @option{--dereference-command-line} (@option{-H}),
6825 @option{--dereference} (@option{-L}), or
6826 @option{--dereference-command-line-symlink-to-dir} options are specified.
6829 @itemx --indicator-style=file-type
6830 @opindex --file-type
6831 @opindex --indicator-style
6832 @cindex file type, marking
6833 Append a character to each file name indicating the file type. This is
6834 like @option{-F}, except that executables are not marked.
6836 @item --indicator-style=@var{word}
6837 @opindex --indicator-style
6838 Append a character indicator with style @var{word} to entry names,
6843 Do not append any character indicator; this is the default.
6845 Append @samp{/} for directories. This is the same as the @option{-p}
6848 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6849 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6850 the same as the @option{--file-type} option.
6852 Append @samp{*} for executable regular files, otherwise behave as for
6853 @samp{file-type}. This is the same as the @option{-F} or
6854 @option{--classify} option.
6859 Print file sizes in 1024-byte blocks, overriding the default block
6860 size (@pxref{Block size}).
6861 This option is equivalent to @option{--block-size=1K}.
6864 @itemx --format=commas
6867 @opindex commas@r{, outputting between files}
6868 List files horizontally, with as many as will fit on each line,
6869 separated by @samp{, } (a comma and a space).
6872 @itemx --indicator-style=slash
6874 @opindex --indicator-style
6875 @cindex file type, marking
6876 Append a @samp{/} to directory names.
6879 @itemx --format=across
6880 @itemx --format=horizontal
6883 @opindex across@r{, listing files}
6884 @opindex horizontal@r{, listing files}
6885 List the files in columns, sorted horizontally.
6888 @itemx --tabsize=@var{cols}
6891 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6892 @command{ls} uses tabs where possible in the output, for efficiency. If
6893 @var{cols} is zero, do not use tabs at all.
6895 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6896 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6897 do not properly align columns to the right of a TAB following a
6898 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6899 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6900 @command{ls} to align using spaces, not tabs.
6903 @itemx --width=@var{cols}
6907 Assume the screen is @var{cols} columns wide. The default is taken
6908 from the terminal settings if possible; otherwise the environment
6909 variable @env{COLUMNS} is used if it is set; otherwise the default
6915 @node Formatting file timestamps
6916 @subsection Formatting file timestamps
6918 By default, file timestamps are listed in abbreviated form. Most
6919 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6920 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6921 for non-recent timestamps, and a date-without-year and time like
6922 @samp{Mar 30 23:45} for recent timestamps.
6924 A timestamp is considered to be @dfn{recent} if it is less than six
6925 months old, and is not dated in the future. If a timestamp dated
6926 today is not listed in recent form, the timestamp is in the future,
6927 which means you probably have clock skew problems which may break
6928 programs like @command{make} that rely on file timestamps.
6931 Time stamps are listed according to the time zone rules specified by
6932 the @env{TZ} environment variable, or by the system default rules if
6933 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6934 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6936 The following option changes how file timestamps are printed.
6939 @item --time-style=@var{style}
6940 @opindex --time-style
6942 List timestamps in style @var{style}. The @var{style} should
6943 be one of the following:
6948 List timestamps using @var{format}, where @var{format} is interpreted
6949 like the format argument of @command{date} (@pxref{date invocation}).
6950 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6951 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6952 with @command{date}, @var{format}'s interpretation is affected by the
6953 @env{LC_TIME} locale category.
6955 If @var{format} contains two format strings separated by a newline,
6956 the former is used for non-recent files and the latter for recent
6957 files; if you want output columns to line up, you may need to insert
6958 spaces in one of the two formats.
6961 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6962 format with nanosecond precision, e.g., @samp{2002-03-30
6963 23:45:56.477817180 -0700}. This style is equivalent to
6964 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6966 This is useful because the time output includes all the information that
6967 is available from the operating system. For example, this can help
6968 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6969 uses the full timestamp to determine whether a file is out of date.
6972 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6973 @samp{2002-03-30 23:45}. These timestamps are shorter than
6974 @samp{full-iso} timestamps, and are usually good enough for everyday
6975 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6978 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6979 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6980 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6981 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6982 nearly the same information in a smaller space and their brevity helps
6983 @command{ls} output fit within traditional 80-column output lines.
6984 The following two @command{ls} invocations are equivalent:
6989 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
6990 ls -l --time-style="iso"
6995 List timestamps in a locale-dependent form. For example, a Finnish
6996 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
6997 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
6998 timestamps typically consume more space than @samp{iso} timestamps and
6999 are harder for programs to parse because locale conventions vary so
7000 widely, but they are easier for many people to read.
7002 The @env{LC_TIME} locale category specifies the timestamp format. The
7003 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7004 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7005 @command{ls} invocations are equivalent:
7010 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7011 ls -l --time-style="locale"
7014 Other locales behave differently. For example, in a German locale,
7015 @option{--time-style="locale"} might be equivalent to
7016 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7017 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7018 @samp{30. M@"ar 23:45}.
7020 @item posix-@var{style}
7022 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7023 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7024 example, the @samp{posix-long-iso} style lists
7025 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7026 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7031 You can specify the default value of the @option{--time-style} option
7032 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7033 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7034 later use the @option{--dired} option and therefore can parse any date
7035 format, but if you are using Emacs 21.1 or 21.2 and specify a
7036 non-@acronym{POSIX} locale you may need to set
7037 @samp{TIME_STYLE="posix-long-iso"}.
7039 To avoid certain denial-of-service attacks, timestamps that would be
7040 longer than 1000 bytes may be treated as errors.
7043 @node Formatting the file names
7044 @subsection Formatting the file names
7046 These options change how file names themselves are printed.
7052 @itemx --quoting-style=escape
7055 @opindex --quoting-style
7056 @cindex backslash sequences for file names
7057 Quote nongraphic characters in file names using alphabetic and octal
7058 backslash sequences like those used in C.
7062 @itemx --quoting-style=literal
7065 @opindex --quoting-style
7066 Do not quote file names. However, with @command{ls} nongraphic
7067 characters are still printed as question marks if the output is a
7068 terminal and you do not specify the @option{--show-control-chars}
7072 @itemx --hide-control-chars
7074 @opindex --hide-control-chars
7075 Print question marks instead of nongraphic characters in file names.
7076 This is the default if the output is a terminal and the program is
7081 @itemx --quoting-style=c
7083 @opindex --quote-name
7084 @opindex --quoting-style
7085 Enclose file names in double quotes and quote nongraphic characters as
7088 @item --quoting-style=@var{word}
7089 @opindex --quoting-style
7090 @cindex quoting style
7091 Use style @var{word} to quote file names and other strings that may
7092 contain arbitrary characters. The @var{word} should
7093 be one of the following:
7097 Output strings as-is; this is the same as the @option{-N} or
7098 @option{--literal} option.
7100 Quote strings for the shell if they contain shell metacharacters or would
7101 cause ambiguous output.
7102 The quoting is suitable for @acronym{POSIX}-compatible shells like
7103 @command{bash}, but it does not always work for incompatible shells
7106 Quote strings for the shell, even if they would normally not require quoting.
7108 Quote strings as for C character string literals, including the
7109 surrounding double-quote characters; this is the same as the
7110 @option{-Q} or @option{--quote-name} option.
7112 Quote strings as for C character string literals, except omit the
7113 surrounding double-quote
7114 characters; this is the same as the @option{-b} or @option{--escape} option.
7116 Quote strings as for C character string literals, except use
7117 surrounding quotation marks appropriate for the
7120 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7121 Quote strings as for C character string literals, except use
7122 surrounding quotation marks appropriate for the locale, and quote
7123 @t{`like this'} instead of @t{"like
7124 this"} in the default C locale. This looks nicer on many displays.
7127 You can specify the default value of the @option{--quoting-style} option
7128 with the environment variable @env{QUOTING_STYLE}. If that environment
7129 variable is not set, the default value is @samp{literal}, but this
7130 default may change to @samp{shell} in a future version of this package.
7132 @item --show-control-chars
7133 @opindex --show-control-chars
7134 Print nongraphic characters as-is in file names.
7135 This is the default unless the output is a terminal and the program is
7141 @node dir invocation
7142 @section @command{dir}: Briefly list directory contents
7145 @cindex directory listing, brief
7147 @command{dir} is equivalent to @code{ls -C
7148 -b}; that is, by default files are listed in columns, sorted vertically,
7149 and special characters are represented by backslash escape sequences.
7151 @xref{ls invocation, @command{ls}}.
7154 @node vdir invocation
7155 @section @command{vdir}: Verbosely list directory contents
7158 @cindex directory listing, verbose
7160 @command{vdir} is equivalent to @code{ls -l
7161 -b}; that is, by default files are listed in long format and special
7162 characters are represented by backslash escape sequences.
7164 @node dircolors invocation
7165 @section @command{dircolors}: Color setup for @command{ls}
7169 @cindex setup for color
7171 @command{dircolors} outputs a sequence of shell commands to set up the
7172 terminal for color output from @command{ls} (and @command{dir}, etc.).
7176 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7179 If @var{file} is specified, @command{dircolors} reads it to determine which
7180 colors to use for which file types and extensions. Otherwise, a
7181 precompiled database is used. For details on the format of these files,
7182 run @samp{dircolors --print-database}.
7184 To make @command{dircolors} read a @file{~/.dircolors} file if it
7185 exists, you can put the following lines in your @file{~/.bashrc} (or
7186 adapt them to your favorite shell):
7190 test -r $d && eval "$(dircolors $d)"
7194 @vindex SHELL @r{environment variable, and color}
7195 The output is a shell command to set the @env{LS_COLORS} environment
7196 variable. You can specify the shell syntax to use on the command line,
7197 or @command{dircolors} will guess it from the value of the @env{SHELL}
7198 environment variable.
7200 The program accepts the following options. Also see @ref{Common options}.
7205 @itemx --bourne-shell
7208 @opindex --bourne-shell
7209 @cindex Bourne shell syntax for color setup
7210 @cindex @command{sh} syntax for color setup
7211 Output Bourne shell commands. This is the default if the @env{SHELL}
7212 environment variable is set and does not end with @samp{csh} or
7221 @cindex C shell syntax for color setup
7222 @cindex @command{csh} syntax for color setup
7223 Output C shell commands. This is the default if @code{SHELL} ends with
7224 @command{csh} or @command{tcsh}.
7227 @itemx --print-database
7229 @opindex --print-database
7230 @cindex color database, printing
7231 @cindex database for color setup, printing
7232 @cindex printing color database
7233 Print the (compiled-in) default color configuration database. This
7234 output is itself a valid configuration file, and is fairly descriptive
7235 of the possibilities.
7242 @node Basic operations
7243 @chapter Basic operations
7245 @cindex manipulating files
7247 This chapter describes the commands for basic file manipulation:
7248 copying, moving (renaming), and deleting (removing).
7251 * cp invocation:: Copy files.
7252 * dd invocation:: Convert and copy a file.
7253 * install invocation:: Copy files and set attributes.
7254 * mv invocation:: Move (rename) files.
7255 * rm invocation:: Remove files or directories.
7256 * shred invocation:: Remove files more securely.
7261 @section @command{cp}: Copy files and directories
7264 @cindex copying files and directories
7265 @cindex files, copying
7266 @cindex directories, copying
7268 @command{cp} copies files (or, optionally, directories). The copy is
7269 completely independent of the original. You can either copy one file to
7270 another, or copy arbitrarily many files to a destination directory.
7274 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7275 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7276 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7281 If two file names are given, @command{cp} copies the first file to the
7285 If the @option{--target-directory} (@option{-t}) option is given, or
7286 failing that if the last file is a directory and the
7287 @option{--no-target-directory} (@option{-T}) option is not given,
7288 @command{cp} copies each @var{source} file to the specified directory,
7289 using the @var{source}s' names.
7292 Generally, files are written just as they are read. For exceptions,
7293 see the @option{--sparse} option below.
7295 By default, @command{cp} does not copy directories. However, the
7296 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7297 copy recursively by descending into source directories and copying files
7298 to corresponding destination directories.
7300 When copying from a symbolic link, @command{cp} normally follows the
7301 link only when not copying
7302 recursively. This default can be overridden with the
7303 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7304 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7305 @option{-H} options. If more than one of these options is specified,
7306 the last one silently overrides the others.
7308 When copying to a symbolic link, @command{cp} follows the
7309 link only when it refers to an existing regular file.
7310 However, when copying to a dangling symbolic link, @command{cp}
7311 refuses by default, and fails with a diagnostic, since the operation
7312 is inherently dangerous. This behavior is contrary to historical
7313 practice and to @acronym{POSIX}.
7314 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7315 the target of a dangling destination symlink, in spite of the possible risk.
7316 Also, when an option like
7317 @option{--backup} or @option{--link} acts to rename or remove the
7318 destination before copying, @command{cp} renames or removes the
7319 symbolic link rather than the file it points to.
7321 By default, @command{cp} copies the contents of special files only
7322 when not copying recursively. This default can be overridden with the
7323 @option{--copy-contents} option.
7325 @cindex self-backups
7326 @cindex backups, making only
7327 @command{cp} generally refuses to copy a file onto itself, with the
7328 following exception: if @option{--force --backup} is specified with
7329 @var{source} and @var{dest} identical, and referring to a regular file,
7330 @command{cp} will make a backup file, either regular or numbered, as
7331 specified in the usual ways (@pxref{Backup options}). This is useful when
7332 you simply want to make a backup of an existing file before changing it.
7334 The program accepts the following options. Also see @ref{Common options}.
7341 Preserve as much as possible of the structure and attributes of the
7342 original files in the copy (but do not attempt to preserve internal
7343 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7344 directory in a different order).
7345 Try to preserve SELinux security context and extended attributes (xattr),
7346 but ignore any failure to do that and print no corresponding diagnostic.
7347 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7350 @itemx @w{@kbd{--backup}[=@var{method}]}
7353 @vindex VERSION_CONTROL
7354 @cindex backups, making
7355 @xref{Backup options}.
7356 Make a backup of each file that would otherwise be overwritten or removed.
7357 As a special case, @command{cp} makes a backup of @var{source} when the force
7358 and backup options are given and @var{source} and @var{dest} are the same
7359 name for an existing, regular file. One useful application of this
7360 combination of options is this tiny Bourne shell script:
7364 # Usage: backup FILE...
7365 # Create a @sc{gnu}-style backup of each listed FILE.
7367 cp --backup --force -- "$i" "$i"
7371 @item --copy-contents
7372 @cindex directories, copying recursively
7373 @cindex copying directories recursively
7374 @cindex recursively copying directories
7375 @cindex non-directories, copying as special files
7376 If copying recursively, copy the contents of any special files (e.g.,
7377 FIFOs and device files) as if they were regular files. This means
7378 trying to read the data in each source file and writing it to the
7379 destination. It is usually a mistake to use this option, as it
7380 normally has undesirable effects on special files like FIFOs and the
7381 ones typically found in the @file{/dev} directory. In most cases,
7382 @code{cp -R --copy-contents} will hang indefinitely trying to read
7383 from FIFOs and special files like @file{/dev/console}, and it will
7384 fill up your destination disk if you use it to copy @file{/dev/zero}.
7385 This option has no effect unless copying recursively, and it does not
7386 affect the copying of symbolic links.
7390 @cindex symbolic links, copying
7391 @cindex hard links, preserving
7392 Copy symbolic links as symbolic links rather than copying the files that
7393 they point to, and preserve hard links between source files in the copies.
7394 Equivalent to @option{--no-dereference --preserve=links}.
7400 When copying without this option and an existing destination file cannot
7401 be opened for writing, the copy fails. However, with @option{--force}),
7402 when a destination file cannot be opened, @command{cp} then removes it and
7403 tries to open it again. Contrast this behavior with that enabled by
7404 @option{--link} and @option{--symbolic-link}, whereby the destination file
7405 is never opened but rather is removed unconditionally. Also see the
7406 description of @option{--remove-destination}.
7408 This option is independent of the @option{--interactive} or
7409 @option{-i} option: neither cancels the effect of the other.
7411 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7416 If a command line argument specifies a symbolic link, then copy the
7417 file it points to rather than the symbolic link itself. However,
7418 copy (preserving its nature) any symbolic link that is encountered
7419 via recursive traversal.
7422 @itemx --interactive
7424 @opindex --interactive
7425 When copying a file other than a directory, prompt whether to
7426 overwrite an existing destination file. The @option{-i} option overrides
7427 a previous @option{-n} option.
7433 Make hard links instead of copies of non-directories.
7436 @itemx --dereference
7438 @opindex --dereference
7439 Follow symbolic links when copying from them.
7440 With this option, @command{cp} cannot create a symbolic link.
7441 For example, a symlink (to regular file) in the source tree will be copied to
7442 a regular file in the destination tree.
7447 @opindex --no-clobber
7448 Do not overwrite an existing file. The @option{-n} option overrides a previous
7449 @option{-i} option. This option is mutually exclusive with @option{-b} or
7450 @option{--backup} option.
7453 @itemx --no-dereference
7455 @opindex --no-dereference
7456 @cindex symbolic links, copying
7457 Copy symbolic links as symbolic links rather than copying the files that
7458 they point to. This option affects only symbolic links in the source;
7459 symbolic links in the destination are always followed if possible.
7462 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7465 @cindex file information, preserving, extended attributes, xattr
7466 Preserve the specified attributes of the original files.
7467 If specified, the @var{attribute_list} must be a comma-separated list
7468 of one or more of the following strings:
7472 Preserve the file mode bits and access control lists.
7474 Preserve the owner and group. On most modern systems,
7475 only users with appropriate privileges may change the owner of a file,
7477 may preserve the group ownership of a file only if they happen to be
7478 a member of the desired group.
7480 Preserve the times of last access and last modification, when possible.
7481 On older systems, it is not possible to preserve these attributes
7482 when the affected file is a symbolic link.
7483 However, many systems now provide the @code{utimensat} function,
7484 which makes it possible even for symbolic links.
7486 Preserve in the destination files
7487 any links between corresponding source files.
7488 Note that with @option{-L} or @option{-H}, this option can convert
7489 symbolic links to hard links. For example,
7491 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7496 Note the inputs: @file{b} is a symlink to regular file @file{a},
7497 yet the files in destination directory, @file{c/}, are hard-linked.
7498 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7499 tells @command{cp} to dereference command line arguments, it sees two files
7500 with the same inode number, and preserves the perceived hard link.
7502 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7504 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7510 Preserve SELinux security context of the file, or fail with full diagnostics.
7512 Preserve extended attributes of the file, or fail with full diagnostics.
7513 If @command{cp} is built without xattr support, ignore this option.
7514 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7515 they are preserved by this option as well.
7517 Preserve all file attributes.
7518 Equivalent to specifying all of the above, but with the difference
7519 that failure to preserve SELinux security context or extended attributes
7520 does not change @command{cp}'s exit status. In contrast to @option{-a},
7521 all but @samp{Operation not supported} warnings are output.
7524 Using @option{--preserve} with no @var{attribute_list} is equivalent
7525 to @option{--preserve=mode,ownership,timestamps}.
7527 In the absence of this option, each destination file is created with the
7528 mode bits of the corresponding source file, minus the bits set in the
7529 umask and minus the set-user-ID and set-group-ID bits.
7530 @xref{File permissions}.
7532 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7533 @cindex file information, preserving
7534 Do not preserve the specified attributes. The @var{attribute_list}
7535 has the same form as for @option{--preserve}.
7539 @cindex parent directories and @command{cp}
7540 Form the name of each destination file by appending to the target
7541 directory a slash and the specified name of the source file. The last
7542 argument given to @command{cp} must be the name of an existing directory.
7543 For example, the command:
7546 cp --parents a/b/c existing_dir
7550 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7551 any missing intermediate directories.
7558 @opindex --recursive
7559 @cindex directories, copying recursively
7560 @cindex copying directories recursively
7561 @cindex recursively copying directories
7562 @cindex non-directories, copying as special files
7563 Copy directories recursively. By default, do not follow symbolic
7564 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7565 @option{--dereference} (@option{-L}), @option{--no-dereference}
7566 (@option{-P}), and @option{-H} options. Special files are copied by
7567 creating a destination file of the same type as the source; see the
7568 @option{--copy-contents} option. It is not portable to use
7569 @option{-r} to copy symbolic links or special files. On some
7570 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7571 @option{-L} and @option{--copy-contents} for historical reasons.
7572 Also, it is not portable to use @option{-R} to copy symbolic links
7573 unless you also specify @option{-P}, as @acronym{POSIX} allows
7574 implementations that dereference symbolic links by default.
7576 @item --reflink[=@var{when}]
7577 @opindex --reflink[=@var{when}]
7580 @cindex copy on write
7581 Perform a lightweight, copy-on-write (COW) copy.
7582 Copying with this option can succeed only on some file systems.
7583 Once it has succeeded, beware that the source and destination files
7584 share the same disk data blocks as long as they remain unmodified.
7585 Thus, if a disk I/O error affects data blocks of one of the files,
7586 the other suffers the exact same fate.
7588 The @var{when} value can be one of the following:
7592 The default behavior: if the copy-on-write operation is not supported
7593 then report the failure for each file and exit with a failure status.
7596 If the copy-on-write operation is not supported then fall back
7597 to the standard copy behaviour.
7601 @item --remove-destination
7602 @opindex --remove-destination
7603 Remove each existing destination file before attempting to open it
7604 (contrast with @option{-f} above).
7606 @item --sparse=@var{when}
7607 @opindex --sparse=@var{when}
7608 @cindex sparse files, copying
7609 @cindex holes, copying files with
7610 @findex read @r{system call, and holes}
7611 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7612 does not occupy any physical disk blocks; the @samp{read} system call
7613 reads these as zeros. This can both save considerable disk space and
7614 increase speed, since many binary files contain lots of consecutive zero
7615 bytes. By default, @command{cp} detects holes in input source files via a crude
7616 heuristic and makes the corresponding output file sparse as well.
7617 Only regular files may be sparse.
7619 The @var{when} value can be one of the following:
7623 The default behavior: if the input file is sparse, attempt to make
7624 the output file sparse, too. However, if an output file exists but
7625 refers to a non-regular file, then do not attempt to make it sparse.
7628 For each sufficiently long sequence of zero bytes in the input file,
7629 attempt to create a corresponding hole in the output file, even if the
7630 input file does not appear to be sparse.
7631 This is useful when the input file resides on a file system
7632 that does not support sparse files
7633 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7634 but the output file is on a type of file system that does support them.
7635 Holes may be created only in regular files, so if the destination file
7636 is of some other type, @command{cp} does not even try to make it sparse.
7639 Never make the output file sparse.
7640 This is useful in creating a file for use with the @command{mkswap} command,
7641 since such a file must not have any holes.
7644 @optStripTrailingSlashes
7647 @itemx --symbolic-link
7649 @opindex --symbolic-link
7650 @cindex symbolic links, copying with
7651 Make symbolic links instead of copies of non-directories. All source
7652 file names must be absolute (starting with @samp{/}) unless the
7653 destination files are in the current directory. This option merely
7654 results in an error message on systems that do not support symbolic links.
7660 @optNoTargetDirectory
7666 @cindex newer files, copying only
7667 Do not copy a non-directory that has an existing destination with the
7668 same or newer modification time. If time stamps are being preserved,
7669 the comparison is to the source time stamp truncated to the
7670 resolutions of the destination file system and of the system calls
7671 used to update time stamps; this avoids duplicate work if several
7672 @samp{cp -pu} commands are executed with the same source and
7679 Print the name of each file before copying it.
7682 @itemx --one-file-system
7684 @opindex --one-file-system
7685 @cindex file systems, omitting copying to different
7686 Skip subdirectories that are on different file systems from the one that
7687 the copy started on.
7688 However, mount point directories @emph{are} copied.
7696 @section @command{dd}: Convert and copy a file
7699 @cindex converting while copying a file
7701 @command{dd} copies a file (from standard input to standard output, by
7702 default) with a changeable I/O block size, while optionally performing
7703 conversions on it. Synopses:
7706 dd [@var{operand}]@dots{}
7710 The only options are @option{--help} and @option{--version}.
7711 @xref{Common options}. @command{dd} accepts the following operands.
7717 Read from @var{file} instead of standard input.
7721 Write to @var{file} instead of standard output. Unless
7722 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7723 bytes (or the size specified with @samp{seek=}).
7725 @item ibs=@var{bytes}
7727 @cindex block size of input
7728 @cindex input block size
7729 Set the input block size to @var{bytes}.
7730 This makes @command{dd} read @var{bytes} per block.
7731 The default is 512 bytes.
7733 @item obs=@var{bytes}
7735 @cindex block size of output
7736 @cindex output block size
7737 Set the output block size to @var{bytes}.
7738 This makes @command{dd} write @var{bytes} per block.
7739 The default is 512 bytes.
7741 @item bs=@var{bytes}
7744 Set both input and output block sizes to @var{bytes}.
7745 This makes @command{dd} read and write @var{bytes} per block,
7746 overriding any @samp{ibs} and @samp{obs} settings.
7747 In addition, if no data-transforming @option{conv} option is specified,
7748 each input block is copied to the output as a single block,
7749 without aggregating short reads.
7751 @item cbs=@var{bytes}
7753 @cindex block size of conversion
7754 @cindex conversion block size
7755 @cindex fixed-length records, converting to variable-length
7756 @cindex variable-length records, converting to fixed-length
7757 Set the conversion block size to @var{bytes}.
7758 When converting variable-length records to fixed-length ones
7759 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7760 use @var{bytes} as the fixed record length.
7762 @item skip=@var{blocks}
7764 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7766 @item seek=@var{blocks}
7768 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7770 @item count=@var{blocks}
7772 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7773 of everything until the end of the file.
7777 Do not print the overall transfer rate and volume statistics
7778 that normally make up the third status line when @command{dd} exits.
7780 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7782 Convert the file as specified by the @var{conversion} argument(s).
7783 (No spaces around any comma(s).)
7790 @opindex ascii@r{, converting to}
7791 Convert @acronym{EBCDIC} to @acronym{ASCII},
7792 using the conversion table specified by @acronym{POSIX}.
7793 This provides a 1:1 translation for all 256 bytes.
7796 @opindex ebcdic@r{, converting to}
7797 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7798 This is the inverse of the @samp{ascii} conversion.
7801 @opindex alternate ebcdic@r{, converting to}
7802 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7803 using the alternate conversion table specified by @acronym{POSIX}.
7804 This is not a 1:1 translation, but reflects common historical practice
7805 for @samp{~}, @samp{[}, and @samp{]}.
7807 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7811 @opindex block @r{(space-padding)}
7812 For each line in the input, output @samp{cbs} bytes, replacing the
7813 input newline with a space and padding with spaces as necessary.
7817 Remove any trailing spaces in each @samp{cbs}-sized input block,
7818 and append a newline.
7820 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7823 @opindex lcase@r{, converting to}
7824 Change uppercase letters to lowercase.
7827 @opindex ucase@r{, converting to}
7828 Change lowercase letters to uppercase.
7830 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7833 @opindex swab @r{(byte-swapping)}
7834 @cindex byte-swapping
7835 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7836 when an odd number of bytes are read---the last byte is simply copied
7837 (since there is nothing to swap it with).
7841 @cindex read errors, ignoring
7842 Continue after read errors.
7846 @cindex creating output file, avoiding
7847 Do not create the output file; the output file must already exist.
7851 @cindex creating output file, requiring
7852 Fail if the output file already exists; @command{dd} must create the
7855 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7859 @cindex truncating output file, avoiding
7860 Do not truncate the output file.
7863 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7864 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7865 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7870 @cindex synchronized data writes, before finishing
7871 Synchronize output data just before finishing. This forces a physical
7872 write of output data.
7876 @cindex synchronized data and metadata writes, before finishing
7877 Synchronize output data and metadata just before finishing. This
7878 forces a physical write of output data and metadata.
7882 @item iflag=@var{flag}[,@var{flag}]@dots{}
7884 Access the input file using the flags specified by the @var{flag}
7885 argument(s). (No spaces around any comma(s).)
7887 @item oflag=@var{flag}[,@var{flag}]@dots{}
7889 Access the output file using the flags specified by the @var{flag}
7890 argument(s). (No spaces around any comma(s).)
7892 Here are the flags. Not every flag is supported on every operating
7899 @cindex appending to the output file
7900 Write in append mode, so that even if some other process is writing to
7901 this file, every @command{dd} write will append to the current
7902 contents of the file. This flag makes sense only for output.
7903 If you combine this flag with the @samp{of=@var{file}} operand,
7904 you should also specify @samp{conv=notrunc} unless you want the
7905 output file to be truncated before being appended to.
7909 @cindex concurrent I/O
7910 Use concurrent I/O mode for data. This mode performs direct I/O
7911 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7912 A file cannot be opened in CIO mode and with a standard open at the
7918 Use direct I/O for data, avoiding the buffer cache.
7919 Note that the kernel may impose restrictions on read or write buffer sizes.
7920 For example, with an ext4 destination file system and a linux-based kernel,
7921 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7922 output buffer size is not a multiple of 512.
7926 @cindex directory I/O
7928 Fail unless the file is a directory. Most operating systems do not
7929 allow I/O to a directory, so this flag has limited utility.
7933 @cindex synchronized data reads
7934 Use synchronized I/O for data. For the output file, this forces a
7935 physical write of output data on each write. For the input file,
7936 this flag can matter when reading from a remote file that has been
7937 written to synchronously by some other process. Metadata (e.g.,
7938 last-access and last-modified time) is not necessarily synchronized.
7942 @cindex synchronized data and metadata I/O
7943 Use synchronized I/O for both data and metadata.
7947 @cindex nonblocking I/O
7948 Use non-blocking I/O.
7953 Do not update the file's access time.
7954 Some older file systems silently ignore this flag, so it is a good
7955 idea to test it on your files before relying on it.
7959 @cindex controlling terminal
7960 Do not assign the file to be a controlling terminal for @command{dd}.
7961 This has no effect when the file is not a terminal.
7962 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7967 @cindex symbolic links, following
7968 Do not follow symbolic links.
7973 Fail if the file has multiple hard links.
7978 Use binary I/O. This option has an effect only on nonstandard
7979 platforms that distinguish binary from text I/O.
7984 Use text I/O. Like @samp{binary}, this option has no effect on
7989 Accumulate full blocks from input. The @code{read} system call
7990 may return early if a full block is not available.
7991 When that happens, continue calling @code{read} to fill the remainder
7993 This flag can be used only with @code{iflag}.
7997 These flags are not supported on all systems, and @samp{dd} rejects
7998 attempts to use them when they are not supported. When reading from
7999 standard input or writing to standard output, the @samp{nofollow} and
8000 @samp{noctty} flags should not be specified, and the other flags
8001 (e.g., @samp{nonblock}) can affect how other processes behave with the
8002 affected file descriptors, even after @command{dd} exits.
8006 @cindex multipliers after numbers
8007 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8008 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8009 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8010 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8012 Use different @command{dd} invocations to use different block sizes for
8013 skipping and I/O@. For example, the following shell commands copy data
8014 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8015 4 KiB label at the start of the disk:
8018 disk=/dev/rdsk/c0t1d0s2
8021 # Copy all but the label from disk to tape.
8022 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8024 # Copy from tape back to disk, but leave the disk label alone.
8025 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8028 Sending an @samp{INFO} signal to a running @command{dd}
8029 process makes it print I/O statistics to standard error
8030 and then resume copying. In the example below,
8031 @command{dd} is run in the background to copy 10 million blocks.
8032 The @command{kill} command makes it output intermediate I/O statistics,
8033 and when @command{dd} completes normally or is killed by the
8034 @code{SIGINT} signal, it outputs the final statistics.
8037 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8038 $ kill -s INFO $pid; wait $pid
8039 3385223+0 records in
8040 3385223+0 records out
8041 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8042 10000000+0 records in
8043 10000000+0 records out
8044 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8047 @vindex POSIXLY_CORRECT
8048 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8049 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8050 environment variable is set.
8055 @node install invocation
8056 @section @command{install}: Copy files and set attributes
8059 @cindex copying files and setting attributes
8061 @command{install} copies files while setting their file mode bits and, if
8062 possible, their owner and group. Synopses:
8065 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8066 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8067 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8068 install [@var{option}]@dots{} -d @var{directory}@dots{}
8073 If two file names are given, @command{install} copies the first file to the
8077 If the @option{--target-directory} (@option{-t}) option is given, or
8078 failing that if the last file is a directory and the
8079 @option{--no-target-directory} (@option{-T}) option is not given,
8080 @command{install} copies each @var{source} file to the specified
8081 directory, using the @var{source}s' names.
8084 If the @option{--directory} (@option{-d}) option is given,
8085 @command{install} creates each @var{directory} and any missing parent
8086 directories. Parent directories are created with mode
8087 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8088 current umask. @xref{Directory Setuid and Setgid}, for how the
8089 set-user-ID and set-group-ID bits of parent directories are inherited.
8092 @cindex Makefiles, installing programs in
8093 @command{install} is similar to @command{cp}, but allows you to control the
8094 attributes of destination files. It is typically used in Makefiles to
8095 copy programs into their destination directories. It refuses to copy
8096 files onto themselves.
8098 @cindex extended attributes, xattr
8099 @command{install} never preserves extended attributes (xattr).
8101 The program accepts the following options. Also see @ref{Common options}.
8111 Compare each pair of source and destination files, and if the destination has
8112 identical content and any specified owner, group, permissions, and possibly
8113 SELinux context, then do not modify the destination at all.
8117 Ignored; for compatibility with old Unix versions of @command{install}.
8121 Create any missing parent directories of @var{dest},
8122 then copy @var{source} to @var{dest}.
8123 This option is ignored if a destination directory is specified
8124 via @option{--target-directory=DIR}.
8129 @opindex --directory
8130 @cindex directories, creating with given attributes
8131 @cindex parent directories, creating missing
8132 @cindex leading directories, creating missing
8133 Create any missing parent directories, giving them the default
8134 attributes. Then create each given directory, setting their owner,
8135 group and mode as given on the command line or to the defaults.
8137 @item -g @var{group}
8138 @itemx --group=@var{group}
8141 @cindex group ownership of installed files, setting
8142 Set the group ownership of installed files or directories to
8143 @var{group}. The default is the process's current group. @var{group}
8144 may be either a group name or a numeric group ID.
8147 @itemx --mode=@var{mode}
8150 @cindex permissions of installed files, setting
8151 Set the file mode bits for the installed file or directory to @var{mode},
8152 which can be either an octal number, or a symbolic mode as in
8153 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8154 point of departure (@pxref{File permissions}).
8155 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8156 execute for the owner, read and execute for group and other, and with
8157 set-user-ID and set-group-ID disabled.
8158 This default is not quite the same as @samp{755}, since it disables
8159 instead of preserving set-user-ID and set-group-ID on directories.
8160 @xref{Directory Setuid and Setgid}.
8162 @item -o @var{owner}
8163 @itemx --owner=@var{owner}
8166 @cindex ownership of installed files, setting
8167 @cindex appropriate privileges
8168 @vindex root @r{as default owner}
8169 If @command{install} has appropriate privileges (is run as root), set the
8170 ownership of installed files or directories to @var{owner}. The default
8171 is @code{root}. @var{owner} may be either a user name or a numeric user
8174 @item --preserve-context
8175 @opindex --preserve-context
8177 @cindex security context
8178 Preserve the SELinux security context of files and directories.
8179 Failure to preserve the context in all of the files or directories
8180 will result in an exit status of 1. If SELinux is disabled then
8181 print a warning and ignore the option.
8184 @itemx --preserve-timestamps
8186 @opindex --preserve-timestamps
8187 @cindex timestamps of installed files, preserving
8188 Set the time of last access and the time of last modification of each
8189 installed file to match those of each corresponding original file.
8190 When a file is installed without this option, its last access and
8191 last modification times are both set to the time of installation.
8192 This option is useful if you want to use the last modification times
8193 of installed files to keep track of when they were last built as opposed
8194 to when they were last installed.
8200 @cindex symbol table information, stripping
8201 @cindex stripping symbol table information
8202 Strip the symbol tables from installed binary executables.
8204 @itemx --strip-program=@var{program}
8205 @opindex --strip-program
8206 @cindex symbol table information, stripping, program
8207 Program used to strip binaries.
8213 @optNoTargetDirectory
8219 Print the name of each file before copying it.
8221 @item -Z @var{context}
8222 @itemx --context=@var{context}
8226 @cindex security context
8227 Set the default SELinux security context to be used for any
8228 created files and directories. If SELinux is disabled then
8229 print a warning and ignore the option.
8237 @section @command{mv}: Move (rename) files
8241 @command{mv} moves or renames files (or directories). Synopses:
8244 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8245 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8246 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8251 If two file names are given, @command{mv} moves the first file to the
8255 If the @option{--target-directory} (@option{-t}) option is given, or
8256 failing that if the last file is a directory and the
8257 @option{--no-target-directory} (@option{-T}) option is not given,
8258 @command{mv} moves each @var{source} file to the specified
8259 directory, using the @var{source}s' names.
8262 @command{mv} can move any type of file from one file system to another.
8263 Prior to version @code{4.0} of the fileutils,
8264 @command{mv} could move only regular files between file systems.
8265 For example, now @command{mv} can move an entire directory hierarchy
8266 including special device files from one partition to another. It first
8267 uses some of the same code that's used by @code{cp -a} to copy the
8268 requested directories and files, then (assuming the copy succeeded)
8269 it removes the originals. If the copy fails, then the part that was
8270 copied to the destination partition is removed. If you were to copy
8271 three directories from one partition to another and the copy of the first
8272 directory succeeded, but the second didn't, the first would be left on
8273 the destination partition and the second and third would be left on the
8276 @cindex extended attributes, xattr
8277 @command{mv} always tries to copy extended attributes (xattr), which may
8278 include SELinux context, ACLs or Capabilities.
8279 Upon failure all but @samp{Operation not supported} warnings are output.
8281 @cindex prompting, and @command{mv}
8282 If a destination file exists but is normally unwritable, standard input
8283 is a terminal, and the @option{-f} or @option{--force} option is not given,
8284 @command{mv} prompts the user for whether to replace the file. (You might
8285 own the file, or have write permission on its directory.) If the
8286 response is not affirmative, the file is skipped.
8288 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8289 when it might be a symlink to a directory.
8290 Otherwise, @command{mv} may do something very surprising, since
8291 its behavior depends on the underlying rename system call.
8292 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8293 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8294 renames not the symlink but rather the directory referenced by the symlink.
8295 @xref{Trailing slashes}.
8297 The program accepts the following options. Also see @ref{Common options}.
8307 @cindex prompts, omitting
8308 Do not prompt the user before removing a destination file.
8310 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8311 options, only the final one takes effect.
8316 @itemx --interactive
8318 @opindex --interactive
8319 @cindex prompts, forcing
8320 Prompt whether to overwrite each existing destination file, regardless
8322 If the response is not affirmative, the file is skipped.
8328 @opindex --no-clobber
8329 @cindex prompts, omitting
8330 Do not overwrite an existing file.
8332 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8338 @cindex newer files, moving only
8339 Do not move a non-directory that has an existing destination with the
8340 same or newer modification time.
8341 If the move is across file system boundaries, the comparison is to the
8342 source time stamp truncated to the resolutions of the destination file
8343 system and of the system calls used to update time stamps; this avoids
8344 duplicate work if several @samp{mv -u} commands are executed with the
8345 same source and destination.
8351 Print the name of each file before moving it.
8353 @optStripTrailingSlashes
8359 @optNoTargetDirectory
8367 @section @command{rm}: Remove files or directories
8370 @cindex removing files or directories
8372 @command{rm} removes each given @var{file}. By default, it does not remove
8373 directories. Synopsis:
8376 rm [@var{option}]@dots{} [@var{file}]@dots{}
8379 @cindex prompting, and @command{rm}
8380 If the @option{-I} or @option{--interactive=once} option is given,
8381 and there are more than three files or the @option{-r}, @option{-R},
8382 or @option{--recursive} are given, then @command{rm} prompts the user
8383 for whether to proceed with the entire operation. If the response is
8384 not affirmative, the entire command is aborted.
8386 Otherwise, if a file is unwritable, standard input is a terminal, and
8387 the @option{-f} or @option{--force} option is not given, or the
8388 @option{-i} or @option{--interactive=always} option @emph{is} given,
8389 @command{rm} prompts the user for whether to remove the file.
8390 If the response is not affirmative, the file is skipped.
8392 Any attempt to remove a file whose last file name component is
8393 @file{.} or @file{..} is rejected without any prompting.
8395 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8396 possible to recover the contents of that file. If you want more assurance
8397 that the contents are truly unrecoverable, consider using @command{shred}.
8399 The program accepts the following options. Also see @ref{Common options}.
8407 Ignore nonexistent files and never prompt the user.
8408 Ignore any previous @option{--interactive} (@option{-i}) option.
8412 Prompt whether to remove each file.
8413 If the response is not affirmative, the file is skipped.
8414 Ignore any previous @option{--force} (@option{-f}) option.
8415 Equivalent to @option{--interactive=always}.
8419 Prompt once whether to proceed with the command, if more than three
8420 files are named or if a recursive removal is requested. Ignore any
8421 previous @option{--force} (@option{-f}) option. Equivalent to
8422 @option{--interactive=once}.
8424 @itemx --interactive [=@var{when}]
8425 @opindex --interactive
8426 Specify when to issue an interactive prompt. @var{when} may be
8430 @vindex never @r{interactive option}
8431 - Do not prompt at all.
8433 @vindex once @r{interactive option}
8434 - Prompt once if more than three files are named or if a recursive
8435 removal is requested. Equivalent to @option{-I}.
8437 @vindex always @r{interactive option}
8438 - Prompt for every file being removed. Equivalent to @option{-i}.
8440 @option{--interactive} with no @var{when} is equivalent to
8441 @option{--interactive=always}.
8443 @itemx --one-file-system
8444 @opindex --one-file-system
8445 @cindex one file system, restricting @command{rm} to
8446 When removing a hierarchy recursively, skip any directory that is on a
8447 file system different from that of the corresponding command line argument.
8449 This option is useful when removing a build ``chroot'' hierarchy,
8450 which normally contains no valuable data. However, it is not uncommon
8451 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8452 use one's start-up file. The catch is that it's easy to forget to
8453 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8454 your normally throw-away chroot, that command will remove everything
8455 under @file{/home}, too.
8456 Use the @option{--one-file-system} option, and it will
8457 warn about and skip directories on other file systems.
8458 Of course, this will not save your @file{/home} if it and your
8459 chroot happen to be on the same file system.
8461 @itemx --preserve-root
8462 @opindex --preserve-root
8463 @cindex root directory, disallow recursive destruction
8464 Fail upon any attempt to remove the root directory, @file{/},
8465 when used with the @option{--recursive} option.
8466 This is the default behavior.
8467 @xref{Treating / specially}.
8469 @itemx --no-preserve-root
8470 @opindex --no-preserve-root
8471 @cindex root directory, allow recursive destruction
8472 Do not treat @file{/} specially when removing recursively.
8473 This option is not recommended unless you really want to
8474 remove all the files on your computer.
8475 @xref{Treating / specially}.
8482 @opindex --recursive
8483 @cindex directories, removing (recursively)
8484 Remove the listed directories and their contents recursively.
8490 Print the name of each file before removing it.
8494 @cindex files beginning with @samp{-}, removing
8495 @cindex @samp{-}, removing files beginning with
8496 One common question is how to remove files whose names begin with a
8497 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8498 function to parse its arguments, lets you use the @samp{--} option to
8499 indicate that all following arguments are non-options. To remove a file
8500 called @file{-f} in the current directory, you could type either:
8513 @opindex - @r{and Unix @command{rm}}
8514 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8515 predates the development of the getopt standard syntax.
8520 @node shred invocation
8521 @section @command{shred}: Remove files more securely
8524 @cindex data, erasing
8525 @cindex erasing data
8527 @command{shred} overwrites devices or files, to help prevent even
8528 very expensive hardware from recovering the data.
8530 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8531 not actually destroyed. Only the index listing where the file is
8532 stored is destroyed, and the storage is made available for reuse.
8533 There are undelete utilities that will attempt to reconstruct the index
8534 and can bring the file back if the parts were not reused.
8536 On a busy system with a nearly-full drive, space can get reused in a few
8537 seconds. But there is no way to know for sure. If you have sensitive
8538 data, you may want to be sure that recovery is not possible by actually
8539 overwriting the file with non-sensitive data.
8541 However, even after doing that, it is possible to take the disk back
8542 to a laboratory and use a lot of sensitive (and expensive) equipment
8543 to look for the faint ``echoes'' of the original data underneath the
8544 overwritten data. If the data has only been overwritten once, it's not
8547 The best way to remove something irretrievably is to destroy the media
8548 it's on with acid, melt it down, or the like. For cheap removable media
8549 like floppy disks, this is the preferred method. However, hard drives
8550 are expensive and hard to melt, so the @command{shred} utility tries
8551 to achieve a similar effect non-destructively.
8553 This uses many overwrite passes, with the data patterns chosen to
8554 maximize the damage they do to the old data. While this will work on
8555 floppies, the patterns are designed for best effect on hard drives.
8556 For more details, see the source code and Peter Gutmann's paper
8557 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8558 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8559 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8560 California, July 22--25, 1996).
8562 @strong{Please note} that @command{shred} relies on a very important assumption:
8563 that the file system overwrites data in place. This is the traditional
8564 way to do things, but many modern file system designs do not satisfy this
8565 assumption. Exceptions include:
8570 Log-structured or journaled file systems, such as those supplied with
8571 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8572 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8575 File systems that write redundant data and carry on even if some writes
8576 fail, such as RAID-based file systems.
8579 File systems that make snapshots, such as Network Appliance's NFS server.
8582 File systems that cache in temporary locations, such as NFS version 3
8586 Compressed file systems.
8589 In the particular case of ext3 file systems, the above disclaimer applies (and
8590 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8591 mode, which journals file data in addition to just metadata. In both
8592 the @code{data=ordered} (default) and @code{data=writeback} modes,
8593 @command{shred} works as usual. Ext3 journaling modes can be changed
8594 by adding the @code{data=something} option to the mount options for a
8595 particular file system in the @file{/etc/fstab} file, as documented in
8596 the mount man page (man mount).
8598 If you are not sure how your file system operates, then you should assume
8599 that it does not overwrite data in place, which means that shred cannot
8600 reliably operate on regular files in your file system.
8602 Generally speaking, it is more reliable to shred a device than a file,
8603 since this bypasses the problem of file system design mentioned above.
8604 However, even shredding devices is not always completely reliable. For
8605 example, most disks map out bad sectors invisibly to the application; if
8606 the bad sectors contain sensitive data, @command{shred} won't be able to
8609 @command{shred} makes no attempt to detect or report this problem, just as
8610 it makes no attempt to do anything about backups. However, since it is
8611 more reliable to shred devices than files, @command{shred} by default does
8612 not truncate or remove the output file. This default is more suitable
8613 for devices, which typically cannot be truncated and should not be
8616 Finally, consider the risk of backups and mirrors.
8617 File system backups and remote mirrors may contain copies of the
8618 file that cannot be removed, and that will allow a shredded file
8619 to be recovered later. So if you keep any data you may later want
8620 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8623 shred [@var{option}]@dots{} @var{file}[@dots{}]
8626 The program accepts the following options. Also see @ref{Common options}.
8634 @cindex force deletion
8635 Override file permissions if necessary to allow overwriting.
8638 @itemx -n @var{number}
8639 @itemx --iterations=@var{number}
8640 @opindex -n @var{number}
8641 @opindex --iterations=@var{number}
8642 @cindex iterations, selecting the number of
8643 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8644 overwrite. You can reduce this to save time, or increase it if you think it's
8645 appropriate. After 25 passes all of the internal overwrite patterns will have
8646 been used at least once.
8648 @item --random-source=@var{file}
8649 @opindex --random-source
8650 @cindex random source for shredding
8651 Use @var{file} as a source of random data used to overwrite and to
8652 choose pass ordering. @xref{Random sources}.
8654 @item -s @var{bytes}
8655 @itemx --size=@var{bytes}
8656 @opindex -s @var{bytes}
8657 @opindex --size=@var{bytes}
8658 @cindex size of file to shred
8659 Shred the first @var{bytes} bytes of the file. The default is to shred
8660 the whole file. @var{bytes} can be followed by a size specification like
8661 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8667 @cindex removing files after shredding
8668 After shredding a file, truncate it (if possible) and then remove it.
8669 If a file has multiple links, only the named links will be removed.
8675 Display to standard error all status updates as sterilization proceeds.
8681 By default, @command{shred} rounds the size of a regular file up to the next
8682 multiple of the file system block size to fully erase the last block of the file.
8683 Use @option{--exact} to suppress that behavior.
8684 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8685 blocks, the resulting file will be 512 bytes long. With this option,
8686 shred does not increase the apparent size of the file.
8692 Normally, the last pass that @command{shred} writes is made up of
8693 random data. If this would be conspicuous on your hard drive (for
8694 example, because it looks like encrypted data), or you just think
8695 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8696 all zero bits. This is in addition to the number of passes specified
8697 by the @option{--iterations} option.
8701 You might use the following command to erase all trace of the
8702 file system you'd created on the floppy disk in your first drive.
8703 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8707 shred --verbose /dev/fd0
8710 Similarly, to erase all data on a selected partition of
8711 your hard disk, you could give a command like this:
8714 shred --verbose /dev/sda5
8717 A @var{file} of @samp{-} denotes standard output.
8718 The intended use of this is to shred a removed temporary file.
8725 echo "Hello, world" >&3
8730 However, the command @samp{shred - >file} does not shred the contents
8731 of @var{file}, since the shell truncates @var{file} before invoking
8732 @command{shred}. Use the command @samp{shred file} or (if using a
8733 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8738 @node Special file types
8739 @chapter Special file types
8741 @cindex special file types
8742 @cindex file types, special
8744 This chapter describes commands which create special types of files (and
8745 @command{rmdir}, which removes directories, one special file type).
8747 @cindex special file types
8749 Although Unix-like operating systems have markedly fewer special file
8750 types than others, not @emph{everything} can be treated only as the
8751 undifferentiated byte stream of @dfn{normal files}. For example, when a
8752 file is created or removed, the system must record this information,
8753 which it does in a @dfn{directory}---a special type of file. Although
8754 you can read directories as normal files, if you're curious, in order
8755 for the system to do its job it must impose a structure, a certain
8756 order, on the bytes of the file. Thus it is a ``special'' type of file.
8758 Besides directories, other special file types include named pipes
8759 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8762 * link invocation:: Make a hard link via the link syscall
8763 * ln invocation:: Make links between files.
8764 * mkdir invocation:: Make directories.
8765 * mkfifo invocation:: Make FIFOs (named pipes).
8766 * mknod invocation:: Make block or character special files.
8767 * readlink invocation:: Print value of a symlink or canonical file name.
8768 * rmdir invocation:: Remove empty directories.
8769 * unlink invocation:: Remove files via the unlink syscall
8773 @node link invocation
8774 @section @command{link}: Make a hard link via the link syscall
8777 @cindex links, creating
8778 @cindex hard links, creating
8779 @cindex creating links (hard only)
8781 @command{link} creates a single hard link at a time.
8782 It is a minimalist interface to the system-provided
8783 @code{link} function. @xref{Hard Links, , , libc,
8784 The GNU C Library Reference Manual}.
8785 It avoids the bells and whistles of the more commonly-used
8786 @command{ln} command (@pxref{ln invocation}).
8790 link @var{filename} @var{linkname}
8793 @var{filename} must specify an existing file, and @var{linkname}
8794 must specify a nonexistent entry in an existing directory.
8795 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8798 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8799 --no-target-directory @var{filename} @var{linkname}}. However, the
8800 @option{--directory} and @option{--no-target-directory} options are
8801 not specified by @acronym{POSIX}, and the @command{link} command is
8802 more portable in practice.
8804 If @var{filename} is a symbolic link, it is unspecified whether
8805 @var{linkname} will be a hard link to the symbolic link or to the
8806 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8807 to specify which behavior is desired.
8813 @section @command{ln}: Make links between files
8816 @cindex links, creating
8817 @cindex hard links, creating
8818 @cindex symbolic (soft) links, creating
8819 @cindex creating links (hard or soft)
8821 @cindex file systems and hard links
8822 @command{ln} makes links between files. By default, it makes hard links;
8823 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8827 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8828 ln [@var{option}]@dots{} @var{target}
8829 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8830 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8836 If two file names are given, @command{ln} creates a link to the first
8837 file from the second.
8840 If one @var{target} is given, @command{ln} creates a link to that file
8841 in the current directory.
8844 If the @option{--target-directory} (@option{-t}) option is given, or
8845 failing that if the last file is a directory and the
8846 @option{--no-target-directory} (@option{-T}) option is not given,
8847 @command{ln} creates a link to each @var{target} file in the specified
8848 directory, using the @var{target}s' names.
8852 Normally @command{ln} does not remove existing files. Use the
8853 @option{--force} (@option{-f}) option to remove them unconditionally,
8854 the @option{--interactive} (@option{-i}) option to remove them
8855 conditionally, and the @option{--backup} (@option{-b}) option to
8858 @cindex hard link, defined
8859 @cindex inode, and hard links
8860 A @dfn{hard link} is another name for an existing file; the link and the
8861 original are indistinguishable. Technically speaking, they share the
8862 same inode, and the inode contains all the information about a
8863 file---indeed, it is not incorrect to say that the inode @emph{is} the
8864 file. Most systems prohibit making a hard link to
8865 a directory; on those where it is allowed, only the super-user can do
8866 so (and with caution, since creating a cycle will cause problems to many
8867 other utilities). Hard links cannot cross file system boundaries. (These
8868 restrictions are not mandated by @acronym{POSIX}, however.)
8870 @cindex dereferencing symbolic links
8871 @cindex symbolic link, defined
8872 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8873 a special file type (which not all kernels support: System V release 3
8874 (and older) systems lack symlinks) in which the link file actually
8875 refers to a different file, by name. When most operations (opening,
8876 reading, writing, and so on) are passed the symbolic link file, the
8877 kernel automatically @dfn{dereferences} the link and operates on the
8878 target of the link. But some operations (e.g., removing) work on the
8879 link file itself, rather than on its target. The owner and group of a
8880 symlink are not significant to file access performed through
8881 the link, but do have implications on deleting a symbolic link from a
8882 directory with the restricted deletion bit set. On the GNU system,
8883 the mode of a symlink has no significance and cannot be changed, but
8884 on some BSD systems, the mode can be changed and will affect whether
8885 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8886 libc, The GNU C Library Reference Manual}.
8888 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8889 occurs when the string in the symlink does not resolve to a file.
8890 There are no restrictions against creating dangling symbolic links.
8891 There are trade-offs to using absolute or relative symlinks. An
8892 absolute symlink always points to the same file, even if the directory
8893 containing the link is moved. However, if the symlink is visible from
8894 more than one machine (such as on a networked file system), the file
8895 pointed to might not always be the same. A relative symbolic link is
8896 resolved in relation to the directory that contains the link, and is
8897 often useful in referring to files on the same device without regards
8898 to what name that device is mounted on when accessed via networked
8901 When creating a relative symlink in a different location than the
8902 current directory, the resolution of the symlink will be different
8903 than the resolution of the same string from the current directory.
8904 Therefore, many users prefer to first change directories to the
8905 location where the relative symlink will be created, so that
8906 tab-completion or other file resolution will find the same target as
8907 what will be placed in the symlink.
8909 The program accepts the following options. Also see @ref{Common options}.
8920 @opindex --directory
8921 @cindex hard links to directories
8922 Allow users with appropriate privileges to attempt to make hard links
8924 However, note that this will probably fail due to
8925 system restrictions, even for the super-user.
8931 Remove existing destination files.
8934 @itemx --interactive
8936 @opindex --interactive
8937 @cindex prompting, and @command{ln}
8938 Prompt whether to remove existing destination files.
8944 If @option{-s} is not in effect, and the source file is a symbolic
8945 link, create the hard link to the file referred to by the symbolic
8946 link, rather than the symbolic link itself.
8949 @itemx --no-dereference
8951 @opindex --no-dereference
8952 Do not treat the last operand specially when it is a symbolic link to
8953 a directory. Instead, treat it as if it were a normal file.
8955 When the destination is an actual directory (not a symlink to one),
8956 there is no ambiguity. The link is created in that directory.
8957 But when the specified destination is a symlink to a directory,
8958 there are two ways to treat the user's request. @command{ln} can
8959 treat the destination just as it would a normal directory and create
8960 the link in it. On the other hand, the destination can be viewed as a
8961 non-directory---as the symlink itself. In that case, @command{ln}
8962 must delete or backup that symlink before creating the new link.
8963 The default is to treat a destination that is a symlink to a directory
8964 just like a directory.
8966 This option is weaker than the @option{--no-target-directory}
8967 (@option{-T}) option, so it has no effect if both options are given.
8973 If @option{-s} is not in effect, and the source file is a symbolic
8974 link, create the hard link to the symbolic link itself. On platforms
8975 where this is not supported by the kernel, this option creates a
8976 symbolic link with identical contents; since symbolic link contents
8977 cannot be edited, any file name resolution performed through either
8978 link will be the same as if a hard link had been created.
8984 Make symbolic links instead of hard links. This option merely produces
8985 an error message on systems that do not support symbolic links.
8991 @optNoTargetDirectory
8997 Print the name of each file after linking it successfully.
9001 @cindex hard links to symbolic links
9002 @cindex symbolic links and @command{ln}
9003 If @option{-L} and @option{-P} are both given, the last one takes
9004 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9005 are silently ignored. If neither option is given, then this
9006 implementation defaults to @option{-P} if the system @code{link} supports
9007 hard links to symbolic links (such as the GNU system), and @option{-L}
9008 if @code{link} follows symbolic links (such as on BSD).
9017 # Create link ../a pointing to a in that directory.
9018 # Not really useful because it points to itself.
9023 # Change to the target before creating symlinks to avoid being confused.
9029 # Hard coded file names don't move well.
9030 ln -s $(pwd)/a /some/dir/
9034 # Relative file names survive directory moves and also
9035 # work across networked file systems.
9036 ln -s afile anotherfile
9037 ln -s ../adir/afile yetanotherfile
9041 @node mkdir invocation
9042 @section @command{mkdir}: Make directories
9045 @cindex directories, creating
9046 @cindex creating directories
9048 @command{mkdir} creates directories with the specified names. Synopsis:
9051 mkdir [@var{option}]@dots{} @var{name}@dots{}
9054 @command{mkdir} creates each directory @var{name} in the order given.
9055 It reports an error if @var{name} already exists, unless the
9056 @option{-p} option is given and @var{name} is a directory.
9058 The program accepts the following options. Also see @ref{Common options}.
9063 @itemx --mode=@var{mode}
9066 @cindex modes of created directories, setting
9067 Set the file permission bits of created directories to @var{mode},
9068 which uses the same syntax as
9069 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9070 everyone) for the point of the departure. @xref{File permissions}.
9072 Normally the directory has the desired file mode bits at the moment it
9073 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9074 special mode bits, but in this case there may be a temporary window
9075 during which the directory exists but its special mode bits are
9076 incorrect. @xref{Directory Setuid and Setgid}, for how the
9077 set-user-ID and set-group-ID bits of directories are inherited unless
9078 overridden in this way.
9084 @cindex parent directories, creating
9085 Make any missing parent directories for each argument, setting their
9086 file permission bits to the umask modified by @samp{u+wx}. Ignore
9087 existing parent directories, and do not change their file permission
9090 To set the file permission bits of any newly-created parent
9091 directories to a value that includes @samp{u+wx}, you can set the
9092 umask before invoking @command{mkdir}. For example, if the shell
9093 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9094 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9095 To set a parent's special mode bits as well, you can invoke
9096 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9097 Setgid}, for how the set-user-ID and set-group-ID bits of
9098 newly-created parent directories are inherited.
9104 Print a message for each created directory. This is most useful with
9107 @item -Z @var{context}
9108 @itemx --context=@var{context}
9112 @cindex security context
9113 Set the default SELinux security context to be used for created directories.
9120 @node mkfifo invocation
9121 @section @command{mkfifo}: Make FIFOs (named pipes)
9124 @cindex FIFOs, creating
9125 @cindex named pipes, creating
9126 @cindex creating FIFOs (named pipes)
9128 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9129 specified names. Synopsis:
9132 mkfifo [@var{option}] @var{name}@dots{}
9135 A @dfn{FIFO} is a special file type that permits independent processes
9136 to communicate. One process opens the FIFO file for writing, and
9137 another for reading, after which data can flow as with the usual
9138 anonymous pipe in shells or elsewhere.
9140 The program accepts the following option. Also see @ref{Common options}.
9145 @itemx --mode=@var{mode}
9148 @cindex modes of created FIFOs, setting
9149 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9150 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9151 for the point of departure. @var{mode} should specify only file
9152 permission bits. @xref{File permissions}.
9154 @item -Z @var{context}
9155 @itemx --context=@var{context}
9159 @cindex security context
9160 Set the default SELinux security context to be used for created FIFOs.
9167 @node mknod invocation
9168 @section @command{mknod}: Make block or character special files
9171 @cindex block special files, creating
9172 @cindex character special files, creating
9174 @command{mknod} creates a FIFO, character special file, or block special
9175 file with the specified name. Synopsis:
9178 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9181 @cindex special files
9182 @cindex block special files
9183 @cindex character special files
9184 Unlike the phrase ``special file type'' above, the term @dfn{special
9185 file} has a technical meaning on Unix: something that can generate or
9186 receive data. Usually this corresponds to a physical piece of hardware,
9187 e.g., a printer or a disk. (These files are typically created at
9188 system-configuration time.) The @command{mknod} command is what creates
9189 files of this type. Such devices can be read either a character at a
9190 time or a ``block'' (many characters) at a time, hence we say there are
9191 @dfn{block special} files and @dfn{character special} files.
9193 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9194 @mayConflictWithShellBuiltIn{mknod}
9196 The arguments after @var{name} specify the type of file to make:
9201 @opindex p @r{for FIFO file}
9205 @opindex b @r{for block special file}
9206 for a block special file
9209 @c Don't document the `u' option -- it's just a synonym for `c'.
9210 @c Do *any* versions of mknod still use it?
9212 @opindex c @r{for character special file}
9213 @c @opindex u @r{for character special file}
9214 for a character special file
9218 When making a block or character special file, the major and minor
9219 device numbers must be given after the file type.
9220 If a major or minor device number begins with @samp{0x} or @samp{0X},
9221 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9222 as octal; otherwise, as decimal.
9224 The program accepts the following option. Also see @ref{Common options}.
9229 @itemx --mode=@var{mode}
9232 Set the mode of created files to @var{mode}, which is symbolic as in
9233 @command{chmod} and uses @samp{a=rw} as the point of departure.
9234 @var{mode} should specify only file permission bits.
9235 @xref{File permissions}.
9237 @item -Z @var{context}
9238 @itemx --context=@var{context}
9242 @cindex security context
9243 Set the default SELinux security context to be used for created files.
9250 @node readlink invocation
9251 @section @command{readlink}: Print value of a symlink or canonical file name
9254 @cindex displaying value of a symbolic link
9255 @cindex canonical file name
9256 @cindex canonicalize a file name
9260 @command{readlink} may work in one of two supported modes:
9266 @command{readlink} outputs the value of the given symbolic link.
9267 If @command{readlink} is invoked with an argument other than the name
9268 of a symbolic link, it produces no output and exits with a nonzero exit code.
9270 @item Canonicalize mode
9272 @command{readlink} outputs the absolute name of the given file which contains
9273 no @file{.}, @file{..} components nor any repeated separators
9274 (@file{/}) or symbolic links.
9279 readlink [@var{option}] @var{file}
9282 By default, @command{readlink} operates in readlink mode.
9284 The program accepts the following options. Also see @ref{Common options}.
9289 @itemx --canonicalize
9291 @opindex --canonicalize
9292 Activate canonicalize mode.
9293 If any component of the file name except the last one is missing or unavailable,
9294 @command{readlink} produces no output and exits with a nonzero exit
9295 code. A trailing slash is ignored.
9298 @itemx --canonicalize-existing
9300 @opindex --canonicalize-existing
9301 Activate canonicalize mode.
9302 If any component is missing or unavailable, @command{readlink} produces
9303 no output and exits with a nonzero exit code. A trailing slash
9304 requires that the name resolve to a directory.
9307 @itemx --canonicalize-missing
9309 @opindex --canonicalize-missing
9310 Activate canonicalize mode.
9311 If any component is missing or unavailable, @command{readlink} treats it
9317 @opindex --no-newline
9318 Do not output the trailing newline.
9328 Suppress most error messages.
9334 Report error messages.
9338 The @command{readlink} utility first appeared in OpenBSD 2.1.
9340 There is a @command{realpath} command on some systems
9341 which operates like @command{readlink} in canonicalize mode.
9346 @node rmdir invocation
9347 @section @command{rmdir}: Remove empty directories
9350 @cindex removing empty directories
9351 @cindex directories, removing empty
9353 @command{rmdir} removes empty directories. Synopsis:
9356 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9359 If any @var{directory} argument does not refer to an existing empty
9360 directory, it is an error.
9362 The program accepts the following options. Also see @ref{Common options}.
9366 @item --ignore-fail-on-non-empty
9367 @opindex --ignore-fail-on-non-empty
9368 @cindex directory deletion, ignoring failures
9369 Ignore each failure to remove a directory that is solely because
9370 the directory is non-empty.
9376 @cindex parent directories, removing
9377 Remove @var{directory}, then try to remove each component of @var{directory}.
9378 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9379 As such, it fails if any of those directories turns out not to be empty.
9380 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9381 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9382 exit unsuccessfully.
9388 @cindex directory deletion, reporting
9389 Give a diagnostic for each successful removal.
9390 @var{directory} is removed.
9394 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9399 @node unlink invocation
9400 @section @command{unlink}: Remove files via the unlink syscall
9403 @cindex removing files or directories (via the unlink syscall)
9405 @command{unlink} deletes a single specified file name.
9406 It is a minimalist interface to the system-provided
9407 @code{unlink} function. @xref{Deleting Files, , , libc,
9408 The GNU C Library Reference Manual}. Synopsis:
9409 It avoids the bells and whistles of the more commonly-used
9410 @command{rm} command (@pxref{rm invocation}).
9413 unlink @var{filename}
9416 On some systems @code{unlink} can be used to delete the name of a
9417 directory. On others, it can be used that way only by a privileged user.
9418 In the GNU system @code{unlink} can never delete the name of a directory.
9420 The @command{unlink} command honors the @option{--help} and
9421 @option{--version} options. To remove a file whose name begins with
9422 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9427 @node Changing file attributes
9428 @chapter Changing file attributes
9430 @cindex changing file attributes
9431 @cindex file attributes, changing
9432 @cindex attributes, file
9434 A file is not merely its contents, a name, and a file type
9435 (@pxref{Special file types}). A file also has an owner (a user ID), a
9436 group (a group ID), permissions (what the owner can do with the file,
9437 what people in the group can do, and what everyone else can do), various
9438 timestamps, and other information. Collectively, we call these a file's
9441 These commands change file attributes.
9444 * chgrp invocation:: Change file groups.
9445 * chmod invocation:: Change access permissions.
9446 * chown invocation:: Change file owners and groups.
9447 * touch invocation:: Change file timestamps.
9451 @node chown invocation
9452 @section @command{chown}: Change file owner and group
9455 @cindex file ownership, changing
9456 @cindex group ownership, changing
9457 @cindex changing file ownership
9458 @cindex changing group ownership
9460 @command{chown} changes the user and/or group ownership of each given @var{file}
9461 to @var{new-owner} or to the user and group of an existing reference file.
9465 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9468 If used, @var{new-owner} specifies the new owner and/or group as follows
9469 (with no embedded white space):
9472 [@var{owner}] [ : [@var{group}] ]
9479 If only an @var{owner} (a user name or numeric user ID) is given, that
9480 user is made the owner of each given file, and the files' group is not
9483 @item owner@samp{:}group
9484 If the @var{owner} is followed by a colon and a @var{group} (a
9485 group name or numeric group ID), with no spaces between them, the group
9486 ownership of the files is changed as well (to @var{group}).
9489 If a colon but no group name follows @var{owner}, that user is
9490 made the owner of the files and the group of the files is changed to
9491 @var{owner}'s login group.
9494 If the colon and following @var{group} are given, but the owner
9495 is omitted, only the group of the files is changed; in this case,
9496 @command{chown} performs the same function as @command{chgrp}.
9499 If only a colon is given, or if @var{new-owner} is empty, neither the
9500 owner nor the group is changed.
9504 If @var{owner} or @var{group} is intended to represent a numeric user
9505 or group ID, then you may specify it with a leading @samp{+}.
9506 @xref{Disambiguating names and IDs}.
9508 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9509 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9510 require support for that, but for backward compatibility @acronym{GNU}
9511 @command{chown} supports @samp{.} so long as no ambiguity results.
9512 New scripts should avoid the use of @samp{.} because it is not
9513 portable, and because it has undesirable results if the entire
9514 @var{owner@samp{.}group} happens to identify a user whose name
9517 The @command{chown} command sometimes clears the set-user-ID or
9518 set-group-ID permission bits. This behavior depends on the policy and
9519 functionality of the underlying @code{chown} system call, which may
9520 make system-dependent file mode modifications outside the control of
9521 the @command{chown} command. For example, the @command{chown} command
9522 might not affect those bits when invoked by a user with appropriate
9523 privileges, or when the
9524 bits signify some function other than executable permission (e.g.,
9526 When in doubt, check the underlying system behavior.
9528 The program accepts the following options. Also see @ref{Common options}.
9536 @cindex changed owners, verbosely describing
9537 Verbosely describe the action for each @var{file} whose ownership
9546 @cindex error messages, omitting
9547 Do not print error messages about files whose ownership cannot be
9550 @itemx @w{@kbd{--from}=@var{old-owner}}
9552 @cindex symbolic links, changing owner
9553 Change a @var{file}'s ownership only if it has current attributes specified
9554 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9556 This option is useful primarily from a security standpoint in that
9557 it narrows considerably the window of potential abuse.
9558 For example, to reflect a user ID numbering change for one user's files
9559 without an option like this, @code{root} might run
9562 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9565 But that is dangerous because the interval between when the @command{find}
9566 tests the existing file's owner and when the @command{chown} is actually run
9568 One way to narrow the gap would be to invoke chown for each file
9572 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9575 But that is very slow if there are many affected files.
9576 With this option, it is safer (the gap is narrower still)
9577 though still not perfect:
9580 chown -h -R --from=OLDUSER NEWUSER /
9584 @opindex --dereference
9585 @cindex symbolic links, changing owner
9587 Do not act on symbolic links themselves but rather on what they point to.
9588 This is the default.
9591 @itemx --no-dereference
9593 @opindex --no-dereference
9594 @cindex symbolic links, changing owner
9596 Act on symbolic links themselves instead of what they point to.
9597 This mode relies on the @code{lchown} system call.
9598 On systems that do not provide the @code{lchown} system call,
9599 @command{chown} fails when a file specified on the command line
9601 By default, no diagnostic is issued for symbolic links encountered
9602 during a recursive traversal, but see @option{--verbose}.
9604 @itemx --preserve-root
9605 @opindex --preserve-root
9606 @cindex root directory, disallow recursive modification
9607 Fail upon any attempt to recursively change the root directory, @file{/}.
9608 Without @option{--recursive}, this option has no effect.
9609 @xref{Treating / specially}.
9611 @itemx --no-preserve-root
9612 @opindex --no-preserve-root
9613 @cindex root directory, allow recursive modification
9614 Cancel the effect of any preceding @option{--preserve-root} option.
9615 @xref{Treating / specially}.
9617 @item --reference=@var{ref_file}
9618 @opindex --reference
9619 Change the user and group of each @var{file} to be the same as those of
9620 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9621 user and group of the symbolic link, but rather those of the file it
9628 Output a diagnostic for every file processed.
9629 If a symbolic link is encountered during a recursive traversal
9630 on a system without the @code{lchown} system call, and @option{--no-dereference}
9631 is in effect, then issue a diagnostic saying neither the symbolic link nor
9632 its referent is being changed.
9637 @opindex --recursive
9638 @cindex recursively changing file ownership
9639 Recursively change ownership of directories and their contents.
9642 @xref{Traversing symlinks}.
9645 @xref{Traversing symlinks}.
9648 @xref{Traversing symlinks}.
9657 # Change the owner of /u to "root".
9660 # Likewise, but also change its group to "staff".
9663 # Change the owner of /u and subfiles to "root".
9668 @node chgrp invocation
9669 @section @command{chgrp}: Change group ownership
9672 @cindex group ownership, changing
9673 @cindex changing group ownership
9675 @command{chgrp} changes the group ownership of each given @var{file}
9676 to @var{group} (which can be either a group name or a numeric group ID)
9677 or to the group of an existing reference file. Synopsis:
9680 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9683 If @var{group} is intended to represent a
9684 numeric group ID, then you may specify it with a leading @samp{+}.
9685 @xref{Disambiguating names and IDs}.
9687 The program accepts the following options. Also see @ref{Common options}.
9695 @cindex changed files, verbosely describing
9696 Verbosely describe the action for each @var{file} whose group actually
9705 @cindex error messages, omitting
9706 Do not print error messages about files whose group cannot be
9710 @opindex --dereference
9711 @cindex symbolic links, changing owner
9713 Do not act on symbolic links themselves but rather on what they point to.
9714 This is the default.
9717 @itemx --no-dereference
9719 @opindex --no-dereference
9720 @cindex symbolic links, changing group
9722 Act on symbolic links themselves instead of what they point to.
9723 This mode relies on the @code{lchown} system call.
9724 On systems that do not provide the @code{lchown} system call,
9725 @command{chgrp} fails when a file specified on the command line
9727 By default, no diagnostic is issued for symbolic links encountered
9728 during a recursive traversal, but see @option{--verbose}.
9730 @itemx --preserve-root
9731 @opindex --preserve-root
9732 @cindex root directory, disallow recursive modification
9733 Fail upon any attempt to recursively change the root directory, @file{/}.
9734 Without @option{--recursive}, this option has no effect.
9735 @xref{Treating / specially}.
9737 @itemx --no-preserve-root
9738 @opindex --no-preserve-root
9739 @cindex root directory, allow recursive modification
9740 Cancel the effect of any preceding @option{--preserve-root} option.
9741 @xref{Treating / specially}.
9743 @item --reference=@var{ref_file}
9744 @opindex --reference
9745 Change the group of each @var{file} to be the same as that of
9746 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9747 group of the symbolic link, but rather that of the file it refers to.
9753 Output a diagnostic for every file processed.
9754 If a symbolic link is encountered during a recursive traversal
9755 on a system without the @code{lchown} system call, and @option{--no-dereference}
9756 is in effect, then issue a diagnostic saying neither the symbolic link nor
9757 its referent is being changed.
9762 @opindex --recursive
9763 @cindex recursively changing group ownership
9764 Recursively change the group ownership of directories and their contents.
9767 @xref{Traversing symlinks}.
9770 @xref{Traversing symlinks}.
9773 @xref{Traversing symlinks}.
9782 # Change the group of /u to "staff".
9785 # Change the group of /u and subfiles to "staff".
9790 @node chmod invocation
9791 @section @command{chmod}: Change access permissions
9794 @cindex changing access permissions
9795 @cindex access permissions, changing
9796 @cindex permissions, changing access
9798 @command{chmod} changes the access permissions of the named files. Synopsis:
9801 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9804 @cindex symbolic links, permissions of
9805 @command{chmod} never changes the permissions of symbolic links, since
9806 the @command{chmod} system call cannot change their permissions.
9807 This is not a problem since the permissions of symbolic links are
9808 never used. However, for each symbolic link listed on the command
9809 line, @command{chmod} changes the permissions of the pointed-to file.
9810 In contrast, @command{chmod} ignores symbolic links encountered during
9811 recursive directory traversals.
9813 A successful use of @command{chmod} clears the set-group-ID bit of a
9814 regular file if the file's group ID does not match the user's
9815 effective group ID or one of the user's supplementary group IDs,
9816 unless the user has appropriate privileges. Additional restrictions
9817 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9818 @var{ref_file} to be ignored. This behavior depends on the policy and
9819 functionality of the underlying @code{chmod} system call. When in
9820 doubt, check the underlying system behavior.
9822 If used, @var{mode} specifies the new file mode bits.
9823 For details, see the section on @ref{File permissions}.
9824 If you really want @var{mode} to have a leading @samp{-}, you should
9825 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9826 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9827 file} (without the @option{--}) complains if it behaves differently
9828 from what @samp{chmod a-w file} would do.
9830 The program accepts the following options. Also see @ref{Common options}.
9838 Verbosely describe the action for each @var{file} whose permissions
9847 @cindex error messages, omitting
9848 Do not print error messages about files whose permissions cannot be
9851 @itemx --preserve-root
9852 @opindex --preserve-root
9853 @cindex root directory, disallow recursive modification
9854 Fail upon any attempt to recursively change the root directory, @file{/}.
9855 Without @option{--recursive}, this option has no effect.
9856 @xref{Treating / specially}.
9858 @itemx --no-preserve-root
9859 @opindex --no-preserve-root
9860 @cindex root directory, allow recursive modification
9861 Cancel the effect of any preceding @option{--preserve-root} option.
9862 @xref{Treating / specially}.
9868 Verbosely describe the action or non-action taken for every @var{file}.
9870 @item --reference=@var{ref_file}
9871 @opindex --reference
9872 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9873 @xref{File permissions}.
9874 If @var{ref_file} is a symbolic link, do not use the mode
9875 of the symbolic link, but rather that of the file it refers to.
9880 @opindex --recursive
9881 @cindex recursively changing access permissions
9882 Recursively change permissions of directories and their contents.
9889 @node touch invocation
9890 @section @command{touch}: Change file timestamps
9893 @cindex changing file timestamps
9894 @cindex file timestamps, changing
9895 @cindex timestamps, changing file
9897 @command{touch} changes the access and/or modification times of the
9898 specified files. Synopsis:
9901 touch [@var{option}]@dots{} @var{file}@dots{}
9904 @cindex empty files, creating
9905 Any @var{file} argument that does not exist is created empty, unless
9906 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9907 (@option{-h}) was in effect.
9909 A @var{file} argument string of @samp{-} is handled specially and
9910 causes @command{touch} to change the times of the file associated with
9913 @cindex permissions, for changing file timestamps
9914 If changing both the access and modification times to the current
9915 time, @command{touch} can change the timestamps for files that the user
9916 running it does not own but has write permission for. Otherwise, the
9917 user must own the files.
9919 Although @command{touch} provides options for changing two of the times---the
9920 times of last access and modification---of a file, there is actually
9921 a standard third one as well: the inode change time. This is often
9922 referred to as a file's @code{ctime}.
9923 The inode change time represents the time when the file's meta-information
9924 last changed. One common example of this is when the permissions of a
9925 file change. Changing the permissions doesn't access the file, so
9926 the atime doesn't change, nor does it modify the file, so the mtime
9927 doesn't change. Yet, something about the file itself has changed,
9928 and this must be noted somewhere. This is the job of the ctime field.
9929 This is necessary, so that, for example, a backup program can make a
9930 fresh copy of the file, including the new permissions value.
9931 Another operation that modifies a file's ctime without affecting
9932 the others is renaming. In any case, it is not possible, in normal
9933 operations, for a user to change the ctime field to a user-specified value.
9934 Some operating systems and file systems support a fourth time: the
9935 birth time, when the file was first created; by definition, this
9936 timestamp never changes.
9939 Time stamps assume the time zone rules specified by the @env{TZ}
9940 environment variable, or by the system default rules if @env{TZ} is
9941 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9942 libc, The GNU C Library Reference Manual}.
9943 You can avoid ambiguities during
9944 daylight saving transitions by using @sc{utc} time stamps.
9946 The program accepts the following options. Also see @ref{Common options}.
9952 @itemx --time=access
9956 @opindex atime@r{, changing}
9957 @opindex access @r{time, changing}
9958 @opindex use @r{time, changing}
9959 Change the access time only.
9964 @opindex --no-create
9965 Do not warn about or create files that do not exist.
9968 @itemx --date=@var{time}
9972 Use @var{time} instead of the current time. It can contain month names,
9973 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9974 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9975 specifies the instant of time that is 489,392,193 nanoseconds after
9976 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9977 minutes east of @acronym{UTC}. @xref{Date input formats}.
9978 File systems that do not support high-resolution time stamps
9979 silently ignore any excess precision here.
9983 @cindex BSD @command{touch} compatibility
9984 Ignored; for compatibility with BSD versions of @command{touch}.
9987 @itemx --no-dereference
9989 @opindex --no-dereference
9990 @cindex symbolic links, changing time
9992 Attempt to change the timestamps of a symbolic link, rather than what
9993 the link refers to. When using this option, empty files are not
9994 created, but option @option{-c} must also be used to avoid warning
9995 about files that do not exist. Not all systems support changing the
9996 timestamps of symlinks, since underlying system support for this
9997 action was not required until @acronym{POSIX} 2008. Also, on some
9998 systems, the mere act of examining a symbolic link changes the access
9999 time, such that only changes to the modification time will persist
10000 long enough to be observable. When coupled with option @option{-r}, a
10001 reference timestamp is taken from a symbolic link rather than the file
10005 @itemx --time=mtime
10006 @itemx --time=modify
10009 @opindex mtime@r{, changing}
10010 @opindex modify @r{time, changing}
10011 Change the modification time only.
10013 @item -r @var{file}
10014 @itemx --reference=@var{file}
10016 @opindex --reference
10017 Use the times of the reference @var{file} instead of the current time.
10018 If this option is combined with the @option{--date=@var{time}}
10019 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10020 the origin for any relative @var{time}s given, but is otherwise ignored.
10021 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10022 equal to five seconds before the corresponding time stamp for @file{foo}.
10023 If @var{file} is a symbolic link, the reference timestamp is taken
10024 from the target of the symlink, unless @option{-h} was also in effect.
10026 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10027 Use the argument (optional four-digit or two-digit years, months,
10028 days, hours, minutes, optional seconds) instead of the current time.
10029 If the year is specified with only two digits, then @var{cc}
10030 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10031 69 @dots{} 99. If no digits of the year are specified,
10032 the argument is interpreted as a date in the current year.
10033 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10037 @vindex _POSIX2_VERSION
10038 On older systems, @command{touch} supports an obsolete syntax, as follows.
10039 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10040 @option{-t} options, and if there are two or more @var{file}s and the
10041 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10042 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10043 any, were moved to the front), and if the represented year
10044 is in the range 1969--1999, that argument is interpreted as the time
10045 for the other files instead of as a file name.
10046 This obsolete behavior can be enabled or disabled with the
10047 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10048 conformance}), but portable scripts should avoid commands whose
10049 behavior depends on this variable.
10050 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10051 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10057 @chapter Disk usage
10061 No disk can hold an infinite amount of data. These commands report
10062 how much disk storage is in use or available, report other file and
10063 file status information, and write buffers to disk.
10066 * df invocation:: Report file system disk space usage.
10067 * du invocation:: Estimate file space usage.
10068 * stat invocation:: Report file or file system status.
10069 * sync invocation:: Synchronize memory and disk.
10070 * truncate invocation:: Shrink or extend the size of a file.
10074 @node df invocation
10075 @section @command{df}: Report file system disk space usage
10078 @cindex file system disk usage
10079 @cindex disk usage by file system
10081 @command{df} reports the amount of disk space used and available on
10082 file systems. Synopsis:
10085 df [@var{option}]@dots{} [@var{file}]@dots{}
10088 With no arguments, @command{df} reports the space used and available on all
10089 currently mounted file systems (of all types). Otherwise, @command{df}
10090 reports on the file system containing each argument @var{file}.
10092 Normally the disk space is printed in units of
10093 1024 bytes, but this can be overridden (@pxref{Block size}).
10094 Non-integer quantities are rounded up to the next higher unit.
10096 @cindex disk device file
10097 @cindex device file, disk
10098 If an argument @var{file} is a disk device file containing a mounted
10099 file system, @command{df} shows the space available on that file system
10100 rather than on the file system containing the device node (i.e., the root
10101 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10102 on unmounted file systems, because on most kinds of systems doing so
10103 requires extremely nonportable intimate knowledge of file system
10106 The program accepts the following options. Also see @ref{Common options}.
10114 @cindex automounter file systems
10115 @cindex ignore file systems
10116 Include in the listing dummy file systems, which
10117 are omitted by default. Such file systems are typically special-purpose
10118 pseudo-file-systems, such as automounter entries.
10120 @item -B @var{size}
10121 @itemx --block-size=@var{size}
10123 @opindex --block-size
10124 @cindex file system sizes
10125 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10126 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10130 @cindex grand total of disk size, usage and available space
10131 Print a grand total of all arguments after all arguments have
10132 been processed. This can be used to find out the total disk size, usage
10133 and available space of all listed devices.
10139 Equivalent to @option{--si}.
10145 @cindex inode usage
10146 List inode usage information instead of block usage. An inode (short
10147 for index node) contains information about a file such as its owner,
10148 permissions, timestamps, and location on the disk.
10152 @cindex kibibytes for file system sizes
10153 Print sizes in 1024-byte blocks, overriding the default block size
10154 (@pxref{Block size}).
10155 This option is equivalent to @option{--block-size=1K}.
10161 @cindex file system types, limiting output to certain
10162 Limit the listing to local file systems. By default, remote file systems
10167 @cindex file system space, retrieving old data more quickly
10168 Do not invoke the @code{sync} system call before getting any usage data.
10169 This may make @command{df} run significantly faster on systems with many
10170 disks, but on some systems (notably SunOS) the results may be slightly
10171 out of date. This is the default.
10174 @itemx --portability
10176 @opindex --portability
10177 @cindex one-line output format
10178 @cindex @acronym{POSIX} output format
10179 @cindex portable output format
10180 @cindex output format, portable
10181 Use the @acronym{POSIX} output format. This is like the default format except
10186 The information about each file system is always printed on exactly
10187 one line; a mount device is never put on a line by itself. This means
10188 that if the mount device name is more than 20 characters long (e.g., for
10189 some network mounts), the columns are misaligned.
10192 The labels in the header output line are changed to conform to @acronym{POSIX}.
10195 The default block size and output format are unaffected by the
10196 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10197 variables. However, the default block size is still affected by
10198 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10199 otherwise. @xref{Block size}.
10206 @cindex file system space, retrieving current data more slowly
10207 Invoke the @code{sync} system call before getting any usage data. On
10208 some systems (notably SunOS), doing this yields more up to date results,
10209 but in general this option makes @command{df} much slower, especially when
10210 there are many or very busy file systems.
10212 @item -t @var{fstype}
10213 @itemx --type=@var{fstype}
10216 @cindex file system types, limiting output to certain
10217 Limit the listing to file systems of type @var{fstype}. Multiple
10218 file system types can be specified by giving multiple @option{-t} options.
10219 By default, nothing is omitted.
10222 @itemx --print-type
10224 @opindex --print-type
10225 @cindex file system types, printing
10226 Print each file system's type. The types printed here are the same ones
10227 you can include or exclude with @option{-t} and @option{-x}. The particular
10228 types printed are whatever is supported by the system. Here are some of
10229 the common names (this list is certainly not exhaustive):
10234 @cindex @acronym{NFS} file system type
10235 An @acronym{NFS} file system, i.e., one mounted over a network from another
10236 machine. This is the one type name which seems to be used uniformly by
10239 @item 4.2@r{, }ufs@r{, }efs@dots{}
10240 @cindex Linux file system types
10241 @cindex local file system types
10242 @opindex 4.2 @r{file system type}
10243 @opindex ufs @r{file system type}
10244 @opindex efs @r{file system type}
10245 A file system on a locally-mounted hard disk. (The system might even
10246 support more than one type here; Linux does.)
10248 @item hsfs@r{, }cdfs
10249 @cindex CD-ROM file system type
10250 @cindex High Sierra file system
10251 @opindex hsfs @r{file system type}
10252 @opindex cdfs @r{file system type}
10253 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10254 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10257 @cindex PC file system
10258 @cindex DOS file system
10259 @cindex MS-DOS file system
10260 @cindex diskette file system
10262 An MS-DOS file system, usually on a diskette.
10266 @item -x @var{fstype}
10267 @itemx --exclude-type=@var{fstype}
10269 @opindex --exclude-type
10270 Limit the listing to file systems not of type @var{fstype}.
10271 Multiple file system types can be eliminated by giving multiple
10272 @option{-x} options. By default, no file system types are omitted.
10275 Ignored; for compatibility with System V versions of @command{df}.
10280 Failure includes the case where no output is generated, so you can
10281 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10282 @var{dir}} to test whether @var{dir} is on a file system of type
10283 @samp{ext3} or @samp{reiserfs}.
10286 @node du invocation
10287 @section @command{du}: Estimate file space usage
10290 @cindex file space usage
10291 @cindex disk usage for files
10293 @command{du} reports the amount of disk space used by the specified files
10294 and for each subdirectory (of directory arguments). Synopsis:
10297 du [@var{option}]@dots{} [@var{file}]@dots{}
10300 With no arguments, @command{du} reports the disk space for the current
10301 directory. Normally the disk space is printed in units of
10302 1024 bytes, but this can be overridden (@pxref{Block size}).
10303 Non-integer quantities are rounded up to the next higher unit.
10305 If two or more hard links point to the same file, only one of the hard
10306 links is counted. The @var{file} argument order affects which links
10307 are counted, and changing the argument order may change the numbers
10308 that @command{du} outputs.
10310 The program accepts the following options. Also see @ref{Common options}.
10318 Show counts for all files, not just directories.
10320 @itemx --apparent-size
10321 @opindex --apparent-size
10322 Print apparent sizes, rather than disk usage. The apparent size of a
10323 file is the number of bytes reported by @code{wc -c} on regular files,
10324 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10325 For example, a file containing the word @samp{zoo} with no newline would,
10326 of course, have an apparent size of 3. Such a small file may require
10327 anywhere from 0 to 16 KiB or more of disk space, depending on
10328 the type and configuration of the file system on which the file resides.
10329 However, a sparse file created with this command:
10332 dd bs=1 seek=2GiB if=/dev/null of=big
10336 has an apparent size of 2 GiB, yet on most modern
10337 systems, it actually uses almost no disk space.
10343 Equivalent to @code{--apparent-size --block-size=1}.
10345 @item -B @var{size}
10346 @itemx --block-size=@var{size}
10348 @opindex --block-size
10350 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10351 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10357 @cindex grand total of disk space
10358 Print a grand total of all arguments after all arguments have
10359 been processed. This can be used to find out the total disk usage of
10360 a given set of files or directories.
10363 @itemx --dereference-args
10365 @opindex --dereference-args
10366 Dereference symbolic links that are command line arguments.
10367 Does not affect other symbolic links. This is helpful for finding
10368 out the disk usage of directories, such as @file{/usr/tmp}, which
10369 are often symbolic links.
10371 @c --files0-from=FILE
10372 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10378 Equivalent to @option{--dereference-args} (@option{-D}).
10382 @cindex kibibytes for file sizes
10383 Print sizes in 1024-byte blocks, overriding the default block size
10384 (@pxref{Block size}).
10385 This option is equivalent to @option{--block-size=1K}.
10388 @itemx --count-links
10390 @opindex --count-links
10391 @cindex hard links, counting in @command{du}
10392 Count the size of all files, even if they have appeared already (as a
10396 @itemx --dereference
10398 @opindex --dereference
10399 @cindex symbolic links, dereferencing in @command{du}
10400 Dereference symbolic links (show the disk space used by the file
10401 or directory that the link points to instead of the space used by
10406 @cindex mebibytes for file sizes
10407 Print sizes in 1,048,576-byte blocks, overriding the default block size
10408 (@pxref{Block size}).
10409 This option is equivalent to @option{--block-size=1M}.
10412 @itemx --no-dereference
10414 @opindex --no-dereference
10415 @cindex symbolic links, dereferencing in @command{du}
10416 For each symbolic links encountered by @command{du},
10417 consider the disk space used by the symbolic link.
10419 @item --max-depth=@var{depth}
10420 @opindex --max-depth=@var{depth}
10421 @cindex limiting output of @command{du}
10422 Show the total for each directory (and file if --all) that is at
10423 most MAX_DEPTH levels down from the root of the hierarchy. The root
10424 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10433 @opindex --summarize
10434 Display only a total for each argument.
10437 @itemx --separate-dirs
10439 @opindex --separate-dirs
10440 Normally, in the output of @command{du} (when not using @option{--summarize}),
10441 the size listed next to a directory name, @var{d}, represents the sum
10442 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10443 With @option{--separate-dirs}, the size reported for a directory name,
10444 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10449 @cindex last modified dates, displaying in @command{du}
10450 Show time of the most recent modification of any file in the directory,
10451 or any of its subdirectories.
10453 @itemx --time=ctime
10454 @itemx --time=status
10457 @opindex ctime@r{, show the most recent}
10458 @opindex status time@r{, show the most recent}
10459 @opindex use time@r{, show the most recent}
10460 Show the most recent status change time (the @samp{ctime} in the inode) of
10461 any file in the directory, instead of the modification time.
10463 @itemx --time=atime
10464 @itemx --time=access
10466 @opindex atime@r{, show the most recent}
10467 @opindex access time@r{, show the most recent}
10468 Show the most recent access time (the @samp{atime} in the inode) of
10469 any file in the directory, instead of the modification time.
10471 @item --time-style=@var{style}
10472 @opindex --time-style
10474 List timestamps in style @var{style}. This option has an effect only if
10475 the @option{--time} option is also specified. The @var{style} should
10476 be one of the following:
10479 @item +@var{format}
10481 List timestamps using @var{format}, where @var{format} is interpreted
10482 like the format argument of @command{date} (@pxref{date invocation}).
10483 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10484 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10485 with @command{date}, @var{format}'s interpretation is affected by the
10486 @env{LC_TIME} locale category.
10489 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10490 format with nanosecond precision, e.g., @samp{2002-03-30
10491 23:45:56.477817180 -0700}. This style is equivalent to
10492 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10495 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10496 @samp{2002-03-30 23:45}. These timestamps are shorter than
10497 @samp{full-iso} timestamps, and are usually good enough for everyday
10498 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10501 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10502 This style is equivalent to @samp{+%Y-%m-%d}.
10506 You can specify the default value of the @option{--time-style} option
10507 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10508 the default style is @samp{long-iso}. For compatibility with @command{ls},
10509 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10510 the newline and any later characters are ignored; if @env{TIME_STYLE}
10511 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10512 @env{TIME_STYLE} is @samp{locale} it is ignored.
10515 @itemx --one-file-system
10517 @opindex --one-file-system
10518 @cindex one file system, restricting @command{du} to
10519 Skip directories that are on different file systems from the one that
10520 the argument being processed is on.
10522 @item --exclude=@var{pattern}
10523 @opindex --exclude=@var{pattern}
10524 @cindex excluding files from @command{du}
10525 When recursing, skip subdirectories or files matching @var{pattern}.
10526 For example, @code{du --exclude='*.o'} excludes files whose names
10529 @item -X @var{file}
10530 @itemx --exclude-from=@var{file}
10531 @opindex -X @var{file}
10532 @opindex --exclude-from=@var{file}
10533 @cindex excluding files from @command{du}
10534 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10535 one per line. If @var{file} is @samp{-}, take the patterns from standard
10540 @cindex NFS mounts from BSD to HP-UX
10541 On BSD systems, @command{du} reports sizes that are half the correct
10542 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10543 systems, it reports sizes that are twice the correct values for
10544 files that are NFS-mounted from BSD systems. This is due to a flaw
10545 in HP-UX; it also affects the HP-UX @command{du} program.
10550 @node stat invocation
10551 @section @command{stat}: Report file or file system status
10554 @cindex file status
10555 @cindex file system status
10557 @command{stat} displays information about the specified file(s). Synopsis:
10560 stat [@var{option}]@dots{} [@var{file}]@dots{}
10563 With no option, @command{stat} reports all information about the given files.
10564 But it also can be used to report the information of the file systems the
10565 given files are located on. If the files are links, @command{stat} can
10566 also give information about the files the links point to.
10568 @mayConflictWithShellBuiltIn{stat}
10573 @itemx --dereference
10575 @opindex --dereference
10576 @cindex symbolic links, dereferencing in @command{stat}
10577 Change how @command{stat} treats symbolic links.
10578 With this option, @command{stat} acts on the file referenced
10579 by each symbolic link argument.
10580 Without it, @command{stat} acts on any symbolic link argument directly.
10583 @itemx --file-system
10585 @opindex --file-system
10586 @cindex file systems
10587 Report information about the file systems where the given files are located
10588 instead of information about the files themselves.
10591 @itemx --format=@var{format}
10593 @opindex --format=@var{format}
10594 @cindex output format
10595 Use @var{format} rather than the default format.
10596 @var{format} is automatically newline-terminated, so
10597 running a command like the following with two or more @var{file}
10598 operands produces a line of output for each operand:
10600 $ stat --format=%d:%i / /usr
10605 @itemx --printf=@var{format}
10606 @opindex --printf=@var{format}
10607 @cindex output format
10608 Use @var{format} rather than the default format.
10609 Like @option{--format}, but interpret backslash escapes,
10610 and do not output a mandatory trailing newline.
10611 If you want a newline, include @samp{\n} in the @var{format}.
10612 Here's how you would use @option{--printf} to print the device
10613 and inode numbers of @file{/} and @file{/usr}:
10615 $ stat --printf='%d:%i\n' / /usr
10624 @cindex terse output
10625 Print the information in terse form, suitable for parsing by other programs.
10629 The valid @var{format} directives for files with @option{--format} and
10630 @option{--printf} are:
10633 @item %a - Access rights in octal
10634 @item %A - Access rights in human readable form
10635 @item %b - Number of blocks allocated (see @samp{%B})
10636 @item %B - The size in bytes of each block reported by @samp{%b}
10637 @item %d - Device number in decimal
10638 @item %D - Device number in hex
10639 @item %f - Raw mode in hex
10640 @item %F - File type
10641 @item %g - Group ID of owner
10642 @item %G - Group name of owner
10643 @item %h - Number of hard links
10644 @item %i - Inode number
10645 @item %n - File name
10646 @item %N - Quoted file name with dereference if symbolic link
10647 @item %o - I/O block size
10648 @item %s - Total size, in bytes
10649 @item %t - Major device type in hex
10650 @item %T - Minor device type in hex
10651 @item %u - User ID of owner
10652 @item %U - User name of owner
10653 @item %x - Time of last access
10654 @item %X - Time of last access as seconds since Epoch
10655 @item %y - Time of last modification
10656 @item %Y - Time of last modification as seconds since Epoch
10657 @item %z - Time of last change
10658 @item %Z - Time of last change as seconds since Epoch
10661 When listing file system information (@option{--file-system} (@option{-f})),
10662 you must use a different set of @var{format} directives:
10665 @item %a - Free blocks available to non-super-user
10666 @item %b - Total data blocks in file system
10667 @item %c - Total file nodes in file system
10668 @item %d - Free file nodes in file system
10669 @item %f - Free blocks in file system
10670 @item %i - File System ID in hex
10671 @item %l - Maximum length of file names
10672 @item %n - File name
10673 @item %s - Block size (for faster transfers)
10674 @item %S - Fundamental block size (for block counts)
10675 @item %t - Type in hex
10676 @item %T - Type in human readable form
10680 Time stamps are listed according to the time zone rules specified by
10681 the @env{TZ} environment variable, or by the system default rules if
10682 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10683 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10688 @node sync invocation
10689 @section @command{sync}: Synchronize data on disk with memory
10692 @cindex synchronize disk and memory
10694 @cindex superblock, writing
10695 @cindex inodes, written buffered
10696 @command{sync} writes any data buffered in memory out to disk. This can
10697 include (but is not limited to) modified superblocks, modified inodes,
10698 and delayed reads and writes. This must be implemented by the kernel;
10699 The @command{sync} program does nothing but exercise the @code{sync} system
10702 @cindex crashes and corruption
10703 The kernel keeps data in memory to avoid doing (relatively slow) disk
10704 reads and writes. This improves performance, but if the computer
10705 crashes, data may be lost or the file system corrupted as a
10706 result. The @command{sync} command ensures everything in memory
10707 is written to disk.
10709 Any arguments are ignored, except for a lone @option{--help} or
10710 @option{--version} (@pxref{Common options}).
10715 @node truncate invocation
10716 @section @command{truncate}: Shrink or extend the size of a file
10719 @cindex truncating, file sizes
10721 @command{truncate} shrinks or extends the size of each @var{file} to the
10722 specified size. Synopsis:
10725 truncate @var{option}@dots{} @var{file}@dots{}
10728 @cindex files, creating
10729 Any @var{file} that does not exist is created.
10731 @cindex sparse files, creating
10732 @cindex holes, creating files with
10733 If a @var{file} is larger than the specified size, the extra data is lost.
10734 If a @var{file} is shorter, it is extended and the extended part (or hole)
10735 reads as zero bytes.
10737 The program accepts the following options. Also see @ref{Common options}.
10744 @opindex --no-create
10745 Do not create files that do not exist.
10750 @opindex --io-blocks
10751 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10753 @item -r @var{rfile}
10754 @itemx --reference=@var{rfile}
10756 @opindex --reference
10757 Set the size of each @var{file} to the same size as @var{rfile}.
10759 @item -s @var{size}
10760 @itemx --size=@var{size}
10763 Set the size of each @var{file} to this @var{size}.
10764 @multiplierSuffixesNoBlocks{size}
10766 @var{size} may also be prefixed by one of the following to adjust
10767 the size of each @var{file} based on their current size:
10769 @samp{+} => extend by
10770 @samp{-} => reduce by
10771 @samp{<} => at most
10772 @samp{>} => at least
10773 @samp{/} => round down to multiple of
10774 @samp{%} => round up to multiple of
10782 @node Printing text
10783 @chapter Printing text
10785 @cindex printing text, commands for
10786 @cindex commands for printing text
10788 This section describes commands that display text strings.
10791 * echo invocation:: Print a line of text.
10792 * printf invocation:: Format and print data.
10793 * yes invocation:: Print a string until interrupted.
10797 @node echo invocation
10798 @section @command{echo}: Print a line of text
10801 @cindex displaying text
10802 @cindex printing text
10803 @cindex text, displaying
10804 @cindex arbitrary text, displaying
10806 @command{echo} writes each given @var{string} to standard output, with a
10807 space between each and a newline after the last one. Synopsis:
10810 echo [@var{option}]@dots{} [@var{string}]@dots{}
10813 @mayConflictWithShellBuiltIn{echo}
10815 The program accepts the following options. Also see @ref{Common options}.
10816 Options must precede operands, and the normally-special argument
10817 @samp{--} has no special meaning and is treated like any other
10823 Do not output the trailing newline.
10827 @cindex backslash escapes
10828 Enable interpretation of the following backslash-escaped characters in
10837 produce no further output
10853 the eight-bit value that is the octal number @var{nnn}
10854 (zero to three octal digits)
10856 the eight-bit value that is the octal number @var{nnn}
10857 (one to three octal digits)
10859 the eight-bit value that is the hexadecimal number @var{hh}
10860 (one or two hexadecimal digits)
10865 @cindex backslash escapes
10866 Disable interpretation of backslash escapes in each @var{string}.
10867 This is the default. If @option{-e} and @option{-E} are both
10868 specified, the last one given takes effect.
10872 @vindex POSIXLY_CORRECT
10873 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10874 @command{echo}'s first argument is not @option{-n} it outputs
10875 option-like arguments instead of treating them as options. For
10876 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10877 plain @samp{hello}.
10879 @acronym{POSIX} does not require support for any options, and says
10880 that the behavior of @command{echo} is implementation-defined if any
10881 @var{string} contains a backslash or if the first argument is
10882 @option{-n}. Portable programs can use the @command{printf} command
10883 if they need to omit trailing newlines or output control characters or
10884 backslashes. @xref{printf invocation}.
10889 @node printf invocation
10890 @section @command{printf}: Format and print data
10893 @command{printf} does formatted printing of text. Synopsis:
10896 printf @var{format} [@var{argument}]@dots{}
10899 @command{printf} prints the @var{format} string, interpreting @samp{%}
10900 directives and @samp{\} escapes to format numeric and string arguments
10901 in a way that is mostly similar to the C @samp{printf} function.
10902 @xref{Output Conversion Syntax,, @command{printf} format directives,
10903 libc, The GNU C Library Reference Manual}, for details.
10904 The differences are listed below.
10906 @mayConflictWithShellBuiltIn{printf}
10911 The @var{format} argument is reused as necessary to convert all the
10912 given @var{argument}s. For example, the command @samp{printf %s a b}
10916 Missing @var{argument}s are treated as null strings or as zeros,
10917 depending on whether the context expects a string or a number. For
10918 example, the command @samp{printf %sx%d} prints @samp{x0}.
10922 An additional escape, @samp{\c}, causes @command{printf} to produce no
10923 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10924 E} prints @samp{ABC}.
10927 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10928 digits, as opposed to C where it can have an unlimited number of
10929 digits. For example, the command @samp{printf '\x07e'} prints two
10930 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10935 @command{printf} has an additional directive, @samp{%b}, which prints its
10936 argument string with @samp{\} escapes interpreted in the same way as in
10937 the @var{format} string, except that octal escapes are of the form
10938 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10939 If a precision is also given, it limits the number of bytes printed
10940 from the converted string.
10943 Numeric arguments must be single C constants, possibly with leading
10944 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10948 @vindex POSIXLY_CORRECT
10949 If the leading character of a numeric argument is @samp{"} or @samp{'}
10950 then its value is the numeric value of the immediately following
10951 character. Any remaining characters are silently ignored if the
10952 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10953 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10954 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10955 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10960 A floating-point argument must use a period before any fractional
10961 digits, but is printed according to the @env{LC_NUMERIC} category of the
10962 current locale. For example, in a locale whose radix character is a
10963 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10964 the command @samp{printf %g 3,14} is an error.
10968 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10969 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10970 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10971 digits) specifying a character to print.
10976 @cindex ISO/IEC 10646
10978 @command{printf} interprets two character syntaxes introduced in
10979 @acronym{ISO} C 99:
10980 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
10981 characters, specified as
10982 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
10983 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
10984 @command{printf} outputs the Unicode characters
10985 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
10986 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
10987 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
10989 The processing of @samp{\u} and @samp{\U} requires a full-featured
10990 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
10991 or when @code{libiconv} is installed prior to this package. Otherwise
10992 @samp{\u} and @samp{\U} will print as-is.
10994 The only options are a lone @option{--help} or
10995 @option{--version}. @xref{Common options}.
10996 Options must precede operands.
10998 The Unicode character syntaxes are useful for writing strings in a locale
10999 independent way. For example, a string containing the Euro currency symbol
11002 $ env printf '\u20AC 14.95'
11006 will be output correctly in all locales supporting the Euro symbol
11007 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11010 $ env printf '\u4e2d\u6587'
11014 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11016 Note that in these examples, the @command{printf} command has been
11017 invoked via @command{env} to ensure that we run the program found via
11018 your shell's search path, and not a shell alias or a built-in function.
11020 For larger strings, you don't need to look up the hexadecimal code
11021 values of each character one by one. @acronym{ASCII} characters mixed with \u
11022 escape sequences is also known as the JAVA source file encoding. You can
11023 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11024 is how to convert a piece of text into a shell script which will output
11025 this text in a locale-independent way:
11028 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11029 '\u4e2d\u6587\n' > sample.txt
11030 $ recode BIG5..JAVA < sample.txt \
11031 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11038 @node yes invocation
11039 @section @command{yes}: Print a string until interrupted
11042 @cindex repeated output of a string
11044 @command{yes} prints the command line arguments, separated by spaces and
11045 followed by a newline, forever until it is killed. If no arguments are
11046 given, it prints @samp{y} followed by a newline forever until killed.
11048 Upon a write error, @command{yes} exits with status @samp{1}.
11050 The only options are a lone @option{--help} or @option{--version}.
11051 To output an argument that begins with
11052 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11053 @xref{Common options}.
11057 @chapter Conditions
11060 @cindex commands for exit status
11061 @cindex exit status commands
11063 This section describes commands that are primarily useful for their exit
11064 status, rather than their output. Thus, they are often used as the
11065 condition of shell @code{if} statements, or as the last command in a
11069 * false invocation:: Do nothing, unsuccessfully.
11070 * true invocation:: Do nothing, successfully.
11071 * test invocation:: Check file types and compare values.
11072 * expr invocation:: Evaluate expressions.
11076 @node false invocation
11077 @section @command{false}: Do nothing, unsuccessfully
11080 @cindex do nothing, unsuccessfully
11081 @cindex failure exit status
11082 @cindex exit status of @command{false}
11084 @command{false} does nothing except return an exit status of 1, meaning
11085 @dfn{failure}. It can be used as a place holder in shell scripts
11086 where an unsuccessful command is needed.
11087 In most modern shells, @command{false} is a built-in command, so when
11088 you use @samp{false} in a script, you're probably using the built-in
11089 command, not the one documented here.
11091 @command{false} honors the @option{--help} and @option{--version} options.
11093 This version of @command{false} is implemented as a C program, and is thus
11094 more secure and faster than a shell script implementation, and may safely
11095 be used as a dummy shell for the purpose of disabling accounts.
11097 Note that @command{false} (unlike all other programs documented herein)
11098 exits unsuccessfully, even when invoked with
11099 @option{--help} or @option{--version}.
11101 Portable programs should not assume that the exit status of
11102 @command{false} is 1, as it is greater than 1 on some
11103 non-@acronym{GNU} hosts.
11106 @node true invocation
11107 @section @command{true}: Do nothing, successfully
11110 @cindex do nothing, successfully
11112 @cindex successful exit
11113 @cindex exit status of @command{true}
11115 @command{true} does nothing except return an exit status of 0, meaning
11116 @dfn{success}. It can be used as a place holder in shell scripts
11117 where a successful command is needed, although the shell built-in
11118 command @code{:} (colon) may do the same thing faster.
11119 In most modern shells, @command{true} is a built-in command, so when
11120 you use @samp{true} in a script, you're probably using the built-in
11121 command, not the one documented here.
11123 @command{true} honors the @option{--help} and @option{--version} options.
11125 Note, however, that it is possible to cause @command{true}
11126 to exit with nonzero status: with the @option{--help} or @option{--version}
11127 option, and with standard
11128 output already closed or redirected to a file that evokes an I/O error.
11129 For example, using a Bourne-compatible shell:
11132 $ ./true --version >&-
11133 ./true: write error: Bad file number
11134 $ ./true --version > /dev/full
11135 ./true: write error: No space left on device
11138 This version of @command{true} is implemented as a C program, and is thus
11139 more secure and faster than a shell script implementation, and may safely
11140 be used as a dummy shell for the purpose of disabling accounts.
11142 @node test invocation
11143 @section @command{test}: Check file types and compare values
11146 @cindex check file types
11147 @cindex compare values
11148 @cindex expression evaluation
11150 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11151 evaluation of the conditional expression @var{expr}. Each part of the
11152 expression must be a separate argument.
11154 @command{test} has file status checks, string operators, and numeric
11155 comparison operators.
11157 @command{test} has an alternate form that uses opening and closing
11158 square brackets instead a leading @samp{test}. For example, instead
11159 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11160 brackets must be separate arguments; for example, @samp{[-d /]} does
11161 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11162 @var{expr} ]} have the same meaning, only the former form is discussed
11168 test @var{expression}
11170 [ @var{expression} ]
11175 @mayConflictWithShellBuiltIn{test}
11177 If @var{expression} is omitted, @command{test} returns false.
11178 If @var{expression} is a single argument,
11179 @command{test} returns false if the argument is null and true otherwise. The argument
11180 can be any string, including strings like @samp{-d}, @samp{-1},
11181 @samp{--}, @samp{--help}, and @samp{--version} that most other
11182 programs would treat as options. To get help and version information,
11183 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11184 the usual closing brackets. @xref{Common options}.
11186 @cindex exit status of @command{test}
11190 0 if the expression is true,
11191 1 if the expression is false,
11192 2 if an error occurred.
11196 * File type tests:: -[bcdfhLpSt]
11197 * Access permission tests:: -[gkruwxOG]
11198 * File characteristic tests:: -e -s -nt -ot -ef
11199 * String tests:: -z -n = !=
11200 * Numeric tests:: -eq -ne -lt -le -gt -ge
11201 * Connectives for test:: ! -a -o
11205 @node File type tests
11206 @subsection File type tests
11208 @cindex file type tests
11210 These options test for particular types of files. (Everything's a file,
11211 but not all files are the same!)
11215 @item -b @var{file}
11217 @cindex block special check
11218 True if @var{file} exists and is a block special device.
11220 @item -c @var{file}
11222 @cindex character special check
11223 True if @var{file} exists and is a character special device.
11225 @item -d @var{file}
11227 @cindex directory check
11228 True if @var{file} exists and is a directory.
11230 @item -f @var{file}
11232 @cindex regular file check
11233 True if @var{file} exists and is a regular file.
11235 @item -h @var{file}
11236 @itemx -L @var{file}
11239 @cindex symbolic link check
11240 True if @var{file} exists and is a symbolic link.
11241 Unlike all other file-related tests, this test does not dereference
11242 @var{file} if it is a symbolic link.
11244 @item -p @var{file}
11246 @cindex named pipe check
11247 True if @var{file} exists and is a named pipe.
11249 @item -S @var{file}
11251 @cindex socket check
11252 True if @var{file} exists and is a socket.
11256 @cindex terminal check
11257 True if @var{fd} is a file descriptor that is associated with a
11263 @node Access permission tests
11264 @subsection Access permission tests
11266 @cindex access permission tests
11267 @cindex permission tests
11269 These options test for particular access permissions.
11273 @item -g @var{file}
11275 @cindex set-group-ID check
11276 True if @var{file} exists and has its set-group-ID bit set.
11278 @item -k @var{file}
11280 @cindex sticky bit check
11281 True if @var{file} exists and has its @dfn{sticky} bit set.
11283 @item -r @var{file}
11285 @cindex readable file check
11286 True if @var{file} exists and read permission is granted.
11288 @item -u @var{file}
11290 @cindex set-user-ID check
11291 True if @var{file} exists and has its set-user-ID bit set.
11293 @item -w @var{file}
11295 @cindex writable file check
11296 True if @var{file} exists and write permission is granted.
11298 @item -x @var{file}
11300 @cindex executable file check
11301 True if @var{file} exists and execute permission is granted
11302 (or search permission, if it is a directory).
11304 @item -O @var{file}
11306 @cindex owned by effective user ID check
11307 True if @var{file} exists and is owned by the current effective user ID.
11309 @item -G @var{file}
11311 @cindex owned by effective group ID check
11312 True if @var{file} exists and is owned by the current effective group ID.
11316 @node File characteristic tests
11317 @subsection File characteristic tests
11319 @cindex file characteristic tests
11321 These options test other file characteristics.
11325 @item -e @var{file}
11327 @cindex existence-of-file check
11328 True if @var{file} exists.
11330 @item -s @var{file}
11332 @cindex nonempty file check
11333 True if @var{file} exists and has a size greater than zero.
11335 @item @var{file1} -nt @var{file2}
11337 @cindex newer-than file check
11338 True if @var{file1} is newer (according to modification date) than
11339 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11341 @item @var{file1} -ot @var{file2}
11343 @cindex older-than file check
11344 True if @var{file1} is older (according to modification date) than
11345 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11347 @item @var{file1} -ef @var{file2}
11349 @cindex same file check
11350 @cindex hard link check
11351 True if @var{file1} and @var{file2} have the same device and inode
11352 numbers, i.e., if they are hard links to each other.
11358 @subsection String tests
11360 @cindex string tests
11362 These options test string characteristics. You may need to quote
11363 @var{string} arguments for the shell. For example:
11369 The quotes here prevent the wrong arguments from being passed to
11370 @command{test} if @samp{$V} is empty or contains special characters.
11374 @item -z @var{string}
11376 @cindex zero-length string check
11377 True if the length of @var{string} is zero.
11379 @item -n @var{string}
11380 @itemx @var{string}
11382 @cindex nonzero-length string check
11383 True if the length of @var{string} is nonzero.
11385 @item @var{string1} = @var{string2}
11387 @cindex equal string check
11388 True if the strings are equal.
11390 @item @var{string1} != @var{string2}
11392 @cindex not-equal string check
11393 True if the strings are not equal.
11398 @node Numeric tests
11399 @subsection Numeric tests
11401 @cindex numeric tests
11402 @cindex arithmetic tests
11404 Numeric relational operators. The arguments must be entirely numeric
11405 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11406 which evaluates to the length of @var{string}.
11410 @item @var{arg1} -eq @var{arg2}
11411 @itemx @var{arg1} -ne @var{arg2}
11412 @itemx @var{arg1} -lt @var{arg2}
11413 @itemx @var{arg1} -le @var{arg2}
11414 @itemx @var{arg1} -gt @var{arg2}
11415 @itemx @var{arg1} -ge @var{arg2}
11422 These arithmetic binary operators return true if @var{arg1} is equal,
11423 not-equal, less-than, less-than-or-equal, greater-than, or
11424 greater-than-or-equal than @var{arg2}, respectively.
11431 test -1 -gt -2 && echo yes
11433 test -l abc -gt 1 && echo yes
11436 @error{} test: integer expression expected before -eq
11440 @node Connectives for test
11441 @subsection Connectives for @command{test}
11443 @cindex logical connectives
11444 @cindex connectives, logical
11446 The usual logical connectives.
11452 True if @var{expr} is false.
11454 @item @var{expr1} -a @var{expr2}
11456 @cindex logical and operator
11457 @cindex and operator
11458 True if both @var{expr1} and @var{expr2} are true.
11460 @item @var{expr1} -o @var{expr2}
11462 @cindex logical or operator
11463 @cindex or operator
11464 True if either @var{expr1} or @var{expr2} is true.
11469 @node expr invocation
11470 @section @command{expr}: Evaluate expressions
11473 @cindex expression evaluation
11474 @cindex evaluation of expressions
11476 @command{expr} evaluates an expression and writes the result on standard
11477 output. Each token of the expression must be a separate argument.
11479 Operands are either integers or strings. Integers consist of one or
11480 more decimal digits, with an optional leading @samp{-}.
11481 @command{expr} converts
11482 anything appearing in an operand position to an integer or a string
11483 depending on the operation being applied to it.
11485 Strings are not quoted for @command{expr} itself, though you may need to
11486 quote them to protect characters with special meaning to the shell,
11487 e.g., spaces. However, regardless of whether it is quoted, a string
11488 operand should not be a parenthesis or any of @command{expr}'s
11489 operators like @code{+}, so you cannot safely pass an arbitrary string
11490 @code{$str} to expr merely by quoting it to the shell. One way to
11491 work around this is to use the @sc{gnu} extension @code{+},
11492 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11493 @code{@w{" $str"}} and to adjust the rest of the expression to take
11494 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11496 You should not pass a negative integer or a string with leading
11497 @samp{-} as @command{expr}'s first argument, as it might be
11498 misinterpreted as an option; this can be avoided by parenthesization.
11499 Also, portable scripts should not use a string operand that happens to
11500 take the form of an integer; this can be worked around by inserting
11501 leading spaces as mentioned above.
11503 @cindex parentheses for grouping
11504 Operators may be given as infix symbols or prefix keywords. Parentheses
11505 may be used for grouping in the usual manner. You must quote
11506 parentheses and many operators to avoid the shell evaluating them,
11509 When built with support for the GNU MP library, @command{expr} uses
11510 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11511 types and may fail due to arithmetic overflow.
11513 The only options are @option{--help} and @option{--version}. @xref{Common
11514 options}. Options must precede operands.
11516 @cindex exit status of @command{expr}
11520 0 if the expression is neither null nor 0,
11521 1 if the expression is null or 0,
11522 2 if the expression is invalid,
11523 3 if an internal error occurred (e.g., arithmetic overflow).
11527 * String expressions:: + : match substr index length
11528 * Numeric expressions:: + - * / %
11529 * Relations for expr:: | & < <= = == != >= >
11530 * Examples of expr:: Examples.
11534 @node String expressions
11535 @subsection String expressions
11537 @cindex string expressions
11538 @cindex expressions, string
11540 @command{expr} supports pattern matching and other string operators. These
11541 have higher precedence than both the numeric and relational operators (in
11542 the next sections).
11546 @item @var{string} : @var{regex}
11547 @cindex pattern matching
11548 @cindex regular expression matching
11549 @cindex matching patterns
11550 Perform pattern matching. The arguments are converted to strings and the
11551 second is considered to be a (basic, a la GNU @code{grep}) regular
11552 expression, with a @code{^} implicitly prepended. The first argument is
11553 then matched against this regular expression.
11555 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11556 @code{:} expression returns the part of @var{string} that matched the
11557 subexpression; otherwise, it returns the number of characters matched.
11559 If the match fails, the @code{:} operator returns the null string if
11560 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11562 @kindex \( @r{regexp operator}
11563 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11564 value; additional pairs are meaningful only for grouping the regular
11565 expression operators.
11567 @kindex \+ @r{regexp operator}
11568 @kindex \? @r{regexp operator}
11569 @kindex \| @r{regexp operator}
11570 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11571 operators which respectively match one or more, zero or one, or separate
11572 alternatives. SunOS and other @command{expr}'s treat these as regular
11573 characters. (@acronym{POSIX} allows either behavior.)
11574 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11575 regular expression syntax. Some examples are in @ref{Examples of expr}.
11577 @item match @var{string} @var{regex}
11579 An alternative way to do pattern matching. This is the same as
11580 @w{@samp{@var{string} : @var{regex}}}.
11582 @item substr @var{string} @var{position} @var{length}
11584 Returns the substring of @var{string} beginning at @var{position}
11585 with length at most @var{length}. If either @var{position} or
11586 @var{length} is negative, zero, or non-numeric, returns the null string.
11588 @item index @var{string} @var{charset}
11590 Returns the first position in @var{string} where the first character in
11591 @var{charset} was found. If no character in @var{charset} is found in
11592 @var{string}, return 0.
11594 @item length @var{string}
11596 Returns the length of @var{string}.
11598 @item + @var{token}
11600 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11601 or an operator like @code{/}.
11602 This makes it possible to test @code{expr length + "$x"} or
11603 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11604 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11605 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11606 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11610 To make @command{expr} interpret keywords as strings, you must use the
11611 @code{quote} operator.
11614 @node Numeric expressions
11615 @subsection Numeric expressions
11617 @cindex numeric expressions
11618 @cindex expressions, numeric
11620 @command{expr} supports the usual numeric operators, in order of increasing
11621 precedence. These numeric operators have lower precedence than the
11622 string operators described in the previous section, and higher precedence
11623 than the connectives (next section).
11631 @cindex subtraction
11632 Addition and subtraction. Both arguments are converted to integers;
11633 an error occurs if this cannot be done.
11639 @cindex multiplication
11642 Multiplication, division, remainder. Both arguments are converted to
11643 integers; an error occurs if this cannot be done.
11648 @node Relations for expr
11649 @subsection Relations for @command{expr}
11651 @cindex connectives, logical
11652 @cindex logical connectives
11653 @cindex relations, numeric or string
11655 @command{expr} supports the usual logical connectives and relations. These
11656 have lower precedence than the string and numeric operators
11657 (previous sections). Here is the list, lowest-precedence operator first.
11663 @cindex logical or operator
11664 @cindex or operator
11665 Returns its first argument if that is neither null nor zero, otherwise
11666 its second argument if it is neither null nor zero, otherwise 0. It
11667 does not evaluate its second argument if its first argument is neither
11672 @cindex logical and operator
11673 @cindex and operator
11674 Return its first argument if neither argument is null or zero, otherwise
11675 0. It does not evaluate its second argument if its first argument is
11678 @item < <= = == != >= >
11685 @cindex comparison operators
11687 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11688 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11689 both arguments to integers and do a numeric comparison; if either
11690 conversion fails, it does a lexicographic comparison using the character
11691 collating sequence specified by the @env{LC_COLLATE} locale.
11696 @node Examples of expr
11697 @subsection Examples of using @command{expr}
11699 @cindex examples of @command{expr}
11700 Here are a few examples, including quoting for shell metacharacters.
11702 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11705 foo=`expr $foo + 1`
11708 To print the non-directory part of the file name stored in
11709 @code{$fname}, which need not contain a @code{/}:
11712 expr $fname : '.*/\(.*\)' '|' $fname
11715 An example showing that @code{\+} is an operator:
11723 expr abc : 'a\(.\)c'
11725 expr index abcdef cz
11728 @error{} expr: syntax error
11729 expr index + index a
11735 @chapter Redirection
11737 @cindex redirection
11738 @cindex commands for redirection
11740 Unix shells commonly provide several forms of @dfn{redirection}---ways
11741 to change the input source or output destination of a command. But one
11742 useful redirection is performed by a separate command, not by the shell;
11743 it's described here.
11746 * tee invocation:: Redirect output to multiple files or processes.
11750 @node tee invocation
11751 @section @command{tee}: Redirect output to multiple files or processes
11754 @cindex pipe fitting
11755 @cindex destinations, multiple output
11756 @cindex read from stdin and write to stdout and files
11758 The @command{tee} command copies standard input to standard output and also
11759 to any files given as arguments. This is useful when you want not only
11760 to send some data down a pipe, but also to save a copy. Synopsis:
11763 tee [@var{option}]@dots{} [@var{file}]@dots{}
11766 If a file being written to does not already exist, it is created. If a
11767 file being written to already exists, the data it previously contained
11768 is overwritten unless the @option{-a} option is used.
11770 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11771 input to standard output, but this is typically not that useful as the
11772 copies are interleaved.
11774 The program accepts the following options. Also see @ref{Common options}.
11781 Append standard input to the given files rather than overwriting
11785 @itemx --ignore-interrupts
11787 @opindex --ignore-interrupts
11788 Ignore interrupt signals.
11792 The @command{tee} command is useful when you happen to be transferring a large
11793 amount of data and also want to summarize that data without reading
11794 it a second time. For example, when you are downloading a DVD image,
11795 you often want to verify its signature or checksum right away.
11796 The inefficient way to do it is simply:
11799 wget http://example.com/some.iso && sha1sum some.iso
11802 One problem with the above is that it makes you wait for the
11803 download to complete before starting the time-consuming SHA1 computation.
11804 Perhaps even more importantly, the above requires reading
11805 the DVD image a second time (the first was from the network).
11807 The efficient way to do it is to interleave the download
11808 and SHA1 computation. Then, you'll get the checksum for
11809 free, because the entire process parallelizes so well:
11812 # slightly contrived, to demonstrate process substitution
11813 wget -O - http://example.com/dvd.iso \
11814 | tee >(sha1sum > dvd.sha1) > dvd.iso
11817 That makes @command{tee} write not just to the expected output file,
11818 but also to a pipe running @command{sha1sum} and saving the final
11819 checksum in a file named @file{dvd.sha1}.
11821 Note, however, that this example relies on a feature of modern shells
11822 called @dfn{process substitution}
11823 (the @samp{>(command)} syntax, above;
11824 @xref{Process Substitution,,Process Substitution, bashref,
11825 The Bash Reference Manual}.),
11826 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11827 but not with @command{/bin/sh}. So if you write code like this
11828 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11830 Since the above example writes to one file and one process,
11831 a more conventional and portable use of @command{tee} is even better:
11834 wget -O - http://example.com/dvd.iso \
11835 | tee dvd.iso | sha1sum > dvd.sha1
11838 You can extend this example to make @command{tee} write to two processes,
11839 computing MD5 and SHA1 checksums in parallel. In this case,
11840 process substitution is required:
11843 wget -O - http://example.com/dvd.iso \
11844 | tee >(sha1sum > dvd.sha1) \
11845 >(md5sum > dvd.md5) \
11849 This technique is also useful when you want to make a @emph{compressed}
11850 copy of the contents of a pipe.
11851 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11852 For a large hierarchy, @samp{du -ak} can run for a long time,
11853 and can easily produce terabytes of data, so you won't want to
11854 rerun the command unnecessarily. Nor will you want to save
11855 the uncompressed output.
11857 Doing it the inefficient way, you can't even start the GUI
11858 until after you've compressed all of the @command{du} output:
11861 du -ak | gzip -9 > /tmp/du.gz
11862 gzip -d /tmp/du.gz | xdiskusage -a
11865 With @command{tee} and process substitution, you start the GUI
11866 right away and eliminate the decompression completely:
11869 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11872 Finally, if you regularly create more than one type of
11873 compressed tarball at once, for example when @code{make dist} creates
11874 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11875 there may be a better way.
11876 Typical @command{automake}-generated @file{Makefile} rules create
11877 the two compressed tar archives with commands in sequence, like this
11878 (slightly simplified):
11881 tardir=your-pkg-M.N
11882 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11883 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11886 However, if the hierarchy you are archiving and compressing is larger
11887 than a couple megabytes, and especially if you are using a multi-processor
11888 system with plenty of memory, then you can do much better by reading the
11889 directory contents only once and running the compression programs in parallel:
11892 tardir=your-pkg-M.N
11893 tar chof - "$tardir" \
11894 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11895 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11901 @node File name manipulation
11902 @chapter File name manipulation
11904 @cindex file name manipulation
11905 @cindex manipulation of file names
11906 @cindex commands for file name manipulation
11908 This section describes commands that manipulate file names.
11911 * basename invocation:: Strip directory and suffix from a file name.
11912 * dirname invocation:: Strip last file name component.
11913 * pathchk invocation:: Check file name validity and portability.
11914 * mktemp invocation:: Create temporary file or directory.
11918 @node basename invocation
11919 @section @command{basename}: Strip directory and suffix from a file name
11922 @cindex strip directory and suffix from file names
11923 @cindex directory, stripping from file names
11924 @cindex suffix, stripping from file names
11925 @cindex file names, stripping directory and suffix
11926 @cindex leading directory components, stripping
11928 @command{basename} removes any leading directory components from
11929 @var{name}. Synopsis:
11932 basename @var{name} [@var{suffix}]
11935 If @var{suffix} is specified and is identical to the end of @var{name},
11936 it is removed from @var{name} as well. Note that since trailing slashes
11937 are removed prior to suffix matching, @var{suffix} will do nothing if it
11938 contains slashes. @command{basename} prints the result on standard
11941 @c This test is used both here and in the section on dirname.
11942 @macro basenameAndDirname
11943 Together, @command{basename} and @command{dirname} are designed such
11944 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11945 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11946 for everything except file names containing a trailing newline.
11948 @basenameAndDirname
11950 @acronym{POSIX} allows the implementation to define the results if
11951 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11952 @command{basename} returns the empty string. In the latter case, the
11953 result is @samp{//} on platforms where @var{//} is distinct from
11954 @var{/}, and @samp{/} on platforms where there is no difference.
11956 The only options are @option{--help} and @option{--version}. @xref{Common
11957 options}. Options must precede operands.
11965 basename /usr/bin/sort
11968 basename include/stdio.h .h
11972 @node dirname invocation
11973 @section @command{dirname}: Strip last file name component
11976 @cindex directory components, printing
11977 @cindex stripping non-directory suffix
11978 @cindex non-directory suffix, stripping
11980 @command{dirname} prints all but the final slash-delimited component of
11981 a string (presumably a file name, but also works on directories). Synopsis:
11987 If @var{name} is a single component, @command{dirname} prints @samp{.}
11988 (meaning the current directory).
11990 @basenameAndDirname
11992 @acronym{POSIX} allows the implementation to define the results if
11993 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
11994 result is @samp{//} on platforms where @var{//} is distinct from
11995 @var{/}, and @samp{/} on platforms where there is no difference.
11997 The only options are @option{--help} and @option{--version}. @xref{Common
12005 # Output "/usr/bin".
12006 dirname /usr/bin/sort
12013 @node pathchk invocation
12014 @section @command{pathchk}: Check file name validity and portability
12017 @cindex file names, checking validity and portability
12018 @cindex valid file names, checking for
12019 @cindex portable file names, checking for
12021 @command{pathchk} checks validity and portability of file names. Synopsis:
12024 pathchk [@var{option}]@dots{} @var{name}@dots{}
12027 For each @var{name}, @command{pathchk} prints an error message if any of
12028 these conditions is true:
12032 One of the existing directories in @var{name} does not have search
12033 (execute) permission,
12035 The length of @var{name} is larger than the maximum supported by the
12038 The length of one component of @var{name} is longer than
12039 its file system's maximum.
12042 A nonexistent @var{name} is not an error, so long a file with that
12043 name could be created under the above conditions.
12045 The program accepts the following options. Also see @ref{Common options}.
12046 Options must precede operands.
12052 Instead of performing checks based on the underlying file system,
12053 print an error message if any of these conditions is true:
12057 A file name is empty.
12060 A file name contains a character outside the @acronym{POSIX} portable file
12061 name character set, namely, the ASCII letters and digits, @samp{.},
12062 @samp{_}, @samp{-}, and @samp{/}.
12065 The length of a file name or one of its components exceeds the
12066 @acronym{POSIX} minimum limits for portability.
12071 Print an error message if a file name is empty, or if it contains a component
12072 that begins with @samp{-}.
12074 @item --portability
12075 @opindex --portability
12076 Print an error message if a file name is not portable to all @acronym{POSIX}
12077 hosts. This option is equivalent to @samp{-p -P}.
12081 @cindex exit status of @command{pathchk}
12085 0 if all specified file names passed all checks,
12089 @node mktemp invocation
12090 @section @command{mktemp}: Create temporary file or directory
12093 @cindex file names, creating temporary
12094 @cindex directory, creating temporary
12095 @cindex temporary files and directories
12097 @command{mktemp} manages the creation of temporary files and
12098 directories. Synopsis:
12101 mktemp [@var{option}]@dots{} [@var{template}]
12104 Safely create a temporary file or directory based on @var{template},
12105 and print its name. If given, @var{template} must include at least
12106 three consecutive @samp{X}s in the last component. If omitted, the template
12107 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12108 implied. The final run of @samp{X}s in the @var{template} will be replaced
12109 by alpha-numeric characters; thus, on a case-sensitive file system,
12110 and with a @var{template} including a run of @var{n} instances of @samp{X},
12111 there are @samp{62**@var{n}} potential file names.
12113 Older scripts used to create temporary files by simply joining the
12114 name of the program with the process id (@samp{$$}) as a suffix.
12115 However, that naming scheme is easily predictable, and suffers from a
12116 race condition where the attacker can create an appropriately named
12117 symbolic link, such that when the script then opens a handle to what
12118 it thought was an unused file, it is instead modifying an existing
12119 file. Using the same scheme to create a directory is slightly safer,
12120 since the @command{mkdir} will fail if the target already exists, but
12121 it is still inferior because it allows for denial of service attacks.
12122 Therefore, modern scripts should use the @command{mktemp} command to
12123 guarantee that the generated name will be unpredictable, and that
12124 knowledge of the temporary file name implies that the file was created
12125 by the current script and cannot be modified by other users.
12127 When creating a file, the resulting file has read and write
12128 permissions for the current user, but no permissions for the group or
12129 others; these permissions are reduced if the current umask is more
12132 Here are some examples (although note that if you repeat them, you
12133 will most likely get different file names):
12138 Create a temporary file in the current directory.
12145 Create a temporary file with a known suffix.
12147 $ mktemp --suffix=.txt file-XXXX
12149 $ mktemp file-XXXX-XXXX.txt
12154 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12155 but falling back to the current directory rather than @file{/tmp}.
12156 Note that @command{mktemp} does not create fifos, but can create a
12157 secure directory in which the fifo can live. Exit the shell if the
12158 directory or fifo could not be created.
12160 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12162 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12166 Create and use a temporary file if possible, but ignore failure. The
12167 file will reside in the directory named by @env{TMPDIR}, if specified,
12168 or else in @file{/tmp}.
12170 $ file=$(mktemp -q) && @{
12171 > # Safe to use $file only within this block. Use quotes,
12172 > # since $TMPDIR, and thus $file, may contain whitespace.
12173 > echo ... > "$file"
12179 Act as a semi-random character generator (it is not fully random,
12180 since it is impacted by the contents of the current directory). To
12181 avoid security holes, do not use the resulting names to create a file.
12191 The program accepts the following options. Also see @ref{Common options}.
12198 @opindex --directory
12199 Create a directory rather than a file. The directory will have read,
12200 write, and search permissions for the current user, but no permissions
12201 for the group or others; these permissions are reduced if the current
12202 umask is more restrictive.
12208 Suppress diagnostics about failure to create a file or directory. The
12209 exit status will still reflect whether a file was created.
12215 Generate a temporary name that does not name an existing file, without
12216 changing the file system contents. Using the output of this command
12217 to create a new file is inherently unsafe, as there is a window of
12218 time between generating the name and using it where another process
12219 can create an object by the same name.
12222 @itemx --tmpdir[=@var{dir}]
12225 Treat @var{template} relative to the directory @var{dir}. If
12226 @var{dir} is not specified (only possible with the long option
12227 @option{--tmpdir}) or is the empty string, use the value of
12228 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12229 specified, @var{template} must not be absolute. However,
12230 @var{template} can still contain slashes, although intermediate
12231 directories must already exist.
12233 @item --suffix=@var{suffix}
12235 Append @var{suffix} to the @var{template}. @var{suffix} must not
12236 contain slash. If @option{--suffix} is specified, @var{template} must
12237 end in @samp{X}; if it is not specified, then an appropriate
12238 @option{--suffix} is inferred by finding the last @samp{X} in
12239 @var{template}. This option exists for use with the default
12240 @var{template} and for the creation of a @var{suffix} that starts with
12245 Treat @var{template} as a single file relative to the value of
12246 @env{TMPDIR} if available, or to the directory specified by
12247 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12248 contain slashes. This option is deprecated; the use of @option{-p}
12249 without @option{-t} offers better defaults (by favoring the command
12250 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12255 @cindex exit status of @command{mktemp}
12259 0 if the file was created,
12264 @node Working context
12265 @chapter Working context
12267 @cindex working context
12268 @cindex commands for printing the working context
12270 This section describes commands that display or alter the context in
12271 which you are working: the current directory, the terminal settings, and
12272 so forth. See also the user-related commands in the next section.
12275 * pwd invocation:: Print working directory.
12276 * stty invocation:: Print or change terminal characteristics.
12277 * printenv invocation:: Print environment variables.
12278 * tty invocation:: Print file name of terminal on standard input.
12282 @node pwd invocation
12283 @section @command{pwd}: Print working directory
12286 @cindex print name of current directory
12287 @cindex current working directory, printing
12288 @cindex working directory, printing
12291 @command{pwd} prints the name of the current directory. Synopsis:
12294 pwd [@var{option}]@dots{}
12297 The program accepts the following options. Also see @ref{Common options}.
12304 If the contents of the environment variable @env{PWD} provide an
12305 absolute name of the current directory with no @samp{.} or @samp{..}
12306 components, but possibly with symbolic links, then output those
12307 contents. Otherwise, fall back to default @option{-P} handling.
12312 @opindex --physical
12313 Print a fully resolved name for the current directory. That is, all
12314 components of the printed name will be actual directory names---none
12315 will be symbolic links.
12318 @cindex symbolic links and @command{pwd}
12319 If @option{-L} and @option{-P} are both given, the last one takes
12320 precedence. If neither option is given, then this implementation uses
12321 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12322 environment variable is set.
12324 @mayConflictWithShellBuiltIn{pwd}
12329 @node stty invocation
12330 @section @command{stty}: Print or change terminal characteristics
12333 @cindex change or print terminal settings
12334 @cindex terminal settings
12335 @cindex line settings of terminal
12337 @command{stty} prints or changes terminal characteristics, such as baud rate.
12341 stty [@var{option}] [@var{setting}]@dots{}
12342 stty [@var{option}]
12345 If given no line settings, @command{stty} prints the baud rate, line
12346 discipline number (on systems that support it), and line settings
12347 that have been changed from the values set by @samp{stty sane}.
12348 By default, mode reading and setting are performed on the tty line
12349 connected to standard input, although this can be modified by the
12350 @option{--file} option.
12352 @command{stty} accepts many non-option arguments that change aspects of
12353 the terminal line operation, as described below.
12355 The program accepts the following options. Also see @ref{Common options}.
12362 Print all current settings in human-readable form. This option may not
12363 be used in combination with any line settings.
12365 @item -F @var{device}
12366 @itemx --file=@var{device}
12369 Set the line opened by the file name specified in @var{device} instead of
12370 the tty line connected to standard input. This option is necessary
12371 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12372 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12373 the @code{clocal} flag is not set. Hence, it is not always possible
12374 to allow the shell to open the device in the traditional manner.
12380 @cindex machine-readable @command{stty} output
12381 Print all current settings in a form that can be used as an argument to
12382 another @command{stty} command to restore the current settings. This option
12383 may not be used in combination with any line settings.
12387 Many settings can be turned off by preceding them with a @samp{-}.
12388 Such arguments are marked below with ``May be negated'' in their
12389 description. The descriptions themselves refer to the positive
12390 case, that is, when @emph{not} negated (unless stated otherwise,
12393 Some settings are not available on all @acronym{POSIX} systems, since they use
12394 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12395 description. On non-@acronym{POSIX} systems, those or other settings also may not
12396 be available, but it's not feasible to document all the variations: just
12402 * Control:: Control settings
12403 * Input:: Input settings
12404 * Output:: Output settings
12405 * Local:: Local settings
12406 * Combination:: Combination settings
12407 * Characters:: Special characters
12408 * Special:: Special settings
12413 @subsection Control settings
12415 @cindex control settings
12421 @cindex two-way parity
12422 Generate parity bit in output and expect parity bit in input.
12428 @cindex even parity
12429 Set odd parity (even if negated). May be negated.
12436 @cindex character size
12437 @cindex eight-bit characters
12438 Set character size to 5, 6, 7, or 8 bits.
12443 Send a hangup signal when the last process closes the tty. May be
12449 Use two stop bits per character (one if negated). May be negated.
12453 Allow input to be received. May be negated.
12457 @cindex modem control
12458 Disable modem control signals. May be negated.
12462 @cindex hardware flow control
12463 @cindex flow control, hardware
12464 @cindex RTS/CTS flow control
12465 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12470 @subsection Input settings
12472 @cindex input settings
12473 These settings control operations on data received from the terminal.
12478 @cindex breaks, ignoring
12479 Ignore break characters. May be negated.
12483 @cindex breaks, cause interrupts
12484 Make breaks cause an interrupt signal. May be negated.
12488 @cindex parity, ignoring
12489 Ignore characters with parity errors. May be negated.
12493 @cindex parity errors, marking
12494 Mark parity errors (with a 255-0-character sequence). May be negated.
12498 Enable input parity checking. May be negated.
12502 @cindex eight-bit input
12503 Clear high (8th) bit of input characters. May be negated.
12507 @cindex newline, translating to return
12508 Translate newline to carriage return. May be negated.
12512 @cindex return, ignoring
12513 Ignore carriage return. May be negated.
12517 @cindex return, translating to newline
12518 Translate carriage return to newline. May be negated.
12522 @cindex input encoding, UTF-8
12523 Assume input characters are UTF-8 encoded. May be negated.
12527 @kindex C-s/C-q flow control
12528 @cindex XON/XOFF flow control
12529 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12536 @cindex software flow control
12537 @cindex flow control, software
12538 Enable sending of @code{stop} character when the system input buffer
12539 is almost full, and @code{start} character when it becomes almost
12540 empty again. May be negated.
12544 @cindex uppercase, translating to lowercase
12545 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12546 negated. Note ilcuc is not implemented, as one would not be able to issue
12547 almost any (lowercase) Unix command, after invoking it.
12551 Allow any character to restart output (only the start character
12552 if negated). Non-@acronym{POSIX}. May be negated.
12556 @cindex beeping at input buffer full
12557 Enable beeping and not flushing input buffer if a character arrives
12558 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12563 @subsection Output settings
12565 @cindex output settings
12566 These settings control operations on data sent to the terminal.
12571 Postprocess output. May be negated.
12575 @cindex lowercase, translating to output
12576 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12577 negated. (Note ouclc is not currently implemented.)
12581 @cindex return, translating to newline
12582 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12586 @cindex newline, translating to crlf
12587 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12592 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12597 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12601 @cindex pad instead of timing for delaying
12602 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12607 @cindex pad character
12608 Use @acronym{ASCII} @sc{del} characters for fill instead of
12609 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12615 Newline delay style. Non-@acronym{POSIX}.
12622 Carriage return delay style. Non-@acronym{POSIX}.
12628 @opindex tab@var{n}
12629 Horizontal tab delay style. Non-@acronym{POSIX}.
12634 Backspace delay style. Non-@acronym{POSIX}.
12639 Vertical tab delay style. Non-@acronym{POSIX}.
12644 Form feed delay style. Non-@acronym{POSIX}.
12649 @subsection Local settings
12651 @cindex local settings
12656 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12657 characters. May be negated.
12661 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12662 special characters. May be negated.
12666 Enable non-@acronym{POSIX} special characters. May be negated.
12670 Echo input characters. May be negated.
12676 Echo @code{erase} characters as backspace-space-backspace. May be
12681 @cindex newline echoing after @code{kill}
12682 Echo a newline after a @code{kill} character. May be negated.
12686 @cindex newline, echoing
12687 Echo newline even if not echoing other characters. May be negated.
12691 @cindex flushing, disabling
12692 Disable flushing after @code{interrupt} and @code{quit} special
12693 characters. May be negated.
12697 @cindex case translation
12698 Enable input and output of uppercase characters by preceding their
12699 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12700 Non-@acronym{POSIX}. May be negated.
12704 @cindex background jobs, stopping at terminal write
12705 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12712 Echo erased characters backward, between @samp{\} and @samp{/}.
12713 Non-@acronym{POSIX}. May be negated.
12719 @cindex control characters, using @samp{^@var{c}}
12720 @cindex hat notation for control characters
12721 Echo control characters in hat notation (@samp{^@var{c}}) instead
12722 of literally. Non-@acronym{POSIX}. May be negated.
12728 Echo the @code{kill} special character by erasing each character on
12729 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12730 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12736 @subsection Combination settings
12738 @cindex combination settings
12739 Combination settings:
12746 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12747 as @code{-parenb cs8}.
12751 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12752 as @code{-parenb cs8}.
12756 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12757 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12761 Reset the @code{erase} and @code{kill} special characters to their default
12768 @c This is too long to write inline.
12770 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12771 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12772 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12773 ff0 isig icanon iexten echo echoe echok -echonl
12774 -noflsh -xcase -tostop -echoprt echoctl echoke
12778 and also sets all special characters to their default values.
12782 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12783 sets the @code{eof} and @code{eol} characters to their default values
12784 if they are the same as the @code{min} and @code{time} characters.
12785 May be negated. If negated, same as @code{raw}.
12792 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12793 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12794 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12798 May be negated. If negated, same as @code{cooked}.
12802 Same as @option{-icanon}. May be negated. If negated, same as
12807 @cindex eight-bit characters
12808 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12809 same as @code{parenb istrip cs7}.
12813 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12814 If negated, same as @code{parenb istrip opost cs7}.
12818 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12822 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12829 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12830 (Used for terminals with uppercase characters only.)
12834 Same as @code{echoe echoctl echoke}.
12838 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12843 @subsection Special characters
12845 @cindex special characters
12846 @cindex characters, special
12848 The special characters' default values vary from system to system.
12849 They are set with the syntax @samp{name value}, where the names are
12850 listed below and the value can be given either literally, in hat
12851 notation (@samp{^@var{c}}), or as an integer which may start with
12852 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12853 any other digit to indicate decimal.
12855 @cindex disabling special characters
12856 @kindex u@r{, and disabling special characters}
12857 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12858 special character. (This is incompatible with Ultrix @command{stty},
12859 which uses a value of @samp{u} to disable a special character. GNU
12860 @command{stty} treats a value @samp{u} like any other, namely to set that
12861 special character to @key{U}.)
12867 Send an interrupt signal.
12871 Send a quit signal.
12875 Erase the last character typed.
12879 Erase the current line.
12883 Send an end of file (terminate the input).
12891 Alternate character to end the line. Non-@acronym{POSIX}.
12895 Switch to a different shell layer. Non-@acronym{POSIX}.
12899 Restart the output after stopping it.
12907 Send a terminal stop signal.
12911 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12915 Redraw the current line. Non-@acronym{POSIX}.
12919 Erase the last word typed. Non-@acronym{POSIX}.
12923 Enter the next character typed literally, even if it is a special
12924 character. Non-@acronym{POSIX}.
12929 @subsection Special settings
12931 @cindex special settings
12936 Set the minimum number of characters that will satisfy a read until
12937 the time value has expired, when @option{-icanon} is set.
12941 Set the number of tenths of a second before reads time out if the minimum
12942 number of characters have not been read, when @option{-icanon} is set.
12944 @item ispeed @var{n}
12946 Set the input speed to @var{n}.
12948 @item ospeed @var{n}
12950 Set the output speed to @var{n}.
12954 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12957 @itemx columns @var{n}
12960 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12966 Print the number of rows and columns that the kernel thinks the
12967 terminal has. (Systems that don't support rows and columns in the kernel
12968 typically use the environment variables @env{LINES} and @env{COLUMNS}
12969 instead; however, GNU @command{stty} does not know anything about them.)
12970 Non-@acronym{POSIX}.
12974 Use line discipline @var{n}. Non-@acronym{POSIX}.
12978 Print the terminal speed.
12981 @cindex baud rate, setting
12982 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
12983 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
12984 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
12985 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
12986 support higher speeds. The @command{stty} command includes support
13003 4000000 where the system supports these.
13004 0 hangs up the line if @option{-clocal} is set.
13008 @node printenv invocation
13009 @section @command{printenv}: Print all or some environment variables
13012 @cindex printing all or some environment variables
13013 @cindex environment variables, printing
13015 @command{printenv} prints environment variable values. Synopsis:
13018 printenv [@var{option}] [@var{variable}]@dots{}
13021 If no @var{variable}s are specified, @command{printenv} prints the value of
13022 every environment variable. Otherwise, it prints the value of each
13023 @var{variable} that is set, and nothing for those that are not set.
13025 The program accepts the following option. Also see @ref{Common options}.
13033 @cindex exit status of @command{printenv}
13037 0 if all variables specified were found
13038 1 if at least one specified variable was not found
13039 2 if a write error occurred
13043 @node tty invocation
13044 @section @command{tty}: Print file name of terminal on standard input
13047 @cindex print terminal file name
13048 @cindex terminal file name, printing
13050 @command{tty} prints the file name of the terminal connected to its standard
13051 input. It prints @samp{not a tty} if standard input is not a terminal.
13055 tty [@var{option}]@dots{}
13058 The program accepts the following option. Also see @ref{Common options}.
13068 Print nothing; only return an exit status.
13072 @cindex exit status of @command{tty}
13076 0 if standard input is a terminal
13077 1 if standard input is not a terminal
13078 2 if given incorrect arguments
13079 3 if a write error occurs
13083 @node User information
13084 @chapter User information
13086 @cindex user information, commands for
13087 @cindex commands for printing user information
13089 This section describes commands that print user-related information:
13090 logins, groups, and so forth.
13093 * id invocation:: Print user identity.
13094 * logname invocation:: Print current login name.
13095 * whoami invocation:: Print effective user ID.
13096 * groups invocation:: Print group names a user is in.
13097 * users invocation:: Print login names of users currently logged in.
13098 * who invocation:: Print who is currently logged in.
13102 @node id invocation
13103 @section @command{id}: Print user identity
13106 @cindex real user and group IDs, printing
13107 @cindex effective user and group IDs, printing
13108 @cindex printing real and effective user and group IDs
13110 @command{id} prints information about the given user, or the process
13111 running it if no user is specified. Synopsis:
13114 id [@var{option}]@dots{} [@var{username}]
13117 @vindex POSIXLY_CORRECT
13118 By default, it prints the real user ID, real group ID, effective user ID
13119 if different from the real user ID, effective group ID if different from
13120 the real group ID, and supplemental group IDs.
13121 In addition, if SELinux
13122 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13123 then print @samp{context=@var{c}}, where @var{c} is the security context.
13125 Each of these numeric values is preceded by an identifying string and
13126 followed by the corresponding user or group name in parentheses.
13128 The options cause @command{id} to print only part of the above information.
13129 Also see @ref{Common options}.
13136 Print only the group ID.
13142 Print only the group ID and the supplementary groups.
13148 Print the user or group name instead of the ID number. Requires
13149 @option{-u}, @option{-g}, or @option{-G}.
13155 Print the real, instead of effective, user or group ID. Requires
13156 @option{-u}, @option{-g}, or @option{-G}.
13162 Print only the user ID.
13169 @cindex security context
13170 Print only the security context of the current user.
13171 If SELinux is disabled then print a warning and
13172 set the exit status to 1.
13178 @macro primaryAndSupplementaryGroups{cmd,arg}
13179 Primary and supplementary groups for a process are normally inherited
13180 from its parent and are usually unchanged since login. This means
13181 that if you change the group database after logging in, @command{\cmd\}
13182 will not reflect your changes within your existing login session.
13183 Running @command{\cmd\} with a \arg\ causes the user and group
13184 database to be consulted afresh, and so will give a different result.
13186 @primaryAndSupplementaryGroups{id,user argument}
13188 @node logname invocation
13189 @section @command{logname}: Print current login name
13192 @cindex printing user's login name
13193 @cindex login name, printing
13194 @cindex user name, printing
13197 @command{logname} prints the calling user's name, as found in a
13198 system-maintained file (often @file{/var/run/utmp} or
13199 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13200 for the calling process, @command{logname} prints
13201 an error message and exits with a status of 1.
13203 The only options are @option{--help} and @option{--version}. @xref{Common
13209 @node whoami invocation
13210 @section @command{whoami}: Print effective user ID
13213 @cindex effective user ID, printing
13214 @cindex printing the effective user ID
13216 @command{whoami} prints the user name associated with the current
13217 effective user ID. It is equivalent to the command @samp{id -un}.
13219 The only options are @option{--help} and @option{--version}. @xref{Common
13225 @node groups invocation
13226 @section @command{groups}: Print group names a user is in
13229 @cindex printing groups a user is in
13230 @cindex supplementary groups, printing
13232 @command{groups} prints the names of the primary and any supplementary
13233 groups for each given @var{username}, or the current process if no names
13234 are given. If more than one name is given, the name of each user is
13236 the list of that user's groups and the user name is separated from the
13237 group list by a colon. Synopsis:
13240 groups [@var{username}]@dots{}
13243 The group lists are equivalent to the output of the command @samp{id -Gn}.
13245 @primaryAndSupplementaryGroups{groups,list of users}
13247 The only options are @option{--help} and @option{--version}. @xref{Common
13253 @node users invocation
13254 @section @command{users}: Print login names of users currently logged in
13257 @cindex printing current usernames
13258 @cindex usernames, printing current
13260 @cindex login sessions, printing users with
13261 @command{users} prints on a single line a blank-separated list of user
13262 names of users currently logged in to the current host. Each user name
13263 corresponds to a login session, so if a user has more than one login
13264 session, that user's name will appear the same number of times in the
13273 With no @var{file} argument, @command{users} extracts its information from
13274 a system-maintained file (often @file{/var/run/utmp} or
13275 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13276 that file instead. A common choice is @file{/var/log/wtmp}.
13278 The only options are @option{--help} and @option{--version}. @xref{Common
13284 @node who invocation
13285 @section @command{who}: Print who is currently logged in
13288 @cindex printing current user information
13289 @cindex information, about current users
13291 @command{who} prints information about users who are currently logged on.
13295 @command{who} [@var{option}] [@var{file}] [am i]
13298 @cindex terminal lines, currently used
13300 @cindex remote hostname
13301 If given no non-option arguments, @command{who} prints the following
13302 information for each user currently logged on: login name, terminal
13303 line, login time, and remote hostname or X display.
13307 If given one non-option argument, @command{who} uses that instead of
13308 a default system-maintained file (often @file{/var/run/utmp} or
13309 @file{/etc/utmp}) as the name of the file containing the record of
13310 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13311 to @command{who} to look at who has previously logged on.
13315 If given two non-option arguments, @command{who} prints only the entry
13316 for the user running it (determined from its standard input), preceded
13317 by the hostname. Traditionally, the two arguments given are @samp{am
13318 i}, as in @samp{who am i}.
13321 Time stamps are listed according to the time zone rules specified by
13322 the @env{TZ} environment variable, or by the system default rules if
13323 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13324 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13326 The program accepts the following options. Also see @ref{Common options}.
13334 Same as @samp{-b -d --login -p -r -t -T -u}.
13340 Print the date and time of last system boot.
13346 Print information corresponding to dead processes.
13352 Print a line of column headings.
13358 List only the entries that correspond to processes via which the
13359 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13363 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13364 is not the default because it can cause significant delays on systems with
13365 automatic dial-up internet access.
13369 Same as @samp{who am i}.
13375 List active processes spawned by init.
13381 Print only the login names and the number of users logged on.
13382 Overrides all other options.
13387 @opindex --runlevel
13388 Print the current (and maybe previous) run-level of the init process.
13392 Ignored; for compatibility with other versions of @command{who}.
13398 Print last system clock change.
13403 After the login time, print the number of hours and minutes that the
13404 user has been idle. @samp{.} means the user was active in the last minute.
13405 @samp{old} means the user has been idle for more than 24 hours.
13416 @opindex --writable
13417 @cindex message status
13418 @pindex write@r{, allowed}
13419 After each login name print a character indicating the user's message status:
13422 @samp{+} allowing @code{write} messages
13423 @samp{-} disallowing @code{write} messages
13424 @samp{?} cannot find terminal device
13432 @node System context
13433 @chapter System context
13435 @cindex system context
13436 @cindex context, system
13437 @cindex commands for system context
13439 This section describes commands that print or change system-wide
13443 * date invocation:: Print or set system date and time.
13444 * arch invocation:: Print machine hardware name.
13445 * nproc invocation:: Print the number of processors.
13446 * uname invocation:: Print system information.
13447 * hostname invocation:: Print or set system name.
13448 * hostid invocation:: Print numeric host identifier.
13449 * uptime invocation:: Print system uptime and load.
13452 @node date invocation
13453 @section @command{date}: Print or set system date and time
13456 @cindex time, printing or setting
13457 @cindex printing the current time
13462 date [@var{option}]@dots{} [+@var{format}]
13463 date [-u|--utc|--universal] @c this avoids a newline in the output
13464 [ MMDDhhmm[[CC]YY][.ss] ]
13468 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13469 it with a default format that depends on the @env{LC_TIME} locale category.
13470 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13471 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13474 Normally, @command{date} uses the time zone rules indicated by the
13475 @env{TZ} environment variable, or the system default rules if @env{TZ}
13476 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13477 @env{TZ}, libc, The GNU C Library Reference Manual}.
13479 @findex strftime @r{and @command{date}}
13480 @cindex time formats
13481 @cindex formatting times
13482 If given an argument that starts with a @samp{+}, @command{date} prints the
13483 current date and time (or the date and time specified by the
13484 @option{--date} option, see below) in the format defined by that argument,
13485 which is similar to that of the @code{strftime} function. Except for
13486 conversion specifiers, which start with @samp{%}, characters in the
13487 format string are printed unchanged. The conversion specifiers are
13493 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13494 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13495 * Literal conversion specifiers:: %[%nt]
13496 * Padding and other flags:: Pad with zeros, spaces, etc.
13497 * Setting the time:: Changing the system clock.
13498 * Options for date:: Instead of the current time.
13500 * Date input formats:: Specifying date strings.
13502 * Examples of date:: Examples.
13505 @node Time conversion specifiers
13506 @subsection Time conversion specifiers
13508 @cindex time conversion specifiers
13509 @cindex conversion specifiers, time
13511 @command{date} conversion specifiers related to times.
13515 hour (@samp{00}@dots{}@samp{23})
13517 hour (@samp{01}@dots{}@samp{12})
13519 hour (@samp{ 0}@dots{}@samp{23}).
13520 This is a @acronym{GNU} extension.
13522 hour (@samp{ 1}@dots{}@samp{12}).
13523 This is a @acronym{GNU} extension.
13525 minute (@samp{00}@dots{}@samp{59})
13527 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13528 This is a @acronym{GNU} extension.
13530 locale's equivalent of either @samp{AM} or @samp{PM};
13531 blank in many locales.
13532 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13534 like @samp{%p}, except lower case.
13535 This is a @acronym{GNU} extension.
13537 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13539 24-hour hour and minute. Same as @samp{%H:%M}.
13540 This is a @acronym{GNU} extension.
13542 @cindex epoch, seconds since
13543 @cindex seconds since the epoch
13544 @cindex beginning of time
13545 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13546 Leap seconds are not counted unless leap second support is available.
13547 @xref{%s-examples}, for examples.
13548 This is a @acronym{GNU} extension.
13550 second (@samp{00}@dots{}@samp{60}).
13551 This may be @samp{60} if leap seconds are supported.
13553 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13555 locale's time representation (e.g., @samp{23:13:48})
13557 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13558 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13559 time zone is determinable. This value reflects the numeric time zone
13560 appropriate for the current time, using the time zone rules specified
13561 by the @env{TZ} environment variable.
13562 The time (and optionally, the time zone rules) can be overridden
13563 by the @option{--date} option.
13564 This is a @acronym{GNU} extension.
13566 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13567 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13568 zone is determinable.
13569 This is a @acronym{GNU} extension.
13571 Numeric time zone to the nearest second with @samp{:} (e.g.,
13572 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13574 This is a @acronym{GNU} extension.
13576 Numeric time zone with @samp{:} using the minimum necessary precision
13577 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13578 no time zone is determinable.
13579 This is a @acronym{GNU} extension.
13581 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13582 time zone is determinable. See @samp{%z} for how it is determined.
13586 @node Date conversion specifiers
13587 @subsection Date conversion specifiers
13589 @cindex date conversion specifiers
13590 @cindex conversion specifiers, date
13592 @command{date} conversion specifiers related to dates.
13596 locale's abbreviated weekday name (e.g., @samp{Sun})
13598 locale's full weekday name, variable length (e.g., @samp{Sunday})
13600 locale's abbreviated month name (e.g., @samp{Jan})
13602 locale's full month name, variable length (e.g., @samp{January})
13604 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13606 century. This is like @samp{%Y}, except the last two digits are omitted.
13607 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13608 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13609 It is normally at least two characters, but it may be more.
13611 day of month (e.g., @samp{01})
13613 date; same as @samp{%m/%d/%y}
13615 day of month, space padded; same as @samp{%_d}
13617 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13618 This is a good choice for a date format, as it is standard and
13619 is easy to sort in the usual case where years are in the range
13621 This is a @acronym{GNU} extension.
13623 year corresponding to the @acronym{ISO} week number, but without the century
13624 (range @samp{00} through @samp{99}). This has the same format and value
13625 as @samp{%y}, except that if the @acronym{ISO} week number (see
13627 to the previous or next year, that year is used instead.
13628 This is a @acronym{GNU} extension.
13630 year corresponding to the @acronym{ISO} week number. This has the
13631 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13633 @samp{%V}) belongs to the previous or next year, that year is used
13635 It is normally useful only if @samp{%V} is also used;
13636 for example, the format @samp{%G-%m-%d} is probably a mistake,
13637 since it combines the ISO week number year with the conventional month and day.
13638 This is a @acronym{GNU} extension.
13642 day of year (@samp{001}@dots{}@samp{366})
13644 month (@samp{01}@dots{}@samp{12})
13646 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13648 week number of year, with Sunday as the first day of the week
13649 (@samp{00}@dots{}@samp{53}).
13650 Days in a new year preceding the first Sunday are in week zero.
13652 @acronym{ISO} week number, that is, the
13653 week number of year, with Monday as the first day of the week
13654 (@samp{01}@dots{}@samp{53}).
13655 If the week containing January 1 has four or more days in
13656 the new year, then it is considered week 1; otherwise, it is week 53 of
13657 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13660 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13662 week number of year, with Monday as first day of week
13663 (@samp{00}@dots{}@samp{53}).
13664 Days in a new year preceding the first Monday are in week zero.
13666 locale's date representation (e.g., @samp{12/31/99})
13668 last two digits of year (@samp{00}@dots{}@samp{99})
13670 year. This is normally at least four characters, but it may be more.
13671 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13672 precedes year @samp{0000}.
13676 @node Literal conversion specifiers
13677 @subsection Literal conversion specifiers
13679 @cindex literal conversion specifiers
13680 @cindex conversion specifiers, literal
13682 @command{date} conversion specifiers that produce literal strings.
13694 @node Padding and other flags
13695 @subsection Padding and other flags
13697 @cindex numeric field padding
13698 @cindex padding of numeric fields
13699 @cindex fields, padding numeric
13701 Unless otherwise specified, @command{date} normally pads numeric fields
13702 with zeros, so that, for
13703 example, numeric months are always output as two digits.
13704 Seconds since the epoch are not padded, though,
13705 since there is no natural width for them.
13707 As a @acronym{GNU} extension, @command{date} recognizes any of the
13708 following optional flags after the @samp{%}:
13712 (hyphen) Do not pad the field; useful if the output is intended for
13715 (underscore) Pad with spaces; useful if you need a fixed
13716 number of characters in the output, but zeros are too distracting.
13718 (zero) Pad with zeros even if the conversion specifier
13719 would normally pad with spaces.
13721 Use upper case characters if possible.
13723 Use opposite case characters if possible.
13724 A field that is normally upper case becomes lower case, and vice versa.
13728 Here are some examples of padding:
13731 date +%d/%m -d "Feb 1"
13733 date +%-d/%-m -d "Feb 1"
13735 date +%_d/%_m -d "Feb 1"
13739 As a @acronym{GNU} extension, you can specify the field width
13740 (after any flag, if present) as a decimal number. If the natural size of the
13741 output of the field has less than the specified number of characters,
13742 the result is written right adjusted and padded to the given
13743 size. For example, @samp{%9B} prints the right adjusted month name in
13744 a field of width 9.
13746 An optional modifier can follow the optional flag and width
13747 specification. The modifiers are:
13751 Use the locale's alternate representation for date and time. This
13752 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13753 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13754 example, @samp{%Ex} might yield a date format based on the Japanese
13758 Use the locale's alternate numeric symbols for numbers. This modifier
13759 applies only to numeric conversion specifiers.
13762 If the format supports the modifier but no alternate representation
13763 is available, it is ignored.
13766 @node Setting the time
13767 @subsection Setting the time
13769 @cindex setting the time
13770 @cindex time setting
13771 @cindex appropriate privileges
13773 If given an argument that does not start with @samp{+}, @command{date} sets
13774 the system clock to the date and time specified by that argument (as
13775 described below). You must have appropriate privileges to set the
13776 system clock. The @option{--date} and @option{--set} options may not be
13777 used with such an argument. The @option{--universal} option may be used
13778 with such an argument to indicate that the specified date and time are
13779 relative to Coordinated Universal Time rather than to the local time
13782 The argument must consist entirely of digits, which have the following
13795 first two digits of year (optional)
13797 last two digits of year (optional)
13802 The @option{--set} option also sets the system clock; see the next section.
13805 @node Options for date
13806 @subsection Options for @command{date}
13808 @cindex @command{date} options
13809 @cindex options for @command{date}
13811 The program accepts the following options. Also see @ref{Common options}.
13815 @item -d @var{datestr}
13816 @itemx --date=@var{datestr}
13819 @cindex parsing date strings
13820 @cindex date strings, parsing
13821 @cindex arbitrary date strings, parsing
13824 @opindex next @var{day}
13825 @opindex last @var{day}
13826 Display the date and time specified in @var{datestr} instead of the
13827 current date and time. @var{datestr} can be in almost any common
13828 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13829 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13830 14:19:13.489392193 +0530"} specifies the instant of time that is
13831 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13832 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13833 Note: input currently must be in locale independent format. E.g., the
13834 LC_TIME=C below is needed to print back the correct date in many locales:
13836 date -d "$(LC_TIME=C date)"
13838 @xref{Date input formats}.
13840 @item -f @var{datefile}
13841 @itemx --file=@var{datefile}
13844 Parse each line in @var{datefile} as with @option{-d} and display the
13845 resulting date and time. If @var{datefile} is @samp{-}, use standard
13846 input. This is useful when you have many dates to process, because the
13847 system overhead of starting up the @command{date} executable many times can
13850 @item -r @var{file}
13851 @itemx --reference=@var{file}
13853 @opindex --reference
13854 Display the date and time of the last modification of @var{file},
13855 instead of the current date and time.
13862 @opindex --rfc-2822
13863 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13864 %z}, evaluated in the C locale so abbreviations are always in English.
13868 Fri, 09 Sep 2005 13:51:39 -0700
13871 This format conforms to
13872 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13873 @acronym{RFCs} 2822} and
13874 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13875 current and previous standards for Internet email.
13877 @item --rfc-3339=@var{timespec}
13878 @opindex --rfc-3339=@var{timespec}
13879 Display the date using a format specified by
13880 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13881 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13882 format, except that it also permits applications to use a space rather
13883 than a @samp{T} to separate dates from times. Unlike the other
13884 standard formats, @acronym{RFC} 3339 format is always suitable as
13885 input for the @option{--date} (@option{-d}) and @option{--file}
13886 (@option{-f}) options, regardless of the current locale.
13888 The argument @var{timespec} specifies how much of the time to include.
13889 It can be one of the following:
13893 Print just the full-date, e.g., @samp{2005-09-14}.
13894 This is equivalent to the format @samp{%Y-%m-%d}.
13897 Print the full-date and full-time separated by a space, e.g.,
13898 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13899 time-offset; here the @samp{+05:30} means that local time is five
13900 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13901 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13904 Like @samp{seconds}, but also print nanoseconds, e.g.,
13905 @samp{2005-09-14 00:56:06.998458565+05:30}.
13906 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13910 @item -s @var{datestr}
13911 @itemx --set=@var{datestr}
13914 Set the date and time to @var{datestr}. See @option{-d} above.
13921 @opindex --universal
13922 @cindex Coordinated Universal Time
13924 @cindex Greenwich Mean Time
13927 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13928 @env{TZ} environment variable were set to the string @samp{UTC0}.
13930 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13931 historical reasons.
13935 @node Examples of date
13936 @subsection Examples of @command{date}
13938 @cindex examples of @command{date}
13940 Here are a few examples. Also see the documentation for the @option{-d}
13941 option in the previous section.
13946 To print the date of the day before yesterday:
13949 date --date='2 days ago'
13953 To print the date of the day three months and one day hence:
13956 date --date='3 months 1 day'
13960 To print the day of year of Christmas in the current year:
13963 date --date='25 Dec' +%j
13967 To print the current full month name and the day of the month:
13973 But this may not be what you want because for the first nine days of
13974 the month, the @samp{%d} expands to a zero-padded two-digit field,
13975 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
13978 To print a date without the leading zero for one-digit days
13979 of the month, you can use the (@acronym{GNU} extension)
13980 @samp{-} flag to suppress
13981 the padding altogether:
13984 date -d 1may '+%B %-d
13988 To print the current date and time in the format required by many
13989 non-@acronym{GNU} versions of @command{date} when setting the system clock:
13992 date +%m%d%H%M%Y.%S
13996 To set the system clock forward by two minutes:
13999 date --set='+2 minutes'
14003 To print the date in @acronym{RFC} 2822 format,
14004 use @samp{date --rfc-2822}. Here is some example output:
14007 Fri, 09 Sep 2005 13:51:39 -0700
14010 @anchor{%s-examples}
14012 To convert a date string to the number of seconds since the epoch
14013 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14014 the @samp{%s} format. That can be useful in sorting and/or graphing
14015 and/or comparing data by date. The following command outputs the
14016 number of the seconds since the epoch for the time two minutes after the
14020 date --date='1970-01-01 00:02:00 +0000' +%s
14024 If you do not specify time zone information in the date string,
14025 @command{date} uses your computer's idea of the time zone when
14026 interpreting the string. For example, if your computer's time zone is
14027 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14028 seconds) behind UTC:
14031 # local time zone used
14032 date --date='1970-01-01 00:02:00' +%s
14037 If you're sorting or graphing dated data, your raw date values may be
14038 represented as seconds since the epoch. But few people can look at
14039 the date @samp{946684800} and casually note ``Oh, that's the first second
14040 of the year 2000 in Greenwich, England.''
14043 date --date='2000-01-01 UTC' +%s
14047 An alternative is to use the @option{--utc} (@option{-u}) option.
14048 Then you may omit @samp{UTC} from the date string. Although this
14049 produces the same result for @samp{%s} and many other format sequences,
14050 with a time zone offset different from zero, it would give a different
14051 result for zone-dependent formats like @samp{%z}.
14054 date -u --date=2000-01-01 +%s
14058 To convert such an unwieldy number of seconds back to
14059 a more readable form, use a command like this:
14062 # local time zone used
14063 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14064 1999-12-31 19:00:00 -0500
14067 Or if you do not mind depending on the @samp{@@} feature present since
14068 coreutils 5.3.0, you could shorten this to:
14071 date -d @@946684800 +"%F %T %z"
14072 1999-12-31 19:00:00 -0500
14075 Often it is better to output UTC-relative date and time:
14078 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14079 2000-01-01 00:00:00 +0000
14085 @node arch invocation
14086 @section @command{arch}: Print machine hardware name
14089 @cindex print machine hardware name
14090 @cindex system information, printing
14092 @command{arch} prints the machine hardware name,
14093 and is equivalent to @samp{uname -m}.
14097 arch [@var{option}]
14100 The program accepts the @ref{Common options} only.
14105 @node nproc invocation
14106 @section @command{nproc}: Print the number of available processors
14109 @cindex Print the number of processors
14110 @cindex system information, printing
14112 Print the number of processing units available to the current process,
14113 which may be less than the number of online processors.
14114 If this information is not accessible, then print the number of
14115 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14116 set, then it will determine the returned value. The result is guaranteed to be
14117 greater than zero. Synopsis:
14120 nproc [@var{option}]
14123 The program accepts the following options. Also see @ref{Common options}.
14129 Print the number of installed processors on the system, which may
14130 be greater than the number online or available to the current process.
14131 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14133 @item --ignore=@var{number}
14135 If possible, exclude this @var{number} of processing units.
14142 @node uname invocation
14143 @section @command{uname}: Print system information
14146 @cindex print system information
14147 @cindex system information, printing
14149 @command{uname} prints information about the machine and operating system
14150 it is run on. If no options are given, @command{uname} acts as if the
14151 @option{-s} option were given. Synopsis:
14154 uname [@var{option}]@dots{}
14157 If multiple options or @option{-a} are given, the selected information is
14158 printed in this order:
14161 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14162 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14165 The information may contain internal spaces, so such output cannot be
14166 parsed reliably. In the following example, @var{release} is
14167 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14171 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14175 The program accepts the following options. Also see @ref{Common options}.
14183 Print all of the below information, except omit the processor type
14184 and the hardware platform name if they are unknown.
14187 @itemx --hardware-platform
14189 @opindex --hardware-platform
14190 @cindex implementation, hardware
14191 @cindex hardware platform
14192 @cindex platform, hardware
14193 Print the hardware platform name
14194 (sometimes called the hardware implementation).
14195 Print @samp{unknown} if the kernel does not make this information
14196 easily available, as is the case with Linux kernels.
14202 @cindex machine type
14203 @cindex hardware class
14204 @cindex hardware type
14205 Print the machine hardware name (sometimes called the hardware class
14211 @opindex --nodename
14214 @cindex network node name
14215 Print the network node hostname.
14220 @opindex --processor
14221 @cindex host processor type
14222 Print the processor type (sometimes called the instruction set
14223 architecture or ISA).
14224 Print @samp{unknown} if the kernel does not make this information
14225 easily available, as is the case with Linux kernels.
14228 @itemx --operating-system
14230 @opindex --operating-system
14231 @cindex operating system name
14232 Print the name of the operating system.
14235 @itemx --kernel-release
14237 @opindex --kernel-release
14238 @cindex kernel release
14239 @cindex release of kernel
14240 Print the kernel release.
14243 @itemx --kernel-name
14245 @opindex --kernel-name
14246 @cindex kernel name
14247 @cindex name of kernel
14248 Print the kernel name.
14249 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14250 ``the implementation of the operating system'', because the
14251 @acronym{POSIX} specification itself has no notion of ``kernel''.
14252 The kernel name might be the same as the operating system name printed
14253 by the @option{-o} or @option{--operating-system} option, but it might
14254 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14255 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14259 @itemx --kernel-version
14261 @opindex --kernel-version
14262 @cindex kernel version
14263 @cindex version of kernel
14264 Print the kernel version.
14271 @node hostname invocation
14272 @section @command{hostname}: Print or set system name
14275 @cindex setting the hostname
14276 @cindex printing the hostname
14277 @cindex system name, printing
14278 @cindex appropriate privileges
14280 With no arguments, @command{hostname} prints the name of the current host
14281 system. With one argument, it sets the current host name to the
14282 specified string. You must have appropriate privileges to set the host
14286 hostname [@var{name}]
14289 The only options are @option{--help} and @option{--version}. @xref{Common
14295 @node hostid invocation
14296 @section @command{hostid}: Print numeric host identifier
14299 @cindex printing the host identifier
14301 @command{hostid} prints the numeric identifier of the current host
14302 in hexadecimal. This command accepts no arguments.
14303 The only options are @option{--help} and @option{--version}.
14304 @xref{Common options}.
14306 For example, here's what it prints on one system I use:
14313 On that system, the 32-bit quantity happens to be closely
14314 related to the system's Internet address, but that isn't always
14319 @node uptime invocation
14320 @section @command{uptime}: Print system uptime and load
14323 @cindex printing the system uptime and load
14325 @command{uptime} prints the current time, the system's uptime, the
14326 number of logged-in users and the current load average.
14328 If an argument is specified, it is used as the file to be read
14329 to discover how many users are logged in. If no argument is
14330 specified, a system default is used (@command{uptime --help} indicates
14331 the default setting).
14333 The only options are @option{--help} and @option{--version}.
14334 @xref{Common options}.
14336 For example, here's what it prints right now on one system I use:
14340 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14343 The precise method of calculation of load average varies somewhat
14344 between systems. Some systems calculate it as the average number of
14345 runnable processes over the last 1, 5 and 15 minutes, but some systems
14346 also include processes in the uninterruptible sleep state (that is,
14347 those processes which are waiting for disk I/O). The Linux kernel
14348 includes uninterruptible processes.
14350 @node SELinux context
14351 @chapter SELinux context
14353 @cindex SELinux context
14354 @cindex SELinux, context
14355 @cindex commands for SELinux context
14357 This section describes commands for operations with SELinux
14361 * chcon invocation:: Change SELinux context of file
14362 * runcon invocation:: Run a command in specified SELinux context
14365 @node chcon invocation
14366 @section @command{chcon}: Change SELinux context of file
14369 @cindex changing security context
14370 @cindex change SELinux context
14372 @command{chcon} changes the SELinux security context of the selected files.
14376 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14377 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14378 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14381 Change the SELinux security context of each @var{file} to @var{context}.
14382 With @option{--reference}, change the security context of each @var{file}
14383 to that of @var{rfile}.
14385 The program accepts the following options. Also see @ref{Common options}.
14390 @itemx --no-dereference
14392 @opindex --no-dereference
14393 @cindex no dereference
14394 Affect symbolic links instead of any referenced file.
14396 @item --reference=@var{rfile}
14397 @opindex --reference
14398 @cindex reference file
14399 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14404 @opindex --recursive
14405 Operate on files and directories recursively.
14408 @xref{Traversing symlinks}.
14411 @xref{Traversing symlinks}.
14414 @xref{Traversing symlinks}.
14421 Output a diagnostic for every file processed.
14423 @item -u @var{user}
14424 @itemx --user=@var{user}
14427 Set user @var{user} in the target security context.
14429 @item -r @var{role}
14430 @itemx --role=@var{role}
14433 Set role @var{role} in the target security context.
14435 @item -t @var{type}
14436 @itemx --type=@var{type}
14439 Set type @var{type} in the target security context.
14441 @item -l @var{range}
14442 @itemx --range=@var{range}
14445 Set range @var{range} in the target security context.
14451 @node runcon invocation
14452 @section @command{runcon}: Run a command in specified SELinux context
14455 @cindex run with security context
14458 @command{runcon} runs file in specified SELinux security context.
14462 runcon @var{context} @var{command} [@var{args}]
14463 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14466 Run @var{command} with completely-specified @var{context}, or with
14467 current or transitioned security context modified by one or more of @var{level},
14468 @var{role}, @var{type} and @var{user}.
14470 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14471 is specified, the first argument is used as the complete context.
14472 Any additional arguments after @var{command}
14473 are interpreted as arguments to the command.
14475 With neither @var{context} nor @var{command}, print the current security context.
14477 The program accepts the following options. Also see @ref{Common options}.
14485 Compute process transition context before modifying.
14487 @item -u @var{user}
14488 @itemx --user=@var{user}
14491 Set user @var{user} in the target security context.
14493 @item -r @var{role}
14494 @itemx --role=@var{role}
14497 Set role @var{role} in the target security context.
14499 @item -t @var{type}
14500 @itemx --type=@var{type}
14503 Set type @var{type} in the target security context.
14505 @item -l @var{range}
14506 @itemx --range=@var{range}
14509 Set range @var{range} in the target security context.
14513 @cindex exit status of @command{runcon}
14517 126 if @var{command} is found but cannot be invoked
14518 127 if @command{runcon} itself fails or if @var{command} cannot be found
14519 the exit status of @var{command} otherwise
14522 @node Modified command invocation
14523 @chapter Modified command invocation
14525 @cindex modified command invocation
14526 @cindex invocation of commands, modified
14527 @cindex commands for invoking other commands
14529 This section describes commands that run other commands in some context
14530 different than the current one: a modified environment, as a different
14534 * chroot invocation:: Modify the root directory.
14535 * env invocation:: Modify environment variables.
14536 * nice invocation:: Modify niceness.
14537 * nohup invocation:: Immunize to hangups.
14538 * stdbuf invocation:: Modify buffering of standard streams.
14539 * su invocation:: Modify user and group ID.
14540 * timeout invocation:: Run with time limit.
14544 @node chroot invocation
14545 @section @command{chroot}: Run a command with a different root directory
14548 @cindex running a program in a specified root directory
14549 @cindex root directory, running a program in a specified
14551 @command{chroot} runs a command with a specified root directory.
14552 On many systems, only the super-user can do this.@footnote{However,
14553 some systems (e.g., FreeBSD) can be configured to allow certain regular
14554 users to use the @code{chroot} system call, and hence to run this program.
14555 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14556 underlying function is non-privileged due to lack of support in MS-Windows.}
14560 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14561 chroot @var{option}
14564 Ordinarily, file names are looked up starting at the root of the
14565 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14566 the directory @var{newroot} (which must exist) and then runs
14567 @var{command} with optional @var{args}. If @var{command} is not
14568 specified, the default is the value of the @env{SHELL} environment
14569 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14570 @var{command} must not be a special built-in utility
14571 (@pxref{Special built-in utilities}).
14573 The program accepts the following options. Also see @ref{Common options}.
14574 Options must precede operands.
14578 @itemx --userspec=@var{user}[:@var{group}]
14579 @opindex --userspec
14580 By default, @var{command} is run with the same credentials
14581 as the invoking process.
14582 Use this option to run it as a different @var{user} and/or with a
14583 different primary @var{group}.
14585 @itemx --groups=@var{groups}
14587 Use this option to specify the supplementary @var{groups} to be
14588 used by the new process.
14589 The items in the list (names or numeric IDs) must be separated by commas.
14593 Here are a few tips to help avoid common problems in using chroot.
14594 To start with a simple example, make @var{command} refer to a statically
14595 linked binary. If you were to use a dynamically linked executable, then
14596 you'd have to arrange to have the shared libraries in the right place under
14597 your new root directory.
14599 For example, if you create a statically linked @command{ls} executable,
14600 and put it in @file{/tmp/empty}, you can run this command as root:
14603 $ chroot /tmp/empty /ls -Rl /
14606 Then you'll see output like this:
14611 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14614 If you want to use a dynamically linked executable, say @command{bash},
14615 then first run @samp{ldd bash} to see what shared objects it needs.
14616 Then, in addition to copying the actual binary, also copy the listed
14617 files to the required positions under your intended new root directory.
14618 Finally, if the executable requires any other files (e.g., data, state,
14619 device files), copy them into place, too.
14621 @cindex exit status of @command{chroot}
14625 125 if @command{chroot} itself fails
14626 126 if @var{command} is found but cannot be invoked
14627 127 if @var{command} cannot be found
14628 the exit status of @var{command} otherwise
14632 @node env invocation
14633 @section @command{env}: Run a command in a modified environment
14636 @cindex environment, running a program in a modified
14637 @cindex modified environment, running a program in a
14638 @cindex running a program in a modified environment
14640 @command{env} runs a command with a modified environment. Synopses:
14643 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14644 [@var{command} [@var{args}]@dots{}]
14648 Operands of the form @samp{@var{variable}=@var{value}} set
14649 the environment variable @var{variable} to value @var{value}.
14650 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14651 to an empty value is different from unsetting it.
14652 These operands are evaluated left-to-right, so if two operands
14653 mention the same variable the earlier is ignored.
14655 Environment variable names can be empty, and can contain any
14656 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14657 However, it is wise to limit yourself to names that
14658 consist solely of underscores, digits, and @acronym{ASCII} letters,
14659 and that begin with a non-digit, as applications like the shell do not
14660 work well with other names.
14663 The first operand that does not contain the character @samp{=}
14664 specifies the program to invoke; it is
14665 searched for according to the @env{PATH} environment variable. Any
14666 remaining arguments are passed as arguments to that program.
14667 The program should not be a special built-in utility
14668 (@pxref{Special built-in utilities}).
14670 Modifications to @env{PATH} take effect prior to searching for
14671 @var{command}. Use caution when reducing @env{PATH}; behavior is
14672 not portable when @env{PATH} is undefined or omits key directories
14673 such as @file{/bin}.
14675 In the rare case that a utility contains a @samp{=} in the name, the
14676 only way to disambiguate it from a variable assignment is to use an
14677 intermediate command for @var{command}, and pass the problematic
14678 program name via @var{args}. For example, if @file{./prog=} is an
14679 executable in the current @env{PATH}:
14682 env prog= true # runs 'true', with prog= in environment
14683 env ./prog= true # runs 'true', with ./prog= in environment
14684 env -- prog= true # runs 'true', with prog= in environment
14685 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14686 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14689 @cindex environment, printing
14691 If no command name is specified following the environment
14692 specifications, the resulting environment is printed. This is like
14693 specifying the @command{printenv} program.
14695 For some examples, suppose the environment passed to @command{env}
14696 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14697 @samp{PATH=.:/gnubin:/hacks}:
14702 Output the current environment.
14704 $ env | LC_ALL=C sort
14707 PATH=.:/gnubin:/hacks
14711 Run @command{foo} with a reduced environment, preserving only the
14712 original @env{PATH} to avoid problems in locating @command{foo}.
14714 env - PATH="$PATH" foo
14718 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14719 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14720 that @command{foo} was found in the file system rather than as a shell
14727 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14728 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14729 @samp{DISPLAY=gnu:0}.
14731 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14735 Attempt to run the program @command{/energy/--} (as that is the only
14736 possible path search result); if the command exists, the environment
14737 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14738 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14740 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14746 The program accepts the following options. Also see @ref{Common options}.
14747 Options must precede operands.
14753 @item -u @var{name}
14754 @itemx --unset=@var{name}
14757 Remove variable @var{name} from the environment, if it was in the
14762 @itemx --ignore-environment
14765 @opindex --ignore-environment
14766 Start with an empty environment, ignoring the inherited environment.
14770 @cindex exit status of @command{env}
14774 0 if no @var{command} is specified and the environment is output
14775 125 if @command{env} itself fails
14776 126 if @var{command} is found but cannot be invoked
14777 127 if @var{command} cannot be found
14778 the exit status of @var{command} otherwise
14782 @node nice invocation
14783 @section @command{nice}: Run a command with modified niceness
14787 @cindex scheduling, affecting
14788 @cindex appropriate privileges
14790 @command{nice} prints or modifies a process's @dfn{niceness},
14791 a parameter that affects whether the process is scheduled favorably.
14795 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14798 If no arguments are given, @command{nice} prints the current niceness.
14799 Otherwise, @command{nice} runs the given @var{command} with its
14800 niceness adjusted. By default, its niceness is incremented by 10.
14802 Niceness values range at least from @minus{}20 (process has high priority
14803 and gets more resources, thus slowing down other processes) through 19
14804 (process has lower priority and runs slowly itself, but has less impact
14805 on the speed of other running processes). Some systems
14806 may have a wider range of nicenesses; conversely, other systems may
14807 enforce more restrictive limits. An attempt to set the niceness
14808 outside the supported range is treated as an attempt to use the
14809 minimum or maximum supported value.
14811 A niceness should not be confused with a scheduling priority, which
14812 lets applications determine the order in which threads are scheduled
14813 to run. Unlike a priority, a niceness is merely advice to the
14814 scheduler, which the scheduler is free to ignore. Also, as a point of
14815 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14816 terms of a @dfn{nice value}, which is the nonnegative difference
14817 between a niceness and the minimum niceness. Though @command{nice}
14818 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14819 term ``niceness'' for compatibility with historical practice.
14821 @var{command} must not be a special built-in utility (@pxref{Special
14822 built-in utilities}).
14824 @mayConflictWithShellBuiltIn{nice}
14826 The program accepts the following option. Also see @ref{Common options}.
14827 Options must precede operands.
14830 @item -n @var{adjustment}
14831 @itemx --adjustment=@var{adjustment}
14833 @opindex --adjustment
14834 Add @var{adjustment} instead of 10 to the command's niceness. If
14835 @var{adjustment} is negative and you lack appropriate privileges,
14836 @command{nice} issues a warning but otherwise acts as if you specified
14839 For compatibility @command{nice} also supports an obsolete
14840 option syntax @option{-@var{adjustment}}. New scripts should use
14841 @option{-n @var{adjustment}} instead.
14845 @cindex exit status of @command{nice}
14849 0 if no @var{command} is specified and the niceness is output
14850 125 if @command{nice} itself fails
14851 126 if @var{command} is found but cannot be invoked
14852 127 if @var{command} cannot be found
14853 the exit status of @var{command} otherwise
14856 It is sometimes useful to run a non-interactive program with reduced niceness.
14859 $ nice factor 4611686018427387903
14862 Since @command{nice} prints the current niceness,
14863 you can invoke it through itself to demonstrate how it works.
14865 The default behavior is to increase the niceness by @samp{10}:
14876 The @var{adjustment} is relative to the current niceness. In the
14877 next example, the first @command{nice} invocation runs the second one
14878 with niceness 10, and it in turn runs the final one with a niceness
14882 $ nice nice -n 3 nice
14886 Specifying a niceness larger than the supported range
14887 is the same as specifying the maximum supported value:
14890 $ nice -n 10000000000 nice
14894 Only a privileged user may run a process with lower niceness:
14898 nice: cannot set niceness: Permission denied
14900 $ sudo nice -n -1 nice
14905 @node nohup invocation
14906 @section @command{nohup}: Run a command immune to hangups
14909 @cindex hangups, immunity to
14910 @cindex immunity to hangups
14911 @cindex logging out and continuing to run
14914 @command{nohup} runs the given @var{command} with hangup signals ignored,
14915 so that the command can continue running in the background after you log
14919 nohup @var{command} [@var{arg}]@dots{}
14922 If standard input is a terminal, it is redirected from
14923 @file{/dev/null} so that terminal sessions do not mistakenly consider
14924 the terminal to be used by the command. This is a @acronym{GNU}
14925 extension; programs intended to be portable to non-@acronym{GNU} hosts
14926 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14930 If standard output is a terminal, the command's standard output is appended
14931 to the file @file{nohup.out}; if that cannot be written to, it is appended
14932 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14933 command is not run.
14934 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14935 @command{nohup} is made readable and writable only to the user,
14936 regardless of the current umask settings.
14938 If standard error is a terminal, it is normally redirected to the same file
14939 descriptor as the (possibly-redirected) standard output.
14940 However, if standard output is closed, standard error terminal output
14941 is instead appended to the file @file{nohup.out} or
14942 @file{$HOME/nohup.out} as above.
14944 To capture the command's output to a file other than @file{nohup.out}
14945 you can redirect it. For example, to capture the output of
14949 nohup make > make.log
14952 @command{nohup} does not automatically put the command it runs in the
14953 background; you must do that explicitly, by ending the command line
14954 with an @samp{&}. Also, @command{nohup} does not alter the
14955 niceness of @var{command}; use @command{nice} for that,
14956 e.g., @samp{nohup nice @var{command}}.
14958 @var{command} must not be a special built-in utility (@pxref{Special
14959 built-in utilities}).
14961 The only options are @option{--help} and @option{--version}. @xref{Common
14962 options}. Options must precede operands.
14964 @cindex exit status of @command{nohup}
14968 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14969 126 if @var{command} is found but cannot be invoked
14970 127 if @var{command} cannot be found
14971 the exit status of @var{command} otherwise
14974 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
14978 @node stdbuf invocation
14979 @section @command{stdbuf}: Run a command with modified I/O stream buffering
14982 @cindex standard streams, buffering
14983 @cindex line buffered
14985 @command{stdbuf} allows one to modify the buffering operations of the
14986 three standard I/O streams associated with a program. Synopsis:
14989 stdbuf @var{option}@dots{} @var{command}
14992 Any additional @var{arg}s are passed as additional arguments to the
14995 The program accepts the following options. Also see @ref{Common options}.
14999 @item -i @var{mode}
15000 @itemx --input=@var{mode}
15003 Adjust the standard input stream buffering.
15005 @item -o @var{mode}
15006 @itemx --output=@var{mode}
15009 Adjust the standard output stream buffering.
15011 @item -e @var{mode}
15012 @itemx --error=@var{mode}
15015 Adjust the standard error stream buffering.
15019 The @var{mode} can be specified as follows:
15024 Set the stream to line buffered mode.
15025 In this mode data is coalesced until a newline is output or
15026 input is read from any stream attached to a terminal device.
15027 This option is invalid with standard input.
15030 Disable buffering of the selected stream.
15031 In this mode data is output immediately and only the
15032 amount of data requested is read from input.
15035 Specify the size of the buffer to use in fully buffered mode.
15036 @multiplierSuffixesNoBlocks{size}
15040 NOTE: If @var{command} adjusts the buffering of its standard streams
15041 (@command{tee} does for e.g.) then that will override corresponding settings
15042 changed by @command{stdbuf}. Also some filters (like @command{dd} and
15043 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
15044 by @command{stdbuf} settings.
15046 @cindex exit status of @command{stdbuf}
15050 125 if @command{stdbuf} itself fails
15051 126 if @var{command} is found but cannot be invoked
15052 127 if @var{command} cannot be found
15053 the exit status of @var{command} otherwise
15057 @node su invocation
15058 @section @command{su}: Run a command with substitute user and group ID
15061 @cindex substitute user and group IDs
15062 @cindex user ID, switching
15063 @cindex super-user, becoming
15064 @cindex root, becoming
15066 @command{su} allows one user to temporarily become another user. It runs a
15067 command (often an interactive shell) with the real and effective user
15068 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15071 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15074 @cindex passwd entry, and @command{su} shell
15076 @flindex /etc/passwd
15077 If no @var{user} is given, the default is @code{root}, the super-user.
15078 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15079 @file{/bin/sh} if none is specified there. If @var{user} has a
15080 password, @command{su} prompts for the password unless run by a user with
15081 effective user ID of zero (the super-user).
15087 @cindex login shell
15088 By default, @command{su} does not change the current directory.
15089 It sets the environment variables @env{HOME} and @env{SHELL}
15090 from the password entry for @var{user}, and if @var{user} is not
15091 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15092 By default, the shell is not a login shell.
15094 Any additional @var{arg}s are passed as additional arguments to the
15097 @cindex @option{-su}
15098 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15099 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15100 to certain shells, etc.).
15103 @command{su} can optionally be compiled to use @code{syslog} to report
15104 failed, and optionally successful, @command{su} attempts. (If the system
15105 supports @code{syslog}.) However, GNU @command{su} does not check if the
15106 user is a member of the @code{wheel} group; see below.
15108 The program accepts the following options. Also see @ref{Common options}.
15111 @item -c @var{command}
15112 @itemx --command=@var{command}
15115 Pass @var{command}, a single command line to run, to the shell with
15116 a @option{-c} option instead of starting an interactive shell.
15123 @cindex file name pattern expansion, disabled
15124 @cindex globbing, disabled
15125 Pass the @option{-f} option to the shell. This probably only makes sense
15126 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15127 option prevents reading the startup file (@file{.cshrc}). With
15128 Bourne-like shells, the @option{-f} option disables file name pattern
15129 expansion (globbing), which is not likely to be useful.
15137 @c other variables already indexed above
15140 @cindex login shell, creating
15141 Make the shell a login shell. This means the following. Unset all
15142 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15143 (which are set as described above), and @env{USER} and @env{LOGNAME}
15144 (which are set, even for the super-user, as described above), and set
15145 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15146 directory. Prepend @samp{-} to the shell's name, intended to make it
15147 read its login startup file(s).
15151 @itemx --preserve-environment
15154 @opindex --preserve-environment
15155 @cindex environment, preserving
15156 @flindex /etc/shells
15157 @cindex restricted shell
15158 Do not change the environment variables @env{HOME}, @env{USER},
15159 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15160 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15161 entry, unless the user running @command{su} is not the super-user and
15162 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15163 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15164 if that file does not exist. Parts of what this option does can be
15165 overridden by @option{--login} and @option{--shell}.
15167 @item -s @var{shell}
15168 @itemx --shell=@var{shell}
15171 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15172 unless the user running @command{su} is not the super-user and @var{user}'s
15173 shell is restricted (see @option{-m} just above).
15177 @cindex exit status of @command{su}
15181 125 if @command{su} itself fails
15182 126 if subshell is found but cannot be invoked
15183 127 if subshell cannot be found
15184 the exit status of the subshell otherwise
15187 @cindex wheel group, not supported
15188 @cindex group wheel, not supported
15190 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15192 (This section is by Richard Stallman.)
15196 Sometimes a few of the users try to hold total power over all the
15197 rest. For example, in 1984, a few users at the MIT AI lab decided to
15198 seize power by changing the operator password on the Twenex system and
15199 keeping it secret from everyone else. (I was able to thwart this coup
15200 and give power back to the users by patching the kernel, but I
15201 wouldn't know how to do that in Unix.)
15203 However, occasionally the rulers do tell someone. Under the usual
15204 @command{su} mechanism, once someone learns the root password who
15205 sympathizes with the ordinary users, he or she can tell the rest. The
15206 ``wheel group'' feature would make this impossible, and thus cement the
15207 power of the rulers.
15209 I'm on the side of the masses, not that of the rulers. If you are
15210 used to supporting the bosses and sysadmins in whatever they do, you
15211 might find this idea strange at first.
15214 @node timeout invocation
15215 @section @command{timeout}: Run a command with a time limit
15219 @cindex run commands with bounded time
15221 @command{timeout} runs the given @var{command} and kills it if it is
15222 still running after the specified time interval. Synopsis:
15225 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15228 @var{command} must not be a special built-in utility (@pxref{Special
15229 built-in utilities}).
15231 The program accepts the following options. Also see @ref{Common options}.
15232 Options must precede operands.
15235 @item -k @var{duration}
15236 @itemx --kill-after=@var{duration}
15238 @opindex --kill-after
15239 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15240 signal, after the specified @var{duration}. Without this option, if the
15241 selected signal proves not to be fatal, @command{timeout} does not kill
15244 @item -s @var{signal}
15245 @itemx --signal=@var{signal}
15248 Send this @var{signal} to @var{command} on timeout, rather than the
15249 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15250 or a number. Also see @xref{Signal specifications}.
15254 @var{duration} is an integer followed by an optional unit:
15256 @samp{s} for seconds (the default)
15257 @samp{m} for minutes
15261 A duration of 0 disables the associated timeout.
15263 @cindex exit status of @command{timeout}
15267 124 if @var{command} times out
15268 125 if @command{timeout} itself fails
15269 126 if @var{command} is found but cannot be invoked
15270 127 if @var{command} cannot be found
15271 the exit status of @var{command} otherwise
15275 @node Process control
15276 @chapter Process control
15278 @cindex processes, commands for controlling
15279 @cindex commands for controlling processes
15282 * kill invocation:: Sending a signal to processes.
15286 @node kill invocation
15287 @section @command{kill}: Send a signal to processes
15290 @cindex send a signal to processes
15292 The @command{kill} command sends a signal to processes, causing them
15293 to terminate or otherwise act upon receiving the signal in some way.
15294 Alternatively, it lists information about signals. Synopses:
15297 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15298 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15301 @mayConflictWithShellBuiltIn{kill}
15303 The first form of the @command{kill} command sends a signal to all
15304 @var{pid} arguments. The default signal to send if none is specified
15305 is @samp{TERM}. The special signal number @samp{0} does not denote a
15306 valid signal, but can be used to test whether the @var{pid} arguments
15307 specify processes to which a signal could be sent.
15309 If @var{pid} is positive, the signal is sent to the process with the
15310 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15311 processes in the process group of the current process. If @var{pid}
15312 is @minus{}1, the signal is sent to all processes for which the user has
15313 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15314 is sent to all processes in the process group that equals the absolute
15315 value of @var{pid}.
15317 If @var{pid} is not positive, a system-dependent set of system
15318 processes is excluded from the list of processes to which the signal
15321 If a negative @var{pid} argument is desired as the first one, it
15322 should be preceded by @option{--}. However, as a common extension to
15323 @acronym{POSIX}, @option{--} is not required with @samp{kill
15324 -@var{signal} -@var{pid}}. The following commands are equivalent:
15333 The first form of the @command{kill} command succeeds if every @var{pid}
15334 argument specifies at least one process that the signal was sent to.
15336 The second form of the @command{kill} command lists signal information.
15337 Either the @option{-l} or @option{--list} option, or the @option{-t}
15338 or @option{--table} option must be specified. Without any
15339 @var{signal} argument, all supported signals are listed. The output
15340 of @option{-l} or @option{--list} is a list of the signal names, one
15341 per line; if @var{signal} is already a name, the signal number is
15342 printed instead. The output of @option{-t} or @option{--table} is a
15343 table of signal numbers, names, and descriptions. This form of the
15344 @command{kill} command succeeds if all @var{signal} arguments are valid
15345 and if there is no output error.
15347 The @command{kill} command also supports the @option{--help} and
15348 @option{--version} options. @xref{Common options}.
15350 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15351 number like @samp{1}, or an exit status of a process terminated by the
15352 signal. A signal name can be given in canonical form or prefixed by
15353 @samp{SIG}. The case of the letters is ignored, except for the
15354 @option{-@var{signal}} option which must use upper case to avoid
15355 ambiguity with lower case option letters. For a list of supported
15356 signal names and numbers see @xref{Signal specifications}.
15361 @cindex delaying commands
15362 @cindex commands for delaying
15364 @c Perhaps @command{wait} or other commands should be described here also?
15367 * sleep invocation:: Delay for a specified time.
15371 @node sleep invocation
15372 @section @command{sleep}: Delay for a specified time
15375 @cindex delay for a specified time
15377 @command{sleep} pauses for an amount of time specified by the sum of
15378 the values of the command line arguments.
15382 sleep @var{number}[smhd]@dots{}
15386 Each argument is a number followed by an optional unit; the default
15387 is seconds. The units are:
15400 Historical implementations of @command{sleep} have required that
15401 @var{number} be an integer, and only accepted a single argument
15402 without a suffix. However, GNU @command{sleep} accepts
15403 arbitrary floating point numbers (using a period before any fractional
15406 The only options are @option{--help} and @option{--version}. @xref{Common
15409 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15410 @mayConflictWithShellBuiltIn{sleep}
15415 @node Numeric operations
15416 @chapter Numeric operations
15418 @cindex numeric operations
15419 These programs do numerically-related operations.
15422 * factor invocation:: Show factors of numbers.
15423 * seq invocation:: Print sequences of numbers.
15427 @node factor invocation
15428 @section @command{factor}: Print prime factors
15431 @cindex prime factors
15433 @command{factor} prints prime factors. Synopses:
15436 factor [@var{number}]@dots{}
15437 factor @var{option}
15440 If no @var{number} is specified on the command line, @command{factor} reads
15441 numbers from standard input, delimited by newlines, tabs, or spaces.
15443 The @command{factor} command supports only a small number of options:
15447 Print a short help on standard output, then exit without further
15451 Print the program version on standard output, then exit without further
15455 Factoring the product of the eighth and ninth Mersenne primes
15456 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15459 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15460 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15461 4951760154835678088235319297: 2147483647 2305843009213693951
15465 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15466 about 20 seconds on the same machine.
15468 Factoring large prime numbers is, in general, hard. The Pollard Rho
15469 algorithm used by @command{factor} is particularly effective for
15470 numbers with relatively small factors. If you wish to factor large
15471 numbers which do not have small factors (for example, numbers which
15472 are the product of two large primes), other methods are far better.
15474 If @command{factor} is built without using GNU MP, only
15475 single-precision arithmetic is available, and so large numbers
15476 (typically @math{2^{64}} and above) will not be supported. The single-precision
15477 code uses an algorithm which is designed for factoring smaller
15483 @node seq invocation
15484 @section @command{seq}: Print numeric sequences
15487 @cindex numeric sequences
15488 @cindex sequence of numbers
15490 @command{seq} prints a sequence of numbers to standard output. Synopses:
15493 seq [@var{option}]@dots{} @var{last}
15494 seq [@var{option}]@dots{} @var{first} @var{last}
15495 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15498 @command{seq} prints the numbers from @var{first} to @var{last} by
15499 @var{increment}. By default, each number is printed on a separate line.
15500 When @var{increment} is not specified, it defaults to @samp{1},
15501 even when @var{first} is larger than @var{last}.
15502 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15503 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15504 Floating-point numbers
15505 may be specified (using a period before any fractional digits).
15507 The program accepts the following options. Also see @ref{Common options}.
15508 Options must precede operands.
15511 @item -f @var{format}
15512 @itemx --format=@var{format}
15513 @opindex -f @var{format}
15514 @opindex --format=@var{format}
15515 @cindex formatting of numbers in @command{seq}
15516 Print all numbers using @var{format}.
15517 @var{format} must contain exactly one of the @samp{printf}-style
15518 floating point conversion specifications @samp{%a}, @samp{%e},
15519 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15520 The @samp{%} may be followed by zero or more flags taken from the set
15521 @samp{-+#0 '}, then an optional width containing one or more digits,
15522 then an optional precision consisting of a @samp{.} followed by zero
15523 or more digits. @var{format} may also contain any number of @samp{%%}
15524 conversion specifications. All conversion specifications have the
15525 same meaning as with @samp{printf}.
15527 The default format is derived from @var{first}, @var{step}, and
15528 @var{last}. If these all use a fixed point decimal representation,
15529 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15530 precision that can represent the output numbers exactly. Otherwise,
15531 the default format is @samp{%g}.
15533 @item -s @var{string}
15534 @itemx --separator=@var{string}
15535 @cindex separator for numbers in @command{seq}
15536 Separate numbers with @var{string}; default is a newline.
15537 The output always terminates with a newline.
15540 @itemx --equal-width
15541 Print all numbers with the same width, by padding with leading zeros.
15542 @var{first}, @var{step}, and @var{last} should all use a fixed point
15543 decimal representation.
15544 (To have other kinds of padding, use @option{--format}).
15548 You can get finer-grained control over output with @option{-f}:
15551 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15557 If you want hexadecimal integer output, you can use @command{printf}
15558 to perform the conversion:
15561 $ printf '%x\n' `seq 1048575 1024 1050623`
15567 For very long lists of numbers, use xargs to avoid
15568 system limitations on the length of an argument list:
15571 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15577 To generate octal output, use the printf @code{%o} format instead
15580 On most systems, seq can produce whole-number output for values up to
15581 at least @math{2^{53}}. Larger integers are approximated. The details
15582 differ depending on your floating-point implementation, but a common
15583 case is that @command{seq} works with integers through @math{2^{64}},
15584 and larger integers may not be numerically correct:
15587 $ seq 18446744073709551616 1 18446744073709551618
15588 18446744073709551616
15589 18446744073709551616
15590 18446744073709551618
15593 Be careful when using @command{seq} with outlandish values: otherwise
15594 you may see surprising results, as @command{seq} uses floating point
15595 internally. For example, on the x86 platform, where the internal
15596 representation uses a 64-bit fraction, the command:
15599 seq 1 0.0000000000000000001 1.0000000000000000009
15602 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15607 @node File permissions
15608 @chapter File permissions
15611 @include getdate.texi
15615 @node Opening the software toolbox
15616 @chapter Opening the Software Toolbox
15618 An earlier version of this chapter appeared in
15619 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15620 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15621 It was written by Arnold Robbins.
15624 * Toolbox introduction:: Toolbox introduction
15625 * I/O redirection:: I/O redirection
15626 * The who command:: The @command{who} command
15627 * The cut command:: The @command{cut} command
15628 * The sort command:: The @command{sort} command
15629 * The uniq command:: The @command{uniq} command
15630 * Putting the tools together:: Putting the tools together
15634 @node Toolbox introduction
15635 @unnumberedsec Toolbox Introduction
15637 This month's column is only peripherally related to the GNU Project, in
15638 that it describes a number of the GNU tools on your GNU/Linux system and how they
15639 might be used. What it's really about is the ``Software Tools'' philosophy
15640 of program development and usage.
15642 The software tools philosophy was an important and integral concept
15643 in the initial design and development of Unix (of which Linux and GNU are
15644 essentially clones). Unfortunately, in the modern day press of
15645 Internetworking and flashy GUIs, it seems to have fallen by the
15646 wayside. This is a shame, since it provides a powerful mental model
15647 for solving many kinds of problems.
15649 Many people carry a Swiss Army knife around in their pants pockets (or
15650 purse). A Swiss Army knife is a handy tool to have: it has several knife
15651 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15652 a number of other things on it. For the everyday, small miscellaneous jobs
15653 where you need a simple, general purpose tool, it's just the thing.
15655 On the other hand, an experienced carpenter doesn't build a house using
15656 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15657 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15658 exactly when and where to use each tool; you won't catch him hammering nails
15659 with the handle of his screwdriver.
15661 The Unix developers at Bell Labs were all professional programmers and trained
15662 computer scientists. They had found that while a one-size-fits-all program
15663 might appeal to a user because there's only one program to use, in practice
15668 difficult to write,
15671 difficult to maintain and
15675 difficult to extend to meet new situations.
15678 Instead, they felt that programs should be specialized tools. In short, each
15679 program ``should do one thing well.'' No more and no less. Such programs are
15680 simpler to design, write, and get right---they only do one thing.
15682 Furthermore, they found that with the right machinery for hooking programs
15683 together, that the whole was greater than the sum of the parts. By combining
15684 several special purpose programs, you could accomplish a specific task
15685 that none of the programs was designed for, and accomplish it much more
15686 quickly and easily than if you had to write a special purpose program.
15687 We will see some (classic) examples of this further on in the column.
15688 (An important additional point was that, if necessary, take a detour
15689 and build any software tools you may need first, if you don't already
15690 have something appropriate in the toolbox.)
15692 @node I/O redirection
15693 @unnumberedsec I/O Redirection
15695 Hopefully, you are familiar with the basics of I/O redirection in the
15696 shell, in particular the concepts of ``standard input,'' ``standard output,''
15697 and ``standard error''. Briefly, ``standard input'' is a data source, where
15698 data comes from. A program should not need to either know or care if the
15699 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15700 card reader. Similarly, ``standard output'' is a data sink, where data goes
15701 to. The program should neither know nor care where this might be.
15702 Programs that only read their standard input, do something to the data,
15703 and then send it on, are called @dfn{filters}, by analogy to filters in a
15706 With the Unix shell, it's very easy to set up data pipelines:
15709 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15712 We start out by creating the raw data; each filter applies some successive
15713 transformation to the data, until by the time it comes out of the pipeline,
15714 it is in the desired form.
15716 This is fine and good for standard input and standard output. Where does the
15717 standard error come in to play? Well, think about @command{filter1} in
15718 the pipeline above. What happens if it encounters an error in the data it
15719 sees? If it writes an error message to standard output, it will just
15720 disappear down the pipeline into @command{filter2}'s input, and the
15721 user will probably never see it. So programs need a place where they can send
15722 error messages so that the user will notice them. This is standard error,
15723 and it is usually connected to your console or window, even if you have
15724 redirected standard output of your program away from your screen.
15726 For filter programs to work together, the format of the data has to be
15727 agreed upon. The most straightforward and easiest format to use is simply
15728 lines of text. Unix data files are generally just streams of bytes, with
15729 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15730 conventionally called a ``newline'' in the Unix literature. (This is
15731 @code{'\n'} if you're a C programmer.) This is the format used by all
15732 the traditional filtering programs. (Many earlier operating systems
15733 had elaborate facilities and special purpose programs for managing
15734 binary data. Unix has always shied away from such things, under the
15735 philosophy that it's easiest to simply be able to view and edit your
15736 data with a text editor.)
15738 OK, enough introduction. Let's take a look at some of the tools, and then
15739 we'll see how to hook them together in interesting ways. In the following
15740 discussion, we will only present those command line options that interest
15741 us. As you should always do, double check your system documentation
15742 for the full story.
15744 @node The who command
15745 @unnumberedsec The @command{who} Command
15747 The first program is the @command{who} command. By itself, it generates a
15748 list of the users who are currently logged in. Although I'm writing
15749 this on a single-user system, we'll pretend that several people are
15754 @print{} arnold console Jan 22 19:57
15755 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15756 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15757 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15760 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15761 There are three people logged in, and I am logged in twice. On traditional
15762 Unix systems, user names are never more than eight characters long. This
15763 little bit of trivia will be useful later. The output of @command{who} is nice,
15764 but the data is not all that exciting.
15766 @node The cut command
15767 @unnumberedsec The @command{cut} Command
15769 The next program we'll look at is the @command{cut} command. This program
15770 cuts out columns or fields of input data. For example, we can tell it
15771 to print just the login name and full name from the @file{/etc/passwd}
15772 file. The @file{/etc/passwd} file has seven fields, separated by
15776 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15779 To get the first and fifth fields, we would use @command{cut} like this:
15782 $ cut -d: -f1,5 /etc/passwd
15783 @print{} root:Operator
15785 @print{} arnold:Arnold D. Robbins
15786 @print{} miriam:Miriam A. Robbins
15790 With the @option{-c} option, @command{cut} will cut out specific characters
15791 (i.e., columns) in the input lines. This is useful for input data
15792 that has fixed width fields, and does not have a field separator. For
15793 example, list the Monday dates for the current month:
15795 @c Is using cal ok? Looked at gcal, but I don't like it.
15806 @node The sort command
15807 @unnumberedsec The @command{sort} Command
15809 Next we'll look at the @command{sort} command. This is one of the most
15810 powerful commands on a Unix-style system; one that you will often find
15811 yourself using when setting up fancy data plumbing.
15814 command reads and sorts each file named on the command line. It then
15815 merges the sorted data and writes it to standard output. It will read
15816 standard input if no files are given on the command line (thus
15817 making it into a filter). The sort is based on the character collating
15818 sequence or based on user-supplied ordering criteria.
15821 @node The uniq command
15822 @unnumberedsec The @command{uniq} Command
15824 Finally (at least for now), we'll look at the @command{uniq} program. When
15825 sorting data, you will often end up with duplicate lines, lines that
15826 are identical. Usually, all you need is one instance of each line.
15827 This is where @command{uniq} comes in. The @command{uniq} program reads its
15828 standard input. It prints only one
15829 copy of each repeated line. It does have several options. Later on,
15830 we'll use the @option{-c} option, which prints each unique line, preceded
15831 by a count of the number of times that line occurred in the input.
15834 @node Putting the tools together
15835 @unnumberedsec Putting the Tools Together
15837 Now, let's suppose this is a large ISP server system with dozens of users
15838 logged in. The management wants the system administrator to write a program that will
15839 generate a sorted list of logged in users. Furthermore, even if a user
15840 is logged in multiple times, his or her name should only show up in the
15843 The administrator could sit down with the system documentation and write a C
15844 program that did this. It would take perhaps a couple of hundred lines
15845 of code and about two hours to write it, test it, and debug it.
15846 However, knowing the software toolbox, the administrator can instead start out
15847 by generating just a list of logged on users:
15857 Next, sort the list:
15860 $ who | cut -c1-8 | sort
15867 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15870 $ who | cut -c1-8 | sort | uniq
15876 The @command{sort} command actually has a @option{-u} option that does what
15877 @command{uniq} does. However, @command{uniq} has other uses for which one
15878 cannot substitute @samp{sort -u}.
15880 The administrator puts this pipeline into a shell script, and makes it available for
15881 all the users on the system (@samp{#} is the system administrator,
15882 or @code{root}, prompt):
15885 # cat > /usr/local/bin/listusers
15886 who | cut -c1-8 | sort | uniq
15888 # chmod +x /usr/local/bin/listusers
15891 There are four major points to note here. First, with just four
15892 programs, on one command line, the administrator was able to save about two
15893 hours worth of work. Furthermore, the shell pipeline is just about as
15894 efficient as the C program would be, and it is much more efficient in
15895 terms of programmer time. People time is much more expensive than
15896 computer time, and in our modern ``there's never enough time to do
15897 everything'' society, saving two hours of programmer time is no mean
15900 Second, it is also important to emphasize that with the
15901 @emph{combination} of the tools, it is possible to do a special
15902 purpose job never imagined by the authors of the individual programs.
15904 Third, it is also valuable to build up your pipeline in stages, as we did here.
15905 This allows you to view the data at each stage in the pipeline, which helps
15906 you acquire the confidence that you are indeed using these tools correctly.
15908 Finally, by bundling the pipeline in a shell script, other users can use
15909 your command, without having to remember the fancy plumbing you set up for
15910 them. In terms of how you run them, shell scripts and compiled programs are
15913 After the previous warm-up exercise, we'll look at two additional, more
15914 complicated pipelines. For them, we need to introduce two more tools.
15916 The first is the @command{tr} command, which stands for ``transliterate.''
15917 The @command{tr} command works on a character-by-character basis, changing
15918 characters. Normally it is used for things like mapping upper case to
15922 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15923 @print{} this example has mixed case!
15926 There are several options of interest:
15930 work on the complement of the listed characters, i.e.,
15931 operations apply to characters not in the given set
15934 delete characters in the first set from the output
15937 squeeze repeated characters in the output into just one character.
15940 We will be using all three options in a moment.
15942 The other command we'll look at is @command{comm}. The @command{comm}
15943 command takes two sorted input files as input data, and prints out the
15944 files' lines in three columns. The output columns are the data lines
15945 unique to the first file, the data lines unique to the second file, and
15946 the data lines that are common to both. The @option{-1}, @option{-2}, and
15947 @option{-3} command line options @emph{omit} the respective columns. (This is
15948 non-intuitive and takes a little getting used to.) For example:
15970 The file name @file{-} tells @command{comm} to read standard input
15971 instead of a regular file.
15973 Now we're ready to build a fancy pipeline. The first application is a word
15974 frequency counter. This helps an author determine if he or she is over-using
15977 The first step is to change the case of all the letters in our input file
15978 to one case. ``The'' and ``the'' are the same word when doing counting.
15981 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
15984 The next step is to get rid of punctuation. Quoted words and unquoted words
15985 should be treated identically; it's easiest to just get the punctuation out of
15989 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
15992 The second @command{tr} command operates on the complement of the listed
15993 characters, which are all the letters, the digits, the underscore, and
15994 the blank. The @samp{\n} represents the newline character; it has to
15995 be left alone. (The @acronym{ASCII} tab character should also be included for
15996 good measure in a production script.)
15998 At this point, we have data consisting of words separated by blank space.
15999 The words only contain alphanumeric characters (and the underscore). The
16000 next step is break the data apart so that we have one word per line. This
16001 makes the counting operation much easier, as we will see shortly.
16004 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16005 > tr -s ' ' '\n' | ...
16008 This command turns blanks into newlines. The @option{-s} option squeezes
16009 multiple newline characters in the output into just one. This helps us
16010 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16011 This is what the shell prints when it notices you haven't finished
16012 typing in all of a command.)
16014 We now have data consisting of one word per line, no punctuation, all one
16015 case. We're ready to count each word:
16018 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16019 > tr -s ' ' '\n' | sort | uniq -c | ...
16022 At this point, the data might look something like this:
16035 The output is sorted by word, not by count! What we want is the most
16036 frequently used words first. Fortunately, this is easy to accomplish,
16037 with the help of two more @command{sort} options:
16041 do a numeric sort, not a textual one
16044 reverse the order of the sort
16047 The final pipeline looks like this:
16050 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16051 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16060 Whew! That's a lot to digest. Yet, the same principles apply. With six
16061 commands, on two lines (really one long one split for convenience), we've
16062 created a program that does something interesting and useful, in much
16063 less time than we could have written a C program to do the same thing.
16065 A minor modification to the above pipeline can give us a simple spelling
16066 checker! To determine if you've spelled a word correctly, all you have to
16067 do is look it up in a dictionary. If it is not there, then chances are
16068 that your spelling is incorrect. So, we need a dictionary.
16069 The conventional location for a dictionary is @file{/usr/dict/words}.
16070 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16071 revision of this article.}
16072 this is a sorted, 45,402 word dictionary.
16074 Now, how to compare our file with the dictionary? As before, we generate
16075 a sorted list of words, one per line:
16078 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16079 > tr -s ' ' '\n' | sort -u | ...
16082 Now, all we need is a list of words that are @emph{not} in the
16083 dictionary. Here is where the @command{comm} command comes in.
16086 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16087 > tr -s ' ' '\n' | sort -u |
16088 > comm -23 - /usr/dict/words
16091 The @option{-2} and @option{-3} options eliminate lines that are only in the
16092 dictionary (the second file), and lines that are in both files. Lines
16093 only in the first file (standard input, our stream of words), are
16094 words that are not in the dictionary. These are likely candidates for
16095 spelling errors. This pipeline was the first cut at a production
16096 spelling checker on Unix.
16098 There are some other tools that deserve brief mention.
16102 search files for text that matches a regular expression
16105 count lines, words, characters
16108 a T-fitting for data pipes, copies data to files and to standard output
16111 the stream editor, an advanced tool
16114 a data manipulation language, another advanced tool
16117 The software tools philosophy also espoused the following bit of
16118 advice: ``Let someone else do the hard part.'' This means, take
16119 something that gives you most of what you need, and then massage it the
16120 rest of the way until it's in the form that you want.
16126 Each program should do one thing well. No more, no less.
16129 Combining programs with appropriate plumbing leads to results where
16130 the whole is greater than the sum of the parts. It also leads to novel
16131 uses of programs that the authors might never have imagined.
16134 Programs should never print extraneous header or trailer data, since these
16135 could get sent on down a pipeline. (A point we didn't mention earlier.)
16138 Let someone else do the hard part.
16141 Know your toolbox! Use each program appropriately. If you don't have an
16142 appropriate tool, build one.
16145 As of this writing, all the programs we've discussed are available via
16146 anonymous @command{ftp} from: @*
16147 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16148 be more recent versions available now.)
16150 None of what I have presented in this column is new. The Software Tools
16151 philosophy was first introduced in the book @cite{Software Tools}, by
16152 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16153 This book showed how to write and use software tools. It was written in
16154 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16155 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16156 was. The last chapter presented a @command{ratfor} to FORTRAN
16157 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16158 lot like C; if you know C, you won't have any problem following the
16161 In 1981, the book was updated and made available as @cite{Software Tools
16162 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16163 still in print and are well worth
16164 reading if you're a programmer. They certainly made a major change in
16165 how I view programming.
16167 The programs in both books are available from
16168 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16169 For a number of years, there was an active
16170 Software Tools Users Group, whose members had ported the original
16171 @command{ratfor} programs to essentially every computer system with a
16172 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16173 as Unix began to spread beyond universities.
16175 With the current proliferation of GNU code and other clones of Unix programs,
16176 these programs now receive little attention; modern C versions are
16177 much more efficient and do more than these programs do. Nevertheless, as
16178 exposition of good programming style, and evangelism for a still-valuable
16179 philosophy, these books are unparalleled, and I recommend them highly.
16181 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16182 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16184 @node GNU Free Documentation License
16185 @appendix GNU Free Documentation License
16189 @node Concept index
16196 @c Local variables:
16197 @c texinfo-column-for-description: 32