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. This option is ignored
1498 if @option{-b} is in effect.
1501 @itemx --squeeze-blank
1503 @opindex --squeeze-blank
1504 @cindex squeezing empty lines
1505 Suppress repeated adjacent empty lines; output just one empty line
1510 Equivalent to @option{-vT}.
1515 @opindex --show-tabs
1516 Display TAB characters as @samp{^I}.
1520 Ignored; for @acronym{POSIX} compatibility.
1523 @itemx --show-nonprinting
1525 @opindex --show-nonprinting
1526 Display control characters except for LFD and TAB using
1527 @samp{^} notation and precede characters that have the high bit set with
1532 On systems like MS-DOS that distinguish between text and binary files,
1533 @command{cat} normally reads and writes in binary mode. However,
1534 @command{cat} reads in text mode if one of the options
1535 @option{-bensAE} is used or if @command{cat} is reading from standard
1536 input and standard input is a terminal. Similarly, @command{cat}
1537 writes in text mode if one of the options @option{-bensAE} is used or
1538 if standard output is a terminal.
1545 # Output f's contents, then standard input, then g's contents.
1548 # Copy standard input to standard output.
1553 @node tac invocation
1554 @section @command{tac}: Concatenate and write files in reverse
1557 @cindex reversing files
1559 @command{tac} copies each @var{file} (@samp{-} means standard input), or
1560 standard input if none are given, to standard output, reversing the
1561 records (lines by default) in each separately. Synopsis:
1564 tac [@var{option}]@dots{} [@var{file}]@dots{}
1567 @dfn{Records} are separated by instances of a string (newline by
1568 default). By default, this separator string is attached to the end of
1569 the record that it follows in the file.
1571 The program accepts the following options. Also see @ref{Common options}.
1579 The separator is attached to the beginning of the record that it
1580 precedes in the file.
1586 Treat the separator string as a regular expression. Users of @command{tac}
1587 on MS-DOS/MS-Windows should note that, since @command{tac} reads files in
1588 binary mode, each line of a text file might end with a CR/LF pair
1589 instead of the Unix-style LF.
1591 @item -s @var{separator}
1592 @itemx --separator=@var{separator}
1594 @opindex --separator
1595 Use @var{separator} as the record separator, instead of newline.
1603 @section @command{nl}: Number lines and write files
1606 @cindex numbering lines
1607 @cindex line numbering
1609 @command{nl} writes each @var{file} (@samp{-} means standard input), or
1610 standard input if none are given, to standard output, with line numbers
1611 added to some or all of the lines. Synopsis:
1614 nl [@var{option}]@dots{} [@var{file}]@dots{}
1617 @cindex logical pages, numbering on
1618 @command{nl} decomposes its input into (logical) pages; by default, the
1619 line number is reset to 1 at the top of each logical page. @command{nl}
1620 treats all of the input files as a single document; it does not reset
1621 line numbers or logical pages between files.
1623 @cindex headers, numbering
1624 @cindex body, numbering
1625 @cindex footers, numbering
1626 A logical page consists of three sections: header, body, and footer.
1627 Any of the sections can be empty. Each can be numbered in a different
1628 style from the others.
1630 The beginnings of the sections of logical pages are indicated in the
1631 input file by a line containing exactly one of these delimiter strings:
1642 The two characters from which these strings are made can be changed from
1643 @samp{\} and @samp{:} via options (see below), but the pattern and
1644 length of each string cannot be changed.
1646 A section delimiter is replaced by an empty line on output. Any text
1647 that comes before the first section delimiter string in the input file
1648 is considered to be part of a body section, so @command{nl} treats a
1649 file that contains no section delimiters as a single body section.
1651 The program accepts the following options. Also see @ref{Common options}.
1655 @item -b @var{style}
1656 @itemx --body-numbering=@var{style}
1658 @opindex --body-numbering
1659 Select the numbering style for lines in the body section of each
1660 logical page. When a line is not numbered, the current line number
1661 is not incremented, but the line number separator character is still
1662 prepended to the line. The styles are:
1668 number only nonempty lines (default for body),
1670 do not number lines (default for header and footer),
1672 number only lines that contain a match for the basic regular
1673 expression @var{bre}.
1674 @xref{Regular Expressions, , Regular Expressions, grep, The GNU Grep Manual}.
1678 @itemx --section-delimiter=@var{cd}
1680 @opindex --section-delimiter
1681 @cindex section delimiters of pages
1682 Set the section delimiter characters to @var{cd}; default is
1683 @samp{\:}. If only @var{c} is given, the second remains @samp{:}.
1684 (Remember to protect @samp{\} or other metacharacters from shell
1685 expansion with quotes or extra backslashes.)
1687 @item -f @var{style}
1688 @itemx --footer-numbering=@var{style}
1690 @opindex --footer-numbering
1691 Analogous to @option{--body-numbering}.
1693 @item -h @var{style}
1694 @itemx --header-numbering=@var{style}
1696 @opindex --header-numbering
1697 Analogous to @option{--body-numbering}.
1699 @item -i @var{number}
1700 @itemx --line-increment=@var{number}
1702 @opindex --line-increment
1703 Increment line numbers by @var{number} (default 1).
1705 @item -l @var{number}
1706 @itemx --join-blank-lines=@var{number}
1708 @opindex --join-blank-lines
1709 @cindex empty lines, numbering
1710 @cindex blank lines, numbering
1711 Consider @var{number} (default 1) consecutive empty lines to be one
1712 logical line for numbering, and only number the last one. Where fewer
1713 than @var{number} consecutive empty lines occur, do not number them.
1714 An empty line is one that contains no characters, not even spaces
1717 @item -n @var{format}
1718 @itemx --number-format=@var{format}
1720 @opindex --number-format
1721 Select the line numbering format (default is @code{rn}):
1725 @opindex ln @r{format for @command{nl}}
1726 left justified, no leading zeros;
1728 @opindex rn @r{format for @command{nl}}
1729 right justified, no leading zeros;
1731 @opindex rz @r{format for @command{nl}}
1732 right justified, leading zeros.
1736 @itemx --no-renumber
1738 @opindex --no-renumber
1739 Do not reset the line number at the start of a logical page.
1741 @item -s @var{string}
1742 @itemx --number-separator=@var{string}
1744 @opindex --number-separator
1745 Separate the line number from the text line in the output with
1746 @var{string} (default is the TAB character).
1748 @item -v @var{number}
1749 @itemx --starting-line-number=@var{number}
1751 @opindex --starting-line-number
1752 Set the initial line number on each logical page to @var{number} (default 1).
1754 @item -w @var{number}
1755 @itemx --number-width=@var{number}
1757 @opindex --number-width
1758 Use @var{number} characters for line numbers (default 6).
1766 @section @command{od}: Write files in octal or other formats
1769 @cindex octal dump of files
1770 @cindex hex dump of files
1771 @cindex ASCII dump of files
1772 @cindex file contents, dumping unambiguously
1774 @command{od} writes an unambiguous representation of each @var{file}
1775 (@samp{-} means standard input), or standard input if none are given.
1779 od [@var{option}]@dots{} [@var{file}]@dots{}
1780 od [-abcdfilosx]@dots{} [@var{file}] [[+]@var{offset}[.][b]]
1781 od [@var{option}]@dots{} --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
1784 Each line of output consists of the offset in the input, followed by
1785 groups of data from the file. By default, @command{od} prints the offset in
1786 octal, and each group of file data is a C @code{short int}'s worth of input
1787 printed as a single octal number.
1789 If @var{offset} is given, it specifies how many input bytes to skip
1790 before formatting and writing. By default, it is interpreted as an
1791 octal number, but the optional trailing decimal point causes it to be
1792 interpreted as decimal. If no decimal is specified and the offset
1793 begins with @samp{0x} or @samp{0X} it is interpreted as a hexadecimal
1794 number. If there is a trailing @samp{b}, the number of bytes skipped
1795 will be @var{offset} multiplied by 512.
1797 If a command is of both the first and second forms, the second form is
1798 assumed if the last operand begins with @samp{+} or (if there are two
1799 operands) a digit. For example, in @samp{od foo 10} and @samp{od +10}
1800 the @samp{10} is an offset, whereas in @samp{od 10} the @samp{10} is a
1803 The program accepts the following options. Also see @ref{Common options}.
1807 @item -A @var{radix}
1808 @itemx --address-radix=@var{radix}
1810 @opindex --address-radix
1811 @cindex radix for file offsets
1812 @cindex file offset radix
1813 Select the base in which file offsets are printed. @var{radix} can
1814 be one of the following:
1824 none (do not print offsets).
1827 The default is octal.
1829 @item -j @var{bytes}
1830 @itemx --skip-bytes=@var{bytes}
1832 @opindex --skip-bytes
1833 Skip @var{bytes} input bytes before formatting and writing. If
1834 @var{bytes} begins with @samp{0x} or @samp{0X}, it is interpreted in
1835 hexadecimal; otherwise, if it begins with @samp{0}, in octal; otherwise,
1837 @multiplierSuffixes{bytes}
1839 @item -N @var{bytes}
1840 @itemx --read-bytes=@var{bytes}
1842 @opindex --read-bytes
1843 Output at most @var{bytes} bytes of the input. Prefixes and suffixes on
1844 @code{bytes} are interpreted as for the @option{-j} option.
1846 @item -S @var{bytes}
1847 @itemx --strings[=@var{bytes}]
1850 @cindex string constants, outputting
1851 Instead of the normal output, output only @dfn{string constants}: at
1852 least @var{bytes} consecutive @acronym{ASCII} graphic characters,
1853 followed by a zero byte (@acronym{ASCII} @sc{nul}).
1854 Prefixes and suffixes on @code{bytes} are interpreted as for the
1857 If @var{n} is omitted with @option{--strings}, the default is 3.
1860 @itemx --format=@var{type}
1863 Select the format in which to output the file data. @var{type} is a
1864 string of one or more of the below type indicator characters. If you
1865 include more than one type indicator character in a single @var{type}
1866 string, or use this option more than once, @command{od} writes one copy
1867 of each output line using each of the data types that you specified,
1868 in the order that you specified.
1870 Adding a trailing ``z'' to any type specification appends a display
1871 of the @acronym{ASCII} character representation of the printable characters
1872 to the output line generated by the type specification.
1876 named character, ignoring high-order bit
1878 @acronym{ASCII} character or backslash escape,
1891 The type @code{a} outputs things like @samp{sp} for space, @samp{nl} for
1892 newline, and @samp{nul} for a zero byte. Only the least significant
1893 seven bits of each byte is used; the high-order bit is ignored.
1894 Type @code{c} outputs
1895 @samp{ }, @samp{\n}, and @code{\0}, respectively.
1898 Except for types @samp{a} and @samp{c}, you can specify the number
1899 of bytes to use in interpreting each number in the given data type
1900 by following the type indicator character with a decimal integer.
1901 Alternately, you can specify the size of one of the C compiler's
1902 built-in data types by following the type indicator character with
1903 one of the following characters. For integers (@samp{d}, @samp{o},
1904 @samp{u}, @samp{x}):
1917 For floating point (@code{f}):
1929 @itemx --output-duplicates
1931 @opindex --output-duplicates
1932 Output consecutive lines that are identical. By default, when two or
1933 more consecutive output lines would be identical, @command{od} outputs only
1934 the first line, and puts just an asterisk on the following line to
1935 indicate the elision.
1938 @itemx --width[=@var{n}]
1941 Dump @code{n} input bytes per output line. This must be a multiple of
1942 the least common multiple of the sizes associated with the specified
1945 If this option is not given at all, the default is 16. If @var{n} is
1946 omitted, the default is 32.
1950 The next several options are shorthands for format specifications.
1951 @sc{gnu} @command{od} accepts any combination of shorthands and format
1952 specification options. These options accumulate.
1958 Output as named characters. Equivalent to @samp{-t a}.
1962 Output as octal bytes. Equivalent to @samp{-t o1}.
1966 Output as @acronym{ASCII} characters or backslash escapes. Equivalent to
1971 Output as unsigned decimal two-byte units. Equivalent to @samp{-t u2}.
1975 Output as floats. Equivalent to @samp{-t fF}.
1979 Output as decimal ints. Equivalent to @samp{-t dI}.
1983 Output as decimal long ints. Equivalent to @samp{-t dL}.
1987 Output as octal two-byte units. Equivalent to @option{-t o2}.
1991 Output as decimal two-byte units. Equivalent to @option{-t d2}.
1995 Output as hexadecimal two-byte units. Equivalent to @samp{-t x2}.
1998 @opindex --traditional
1999 Recognize the non-option label argument that traditional @command{od}
2000 accepted. The following syntax:
2003 od --traditional [@var{file}] [[+]@var{offset}[.][b] [[+]@var{label}[.][b]]]
2007 can be used to specify at most one file and optional arguments
2008 specifying an offset and a pseudo-start address, @var{label}.
2009 The @var{label} argument is interpreted
2010 just like @var{offset}, but it specifies an initial pseudo-address. The
2011 pseudo-addresses are displayed in parentheses following any normal
2018 @node base64 invocation
2019 @section @command{base64}: Transform data into printable data
2022 @cindex base64 encoding
2024 @command{base64} transforms data read from a file, or standard input,
2025 into (or from) base64 encoded form. The base64 encoded form uses
2026 printable @acronym{ASCII} characters to represent binary data.
2030 base64 [@var{option}]@dots{} [@var{file}]
2031 base64 --decode [@var{option}]@dots{} [@var{file}]
2034 The base64 encoding expands data to roughly 133% of the original.
2035 The format conforms to
2036 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc4648.txt, RFC 4648}.
2038 The program accepts the following options. Also see @ref{Common options}.
2043 @itemx --wrap=@var{cols}
2047 @cindex column to wrap data after
2048 During encoding, wrap lines after @var{cols} characters. This must be
2051 The default is to wrap after 76 characters. Use the value 0 to
2052 disable line wrapping altogether.
2058 @cindex Decode base64 data
2059 @cindex Base64 decoding
2060 Change the mode of operation, from the default of encoding data, to
2061 decoding data. Input is expected to be base64 encoded data, and the
2062 output will be the original data.
2065 @itemx --ignore-garbage
2067 @opindex --ignore-garbage
2068 @cindex Ignore garbage in base64 stream
2069 When decoding, newlines are always accepted.
2070 During decoding, ignore unrecognized bytes,
2071 to permit distorted data to be decoded.
2078 @node Formatting file contents
2079 @chapter Formatting file contents
2081 @cindex formatting file contents
2083 These commands reformat the contents of files.
2086 * fmt invocation:: Reformat paragraph text.
2087 * pr invocation:: Paginate or columnate files for printing.
2088 * fold invocation:: Wrap input lines to fit in specified width.
2092 @node fmt invocation
2093 @section @command{fmt}: Reformat paragraph text
2096 @cindex reformatting paragraph text
2097 @cindex paragraphs, reformatting
2098 @cindex text, reformatting
2100 @command{fmt} fills and joins lines to produce output lines of (at most)
2101 a given number of characters (75 by default). Synopsis:
2104 fmt [@var{option}]@dots{} [@var{file}]@dots{}
2107 @command{fmt} reads from the specified @var{file} arguments (or standard
2108 input if none are given), and writes to standard output.
2110 By default, blank lines, spaces between words, and indentation are
2111 preserved in the output; successive input lines with different
2112 indentation are not joined; tabs are expanded on input and introduced on
2115 @cindex line-breaking
2116 @cindex sentences and line-breaking
2117 @cindex Knuth, Donald E.
2118 @cindex Plass, Michael F.
2119 @command{fmt} prefers breaking lines at the end of a sentence, and tries to
2120 avoid line breaks after the first word of a sentence or before the last
2121 word of a sentence. A @dfn{sentence break} is defined as either the end
2122 of a paragraph or a word ending in any of @samp{.?!}, followed by two
2123 spaces or end of line, ignoring any intervening parentheses or quotes.
2124 Like @TeX{}, @command{fmt} reads entire ``paragraphs'' before choosing line
2125 breaks; the algorithm is a variant of that given by Donald E. Knuth
2126 and Michael F. Plass in ``Breaking Paragraphs Into Lines'',
2127 @cite{Software---Practice & Experience} @b{11}, 11 (November 1981),
2130 The program accepts the following options. Also see @ref{Common options}.
2135 @itemx --crown-margin
2137 @opindex --crown-margin
2138 @cindex crown margin
2139 @dfn{Crown margin} mode: preserve the indentation of the first two
2140 lines within a paragraph, and align the left margin of each subsequent
2141 line with that of the second line.
2144 @itemx --tagged-paragraph
2146 @opindex --tagged-paragraph
2147 @cindex tagged paragraphs
2148 @dfn{Tagged paragraph} mode: like crown margin mode, except that if
2149 indentation of the first line of a paragraph is the same as the
2150 indentation of the second, the first line is treated as a one-line
2156 @opindex --split-only
2157 Split lines only. Do not join short lines to form longer ones. This
2158 prevents sample lines of code, and other such ``formatted'' text from
2159 being unduly combined.
2162 @itemx --uniform-spacing
2164 @opindex --uniform-spacing
2165 Uniform spacing. Reduce spacing between words to one space, and spacing
2166 between sentences to two spaces.
2169 @itemx -w @var{width}
2170 @itemx --width=@var{width}
2171 @opindex -@var{width}
2174 Fill output lines up to @var{width} characters (default 75). @command{fmt}
2175 initially tries to make lines about 7% shorter than this, to give it
2176 room to balance line lengths.
2178 @item -p @var{prefix}
2179 @itemx --prefix=@var{prefix}
2180 Only lines beginning with @var{prefix} (possibly preceded by whitespace)
2181 are subject to formatting. The prefix and any preceding whitespace are
2182 stripped for the formatting and then re-attached to each formatted output
2183 line. One use is to format certain kinds of program comments, while
2184 leaving the code unchanged.
2192 @section @command{pr}: Paginate or columnate files for printing
2195 @cindex printing, preparing files for
2196 @cindex multicolumn output, generating
2197 @cindex merging files in parallel
2199 @command{pr} writes each @var{file} (@samp{-} means standard input), or
2200 standard input if none are given, to standard output, paginating and
2201 optionally outputting in multicolumn format; optionally merges all
2202 @var{file}s, printing all in parallel, one per column. Synopsis:
2205 pr [@var{option}]@dots{} [@var{file}]@dots{}
2209 By default, a 5-line header is printed at each page: two blank lines;
2210 a line with the date, the file name, and the page count; and two more
2211 blank lines. A footer of five blank lines is also printed.
2212 The default @var{page_length} is 66
2213 lines. The default number of text lines is therefore 56.
2214 The text line of the header takes the form
2215 @samp{@var{date} @var{string} @var{page}}, with spaces inserted around
2216 @var{string} so that the line takes up the full @var{page_width}. Here,
2217 @var{date} is the date (see the @option{-D} or @option{--date-format}
2218 option for details), @var{string} is the centered header string, and
2219 @var{page} identifies the page number. The @env{LC_MESSAGES} locale
2220 category affects the spelling of @var{page}; in the default C locale, it
2221 is @samp{Page @var{number}} where @var{number} is the decimal page
2224 Form feeds in the input cause page breaks in the output. Multiple form
2225 feeds produce empty pages.
2227 Columns are of equal width, separated by an optional string (default
2228 is @samp{space}). For multicolumn output, lines will always be truncated to
2229 @var{page_width} (default 72), unless you use the @option{-J} option.
2231 column output no line truncation occurs by default. Use @option{-W} option to
2232 truncate lines in that case.
2234 The following changes were made in version 1.22i and apply to later
2235 versions of @command{pr}:
2236 @c FIXME: this whole section here sounds very awkward to me. I
2237 @c made a few small changes, but really it all needs to be redone. - Brian
2238 @c OK, I fixed another sentence or two, but some of it I just don't understand.
2243 Some small @var{letter options} (@option{-s}, @option{-w}) have been
2244 redefined for better @acronym{POSIX} compliance. The output of some further
2245 cases has been adapted to other Unix systems. These changes are not
2246 compatible with earlier versions of the program.
2249 Some @var{new capital letter} options (@option{-J}, @option{-S}, @option{-W})
2250 have been introduced to turn off unexpected interferences of small letter
2251 options. The @option{-N} option and the second argument @var{last_page}
2252 of @samp{+FIRST_PAGE} offer more flexibility. The detailed handling of
2253 form feeds set in the input files requires the @option{-T} option.
2256 Capital letter options override small letter ones.
2259 Some of the option-arguments (compare @option{-s}, @option{-e},
2260 @option{-i}, @option{-n}) cannot be specified as separate arguments from the
2261 preceding option letter (already stated in the @acronym{POSIX} specification).
2264 The program accepts the following options. Also see @ref{Common options}.
2268 @item +@var{first_page}[:@var{last_page}]
2269 @itemx --pages=@var{first_page}[:@var{last_page}]
2270 @c The two following @opindex lines evoke warnings because they contain `:'
2271 @c The `info' spec does not permit that. If we use those lines, we end
2272 @c up with truncated index entries that don't work.
2273 @c @opindex +@var{first_page}[:@var{last_page}]
2274 @c @opindex --pages=@var{first_page}[:@var{last_page}]
2275 @opindex +@var{page_range}
2276 @opindex --pages=@var{page_range}
2277 Begin printing with page @var{first_page} and stop with @var{last_page}.
2278 Missing @samp{:@var{last_page}} implies end of file. While estimating
2279 the number of skipped pages each form feed in the input file results
2280 in a new page. Page counting with and without @samp{+@var{first_page}}
2281 is identical. By default, counting starts with the first page of input
2282 file (not first page printed). Line numbering may be altered by @option{-N}
2286 @itemx --columns=@var{column}
2287 @opindex -@var{column}
2289 @cindex down columns
2290 With each single @var{file}, produce @var{column} columns of output
2291 (default is 1) and print columns down, unless @option{-a} is used. The
2292 column width is automatically decreased as @var{column} increases; unless
2293 you use the @option{-W/-w} option to increase @var{page_width} as well.
2294 This option might well cause some lines to be truncated. The number of
2295 lines in the columns on each page are balanced. The options @option{-e}
2296 and @option{-i} are on for multiple text-column output. Together with
2297 @option{-J} option column alignment and line truncation is turned off.
2298 Lines of full length are joined in a free field format and @option{-S}
2299 option may set field separators. @option{-@var{column}} may not be used
2300 with @option{-m} option.
2306 @cindex across columns
2307 With each single @var{file}, print columns across rather than down. The
2308 @option{-@var{column}} option must be given with @var{column} greater than one.
2309 If a line is too long to fit in a column, it is truncated.
2312 @itemx --show-control-chars
2314 @opindex --show-control-chars
2315 Print control characters using hat notation (e.g., @samp{^G}); print
2316 other nonprinting characters in octal backslash notation. By default,
2317 nonprinting characters are not changed.
2320 @itemx --double-space
2322 @opindex --double-space
2323 @cindex double spacing
2324 Double space the output.
2326 @item -D @var{format}
2327 @itemx --date-format=@var{format}
2328 @cindex time formats
2329 @cindex formatting times
2330 Format header dates using @var{format}, using the same conventions as
2331 for the command @samp{date +@var{format}}; @xref{date invocation}.
2332 Except for directives, which start with
2333 @samp{%}, characters in @var{format} are printed unchanged. You can use
2334 this option to specify an arbitrary string in place of the header date,
2335 e.g., @option{--date-format="Monday morning"}.
2337 @vindex POSIXLY_CORRECT
2339 The default date format is @samp{%Y-%m-%d %H:%M} (for example,
2340 @samp{2001-12-04 23:59});
2341 but if the @env{POSIXLY_CORRECT} environment variable is set
2342 and the @env{LC_TIME} locale category specifies the @acronym{POSIX}
2343 locale, the default is @samp{%b %e %H:%M %Y} (for example,
2344 @samp{Dec@ @ 4 23:59 2001}.
2347 Time stamps are listed according to the time zone rules specified by
2348 the @env{TZ} environment variable, or by the system default rules if
2349 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
2350 with @env{TZ}, libc, The GNU C Library Reference Manual}.
2352 @item -e[@var{in-tabchar}[@var{in-tabwidth}]]
2353 @itemx --expand-tabs[=@var{in-tabchar}[@var{in-tabwidth}]]
2355 @opindex --expand-tabs
2357 Expand @var{tab}s to spaces on input. Optional argument @var{in-tabchar} is
2358 the input tab character (default is the TAB character). Second optional
2359 argument @var{in-tabwidth} is the input tab character's width (default
2367 @opindex --form-feed
2368 Use a form feed instead of newlines to separate output pages. This does
2369 not alter the default page length of 66 lines.
2371 @item -h @var{header}
2372 @itemx --header=@var{header}
2375 Replace the file name in the header with the centered string @var{header}.
2376 When using the shell, @var{header} should be quoted and should be
2377 separated from @option{-h} by a space.
2379 @item -i[@var{out-tabchar}[@var{out-tabwidth}]]
2380 @itemx --output-tabs[=@var{out-tabchar}[@var{out-tabwidth}]]
2382 @opindex --output-tabs
2384 Replace spaces with @var{tab}s on output. Optional argument @var{out-tabchar}
2385 is the output tab character (default is the TAB character). Second optional
2386 argument @var{out-tabwidth} is the output tab character's width (default
2392 @opindex --join-lines
2393 Merge lines of full length. Used together with the column options
2394 @option{-@var{column}}, @option{-a -@var{column}} or @option{-m}. Turns off
2395 @option{-W/-w} line truncation;
2396 no column alignment used; may be used with
2397 @option{--sep-string[=@var{string}]}. @option{-J} has been introduced
2398 (together with @option{-W} and @option{--sep-string})
2399 to disentangle the old (@acronym{POSIX}-compliant) options @option{-w} and
2400 @option{-s} along with the three column options.
2403 @item -l @var{page_length}
2404 @itemx --length=@var{page_length}
2407 Set the page length to @var{page_length} (default 66) lines, including
2408 the lines of the header [and the footer]. If @var{page_length} is less
2409 than or equal to 10, the header and footer are omitted, as if the
2410 @option{-t} option had been given.
2416 Merge and print all @var{file}s in parallel, one in each column. If a
2417 line is too long to fit in a column, it is truncated, unless the @option{-J}
2418 option is used. @option{--sep-string[=@var{string}]} may be used.
2420 some @var{file}s (form feeds set) produce empty columns, still marked
2421 by @var{string}. The result is a continuous line numbering and column
2422 marking throughout the whole merged file. Completely empty merged pages
2423 show no separators or line numbers. The default header becomes
2424 @samp{@var{date} @var{page}} with spaces inserted in the middle; this
2425 may be used with the @option{-h} or @option{--header} option to fill up
2426 the middle blank part.
2428 @item -n[@var{number-separator}[@var{digits}]]
2429 @itemx --number-lines[=@var{number-separator}[@var{digits}]]
2431 @opindex --number-lines
2432 Provide @var{digits} digit line numbering (default for @var{digits} is
2433 5). With multicolumn output the number occupies the first @var{digits}
2434 column positions of each text column or only each line of @option{-m}
2435 output. With single column output the number precedes each line just as
2436 @option{-m} does. Default counting of the line numbers starts with the
2437 first line of the input file (not the first line printed, compare the
2438 @option{--page} option and @option{-N} option).
2439 Optional argument @var{number-separator} is the character appended to
2440 the line number to separate it from the text followed. The default
2441 separator is the TAB character. In a strict sense a TAB is always
2442 printed with single column output only. The TAB width varies
2443 with the TAB position, e.g., with the left @var{margin} specified
2444 by @option{-o} option. With multicolumn output priority is given to
2445 @samp{equal width of output columns} (a @acronym{POSIX} specification).
2446 The TAB width is fixed to the value of the first column and does
2447 not change with different values of left @var{margin}. That means a
2448 fixed number of spaces is always printed in the place of the
2449 @var{number-separator} TAB. The tabification depends upon the output
2452 @item -N @var{line_number}
2453 @itemx --first-line-number=@var{line_number}
2455 @opindex --first-line-number
2456 Start line counting with the number @var{line_number} at first line of
2457 first page printed (in most cases not the first line of the input file).
2459 @item -o @var{margin}
2460 @itemx --indent=@var{margin}
2463 @cindex indenting lines
2465 Indent each line with a margin @var{margin} spaces wide (default is zero).
2466 The total page width is the size of the margin plus the @var{page_width}
2467 set with the @option{-W/-w} option. A limited overflow may occur with
2468 numbered single column output (compare @option{-n} option).
2471 @itemx --no-file-warnings
2473 @opindex --no-file-warnings
2474 Do not print a warning message when an argument @var{file} cannot be
2475 opened. (The exit status will still be nonzero, however.)
2477 @item -s[@var{char}]
2478 @itemx --separator[=@var{char}]
2480 @opindex --separator
2481 Separate columns by a single character @var{char}. The default for
2482 @var{char} is the TAB character without @option{-w} and @samp{no
2483 character} with @option{-w}. Without @option{-s} the default separator
2484 @samp{space} is set. @option{-s[char]} turns off line truncation of all
2485 three column options (@option{-COLUMN}|@option{-a -COLUMN}|@option{-m}) unless
2486 @option{-w} is set. This is a @acronym{POSIX}-compliant formulation.
2489 @item -S@var{string}
2490 @itemx --sep-string[=@var{string}]
2492 @opindex --sep-string
2493 Use @var{string} to separate output columns. The @option{-S} option doesn't
2494 affect the @option{-W/-w} option, unlike the @option{-s} option which does. It
2495 does not affect line truncation or column alignment.
2496 Without @option{-S}, and with @option{-J}, @command{pr} uses the default output
2498 Without @option{-S} or @option{-J}, @command{pr} uses a @samp{space}
2499 (same as @option{-S"@w{ }"}). @option{--sep-string} with no
2500 @samp{=@var{string}} is equivalent to @option{--sep-string=""}.
2503 @itemx --omit-header
2505 @opindex --omit-header
2506 Do not print the usual header [and footer] on each page, and do not fill
2507 out the bottom of pages (with blank lines or a form feed). No page
2508 structure is produced, but form feeds set in the input files are retained.
2509 The predefined pagination is not changed. @option{-t} or @option{-T} may be
2510 useful together with other options; e.g.: @option{-t -e4}, expand TAB characters
2511 in the input file to 4 spaces but don't make any other changes. Use of
2512 @option{-t} overrides @option{-h}.
2515 @itemx --omit-pagination
2517 @opindex --omit-pagination
2518 Do not print header [and footer]. In addition eliminate all form feeds
2519 set in the input files.
2522 @itemx --show-nonprinting
2524 @opindex --show-nonprinting
2525 Print nonprinting characters in octal backslash notation.
2527 @item -w @var{page_width}
2528 @itemx --width=@var{page_width}
2531 Set page width to @var{page_width} characters for multiple text-column
2532 output only (default for @var{page_width} is 72). @option{-s[CHAR]} turns
2533 off the default page width and any line truncation and column alignment.
2534 Lines of full length are merged, regardless of the column options
2535 set. No @var{page_width} setting is possible with single column output.
2536 A @acronym{POSIX}-compliant formulation.
2538 @item -W @var{page_width}
2539 @itemx --page_width=@var{page_width}
2541 @opindex --page_width
2542 Set the page width to @var{page_width} characters. That's valid with and
2543 without a column option. Text lines are truncated, unless @option{-J}
2544 is used. Together with one of the three column options
2545 (@option{-@var{column}}, @option{-a -@var{column}} or @option{-m}) column
2546 alignment is always used. The separator options @option{-S} or @option{-s}
2547 don't affect the @option{-W} option. Default is 72 characters. Without
2548 @option{-W @var{page_width}} and without any of the column options NO line
2549 truncation is used (defined to keep downward compatibility and to meet
2550 most frequent tasks). That's equivalent to @option{-W 72 -J}. The header
2551 line is never truncated.
2558 @node fold invocation
2559 @section @command{fold}: Wrap input lines to fit in specified width
2562 @cindex wrapping long input lines
2563 @cindex folding long input lines
2565 @command{fold} writes each @var{file} (@option{-} means standard input), or
2566 standard input if none are given, to standard output, breaking long
2570 fold [@var{option}]@dots{} [@var{file}]@dots{}
2573 By default, @command{fold} breaks lines wider than 80 columns. The output
2574 is split into as many lines as necessary.
2576 @cindex screen columns
2577 @command{fold} counts screen columns by default; thus, a tab may count more
2578 than one column, backspace decreases the column count, and carriage
2579 return sets the column to zero.
2581 The program accepts the following options. Also see @ref{Common options}.
2589 Count bytes rather than columns, so that tabs, backspaces, and carriage
2590 returns are each counted as taking up one column, just like other
2597 Break at word boundaries: the line is broken after the last blank before
2598 the maximum line length. If the line contains no such blanks, the line
2599 is broken at the maximum line length as usual.
2601 @item -w @var{width}
2602 @itemx --width=@var{width}
2605 Use a maximum line length of @var{width} columns instead of 80.
2607 For compatibility @command{fold} supports an obsolete option syntax
2608 @option{-@var{width}}. New scripts should use @option{-w @var{width}}
2616 @node Output of parts of files
2617 @chapter Output of parts of files
2619 @cindex output of parts of files
2620 @cindex parts of files, output of
2622 These commands output pieces of the input.
2625 * head invocation:: Output the first part of files.
2626 * tail invocation:: Output the last part of files.
2627 * split invocation:: Split a file into fixed-size pieces.
2628 * csplit invocation:: Split a file into context-determined pieces.
2631 @node head invocation
2632 @section @command{head}: Output the first part of files
2635 @cindex initial part of files, outputting
2636 @cindex first part of files, outputting
2638 @command{head} prints the first part (10 lines by default) of each
2639 @var{file}; it reads from standard input if no files are given or
2640 when given a @var{file} of @option{-}. Synopsis:
2643 head [@var{option}]@dots{} [@var{file}]@dots{}
2646 If more than one @var{file} is specified, @command{head} prints a
2647 one-line header consisting of:
2650 ==> @var{file name} <==
2654 before the output for each @var{file}.
2656 The program accepts the following options. Also see @ref{Common options}.
2661 @itemx --bytes=@var{k}
2664 Print the first @var{k} bytes, instead of initial lines.
2665 However, if @var{k} starts with a @samp{-},
2666 print all but the last @var{k} bytes of each file.
2667 @multiplierSuffixes{k}
2670 @itemx --lines=@var{k}
2673 Output the first @var{k} lines.
2674 However, if @var{k} starts with a @samp{-},
2675 print all but the last @var{k} lines of each file.
2676 Size multiplier suffixes are the same as with the @option{-c} option.
2684 Never print file name headers.
2690 Always print file name headers.
2694 For compatibility @command{head} also supports an obsolete option syntax
2695 @option{-@var{count}@var{options}}, which is recognized only if it is
2696 specified first. @var{count} is a decimal number optionally followed
2697 by a size letter (@samp{b}, @samp{k}, @samp{m}) as in @option{-c}, or
2698 @samp{l} to mean count by lines, or other option letters (@samp{cqv}).
2699 Scripts intended for standard hosts should use @option{-c @var{count}}
2700 or @option{-n @var{count}} instead. If your script must also run on
2701 hosts that support only the obsolete syntax, it is usually simpler to
2702 avoid @command{head}, e.g., by using @samp{sed 5q} instead of
2708 @node tail invocation
2709 @section @command{tail}: Output the last part of files
2712 @cindex last part of files, outputting
2714 @command{tail} prints the last part (10 lines by default) of each
2715 @var{file}; it reads from standard input if no files are given or
2716 when given a @var{file} of @samp{-}. Synopsis:
2719 tail [@var{option}]@dots{} [@var{file}]@dots{}
2722 If more than one @var{file} is specified, @command{tail} prints a
2723 one-line header consisting of:
2726 ==> @var{file name} <==
2730 before the output for each @var{file}.
2732 @cindex BSD @command{tail}
2733 @sc{gnu} @command{tail} can output any amount of data (some other versions of
2734 @command{tail} cannot). It also has no @option{-r} option (print in
2735 reverse), since reversing a file is really a different job from printing
2736 the end of a file; BSD @command{tail} (which is the one with @option{-r}) can
2737 only reverse files that are at most as large as its buffer, which is
2738 typically 32 KiB@. A more reliable and versatile way to reverse files is
2739 the @sc{gnu} @command{tac} command.
2741 The program accepts the following options. Also see @ref{Common options}.
2746 @itemx --bytes=@var{k}
2749 Output the last @var{k} bytes, instead of final lines.
2750 However, if @var{k} starts with a @samp{+}, start printing with the
2751 @var{k}th byte from the start of each file, instead of from the end.
2752 @multiplierSuffixes{k}
2755 @itemx --follow[=@var{how}]
2758 @cindex growing files
2759 @vindex name @r{follow option}
2760 @vindex descriptor @r{follow option}
2761 Loop forever trying to read more characters at the end of the file,
2762 presumably because the file is growing.
2763 If more than one file is given, @command{tail} prints a header whenever it
2764 gets output from a different file, to indicate which file that output is
2767 There are two ways to specify how you'd like to track files with this option,
2768 but that difference is noticeable only when a followed file is removed or
2770 If you'd like to continue to track the end of a growing file even after
2771 it has been unlinked, use @option{--follow=descriptor}. This is the default
2772 behavior, but it is not useful if you're tracking a log file that may be
2773 rotated (removed or renamed, then reopened). In that case, use
2774 @option{--follow=name} to track the named file, perhaps by reopening it
2775 periodically to see if it has been removed and recreated by some other program.
2776 Note that the inotify-based implementation handles this case without
2777 the need for any periodic reopening.
2779 No matter which method you use, if the tracked file is determined to have
2780 shrunk, @command{tail} prints a message saying the file has been truncated
2781 and resumes tracking the end of the file from the newly-determined endpoint.
2783 When a file is removed, @command{tail}'s behavior depends on whether it is
2784 following the name or the descriptor. When following by name, tail can
2785 detect that a file has been removed and gives a message to that effect,
2786 and if @option{--retry} has been specified it will continue checking
2787 periodically to see if the file reappears.
2788 When following a descriptor, tail does not detect that the file has
2789 been unlinked or renamed and issues no message; even though the file
2790 may no longer be accessible via its original name, it may still be
2793 The option values @samp{descriptor} and @samp{name} may be specified only
2794 with the long form of the option, not with @option{-f}.
2796 The @option{-f} option is ignored if
2797 no @var{file} operand is specified and standard input is a FIFO or a pipe.
2798 Likewise, the @option{-f} option has no effect for any
2799 operand specified as @samp{-}, when standard input is a FIFO or a pipe.
2803 This option is the same as @option{--follow=name --retry}. That is, tail
2804 will attempt to reopen a file when it is removed. Should this fail, tail
2805 will keep trying until it becomes accessible again.
2809 This option is useful mainly when following by name (i.e., with
2810 @option{--follow=name}).
2811 Without this option, when tail encounters a file that doesn't
2812 exist or is otherwise inaccessible, it reports that fact and
2813 never checks it again.
2815 @itemx --sleep-interval=@var{number}
2816 @opindex --sleep-interval
2817 Change the number of seconds to wait between iterations (the default is 1.0).
2818 During one iteration, every specified file is checked to see if it has
2820 Historical implementations of @command{tail} have required that
2821 @var{number} be an integer. However, GNU @command{tail} accepts
2822 an arbitrary floating point number (using a period before any
2825 @itemx --pid=@var{pid}
2827 When following by name or by descriptor, you may specify the process ID,
2828 @var{pid}, of the sole writer of all @var{file} arguments. Then, shortly
2829 after that process terminates, tail will also terminate. This will
2830 work properly only if the writer and the tailing process are running on
2831 the same machine. For example, to save the output of a build in a file
2832 and to watch the file grow, if you invoke @command{make} and @command{tail}
2833 like this then the tail process will stop when your build completes.
2834 Without this option, you would have had to kill the @code{tail -f}
2838 $ make >& makerr & tail --pid=$! -f makerr
2841 If you specify a @var{pid} that is not in use or that does not correspond
2842 to the process that is writing to the tailed files, then @command{tail}
2843 may terminate long before any @var{file}s stop growing or it may not
2844 terminate until long after the real writer has terminated.
2845 Note that @option{--pid} cannot be supported on some systems; @command{tail}
2846 will print a warning if this is the case.
2848 @itemx --max-unchanged-stats=@var{n}
2849 @opindex --max-unchanged-stats
2850 When tailing a file by name, if there have been @var{n} (default
2851 n=@value{DEFAULT_MAX_N_UNCHANGED_STATS_BETWEEN_OPENS}) consecutive
2852 iterations for which the file has not changed, then
2853 @code{open}/@code{fstat} the file to determine if that file name is
2854 still associated with the same device/inode-number pair as before.
2855 When following a log file that is rotated, this is approximately the
2856 number of seconds between when tail prints the last pre-rotation lines
2857 and when it prints the lines that have accumulated in the new log file.
2858 This option is meaningful only when following by name.
2861 @itemx --lines=@var{k}
2864 Output the last @var{k} lines.
2865 However, if @var{k} starts with a @samp{+}, start printing with the
2866 @var{k}th line from the start of each file, instead of from the end.
2867 Size multiplier suffixes are the same as with the @option{-c} option.
2875 Never print file name headers.
2881 Always print file name headers.
2885 For compatibility @command{tail} also supports an obsolete usage
2886 @samp{tail -[@var{count}][bcl][f] [@var{file}]}, which is recognized
2887 only if it does not conflict with the usage described
2888 above. This obsolete form uses exactly one option and at most one
2889 file. In the option, @var{count} is an optional decimal number optionally
2890 followed by a size letter (@samp{b}, @samp{c}, @samp{l}) to mean count
2891 by 512-byte blocks, bytes, or lines, optionally followed by @samp{f}
2892 which has the same meaning as @option{-f}.
2894 @vindex _POSIX2_VERSION
2895 On older systems, the leading @samp{-} can be replaced by @samp{+} in
2896 the obsolete option syntax with the same meaning as in counts, and
2897 obsolete usage overrides normal usage when the two conflict.
2898 This obsolete behavior can be enabled or disabled with the
2899 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
2902 Scripts intended for use on standard hosts should avoid obsolete
2903 syntax and should use @option{-c @var{count}[b]}, @option{-n
2904 @var{count}}, and/or @option{-f} instead. If your script must also
2905 run on hosts that support only the obsolete syntax, you can often
2906 rewrite it to avoid problematic usages, e.g., by using @samp{sed -n
2907 '$p'} rather than @samp{tail -1}. If that's not possible, the script
2908 can use a test like @samp{if tail -c +1 </dev/null >/dev/null 2>&1;
2909 then @dots{}} to decide which syntax to use.
2911 Even if your script assumes the standard behavior, you should still
2912 beware usages whose behaviors differ depending on the @acronym{POSIX}
2913 version. For example, avoid @samp{tail - main.c}, since it might be
2914 interpreted as either @samp{tail main.c} or as @samp{tail -- -
2915 main.c}; avoid @samp{tail -c 4}, since it might mean either @samp{tail
2916 -c4} or @samp{tail -c 10 4}; and avoid @samp{tail +4}, since it might
2917 mean either @samp{tail ./+4} or @samp{tail -n +4}.
2922 @node split invocation
2923 @section @command{split}: Split a file into fixed-size pieces
2926 @cindex splitting a file into pieces
2927 @cindex pieces, splitting a file into
2929 @command{split} creates output files containing consecutive sections of
2930 @var{input} (standard input if none is given or @var{input} is
2931 @samp{-}). Synopsis:
2934 split [@var{option}] [@var{input} [@var{prefix}]]
2937 By default, @command{split} puts 1000 lines of @var{input} (or whatever is
2938 left over for the last section), into each output file.
2940 @cindex output file name prefix
2941 The output files' names consist of @var{prefix} (@samp{x} by default)
2942 followed by a group of characters (@samp{aa}, @samp{ab}, @dots{} by
2943 default), such that concatenating the output files in traditional
2944 sorted order by file name produces
2945 the original input file. If the output file names are exhausted,
2946 @command{split} reports an error without deleting the output files
2949 The program accepts the following options. Also see @ref{Common options}.
2953 @item -l @var{lines}
2954 @itemx --lines=@var{lines}
2957 Put @var{lines} lines of @var{input} into each output file.
2959 For compatibility @command{split} also supports an obsolete
2960 option syntax @option{-@var{lines}}. New scripts should use @option{-l
2961 @var{lines}} instead.
2964 @itemx --bytes=@var{size}
2967 Put @var{size} bytes of @var{input} into each output file.
2968 @multiplierSuffixes{size}
2971 @itemx --line-bytes=@var{size}
2973 @opindex --line-bytes
2974 Put into each output file as many complete lines of @var{input} as
2975 possible without exceeding @var{size} bytes. Individual lines longer than
2976 @var{size} bytes are broken into multiple files.
2977 @var{size} has the same format as for the @option{--bytes} option.
2979 @item -a @var{length}
2980 @itemx --suffix-length=@var{length}
2982 @opindex --suffix-length
2983 Use suffixes of length @var{length}. The default @var{length} is 2.
2986 @itemx --numeric-suffixes
2988 @opindex --numeric-suffixes
2989 Use digits in suffixes rather than lower-case letters.
2993 Write a diagnostic just before each output file is opened.
3000 @node csplit invocation
3001 @section @command{csplit}: Split a file into context-determined pieces
3004 @cindex context splitting
3005 @cindex splitting a file into pieces by context
3007 @command{csplit} creates zero or more output files containing sections of
3008 @var{input} (standard input if @var{input} is @samp{-}). Synopsis:
3011 csplit [@var{option}]@dots{} @var{input} @var{pattern}@dots{}
3014 The contents of the output files are determined by the @var{pattern}
3015 arguments, as detailed below. An error occurs if a @var{pattern}
3016 argument refers to a nonexistent line of the input file (e.g., if no
3017 remaining line matches a given regular expression). After every
3018 @var{pattern} has been matched, any remaining input is copied into one
3021 By default, @command{csplit} prints the number of bytes written to each
3022 output file after it has been created.
3024 The types of pattern arguments are:
3029 Create an output file containing the input up to but not including line
3030 @var{n} (a positive integer). If followed by a repeat count, also
3031 create an output file containing the next @var{n} lines of the input
3032 file once for each repeat.
3034 @item /@var{regexp}/[@var{offset}]
3035 Create an output file containing the current line up to (but not
3036 including) the next line of the input file that contains a match for
3037 @var{regexp}. The optional @var{offset} is an integer.
3038 If it is given, the input up to (but not including) the
3039 matching line plus or minus @var{offset} is put into the output file,
3040 and the line after that begins the next section of input.
3042 @item %@var{regexp}%[@var{offset}]
3043 Like the previous type, except that it does not create an output
3044 file, so that section of the input file is effectively ignored.
3046 @item @{@var{repeat-count}@}
3047 Repeat the previous pattern @var{repeat-count} additional
3048 times. The @var{repeat-count} can either be a positive integer or an
3049 asterisk, meaning repeat as many times as necessary until the input is
3054 The output files' names consist of a prefix (@samp{xx} by default)
3055 followed by a suffix. By default, the suffix is an ascending sequence
3056 of two-digit decimal numbers from @samp{00} to @samp{99}. In any case,
3057 concatenating the output files in sorted order by file name produces the
3058 original input file.
3060 By default, if @command{csplit} encounters an error or receives a hangup,
3061 interrupt, quit, or terminate signal, it removes any output files
3062 that it has created so far before it exits.
3064 The program accepts the following options. Also see @ref{Common options}.
3068 @item -f @var{prefix}
3069 @itemx --prefix=@var{prefix}
3072 @cindex output file name prefix
3073 Use @var{prefix} as the output file name prefix.
3075 @item -b @var{suffix}
3076 @itemx --suffix=@var{suffix}
3079 @cindex output file name suffix
3080 Use @var{suffix} as the output file name suffix. When this option is
3081 specified, the suffix string must include exactly one
3082 @code{printf(3)}-style conversion specification, possibly including
3083 format specification flags, a field width, a precision specifications,
3084 or all of these kinds of modifiers. The format letter must convert a
3085 binary integer argument to readable form; thus, only @samp{d}, @samp{i},
3086 @samp{u}, @samp{o}, @samp{x}, and @samp{X} conversions are allowed. The
3087 entire @var{suffix} is given (with the current output file number) to
3088 @code{sprintf(3)} to form the file name suffixes for each of the
3089 individual output files in turn. If this option is used, the
3090 @option{--digits} option is ignored.
3092 @item -n @var{digits}
3093 @itemx --digits=@var{digits}
3096 Use output file names containing numbers that are @var{digits} digits
3097 long instead of the default 2.
3102 @opindex --keep-files
3103 Do not remove output files when errors are encountered.
3106 @itemx --elide-empty-files
3108 @opindex --elide-empty-files
3109 Suppress the generation of zero-length output files. (In cases where
3110 the section delimiters of the input file are supposed to mark the first
3111 lines of each of the sections, the first output file will generally be a
3112 zero-length file unless you use this option.) The output file sequence
3113 numbers always run consecutively starting from 0, even when this option
3124 Do not print counts of output file sizes.
3130 Here is an example of its usage.
3131 First, create an empty directory for the exercise,
3138 Now, split the sequence of 1..14 on lines that end with 0 or 5:
3141 $ seq 14 | csplit - '/[05]$/' '@{*@}'
3147 Each number printed above is the size of an output
3148 file that csplit has just created.
3149 List the names of those output files:
3156 Use @command{head} to show their contents:
3181 @node Summarizing files
3182 @chapter Summarizing files
3184 @cindex summarizing files
3186 These commands generate just a few numbers representing entire
3190 * wc invocation:: Print newline, word, and byte counts.
3191 * sum invocation:: Print checksum and block counts.
3192 * cksum invocation:: Print CRC checksum and byte counts.
3193 * md5sum invocation:: Print or check MD5 digests.
3194 * sha1sum invocation:: Print or check SHA-1 digests.
3195 * sha2 utilities:: Print or check SHA-2 digests.
3200 @section @command{wc}: Print newline, word, and byte counts
3204 @cindex character count
3208 @command{wc} counts the number of bytes, characters, whitespace-separated
3209 words, and newlines in each given @var{file}, or standard input if none
3210 are given or for a @var{file} of @samp{-}. Synopsis:
3213 wc [@var{option}]@dots{} [@var{file}]@dots{}
3216 @cindex total counts
3217 @command{wc} prints one line of counts for each file, and if the file was
3218 given as an argument, it prints the file name following the counts. If
3219 more than one @var{file} is given, @command{wc} prints a final line
3220 containing the cumulative counts, with the file name @file{total}. The
3221 counts are printed in this order: newlines, words, characters, bytes,
3222 maximum line length.
3223 Each count is printed right-justified in a field with at least one
3224 space between fields so that the numbers and file names normally line
3225 up nicely in columns. The width of the count fields varies depending
3226 on the inputs, so you should not depend on a particular field width.
3227 However, as a @acronym{GNU} extension, if only one count is printed,
3228 it is guaranteed to be printed without leading spaces.
3230 By default, @command{wc} prints three counts: the newline, words, and byte
3231 counts. Options can specify that only certain counts be printed.
3232 Options do not undo others previously given, so
3239 prints both the byte counts and the word counts.
3241 With the @option{--max-line-length} option, @command{wc} prints the length
3242 of the longest line per file, and if there is more than one file it
3243 prints the maximum (not the sum) of those lengths. The line lengths here
3244 are measured in screen columns, according to the current locale and
3245 assuming tab positions in every 8th column.
3247 The program accepts the following options. Also see @ref{Common options}.
3255 Print only the byte counts.
3261 Print only the character counts.
3267 Print only the word counts.
3273 Print only the newline counts.
3276 @itemx --max-line-length
3278 @opindex --max-line-length
3279 Print only the maximum line lengths.
3281 @macro filesZeroFromOption{cmd,withTotalOption,subListOutput}
3282 @itemx --files0-from=@var{file}
3283 @opindex --files0-from=@var{file}
3284 @c This is commented out to avoid a texi2dvi failure.
3285 @c texi2dvi (GNU Texinfo 4.11) 1.104
3286 @c @cindex including files from @command{\cmd\}
3287 Disallow processing files named on the command line, and instead process
3288 those named in file @var{file}; each name being terminated by a zero byte
3289 (@acronym{ASCII} @sc{nul}).
3290 This is useful \withTotalOption\
3291 when the list of file names is so long that it may exceed a command line
3293 In such cases, running @command{\cmd\} via @command{xargs} is undesirable
3294 because it splits the list into pieces and makes @command{\cmd\} print
3295 \subListOutput\ for each sublist rather than for the entire list.
3296 One way to produce a list of @acronym{ASCII} @sc{nul} terminated file names is with @sc{gnu}
3297 @command{find}, using its @option{-print0} predicate.
3298 If @var{file} is @samp{-} then the @acronym{ASCII} @sc{nul} terminated file names
3299 are read from standard input.
3301 @filesZeroFromOption{wc,,a total}
3303 For example, to find the length of the longest line in any @file{.c} or
3304 @file{.h} file in the current hierarchy, do this:
3307 find . -name '*.[ch]' -print0 |
3308 wc -L --files0-from=- | tail -n1
3316 @node sum invocation
3317 @section @command{sum}: Print checksum and block counts
3320 @cindex 16-bit checksum
3321 @cindex checksum, 16-bit
3323 @command{sum} computes a 16-bit checksum for each given @var{file}, or
3324 standard input if none are given or for a @var{file} of @samp{-}. Synopsis:
3327 sum [@var{option}]@dots{} [@var{file}]@dots{}
3330 @command{sum} prints the checksum for each @var{file} followed by the
3331 number of blocks in the file (rounded up). If more than one @var{file}
3332 is given, file names are also printed (by default). (With the
3333 @option{--sysv} option, corresponding file names are printed when there is
3334 at least one file argument.)
3336 By default, @sc{gnu} @command{sum} computes checksums using an algorithm
3337 compatible with BSD @command{sum} and prints file sizes in units of
3340 The program accepts the following options. Also see @ref{Common options}.
3346 @cindex BSD @command{sum}
3347 Use the default (BSD compatible) algorithm. This option is included for
3348 compatibility with the System V @command{sum}. Unless @option{-s} was also
3349 given, it has no effect.
3355 @cindex System V @command{sum}
3356 Compute checksums using an algorithm compatible with System V
3357 @command{sum}'s default, and print file sizes in units of 512-byte blocks.
3361 @command{sum} is provided for compatibility; the @command{cksum} program (see
3362 next section) is preferable in new applications.
3367 @node cksum invocation
3368 @section @command{cksum}: Print CRC checksum and byte counts
3371 @cindex cyclic redundancy check
3372 @cindex CRC checksum
3374 @command{cksum} computes a cyclic redundancy check (CRC) checksum for each
3375 given @var{file}, or standard input if none are given or for a
3376 @var{file} of @samp{-}. Synopsis:
3379 cksum [@var{option}]@dots{} [@var{file}]@dots{}
3382 @command{cksum} prints the CRC checksum for each file along with the number
3383 of bytes in the file, and the file name unless no arguments were given.
3385 @command{cksum} is typically used to ensure that files
3386 transferred by unreliable means (e.g., netnews) have not been corrupted,
3387 by comparing the @command{cksum} output for the received files with the
3388 @command{cksum} output for the original files (typically given in the
3391 The CRC algorithm is specified by the @acronym{POSIX} standard. It is not
3392 compatible with the BSD or System V @command{sum} algorithms (see the
3393 previous section); it is more robust.
3395 The only options are @option{--help} and @option{--version}. @xref{Common
3401 @node md5sum invocation
3402 @section @command{md5sum}: Print or check MD5 digests
3406 @cindex 128-bit checksum
3407 @cindex checksum, 128-bit
3408 @cindex fingerprint, 128-bit
3409 @cindex message-digest, 128-bit
3411 @command{md5sum} computes a 128-bit checksum (or @dfn{fingerprint} or
3412 @dfn{message-digest}) for each specified @var{file}.
3414 Note: The MD5 digest is more reliable than a simple CRC (provided by
3415 the @command{cksum} command) for detecting accidental file corruption,
3416 as the chances of accidentally having two files with identical MD5
3417 are vanishingly small. However, it should not be considered truly
3418 secure against malicious tampering: although finding a file with a
3419 given MD5 fingerprint, or modifying a file so as to retain its MD5 are
3420 considered infeasible at the moment, it is known how to produce
3421 different files with identical MD5 (a ``collision''), something which
3422 can be a security issue in certain contexts. For more secure hashes,
3423 consider using SHA-1 or SHA-2. @xref{sha1sum invocation}, and
3424 @ref{sha2 utilities}.
3426 If a @var{file} is specified as @samp{-} or if no files are given
3427 @command{md5sum} computes the checksum for the standard input.
3428 @command{md5sum} can also determine whether a file and checksum are
3429 consistent. Synopsis:
3432 md5sum [@var{option}]@dots{} [@var{file}]@dots{}
3435 For each @var{file}, @samp{md5sum} outputs the MD5 checksum, a flag
3436 indicating a binary or text input file, and the file name.
3437 If @var{file} contains a backslash or newline, the
3438 line is started with a backslash, and each problematic character in
3439 the file name is escaped with a backslash, making the output
3440 unambiguous even in the presence of arbitrary file names.
3441 If @var{file} is omitted or specified as @samp{-}, standard input is read.
3443 The program accepts the following options. Also see @ref{Common options}.
3451 @cindex binary input files
3452 Treat each input file as binary, by reading it in binary mode and
3453 outputting a @samp{*} flag. This is the inverse of @option{--text}.
3454 On systems like @acronym{GNU} that do not distinguish between binary
3455 and text files, this option merely flags each input file as binary:
3456 the MD5 checksum is unaffected. This option is the default on systems
3457 like MS-DOS that distinguish between binary and text files, except
3458 for reading standard input when standard input is a terminal.
3462 Read file names and checksum information (not data) from each
3463 @var{file} (or from stdin if no @var{file} was specified) and report
3464 whether the checksums match the contents of the named files.
3465 The input to this mode of @command{md5sum} is usually the output of
3466 a prior, checksum-generating run of @samp{md5sum}.
3467 Each valid line of input consists of an MD5 checksum, a binary/text
3468 flag, and then a file name.
3469 Binary files are marked with @samp{*}, text with @samp{ }.
3470 For each such line, @command{md5sum} reads the named file and computes its
3471 MD5 checksum. Then, if the computed message digest does not match the
3472 one on the line with the file name, the file is noted as having
3473 failed the test. Otherwise, the file passes the test.
3474 By default, for each valid line, one line is written to standard
3475 output indicating whether the named file passed the test.
3476 After all checks have been performed, if there were any failures,
3477 a warning is issued to standard error.
3478 Use the @option{--status} option to inhibit that output.
3479 If any listed file cannot be opened or read, if any valid line has
3480 an MD5 checksum inconsistent with the associated file, or if no valid
3481 line is found, @command{md5sum} exits with nonzero status. Otherwise,
3482 it exits successfully.
3486 @cindex verifying MD5 checksums
3487 This option is useful only when verifying checksums.
3488 When verifying checksums, don't generate an 'OK' message per successfully
3489 checked file. Files that fail the verification are reported in the
3490 default one-line-per-file format. If there is any checksum mismatch,
3491 print a warning summarizing the failures to standard error.
3495 @cindex verifying MD5 checksums
3496 This option is useful only when verifying checksums.
3497 When verifying checksums, don't generate the default one-line-per-file
3498 diagnostic and don't output the warning summarizing any failures.
3499 Failures to open or read a file still evoke individual diagnostics to
3501 If all listed files are readable and are consistent with the associated
3502 MD5 checksums, exit successfully. Otherwise exit with a status code
3503 indicating there was a failure.
3509 @cindex text input files
3510 Treat each input file as text, by reading it in text mode and
3511 outputting a @samp{ } flag. This is the inverse of @option{--binary}.
3512 This option is the default on systems like @acronym{GNU} that do not
3513 distinguish between binary and text files. On other systems, it is
3514 the default for reading standard input when standard input is a
3521 @cindex verifying MD5 checksums
3522 When verifying checksums, warn about improperly formatted MD5 checksum lines.
3523 This option is useful only if all but a few lines in the checked input
3531 @node sha1sum invocation
3532 @section @command{sha1sum}: Print or check SHA-1 digests
3536 @cindex 160-bit checksum
3537 @cindex checksum, 160-bit
3538 @cindex fingerprint, 160-bit
3539 @cindex message-digest, 160-bit
3541 @command{sha1sum} computes a 160-bit checksum for each specified
3542 @var{file}. The usage and options of this command are precisely the
3543 same as for @command{md5sum}. @xref{md5sum invocation}.
3545 Note: The SHA-1 digest is more secure than MD5, and no collisions of
3546 it are known (different files having the same fingerprint). However,
3547 it is known that they can be produced with considerable, but not
3548 unreasonable, resources. For this reason, it is generally considered
3549 that SHA-1 should be gradually phased out in favor of the more secure
3550 SHA-2 hash algorithms. @xref{sha2 utilities}.
3553 @node sha2 utilities
3554 @section sha2 utilities: Print or check SHA-2 digests
3561 @cindex 224-bit checksum
3562 @cindex 256-bit checksum
3563 @cindex 384-bit checksum
3564 @cindex 512-bit checksum
3565 @cindex checksum, 224-bit
3566 @cindex checksum, 256-bit
3567 @cindex checksum, 384-bit
3568 @cindex checksum, 512-bit
3569 @cindex fingerprint, 224-bit
3570 @cindex fingerprint, 256-bit
3571 @cindex fingerprint, 384-bit
3572 @cindex fingerprint, 512-bit
3573 @cindex message-digest, 224-bit
3574 @cindex message-digest, 256-bit
3575 @cindex message-digest, 384-bit
3576 @cindex message-digest, 512-bit
3578 The commands @command{sha224sum}, @command{sha256sum},
3579 @command{sha384sum} and @command{sha512sum} compute checksums of
3580 various lengths (respectively 224, 256, 384 and 512 bits),
3581 collectively known as the SHA-2 hashes. The usage and options of
3582 these commands are precisely the same as for @command{md5sum}.
3583 @xref{md5sum invocation}.
3585 Note: The SHA384 and SHA512 digests are considerably slower to
3586 compute, especially on 32-bit computers, than SHA224 or SHA256.
3589 @node Operating on sorted files
3590 @chapter Operating on sorted files
3592 @cindex operating on sorted files
3593 @cindex sorted files, operations on
3595 These commands work with (or produce) sorted files.
3598 * sort invocation:: Sort text files.
3599 * shuf invocation:: Shuffle text files.
3600 * uniq invocation:: Uniquify files.
3601 * comm invocation:: Compare two sorted files line by line.
3602 * ptx invocation:: Produce a permuted index of file contents.
3603 * tsort invocation:: Topological sort.
3607 @node sort invocation
3608 @section @command{sort}: Sort text files
3611 @cindex sorting files
3613 @command{sort} sorts, merges, or compares all the lines from the given
3614 files, or standard input if none are given or for a @var{file} of
3615 @samp{-}. By default, @command{sort} writes the results to standard
3619 sort [@var{option}]@dots{} [@var{file}]@dots{}
3622 @command{sort} has three modes of operation: sort (the default), merge,
3623 and check for sortedness. The following options change the operation
3630 @itemx --check=diagnose-first
3633 @cindex checking for sortedness
3634 Check whether the given file is already sorted: if it is not all
3635 sorted, print a diagnostic containing the first out-of-order line and
3636 exit with a status of 1.
3637 Otherwise, exit successfully.
3638 At most one input file can be given.
3641 @itemx --check=quiet
3642 @itemx --check=silent
3645 @cindex checking for sortedness
3646 Exit successfully if the given file is already sorted, and
3647 exit with status 1 otherwise.
3648 At most one input file can be given.
3649 This is like @option{-c}, except it does not print a diagnostic.
3655 @cindex merging sorted files
3656 Merge the given files by sorting them as a group. Each input file must
3657 always be individually sorted. It always works to sort instead of
3658 merge; merging is provided because it is faster, in the case where it
3663 @cindex sort stability
3664 @cindex sort's last-resort comparison
3665 A pair of lines is compared as follows:
3666 @command{sort} compares each pair of fields, in the
3667 order specified on the command line, according to the associated
3668 ordering options, until a difference is found or no fields are left.
3669 If no key fields are specified, @command{sort} uses a default key of
3670 the entire line. Finally, as a last resort when all keys compare
3671 equal, @command{sort} compares entire lines as if no ordering options
3672 other than @option{--reverse} (@option{-r}) were specified. The
3673 @option{--stable} (@option{-s}) option disables this @dfn{last-resort
3674 comparison} so that lines in which all fields compare equal are left
3675 in their original relative order. The @option{--unique}
3676 (@option{-u}) option also disables the last-resort comparison.
3680 Unless otherwise specified, all comparisons use the character collating
3681 sequence specified by the @env{LC_COLLATE} locale.@footnote{If you
3682 use a non-@acronym{POSIX} locale (e.g., by setting @env{LC_ALL}
3683 to @samp{en_US}), then @command{sort} may produce output that is sorted
3684 differently than you're accustomed to. In that case, set the @env{LC_ALL}
3685 environment variable to @samp{C}. Note that setting only @env{LC_COLLATE}
3686 has two problems. First, it is ineffective if @env{LC_ALL} is also set.
3687 Second, it has undefined behavior if @env{LC_CTYPE} (or @env{LANG}, if
3688 @env{LC_CTYPE} is unset) is set to an incompatible value. For example,
3689 you get undefined behavior if @env{LC_CTYPE} is @code{ja_JP.PCK} but
3690 @env{LC_COLLATE} is @code{en_US.UTF-8}.}
3692 @sc{gnu} @command{sort} (as specified for all @sc{gnu} utilities) has no
3693 limit on input line length or restrictions on bytes allowed within lines.
3694 In addition, if the final byte of an input file is not a newline, @sc{gnu}
3695 @command{sort} silently supplies one. A line's trailing newline is not
3696 part of the line for comparison purposes.
3698 @cindex exit status of @command{sort}
3702 0 if no error occurred
3703 1 if invoked with @option{-c} or @option{-C} and the input is not sorted
3704 2 if an error occurred
3708 If the environment variable @env{TMPDIR} is set, @command{sort} uses its
3709 value as the directory for temporary files instead of @file{/tmp}. The
3710 @option{--temporary-directory} (@option{-T}) option in turn overrides
3711 the environment variable.
3713 The following options affect the ordering of output lines. They may be
3714 specified globally or as part of a specific key field. If no key
3715 fields are specified, global options apply to comparison of entire
3716 lines; otherwise the global options are inherited by key fields that do
3717 not specify any special options of their own. In pre-@acronym{POSIX}
3718 versions of @command{sort}, global options affect only later key fields,
3719 so portable shell scripts should specify global options first.
3724 @itemx --ignore-leading-blanks
3726 @opindex --ignore-leading-blanks
3727 @cindex blanks, ignoring leading
3729 Ignore leading blanks when finding sort keys in each line.
3730 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3731 can change this. Note blanks may be ignored by your locale's collating
3732 rules, but without this option they will be significant for character
3733 positions specified in keys with the @option{-k} option.
3736 @itemx --dictionary-order
3738 @opindex --dictionary-order
3739 @cindex dictionary order
3740 @cindex phone directory order
3741 @cindex telephone directory order
3743 Sort in @dfn{phone directory} order: ignore all characters except
3744 letters, digits and blanks when sorting.
3745 By default letters and digits are those of @acronym{ASCII} and a blank
3746 is a space or a tab, but the @env{LC_CTYPE} locale can change this.
3749 @itemx --ignore-case
3751 @opindex --ignore-case
3752 @cindex ignoring case
3753 @cindex case folding
3755 Fold lowercase characters into the equivalent uppercase characters when
3756 comparing so that, for example, @samp{b} and @samp{B} sort as equal.
3757 The @env{LC_CTYPE} locale determines character types.
3758 When used with @option{--unique} those lower case equivalent lines are
3759 thrown away. (There is currently no way to throw away the upper case
3760 equivalent instead. (Any @option{--reverse} given would only affect
3761 the final result, after the throwing away.))
3764 @itemx --general-numeric-sort
3765 @itemx --sort=general-numeric
3767 @opindex --general-numeric-sort
3769 @cindex general numeric sort
3771 Sort numerically, using the standard C function @code{strtold} to convert
3772 a prefix of each line to a long double-precision floating point number.
3773 This allows floating point numbers to be specified in scientific notation,
3774 like @code{1.0e-34} and @code{10e100}.
3775 The @env{LC_NUMERIC} locale determines the decimal-point character.
3776 Do not report overflow, underflow, or conversion errors.
3777 Use the following collating sequence:
3781 Lines that do not start with numbers (all considered to be equal).
3783 NaNs (``Not a Number'' values, in IEEE floating point arithmetic)
3784 in a consistent but machine-dependent order.
3788 Finite numbers in ascending numeric order (with @math{-0} and @math{+0} equal).
3793 Use this option only if there is no alternative; it is much slower than
3794 @option{--numeric-sort} (@option{-n}) and it can lose information when
3795 converting to floating point.
3798 @itemx --human-numeric-sort
3799 @itemx --sort=human-numeric
3801 @opindex --human-numeric-sort
3803 @cindex human numeric sort
3805 Sort numerically, as per the @option{--numeric-sort} option below, and in
3806 addition handle IEC or SI suffixes like MiB, MB etc (@ref{Block size}).
3807 Note a mixture of IEC and SI suffixes is not supported and will
3808 be flagged as an error. Also the numbers must be abbreviated uniformly.
3809 I.E. values with different precisions like 6000K and 5M will be sorted
3813 @itemx --ignore-nonprinting
3815 @opindex --ignore-nonprinting
3816 @cindex nonprinting characters, ignoring
3817 @cindex unprintable characters, ignoring
3819 Ignore nonprinting characters.
3820 The @env{LC_CTYPE} locale determines character types.
3821 This option has no effect if the stronger @option{--dictionary-order}
3822 (@option{-d}) option is also given.
3828 @opindex --month-sort
3830 @cindex months, sorting by
3832 An initial string, consisting of any amount of blanks, followed
3833 by a month name abbreviation, is folded to UPPER case and
3834 compared in the order @samp{JAN} < @samp{FEB} < @dots{} < @samp{DEC}.
3835 Invalid names compare low to valid names. The @env{LC_TIME} locale
3836 category determines the month spellings.
3837 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3841 @itemx --numeric-sort
3842 @itemx --sort=numeric
3844 @opindex --numeric-sort
3846 @cindex numeric sort
3848 Sort numerically. The number begins each line and consists
3849 of optional blanks, an optional @samp{-} sign, and zero or more
3850 digits possibly separated by thousands separators, optionally followed
3851 by a decimal-point character and zero or more digits. An empty
3852 number is treated as @samp{0}. The @env{LC_NUMERIC}
3853 locale specifies the decimal-point character and thousands separator.
3854 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
3857 Comparison is exact; there is no rounding error.
3859 Neither a leading @samp{+} nor exponential notation is recognized.
3860 To compare such strings numerically, use the
3861 @option{--general-numeric-sort} (@option{-g}) option.
3864 @itemx --version-sort
3866 @opindex --version-sort
3867 @cindex version number sort
3868 Sort by version name and number. It behaves like a standard sort,
3869 except that each sequence of decimal digits is treated numerically
3870 as an index/version number. (@xref{Details about version sort}.)
3876 @cindex reverse sorting
3877 Reverse the result of comparison, so that lines with greater key values
3878 appear earlier in the output instead of later.
3881 @itemx --random-sort
3882 @itemx --sort=random
3884 @opindex --random-sort
3887 Sort by hashing the input keys and then sorting the hash values.
3888 Choose the hash function at random, ensuring that it is free of
3889 collisions so that differing keys have differing hash values. This is
3890 like a random permutation of the inputs (@pxref{shuf invocation}),
3891 except that keys with the same value sort together.
3893 If multiple random sort fields are specified, the same random hash
3894 function is used for all fields. To use different random hash
3895 functions for different fields, you can invoke @command{sort} more
3898 The choice of hash function is affected by the
3899 @option{--random-source} option.
3907 @item --compress-program=@var{prog}
3908 Compress any temporary files with the program @var{prog}.
3910 With no arguments, @var{prog} must compress standard input to standard
3911 output, and when given the @option{-d} option it must decompress
3912 standard input to standard output.
3914 Terminate with an error if @var{prog} exits with nonzero status.
3916 White space and the backslash character should not appear in
3917 @var{prog}; they are reserved for future use.
3919 @filesZeroFromOption{sort,,sorted output}
3921 @item -k @var{pos1}[,@var{pos2}]
3922 @itemx --key=@var{pos1}[,@var{pos2}]
3926 Specify a sort field that consists of the part of the line between
3927 @var{pos1} and @var{pos2} (or the end of the line, if @var{pos2} is
3928 omitted), @emph{inclusive}.
3930 Each @var{pos} has the form @samp{@var{f}[.@var{c}][@var{opts}]},
3931 where @var{f} is the number of the field to use, and @var{c} is the number
3932 of the first character from the beginning of the field. Fields and character
3933 positions are numbered starting with 1; a character position of zero in
3934 @var{pos2} indicates the field's last character. If @samp{.@var{c}} is
3935 omitted from @var{pos1}, it defaults to 1 (the beginning of the field);
3936 if omitted from @var{pos2}, it defaults to 0 (the end of the field).
3937 @var{opts} are ordering options, allowing individual keys to be sorted
3938 according to different rules; see below for details. Keys can span
3941 Example: To sort on the second field, use @option{--key=2,2}
3942 (@option{-k 2,2}). See below for more notes on keys and more examples.
3943 See also the @option{--debug} option to help determine the part
3944 of the line being used in the sort.
3947 Highlight the portion of each line used for sorting.
3948 Also issue warnings about questionable usage to stderr.
3950 @item --batch-size=@var{nmerge}
3951 @opindex --batch-size
3952 @cindex number of inputs to merge, nmerge
3953 Merge at most @var{nmerge} inputs at once.
3955 When @command{sort} has to merge more than @var{nmerge} inputs,
3956 it merges them in groups of @var{nmerge}, saving the result in
3957 a temporary file, which is then used as an input in a subsequent merge.
3959 A large value of @var{nmerge} may improve merge performance and decrease
3960 temporary storage utilization at the expense of increased memory usage
3961 and I/0. Conversely a small value of @var{nmerge} may reduce memory
3962 requirements and I/0 at the expense of temporary storage consumption and
3965 The value of @var{nmerge} must be at least 2. The default value is
3966 currently 16, but this is implementation-dependent and may change in
3969 The value of @var{nmerge} may be bounded by a resource limit for open
3970 file descriptors. The commands @samp{ulimit -n} or @samp{getconf
3971 OPEN_MAX} may display limits for your systems; these limits may be
3972 modified further if your program already has some files open, or if
3973 the operating system has other limits on the number of open files. If
3974 the value of @var{nmerge} exceeds the resource limit, @command{sort}
3975 silently uses a smaller value.
3977 @item -o @var{output-file}
3978 @itemx --output=@var{output-file}
3981 @cindex overwriting of input, allowed
3982 Write output to @var{output-file} instead of standard output.
3983 Normally, @command{sort} reads all input before opening
3984 @var{output-file}, so you can safely sort a file in place by using
3985 commands like @code{sort -o F F} and @code{cat F | sort -o F}.
3986 However, @command{sort} with @option{--merge} (@option{-m}) can open
3987 the output file before reading all input, so a command like @code{cat
3988 F | sort -m -o F - G} is not safe as @command{sort} might start
3989 writing @file{F} before @command{cat} is done reading it.
3991 @vindex POSIXLY_CORRECT
3992 On newer systems, @option{-o} cannot appear after an input file if
3993 @env{POSIXLY_CORRECT} is set, e.g., @samp{sort F -o F}. Portable
3994 scripts should specify @option{-o @var{output-file}} before any input
3997 @item --random-source=@var{file}
3998 @opindex --random-source
3999 @cindex random source for sorting
4000 Use @var{file} as a source of random data used to determine which
4001 random hash function to use with the @option{-R} option. @xref{Random
4008 @cindex sort stability
4009 @cindex sort's last-resort comparison
4011 Make @command{sort} stable by disabling its last-resort comparison.
4012 This option has no effect if no fields or global ordering options
4013 other than @option{--reverse} (@option{-r}) are specified.
4016 @itemx --buffer-size=@var{size}
4018 @opindex --buffer-size
4019 @cindex size for main memory sorting
4020 Use a main-memory sort buffer of the given @var{size}. By default,
4021 @var{size} is in units of 1024 bytes. Appending @samp{%} causes
4022 @var{size} to be interpreted as a percentage of physical memory.
4023 Appending @samp{K} multiplies @var{size} by 1024 (the default),
4024 @samp{M} by 1,048,576, @samp{G} by 1,073,741,824, and so on for
4025 @samp{T}, @samp{P}, @samp{E}, @samp{Z}, and @samp{Y}. Appending
4026 @samp{b} causes @var{size} to be interpreted as a byte count, with no
4029 This option can improve the performance of @command{sort} by causing it
4030 to start with a larger or smaller sort buffer than the default.
4031 However, this option affects only the initial buffer size. The buffer
4032 grows beyond @var{size} if @command{sort} encounters input lines larger
4035 @item -t @var{separator}
4036 @itemx --field-separator=@var{separator}
4038 @opindex --field-separator
4039 @cindex field separator character
4040 Use character @var{separator} as the field separator when finding the
4041 sort keys in each line. By default, fields are separated by the empty
4042 string between a non-blank character and a blank character.
4043 By default a blank is a space or a tab, but the @env{LC_CTYPE} locale
4046 That is, given the input line @w{@samp{ foo bar}}, @command{sort} breaks it
4047 into fields @w{@samp{ foo}} and @w{@samp{ bar}}. The field separator is
4048 not considered to be part of either the field preceding or the field
4049 following, so with @samp{sort @w{-t " "}} the same input line has
4050 three fields: an empty field, @samp{foo}, and @samp{bar}.
4051 However, fields that extend to the end of the line,
4052 as @option{-k 2}, or fields consisting of a range, as @option{-k 2,3},
4053 retain the field separators present between the endpoints of the range.
4055 To specify @acronym{ASCII} @sc{nul} as the field separator,
4056 use the two-character string @samp{\0}, e.g., @samp{sort -t '\0'}.
4058 @item -T @var{tempdir}
4059 @itemx --temporary-directory=@var{tempdir}
4061 @opindex --temporary-directory
4062 @cindex temporary directory
4064 Use directory @var{tempdir} to store temporary files, overriding the
4065 @env{TMPDIR} environment variable. If this option is given more than
4066 once, temporary files are stored in all the directories given. If you
4067 have a large sort or merge that is I/O-bound, you can often improve
4068 performance by using this option to specify directories on different
4069 disks and controllers.
4075 @cindex uniquifying output
4077 Normally, output only the first of a sequence of lines that compare
4078 equal. For the @option{--check} (@option{-c} or @option{-C}) option,
4079 check that no pair of consecutive lines compares equal.
4081 This option also disables the default last-resort comparison.
4083 The commands @code{sort -u} and @code{sort | uniq} are equivalent, but
4084 this equivalence does not extend to arbitrary @command{sort} options.
4085 For example, @code{sort -n -u} inspects only the value of the initial
4086 numeric string when checking for uniqueness, whereas @code{sort -n |
4087 uniq} inspects the entire line. @xref{uniq invocation}.
4089 @macro zeroTerminatedOption
4091 @itemx --zero-terminated
4093 @opindex --zero-terminated
4094 @cindex process zero-terminated items
4095 Delimit items with a zero byte rather than a newline (@acronym{ASCII} @sc{lf}).
4096 I.E. treat input as items separated by @acronym{ASCII} @sc{nul}
4097 and terminate output items with @acronym{ASCII} @sc{nul}.
4098 This option can be useful in conjunction with @samp{perl -0} or
4099 @samp{find -print0} and @samp{xargs -0} which do the same in order to
4100 reliably handle arbitrary file names (even those containing blanks
4101 or other special characters).
4103 @zeroTerminatedOption
4107 Historical (BSD and System V) implementations of @command{sort} have
4108 differed in their interpretation of some options, particularly
4109 @option{-b}, @option{-f}, and @option{-n}. @sc{gnu} sort follows the @acronym{POSIX}
4110 behavior, which is usually (but not always!) like the System V behavior.
4111 According to @acronym{POSIX}, @option{-n} no longer implies @option{-b}. For
4112 consistency, @option{-M} has been changed in the same way. This may
4113 affect the meaning of character positions in field specifications in
4114 obscure cases. The only fix is to add an explicit @option{-b}.
4116 A position in a sort field specified with @option{-k} may have any
4117 of the option letters @samp{MbdfghinRrV} appended to it, in which case no
4118 global ordering options are inherited by that particular field. The
4119 @option{-b} option may be independently attached to either or both of
4120 the start and end positions of a field specification, and if it is
4121 inherited from the global options it will be attached to both.
4122 If input lines can contain leading or adjacent blanks and @option{-t}
4123 is not used, then @option{-k} is typically combined with @option{-b} or
4124 an option that implicitly ignores leading blanks (@samp{Mghn}) as otherwise
4125 the varying numbers of leading blanks in fields can cause confusing results.
4127 If the start position in a sort field specifier falls after the end of
4128 the line or after the end field, the field is empty. If the @option{-b}
4129 option was specified, the @samp{.@var{c}} part of a field specification
4130 is counted from the first nonblank character of the field.
4132 @vindex _POSIX2_VERSION
4133 @vindex POSIXLY_CORRECT
4134 On older systems, @command{sort} supports an obsolete origin-zero
4135 syntax @samp{+@var{pos1} [-@var{pos2}]} for specifying sort keys.
4136 The obsolete sequence @samp{sort +@var{a}.@var{x} -@var{b}.@var{y}}
4137 is equivalent to @samp{sort -k @var{a+1}.@var{x+1},@var{b}} if @var{y}
4138 is @samp{0} or absent, otherwise it is equivalent to @samp{sort -k
4139 @var{a+1}.@var{x+1},@var{b+1}.@var{y}}.
4141 This obsolete behavior can be enabled or disabled with the
4142 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4143 conformance}); it can also be enabled when @env{POSIXLY_CORRECT} is
4144 not set by using the obsolete syntax with @samp{-@var{pos2}} present.
4146 Scripts intended for use on standard hosts should avoid obsolete
4147 syntax and should use @option{-k} instead. For example, avoid
4148 @samp{sort +2}, since it might be interpreted as either @samp{sort
4149 ./+2} or @samp{sort -k 3}. If your script must also run on hosts that
4150 support only the obsolete syntax, it can use a test like @samp{if sort
4151 -k 1 </dev/null >/dev/null 2>&1; then @dots{}} to decide which syntax
4154 Here are some examples to illustrate various combinations of options.
4159 Sort in descending (reverse) numeric order.
4166 Sort alphabetically, omitting the first and second fields
4167 and the blanks at the start of the third field.
4168 This uses a single key composed of the characters beginning
4169 at the start of the first nonblank character in field three
4170 and extending to the end of each line.
4177 Sort numerically on the second field and resolve ties by sorting
4178 alphabetically on the third and fourth characters of field five.
4179 Use @samp{:} as the field delimiter.
4182 sort -t : -k 2,2n -k 5.3,5.4
4185 Note that if you had written @option{-k 2n} instead of @option{-k 2,2n}
4186 @command{sort} would have used all characters beginning in the second field
4187 and extending to the end of the line as the primary @emph{numeric}
4188 key. For the large majority of applications, treating keys spanning
4189 more than one field as numeric will not do what you expect.
4191 Also note that the @samp{n} modifier was applied to the field-end
4192 specifier for the first key. It would have been equivalent to
4193 specify @option{-k 2n,2} or @option{-k 2n,2n}. All modifiers except
4194 @samp{b} apply to the associated @emph{field}, regardless of whether
4195 the modifier character is attached to the field-start and/or the
4196 field-end part of the key specifier.
4199 Sort the password file on the fifth field and ignore any
4200 leading blanks. Sort lines with equal values in field five
4201 on the numeric user ID in field three. Fields are separated
4205 sort -t : -k 5b,5 -k 3,3n /etc/passwd
4206 sort -t : -n -k 5b,5 -k 3,3 /etc/passwd
4207 sort -t : -b -k 5,5 -k 3,3n /etc/passwd
4210 These three commands have equivalent effect. The first specifies that
4211 the first key's start position ignores leading blanks and the second
4212 key is sorted numerically. The other two commands rely on global
4213 options being inherited by sort keys that lack modifiers. The inheritance
4214 works in this case because @option{-k 5b,5b} and @option{-k 5b,5} are
4215 equivalent, as the location of a field-end lacking a @samp{.@var{c}}
4216 character position is not affected by whether initial blanks are
4220 Sort a set of log files, primarily by IPv4 address and secondarily by
4221 time stamp. If two lines' primary and secondary keys are identical,
4222 output the lines in the same order that they were input. The log
4223 files contain lines that look like this:
4226 4.150.156.3 - - [01/Apr/2004:06:31:51 +0000] message 1
4227 211.24.3.231 - - [24/Apr/2004:20:17:39 +0000] message 2
4230 Fields are separated by exactly one space. Sort IPv4 addresses
4231 lexicographically, e.g., 212.61.52.2 sorts before 212.129.233.201
4232 because 61 is less than 129.
4235 sort -s -t ' ' -k 4.9n -k 4.5M -k 4.2n -k 4.14,4.21 file*.log |
4236 sort -s -t '.' -k 1,1n -k 2,2n -k 3,3n -k 4,4n
4239 This example cannot be done with a single @command{sort} invocation,
4240 since IPv4 address components are separated by @samp{.} while dates
4241 come just after a space. So it is broken down into two invocations of
4242 @command{sort}: the first sorts by time stamp and the second by IPv4
4243 address. The time stamp is sorted by year, then month, then day, and
4244 finally by hour-minute-second field, using @option{-k} to isolate each
4245 field. Except for hour-minute-second there's no need to specify the
4246 end of each key field, since the @samp{n} and @samp{M} modifiers sort
4247 based on leading prefixes that cannot cross field boundaries. The
4248 IPv4 addresses are sorted lexicographically. The second sort uses
4249 @samp{-s} so that ties in the primary key are broken by the secondary
4250 key; the first sort uses @samp{-s} so that the combination of the two
4254 Generate a tags file in case-insensitive sorted order.
4257 find src -type f -print0 | sort -z -f | xargs -0 etags --append
4260 The use of @option{-print0}, @option{-z}, and @option{-0} in this case means
4261 that file names that contain blanks or other special characters are
4263 by the sort operation.
4265 @c This example is a bit contrived and needs more explanation.
4267 @c Sort records separated by an arbitrary string by using a pipe to convert
4268 @c each record delimiter string to @samp{\0}, then using sort's -z option,
4269 @c and converting each @samp{\0} back to the original record delimiter.
4272 @c printf 'c\n\nb\n\na\n'|perl -0pe 's/\n\n/\n\0/g'|sort -z|perl -0pe 's/\0/\n/g'
4276 Use the common @acronym{DSU, Decorate Sort Undecorate} idiom to
4277 sort lines according to their length.
4280 awk '@{print length, $0@}' /etc/passwd | sort -n | cut -f2- -d' '
4283 In general this technique can be used to sort data that the @command{sort}
4284 command does not support, or is inefficient at, sorting directly.
4287 Shuffle a list of directories, but preserve the order of files within
4288 each directory. For instance, one could use this to generate a music
4289 playlist in which albums are shuffled but the songs of each album are
4293 ls */* | sort -t / -k 1,1R -k 2,2
4299 @node shuf invocation
4300 @section @command{shuf}: Shuffling text
4303 @cindex shuffling files
4305 @command{shuf} shuffles its input by outputting a random permutation
4306 of its input lines. Each output permutation is equally likely.
4310 shuf [@var{option}]@dots{} [@var{file}]
4311 shuf -e [@var{option}]@dots{} [@var{arg}]@dots{}
4312 shuf -i @var{lo}-@var{hi} [@var{option}]@dots{}
4315 @command{shuf} has three modes of operation that affect where it
4316 obtains its input lines. By default, it reads lines from standard
4317 input. The following options change the operation mode:
4325 @cindex command-line operands to shuffle
4326 Treat each command-line operand as an input line.
4328 @item -i @var{lo}-@var{hi}
4329 @itemx --input-range=@var{lo}-@var{hi}
4331 @opindex --input-range
4332 @cindex input range to shuffle
4333 Act as if input came from a file containing the range of unsigned
4334 decimal integers @var{lo}@dots{}@var{hi}, one per line.
4338 @command{shuf}'s other options can affect its behavior in all
4343 @item -n @var{lines}
4344 @itemx --head-count=@var{count}
4346 @opindex --head-count
4347 @cindex head of output
4348 Output at most @var{count} lines. By default, all input lines are
4351 @item -o @var{output-file}
4352 @itemx --output=@var{output-file}
4355 @cindex overwriting of input, allowed
4356 Write output to @var{output-file} instead of standard output.
4357 @command{shuf} reads all input before opening
4358 @var{output-file}, so you can safely shuffle a file in place by using
4359 commands like @code{shuf -o F <F} and @code{cat F | shuf -o F}.
4361 @item --random-source=@var{file}
4362 @opindex --random-source
4363 @cindex random source for shuffling
4364 Use @var{file} as a source of random data used to determine which
4365 permutation to generate. @xref{Random sources}.
4367 @zeroTerminatedOption
4383 might produce the output
4393 Similarly, the command:
4396 shuf -e clubs hearts diamonds spades
4410 and the command @samp{shuf -i 1-4} might output:
4420 These examples all have four input lines, so @command{shuf} might
4421 produce any of the twenty-four possible permutations of the input. In
4422 general, if there are @var{n} input lines, there are @var{n}! (i.e.,
4423 @var{n} factorial, or @var{n} * (@var{n} - 1) * @dots{} * 1) possible
4424 output permutations.
4429 @node uniq invocation
4430 @section @command{uniq}: Uniquify files
4433 @cindex uniquify files
4435 @command{uniq} writes the unique lines in the given @file{input}, or
4436 standard input if nothing is given or for an @var{input} name of
4440 uniq [@var{option}]@dots{} [@var{input} [@var{output}]]
4443 By default, @command{uniq} prints its input lines, except that
4444 it discards all but the first of adjacent repeated lines, so that
4445 no output lines are repeated. Optionally, it can instead discard
4446 lines that are not repeated, or all repeated lines.
4448 The input need not be sorted, but repeated input lines are detected
4449 only if they are adjacent. If you want to discard non-adjacent
4450 duplicate lines, perhaps you want to use @code{sort -u}.
4451 @xref{sort invocation}.
4454 Comparisons honor the rules specified by the @env{LC_COLLATE}
4457 If no @var{output} file is specified, @command{uniq} writes to standard
4460 The program accepts the following options. Also see @ref{Common options}.
4465 @itemx --skip-fields=@var{n}
4467 @opindex --skip-fields
4468 Skip @var{n} fields on each line before checking for uniqueness. Use
4469 a null string for comparison if a line has fewer than @var{n} fields. Fields
4470 are sequences of non-space non-tab characters that are separated from
4471 each other by at least one space or tab.
4473 For compatibility @command{uniq} supports an obsolete option syntax
4474 @option{-@var{n}}. New scripts should use @option{-f @var{n}} instead.
4477 @itemx --skip-chars=@var{n}
4479 @opindex --skip-chars
4480 Skip @var{n} characters before checking for uniqueness. Use a null string
4481 for comparison if a line has fewer than @var{n} characters. If you use both
4482 the field and character skipping options, fields are skipped over first.
4484 @vindex _POSIX2_VERSION
4485 On older systems, @command{uniq} supports an obsolete option syntax
4487 This obsolete behavior can be enabled or disabled with the
4488 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
4489 conformance}), but portable scripts should avoid commands whose
4490 behavior depends on this variable.
4491 For example, use @samp{uniq ./+10} or @samp{uniq -s 10} rather than
4492 the ambiguous @samp{uniq +10}.
4498 Print the number of times each line occurred along with the line.
4501 @itemx --ignore-case
4503 @opindex --ignore-case
4504 Ignore differences in case when comparing lines.
4510 @cindex repeated lines, outputting
4511 Discard lines that are not repeated. When used by itself, this option
4512 causes @command{uniq} to print the first copy of each repeated line,
4516 @itemx --all-repeated[=@var{delimit-method}]
4518 @opindex --all-repeated
4519 @cindex all repeated lines, outputting
4520 Do not discard the second and subsequent repeated input lines,
4521 but discard lines that are not repeated.
4522 This option is useful mainly in conjunction with other options e.g.,
4523 to ignore case or to compare only selected fields.
4524 The optional @var{delimit-method} tells how to delimit
4525 groups of repeated lines, and must be one of the following:
4530 Do not delimit groups of repeated lines.
4531 This is equivalent to @option{--all-repeated} (@option{-D}).
4534 Output a newline before each group of repeated lines.
4535 With @option{--zero-terminated} (@option{-z}), use a zero
4536 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4539 Separate groups of repeated lines with a single newline.
4540 With @option{--zero-terminated} (@option{-z}), use a zero
4541 byte (@acronym{ASCII} @sc{nul}) instead of a newline.
4542 This is the same as using @samp{prepend}, except that
4543 no delimiter is inserted before the first group, and hence
4544 may be better suited for output direct to users.
4547 Note that when groups are delimited and the input stream contains
4548 two or more consecutive blank lines, then the output is ambiguous.
4549 To avoid that, filter the input through @samp{tr -s '\n'} to replace
4550 each sequence of consecutive newlines with a single newline.
4552 This is a @sc{gnu} extension.
4553 @c FIXME: give an example showing *how* it's useful
4559 @cindex unique lines, outputting
4560 Discard the first repeated line. When used by itself, this option
4561 causes @command{uniq} to print unique lines, and nothing else.
4564 @itemx --check-chars=@var{n}
4566 @opindex --check-chars
4567 Compare at most @var{n} characters on each line (after skipping any specified
4568 fields and characters). By default the entire rest of the lines are
4571 @zeroTerminatedOption
4578 @node comm invocation
4579 @section @command{comm}: Compare two sorted files line by line
4582 @cindex line-by-line comparison
4583 @cindex comparing sorted files
4585 @command{comm} writes to standard output lines that are common, and lines
4586 that are unique, to two input files; a file name of @samp{-} means
4587 standard input. Synopsis:
4590 comm [@var{option}]@dots{} @var{file1} @var{file2}
4594 Before @command{comm} can be used, the input files must be sorted using the
4595 collating sequence specified by the @env{LC_COLLATE} locale.
4596 If an input file ends in a non-newline
4597 character, a newline is silently appended. The @command{sort} command with
4598 no options always outputs a file that is suitable input to @command{comm}.
4600 @cindex differing lines
4601 @cindex common lines
4602 With no options, @command{comm} produces three-column output. Column one
4603 contains lines unique to @var{file1}, column two contains lines unique
4604 to @var{file2}, and column three contains lines common to both files.
4605 Columns are separated by a single TAB character.
4606 @c FIXME: when there's an option to supply an alternative separator
4607 @c string, append `by default' to the above sentence.
4612 The options @option{-1}, @option{-2}, and @option{-3} suppress printing of
4613 the corresponding columns (and separators). Also see @ref{Common options}.
4615 Unlike some other comparison utilities, @command{comm} has an exit
4616 status that does not depend on the result of the comparison.
4617 Upon normal completion @command{comm} produces an exit code of zero.
4618 If there is an error it exits with nonzero status.
4620 @macro checkOrderOption{cmd}
4621 If the @option{--check-order} option is given, unsorted inputs will
4622 cause a fatal error message. If the option @option{--nocheck-order}
4623 is given, unsorted inputs will never cause an error message. If
4624 neither of these options is given, wrongly sorted inputs are diagnosed
4625 only if an input file is found to contain unpairable lines. If an
4626 input file is diagnosed as being unsorted, the @command{\cmd\} command
4627 will exit with a nonzero status (and the output should not be used).
4629 Forcing @command{\cmd\} to process wrongly sorted input files
4630 containing unpairable lines by specifying @option{--nocheck-order} is
4631 not guaranteed to produce any particular output. The output will
4632 probably not correspond with whatever you hoped it would be.
4634 @checkOrderOption{comm}
4639 Fail with an error message if either input file is wrongly ordered.
4641 @item --nocheck-order
4642 Do not check that both input files are in sorted order.
4646 @item --output-delimiter=@var{str}
4647 Print @var{str} between adjacent output columns,
4648 rather than the default of a single TAB character.
4650 The delimiter @var{str} may not be empty.
4654 @node ptx invocation
4655 @section @command{ptx}: Produce permuted indexes
4659 @command{ptx} reads a text file and essentially produces a permuted index, with
4660 each keyword in its context. The calling sketch is either one of:
4663 ptx [@var{option} @dots{}] [@var{file} @dots{}]
4664 ptx -G [@var{option} @dots{}] [@var{input} [@var{output}]]
4667 The @option{-G} (or its equivalent: @option{--traditional}) option disables
4668 all @sc{gnu} extensions and reverts to traditional mode, thus introducing some
4669 limitations and changing several of the program's default option values.
4670 When @option{-G} is not specified, @sc{gnu} extensions are always enabled.
4671 @sc{gnu} extensions to @command{ptx} are documented wherever appropriate in this
4672 document. For the full list, see @xref{Compatibility in ptx}.
4674 Individual options are explained in the following sections.
4676 When @sc{gnu} extensions are enabled, there may be zero, one or several
4677 @var{file}s after the options. If there is no @var{file}, the program
4678 reads the standard input. If there is one or several @var{file}s, they
4679 give the name of input files which are all read in turn, as if all the
4680 input files were concatenated. However, there is a full contextual
4681 break between each file and, when automatic referencing is requested,
4682 file names and line numbers refer to individual text input files. In
4683 all cases, the program outputs the permuted index to the standard
4686 When @sc{gnu} extensions are @emph{not} enabled, that is, when the program
4687 operates in traditional mode, there may be zero, one or two parameters
4688 besides the options. If there are no parameters, the program reads the
4689 standard input and outputs the permuted index to the standard output.
4690 If there is only one parameter, it names the text @var{input} to be read
4691 instead of the standard input. If two parameters are given, they give
4692 respectively the name of the @var{input} file to read and the name of
4693 the @var{output} file to produce. @emph{Be very careful} to note that,
4694 in this case, the contents of file given by the second parameter is
4695 destroyed. This behavior is dictated by System V @command{ptx}
4696 compatibility; @sc{gnu} Standards normally discourage output parameters not
4697 introduced by an option.
4699 Note that for @emph{any} file named as the value of an option or as an
4700 input text file, a single dash @kbd{-} may be used, in which case
4701 standard input is assumed. However, it would not make sense to use this
4702 convention more than once per program invocation.
4705 * General options in ptx:: Options which affect general program behavior.
4706 * Charset selection in ptx:: Underlying character set considerations.
4707 * Input processing in ptx:: Input fields, contexts, and keyword selection.
4708 * Output formatting in ptx:: Types of output format, and sizing the fields.
4709 * Compatibility in ptx::
4713 @node General options in ptx
4714 @subsection General options
4719 @itemx --traditional
4720 As already explained, this option disables all @sc{gnu} extensions to
4721 @command{ptx} and switches to traditional mode.
4724 Print a short help on standard output, then exit without further
4728 Print the program version on standard output, then exit without further
4736 @node Charset selection in ptx
4737 @subsection Charset selection
4739 @c FIXME: People don't necessarily know what an IBM-PC was these days.
4740 As it is set up now, the program assumes that the input file is coded
4741 using 8-bit @acronym{ISO} 8859-1 code, also known as Latin-1 character set,
4742 @emph{unless} it is compiled for MS-DOS, in which case it uses the
4743 character set of the IBM-PC@. (@sc{gnu} @command{ptx} is not known to work on
4744 smaller MS-DOS machines anymore.) Compared to 7-bit @acronym{ASCII}, the set
4745 of characters which are letters is different; this alters the behavior
4746 of regular expression matching. Thus, the default regular expression
4747 for a keyword allows foreign or diacriticized letters. Keyword sorting,
4748 however, is still crude; it obeys the underlying character set ordering
4754 @itemx --ignore-case
4755 Fold lower case letters to upper case for sorting.
4760 @node Input processing in ptx
4761 @subsection Word selection and input processing
4766 @itemx --break-file=@var{file}
4768 This option provides an alternative (to @option{-W}) method of describing
4769 which characters make up words. It introduces the name of a
4770 file which contains a list of characters which can@emph{not} be part of
4771 one word; this file is called the @dfn{Break file}. Any character which
4772 is not part of the Break file is a word constituent. If both options
4773 @option{-b} and @option{-W} are specified, then @option{-W} has precedence and
4774 @option{-b} is ignored.
4776 When @sc{gnu} extensions are enabled, the only way to avoid newline as a
4777 break character is to write all the break characters in the file with no
4778 newline at all, not even at the end of the file. When @sc{gnu} extensions
4779 are disabled, spaces, tabs and newlines are always considered as break
4780 characters even if not included in the Break file.
4783 @itemx --ignore-file=@var{file}
4785 The file associated with this option contains a list of words which will
4786 never be taken as keywords in concordance output. It is called the
4787 @dfn{Ignore file}. The file contains exactly one word in each line; the
4788 end of line separation of words is not subject to the value of the
4792 @itemx --only-file=@var{file}
4794 The file associated with this option contains a list of words which will
4795 be retained in concordance output; any word not mentioned in this file
4796 is ignored. The file is called the @dfn{Only file}. The file contains
4797 exactly one word in each line; the end of line separation of words is
4798 not subject to the value of the @option{-S} option.
4800 There is no default for the Only file. When both an Only file and an
4801 Ignore file are specified, a word is considered a keyword only
4802 if it is listed in the Only file and not in the Ignore file.
4807 On each input line, the leading sequence of non-white space characters will be
4808 taken to be a reference that has the purpose of identifying this input
4809 line in the resulting permuted index. For more information about reference
4810 production, see @xref{Output formatting in ptx}.
4811 Using this option changes the default value for option @option{-S}.
4813 Using this option, the program does not try very hard to remove
4814 references from contexts in output, but it succeeds in doing so
4815 @emph{when} the context ends exactly at the newline. If option
4816 @option{-r} is used with @option{-S} default value, or when @sc{gnu} extensions
4817 are disabled, this condition is always met and references are completely
4818 excluded from the output contexts.
4820 @item -S @var{regexp}
4821 @itemx --sentence-regexp=@var{regexp}
4823 This option selects which regular expression will describe the end of a
4824 line or the end of a sentence. In fact, this regular expression is not
4825 the only distinction between end of lines or end of sentences, and input
4826 line boundaries have no special significance outside this option. By
4827 default, when @sc{gnu} extensions are enabled and if @option{-r} option is not
4828 used, end of sentences are used. In this case, this @var{regex} is
4829 imported from @sc{gnu} Emacs:
4832 [.?!][]\"')@}]*\\($\\|\t\\| \\)[ \t\n]*
4835 Whenever @sc{gnu} extensions are disabled or if @option{-r} option is used, end
4836 of lines are used; in this case, the default @var{regexp} is just:
4842 Using an empty @var{regexp} is equivalent to completely disabling end of
4843 line or end of sentence recognition. In this case, the whole file is
4844 considered to be a single big line or sentence. The user might want to
4845 disallow all truncation flag generation as well, through option @option{-F
4846 ""}. @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4849 When the keywords happen to be near the beginning of the input line or
4850 sentence, this often creates an unused area at the beginning of the
4851 output context line; when the keywords happen to be near the end of the
4852 input line or sentence, this often creates an unused area at the end of
4853 the output context line. The program tries to fill those unused areas
4854 by wrapping around context in them; the tail of the input line or
4855 sentence is used to fill the unused area on the left of the output line;
4856 the head of the input line or sentence is used to fill the unused area
4857 on the right of the output line.
4859 As a matter of convenience to the user, many usual backslashed escape
4860 sequences from the C language are recognized and converted to the
4861 corresponding characters by @command{ptx} itself.
4863 @item -W @var{regexp}
4864 @itemx --word-regexp=@var{regexp}
4866 This option selects which regular expression will describe each keyword.
4867 By default, if @sc{gnu} extensions are enabled, a word is a sequence of
4868 letters; the @var{regexp} used is @samp{\w+}. When @sc{gnu} extensions are
4869 disabled, a word is by default anything which ends with a space, a tab
4870 or a newline; the @var{regexp} used is @samp{[^ \t\n]+}.
4872 An empty @var{regexp} is equivalent to not using this option.
4873 @xref{Regexps, , Syntax of Regular Expressions, emacs, The GNU Emacs
4876 As a matter of convenience to the user, many usual backslashed escape
4877 sequences, as found in the C language, are recognized and converted to
4878 the corresponding characters by @command{ptx} itself.
4883 @node Output formatting in ptx
4884 @subsection Output formatting
4886 Output format is mainly controlled by the @option{-O} and @option{-T} options
4887 described in the table below. When neither @option{-O} nor @option{-T} are
4888 selected, and if @sc{gnu} extensions are enabled, the program chooses an
4889 output format suitable for a dumb terminal. Each keyword occurrence is
4890 output to the center of one line, surrounded by its left and right
4891 contexts. Each field is properly justified, so the concordance output
4892 can be readily observed. As a special feature, if automatic
4893 references are selected by option @option{-A} and are output before the
4894 left context, that is, if option @option{-R} is @emph{not} selected, then
4895 a colon is added after the reference; this nicely interfaces with @sc{gnu}
4896 Emacs @code{next-error} processing. In this default output format, each
4897 white space character, like newline and tab, is merely changed to
4898 exactly one space, with no special attempt to compress consecutive
4899 spaces. This might change in the future. Except for those white space
4900 characters, every other character of the underlying set of 256
4901 characters is transmitted verbatim.
4903 Output format is further controlled by the following options.
4907 @item -g @var{number}
4908 @itemx --gap-size=@var{number}
4910 Select the size of the minimum white space gap between the fields on the
4913 @item -w @var{number}
4914 @itemx --width=@var{number}
4916 Select the maximum output width of each final line. If references are
4917 used, they are included or excluded from the maximum output width
4918 depending on the value of option @option{-R}. If this option is not
4919 selected, that is, when references are output before the left context,
4920 the maximum output width takes into account the maximum length of all
4921 references. If this option is selected, that is, when references are
4922 output after the right context, the maximum output width does not take
4923 into account the space taken by references, nor the gap that precedes
4927 @itemx --auto-reference
4929 Select automatic references. Each input line will have an automatic
4930 reference made up of the file name and the line ordinal, with a single
4931 colon between them. However, the file name will be empty when standard
4932 input is being read. If both @option{-A} and @option{-r} are selected, then
4933 the input reference is still read and skipped, but the automatic
4934 reference is used at output time, overriding the input reference.
4937 @itemx --right-side-refs
4939 In the default output format, when option @option{-R} is not used, any
4940 references produced by the effect of options @option{-r} or @option{-A} are
4941 placed to the far right of output lines, after the right context. With
4942 default output format, when the @option{-R} option is specified, references
4943 are rather placed at the beginning of each output line, before the left
4944 context. For any other output format, option @option{-R} is
4945 ignored, with one exception: with @option{-R} the width of references
4946 is @emph{not} taken into account in total output width given by @option{-w}.
4948 This option is automatically selected whenever @sc{gnu} extensions are
4951 @item -F @var{string}
4952 @itemx --flac-truncation=@var{string}
4954 This option will request that any truncation in the output be reported
4955 using the string @var{string}. Most output fields theoretically extend
4956 towards the beginning or the end of the current line, or current
4957 sentence, as selected with option @option{-S}. But there is a maximum
4958 allowed output line width, changeable through option @option{-w}, which is
4959 further divided into space for various output fields. When a field has
4960 to be truncated because it cannot extend beyond the beginning or the end of
4961 the current line to fit in, then a truncation occurs. By default,
4962 the string used is a single slash, as in @option{-F /}.
4964 @var{string} may have more than one character, as in @option{-F ...}.
4965 Also, in the particular case when @var{string} is empty (@option{-F ""}),
4966 truncation flagging is disabled, and no truncation marks are appended in
4969 As a matter of convenience to the user, many usual backslashed escape
4970 sequences, as found in the C language, are recognized and converted to
4971 the corresponding characters by @command{ptx} itself.
4973 @item -M @var{string}
4974 @itemx --macro-name=@var{string}
4976 Select another @var{string} to be used instead of @samp{xx}, while
4977 generating output suitable for @command{nroff}, @command{troff} or @TeX{}.
4980 @itemx --format=roff
4982 Choose an output format suitable for @command{nroff} or @command{troff}
4983 processing. Each output line will look like:
4986 .xx "@var{tail}" "@var{before}" "@var{keyword_and_after}" "@var{head}" "@var{ref}"
4989 so it will be possible to write a @samp{.xx} roff macro to take care of
4990 the output typesetting. This is the default output format when @sc{gnu}
4991 extensions are disabled. Option @option{-M} can be used to change
4992 @samp{xx} to another macro name.
4994 In this output format, each non-graphical character, like newline and
4995 tab, is merely changed to exactly one space, with no special attempt to
4996 compress consecutive spaces. Each quote character: @kbd{"} is doubled
4997 so it will be correctly processed by @command{nroff} or @command{troff}.
5002 Choose an output format suitable for @TeX{} processing. Each output
5003 line will look like:
5006 \xx @{@var{tail}@}@{@var{before}@}@{@var{keyword}@}@{@var{after}@}@{@var{head}@}@{@var{ref}@}
5010 so it will be possible to write a @code{\xx} definition to take care of
5011 the output typesetting. Note that when references are not being
5012 produced, that is, neither option @option{-A} nor option @option{-r} is
5013 selected, the last parameter of each @code{\xx} call is inhibited.
5014 Option @option{-M} can be used to change @samp{xx} to another macro
5017 In this output format, some special characters, like @kbd{$}, @kbd{%},
5018 @kbd{&}, @kbd{#} and @kbd{_} are automatically protected with a
5019 backslash. Curly brackets @kbd{@{}, @kbd{@}} are protected with a
5020 backslash and a pair of dollar signs (to force mathematical mode). The
5021 backslash itself produces the sequence @code{\backslash@{@}}.
5022 Circumflex and tilde diacritical marks produce the sequence @code{^\@{ @}} and
5023 @code{~\@{ @}} respectively. Other diacriticized characters of the
5024 underlying character set produce an appropriate @TeX{} sequence as far
5025 as possible. The other non-graphical characters, like newline and tab,
5026 and all other characters which are not part of @acronym{ASCII}, are merely
5027 changed to exactly one space, with no special attempt to compress
5028 consecutive spaces. Let me know how to improve this special character
5029 processing for @TeX{}.
5034 @node Compatibility in ptx
5035 @subsection The @sc{gnu} extensions to @command{ptx}
5037 This version of @command{ptx} contains a few features which do not exist in
5038 System V @command{ptx}. These extra features are suppressed by using the
5039 @option{-G} command line option, unless overridden by other command line
5040 options. Some @sc{gnu} extensions cannot be recovered by overriding, so the
5041 simple rule is to avoid @option{-G} if you care about @sc{gnu} extensions.
5042 Here are the differences between this program and System V @command{ptx}.
5047 This program can read many input files at once, it always writes the
5048 resulting concordance on standard output. On the other hand, System V
5049 @command{ptx} reads only one file and sends the result to standard output
5050 or, if a second @var{file} parameter is given on the command, to that
5053 Having output parameters not introduced by options is a dangerous
5054 practice which @sc{gnu} avoids as far as possible. So, for using @command{ptx}
5055 portably between @sc{gnu} and System V, you should always use it with a
5056 single input file, and always expect the result on standard output. You
5057 might also want to automatically configure in a @option{-G} option to
5058 @command{ptx} calls in products using @command{ptx}, if the configurator finds
5059 that the installed @command{ptx} accepts @option{-G}.
5062 The only options available in System V @command{ptx} are options @option{-b},
5063 @option{-f}, @option{-g}, @option{-i}, @option{-o}, @option{-r}, @option{-t} and
5064 @option{-w}. All other options are @sc{gnu} extensions and are not repeated in
5065 this enumeration. Moreover, some options have a slightly different
5066 meaning when @sc{gnu} extensions are enabled, as explained below.
5069 By default, concordance output is not formatted for @command{troff} or
5070 @command{nroff}. It is rather formatted for a dumb terminal. @command{troff}
5071 or @command{nroff} output may still be selected through option @option{-O}.
5074 Unless @option{-R} option is used, the maximum reference width is
5075 subtracted from the total output line width. With @sc{gnu} extensions
5076 disabled, width of references is not taken into account in the output
5077 line width computations.
5080 All 256 bytes, even @acronym{ASCII} @sc{nul} bytes, are always read and
5081 processed from input file with no adverse effect, even if @sc{gnu} extensions
5082 are disabled. However, System V @command{ptx} does not accept 8-bit characters,
5083 a few control characters are rejected, and the tilde @kbd{~} is also rejected.
5086 Input line length is only limited by available memory, even if @sc{gnu}
5087 extensions are disabled. However, System V @command{ptx} processes only
5088 the first 200 characters in each line.
5091 The break (non-word) characters default to be every character except all
5092 letters of the underlying character set, diacriticized or not. When @sc{gnu}
5093 extensions are disabled, the break characters default to space, tab and
5097 The program makes better use of output line width. If @sc{gnu} extensions
5098 are disabled, the program rather tries to imitate System V @command{ptx},
5099 but still, there are some slight disposition glitches this program does
5100 not completely reproduce.
5103 The user can specify both an Ignore file and an Only file. This is not
5104 allowed with System V @command{ptx}.
5109 @node tsort invocation
5110 @section @command{tsort}: Topological sort
5113 @cindex topological sort
5115 @command{tsort} performs a topological sort on the given @var{file}, or
5116 standard input if no input file is given or for a @var{file} of
5117 @samp{-}. For more details and some history, see @ref{tsort background}.
5121 tsort [@var{option}] [@var{file}]
5124 @command{tsort} reads its input as pairs of strings, separated by blanks,
5125 indicating a partial ordering. The output is a total ordering that
5126 corresponds to the given partial ordering.
5140 will produce the output
5151 Consider a more realistic example.
5152 You have a large set of functions all in one file, and they may all be
5153 declared static except one. Currently that one (say @code{main}) is the
5154 first function defined in the file, and the ones it calls directly follow
5155 it, followed by those they call, etc. Let's say that you are determined
5156 to take advantage of prototypes, so you have to choose between declaring
5157 all of those functions (which means duplicating a lot of information from
5158 the definitions) and rearranging the functions so that as many as possible
5159 are defined before they are used. One way to automate the latter process
5160 is to get a list for each function of the functions it calls directly.
5161 Many programs can generate such lists. They describe a call graph.
5162 Consider the following list, in which a given line indicates that the
5163 function on the left calls the one on the right directly.
5169 tail_file pretty_name
5170 tail_file write_header
5172 tail_forever recheck
5173 tail_forever pretty_name
5174 tail_forever write_header
5175 tail_forever dump_remainder
5178 tail_lines start_lines
5179 tail_lines dump_remainder
5180 tail_lines file_lines
5181 tail_lines pipe_lines
5183 tail_bytes start_bytes
5184 tail_bytes dump_remainder
5185 tail_bytes pipe_bytes
5186 file_lines dump_remainder
5190 then you can use @command{tsort} to produce an ordering of those
5191 functions that satisfies your requirement.
5194 example$ tsort call-graph | tac
5214 @command{tsort} detects any cycles in the input and writes the first cycle
5215 encountered to standard error.
5217 Note that for a given partial ordering, generally there is no unique
5218 total ordering. In the context of the call graph above, the function
5219 @code{parse_options} may be placed anywhere in the list as long as it
5220 precedes @code{main}.
5222 The only options are @option{--help} and @option{--version}. @xref{Common
5228 * tsort background:: Where tsort came from.
5231 @node tsort background
5232 @subsection @command{tsort}: Background
5234 @command{tsort} exists because very early versions of the Unix linker processed
5235 an archive file exactly once, and in order. As @command{ld} read each object
5236 in the archive, it decided whether it was needed in the program based on
5237 whether it defined any symbols which were undefined at that point in
5240 This meant that dependencies within the archive had to be handled
5241 specially. For example, @code{scanf} probably calls @code{read}. That means
5242 that in a single pass through an archive, it was important for @code{scanf.o}
5243 to appear before read.o, because otherwise a program which calls
5244 @code{scanf} but not @code{read} might end up with an unexpected unresolved
5245 reference to @code{read}.
5247 The way to address this problem was to first generate a set of
5248 dependencies of one object file on another. This was done by a shell
5249 script called @command{lorder}. The GNU tools don't provide a version of
5250 lorder, as far as I know, but you can still find it in BSD
5253 Then you ran @command{tsort} over the @command{lorder} output, and you used the
5254 resulting sort to define the order in which you added objects to the archive.
5256 This whole procedure has been obsolete since about 1980, because
5257 Unix archives now contain a symbol table (traditionally built by
5258 @command{ranlib}, now generally built by @command{ar} itself), and the Unix
5259 linker uses the symbol table to effectively make multiple passes over
5262 Anyhow, that's where tsort came from. To solve an old problem with
5263 the way the linker handled archive files, which has since been solved
5267 @node Operating on fields
5268 @chapter Operating on fields
5271 * cut invocation:: Print selected parts of lines.
5272 * paste invocation:: Merge lines of files.
5273 * join invocation:: Join lines on a common field.
5277 @node cut invocation
5278 @section @command{cut}: Print selected parts of lines
5281 @command{cut} writes to standard output selected parts of each line of each
5282 input file, or standard input if no files are given or for a file name of
5286 cut @var{option}@dots{} [@var{file}]@dots{}
5289 In the table which follows, the @var{byte-list}, @var{character-list},
5290 and @var{field-list} are one or more numbers or ranges (two numbers
5291 separated by a dash) separated by commas. Bytes, characters, and
5292 fields are numbered starting at 1. Incomplete ranges may be
5293 given: @option{-@var{m}} means @samp{1-@var{m}}; @samp{@var{n}-} means
5294 @samp{@var{n}} through end of line or last field. The list elements
5295 can be repeated, can overlap, and can be specified in any order; but
5296 the selected input is written in the same order that it is read, and
5297 is written exactly once.
5299 The program accepts the following options. Also see @ref{Common
5304 @item -b @var{byte-list}
5305 @itemx --bytes=@var{byte-list}
5308 Select for printing only the bytes in positions listed in
5309 @var{byte-list}. Tabs and backspaces are treated like any other
5310 character; they take up 1 byte. If an output delimiter is specified,
5311 (see the description of @option{--output-delimiter}), then output that
5312 string between ranges of selected bytes.
5314 @item -c @var{character-list}
5315 @itemx --characters=@var{character-list}
5317 @opindex --characters
5318 Select for printing only the characters in positions listed in
5319 @var{character-list}. The same as @option{-b} for now, but
5320 internationalization will change that. Tabs and backspaces are
5321 treated like any other character; they take up 1 character. If an
5322 output delimiter is specified, (see the description of
5323 @option{--output-delimiter}), then output that string between ranges
5326 @item -f @var{field-list}
5327 @itemx --fields=@var{field-list}
5330 Select for printing only the fields listed in @var{field-list}.
5331 Fields are separated by a TAB character by default. Also print any
5332 line that contains no delimiter character, unless the
5333 @option{--only-delimited} (@option{-s}) option is specified.
5334 Note @command{cut} does not support specifying runs of whitespace as a
5335 delimiter, so to achieve that common functionality one can pre-process
5336 with @command{tr} like:
5338 tr -s '[:blank:]' '\t' | cut -f@dots{}
5341 @item -d @var{input_delim_byte}
5342 @itemx --delimiter=@var{input_delim_byte}
5344 @opindex --delimiter
5345 With @option{-f}, use the first byte of @var{input_delim_byte} as
5346 the input fields separator (default is TAB).
5350 Do not split multi-byte characters (no-op for now).
5353 @itemx --only-delimited
5355 @opindex --only-delimited
5356 For @option{-f}, do not print lines that do not contain the field separator
5357 character. Normally, any line without a field separator is printed verbatim.
5359 @item --output-delimiter=@var{output_delim_string}
5360 @opindex --output-delimiter
5361 With @option{-f}, output fields are separated by @var{output_delim_string}.
5362 The default with @option{-f} is to use the input delimiter.
5363 When using @option{-b} or @option{-c} to select ranges of byte or
5364 character offsets (as opposed to ranges of fields),
5365 output @var{output_delim_string} between non-overlapping
5366 ranges of selected bytes.
5369 @opindex --complement
5370 This option is a @acronym{GNU} extension.
5371 Select for printing the complement of the bytes, characters or fields
5372 selected with the @option{-b}, @option{-c} or @option{-f} options.
5373 In other words, do @emph{not} print the bytes, characters or fields
5374 specified via those options. This option is useful when you have
5375 many fields and want to print all but a few of them.
5382 @node paste invocation
5383 @section @command{paste}: Merge lines of files
5386 @cindex merging files
5388 @command{paste} writes to standard output lines consisting of sequentially
5389 corresponding lines of each given file, separated by a TAB character.
5390 Standard input is used for a file name of @samp{-} or if no input files
5412 paste [@var{option}]@dots{} [@var{file}]@dots{}
5415 The program accepts the following options. Also see @ref{Common options}.
5423 Paste the lines of one file at a time rather than one line from each
5424 file. Using the above example data:
5427 $ paste -s num2 let3
5432 @item -d @var{delim-list}
5433 @itemx --delimiters=@var{delim-list}
5435 @opindex --delimiters
5436 Consecutively use the characters in @var{delim-list} instead of
5437 TAB to separate merged lines. When @var{delim-list} is
5438 exhausted, start again at its beginning. Using the above example data:
5441 $ paste -d '%_' num2 let3 num2
5452 @node join invocation
5453 @section @command{join}: Join lines on a common field
5456 @cindex common field, joining on
5458 @command{join} writes to standard output a line for each pair of input
5459 lines that have identical join fields. Synopsis:
5462 join [@var{option}]@dots{} @var{file1} @var{file2}
5465 Either @var{file1} or @var{file2} (but not both) can be @samp{-},
5466 meaning standard input. @var{file1} and @var{file2} should be
5467 sorted on the join fields.
5470 Normally, the sort order is that of the
5471 collating sequence specified by the @env{LC_COLLATE} locale. Unless
5472 the @option{-t} option is given, the sort comparison ignores blanks at
5473 the start of the join field, as in @code{sort -b}. If the
5474 @option{--ignore-case} option is given, the sort comparison ignores
5475 the case of characters in the join field, as in @code{sort -f}.
5477 The @command{sort} and @command{join} commands should use consistent
5478 locales and options if the output of @command{sort} is fed to
5479 @command{join}. You can use a command like @samp{sort -k 1b,1} to
5480 sort a file on its default join field, but if you select a non-default
5481 locale, join field, separator, or comparison options, then you should
5482 do so consistently between @command{join} and @command{sort}.
5483 If @samp{join -t ''} is specified then the whole line is considered which
5484 matches the default operation of sort.
5486 If the input has no unpairable lines, a @acronym{GNU} extension is
5487 available; the sort order can be any order that considers two fields
5488 to be equal if and only if the sort comparison described above
5489 considers them to be equal. For example:
5506 @checkOrderOption{join}
5510 @item the join field is the first field in each line;
5511 @item fields in the input are separated by one or more blanks, with leading
5512 blanks on the line ignored;
5513 @item fields in the output are separated by a space;
5514 @item each output line consists of the join field, the remaining
5515 fields from @var{file1}, then the remaining fields from @var{file2}.
5518 The program accepts the following options. Also see @ref{Common options}.
5522 @item -a @var{file-number}
5524 Print a line for each unpairable line in file @var{file-number} (either
5525 @samp{1} or @samp{2}), in addition to the normal output.
5528 Fail with an error message if either input file is wrongly ordered.
5530 @item --nocheck-order
5531 Do not check that both input files are in sorted order. This is the default.
5533 @item -e @var{string}
5535 Replace those output fields that are missing in the input with
5540 Treat the first line of each input file as a header line. The header lines will
5541 be joined and printed as the first output line. If @option{-o} is used to
5542 specify output format, the header line will be printed according to the
5543 specified format. The header lines will not be checked for ordering even if
5544 @option{--check-order} is specified. Also if the header lines from each file
5545 do not match, the heading fields from the first file will be used.
5548 @itemx --ignore-case
5550 @opindex --ignore-case
5551 Ignore differences in case when comparing keys.
5552 With this option, the lines of the input files must be ordered in the same way.
5553 Use @samp{sort -f} to produce this ordering.
5555 @item -1 @var{field}
5557 Join on field @var{field} (a positive integer) of file 1.
5559 @item -2 @var{field}
5561 Join on field @var{field} (a positive integer) of file 2.
5563 @item -j @var{field}
5564 Equivalent to @option{-1 @var{field} -2 @var{field}}.
5566 @item -o @var{field-list}
5567 Construct each output line according to the format in @var{field-list}.
5568 Each element in @var{field-list} is either the single character @samp{0} or
5569 has the form @var{m.n} where the file number, @var{m}, is @samp{1} or
5570 @samp{2} and @var{n} is a positive field number.
5572 A field specification of @samp{0} denotes the join field.
5573 In most cases, the functionality of the @samp{0} field spec
5574 may be reproduced using the explicit @var{m.n} that corresponds
5575 to the join field. However, when printing unpairable lines
5576 (using either of the @option{-a} or @option{-v} options), there is no way
5577 to specify the join field using @var{m.n} in @var{field-list}
5578 if there are unpairable lines in both files.
5579 To give @command{join} that functionality, @acronym{POSIX} invented the @samp{0}
5580 field specification notation.
5582 The elements in @var{field-list}
5583 are separated by commas or blanks.
5584 Blank separators typically need to be quoted for the shell. For
5585 example, the commands @samp{join -o 1.2,2.2} and @samp{join -o '1.2
5586 2.2'} are equivalent.
5588 All output lines---including those printed because of any -a or -v
5589 option---are subject to the specified @var{field-list}.
5592 Use character @var{char} as the input and output field separator.
5593 Treat as significant each occurrence of @var{char} in the input file.
5594 Use @samp{sort -t @var{char}}, without the @option{-b} option of
5595 @samp{sort}, to produce this ordering. If @samp{join -t ''} is specified,
5596 the whole line is considered, matching the default operation of sort.
5597 If @samp{-t '\0'} is specified then the @acronym{ASCII} @sc{nul}
5598 character is used to delimit the fields.
5600 @item -v @var{file-number}
5601 Print a line for each unpairable line in file @var{file-number}
5602 (either @samp{1} or @samp{2}), instead of the normal output.
5609 @node Operating on characters
5610 @chapter Operating on characters
5612 @cindex operating on characters
5614 This commands operate on individual characters.
5617 * tr invocation:: Translate, squeeze, and/or delete characters.
5618 * expand invocation:: Convert tabs to spaces.
5619 * unexpand invocation:: Convert spaces to tabs.
5624 @section @command{tr}: Translate, squeeze, and/or delete characters
5631 tr [@var{option}]@dots{} @var{set1} [@var{set2}]
5634 @command{tr} copies standard input to standard output, performing
5635 one of the following operations:
5639 translate, and optionally squeeze repeated characters in the result,
5641 squeeze repeated characters,
5645 delete characters, then squeeze repeated characters from the result.
5648 The @var{set1} and (if given) @var{set2} arguments define ordered
5649 sets of characters, referred to below as @var{set1} and @var{set2}. These
5650 sets are the characters of the input that @command{tr} operates on.
5651 The @option{--complement} (@option{-c}, @option{-C}) option replaces
5653 complement (all of the characters that are not in @var{set1}).
5655 Currently @command{tr} fully supports only single-byte characters.
5656 Eventually it will support multibyte characters; when it does, the
5657 @option{-C} option will cause it to complement the set of characters,
5658 whereas @option{-c} will cause it to complement the set of values.
5659 This distinction will matter only when some values are not characters,
5660 and this is possible only in locales using multibyte encodings when
5661 the input contains encoding errors.
5663 The program accepts the @option{--help} and @option{--version}
5664 options. @xref{Common options}. Options must precede operands.
5669 * Character sets:: Specifying sets of characters.
5670 * Translating:: Changing one set of characters to another.
5671 * Squeezing:: Squeezing repeats and deleting.
5675 @node Character sets
5676 @subsection Specifying sets of characters
5678 @cindex specifying sets of characters
5680 The format of the @var{set1} and @var{set2} arguments resembles
5681 the format of regular expressions; however, they are not regular
5682 expressions, only lists of characters. Most characters simply
5683 represent themselves in these strings, but the strings can contain
5684 the shorthands listed below, for convenience. Some of them can be
5685 used only in @var{set1} or @var{set2}, as noted below.
5689 @item Backslash escapes
5690 @cindex backslash escapes
5692 The following backslash escape sequences are recognized:
5710 The character with the value given by @var{ooo}, which is 1 to 3
5716 While a backslash followed by a character not listed above is
5717 interpreted as that character, the backslash also effectively
5718 removes any special significance, so it is useful to escape
5719 @samp{[}, @samp{]}, @samp{*}, and @samp{-}.
5724 The notation @samp{@var{m}-@var{n}} expands to all of the characters
5725 from @var{m} through @var{n}, in ascending order. @var{m} should
5726 collate before @var{n}; if it doesn't, an error results. As an example,
5727 @samp{0-9} is the same as @samp{0123456789}.
5729 @sc{gnu} @command{tr} does not support the System V syntax that uses square
5730 brackets to enclose ranges. Translations specified in that format
5731 sometimes work as expected, since the brackets are often transliterated
5732 to themselves. However, they should be avoided because they sometimes
5733 behave unexpectedly. For example, @samp{tr -d '[0-9]'} deletes brackets
5736 Many historically common and even accepted uses of ranges are not
5737 portable. For example, on @acronym{EBCDIC} hosts using the @samp{A-Z}
5738 range will not do what most would expect because @samp{A} through @samp{Z}
5739 are not contiguous as they are in @acronym{ASCII}.
5740 If you can rely on a @acronym{POSIX} compliant version of @command{tr}, then
5741 the best way to work around this is to use character classes (see below).
5742 Otherwise, it is most portable (and most ugly) to enumerate the members
5745 @item Repeated characters
5746 @cindex repeated characters
5748 The notation @samp{[@var{c}*@var{n}]} in @var{set2} expands to @var{n}
5749 copies of character @var{c}. Thus, @samp{[y*6]} is the same as
5750 @samp{yyyyyy}. The notation @samp{[@var{c}*]} in @var{string2} expands
5751 to as many copies of @var{c} as are needed to make @var{set2} as long as
5752 @var{set1}. If @var{n} begins with @samp{0}, it is interpreted in
5753 octal, otherwise in decimal.
5755 @item Character classes
5756 @cindex character classes
5758 The notation @samp{[:@var{class}:]} expands to all of the characters in
5759 the (predefined) class @var{class}. The characters expand in no
5760 particular order, except for the @code{upper} and @code{lower} classes,
5761 which expand in ascending order. When the @option{--delete} (@option{-d})
5762 and @option{--squeeze-repeats} (@option{-s}) options are both given, any
5763 character class can be used in @var{set2}. Otherwise, only the
5764 character classes @code{lower} and @code{upper} are accepted in
5765 @var{set2}, and then only if the corresponding character class
5766 (@code{upper} and @code{lower}, respectively) is specified in the same
5767 relative position in @var{set1}. Doing this specifies case conversion.
5768 The class names are given below; an error results when an invalid class
5780 Horizontal whitespace.
5789 Printable characters, not including space.
5795 Printable characters, including space.
5798 Punctuation characters.
5801 Horizontal or vertical whitespace.
5810 @item Equivalence classes
5811 @cindex equivalence classes
5813 The syntax @samp{[=@var{c}=]} expands to all of the characters that are
5814 equivalent to @var{c}, in no particular order. Equivalence classes are
5815 a relatively recent invention intended to support non-English alphabets.
5816 But there seems to be no standard way to define them or determine their
5817 contents. Therefore, they are not fully implemented in @sc{gnu} @command{tr};
5818 each character's equivalence class consists only of that character,
5819 which is of no particular use.
5825 @subsection Translating
5827 @cindex translating characters
5829 @command{tr} performs translation when @var{set1} and @var{set2} are
5830 both given and the @option{--delete} (@option{-d}) option is not given.
5831 @command{tr} translates each character of its input that is in @var{set1}
5832 to the corresponding character in @var{set2}. Characters not in
5833 @var{set1} are passed through unchanged. When a character appears more
5834 than once in @var{set1} and the corresponding characters in @var{set2}
5835 are not all the same, only the final one is used. For example, these
5836 two commands are equivalent:
5843 A common use of @command{tr} is to convert lowercase characters to
5844 uppercase. This can be done in many ways. Here are three of them:
5847 tr abcdefghijklmnopqrstuvwxyz ABCDEFGHIJKLMNOPQRSTUVWXYZ
5849 tr '[:lower:]' '[:upper:]'
5853 But note that using ranges like @code{a-z} above is not portable.
5855 When @command{tr} is performing translation, @var{set1} and @var{set2}
5856 typically have the same length. If @var{set1} is shorter than
5857 @var{set2}, the extra characters at the end of @var{set2} are ignored.
5859 On the other hand, making @var{set1} longer than @var{set2} is not
5860 portable; @acronym{POSIX} says that the result is undefined. In this situation,
5861 BSD @command{tr} pads @var{set2} to the length of @var{set1} by repeating
5862 the last character of @var{set2} as many times as necessary. System V
5863 @command{tr} truncates @var{set1} to the length of @var{set2}.
5865 By default, @sc{gnu} @command{tr} handles this case like BSD @command{tr}.
5866 When the @option{--truncate-set1} (@option{-t}) option is given,
5867 @sc{gnu} @command{tr} handles this case like the System V @command{tr}
5868 instead. This option is ignored for operations other than translation.
5870 Acting like System V @command{tr} in this case breaks the relatively common
5874 tr -cs A-Za-z0-9 '\012'
5878 because it converts only zero bytes (the first element in the
5879 complement of @var{set1}), rather than all non-alphanumerics, to
5883 By the way, the above idiom is not portable because it uses ranges, and
5884 it assumes that the octal code for newline is 012.
5885 Assuming a @acronym{POSIX} compliant @command{tr}, here is a better way to write it:
5888 tr -cs '[:alnum:]' '[\n*]'
5893 @subsection Squeezing repeats and deleting
5895 @cindex squeezing repeat characters
5896 @cindex deleting characters
5898 When given just the @option{--delete} (@option{-d}) option, @command{tr}
5899 removes any input characters that are in @var{set1}.
5901 When given just the @option{--squeeze-repeats} (@option{-s}) option,
5902 @command{tr} replaces each input sequence of a repeated character that
5903 is in @var{set1} with a single occurrence of that character.
5905 When given both @option{--delete} and @option{--squeeze-repeats}, @command{tr}
5906 first performs any deletions using @var{set1}, then squeezes repeats
5907 from any remaining characters using @var{set2}.
5909 The @option{--squeeze-repeats} option may also be used when translating,
5910 in which case @command{tr} first performs translation, then squeezes
5911 repeats from any remaining characters using @var{set2}.
5913 Here are some examples to illustrate various combinations of options:
5918 Remove all zero bytes:
5925 Put all words on lines by themselves. This converts all
5926 non-alphanumeric characters to newlines, then squeezes each string
5927 of repeated newlines into a single newline:
5930 tr -cs '[:alnum:]' '[\n*]'
5934 Convert each sequence of repeated newlines to a single newline:
5941 Find doubled occurrences of words in a document.
5942 @c Separate the following two "the"s, so typo checkers don't complain.
5943 For example, people often write ``the @w{}the'' with the repeated words
5944 separated by a newline. The Bourne shell script below works first
5945 by converting each sequence of punctuation and blank characters to a
5946 single newline. That puts each ``word'' on a line by itself.
5947 Next it maps all uppercase characters to lower case, and finally it
5948 runs @command{uniq} with the @option{-d} option to print out only the words
5954 | tr -s '[:punct:][:blank:]' '[\n*]' \
5955 | tr '[:upper:]' '[:lower:]' \
5960 Deleting a small set of characters is usually straightforward. For example,
5961 to remove all @samp{a}s, @samp{x}s, and @samp{M}s you would do this:
5967 However, when @samp{-} is one of those characters, it can be tricky because
5968 @samp{-} has special meanings. Performing the same task as above but also
5969 removing all @samp{-} characters, we might try @code{tr -d -axM}, but
5970 that would fail because @command{tr} would try to interpret @option{-a} as
5971 a command-line option. Alternatively, we could try putting the hyphen
5972 inside the string, @code{tr -d a-xM}, but that wouldn't work either because
5973 it would make @command{tr} interpret @code{a-x} as the range of characters
5974 @samp{a}@dots{}@samp{x} rather than the three.
5975 One way to solve the problem is to put the hyphen at the end of the list
5982 Or you can use @samp{--} to terminate option processing:
5988 More generally, use the character class notation @code{[=c=]}
5989 with @samp{-} (or any other character) in place of the @samp{c}:
5995 Note how single quotes are used in the above example to protect the
5996 square brackets from interpretation by a shell.
6001 @node expand invocation
6002 @section @command{expand}: Convert tabs to spaces
6005 @cindex tabs to spaces, converting
6006 @cindex converting tabs to spaces
6008 @command{expand} writes the contents of each given @var{file}, or standard
6009 input if none are given or for a @var{file} of @samp{-}, to standard
6010 output, with tab characters converted to the appropriate number of
6014 expand [@var{option}]@dots{} [@var{file}]@dots{}
6017 By default, @command{expand} converts all tabs to spaces. It preserves
6018 backspace characters in the output; they decrement the column count for
6019 tab calculations. The default action is equivalent to @option{-t 8} (set
6020 tabs every 8 columns).
6022 The program accepts the following options. Also see @ref{Common options}.
6026 @item -t @var{tab1}[,@var{tab2}]@dots{}
6027 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6030 @cindex tab stops, setting
6031 If only one tab stop is given, set the tabs @var{tab1} spaces apart
6032 (default is 8). Otherwise, set the tabs at columns @var{tab1},
6033 @var{tab2}, @dots{} (numbered from 0), and replace any tabs beyond the
6034 last tab stop given with single spaces. Tab stops can be separated by
6035 blanks as well as by commas.
6037 For compatibility, GNU @command{expand} also accepts the obsolete
6038 option syntax, @option{-@var{t1}[,@var{t2}]@dots{}}. New scripts
6039 should use @option{-t @var{t1}[,@var{t2}]@dots{}} instead.
6045 @cindex initial tabs, converting
6046 Only convert initial tabs (those that precede all non-space or non-tab
6047 characters) on each line to spaces.
6054 @node unexpand invocation
6055 @section @command{unexpand}: Convert spaces to tabs
6059 @command{unexpand} writes the contents of each given @var{file}, or
6060 standard input if none are given or for a @var{file} of @samp{-}, to
6061 standard output, converting blanks at the beginning of each line into
6062 as many tab characters as needed. In the default @acronym{POSIX}
6063 locale, a @dfn{blank} is a space or a tab; other locales may specify
6064 additional blank characters. Synopsis:
6067 unexpand [@var{option}]@dots{} [@var{file}]@dots{}
6070 By default, @command{unexpand} converts only initial blanks (those
6071 that precede all non-blank characters) on each line. It
6072 preserves backspace characters in the output; they decrement the column
6073 count for tab calculations. By default, tabs are set at every 8th
6076 The program accepts the following options. Also see @ref{Common options}.
6080 @item -t @var{tab1}[,@var{tab2}]@dots{}
6081 @itemx --tabs=@var{tab1}[,@var{tab2}]@dots{}
6084 If only one tab stop is given, set the tabs @var{tab1} columns apart
6085 instead of the default 8. Otherwise, set the tabs at columns
6086 @var{tab1}, @var{tab2}, @dots{} (numbered from 0), and leave blanks
6087 beyond the tab stops given unchanged. Tab stops can be separated by
6088 blanks as well as by commas. This option implies the @option{-a} option.
6090 For compatibility, GNU @command{unexpand} supports the obsolete option syntax,
6091 @option{-@var{tab1}[,@var{tab2}]@dots{}}, where tab stops must be
6092 separated by commas. (Unlike @option{-t}, this obsolete option does
6093 not imply @option{-a}.) New scripts should use @option{--first-only -t
6094 @var{tab1}[,@var{tab2}]@dots{}} instead.
6100 Also convert all sequences of two or more blanks just before a tab stop,
6101 even if they occur after non-blank characters in a line.
6108 @node Directory listing
6109 @chapter Directory listing
6111 This chapter describes the @command{ls} command and its variants @command{dir}
6112 and @command{vdir}, which list information about files.
6115 * ls invocation:: List directory contents.
6116 * dir invocation:: Briefly ls.
6117 * vdir invocation:: Verbosely ls.
6118 * dircolors invocation:: Color setup for ls, etc.
6123 @section @command{ls}: List directory contents
6126 @cindex directory listing
6128 The @command{ls} program lists information about files (of any type,
6129 including directories). Options and file arguments can be intermixed
6130 arbitrarily, as usual.
6132 For non-option command-line arguments that are directories, by default
6133 @command{ls} lists the contents of directories, not recursively, and
6134 omitting files with names beginning with @samp{.}. For other non-option
6135 arguments, by default @command{ls} lists just the file name. If no
6136 non-option argument is specified, @command{ls} operates on the current
6137 directory, acting as if it had been invoked with a single argument of @samp{.}.
6140 By default, the output is sorted alphabetically, according to the locale
6141 settings in effect.@footnote{If you use a non-@acronym{POSIX}
6142 locale (e.g., by setting @env{LC_ALL} to @samp{en_US}), then @command{ls} may
6143 produce output that is sorted differently than you're accustomed to.
6144 In that case, set the @env{LC_ALL} environment variable to @samp{C}.}
6145 If standard output is
6146 a terminal, the output is in columns (sorted vertically) and control
6147 characters are output as question marks; otherwise, the output is listed
6148 one per line and control characters are output as-is.
6150 Because @command{ls} is such a fundamental program, it has accumulated many
6151 options over the years. They are described in the subsections below;
6152 within each section, options are listed alphabetically (ignoring case).
6153 The division of options into the subsections is not absolute, since some
6154 options affect more than one aspect of @command{ls}'s operation.
6156 @cindex exit status of @command{ls}
6161 1 minor problems (e.g., failure to access a file or directory not
6162 specified as a command line argument. This happens when listing a
6163 directory in which entries are actively being removed or renamed.)
6164 2 serious trouble (e.g., memory exhausted, invalid option, failure
6165 to access a file or directory specified as a command line argument
6166 or a directory loop)
6169 Also see @ref{Common options}.
6172 * Which files are listed::
6173 * What information is listed::
6174 * Sorting the output::
6175 * Details about version sort::
6176 * General output formatting::
6177 * Formatting file timestamps::
6178 * Formatting the file names::
6182 @node Which files are listed
6183 @subsection Which files are listed
6185 These options determine which files @command{ls} lists information for.
6186 By default, @command{ls} lists files and the contents of any
6187 directories on the command line, except that in directories it ignores
6188 files whose names start with @samp{.}.
6196 In directories, do not ignore file names that start with @samp{.}.
6201 @opindex --almost-all
6202 In directories, do not ignore all file names that start with @samp{.};
6203 ignore only @file{.} and @file{..}. The @option{--all} (@option{-a})
6204 option overrides this option.
6207 @itemx --ignore-backups
6209 @opindex --ignore-backups
6210 @cindex backup files, ignoring
6211 In directories, ignore files that end with @samp{~}. This option is
6212 equivalent to @samp{--ignore='*~' --ignore='.*~'}.
6217 @opindex --directory
6218 List just the names of directories, as with other types of files, rather
6219 than listing their contents.
6220 @c The following sentence is the same as the one for -F.
6221 Do not follow symbolic links listed on the
6222 command line unless the @option{--dereference-command-line} (@option{-H}),
6223 @option{--dereference} (@option{-L}), or
6224 @option{--dereference-command-line-symlink-to-dir} options are specified.
6227 @itemx --dereference-command-line
6229 @opindex --dereference-command-line
6230 @cindex symbolic links, dereferencing
6231 If a command line argument specifies a symbolic link, show information
6232 for the file the link references rather than for the link itself.
6234 @itemx --dereference-command-line-symlink-to-dir
6235 @opindex --dereference-command-line-symlink-to-dir
6236 @cindex symbolic links, dereferencing
6237 Do not dereference symbolic links, with one exception:
6238 if a command line argument specifies a symbolic link that refers to
6239 a directory, show information for that directory rather than for the
6241 This is the default behavior when no other dereferencing-related
6242 option has been specified (@option{--classify} (@option{-F}),
6243 @option{--directory} (@option{-d}),
6245 @option{--dereference} (@option{-L}), or
6246 @option{--dereference-command-line} (@option{-H})).
6248 @item --group-directories-first
6249 @opindex --group-directories-first
6250 Group all the directories before the files and then sort the
6251 directories and the files separately using the selected sort key
6252 (see --sort option).
6253 That is, this option specifies a primary sort key,
6254 and the --sort option specifies a secondary key.
6255 However, any use of @option{--sort=none}
6256 (@option{-U}) disables this option altogether.
6258 @item --hide=PATTERN
6259 @opindex --hide=@var{pattern}
6260 In directories, ignore files whose names match the shell pattern
6261 @var{pattern}, unless the @option{--all} (@option{-a}) or
6262 @option{--almost-all} (@option{-A}) is also given. This
6263 option acts like @option{--ignore=@var{pattern}} except that it has no
6264 effect if @option{--all} (@option{-a}) or @option{--almost-all}
6265 (@option{-A}) is also given.
6267 This option can be useful in shell aliases. For example, if
6268 @command{lx} is an alias for @samp{ls --hide='*~'} and @command{ly} is
6269 an alias for @samp{ls --ignore='*~'}, then the command @samp{lx -A}
6270 lists the file @file{README~} even though @samp{ly -A} would not.
6272 @item -I @var{pattern}
6273 @itemx --ignore=@var{pattern}
6275 @opindex --ignore=@var{pattern}
6276 In directories, ignore files whose names match the shell pattern
6277 (not regular expression) @var{pattern}. As
6278 in the shell, an initial @samp{.} in a file name does not match a
6279 wildcard at the start of @var{pattern}. Sometimes it is useful
6280 to give this option several times. For example,
6283 $ ls --ignore='.??*' --ignore='.[^.]' --ignore='#*'
6286 The first option ignores names of length 3 or more that start with @samp{.},
6287 the second ignores all two-character names that start with @samp{.}
6288 except @samp{..}, and the third ignores names that start with @samp{#}.
6291 @itemx --dereference
6293 @opindex --dereference
6294 @cindex symbolic links, dereferencing
6295 When showing file information for a symbolic link, show information
6296 for the file the link references rather than the link itself.
6297 However, even with this option, @command{ls} still prints the name
6298 of the link itself, not the name of the file that the link points to.
6303 @opindex --recursive
6304 @cindex recursive directory listing
6305 @cindex directory listing, recursive
6306 List the contents of all directories recursively.
6311 @node What information is listed
6312 @subsection What information is listed
6314 These options affect the information that @command{ls} displays. By
6315 default, only file names are shown.
6321 @cindex hurd, author, printing
6322 List each file's author when producing long format directory listings.
6323 In GNU/Hurd, file authors can differ from their owners, but in other
6324 operating systems the two are the same.
6330 @cindex dired Emacs mode support
6331 With the long listing (@option{-l}) format, print an additional line after
6335 //DIRED// @var{beg1} @var{end1} @var{beg2} @var{end2} @dots{}
6339 The @var{begn} and @var{endn} are unsigned integers that record the
6340 byte position of the beginning and end of each file name in the output.
6341 This makes it easy for Emacs to find the names, even when they contain
6342 unusual characters such as space or newline, without fancy searching.
6344 If directories are being listed recursively (@option{-R}), output a similar
6345 line with offsets for each subdirectory name:
6348 //SUBDIRED// @var{beg1} @var{end1} @dots{}
6351 Finally, output a line of the form:
6354 //DIRED-OPTIONS// --quoting-style=@var{word}
6358 where @var{word} is the quoting style (@pxref{Formatting the file names}).
6360 Here is an actual example:
6363 $ mkdir -p a/sub/deeper a/sub2
6365 $ touch a/sub/deeper/file
6366 $ ls -gloRF --dired a
6369 -rw-r--r-- 1 0 Jun 10 12:27 f1
6370 -rw-r--r-- 1 0 Jun 10 12:27 f2
6371 drwxr-xr-x 3 4096 Jun 10 12:27 sub/
6372 drwxr-xr-x 2 4096 Jun 10 12:27 sub2/
6376 drwxr-xr-x 2 4096 Jun 10 12:27 deeper/
6380 -rw-r--r-- 1 0 Jun 10 12:27 file
6384 //DIRED// 48 50 84 86 120 123 158 162 217 223 282 286
6385 //SUBDIRED// 2 3 167 172 228 240 290 296
6386 //DIRED-OPTIONS// --quoting-style=literal
6389 Note that the pairs of offsets on the @samp{//DIRED//} line above delimit
6390 these names: @file{f1}, @file{f2}, @file{sub}, @file{sub2}, @file{deeper},
6392 The offsets on the @samp{//SUBDIRED//} line delimit the following
6393 directory names: @file{a}, @file{a/sub}, @file{a/sub/deeper}, @file{a/sub2}.
6395 Here is an example of how to extract the fifth entry name, @samp{deeper},
6396 corresponding to the pair of offsets, 222 and 228:
6399 $ ls -gloRF --dired a > out
6400 $ dd bs=1 skip=222 count=6 < out 2>/dev/null; echo
6404 Note that although the listing above includes a trailing slash
6405 for the @samp{deeper} entry, the offsets select the name without
6406 the trailing slash. However, if you invoke @command{ls} with @option{--dired}
6407 along with an option like @option{--escape} (aka @option{-b}) and operate
6408 on a file whose name contains special characters, notice that the backslash
6413 $ ls -blog --dired 'a b'
6414 -rw-r--r-- 1 0 Jun 10 12:28 a\ b
6416 //DIRED-OPTIONS// --quoting-style=escape
6419 If you use a quoting style that adds quote marks
6420 (e.g., @option{--quoting-style=c}), then the offsets include the quote marks.
6421 So beware that the user may select the quoting style via the environment
6422 variable @env{QUOTING_STYLE}. Hence, applications using @option{--dired}
6423 should either specify an explicit @option{--quoting-style=literal} option
6424 (aka @option{-N} or @option{--literal}) on the command line, or else be
6425 prepared to parse the escaped names.
6428 @opindex --full-time
6429 Produce long format directory listings, and list times in full. It is
6430 equivalent to using @option{--format=long} with
6431 @option{--time-style=full-iso} (@pxref{Formatting file timestamps}).
6435 Produce long format directory listings, but don't display owner information.
6441 Inhibit display of group information in a long format directory listing.
6442 (This is the default in some non-@sc{gnu} versions of @command{ls}, so we
6443 provide this option for compatibility.)
6451 @cindex inode number, printing
6452 Print the inode number (also called the file serial number and index
6453 number) of each file to the left of the file name. (This number
6454 uniquely identifies each file within a particular file system.)
6457 @itemx --format=long
6458 @itemx --format=verbose
6461 @opindex long ls @r{format}
6462 @opindex verbose ls @r{format}
6463 In addition to the name of each file, print the file type, file mode bits,
6464 number of hard links, owner name, group name, size, and
6465 timestamp (@pxref{Formatting file timestamps}), normally
6466 the modification time. Print question marks for information that
6467 cannot be determined.
6469 Normally the size is printed as a byte count without punctuation, but
6470 this can be overridden (@pxref{Block size}). For example, @option{-h}
6471 prints an abbreviated, human-readable count, and
6472 @samp{--block-size="'1"} prints a byte count with the thousands
6473 separator of the current locale.
6475 For each directory that is listed, preface the files with a line
6476 @samp{total @var{blocks}}, where @var{blocks} is the total disk allocation
6477 for all files in that directory. The block size currently defaults to 1024
6478 bytes, but this can be overridden (@pxref{Block size}).
6479 The @var{blocks} computed counts each hard link separately;
6480 this is arguably a deficiency.
6482 The file type is one of the following characters:
6484 @c The commented-out entries are ones we're not sure about.
6492 character special file
6494 high performance (``contiguous data'') file
6498 door (Solaris 2.5 and up)
6500 @c semaphore, if this is a distinct file type
6504 @c multiplexed file (7th edition Unix; obsolete)
6506 off-line (``migrated'') file (Cray DMF)
6508 network special file (HP-UX)
6512 port (Solaris 10 and up)
6514 @c message queue, if this is a distinct file type
6518 @c shared memory object, if this is a distinct file type
6520 @c typed memory object, if this is a distinct file type
6522 @c whiteout (4.4BSD; not implemented)
6524 some other file type
6527 @cindex permissions, output by @command{ls}
6528 The file mode bits listed are similar to symbolic mode specifications
6529 (@pxref{Symbolic Modes}). But @command{ls} combines multiple bits into the
6530 third character of each set of permissions as follows:
6534 If the set-user-ID or set-group-ID bit and the corresponding executable bit
6538 If the set-user-ID or set-group-ID bit is set but the corresponding
6539 executable bit is not set.
6542 If the restricted deletion flag or sticky bit, and the
6543 other-executable bit, are both set. The restricted deletion flag is
6544 another name for the sticky bit. @xref{Mode Structure}.
6547 If the restricted deletion flag or sticky bit is set but the
6548 other-executable bit is not set.
6551 If the executable bit is set and none of the above apply.
6557 Following the file mode bits is a single character that specifies
6558 whether an alternate access method such as an access control list
6559 applies to the file. When the character following the file mode bits is a
6560 space, there is no alternate access method. When it is a printing
6561 character, then there is such a method.
6563 GNU @command{ls} uses a @samp{.} character to indicate a file
6564 with an SELinux security context, but no other alternate access method.
6566 A file with any other combination of alternate access methods
6567 is marked with a @samp{+} character.
6570 @itemx --numeric-uid-gid
6572 @opindex --numeric-uid-gid
6573 @cindex numeric uid and gid
6574 @cindex numeric user and group IDs
6575 Produce long format directory listings, but
6576 display numeric user and group IDs instead of the owner and group names.
6580 Produce long format directory listings, but don't display group information.
6581 It is equivalent to using @option{--format=long} with @option{--no-group} .
6587 @cindex disk allocation
6588 @cindex size of files, reporting
6589 Print the disk allocation of each file to the left of the file name.
6590 This is the amount of disk space used by the file, which is usually a
6591 bit more than the file's size, but it can be less if the file has holes.
6593 Normally the disk allocation is printed in units of
6594 1024 bytes, but this can be overridden (@pxref{Block size}).
6596 @cindex NFS mounts from BSD to HP-UX
6597 For files that are NFS-mounted from an HP-UX system to a BSD system,
6598 this option reports sizes that are half the correct values. On HP-UX
6599 systems, it reports sizes that are twice the correct values for files
6600 that are NFS-mounted from BSD systems. This is due to a flaw in HP-UX;
6601 it also affects the HP-UX @command{ls} program.
6610 @cindex security context
6611 Display the SELinux security context or @samp{?} if none is found.
6612 When used with the @option{-l} option, print the security context
6613 to the left of the size column.
6618 @node Sorting the output
6619 @subsection Sorting the output
6621 @cindex sorting @command{ls} output
6622 These options change the order in which @command{ls} sorts the information
6623 it outputs. By default, sorting is done by character code
6624 (e.g., @acronym{ASCII} order).
6630 @itemx --time=status
6633 @opindex ctime@r{, printing or sorting by}
6634 @opindex status time@r{, printing or sorting by}
6635 @opindex use time@r{, printing or sorting files by}
6636 If the long listing format (e.g., @option{-l}, @option{-o}) is being used,
6637 print the status change time (the @samp{ctime} in the inode) instead of
6638 the modification time.
6639 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6640 or when not using a long listing format,
6641 sort according to the status change time.
6645 @cindex unsorted directory listing
6646 @cindex directory order, listing by
6647 Primarily, like @option{-U}---do not sort; list the files in whatever
6648 order they are stored in the directory. But also enable @option{-a} (list
6649 all files) and disable @option{-l}, @option{--color}, and @option{-s} (if they
6650 were specified before the @option{-f}).
6656 @cindex reverse sorting
6657 Reverse whatever the sorting method is---e.g., list files in reverse
6658 alphabetical order, youngest first, smallest first, or whatever.
6664 @opindex size of files@r{, sorting files by}
6665 Sort by file size, largest first.
6671 @opindex modification time@r{, sorting files by}
6672 Sort by modification time (the @samp{mtime} in the inode), newest first.
6676 @itemx --time=access
6680 @opindex use time@r{, printing or sorting files by}
6681 @opindex atime@r{, printing or sorting files by}
6682 @opindex access time@r{, printing or sorting files by}
6683 If the long listing format (e.g., @option{--format=long}) is being used,
6684 print the last access time (the @samp{atime} in the inode).
6685 When explicitly sorting by time (@option{--sort=time} or @option{-t})
6686 or when not using a long listing format, sort according to the access time.
6692 @opindex none@r{, sorting option for @command{ls}}
6693 Do not sort; list the files in whatever order they are
6694 stored in the directory. (Do not do any of the other unrelated things
6695 that @option{-f} does.) This is especially useful when listing very large
6696 directories, since not doing any sorting can be noticeably faster.
6699 @itemx --sort=version
6702 @opindex version@r{, sorting option for @command{ls}}
6703 Sort by version name and number, lowest first. It behaves like a default
6704 sort, except that each sequence of decimal digits is treated numerically
6705 as an index/version number. (@xref{Details about version sort}.)
6708 @itemx --sort=extension
6711 @opindex extension@r{, sorting files by}
6712 Sort directory contents alphabetically by file extension (characters
6713 after the last @samp{.}); files with no extension are sorted first.
6718 @node Details about version sort
6719 @subsection Details about version sort
6721 Version sorting handles the fact that file names frequently include indices or
6722 version numbers. Standard sorting usually does not produce the order that one
6723 expects because comparisons are made on a character-by-character basis.
6724 Version sorting is especially useful when browsing directories that contain
6725 many files with indices/version numbers in their names:
6729 abc.zml-1.gz abc.zml-1.gz
6730 abc.zml-12.gz abc.zml-2.gz
6731 abc.zml-2.gz abc.zml-12.gz
6734 Version-sorted strings are compared such that if @var{ver1} and @var{ver2}
6735 are version numbers and @var{prefix} and @var{suffix} (@var{suffix} matching
6736 the regular expression @samp{(\.[A-Za-z~][A-Za-z0-9~]*)*}) are strings then
6737 @var{ver1} < @var{ver2} implies that the name composed of
6738 ``@var{prefix} @var{ver1} @var{suffix}'' sorts before
6739 ``@var{prefix} @var{ver2} @var{suffix}''.
6741 Note also that leading zeros of numeric parts are ignored:
6745 abc-1.007.tgz abc-1.01a.tgz
6746 abc-1.012b.tgz abc-1.007.tgz
6747 abc-1.01a.tgz abc-1.012b.tgz
6750 This functionality is implemented using gnulib's @code{filevercmp} function,
6751 which has some caveats worth noting.
6754 @item @env{LC_COLLATE} is ignored, which means @samp{ls -v} and @samp{sort -V}
6755 will sort non-numeric prefixes as if the @env{LC_COLLATE} locale category
6756 was set to @samp{C}.
6757 @item Some suffixes will not be matched by the regular
6758 expression mentioned above. Consequently these examples may
6759 not sort as you expect:
6767 abc-1.2.3.4.x86_64.rpm
6768 abc-1.2.3.x86_64.rpm
6772 @node General output formatting
6773 @subsection General output formatting
6775 These options affect the appearance of the overall output.
6780 @itemx --format=single-column
6783 @opindex single-column @r{output of files}
6784 List one file per line. This is the default for @command{ls} when standard
6785 output is not a terminal.
6788 @itemx --format=vertical
6791 @opindex vertical @r{sorted files in columns}
6792 List files in columns, sorted vertically. This is the default for
6793 @command{ls} if standard output is a terminal. It is always the default
6794 for the @command{dir} program.
6795 @sc{gnu} @command{ls} uses variable width columns to display as many files as
6796 possible in the fewest lines.
6798 @item --color [=@var{when}]
6800 @cindex color, distinguishing file types with
6801 Specify whether to use color for distinguishing file types. @var{when}
6802 may be omitted, or one of:
6805 @vindex none @r{color option}
6806 - Do not use color at all. This is the default.
6808 @vindex auto @r{color option}
6809 @cindex terminal, using color iff
6810 - Only use color if standard output is a terminal.
6812 @vindex always @r{color option}
6815 Specifying @option{--color} and no @var{when} is equivalent to
6816 @option{--color=always}.
6817 Piping a colorized listing through a pager like @command{more} or
6818 @command{less} usually produces unreadable results. However, using
6819 @code{more -f} does seem to work.
6823 @itemx --indicator-style=classify
6826 @opindex --indicator-style
6827 @cindex file type and executables, marking
6828 @cindex executables and file type, marking
6829 Append a character to each file name indicating the file type. Also,
6830 for regular files that are executable, append @samp{*}. The file type
6831 indicators are @samp{/} for directories, @samp{@@} for symbolic links,
6832 @samp{|} for FIFOs, @samp{=} for sockets, @samp{>} for doors,
6833 and nothing for regular files.
6834 @c The following sentence is the same as the one for -d.
6835 Do not follow symbolic links listed on the
6836 command line unless the @option{--dereference-command-line} (@option{-H}),
6837 @option{--dereference} (@option{-L}), or
6838 @option{--dereference-command-line-symlink-to-dir} options are specified.
6841 @itemx --indicator-style=file-type
6842 @opindex --file-type
6843 @opindex --indicator-style
6844 @cindex file type, marking
6845 Append a character to each file name indicating the file type. This is
6846 like @option{-F}, except that executables are not marked.
6848 @item --indicator-style=@var{word}
6849 @opindex --indicator-style
6850 Append a character indicator with style @var{word} to entry names,
6855 Do not append any character indicator; this is the default.
6857 Append @samp{/} for directories. This is the same as the @option{-p}
6860 Append @samp{/} for directories, @samp{@@} for symbolic links, @samp{|}
6861 for FIFOs, @samp{=} for sockets, and nothing for regular files. This is
6862 the same as the @option{--file-type} option.
6864 Append @samp{*} for executable regular files, otherwise behave as for
6865 @samp{file-type}. This is the same as the @option{-F} or
6866 @option{--classify} option.
6871 Print file sizes in 1024-byte blocks, overriding the default block
6872 size (@pxref{Block size}).
6873 This option is equivalent to @option{--block-size=1K}.
6876 @itemx --format=commas
6879 @opindex commas@r{, outputting between files}
6880 List files horizontally, with as many as will fit on each line,
6881 separated by @samp{, } (a comma and a space).
6884 @itemx --indicator-style=slash
6886 @opindex --indicator-style
6887 @cindex file type, marking
6888 Append a @samp{/} to directory names.
6891 @itemx --format=across
6892 @itemx --format=horizontal
6895 @opindex across@r{, listing files}
6896 @opindex horizontal@r{, listing files}
6897 List the files in columns, sorted horizontally.
6900 @itemx --tabsize=@var{cols}
6903 Assume that each tab stop is @var{cols} columns wide. The default is 8.
6904 @command{ls} uses tabs where possible in the output, for efficiency. If
6905 @var{cols} is zero, do not use tabs at all.
6907 @c FIXME: remove in 2009, if Apple Terminal has been fixed for long enough.
6908 Some terminal emulators (at least Apple Terminal 1.5 (133) from Mac OS X 10.4.8)
6909 do not properly align columns to the right of a TAB following a
6910 non-@acronym{ASCII} byte. If you use such a terminal emulator, use the
6911 @option{-T0} option or put @code{TABSIZE=0} in your environment to tell
6912 @command{ls} to align using spaces, not tabs.
6915 @itemx --width=@var{cols}
6919 Assume the screen is @var{cols} columns wide. The default is taken
6920 from the terminal settings if possible; otherwise the environment
6921 variable @env{COLUMNS} is used if it is set; otherwise the default
6927 @node Formatting file timestamps
6928 @subsection Formatting file timestamps
6930 By default, file timestamps are listed in abbreviated form. Most
6931 locales use a timestamp like @samp{2002-03-30 23:45}. However, the
6932 default @acronym{POSIX} locale uses a date like @samp{Mar 30@ @ 2002}
6933 for non-recent timestamps, and a date-without-year and time like
6934 @samp{Mar 30 23:45} for recent timestamps.
6936 A timestamp is considered to be @dfn{recent} if it is less than six
6937 months old, and is not dated in the future. If a timestamp dated
6938 today is not listed in recent form, the timestamp is in the future,
6939 which means you probably have clock skew problems which may break
6940 programs like @command{make} that rely on file timestamps.
6943 Time stamps are listed according to the time zone rules specified by
6944 the @env{TZ} environment variable, or by the system default rules if
6945 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
6946 with @env{TZ}, libc, The GNU C Library Reference Manual}.
6948 The following option changes how file timestamps are printed.
6951 @item --time-style=@var{style}
6952 @opindex --time-style
6954 List timestamps in style @var{style}. The @var{style} should
6955 be one of the following:
6960 List timestamps using @var{format}, where @var{format} is interpreted
6961 like the format argument of @command{date} (@pxref{date invocation}).
6962 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
6963 @command{ls} to list timestamps like @samp{2002-03-30 23:45:56}. As
6964 with @command{date}, @var{format}'s interpretation is affected by the
6965 @env{LC_TIME} locale category.
6967 If @var{format} contains two format strings separated by a newline,
6968 the former is used for non-recent files and the latter for recent
6969 files; if you want output columns to line up, you may need to insert
6970 spaces in one of the two formats.
6973 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
6974 format with nanosecond precision, e.g., @samp{2002-03-30
6975 23:45:56.477817180 -0700}. This style is equivalent to
6976 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
6978 This is useful because the time output includes all the information that
6979 is available from the operating system. For example, this can help
6980 explain @command{make}'s behavior, since @acronym{GNU} @command{make}
6981 uses the full timestamp to determine whether a file is out of date.
6984 List @acronym{ISO} 8601 date and time in minutes, e.g.,
6985 @samp{2002-03-30 23:45}. These timestamps are shorter than
6986 @samp{full-iso} timestamps, and are usually good enough for everyday
6987 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
6990 List @acronym{ISO} 8601 dates for non-recent timestamps (e.g.,
6991 @samp{2002-03-30@ }), and @acronym{ISO} 8601 month, day, hour, and
6992 minute for recent timestamps (e.g., @samp{03-30 23:45}). These
6993 timestamps are uglier than @samp{long-iso} timestamps, but they carry
6994 nearly the same information in a smaller space and their brevity helps
6995 @command{ls} output fit within traditional 80-column output lines.
6996 The following two @command{ls} invocations are equivalent:
7001 ls -l --time-style="+%Y-%m-%d $newline%m-%d %H:%M"
7002 ls -l --time-style="iso"
7007 List timestamps in a locale-dependent form. For example, a Finnish
7008 locale might list non-recent timestamps like @samp{maalis 30@ @ 2002}
7009 and recent timestamps like @samp{maalis 30 23:45}. Locale-dependent
7010 timestamps typically consume more space than @samp{iso} timestamps and
7011 are harder for programs to parse because locale conventions vary so
7012 widely, but they are easier for many people to read.
7014 The @env{LC_TIME} locale category specifies the timestamp format. The
7015 default @acronym{POSIX} locale uses timestamps like @samp{Mar 30@
7016 @ 2002} and @samp{Mar 30 23:45}; in this locale, the following two
7017 @command{ls} invocations are equivalent:
7022 ls -l --time-style="+%b %e %Y$newline%b %e %H:%M"
7023 ls -l --time-style="locale"
7026 Other locales behave differently. For example, in a German locale,
7027 @option{--time-style="locale"} might be equivalent to
7028 @option{--time-style="+%e. %b %Y $newline%e. %b %H:%M"}
7029 and might generate timestamps like @samp{30. M@"ar 2002@ } and
7030 @samp{30. M@"ar 23:45}.
7032 @item posix-@var{style}
7034 List @acronym{POSIX}-locale timestamps if the @env{LC_TIME} locale
7035 category is @acronym{POSIX}, @var{style} timestamps otherwise. For
7036 example, the @samp{posix-long-iso} style lists
7037 timestamps like @samp{Mar 30@ @ 2002} and @samp{Mar 30 23:45} when in
7038 the @acronym{POSIX} locale, and like @samp{2002-03-30 23:45} otherwise.
7043 You can specify the default value of the @option{--time-style} option
7044 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
7045 the default style is @samp{locale}. @acronym{GNU} Emacs 21.3 and
7046 later use the @option{--dired} option and therefore can parse any date
7047 format, but if you are using Emacs 21.1 or 21.2 and specify a
7048 non-@acronym{POSIX} locale you may need to set
7049 @samp{TIME_STYLE="posix-long-iso"}.
7051 To avoid certain denial-of-service attacks, timestamps that would be
7052 longer than 1000 bytes may be treated as errors.
7055 @node Formatting the file names
7056 @subsection Formatting the file names
7058 These options change how file names themselves are printed.
7064 @itemx --quoting-style=escape
7067 @opindex --quoting-style
7068 @cindex backslash sequences for file names
7069 Quote nongraphic characters in file names using alphabetic and octal
7070 backslash sequences like those used in C.
7074 @itemx --quoting-style=literal
7077 @opindex --quoting-style
7078 Do not quote file names. However, with @command{ls} nongraphic
7079 characters are still printed as question marks if the output is a
7080 terminal and you do not specify the @option{--show-control-chars}
7084 @itemx --hide-control-chars
7086 @opindex --hide-control-chars
7087 Print question marks instead of nongraphic characters in file names.
7088 This is the default if the output is a terminal and the program is
7093 @itemx --quoting-style=c
7095 @opindex --quote-name
7096 @opindex --quoting-style
7097 Enclose file names in double quotes and quote nongraphic characters as
7100 @item --quoting-style=@var{word}
7101 @opindex --quoting-style
7102 @cindex quoting style
7103 Use style @var{word} to quote file names and other strings that may
7104 contain arbitrary characters. The @var{word} should
7105 be one of the following:
7109 Output strings as-is; this is the same as the @option{-N} or
7110 @option{--literal} option.
7112 Quote strings for the shell if they contain shell metacharacters or would
7113 cause ambiguous output.
7114 The quoting is suitable for @acronym{POSIX}-compatible shells like
7115 @command{bash}, but it does not always work for incompatible shells
7118 Quote strings for the shell, even if they would normally not require quoting.
7120 Quote strings as for C character string literals, including the
7121 surrounding double-quote characters; this is the same as the
7122 @option{-Q} or @option{--quote-name} option.
7124 Quote strings as for C character string literals, except omit the
7125 surrounding double-quote
7126 characters; this is the same as the @option{-b} or @option{--escape} option.
7128 Quote strings as for C character string literals, except use
7129 surrounding quotation marks appropriate for the
7132 @c Use @t instead of @samp to avoid duplicate quoting in some output styles.
7133 Quote strings as for C character string literals, except use
7134 surrounding quotation marks appropriate for the locale, and quote
7135 @t{`like this'} instead of @t{"like
7136 this"} in the default C locale. This looks nicer on many displays.
7139 You can specify the default value of the @option{--quoting-style} option
7140 with the environment variable @env{QUOTING_STYLE}. If that environment
7141 variable is not set, the default value is @samp{literal}, but this
7142 default may change to @samp{shell} in a future version of this package.
7144 @item --show-control-chars
7145 @opindex --show-control-chars
7146 Print nongraphic characters as-is in file names.
7147 This is the default unless the output is a terminal and the program is
7153 @node dir invocation
7154 @section @command{dir}: Briefly list directory contents
7157 @cindex directory listing, brief
7159 @command{dir} is equivalent to @code{ls -C
7160 -b}; that is, by default files are listed in columns, sorted vertically,
7161 and special characters are represented by backslash escape sequences.
7163 @xref{ls invocation, @command{ls}}.
7166 @node vdir invocation
7167 @section @command{vdir}: Verbosely list directory contents
7170 @cindex directory listing, verbose
7172 @command{vdir} is equivalent to @code{ls -l
7173 -b}; that is, by default files are listed in long format and special
7174 characters are represented by backslash escape sequences.
7176 @node dircolors invocation
7177 @section @command{dircolors}: Color setup for @command{ls}
7181 @cindex setup for color
7183 @command{dircolors} outputs a sequence of shell commands to set up the
7184 terminal for color output from @command{ls} (and @command{dir}, etc.).
7188 eval "`dircolors [@var{option}]@dots{} [@var{file}]`"
7191 If @var{file} is specified, @command{dircolors} reads it to determine which
7192 colors to use for which file types and extensions. Otherwise, a
7193 precompiled database is used. For details on the format of these files,
7194 run @samp{dircolors --print-database}.
7196 To make @command{dircolors} read a @file{~/.dircolors} file if it
7197 exists, you can put the following lines in your @file{~/.bashrc} (or
7198 adapt them to your favorite shell):
7202 test -r $d && eval "$(dircolors $d)"
7206 @vindex SHELL @r{environment variable, and color}
7207 The output is a shell command to set the @env{LS_COLORS} environment
7208 variable. You can specify the shell syntax to use on the command line,
7209 or @command{dircolors} will guess it from the value of the @env{SHELL}
7210 environment variable.
7212 The program accepts the following options. Also see @ref{Common options}.
7217 @itemx --bourne-shell
7220 @opindex --bourne-shell
7221 @cindex Bourne shell syntax for color setup
7222 @cindex @command{sh} syntax for color setup
7223 Output Bourne shell commands. This is the default if the @env{SHELL}
7224 environment variable is set and does not end with @samp{csh} or
7233 @cindex C shell syntax for color setup
7234 @cindex @command{csh} syntax for color setup
7235 Output C shell commands. This is the default if @code{SHELL} ends with
7236 @command{csh} or @command{tcsh}.
7239 @itemx --print-database
7241 @opindex --print-database
7242 @cindex color database, printing
7243 @cindex database for color setup, printing
7244 @cindex printing color database
7245 Print the (compiled-in) default color configuration database. This
7246 output is itself a valid configuration file, and is fairly descriptive
7247 of the possibilities.
7254 @node Basic operations
7255 @chapter Basic operations
7257 @cindex manipulating files
7259 This chapter describes the commands for basic file manipulation:
7260 copying, moving (renaming), and deleting (removing).
7263 * cp invocation:: Copy files.
7264 * dd invocation:: Convert and copy a file.
7265 * install invocation:: Copy files and set attributes.
7266 * mv invocation:: Move (rename) files.
7267 * rm invocation:: Remove files or directories.
7268 * shred invocation:: Remove files more securely.
7273 @section @command{cp}: Copy files and directories
7276 @cindex copying files and directories
7277 @cindex files, copying
7278 @cindex directories, copying
7280 @command{cp} copies files (or, optionally, directories). The copy is
7281 completely independent of the original. You can either copy one file to
7282 another, or copy arbitrarily many files to a destination directory.
7286 cp [@var{option}]@dots{} [-T] @var{source} @var{dest}
7287 cp [@var{option}]@dots{} @var{source}@dots{} @var{directory}
7288 cp [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
7293 If two file names are given, @command{cp} copies the first file to the
7297 If the @option{--target-directory} (@option{-t}) option is given, or
7298 failing that if the last file is a directory and the
7299 @option{--no-target-directory} (@option{-T}) option is not given,
7300 @command{cp} copies each @var{source} file to the specified directory,
7301 using the @var{source}s' names.
7304 Generally, files are written just as they are read. For exceptions,
7305 see the @option{--sparse} option below.
7307 By default, @command{cp} does not copy directories. However, the
7308 @option{-R}, @option{-a}, and @option{-r} options cause @command{cp} to
7309 copy recursively by descending into source directories and copying files
7310 to corresponding destination directories.
7312 When copying from a symbolic link, @command{cp} normally follows the
7313 link only when not copying
7314 recursively. This default can be overridden with the
7315 @option{--archive} (@option{-a}), @option{-d}, @option{--dereference}
7316 (@option{-L}), @option{--no-dereference} (@option{-P}), and
7317 @option{-H} options. If more than one of these options is specified,
7318 the last one silently overrides the others.
7320 When copying to a symbolic link, @command{cp} follows the
7321 link only when it refers to an existing regular file.
7322 However, when copying to a dangling symbolic link, @command{cp}
7323 refuses by default, and fails with a diagnostic, since the operation
7324 is inherently dangerous. This behavior is contrary to historical
7325 practice and to @acronym{POSIX}.
7326 Set @env{POSIXLY_CORRECT} to make @command{cp} attempt to create
7327 the target of a dangling destination symlink, in spite of the possible risk.
7328 Also, when an option like
7329 @option{--backup} or @option{--link} acts to rename or remove the
7330 destination before copying, @command{cp} renames or removes the
7331 symbolic link rather than the file it points to.
7333 By default, @command{cp} copies the contents of special files only
7334 when not copying recursively. This default can be overridden with the
7335 @option{--copy-contents} option.
7337 @cindex self-backups
7338 @cindex backups, making only
7339 @command{cp} generally refuses to copy a file onto itself, with the
7340 following exception: if @option{--force --backup} is specified with
7341 @var{source} and @var{dest} identical, and referring to a regular file,
7342 @command{cp} will make a backup file, either regular or numbered, as
7343 specified in the usual ways (@pxref{Backup options}). This is useful when
7344 you simply want to make a backup of an existing file before changing it.
7346 The program accepts the following options. Also see @ref{Common options}.
7353 Preserve as much as possible of the structure and attributes of the
7354 original files in the copy (but do not attempt to preserve internal
7355 directory structure; i.e., @samp{ls -U} may list the entries in a copied
7356 directory in a different order).
7357 Try to preserve SELinux security context and extended attributes (xattr),
7358 but ignore any failure to do that and print no corresponding diagnostic.
7359 Equivalent to @option{-dR --preserve=all} with the reduced diagnostics.
7362 @itemx @w{@kbd{--backup}[=@var{method}]}
7365 @vindex VERSION_CONTROL
7366 @cindex backups, making
7367 @xref{Backup options}.
7368 Make a backup of each file that would otherwise be overwritten or removed.
7369 As a special case, @command{cp} makes a backup of @var{source} when the force
7370 and backup options are given and @var{source} and @var{dest} are the same
7371 name for an existing, regular file. One useful application of this
7372 combination of options is this tiny Bourne shell script:
7376 # Usage: backup FILE...
7377 # Create a @sc{gnu}-style backup of each listed FILE.
7379 cp --backup --force -- "$i" "$i"
7383 @item --copy-contents
7384 @cindex directories, copying recursively
7385 @cindex copying directories recursively
7386 @cindex recursively copying directories
7387 @cindex non-directories, copying as special files
7388 If copying recursively, copy the contents of any special files (e.g.,
7389 FIFOs and device files) as if they were regular files. This means
7390 trying to read the data in each source file and writing it to the
7391 destination. It is usually a mistake to use this option, as it
7392 normally has undesirable effects on special files like FIFOs and the
7393 ones typically found in the @file{/dev} directory. In most cases,
7394 @code{cp -R --copy-contents} will hang indefinitely trying to read
7395 from FIFOs and special files like @file{/dev/console}, and it will
7396 fill up your destination disk if you use it to copy @file{/dev/zero}.
7397 This option has no effect unless copying recursively, and it does not
7398 affect the copying of symbolic links.
7402 @cindex symbolic links, copying
7403 @cindex hard links, preserving
7404 Copy symbolic links as symbolic links rather than copying the files that
7405 they point to, and preserve hard links between source files in the copies.
7406 Equivalent to @option{--no-dereference --preserve=links}.
7412 When copying without this option and an existing destination file cannot
7413 be opened for writing, the copy fails. However, with @option{--force}),
7414 when a destination file cannot be opened, @command{cp} then removes it and
7415 tries to open it again. Contrast this behavior with that enabled by
7416 @option{--link} and @option{--symbolic-link}, whereby the destination file
7417 is never opened but rather is removed unconditionally. Also see the
7418 description of @option{--remove-destination}.
7420 This option is independent of the @option{--interactive} or
7421 @option{-i} option: neither cancels the effect of the other.
7423 This option is redundant if the @option{--no-clobber} or @option{-n} option is
7428 If a command line argument specifies a symbolic link, then copy the
7429 file it points to rather than the symbolic link itself. However,
7430 copy (preserving its nature) any symbolic link that is encountered
7431 via recursive traversal.
7434 @itemx --interactive
7436 @opindex --interactive
7437 When copying a file other than a directory, prompt whether to
7438 overwrite an existing destination file. The @option{-i} option overrides
7439 a previous @option{-n} option.
7445 Make hard links instead of copies of non-directories.
7448 @itemx --dereference
7450 @opindex --dereference
7451 Follow symbolic links when copying from them.
7452 With this option, @command{cp} cannot create a symbolic link.
7453 For example, a symlink (to regular file) in the source tree will be copied to
7454 a regular file in the destination tree.
7459 @opindex --no-clobber
7460 Do not overwrite an existing file. The @option{-n} option overrides a previous
7461 @option{-i} option. This option is mutually exclusive with @option{-b} or
7462 @option{--backup} option.
7465 @itemx --no-dereference
7467 @opindex --no-dereference
7468 @cindex symbolic links, copying
7469 Copy symbolic links as symbolic links rather than copying the files that
7470 they point to. This option affects only symbolic links in the source;
7471 symbolic links in the destination are always followed if possible.
7474 @itemx @w{@kbd{--preserve}[=@var{attribute_list}]}
7477 @cindex file information, preserving, extended attributes, xattr
7478 Preserve the specified attributes of the original files.
7479 If specified, the @var{attribute_list} must be a comma-separated list
7480 of one or more of the following strings:
7484 Preserve the file mode bits and access control lists.
7486 Preserve the owner and group. On most modern systems,
7487 only users with appropriate privileges may change the owner of a file,
7489 may preserve the group ownership of a file only if they happen to be
7490 a member of the desired group.
7492 Preserve the times of last access and last modification, when possible.
7493 On older systems, it is not possible to preserve these attributes
7494 when the affected file is a symbolic link.
7495 However, many systems now provide the @code{utimensat} function,
7496 which makes it possible even for symbolic links.
7498 Preserve in the destination files
7499 any links between corresponding source files.
7500 Note that with @option{-L} or @option{-H}, this option can convert
7501 symbolic links to hard links. For example,
7503 $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
7508 Note the inputs: @file{b} is a symlink to regular file @file{a},
7509 yet the files in destination directory, @file{c/}, are hard-linked.
7510 Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
7511 tells @command{cp} to dereference command line arguments, it sees two files
7512 with the same inode number, and preserves the perceived hard link.
7514 Here is a similar example that exercises @command{cp}'s @option{-L} option:
7516 $ mkdir b c; (cd b; : > a; ln -s a b); cp -aL b c; ls -i1 c/b
7522 Preserve SELinux security context of the file, or fail with full diagnostics.
7524 Preserve extended attributes of the file, or fail with full diagnostics.
7525 If @command{cp} is built without xattr support, ignore this option.
7526 If SELinux context, ACLs or Capabilities are implemented using xattrs,
7527 they are preserved by this option as well.
7529 Preserve all file attributes.
7530 Equivalent to specifying all of the above, but with the difference
7531 that failure to preserve SELinux security context or extended attributes
7532 does not change @command{cp}'s exit status. In contrast to @option{-a},
7533 all but @samp{Operation not supported} warnings are output.
7536 Using @option{--preserve} with no @var{attribute_list} is equivalent
7537 to @option{--preserve=mode,ownership,timestamps}.
7539 In the absence of this option, each destination file is created with the
7540 mode bits of the corresponding source file, minus the bits set in the
7541 umask and minus the set-user-ID and set-group-ID bits.
7542 @xref{File permissions}.
7544 @itemx @w{@kbd{--no-preserve}=@var{attribute_list}}
7545 @cindex file information, preserving
7546 Do not preserve the specified attributes. The @var{attribute_list}
7547 has the same form as for @option{--preserve}.
7551 @cindex parent directories and @command{cp}
7552 Form the name of each destination file by appending to the target
7553 directory a slash and the specified name of the source file. The last
7554 argument given to @command{cp} must be the name of an existing directory.
7555 For example, the command:
7558 cp --parents a/b/c existing_dir
7562 copies the file @file{a/b/c} to @file{existing_dir/a/b/c}, creating
7563 any missing intermediate directories.
7570 @opindex --recursive
7571 @cindex directories, copying recursively
7572 @cindex copying directories recursively
7573 @cindex recursively copying directories
7574 @cindex non-directories, copying as special files
7575 Copy directories recursively. By default, do not follow symbolic
7576 links in the source; see the @option{--archive} (@option{-a}), @option{-d},
7577 @option{--dereference} (@option{-L}), @option{--no-dereference}
7578 (@option{-P}), and @option{-H} options. Special files are copied by
7579 creating a destination file of the same type as the source; see the
7580 @option{--copy-contents} option. It is not portable to use
7581 @option{-r} to copy symbolic links or special files. On some
7582 non-@sc{gnu} systems, @option{-r} implies the equivalent of
7583 @option{-L} and @option{--copy-contents} for historical reasons.
7584 Also, it is not portable to use @option{-R} to copy symbolic links
7585 unless you also specify @option{-P}, as @acronym{POSIX} allows
7586 implementations that dereference symbolic links by default.
7588 @item --reflink[=@var{when}]
7589 @opindex --reflink[=@var{when}]
7592 @cindex copy on write
7593 Perform a lightweight, copy-on-write (COW) copy.
7594 Copying with this option can succeed only on some file systems.
7595 Once it has succeeded, beware that the source and destination files
7596 share the same disk data blocks as long as they remain unmodified.
7597 Thus, if a disk I/O error affects data blocks of one of the files,
7598 the other suffers the exact same fate.
7600 The @var{when} value can be one of the following:
7604 The default behavior: if the copy-on-write operation is not supported
7605 then report the failure for each file and exit with a failure status.
7608 If the copy-on-write operation is not supported then fall back
7609 to the standard copy behaviour.
7613 @item --remove-destination
7614 @opindex --remove-destination
7615 Remove each existing destination file before attempting to open it
7616 (contrast with @option{-f} above).
7618 @item --sparse=@var{when}
7619 @opindex --sparse=@var{when}
7620 @cindex sparse files, copying
7621 @cindex holes, copying files with
7622 @findex read @r{system call, and holes}
7623 A @dfn{sparse file} contains @dfn{holes}---a sequence of zero bytes that
7624 does not occupy any physical disk blocks; the @samp{read} system call
7625 reads these as zeros. This can both save considerable disk space and
7626 increase speed, since many binary files contain lots of consecutive zero
7627 bytes. By default, @command{cp} detects holes in input source files via a crude
7628 heuristic and makes the corresponding output file sparse as well.
7629 Only regular files may be sparse.
7631 The @var{when} value can be one of the following:
7635 The default behavior: if the input file is sparse, attempt to make
7636 the output file sparse, too. However, if an output file exists but
7637 refers to a non-regular file, then do not attempt to make it sparse.
7640 For each sufficiently long sequence of zero bytes in the input file,
7641 attempt to create a corresponding hole in the output file, even if the
7642 input file does not appear to be sparse.
7643 This is useful when the input file resides on a file system
7644 that does not support sparse files
7645 (for example, @samp{efs} file systems in SGI IRIX 5.3 and earlier),
7646 but the output file is on a type of file system that does support them.
7647 Holes may be created only in regular files, so if the destination file
7648 is of some other type, @command{cp} does not even try to make it sparse.
7651 Never make the output file sparse.
7652 This is useful in creating a file for use with the @command{mkswap} command,
7653 since such a file must not have any holes.
7656 @optStripTrailingSlashes
7659 @itemx --symbolic-link
7661 @opindex --symbolic-link
7662 @cindex symbolic links, copying with
7663 Make symbolic links instead of copies of non-directories. All source
7664 file names must be absolute (starting with @samp{/}) unless the
7665 destination files are in the current directory. This option merely
7666 results in an error message on systems that do not support symbolic links.
7672 @optNoTargetDirectory
7678 @cindex newer files, copying only
7679 Do not copy a non-directory that has an existing destination with the
7680 same or newer modification time. If time stamps are being preserved,
7681 the comparison is to the source time stamp truncated to the
7682 resolutions of the destination file system and of the system calls
7683 used to update time stamps; this avoids duplicate work if several
7684 @samp{cp -pu} commands are executed with the same source and
7691 Print the name of each file before copying it.
7694 @itemx --one-file-system
7696 @opindex --one-file-system
7697 @cindex file systems, omitting copying to different
7698 Skip subdirectories that are on different file systems from the one that
7699 the copy started on.
7700 However, mount point directories @emph{are} copied.
7708 @section @command{dd}: Convert and copy a file
7711 @cindex converting while copying a file
7713 @command{dd} copies a file (from standard input to standard output, by
7714 default) with a changeable I/O block size, while optionally performing
7715 conversions on it. Synopses:
7718 dd [@var{operand}]@dots{}
7722 The only options are @option{--help} and @option{--version}.
7723 @xref{Common options}. @command{dd} accepts the following operands.
7729 Read from @var{file} instead of standard input.
7733 Write to @var{file} instead of standard output. Unless
7734 @samp{conv=notrunc} is given, @command{dd} truncates @var{file} to zero
7735 bytes (or the size specified with @samp{seek=}).
7737 @item ibs=@var{bytes}
7739 @cindex block size of input
7740 @cindex input block size
7741 Set the input block size to @var{bytes}.
7742 This makes @command{dd} read @var{bytes} per block.
7743 The default is 512 bytes.
7745 @item obs=@var{bytes}
7747 @cindex block size of output
7748 @cindex output block size
7749 Set the output block size to @var{bytes}.
7750 This makes @command{dd} write @var{bytes} per block.
7751 The default is 512 bytes.
7753 @item bs=@var{bytes}
7756 Set both input and output block sizes to @var{bytes}.
7757 This makes @command{dd} read and write @var{bytes} per block,
7758 overriding any @samp{ibs} and @samp{obs} settings.
7759 In addition, if no data-transforming @option{conv} option is specified,
7760 each input block is copied to the output as a single block,
7761 without aggregating short reads.
7763 @item cbs=@var{bytes}
7765 @cindex block size of conversion
7766 @cindex conversion block size
7767 @cindex fixed-length records, converting to variable-length
7768 @cindex variable-length records, converting to fixed-length
7769 Set the conversion block size to @var{bytes}.
7770 When converting variable-length records to fixed-length ones
7771 (@option{conv=block}) or the reverse (@option{conv=unblock}),
7772 use @var{bytes} as the fixed record length.
7774 @item skip=@var{blocks}
7776 Skip @var{blocks} @samp{ibs}-byte blocks in the input file before copying.
7778 @item seek=@var{blocks}
7780 Skip @var{blocks} @samp{obs}-byte blocks in the output file before copying.
7782 @item count=@var{blocks}
7784 Copy @var{blocks} @samp{ibs}-byte blocks from the input file, instead
7785 of everything until the end of the file.
7789 Do not print the overall transfer rate and volume statistics
7790 that normally make up the third status line when @command{dd} exits.
7792 @item conv=@var{conversion}[,@var{conversion}]@dots{}
7794 Convert the file as specified by the @var{conversion} argument(s).
7795 (No spaces around any comma(s).)
7802 @opindex ascii@r{, converting to}
7803 Convert @acronym{EBCDIC} to @acronym{ASCII},
7804 using the conversion table specified by @acronym{POSIX}.
7805 This provides a 1:1 translation for all 256 bytes.
7808 @opindex ebcdic@r{, converting to}
7809 Convert @acronym{ASCII} to @acronym{EBCDIC}.
7810 This is the inverse of the @samp{ascii} conversion.
7813 @opindex alternate ebcdic@r{, converting to}
7814 Convert @acronym{ASCII} to alternate @acronym{EBCDIC},
7815 using the alternate conversion table specified by @acronym{POSIX}.
7816 This is not a 1:1 translation, but reflects common historical practice
7817 for @samp{~}, @samp{[}, and @samp{]}.
7819 The @samp{ascii}, @samp{ebcdic}, and @samp{ibm} conversions are
7823 @opindex block @r{(space-padding)}
7824 For each line in the input, output @samp{cbs} bytes, replacing the
7825 input newline with a space and padding with spaces as necessary.
7829 Remove any trailing spaces in each @samp{cbs}-sized input block,
7830 and append a newline.
7832 The @samp{block} and @samp{unblock} conversions are mutually exclusive.
7835 @opindex lcase@r{, converting to}
7836 Change uppercase letters to lowercase.
7839 @opindex ucase@r{, converting to}
7840 Change lowercase letters to uppercase.
7842 The @samp{lcase} and @samp{ucase} conversions are mutually exclusive.
7845 @opindex swab @r{(byte-swapping)}
7846 @cindex byte-swapping
7847 Swap every pair of input bytes. @sc{gnu} @command{dd}, unlike others, works
7848 when an odd number of bytes are read---the last byte is simply copied
7849 (since there is nothing to swap it with).
7853 @cindex read errors, ignoring
7854 Continue after read errors.
7858 @cindex creating output file, avoiding
7859 Do not create the output file; the output file must already exist.
7863 @cindex creating output file, requiring
7864 Fail if the output file already exists; @command{dd} must create the
7867 The @samp{excl} and @samp{nocreat} conversions are mutually exclusive.
7871 @cindex truncating output file, avoiding
7872 Do not truncate the output file.
7875 @opindex sync @r{(padding with @acronym{ASCII} @sc{nul}s)}
7876 Pad every input block to size of @samp{ibs} with trailing zero bytes.
7877 When used with @samp{block} or @samp{unblock}, pad with spaces instead of
7882 @cindex synchronized data writes, before finishing
7883 Synchronize output data just before finishing. This forces a physical
7884 write of output data.
7888 @cindex synchronized data and metadata writes, before finishing
7889 Synchronize output data and metadata just before finishing. This
7890 forces a physical write of output data and metadata.
7894 @item iflag=@var{flag}[,@var{flag}]@dots{}
7896 Access the input file using the flags specified by the @var{flag}
7897 argument(s). (No spaces around any comma(s).)
7899 @item oflag=@var{flag}[,@var{flag}]@dots{}
7901 Access the output file using the flags specified by the @var{flag}
7902 argument(s). (No spaces around any comma(s).)
7904 Here are the flags. Not every flag is supported on every operating
7911 @cindex appending to the output file
7912 Write in append mode, so that even if some other process is writing to
7913 this file, every @command{dd} write will append to the current
7914 contents of the file. This flag makes sense only for output.
7915 If you combine this flag with the @samp{of=@var{file}} operand,
7916 you should also specify @samp{conv=notrunc} unless you want the
7917 output file to be truncated before being appended to.
7921 @cindex concurrent I/O
7922 Use concurrent I/O mode for data. This mode performs direct I/O
7923 and drops the @acronym{POSIX} requirement to serialize all I/O to the same file.
7924 A file cannot be opened in CIO mode and with a standard open at the
7930 Use direct I/O for data, avoiding the buffer cache.
7931 Note that the kernel may impose restrictions on read or write buffer sizes.
7932 For example, with an ext4 destination file system and a linux-based kernel,
7933 using @samp{oflag=direct} will cause writes to fail with @code{EINVAL} if the
7934 output buffer size is not a multiple of 512.
7938 @cindex directory I/O
7940 Fail unless the file is a directory. Most operating systems do not
7941 allow I/O to a directory, so this flag has limited utility.
7945 @cindex synchronized data reads
7946 Use synchronized I/O for data. For the output file, this forces a
7947 physical write of output data on each write. For the input file,
7948 this flag can matter when reading from a remote file that has been
7949 written to synchronously by some other process. Metadata (e.g.,
7950 last-access and last-modified time) is not necessarily synchronized.
7954 @cindex synchronized data and metadata I/O
7955 Use synchronized I/O for both data and metadata.
7959 @cindex nonblocking I/O
7960 Use non-blocking I/O.
7965 Do not update the file's access time.
7966 Some older file systems silently ignore this flag, so it is a good
7967 idea to test it on your files before relying on it.
7971 @cindex controlling terminal
7972 Do not assign the file to be a controlling terminal for @command{dd}.
7973 This has no effect when the file is not a terminal.
7974 On many hosts (e.g., @acronym{GNU}/Linux hosts), this option has no effect
7979 @cindex symbolic links, following
7980 Do not follow symbolic links.
7985 Fail if the file has multiple hard links.
7990 Use binary I/O. This option has an effect only on nonstandard
7991 platforms that distinguish binary from text I/O.
7996 Use text I/O. Like @samp{binary}, this option has no effect on
8001 Accumulate full blocks from input. The @code{read} system call
8002 may return early if a full block is not available.
8003 When that happens, continue calling @code{read} to fill the remainder
8005 This flag can be used only with @code{iflag}.
8009 These flags are not supported on all systems, and @samp{dd} rejects
8010 attempts to use them when they are not supported. When reading from
8011 standard input or writing to standard output, the @samp{nofollow} and
8012 @samp{noctty} flags should not be specified, and the other flags
8013 (e.g., @samp{nonblock}) can affect how other processes behave with the
8014 affected file descriptors, even after @command{dd} exits.
8018 @cindex multipliers after numbers
8019 The numeric-valued strings above (@var{bytes} and @var{blocks}) can be
8020 followed by a multiplier: @samp{b}=512, @samp{c}=1,
8021 @samp{w}=2, @samp{x@var{m}}=@var{m}, or any of the
8022 standard block size suffixes like @samp{k}=1024 (@pxref{Block size}).
8024 Any block size you specify via @samp{bs=}, @samp{ibs=}, @samp{obs=}, @samp{cbs=}
8025 should not be too large---values larger than a few megabytes
8026 are generally wasteful or (as in the gigabyte..exabyte case) downright
8027 counterproductive or error-inducing.
8029 Use different @command{dd} invocations to use different block sizes for
8030 skipping and I/O@. For example, the following shell commands copy data
8031 in 512 KiB blocks between a disk and a tape, but do not save or restore a
8032 4 KiB label at the start of the disk:
8035 disk=/dev/rdsk/c0t1d0s2
8038 # Copy all but the label from disk to tape.
8039 (dd bs=4k skip=1 count=0 && dd bs=512k) <$disk >$tape
8041 # Copy from tape back to disk, but leave the disk label alone.
8042 (dd bs=4k seek=1 count=0 && dd bs=512k) <$tape >$disk
8045 Sending an @samp{INFO} signal to a running @command{dd}
8046 process makes it print I/O statistics to standard error
8047 and then resume copying. In the example below,
8048 @command{dd} is run in the background to copy 10 million blocks.
8049 The @command{kill} command makes it output intermediate I/O statistics,
8050 and when @command{dd} completes normally or is killed by the
8051 @code{SIGINT} signal, it outputs the final statistics.
8054 $ dd if=/dev/zero of=/dev/null count=10MB & pid=$!
8055 $ kill -s INFO $pid; wait $pid
8056 3385223+0 records in
8057 3385223+0 records out
8058 1733234176 bytes (1.7 GB) copied, 6.42173 seconds, 270 MB/s
8059 10000000+0 records in
8060 10000000+0 records out
8061 5120000000 bytes (5.1 GB) copied, 18.913 seconds, 271 MB/s
8064 @vindex POSIXLY_CORRECT
8065 On systems lacking the @samp{INFO} signal @command{dd} responds to the
8066 @samp{USR1} signal instead, unless the @env{POSIXLY_CORRECT}
8067 environment variable is set.
8072 @node install invocation
8073 @section @command{install}: Copy files and set attributes
8076 @cindex copying files and setting attributes
8078 @command{install} copies files while setting their file mode bits and, if
8079 possible, their owner and group. Synopses:
8082 install [@var{option}]@dots{} [-T] @var{source} @var{dest}
8083 install [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8084 install [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8085 install [@var{option}]@dots{} -d @var{directory}@dots{}
8090 If two file names are given, @command{install} copies the first file to the
8094 If the @option{--target-directory} (@option{-t}) option is given, or
8095 failing that if the last file is a directory and the
8096 @option{--no-target-directory} (@option{-T}) option is not given,
8097 @command{install} copies each @var{source} file to the specified
8098 directory, using the @var{source}s' names.
8101 If the @option{--directory} (@option{-d}) option is given,
8102 @command{install} creates each @var{directory} and any missing parent
8103 directories. Parent directories are created with mode
8104 @samp{u=rwx,go=rx} (755), regardless of the @option{-m} option or the
8105 current umask. @xref{Directory Setuid and Setgid}, for how the
8106 set-user-ID and set-group-ID bits of parent directories are inherited.
8109 @cindex Makefiles, installing programs in
8110 @command{install} is similar to @command{cp}, but allows you to control the
8111 attributes of destination files. It is typically used in Makefiles to
8112 copy programs into their destination directories. It refuses to copy
8113 files onto themselves.
8115 @cindex extended attributes, xattr
8116 @command{install} never preserves extended attributes (xattr).
8118 The program accepts the following options. Also see @ref{Common options}.
8128 Compare each pair of source and destination files, and if the destination has
8129 identical content and any specified owner, group, permissions, and possibly
8130 SELinux context, then do not modify the destination at all.
8134 Ignored; for compatibility with old Unix versions of @command{install}.
8138 Create any missing parent directories of @var{dest},
8139 then copy @var{source} to @var{dest}.
8140 This option is ignored if a destination directory is specified
8141 via @option{--target-directory=DIR}.
8146 @opindex --directory
8147 @cindex directories, creating with given attributes
8148 @cindex parent directories, creating missing
8149 @cindex leading directories, creating missing
8150 Create any missing parent directories, giving them the default
8151 attributes. Then create each given directory, setting their owner,
8152 group and mode as given on the command line or to the defaults.
8154 @item -g @var{group}
8155 @itemx --group=@var{group}
8158 @cindex group ownership of installed files, setting
8159 Set the group ownership of installed files or directories to
8160 @var{group}. The default is the process's current group. @var{group}
8161 may be either a group name or a numeric group ID.
8164 @itemx --mode=@var{mode}
8167 @cindex permissions of installed files, setting
8168 Set the file mode bits for the installed file or directory to @var{mode},
8169 which can be either an octal number, or a symbolic mode as in
8170 @command{chmod}, with @samp{a=} (no access allowed to anyone) as the
8171 point of departure (@pxref{File permissions}).
8172 The default mode is @samp{u=rwx,go=rx,a-s}---read, write, and
8173 execute for the owner, read and execute for group and other, and with
8174 set-user-ID and set-group-ID disabled.
8175 This default is not quite the same as @samp{755}, since it disables
8176 instead of preserving set-user-ID and set-group-ID on directories.
8177 @xref{Directory Setuid and Setgid}.
8179 @item -o @var{owner}
8180 @itemx --owner=@var{owner}
8183 @cindex ownership of installed files, setting
8184 @cindex appropriate privileges
8185 @vindex root @r{as default owner}
8186 If @command{install} has appropriate privileges (is run as root), set the
8187 ownership of installed files or directories to @var{owner}. The default
8188 is @code{root}. @var{owner} may be either a user name or a numeric user
8191 @item --preserve-context
8192 @opindex --preserve-context
8194 @cindex security context
8195 Preserve the SELinux security context of files and directories.
8196 Failure to preserve the context in all of the files or directories
8197 will result in an exit status of 1. If SELinux is disabled then
8198 print a warning and ignore the option.
8201 @itemx --preserve-timestamps
8203 @opindex --preserve-timestamps
8204 @cindex timestamps of installed files, preserving
8205 Set the time of last access and the time of last modification of each
8206 installed file to match those of each corresponding original file.
8207 When a file is installed without this option, its last access and
8208 last modification times are both set to the time of installation.
8209 This option is useful if you want to use the last modification times
8210 of installed files to keep track of when they were last built as opposed
8211 to when they were last installed.
8217 @cindex symbol table information, stripping
8218 @cindex stripping symbol table information
8219 Strip the symbol tables from installed binary executables.
8221 @itemx --strip-program=@var{program}
8222 @opindex --strip-program
8223 @cindex symbol table information, stripping, program
8224 Program used to strip binaries.
8230 @optNoTargetDirectory
8236 Print the name of each file before copying it.
8238 @item -Z @var{context}
8239 @itemx --context=@var{context}
8243 @cindex security context
8244 Set the default SELinux security context to be used for any
8245 created files and directories. If SELinux is disabled then
8246 print a warning and ignore the option.
8254 @section @command{mv}: Move (rename) files
8258 @command{mv} moves or renames files (or directories). Synopses:
8261 mv [@var{option}]@dots{} [-T] @var{source} @var{dest}
8262 mv [@var{option}]@dots{} @var{source}@dots{} @var{directory}
8263 mv [@var{option}]@dots{} -t @var{directory} @var{source}@dots{}
8268 If two file names are given, @command{mv} moves the first file to the
8272 If the @option{--target-directory} (@option{-t}) option is given, or
8273 failing that if the last file is a directory and the
8274 @option{--no-target-directory} (@option{-T}) option is not given,
8275 @command{mv} moves each @var{source} file to the specified
8276 directory, using the @var{source}s' names.
8279 @command{mv} can move any type of file from one file system to another.
8280 Prior to version @code{4.0} of the fileutils,
8281 @command{mv} could move only regular files between file systems.
8282 For example, now @command{mv} can move an entire directory hierarchy
8283 including special device files from one partition to another. It first
8284 uses some of the same code that's used by @code{cp -a} to copy the
8285 requested directories and files, then (assuming the copy succeeded)
8286 it removes the originals. If the copy fails, then the part that was
8287 copied to the destination partition is removed. If you were to copy
8288 three directories from one partition to another and the copy of the first
8289 directory succeeded, but the second didn't, the first would be left on
8290 the destination partition and the second and third would be left on the
8293 @cindex extended attributes, xattr
8294 @command{mv} always tries to copy extended attributes (xattr), which may
8295 include SELinux context, ACLs or Capabilities.
8296 Upon failure all but @samp{Operation not supported} warnings are output.
8298 @cindex prompting, and @command{mv}
8299 If a destination file exists but is normally unwritable, standard input
8300 is a terminal, and the @option{-f} or @option{--force} option is not given,
8301 @command{mv} prompts the user for whether to replace the file. (You might
8302 own the file, or have write permission on its directory.) If the
8303 response is not affirmative, the file is skipped.
8305 @emph{Warning}: Avoid specifying a source name with a trailing slash,
8306 when it might be a symlink to a directory.
8307 Otherwise, @command{mv} may do something very surprising, since
8308 its behavior depends on the underlying rename system call.
8309 On a system with a modern Linux-based kernel, it fails with @code{errno=ENOTDIR}.
8310 However, on other systems (at least FreeBSD 6.1 and Solaris 10) it silently
8311 renames not the symlink but rather the directory referenced by the symlink.
8312 @xref{Trailing slashes}.
8314 The program accepts the following options. Also see @ref{Common options}.
8324 @cindex prompts, omitting
8325 Do not prompt the user before removing a destination file.
8327 If you specify more than one of the @option{-i}, @option{-f}, @option{-n}
8328 options, only the final one takes effect.
8333 @itemx --interactive
8335 @opindex --interactive
8336 @cindex prompts, forcing
8337 Prompt whether to overwrite each existing destination file, regardless
8339 If the response is not affirmative, the file is skipped.
8345 @opindex --no-clobber
8346 @cindex prompts, omitting
8347 Do not overwrite an existing file.
8349 This option is mutually exclusive with @option{-b} or @option{--backup} option.
8355 @cindex newer files, moving only
8356 Do not move a non-directory that has an existing destination with the
8357 same or newer modification time.
8358 If the move is across file system boundaries, the comparison is to the
8359 source time stamp truncated to the resolutions of the destination file
8360 system and of the system calls used to update time stamps; this avoids
8361 duplicate work if several @samp{mv -u} commands are executed with the
8362 same source and destination.
8368 Print the name of each file before moving it.
8370 @optStripTrailingSlashes
8376 @optNoTargetDirectory
8384 @section @command{rm}: Remove files or directories
8387 @cindex removing files or directories
8389 @command{rm} removes each given @var{file}. By default, it does not remove
8390 directories. Synopsis:
8393 rm [@var{option}]@dots{} [@var{file}]@dots{}
8396 @cindex prompting, and @command{rm}
8397 If the @option{-I} or @option{--interactive=once} option is given,
8398 and there are more than three files or the @option{-r}, @option{-R},
8399 or @option{--recursive} are given, then @command{rm} prompts the user
8400 for whether to proceed with the entire operation. If the response is
8401 not affirmative, the entire command is aborted.
8403 Otherwise, if a file is unwritable, standard input is a terminal, and
8404 the @option{-f} or @option{--force} option is not given, or the
8405 @option{-i} or @option{--interactive=always} option @emph{is} given,
8406 @command{rm} prompts the user for whether to remove the file.
8407 If the response is not affirmative, the file is skipped.
8409 Any attempt to remove a file whose last file name component is
8410 @file{.} or @file{..} is rejected without any prompting.
8412 @emph{Warning}: If you use @command{rm} to remove a file, it is usually
8413 possible to recover the contents of that file. If you want more assurance
8414 that the contents are truly unrecoverable, consider using @command{shred}.
8416 The program accepts the following options. Also see @ref{Common options}.
8424 Ignore nonexistent files and never prompt the user.
8425 Ignore any previous @option{--interactive} (@option{-i}) option.
8429 Prompt whether to remove each file.
8430 If the response is not affirmative, the file is skipped.
8431 Ignore any previous @option{--force} (@option{-f}) option.
8432 Equivalent to @option{--interactive=always}.
8436 Prompt once whether to proceed with the command, if more than three
8437 files are named or if a recursive removal is requested. Ignore any
8438 previous @option{--force} (@option{-f}) option. Equivalent to
8439 @option{--interactive=once}.
8441 @itemx --interactive [=@var{when}]
8442 @opindex --interactive
8443 Specify when to issue an interactive prompt. @var{when} may be
8447 @vindex never @r{interactive option}
8448 - Do not prompt at all.
8450 @vindex once @r{interactive option}
8451 - Prompt once if more than three files are named or if a recursive
8452 removal is requested. Equivalent to @option{-I}.
8454 @vindex always @r{interactive option}
8455 - Prompt for every file being removed. Equivalent to @option{-i}.
8457 @option{--interactive} with no @var{when} is equivalent to
8458 @option{--interactive=always}.
8460 @itemx --one-file-system
8461 @opindex --one-file-system
8462 @cindex one file system, restricting @command{rm} to
8463 When removing a hierarchy recursively, skip any directory that is on a
8464 file system different from that of the corresponding command line argument.
8466 This option is useful when removing a build ``chroot'' hierarchy,
8467 which normally contains no valuable data. However, it is not uncommon
8468 to bind-mount @file{/home} into such a hierarchy, to make it easier to
8469 use one's start-up file. The catch is that it's easy to forget to
8470 unmount @file{/home}. Then, when you use @command{rm -rf} to remove
8471 your normally throw-away chroot, that command will remove everything
8472 under @file{/home}, too.
8473 Use the @option{--one-file-system} option, and it will
8474 warn about and skip directories on other file systems.
8475 Of course, this will not save your @file{/home} if it and your
8476 chroot happen to be on the same file system.
8478 @itemx --preserve-root
8479 @opindex --preserve-root
8480 @cindex root directory, disallow recursive destruction
8481 Fail upon any attempt to remove the root directory, @file{/},
8482 when used with the @option{--recursive} option.
8483 This is the default behavior.
8484 @xref{Treating / specially}.
8486 @itemx --no-preserve-root
8487 @opindex --no-preserve-root
8488 @cindex root directory, allow recursive destruction
8489 Do not treat @file{/} specially when removing recursively.
8490 This option is not recommended unless you really want to
8491 remove all the files on your computer.
8492 @xref{Treating / specially}.
8499 @opindex --recursive
8500 @cindex directories, removing (recursively)
8501 Remove the listed directories and their contents recursively.
8507 Print the name of each file before removing it.
8511 @cindex files beginning with @samp{-}, removing
8512 @cindex @samp{-}, removing files beginning with
8513 One common question is how to remove files whose names begin with a
8514 @samp{-}. @sc{gnu} @command{rm}, like every program that uses the @code{getopt}
8515 function to parse its arguments, lets you use the @samp{--} option to
8516 indicate that all following arguments are non-options. To remove a file
8517 called @file{-f} in the current directory, you could type either:
8530 @opindex - @r{and Unix @command{rm}}
8531 The Unix @command{rm} program's use of a single @samp{-} for this purpose
8532 predates the development of the getopt standard syntax.
8537 @node shred invocation
8538 @section @command{shred}: Remove files more securely
8541 @cindex data, erasing
8542 @cindex erasing data
8544 @command{shred} overwrites devices or files, to help prevent even
8545 very expensive hardware from recovering the data.
8547 Ordinarily when you remove a file (@pxref{rm invocation}), the data is
8548 not actually destroyed. Only the index listing where the file is
8549 stored is destroyed, and the storage is made available for reuse.
8550 There are undelete utilities that will attempt to reconstruct the index
8551 and can bring the file back if the parts were not reused.
8553 On a busy system with a nearly-full drive, space can get reused in a few
8554 seconds. But there is no way to know for sure. If you have sensitive
8555 data, you may want to be sure that recovery is not possible by actually
8556 overwriting the file with non-sensitive data.
8558 However, even after doing that, it is possible to take the disk back
8559 to a laboratory and use a lot of sensitive (and expensive) equipment
8560 to look for the faint ``echoes'' of the original data underneath the
8561 overwritten data. If the data has only been overwritten once, it's not
8564 The best way to remove something irretrievably is to destroy the media
8565 it's on with acid, melt it down, or the like. For cheap removable media
8566 like floppy disks, this is the preferred method. However, hard drives
8567 are expensive and hard to melt, so the @command{shred} utility tries
8568 to achieve a similar effect non-destructively.
8570 This uses many overwrite passes, with the data patterns chosen to
8571 maximize the damage they do to the old data. While this will work on
8572 floppies, the patterns are designed for best effect on hard drives.
8573 For more details, see the source code and Peter Gutmann's paper
8574 @uref{http://www.cs.auckland.ac.nz/~pgut001/pubs/secure_del.html,
8575 @cite{Secure Deletion of Data from Magnetic and Solid-State Memory}},
8576 from the proceedings of the Sixth @acronym{USENIX} Security Symposium (San Jose,
8577 California, July 22--25, 1996).
8579 @strong{Please note} that @command{shred} relies on a very important assumption:
8580 that the file system overwrites data in place. This is the traditional
8581 way to do things, but many modern file system designs do not satisfy this
8582 assumption. Exceptions include:
8587 Log-structured or journaled file systems, such as those supplied with
8588 AIX and Solaris, and JFS, ReiserFS, XFS, Ext3 (in @code{data=journal} mode),
8589 BFS, NTFS, etc.@: when they are configured to journal @emph{data}.
8592 File systems that write redundant data and carry on even if some writes
8593 fail, such as RAID-based file systems.
8596 File systems that make snapshots, such as Network Appliance's NFS server.
8599 File systems that cache in temporary locations, such as NFS version 3
8603 Compressed file systems.
8606 In the particular case of ext3 file systems, the above disclaimer applies (and
8607 @command{shred} is thus of limited effectiveness) only in @code{data=journal}
8608 mode, which journals file data in addition to just metadata. In both
8609 the @code{data=ordered} (default) and @code{data=writeback} modes,
8610 @command{shred} works as usual. Ext3 journaling modes can be changed
8611 by adding the @code{data=something} option to the mount options for a
8612 particular file system in the @file{/etc/fstab} file, as documented in
8613 the mount man page (man mount).
8615 If you are not sure how your file system operates, then you should assume
8616 that it does not overwrite data in place, which means that shred cannot
8617 reliably operate on regular files in your file system.
8619 Generally speaking, it is more reliable to shred a device than a file,
8620 since this bypasses the problem of file system design mentioned above.
8621 However, even shredding devices is not always completely reliable. For
8622 example, most disks map out bad sectors invisibly to the application; if
8623 the bad sectors contain sensitive data, @command{shred} won't be able to
8626 @command{shred} makes no attempt to detect or report this problem, just as
8627 it makes no attempt to do anything about backups. However, since it is
8628 more reliable to shred devices than files, @command{shred} by default does
8629 not truncate or remove the output file. This default is more suitable
8630 for devices, which typically cannot be truncated and should not be
8633 Finally, consider the risk of backups and mirrors.
8634 File system backups and remote mirrors may contain copies of the
8635 file that cannot be removed, and that will allow a shredded file
8636 to be recovered later. So if you keep any data you may later want
8637 to destroy using @command{shred}, be sure that it is not backed up or mirrored.
8640 shred [@var{option}]@dots{} @var{file}[@dots{}]
8643 The program accepts the following options. Also see @ref{Common options}.
8651 @cindex force deletion
8652 Override file permissions if necessary to allow overwriting.
8655 @itemx -n @var{number}
8656 @itemx --iterations=@var{number}
8657 @opindex -n @var{number}
8658 @opindex --iterations=@var{number}
8659 @cindex iterations, selecting the number of
8660 By default, @command{shred} uses @value{SHRED_DEFAULT_PASSES} passes of
8661 overwrite. You can reduce this to save time, or increase it if you think it's
8662 appropriate. After 25 passes all of the internal overwrite patterns will have
8663 been used at least once.
8665 @item --random-source=@var{file}
8666 @opindex --random-source
8667 @cindex random source for shredding
8668 Use @var{file} as a source of random data used to overwrite and to
8669 choose pass ordering. @xref{Random sources}.
8671 @item -s @var{bytes}
8672 @itemx --size=@var{bytes}
8673 @opindex -s @var{bytes}
8674 @opindex --size=@var{bytes}
8675 @cindex size of file to shred
8676 Shred the first @var{bytes} bytes of the file. The default is to shred
8677 the whole file. @var{bytes} can be followed by a size specification like
8678 @samp{K}, @samp{M}, or @samp{G} to specify a multiple. @xref{Block size}.
8684 @cindex removing files after shredding
8685 After shredding a file, truncate it (if possible) and then remove it.
8686 If a file has multiple links, only the named links will be removed.
8692 Display to standard error all status updates as sterilization proceeds.
8698 By default, @command{shred} rounds the size of a regular file up to the next
8699 multiple of the file system block size to fully erase the last block of the file.
8700 Use @option{--exact} to suppress that behavior.
8701 Thus, by default if you shred a 10-byte regular file on a system with 512-byte
8702 blocks, the resulting file will be 512 bytes long. With this option,
8703 shred does not increase the apparent size of the file.
8709 Normally, the last pass that @command{shred} writes is made up of
8710 random data. If this would be conspicuous on your hard drive (for
8711 example, because it looks like encrypted data), or you just think
8712 it's tidier, the @option{--zero} option adds an additional overwrite pass with
8713 all zero bits. This is in addition to the number of passes specified
8714 by the @option{--iterations} option.
8718 You might use the following command to erase all trace of the
8719 file system you'd created on the floppy disk in your first drive.
8720 That command takes about 20 minutes to erase a ``1.44MB'' (actually
8724 shred --verbose /dev/fd0
8727 Similarly, to erase all data on a selected partition of
8728 your hard disk, you could give a command like this:
8731 shred --verbose /dev/sda5
8734 A @var{file} of @samp{-} denotes standard output.
8735 The intended use of this is to shred a removed temporary file.
8742 echo "Hello, world" >&3
8747 However, the command @samp{shred - >file} does not shred the contents
8748 of @var{file}, since the shell truncates @var{file} before invoking
8749 @command{shred}. Use the command @samp{shred file} or (if using a
8750 Bourne-compatible shell) the command @samp{shred - 1<>file} instead.
8755 @node Special file types
8756 @chapter Special file types
8758 @cindex special file types
8759 @cindex file types, special
8761 This chapter describes commands which create special types of files (and
8762 @command{rmdir}, which removes directories, one special file type).
8764 @cindex special file types
8766 Although Unix-like operating systems have markedly fewer special file
8767 types than others, not @emph{everything} can be treated only as the
8768 undifferentiated byte stream of @dfn{normal files}. For example, when a
8769 file is created or removed, the system must record this information,
8770 which it does in a @dfn{directory}---a special type of file. Although
8771 you can read directories as normal files, if you're curious, in order
8772 for the system to do its job it must impose a structure, a certain
8773 order, on the bytes of the file. Thus it is a ``special'' type of file.
8775 Besides directories, other special file types include named pipes
8776 (FIFOs), symbolic links, sockets, and so-called @dfn{special files}.
8779 * link invocation:: Make a hard link via the link syscall
8780 * ln invocation:: Make links between files.
8781 * mkdir invocation:: Make directories.
8782 * mkfifo invocation:: Make FIFOs (named pipes).
8783 * mknod invocation:: Make block or character special files.
8784 * readlink invocation:: Print value of a symlink or canonical file name.
8785 * rmdir invocation:: Remove empty directories.
8786 * unlink invocation:: Remove files via the unlink syscall
8790 @node link invocation
8791 @section @command{link}: Make a hard link via the link syscall
8794 @cindex links, creating
8795 @cindex hard links, creating
8796 @cindex creating links (hard only)
8798 @command{link} creates a single hard link at a time.
8799 It is a minimalist interface to the system-provided
8800 @code{link} function. @xref{Hard Links, , , libc,
8801 The GNU C Library Reference Manual}.
8802 It avoids the bells and whistles of the more commonly-used
8803 @command{ln} command (@pxref{ln invocation}).
8807 link @var{filename} @var{linkname}
8810 @var{filename} must specify an existing file, and @var{linkname}
8811 must specify a nonexistent entry in an existing directory.
8812 @command{link} simply calls @code{link (@var{filename}, @var{linkname})}
8815 On a @acronym{GNU} system, this command acts like @samp{ln --directory
8816 --no-target-directory @var{filename} @var{linkname}}. However, the
8817 @option{--directory} and @option{--no-target-directory} options are
8818 not specified by @acronym{POSIX}, and the @command{link} command is
8819 more portable in practice.
8821 If @var{filename} is a symbolic link, it is unspecified whether
8822 @var{linkname} will be a hard link to the symbolic link or to the
8823 target of the symbolic link. Use @command{ln -P} or @command{ln -L}
8824 to specify which behavior is desired.
8830 @section @command{ln}: Make links between files
8833 @cindex links, creating
8834 @cindex hard links, creating
8835 @cindex symbolic (soft) links, creating
8836 @cindex creating links (hard or soft)
8838 @cindex file systems and hard links
8839 @command{ln} makes links between files. By default, it makes hard links;
8840 with the @option{-s} option, it makes symbolic (or @dfn{soft}) links.
8844 ln [@var{option}]@dots{} [-T] @var{target} @var{linkname}
8845 ln [@var{option}]@dots{} @var{target}
8846 ln [@var{option}]@dots{} @var{target}@dots{} @var{directory}
8847 ln [@var{option}]@dots{} -t @var{directory} @var{target}@dots{}
8853 If two file names are given, @command{ln} creates a link to the first
8854 file from the second.
8857 If one @var{target} is given, @command{ln} creates a link to that file
8858 in the current directory.
8861 If the @option{--target-directory} (@option{-t}) option is given, or
8862 failing that if the last file is a directory and the
8863 @option{--no-target-directory} (@option{-T}) option is not given,
8864 @command{ln} creates a link to each @var{target} file in the specified
8865 directory, using the @var{target}s' names.
8869 Normally @command{ln} does not remove existing files. Use the
8870 @option{--force} (@option{-f}) option to remove them unconditionally,
8871 the @option{--interactive} (@option{-i}) option to remove them
8872 conditionally, and the @option{--backup} (@option{-b}) option to
8875 @cindex hard link, defined
8876 @cindex inode, and hard links
8877 A @dfn{hard link} is another name for an existing file; the link and the
8878 original are indistinguishable. Technically speaking, they share the
8879 same inode, and the inode contains all the information about a
8880 file---indeed, it is not incorrect to say that the inode @emph{is} the
8881 file. Most systems prohibit making a hard link to
8882 a directory; on those where it is allowed, only the super-user can do
8883 so (and with caution, since creating a cycle will cause problems to many
8884 other utilities). Hard links cannot cross file system boundaries. (These
8885 restrictions are not mandated by @acronym{POSIX}, however.)
8887 @cindex dereferencing symbolic links
8888 @cindex symbolic link, defined
8889 @dfn{Symbolic links} (@dfn{symlinks} for short), on the other hand, are
8890 a special file type (which not all kernels support: System V release 3
8891 (and older) systems lack symlinks) in which the link file actually
8892 refers to a different file, by name. When most operations (opening,
8893 reading, writing, and so on) are passed the symbolic link file, the
8894 kernel automatically @dfn{dereferences} the link and operates on the
8895 target of the link. But some operations (e.g., removing) work on the
8896 link file itself, rather than on its target. The owner and group of a
8897 symlink are not significant to file access performed through
8898 the link, but do have implications on deleting a symbolic link from a
8899 directory with the restricted deletion bit set. On the GNU system,
8900 the mode of a symlink has no significance and cannot be changed, but
8901 on some BSD systems, the mode can be changed and will affect whether
8902 the symlink will be traversed in file name resolution. @xref{Symbolic Links,,,
8903 libc, The GNU C Library Reference Manual}.
8905 Symbolic links can contain arbitrary strings; a @dfn{dangling symlink}
8906 occurs when the string in the symlink does not resolve to a file.
8907 There are no restrictions against creating dangling symbolic links.
8908 There are trade-offs to using absolute or relative symlinks. An
8909 absolute symlink always points to the same file, even if the directory
8910 containing the link is moved. However, if the symlink is visible from
8911 more than one machine (such as on a networked file system), the file
8912 pointed to might not always be the same. A relative symbolic link is
8913 resolved in relation to the directory that contains the link, and is
8914 often useful in referring to files on the same device without regards
8915 to what name that device is mounted on when accessed via networked
8918 When creating a relative symlink in a different location than the
8919 current directory, the resolution of the symlink will be different
8920 than the resolution of the same string from the current directory.
8921 Therefore, many users prefer to first change directories to the
8922 location where the relative symlink will be created, so that
8923 tab-completion or other file resolution will find the same target as
8924 what will be placed in the symlink.
8926 The program accepts the following options. Also see @ref{Common options}.
8937 @opindex --directory
8938 @cindex hard links to directories
8939 Allow users with appropriate privileges to attempt to make hard links
8941 However, note that this will probably fail due to
8942 system restrictions, even for the super-user.
8948 Remove existing destination files.
8951 @itemx --interactive
8953 @opindex --interactive
8954 @cindex prompting, and @command{ln}
8955 Prompt whether to remove existing destination files.
8961 If @option{-s} is not in effect, and the source file is a symbolic
8962 link, create the hard link to the file referred to by the symbolic
8963 link, rather than the symbolic link itself.
8966 @itemx --no-dereference
8968 @opindex --no-dereference
8969 Do not treat the last operand specially when it is a symbolic link to
8970 a directory. Instead, treat it as if it were a normal file.
8972 When the destination is an actual directory (not a symlink to one),
8973 there is no ambiguity. The link is created in that directory.
8974 But when the specified destination is a symlink to a directory,
8975 there are two ways to treat the user's request. @command{ln} can
8976 treat the destination just as it would a normal directory and create
8977 the link in it. On the other hand, the destination can be viewed as a
8978 non-directory---as the symlink itself. In that case, @command{ln}
8979 must delete or backup that symlink before creating the new link.
8980 The default is to treat a destination that is a symlink to a directory
8981 just like a directory.
8983 This option is weaker than the @option{--no-target-directory}
8984 (@option{-T}) option, so it has no effect if both options are given.
8990 If @option{-s} is not in effect, and the source file is a symbolic
8991 link, create the hard link to the symbolic link itself. On platforms
8992 where this is not supported by the kernel, this option creates a
8993 symbolic link with identical contents; since symbolic link contents
8994 cannot be edited, any file name resolution performed through either
8995 link will be the same as if a hard link had been created.
9001 Make symbolic links instead of hard links. This option merely produces
9002 an error message on systems that do not support symbolic links.
9008 @optNoTargetDirectory
9014 Print the name of each file after linking it successfully.
9018 @cindex hard links to symbolic links
9019 @cindex symbolic links and @command{ln}
9020 If @option{-L} and @option{-P} are both given, the last one takes
9021 precedence. If @option{-s} is also given, @option{-L} and @option{-P}
9022 are silently ignored. If neither option is given, then this
9023 implementation defaults to @option{-P} if the system @code{link} supports
9024 hard links to symbolic links (such as the GNU system), and @option{-L}
9025 if @code{link} follows symbolic links (such as on BSD).
9034 # Create link ../a pointing to a in that directory.
9035 # Not really useful because it points to itself.
9040 # Change to the target before creating symlinks to avoid being confused.
9046 # Hard coded file names don't move well.
9047 ln -s $(pwd)/a /some/dir/
9051 # Relative file names survive directory moves and also
9052 # work across networked file systems.
9053 ln -s afile anotherfile
9054 ln -s ../adir/afile yetanotherfile
9058 @node mkdir invocation
9059 @section @command{mkdir}: Make directories
9062 @cindex directories, creating
9063 @cindex creating directories
9065 @command{mkdir} creates directories with the specified names. Synopsis:
9068 mkdir [@var{option}]@dots{} @var{name}@dots{}
9071 @command{mkdir} creates each directory @var{name} in the order given.
9072 It reports an error if @var{name} already exists, unless the
9073 @option{-p} option is given and @var{name} is a directory.
9075 The program accepts the following options. Also see @ref{Common options}.
9080 @itemx --mode=@var{mode}
9083 @cindex modes of created directories, setting
9084 Set the file permission bits of created directories to @var{mode},
9085 which uses the same syntax as
9086 in @command{chmod} and uses @samp{a=rwx} (read, write and execute allowed for
9087 everyone) for the point of the departure. @xref{File permissions}.
9089 Normally the directory has the desired file mode bits at the moment it
9090 is created. As a @acronym{GNU} extension, @var{mode} may also mention
9091 special mode bits, but in this case there may be a temporary window
9092 during which the directory exists but its special mode bits are
9093 incorrect. @xref{Directory Setuid and Setgid}, for how the
9094 set-user-ID and set-group-ID bits of directories are inherited unless
9095 overridden in this way.
9101 @cindex parent directories, creating
9102 Make any missing parent directories for each argument, setting their
9103 file permission bits to the umask modified by @samp{u+wx}. Ignore
9104 existing parent directories, and do not change their file permission
9107 To set the file permission bits of any newly-created parent
9108 directories to a value that includes @samp{u+wx}, you can set the
9109 umask before invoking @command{mkdir}. For example, if the shell
9110 command @samp{(umask u=rwx,go=rx; mkdir -p P/Q)} creates the parent
9111 @file{P} it sets the parent's permission bits to @samp{u=rwx,go=rx}.
9112 To set a parent's special mode bits as well, you can invoke
9113 @command{chmod} after @command{mkdir}. @xref{Directory Setuid and
9114 Setgid}, for how the set-user-ID and set-group-ID bits of
9115 newly-created parent directories are inherited.
9121 Print a message for each created directory. This is most useful with
9124 @item -Z @var{context}
9125 @itemx --context=@var{context}
9129 @cindex security context
9130 Set the default SELinux security context to be used for created directories.
9137 @node mkfifo invocation
9138 @section @command{mkfifo}: Make FIFOs (named pipes)
9141 @cindex FIFOs, creating
9142 @cindex named pipes, creating
9143 @cindex creating FIFOs (named pipes)
9145 @command{mkfifo} creates FIFOs (also called @dfn{named pipes}) with the
9146 specified names. Synopsis:
9149 mkfifo [@var{option}] @var{name}@dots{}
9152 A @dfn{FIFO} is a special file type that permits independent processes
9153 to communicate. One process opens the FIFO file for writing, and
9154 another for reading, after which data can flow as with the usual
9155 anonymous pipe in shells or elsewhere.
9157 The program accepts the following option. Also see @ref{Common options}.
9162 @itemx --mode=@var{mode}
9165 @cindex modes of created FIFOs, setting
9166 Set the mode of created FIFOs to @var{mode}, which is symbolic as in
9167 @command{chmod} and uses @samp{a=rw} (read and write allowed for everyone)
9168 for the point of departure. @var{mode} should specify only file
9169 permission bits. @xref{File permissions}.
9171 @item -Z @var{context}
9172 @itemx --context=@var{context}
9176 @cindex security context
9177 Set the default SELinux security context to be used for created FIFOs.
9184 @node mknod invocation
9185 @section @command{mknod}: Make block or character special files
9188 @cindex block special files, creating
9189 @cindex character special files, creating
9191 @command{mknod} creates a FIFO, character special file, or block special
9192 file with the specified name. Synopsis:
9195 mknod [@var{option}]@dots{} @var{name} @var{type} [@var{major} @var{minor}]
9198 @cindex special files
9199 @cindex block special files
9200 @cindex character special files
9201 Unlike the phrase ``special file type'' above, the term @dfn{special
9202 file} has a technical meaning on Unix: something that can generate or
9203 receive data. Usually this corresponds to a physical piece of hardware,
9204 e.g., a printer or a disk. (These files are typically created at
9205 system-configuration time.) The @command{mknod} command is what creates
9206 files of this type. Such devices can be read either a character at a
9207 time or a ``block'' (many characters) at a time, hence we say there are
9208 @dfn{block special} files and @dfn{character special} files.
9210 @c mknod is a shell built-in at least with OpenBSD's /bin/sh
9211 @mayConflictWithShellBuiltIn{mknod}
9213 The arguments after @var{name} specify the type of file to make:
9218 @opindex p @r{for FIFO file}
9222 @opindex b @r{for block special file}
9223 for a block special file
9226 @c Don't document the `u' option -- it's just a synonym for `c'.
9227 @c Do *any* versions of mknod still use it?
9229 @opindex c @r{for character special file}
9230 @c @opindex u @r{for character special file}
9231 for a character special file
9235 When making a block or character special file, the major and minor
9236 device numbers must be given after the file type.
9237 If a major or minor device number begins with @samp{0x} or @samp{0X},
9238 it is interpreted as hexadecimal; otherwise, if it begins with @samp{0},
9239 as octal; otherwise, as decimal.
9241 The program accepts the following option. Also see @ref{Common options}.
9246 @itemx --mode=@var{mode}
9249 Set the mode of created files to @var{mode}, which is symbolic as in
9250 @command{chmod} and uses @samp{a=rw} as the point of departure.
9251 @var{mode} should specify only file permission bits.
9252 @xref{File permissions}.
9254 @item -Z @var{context}
9255 @itemx --context=@var{context}
9259 @cindex security context
9260 Set the default SELinux security context to be used for created files.
9267 @node readlink invocation
9268 @section @command{readlink}: Print value of a symlink or canonical file name
9271 @cindex displaying value of a symbolic link
9272 @cindex canonical file name
9273 @cindex canonicalize a file name
9277 @command{readlink} may work in one of two supported modes:
9283 @command{readlink} outputs the value of the given symbolic link.
9284 If @command{readlink} is invoked with an argument other than the name
9285 of a symbolic link, it produces no output and exits with a nonzero exit code.
9287 @item Canonicalize mode
9289 @command{readlink} outputs the absolute name of the given file which contains
9290 no @file{.}, @file{..} components nor any repeated separators
9291 (@file{/}) or symbolic links.
9296 readlink [@var{option}] @var{file}
9299 By default, @command{readlink} operates in readlink mode.
9301 The program accepts the following options. Also see @ref{Common options}.
9306 @itemx --canonicalize
9308 @opindex --canonicalize
9309 Activate canonicalize mode.
9310 If any component of the file name except the last one is missing or unavailable,
9311 @command{readlink} produces no output and exits with a nonzero exit
9312 code. A trailing slash is ignored.
9315 @itemx --canonicalize-existing
9317 @opindex --canonicalize-existing
9318 Activate canonicalize mode.
9319 If any component is missing or unavailable, @command{readlink} produces
9320 no output and exits with a nonzero exit code. A trailing slash
9321 requires that the name resolve to a directory.
9324 @itemx --canonicalize-missing
9326 @opindex --canonicalize-missing
9327 Activate canonicalize mode.
9328 If any component is missing or unavailable, @command{readlink} treats it
9334 @opindex --no-newline
9335 Do not output the trailing newline.
9345 Suppress most error messages.
9351 Report error messages.
9355 The @command{readlink} utility first appeared in OpenBSD 2.1.
9357 There is a @command{realpath} command on some systems
9358 which operates like @command{readlink} in canonicalize mode.
9363 @node rmdir invocation
9364 @section @command{rmdir}: Remove empty directories
9367 @cindex removing empty directories
9368 @cindex directories, removing empty
9370 @command{rmdir} removes empty directories. Synopsis:
9373 rmdir [@var{option}]@dots{} @var{directory}@dots{}
9376 If any @var{directory} argument does not refer to an existing empty
9377 directory, it is an error.
9379 The program accepts the following options. Also see @ref{Common options}.
9383 @item --ignore-fail-on-non-empty
9384 @opindex --ignore-fail-on-non-empty
9385 @cindex directory deletion, ignoring failures
9386 Ignore each failure to remove a directory that is solely because
9387 the directory is non-empty.
9393 @cindex parent directories, removing
9394 Remove @var{directory}, then try to remove each component of @var{directory}.
9395 So, for example, @samp{rmdir -p a/b/c} is similar to @samp{rmdir a/b/c a/b a}.
9396 As such, it fails if any of those directories turns out not to be empty.
9397 Use the @option{--ignore-fail-on-non-empty} option to make it so such
9398 a failure does not evoke a diagnostic and does not cause @command{rmdir} to
9399 exit unsuccessfully.
9405 @cindex directory deletion, reporting
9406 Give a diagnostic for each successful removal.
9407 @var{directory} is removed.
9411 @xref{rm invocation}, for how to remove non-empty directories (recursively).
9416 @node unlink invocation
9417 @section @command{unlink}: Remove files via the unlink syscall
9420 @cindex removing files or directories (via the unlink syscall)
9422 @command{unlink} deletes a single specified file name.
9423 It is a minimalist interface to the system-provided
9424 @code{unlink} function. @xref{Deleting Files, , , libc,
9425 The GNU C Library Reference Manual}. Synopsis:
9426 It avoids the bells and whistles of the more commonly-used
9427 @command{rm} command (@pxref{rm invocation}).
9430 unlink @var{filename}
9433 On some systems @code{unlink} can be used to delete the name of a
9434 directory. On others, it can be used that way only by a privileged user.
9435 In the GNU system @code{unlink} can never delete the name of a directory.
9437 The @command{unlink} command honors the @option{--help} and
9438 @option{--version} options. To remove a file whose name begins with
9439 @samp{-}, prefix the name with @samp{./}, e.g., @samp{unlink ./--help}.
9444 @node Changing file attributes
9445 @chapter Changing file attributes
9447 @cindex changing file attributes
9448 @cindex file attributes, changing
9449 @cindex attributes, file
9451 A file is not merely its contents, a name, and a file type
9452 (@pxref{Special file types}). A file also has an owner (a user ID), a
9453 group (a group ID), permissions (what the owner can do with the file,
9454 what people in the group can do, and what everyone else can do), various
9455 timestamps, and other information. Collectively, we call these a file's
9458 These commands change file attributes.
9461 * chgrp invocation:: Change file groups.
9462 * chmod invocation:: Change access permissions.
9463 * chown invocation:: Change file owners and groups.
9464 * touch invocation:: Change file timestamps.
9468 @node chown invocation
9469 @section @command{chown}: Change file owner and group
9472 @cindex file ownership, changing
9473 @cindex group ownership, changing
9474 @cindex changing file ownership
9475 @cindex changing group ownership
9477 @command{chown} changes the user and/or group ownership of each given @var{file}
9478 to @var{new-owner} or to the user and group of an existing reference file.
9482 chown [@var{option}]@dots{} @{@var{new-owner} | --reference=@var{ref_file}@} @var{file}@dots{}
9485 If used, @var{new-owner} specifies the new owner and/or group as follows
9486 (with no embedded white space):
9489 [@var{owner}] [ : [@var{group}] ]
9496 If only an @var{owner} (a user name or numeric user ID) is given, that
9497 user is made the owner of each given file, and the files' group is not
9500 @item owner@samp{:}group
9501 If the @var{owner} is followed by a colon and a @var{group} (a
9502 group name or numeric group ID), with no spaces between them, the group
9503 ownership of the files is changed as well (to @var{group}).
9506 If a colon but no group name follows @var{owner}, that user is
9507 made the owner of the files and the group of the files is changed to
9508 @var{owner}'s login group.
9511 If the colon and following @var{group} are given, but the owner
9512 is omitted, only the group of the files is changed; in this case,
9513 @command{chown} performs the same function as @command{chgrp}.
9516 If only a colon is given, or if @var{new-owner} is empty, neither the
9517 owner nor the group is changed.
9521 If @var{owner} or @var{group} is intended to represent a numeric user
9522 or group ID, then you may specify it with a leading @samp{+}.
9523 @xref{Disambiguating names and IDs}.
9525 Some older scripts may still use @samp{.} in place of the @samp{:} separator.
9526 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
9527 require support for that, but for backward compatibility @acronym{GNU}
9528 @command{chown} supports @samp{.} so long as no ambiguity results.
9529 New scripts should avoid the use of @samp{.} because it is not
9530 portable, and because it has undesirable results if the entire
9531 @var{owner@samp{.}group} happens to identify a user whose name
9534 The @command{chown} command sometimes clears the set-user-ID or
9535 set-group-ID permission bits. This behavior depends on the policy and
9536 functionality of the underlying @code{chown} system call, which may
9537 make system-dependent file mode modifications outside the control of
9538 the @command{chown} command. For example, the @command{chown} command
9539 might not affect those bits when invoked by a user with appropriate
9540 privileges, or when the
9541 bits signify some function other than executable permission (e.g.,
9543 When in doubt, check the underlying system behavior.
9545 The program accepts the following options. Also see @ref{Common options}.
9553 @cindex changed owners, verbosely describing
9554 Verbosely describe the action for each @var{file} whose ownership
9563 @cindex error messages, omitting
9564 Do not print error messages about files whose ownership cannot be
9567 @itemx @w{@kbd{--from}=@var{old-owner}}
9569 @cindex symbolic links, changing owner
9570 Change a @var{file}'s ownership only if it has current attributes specified
9571 by @var{old-owner}. @var{old-owner} has the same form as @var{new-owner}
9573 This option is useful primarily from a security standpoint in that
9574 it narrows considerably the window of potential abuse.
9575 For example, to reflect a user ID numbering change for one user's files
9576 without an option like this, @code{root} might run
9579 find / -owner OLDUSER -print0 | xargs -0 chown -h NEWUSER
9582 But that is dangerous because the interval between when the @command{find}
9583 tests the existing file's owner and when the @command{chown} is actually run
9585 One way to narrow the gap would be to invoke chown for each file
9589 find / -owner OLDUSER -exec chown -h NEWUSER @{@} \;
9592 But that is very slow if there are many affected files.
9593 With this option, it is safer (the gap is narrower still)
9594 though still not perfect:
9597 chown -h -R --from=OLDUSER NEWUSER /
9601 @opindex --dereference
9602 @cindex symbolic links, changing owner
9604 Do not act on symbolic links themselves but rather on what they point to.
9605 This is the default.
9608 @itemx --no-dereference
9610 @opindex --no-dereference
9611 @cindex symbolic links, changing owner
9613 Act on symbolic links themselves instead of what they point to.
9614 This mode relies on the @code{lchown} system call.
9615 On systems that do not provide the @code{lchown} system call,
9616 @command{chown} fails when a file specified on the command line
9618 By default, no diagnostic is issued for symbolic links encountered
9619 during a recursive traversal, but see @option{--verbose}.
9621 @itemx --preserve-root
9622 @opindex --preserve-root
9623 @cindex root directory, disallow recursive modification
9624 Fail upon any attempt to recursively change the root directory, @file{/}.
9625 Without @option{--recursive}, this option has no effect.
9626 @xref{Treating / specially}.
9628 @itemx --no-preserve-root
9629 @opindex --no-preserve-root
9630 @cindex root directory, allow recursive modification
9631 Cancel the effect of any preceding @option{--preserve-root} option.
9632 @xref{Treating / specially}.
9634 @item --reference=@var{ref_file}
9635 @opindex --reference
9636 Change the user and group of each @var{file} to be the same as those of
9637 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9638 user and group of the symbolic link, but rather those of the file it
9645 Output a diagnostic for every file processed.
9646 If a symbolic link is encountered during a recursive traversal
9647 on a system without the @code{lchown} system call, and @option{--no-dereference}
9648 is in effect, then issue a diagnostic saying neither the symbolic link nor
9649 its referent is being changed.
9654 @opindex --recursive
9655 @cindex recursively changing file ownership
9656 Recursively change ownership of directories and their contents.
9659 @xref{Traversing symlinks}.
9662 @xref{Traversing symlinks}.
9665 @xref{Traversing symlinks}.
9674 # Change the owner of /u to "root".
9677 # Likewise, but also change its group to "staff".
9680 # Change the owner of /u and subfiles to "root".
9685 @node chgrp invocation
9686 @section @command{chgrp}: Change group ownership
9689 @cindex group ownership, changing
9690 @cindex changing group ownership
9692 @command{chgrp} changes the group ownership of each given @var{file}
9693 to @var{group} (which can be either a group name or a numeric group ID)
9694 or to the group of an existing reference file. Synopsis:
9697 chgrp [@var{option}]@dots{} @{@var{group} | --reference=@var{ref_file}@} @var{file}@dots{}
9700 If @var{group} is intended to represent a
9701 numeric group ID, then you may specify it with a leading @samp{+}.
9702 @xref{Disambiguating names and IDs}.
9704 The program accepts the following options. Also see @ref{Common options}.
9712 @cindex changed files, verbosely describing
9713 Verbosely describe the action for each @var{file} whose group actually
9722 @cindex error messages, omitting
9723 Do not print error messages about files whose group cannot be
9727 @opindex --dereference
9728 @cindex symbolic links, changing owner
9730 Do not act on symbolic links themselves but rather on what they point to.
9731 This is the default.
9734 @itemx --no-dereference
9736 @opindex --no-dereference
9737 @cindex symbolic links, changing group
9739 Act on symbolic links themselves instead of what they point to.
9740 This mode relies on the @code{lchown} system call.
9741 On systems that do not provide the @code{lchown} system call,
9742 @command{chgrp} fails when a file specified on the command line
9744 By default, no diagnostic is issued for symbolic links encountered
9745 during a recursive traversal, but see @option{--verbose}.
9747 @itemx --preserve-root
9748 @opindex --preserve-root
9749 @cindex root directory, disallow recursive modification
9750 Fail upon any attempt to recursively change the root directory, @file{/}.
9751 Without @option{--recursive}, this option has no effect.
9752 @xref{Treating / specially}.
9754 @itemx --no-preserve-root
9755 @opindex --no-preserve-root
9756 @cindex root directory, allow recursive modification
9757 Cancel the effect of any preceding @option{--preserve-root} option.
9758 @xref{Treating / specially}.
9760 @item --reference=@var{ref_file}
9761 @opindex --reference
9762 Change the group of each @var{file} to be the same as that of
9763 @var{ref_file}. If @var{ref_file} is a symbolic link, do not use the
9764 group of the symbolic link, but rather that of the file it refers to.
9770 Output a diagnostic for every file processed.
9771 If a symbolic link is encountered during a recursive traversal
9772 on a system without the @code{lchown} system call, and @option{--no-dereference}
9773 is in effect, then issue a diagnostic saying neither the symbolic link nor
9774 its referent is being changed.
9779 @opindex --recursive
9780 @cindex recursively changing group ownership
9781 Recursively change the group ownership of directories and their contents.
9784 @xref{Traversing symlinks}.
9787 @xref{Traversing symlinks}.
9790 @xref{Traversing symlinks}.
9799 # Change the group of /u to "staff".
9802 # Change the group of /u and subfiles to "staff".
9807 @node chmod invocation
9808 @section @command{chmod}: Change access permissions
9811 @cindex changing access permissions
9812 @cindex access permissions, changing
9813 @cindex permissions, changing access
9815 @command{chmod} changes the access permissions of the named files. Synopsis:
9818 chmod [@var{option}]@dots{} @{@var{mode} | --reference=@var{ref_file}@} @var{file}@dots{}
9821 @cindex symbolic links, permissions of
9822 @command{chmod} never changes the permissions of symbolic links, since
9823 the @command{chmod} system call cannot change their permissions.
9824 This is not a problem since the permissions of symbolic links are
9825 never used. However, for each symbolic link listed on the command
9826 line, @command{chmod} changes the permissions of the pointed-to file.
9827 In contrast, @command{chmod} ignores symbolic links encountered during
9828 recursive directory traversals.
9830 A successful use of @command{chmod} clears the set-group-ID bit of a
9831 regular file if the file's group ID does not match the user's
9832 effective group ID or one of the user's supplementary group IDs,
9833 unless the user has appropriate privileges. Additional restrictions
9834 may cause the set-user-ID and set-group-ID bits of @var{mode} or
9835 @var{ref_file} to be ignored. This behavior depends on the policy and
9836 functionality of the underlying @code{chmod} system call. When in
9837 doubt, check the underlying system behavior.
9839 If used, @var{mode} specifies the new file mode bits.
9840 For details, see the section on @ref{File permissions}.
9841 If you really want @var{mode} to have a leading @samp{-}, you should
9842 use @option{--} first, e.g., @samp{chmod -- -w file}. Typically,
9843 though, @samp{chmod a-w file} is preferable, and @command{chmod -w
9844 file} (without the @option{--}) complains if it behaves differently
9845 from what @samp{chmod a-w file} would do.
9847 The program accepts the following options. Also see @ref{Common options}.
9855 Verbosely describe the action for each @var{file} whose permissions
9864 @cindex error messages, omitting
9865 Do not print error messages about files whose permissions cannot be
9868 @itemx --preserve-root
9869 @opindex --preserve-root
9870 @cindex root directory, disallow recursive modification
9871 Fail upon any attempt to recursively change the root directory, @file{/}.
9872 Without @option{--recursive}, this option has no effect.
9873 @xref{Treating / specially}.
9875 @itemx --no-preserve-root
9876 @opindex --no-preserve-root
9877 @cindex root directory, allow recursive modification
9878 Cancel the effect of any preceding @option{--preserve-root} option.
9879 @xref{Treating / specially}.
9885 Verbosely describe the action or non-action taken for every @var{file}.
9887 @item --reference=@var{ref_file}
9888 @opindex --reference
9889 Change the mode of each @var{file} to be the same as that of @var{ref_file}.
9890 @xref{File permissions}.
9891 If @var{ref_file} is a symbolic link, do not use the mode
9892 of the symbolic link, but rather that of the file it refers to.
9897 @opindex --recursive
9898 @cindex recursively changing access permissions
9899 Recursively change permissions of directories and their contents.
9906 @node touch invocation
9907 @section @command{touch}: Change file timestamps
9910 @cindex changing file timestamps
9911 @cindex file timestamps, changing
9912 @cindex timestamps, changing file
9914 @command{touch} changes the access and/or modification times of the
9915 specified files. Synopsis:
9918 touch [@var{option}]@dots{} @var{file}@dots{}
9921 @cindex empty files, creating
9922 Any @var{file} argument that does not exist is created empty, unless
9923 option @option{--no-create} (@option{-c}) or @option{--no-dereference}
9924 (@option{-h}) was in effect.
9926 A @var{file} argument string of @samp{-} is handled specially and
9927 causes @command{touch} to change the times of the file associated with
9930 @cindex permissions, for changing file timestamps
9931 If changing both the access and modification times to the current
9932 time, @command{touch} can change the timestamps for files that the user
9933 running it does not own but has write permission for. Otherwise, the
9934 user must own the files.
9936 Although @command{touch} provides options for changing two of the times---the
9937 times of last access and modification---of a file, there is actually
9938 a standard third one as well: the inode change time. This is often
9939 referred to as a file's @code{ctime}.
9940 The inode change time represents the time when the file's meta-information
9941 last changed. One common example of this is when the permissions of a
9942 file change. Changing the permissions doesn't access the file, so
9943 the atime doesn't change, nor does it modify the file, so the mtime
9944 doesn't change. Yet, something about the file itself has changed,
9945 and this must be noted somewhere. This is the job of the ctime field.
9946 This is necessary, so that, for example, a backup program can make a
9947 fresh copy of the file, including the new permissions value.
9948 Another operation that modifies a file's ctime without affecting
9949 the others is renaming. In any case, it is not possible, in normal
9950 operations, for a user to change the ctime field to a user-specified value.
9951 Some operating systems and file systems support a fourth time: the
9952 birth time, when the file was first created; by definition, this
9953 timestamp never changes.
9956 Time stamps assume the time zone rules specified by the @env{TZ}
9957 environment variable, or by the system default rules if @env{TZ} is
9958 not set. @xref{TZ Variable,, Specifying the Time Zone with @env{TZ},
9959 libc, The GNU C Library Reference Manual}.
9960 You can avoid ambiguities during
9961 daylight saving transitions by using @sc{utc} time stamps.
9963 The program accepts the following options. Also see @ref{Common options}.
9969 @itemx --time=access
9973 @opindex atime@r{, changing}
9974 @opindex access @r{time, changing}
9975 @opindex use @r{time, changing}
9976 Change the access time only.
9981 @opindex --no-create
9982 Do not warn about or create files that do not exist.
9985 @itemx --date=@var{time}
9989 Use @var{time} instead of the current time. It can contain month names,
9990 time zones, @samp{am} and @samp{pm}, @samp{yesterday}, etc. For
9991 example, @option{--date="2004-02-27 14:19:13.489392193 +0530"}
9992 specifies the instant of time that is 489,392,193 nanoseconds after
9993 February 27, 2004 at 2:19:13 PM in a time zone that is 5 hours and 30
9994 minutes east of @acronym{UTC}. @xref{Date input formats}.
9995 File systems that do not support high-resolution time stamps
9996 silently ignore any excess precision here.
10000 @cindex BSD @command{touch} compatibility
10001 Ignored; for compatibility with BSD versions of @command{touch}.
10004 @itemx --no-dereference
10006 @opindex --no-dereference
10007 @cindex symbolic links, changing time
10009 Attempt to change the timestamps of a symbolic link, rather than what
10010 the link refers to. When using this option, empty files are not
10011 created, but option @option{-c} must also be used to avoid warning
10012 about files that do not exist. Not all systems support changing the
10013 timestamps of symlinks, since underlying system support for this
10014 action was not required until @acronym{POSIX} 2008. Also, on some
10015 systems, the mere act of examining a symbolic link changes the access
10016 time, such that only changes to the modification time will persist
10017 long enough to be observable. When coupled with option @option{-r}, a
10018 reference timestamp is taken from a symbolic link rather than the file
10022 @itemx --time=mtime
10023 @itemx --time=modify
10026 @opindex mtime@r{, changing}
10027 @opindex modify @r{time, changing}
10028 Change the modification time only.
10030 @item -r @var{file}
10031 @itemx --reference=@var{file}
10033 @opindex --reference
10034 Use the times of the reference @var{file} instead of the current time.
10035 If this option is combined with the @option{--date=@var{time}}
10036 (@option{-d @var{time}}) option, the reference @var{file}'s time is
10037 the origin for any relative @var{time}s given, but is otherwise ignored.
10038 For example, @samp{-r foo -d '-5 seconds'} specifies a time stamp
10039 equal to five seconds before the corresponding time stamp for @file{foo}.
10040 If @var{file} is a symbolic link, the reference timestamp is taken
10041 from the target of the symlink, unless @option{-h} was also in effect.
10043 @item -t [[@var{cc}]@var{yy}]@var{mmddhhmm}[.@var{ss}]
10044 Use the argument (optional four-digit or two-digit years, months,
10045 days, hours, minutes, optional seconds) instead of the current time.
10046 If the year is specified with only two digits, then @var{cc}
10047 is 20 for years in the range 0 @dots{} 68, and 19 for years in
10048 69 @dots{} 99. If no digits of the year are specified,
10049 the argument is interpreted as a date in the current year.
10050 Note that @var{ss} may be @samp{60}, to accommodate leap seconds.
10054 @vindex _POSIX2_VERSION
10055 On older systems, @command{touch} supports an obsolete syntax, as follows.
10056 If no timestamp is given with any of the @option{-d}, @option{-r}, or
10057 @option{-t} options, and if there are two or more @var{file}s and the
10058 first @var{file} is of the form @samp{@var{mmddhhmm}[@var{yy}]} and this
10059 would be a valid argument to the @option{-t} option (if the @var{yy}, if
10060 any, were moved to the front), and if the represented year
10061 is in the range 1969--1999, that argument is interpreted as the time
10062 for the other files instead of as a file name.
10063 This obsolete behavior can be enabled or disabled with the
10064 @env{_POSIX2_VERSION} environment variable (@pxref{Standards
10065 conformance}), but portable scripts should avoid commands whose
10066 behavior depends on this variable.
10067 For example, use @samp{touch ./12312359 main.c} or @samp{touch -t
10068 12312359 main.c} rather than the ambiguous @samp{touch 12312359 main.c}.
10074 @chapter Disk usage
10078 No disk can hold an infinite amount of data. These commands report
10079 how much disk storage is in use or available, report other file and
10080 file status information, and write buffers to disk.
10083 * df invocation:: Report file system disk space usage.
10084 * du invocation:: Estimate file space usage.
10085 * stat invocation:: Report file or file system status.
10086 * sync invocation:: Synchronize memory and disk.
10087 * truncate invocation:: Shrink or extend the size of a file.
10091 @node df invocation
10092 @section @command{df}: Report file system disk space usage
10095 @cindex file system disk usage
10096 @cindex disk usage by file system
10098 @command{df} reports the amount of disk space used and available on
10099 file systems. Synopsis:
10102 df [@var{option}]@dots{} [@var{file}]@dots{}
10105 With no arguments, @command{df} reports the space used and available on all
10106 currently mounted file systems (of all types). Otherwise, @command{df}
10107 reports on the file system containing each argument @var{file}.
10109 Normally the disk space is printed in units of
10110 1024 bytes, but this can be overridden (@pxref{Block size}).
10111 Non-integer quantities are rounded up to the next higher unit.
10113 @cindex disk device file
10114 @cindex device file, disk
10115 If an argument @var{file} is a disk device file containing a mounted
10116 file system, @command{df} shows the space available on that file system
10117 rather than on the file system containing the device node (i.e., the root
10118 file system). @sc{gnu} @command{df} does not attempt to determine the disk usage
10119 on unmounted file systems, because on most kinds of systems doing so
10120 requires extremely nonportable intimate knowledge of file system
10123 The program accepts the following options. Also see @ref{Common options}.
10131 @cindex automounter file systems
10132 @cindex ignore file systems
10133 Include in the listing dummy file systems, which
10134 are omitted by default. Such file systems are typically special-purpose
10135 pseudo-file-systems, such as automounter entries.
10137 @item -B @var{size}
10138 @itemx --block-size=@var{size}
10140 @opindex --block-size
10141 @cindex file system sizes
10142 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10143 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10147 @cindex grand total of disk size, usage and available space
10148 Print a grand total of all arguments after all arguments have
10149 been processed. This can be used to find out the total disk size, usage
10150 and available space of all listed devices.
10156 Equivalent to @option{--si}.
10162 @cindex inode usage
10163 List inode usage information instead of block usage. An inode (short
10164 for index node) contains information about a file such as its owner,
10165 permissions, timestamps, and location on the disk.
10169 @cindex kibibytes for file system sizes
10170 Print sizes in 1024-byte blocks, overriding the default block size
10171 (@pxref{Block size}).
10172 This option is equivalent to @option{--block-size=1K}.
10178 @cindex file system types, limiting output to certain
10179 Limit the listing to local file systems. By default, remote file systems
10184 @cindex file system space, retrieving old data more quickly
10185 Do not invoke the @code{sync} system call before getting any usage data.
10186 This may make @command{df} run significantly faster on systems with many
10187 disks, but on some systems (notably SunOS) the results may be slightly
10188 out of date. This is the default.
10191 @itemx --portability
10193 @opindex --portability
10194 @cindex one-line output format
10195 @cindex @acronym{POSIX} output format
10196 @cindex portable output format
10197 @cindex output format, portable
10198 Use the @acronym{POSIX} output format. This is like the default format except
10203 The information about each file system is always printed on exactly
10204 one line; a mount device is never put on a line by itself. This means
10205 that if the mount device name is more than 20 characters long (e.g., for
10206 some network mounts), the columns are misaligned.
10209 The labels in the header output line are changed to conform to @acronym{POSIX}.
10212 The default block size and output format are unaffected by the
10213 @env{DF_BLOCK_SIZE}, @env{BLOCK_SIZE} and @env{BLOCKSIZE} environment
10214 variables. However, the default block size is still affected by
10215 @env{POSIXLY_CORRECT}: it is 512 if @env{POSIXLY_CORRECT} is set, 1024
10216 otherwise. @xref{Block size}.
10223 @cindex file system space, retrieving current data more slowly
10224 Invoke the @code{sync} system call before getting any usage data. On
10225 some systems (notably SunOS), doing this yields more up to date results,
10226 but in general this option makes @command{df} much slower, especially when
10227 there are many or very busy file systems.
10229 @item -t @var{fstype}
10230 @itemx --type=@var{fstype}
10233 @cindex file system types, limiting output to certain
10234 Limit the listing to file systems of type @var{fstype}. Multiple
10235 file system types can be specified by giving multiple @option{-t} options.
10236 By default, nothing is omitted.
10239 @itemx --print-type
10241 @opindex --print-type
10242 @cindex file system types, printing
10243 Print each file system's type. The types printed here are the same ones
10244 you can include or exclude with @option{-t} and @option{-x}. The particular
10245 types printed are whatever is supported by the system. Here are some of
10246 the common names (this list is certainly not exhaustive):
10251 @cindex @acronym{NFS} file system type
10252 An @acronym{NFS} file system, i.e., one mounted over a network from another
10253 machine. This is the one type name which seems to be used uniformly by
10256 @item 4.2@r{, }ufs@r{, }efs@dots{}
10257 @cindex Linux file system types
10258 @cindex local file system types
10259 @opindex 4.2 @r{file system type}
10260 @opindex ufs @r{file system type}
10261 @opindex efs @r{file system type}
10262 A file system on a locally-mounted hard disk. (The system might even
10263 support more than one type here; Linux does.)
10265 @item hsfs@r{, }cdfs
10266 @cindex CD-ROM file system type
10267 @cindex High Sierra file system
10268 @opindex hsfs @r{file system type}
10269 @opindex cdfs @r{file system type}
10270 A file system on a CD-ROM drive. HP-UX uses @samp{cdfs}, most other
10271 systems use @samp{hsfs} (@samp{hs} for ``High Sierra'').
10274 @cindex PC file system
10275 @cindex DOS file system
10276 @cindex MS-DOS file system
10277 @cindex diskette file system
10279 An MS-DOS file system, usually on a diskette.
10283 @item -x @var{fstype}
10284 @itemx --exclude-type=@var{fstype}
10286 @opindex --exclude-type
10287 Limit the listing to file systems not of type @var{fstype}.
10288 Multiple file system types can be eliminated by giving multiple
10289 @option{-x} options. By default, no file system types are omitted.
10292 Ignored; for compatibility with System V versions of @command{df}.
10297 Failure includes the case where no output is generated, so you can
10298 inspect the exit status of a command like @samp{df -t ext3 -t reiserfs
10299 @var{dir}} to test whether @var{dir} is on a file system of type
10300 @samp{ext3} or @samp{reiserfs}.
10303 @node du invocation
10304 @section @command{du}: Estimate file space usage
10307 @cindex file space usage
10308 @cindex disk usage for files
10310 @command{du} reports the amount of disk space used by the specified files
10311 and for each subdirectory (of directory arguments). Synopsis:
10314 du [@var{option}]@dots{} [@var{file}]@dots{}
10317 With no arguments, @command{du} reports the disk space for the current
10318 directory. Normally the disk space is printed in units of
10319 1024 bytes, but this can be overridden (@pxref{Block size}).
10320 Non-integer quantities are rounded up to the next higher unit.
10322 If two or more hard links point to the same file, only one of the hard
10323 links is counted. The @var{file} argument order affects which links
10324 are counted, and changing the argument order may change the numbers
10325 that @command{du} outputs.
10327 The program accepts the following options. Also see @ref{Common options}.
10335 Show counts for all files, not just directories.
10337 @itemx --apparent-size
10338 @opindex --apparent-size
10339 Print apparent sizes, rather than disk usage. The apparent size of a
10340 file is the number of bytes reported by @code{wc -c} on regular files,
10341 or more generally, @code{ls -l --block-size=1} or @code{stat --format=%s}.
10342 For example, a file containing the word @samp{zoo} with no newline would,
10343 of course, have an apparent size of 3. Such a small file may require
10344 anywhere from 0 to 16 KiB or more of disk space, depending on
10345 the type and configuration of the file system on which the file resides.
10346 However, a sparse file created with this command:
10349 dd bs=1 seek=2GiB if=/dev/null of=big
10353 has an apparent size of 2 GiB, yet on most modern
10354 systems, it actually uses almost no disk space.
10360 Equivalent to @code{--apparent-size --block-size=1}.
10362 @item -B @var{size}
10363 @itemx --block-size=@var{size}
10365 @opindex --block-size
10367 Scale sizes by @var{size} before printing them (@pxref{Block size}).
10368 For example, @option{-BG} prints sizes in units of 1,073,741,824 bytes.
10374 @cindex grand total of disk space
10375 Print a grand total of all arguments after all arguments have
10376 been processed. This can be used to find out the total disk usage of
10377 a given set of files or directories.
10380 @itemx --dereference-args
10382 @opindex --dereference-args
10383 Dereference symbolic links that are command line arguments.
10384 Does not affect other symbolic links. This is helpful for finding
10385 out the disk usage of directories, such as @file{/usr/tmp}, which
10386 are often symbolic links.
10388 @c --files0-from=FILE
10389 @filesZeroFromOption{du,, with the @option{--total} (@option{-c}) option}
10395 Equivalent to @option{--dereference-args} (@option{-D}).
10399 @cindex kibibytes for file sizes
10400 Print sizes in 1024-byte blocks, overriding the default block size
10401 (@pxref{Block size}).
10402 This option is equivalent to @option{--block-size=1K}.
10405 @itemx --count-links
10407 @opindex --count-links
10408 @cindex hard links, counting in @command{du}
10409 Count the size of all files, even if they have appeared already (as a
10413 @itemx --dereference
10415 @opindex --dereference
10416 @cindex symbolic links, dereferencing in @command{du}
10417 Dereference symbolic links (show the disk space used by the file
10418 or directory that the link points to instead of the space used by
10423 @cindex mebibytes for file sizes
10424 Print sizes in 1,048,576-byte blocks, overriding the default block size
10425 (@pxref{Block size}).
10426 This option is equivalent to @option{--block-size=1M}.
10429 @itemx --no-dereference
10431 @opindex --no-dereference
10432 @cindex symbolic links, dereferencing in @command{du}
10433 For each symbolic links encountered by @command{du},
10434 consider the disk space used by the symbolic link.
10436 @item -d @var{depth}
10437 @item --max-depth=@var{depth}
10438 @opindex -d @var{depth}
10439 @opindex --max-depth=@var{depth}
10440 @cindex limiting output of @command{du}
10441 Show the total for each directory (and file if --all) that is at
10442 most MAX_DEPTH levels down from the root of the hierarchy. The root
10443 is at level 0, so @code{du --max-depth=0} is equivalent to @code{du -s}.
10452 @opindex --summarize
10453 Display only a total for each argument.
10456 @itemx --separate-dirs
10458 @opindex --separate-dirs
10459 Normally, in the output of @command{du} (when not using @option{--summarize}),
10460 the size listed next to a directory name, @var{d}, represents the sum
10461 of sizes of all entries beneath @var{d} as well as the size of @var{d} itself.
10462 With @option{--separate-dirs}, the size reported for a directory name,
10463 @var{d}, is merely the @code{stat.st_size}-derived size of the directory
10468 @cindex last modified dates, displaying in @command{du}
10469 Show time of the most recent modification of any file in the directory,
10470 or any of its subdirectories.
10472 @itemx --time=ctime
10473 @itemx --time=status
10476 @opindex ctime@r{, show the most recent}
10477 @opindex status time@r{, show the most recent}
10478 @opindex use time@r{, show the most recent}
10479 Show the most recent status change time (the @samp{ctime} in the inode) of
10480 any file in the directory, instead of the modification time.
10482 @itemx --time=atime
10483 @itemx --time=access
10485 @opindex atime@r{, show the most recent}
10486 @opindex access time@r{, show the most recent}
10487 Show the most recent access time (the @samp{atime} in the inode) of
10488 any file in the directory, instead of the modification time.
10490 @item --time-style=@var{style}
10491 @opindex --time-style
10493 List timestamps in style @var{style}. This option has an effect only if
10494 the @option{--time} option is also specified. The @var{style} should
10495 be one of the following:
10498 @item +@var{format}
10500 List timestamps using @var{format}, where @var{format} is interpreted
10501 like the format argument of @command{date} (@pxref{date invocation}).
10502 For example, @option{--time-style="+%Y-%m-%d %H:%M:%S"} causes
10503 @command{du} to list timestamps like @samp{2002-03-30 23:45:56}. As
10504 with @command{date}, @var{format}'s interpretation is affected by the
10505 @env{LC_TIME} locale category.
10508 List timestamps in full using @acronym{ISO} 8601 date, time, and time zone
10509 format with nanosecond precision, e.g., @samp{2002-03-30
10510 23:45:56.477817180 -0700}. This style is equivalent to
10511 @samp{+%Y-%m-%d %H:%M:%S.%N %z}.
10514 List @acronym{ISO} 8601 date and time in minutes, e.g.,
10515 @samp{2002-03-30 23:45}. These timestamps are shorter than
10516 @samp{full-iso} timestamps, and are usually good enough for everyday
10517 work. This style is equivalent to @samp{+%Y-%m-%d %H:%M}.
10520 List @acronym{ISO} 8601 dates for timestamps, e.g., @samp{2002-03-30}.
10521 This style is equivalent to @samp{+%Y-%m-%d}.
10525 You can specify the default value of the @option{--time-style} option
10526 with the environment variable @env{TIME_STYLE}; if @env{TIME_STYLE} is not set
10527 the default style is @samp{long-iso}. For compatibility with @command{ls},
10528 if @env{TIME_STYLE} begins with @samp{+} and contains a newline,
10529 the newline and any later characters are ignored; if @env{TIME_STYLE}
10530 begins with @samp{posix-} the @samp{posix-} is ignored; and if
10531 @env{TIME_STYLE} is @samp{locale} it is ignored.
10534 @itemx --one-file-system
10536 @opindex --one-file-system
10537 @cindex one file system, restricting @command{du} to
10538 Skip directories that are on different file systems from the one that
10539 the argument being processed is on.
10541 @item --exclude=@var{pattern}
10542 @opindex --exclude=@var{pattern}
10543 @cindex excluding files from @command{du}
10544 When recursing, skip subdirectories or files matching @var{pattern}.
10545 For example, @code{du --exclude='*.o'} excludes files whose names
10548 @item -X @var{file}
10549 @itemx --exclude-from=@var{file}
10550 @opindex -X @var{file}
10551 @opindex --exclude-from=@var{file}
10552 @cindex excluding files from @command{du}
10553 Like @option{--exclude}, except take the patterns to exclude from @var{file},
10554 one per line. If @var{file} is @samp{-}, take the patterns from standard
10559 @cindex NFS mounts from BSD to HP-UX
10560 On BSD systems, @command{du} reports sizes that are half the correct
10561 values for files that are NFS-mounted from HP-UX systems. On HP-UX
10562 systems, it reports sizes that are twice the correct values for
10563 files that are NFS-mounted from BSD systems. This is due to a flaw
10564 in HP-UX; it also affects the HP-UX @command{du} program.
10569 @node stat invocation
10570 @section @command{stat}: Report file or file system status
10573 @cindex file status
10574 @cindex file system status
10576 @command{stat} displays information about the specified file(s). Synopsis:
10579 stat [@var{option}]@dots{} [@var{file}]@dots{}
10582 With no option, @command{stat} reports all information about the given files.
10583 But it also can be used to report the information of the file systems the
10584 given files are located on. If the files are links, @command{stat} can
10585 also give information about the files the links point to.
10587 @mayConflictWithShellBuiltIn{stat}
10592 @itemx --dereference
10594 @opindex --dereference
10595 @cindex symbolic links, dereferencing in @command{stat}
10596 Change how @command{stat} treats symbolic links.
10597 With this option, @command{stat} acts on the file referenced
10598 by each symbolic link argument.
10599 Without it, @command{stat} acts on any symbolic link argument directly.
10602 @itemx --file-system
10604 @opindex --file-system
10605 @cindex file systems
10606 Report information about the file systems where the given files are located
10607 instead of information about the files themselves.
10610 @itemx --format=@var{format}
10612 @opindex --format=@var{format}
10613 @cindex output format
10614 Use @var{format} rather than the default format.
10615 @var{format} is automatically newline-terminated, so
10616 running a command like the following with two or more @var{file}
10617 operands produces a line of output for each operand:
10619 $ stat --format=%d:%i / /usr
10624 @itemx --printf=@var{format}
10625 @opindex --printf=@var{format}
10626 @cindex output format
10627 Use @var{format} rather than the default format.
10628 Like @option{--format}, but interpret backslash escapes,
10629 and do not output a mandatory trailing newline.
10630 If you want a newline, include @samp{\n} in the @var{format}.
10631 Here's how you would use @option{--printf} to print the device
10632 and inode numbers of @file{/} and @file{/usr}:
10634 $ stat --printf='%d:%i\n' / /usr
10643 @cindex terse output
10644 Print the information in terse form, suitable for parsing by other programs.
10648 The valid @var{format} directives for files with @option{--format} and
10649 @option{--printf} are:
10652 @item %a - Access rights in octal
10653 @item %A - Access rights in human readable form
10654 @item %b - Number of blocks allocated (see @samp{%B})
10655 @item %B - The size in bytes of each block reported by @samp{%b}
10656 @item %d - Device number in decimal
10657 @item %D - Device number in hex
10658 @item %f - Raw mode in hex
10659 @item %F - File type
10660 @item %g - Group ID of owner
10661 @item %G - Group name of owner
10662 @item %h - Number of hard links
10663 @item %i - Inode number
10664 @item %n - File name
10665 @item %N - Quoted file name with dereference if symbolic link
10666 @item %o - I/O block size
10667 @item %s - Total size, in bytes
10668 @item %t - Major device type in hex
10669 @item %T - Minor device type in hex
10670 @item %u - User ID of owner
10671 @item %U - User name of owner
10672 @item %x - Time of last access
10673 @item %X - Time of last access as seconds since Epoch
10674 @item %y - Time of last modification
10675 @item %Y - Time of last modification as seconds since Epoch
10676 @item %z - Time of last change
10677 @item %Z - Time of last change as seconds since Epoch
10680 When listing file system information (@option{--file-system} (@option{-f})),
10681 you must use a different set of @var{format} directives:
10684 @item %a - Free blocks available to non-super-user
10685 @item %b - Total data blocks in file system
10686 @item %c - Total file nodes in file system
10687 @item %d - Free file nodes in file system
10688 @item %f - Free blocks in file system
10689 @item %i - File System ID in hex
10690 @item %l - Maximum length of file names
10691 @item %n - File name
10692 @item %s - Block size (for faster transfers)
10693 @item %S - Fundamental block size (for block counts)
10694 @item %t - Type in hex
10695 @item %T - Type in human readable form
10699 Time stamps are listed according to the time zone rules specified by
10700 the @env{TZ} environment variable, or by the system default rules if
10701 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
10702 with @env{TZ}, libc, The GNU C Library Reference Manual}.
10707 @node sync invocation
10708 @section @command{sync}: Synchronize data on disk with memory
10711 @cindex synchronize disk and memory
10713 @cindex superblock, writing
10714 @cindex inodes, written buffered
10715 @command{sync} writes any data buffered in memory out to disk. This can
10716 include (but is not limited to) modified superblocks, modified inodes,
10717 and delayed reads and writes. This must be implemented by the kernel;
10718 The @command{sync} program does nothing but exercise the @code{sync} system
10721 @cindex crashes and corruption
10722 The kernel keeps data in memory to avoid doing (relatively slow) disk
10723 reads and writes. This improves performance, but if the computer
10724 crashes, data may be lost or the file system corrupted as a
10725 result. The @command{sync} command ensures everything in memory
10726 is written to disk.
10728 Any arguments are ignored, except for a lone @option{--help} or
10729 @option{--version} (@pxref{Common options}).
10734 @node truncate invocation
10735 @section @command{truncate}: Shrink or extend the size of a file
10738 @cindex truncating, file sizes
10740 @command{truncate} shrinks or extends the size of each @var{file} to the
10741 specified size. Synopsis:
10744 truncate @var{option}@dots{} @var{file}@dots{}
10747 @cindex files, creating
10748 Any @var{file} that does not exist is created.
10750 @cindex sparse files, creating
10751 @cindex holes, creating files with
10752 If a @var{file} is larger than the specified size, the extra data is lost.
10753 If a @var{file} is shorter, it is extended and the extended part (or hole)
10754 reads as zero bytes.
10756 The program accepts the following options. Also see @ref{Common options}.
10763 @opindex --no-create
10764 Do not create files that do not exist.
10769 @opindex --io-blocks
10770 Treat @var{size} as number of I/O blocks of the @var{file} rather than bytes.
10772 @item -r @var{rfile}
10773 @itemx --reference=@var{rfile}
10775 @opindex --reference
10776 Base the size of each @var{file} on the size of @var{rfile}.
10778 @item -s @var{size}
10779 @itemx --size=@var{size}
10782 Set or adjust the size of each @var{file} according to @var{size}.
10783 @multiplierSuffixesNoBlocks{size}
10785 @var{size} may also be prefixed by one of the following to adjust
10786 the size of each @var{file} based on their current size:
10788 @samp{+} => extend by
10789 @samp{-} => reduce by
10790 @samp{<} => at most
10791 @samp{>} => at least
10792 @samp{/} => round down to multiple of
10793 @samp{%} => round up to multiple of
10801 @node Printing text
10802 @chapter Printing text
10804 @cindex printing text, commands for
10805 @cindex commands for printing text
10807 This section describes commands that display text strings.
10810 * echo invocation:: Print a line of text.
10811 * printf invocation:: Format and print data.
10812 * yes invocation:: Print a string until interrupted.
10816 @node echo invocation
10817 @section @command{echo}: Print a line of text
10820 @cindex displaying text
10821 @cindex printing text
10822 @cindex text, displaying
10823 @cindex arbitrary text, displaying
10825 @command{echo} writes each given @var{string} to standard output, with a
10826 space between each and a newline after the last one. Synopsis:
10829 echo [@var{option}]@dots{} [@var{string}]@dots{}
10832 @mayConflictWithShellBuiltIn{echo}
10834 The program accepts the following options. Also see @ref{Common options}.
10835 Options must precede operands, and the normally-special argument
10836 @samp{--} has no special meaning and is treated like any other
10842 Do not output the trailing newline.
10846 @cindex backslash escapes
10847 Enable interpretation of the following backslash-escaped characters in
10856 produce no further output
10872 the eight-bit value that is the octal number @var{nnn}
10873 (zero to three octal digits)
10875 the eight-bit value that is the octal number @var{nnn}
10876 (one to three octal digits)
10878 the eight-bit value that is the hexadecimal number @var{hh}
10879 (one or two hexadecimal digits)
10884 @cindex backslash escapes
10885 Disable interpretation of backslash escapes in each @var{string}.
10886 This is the default. If @option{-e} and @option{-E} are both
10887 specified, the last one given takes effect.
10891 @vindex POSIXLY_CORRECT
10892 If the @env{POSIXLY_CORRECT} environment variable is set, then when
10893 @command{echo}'s first argument is not @option{-n} it outputs
10894 option-like arguments instead of treating them as options. For
10895 example, @code{echo -ne hello} outputs @samp{-ne hello} instead of
10896 plain @samp{hello}.
10898 @acronym{POSIX} does not require support for any options, and says
10899 that the behavior of @command{echo} is implementation-defined if any
10900 @var{string} contains a backslash or if the first argument is
10901 @option{-n}. Portable programs can use the @command{printf} command
10902 if they need to omit trailing newlines or output control characters or
10903 backslashes. @xref{printf invocation}.
10908 @node printf invocation
10909 @section @command{printf}: Format and print data
10912 @command{printf} does formatted printing of text. Synopsis:
10915 printf @var{format} [@var{argument}]@dots{}
10918 @command{printf} prints the @var{format} string, interpreting @samp{%}
10919 directives and @samp{\} escapes to format numeric and string arguments
10920 in a way that is mostly similar to the C @samp{printf} function.
10921 @xref{Output Conversion Syntax,, @command{printf} format directives,
10922 libc, The GNU C Library Reference Manual}, for details.
10923 The differences are listed below.
10925 @mayConflictWithShellBuiltIn{printf}
10930 The @var{format} argument is reused as necessary to convert all the
10931 given @var{argument}s. For example, the command @samp{printf %s a b}
10935 Missing @var{argument}s are treated as null strings or as zeros,
10936 depending on whether the context expects a string or a number. For
10937 example, the command @samp{printf %sx%d} prints @samp{x0}.
10941 An additional escape, @samp{\c}, causes @command{printf} to produce no
10942 further output. For example, the command @samp{printf 'A%sC\cD%sF' B
10943 E} prints @samp{ABC}.
10946 The hexadecimal escape sequence @samp{\x@var{hh}} has at most two
10947 digits, as opposed to C where it can have an unlimited number of
10948 digits. For example, the command @samp{printf '\x07e'} prints two
10949 bytes, whereas the C statement @samp{printf ("\x07e")} prints just
10954 @command{printf} has an additional directive, @samp{%b}, which prints its
10955 argument string with @samp{\} escapes interpreted in the same way as in
10956 the @var{format} string, except that octal escapes are of the form
10957 @samp{\0@var{ooo}} where @var{ooo} is 0 to 3 octal digits.
10958 If a precision is also given, it limits the number of bytes printed
10959 from the converted string.
10962 Numeric arguments must be single C constants, possibly with leading
10963 @samp{+} or @samp{-}. For example, @samp{printf %.4d -3} outputs
10967 @vindex POSIXLY_CORRECT
10968 If the leading character of a numeric argument is @samp{"} or @samp{'}
10969 then its value is the numeric value of the immediately following
10970 character. Any remaining characters are silently ignored if the
10971 @env{POSIXLY_CORRECT} environment variable is set; otherwise, a
10972 warning is printed. For example, @samp{printf "%d" "'a"} outputs
10973 @samp{97} on hosts that use the @acronym{ASCII} character set, since
10974 @samp{a} has the numeric value 97 in @acronym{ASCII}.
10979 A floating-point argument must use a period before any fractional
10980 digits, but is printed according to the @env{LC_NUMERIC} category of the
10981 current locale. For example, in a locale whose radix character is a
10982 comma, the command @samp{printf %g 3.14} outputs @samp{3,14} whereas
10983 the command @samp{printf %g 3,14} is an error.
10987 @command{printf} interprets @samp{\@var{ooo}} in @var{format} as an octal number
10988 (if @var{ooo} is 1 to 3 octal digits) specifying a character to print,
10989 and @samp{\x@var{hh}} as a hexadecimal number (if @var{hh} is 1 to 2 hex
10990 digits) specifying a character to print.
10995 @cindex ISO/IEC 10646
10997 @command{printf} interprets two character syntaxes introduced in
10998 @acronym{ISO} C 99:
10999 @samp{\u} for 16-bit Unicode (@acronym{ISO}/@acronym{IEC} 10646)
11000 characters, specified as
11001 four hexadecimal digits @var{hhhh}, and @samp{\U} for 32-bit Unicode
11002 characters, specified as eight hexadecimal digits @var{hhhhhhhh}.
11003 @command{printf} outputs the Unicode characters
11004 according to the @env{LC_CTYPE} locale. Unicode characters in the ranges
11005 U+0000...U+009F, U+D800...U+DFFF cannot be specified by this syntax, except
11006 for U+0024 ($), U+0040 (@@), and U+0060 (@`).
11008 The processing of @samp{\u} and @samp{\U} requires a full-featured
11009 @code{iconv} facility. It is activated on systems with glibc 2.2 (or newer),
11010 or when @code{libiconv} is installed prior to this package. Otherwise
11011 @samp{\u} and @samp{\U} will print as-is.
11013 The only options are a lone @option{--help} or
11014 @option{--version}. @xref{Common options}.
11015 Options must precede operands.
11017 The Unicode character syntaxes are useful for writing strings in a locale
11018 independent way. For example, a string containing the Euro currency symbol
11021 $ env printf '\u20AC 14.95'
11025 will be output correctly in all locales supporting the Euro symbol
11026 (@acronym{ISO}-8859-15, UTF-8, and others). Similarly, a Chinese string
11029 $ env printf '\u4e2d\u6587'
11033 will be output correctly in all Chinese locales (GB2312, BIG5, UTF-8, etc).
11035 Note that in these examples, the @command{printf} command has been
11036 invoked via @command{env} to ensure that we run the program found via
11037 your shell's search path, and not a shell alias or a built-in function.
11039 For larger strings, you don't need to look up the hexadecimal code
11040 values of each character one by one. @acronym{ASCII} characters mixed with \u
11041 escape sequences is also known as the JAVA source file encoding. You can
11042 use GNU recode 3.5c (or newer) to convert strings to this encoding. Here
11043 is how to convert a piece of text into a shell script which will output
11044 this text in a locale-independent way:
11047 $ LC_CTYPE=zh_CN.big5 /usr/local/bin/printf \
11048 '\u4e2d\u6587\n' > sample.txt
11049 $ recode BIG5..JAVA < sample.txt \
11050 | sed -e "s|^|/usr/local/bin/printf '|" -e "s|$|\\\\n'|" \
11057 @node yes invocation
11058 @section @command{yes}: Print a string until interrupted
11061 @cindex repeated output of a string
11063 @command{yes} prints the command line arguments, separated by spaces and
11064 followed by a newline, forever until it is killed. If no arguments are
11065 given, it prints @samp{y} followed by a newline forever until killed.
11067 Upon a write error, @command{yes} exits with status @samp{1}.
11069 The only options are a lone @option{--help} or @option{--version}.
11070 To output an argument that begins with
11071 @samp{-}, precede it with @option{--}, e.g., @samp{yes -- --help}.
11072 @xref{Common options}.
11076 @chapter Conditions
11079 @cindex commands for exit status
11080 @cindex exit status commands
11082 This section describes commands that are primarily useful for their exit
11083 status, rather than their output. Thus, they are often used as the
11084 condition of shell @code{if} statements, or as the last command in a
11088 * false invocation:: Do nothing, unsuccessfully.
11089 * true invocation:: Do nothing, successfully.
11090 * test invocation:: Check file types and compare values.
11091 * expr invocation:: Evaluate expressions.
11095 @node false invocation
11096 @section @command{false}: Do nothing, unsuccessfully
11099 @cindex do nothing, unsuccessfully
11100 @cindex failure exit status
11101 @cindex exit status of @command{false}
11103 @command{false} does nothing except return an exit status of 1, meaning
11104 @dfn{failure}. It can be used as a place holder in shell scripts
11105 where an unsuccessful command is needed.
11106 In most modern shells, @command{false} is a built-in command, so when
11107 you use @samp{false} in a script, you're probably using the built-in
11108 command, not the one documented here.
11110 @command{false} honors the @option{--help} and @option{--version} options.
11112 This version of @command{false} is implemented as a C program, and is thus
11113 more secure and faster than a shell script implementation, and may safely
11114 be used as a dummy shell for the purpose of disabling accounts.
11116 Note that @command{false} (unlike all other programs documented herein)
11117 exits unsuccessfully, even when invoked with
11118 @option{--help} or @option{--version}.
11120 Portable programs should not assume that the exit status of
11121 @command{false} is 1, as it is greater than 1 on some
11122 non-@acronym{GNU} hosts.
11125 @node true invocation
11126 @section @command{true}: Do nothing, successfully
11129 @cindex do nothing, successfully
11131 @cindex successful exit
11132 @cindex exit status of @command{true}
11134 @command{true} does nothing except return an exit status of 0, meaning
11135 @dfn{success}. It can be used as a place holder in shell scripts
11136 where a successful command is needed, although the shell built-in
11137 command @code{:} (colon) may do the same thing faster.
11138 In most modern shells, @command{true} is a built-in command, so when
11139 you use @samp{true} in a script, you're probably using the built-in
11140 command, not the one documented here.
11142 @command{true} honors the @option{--help} and @option{--version} options.
11144 Note, however, that it is possible to cause @command{true}
11145 to exit with nonzero status: with the @option{--help} or @option{--version}
11146 option, and with standard
11147 output already closed or redirected to a file that evokes an I/O error.
11148 For example, using a Bourne-compatible shell:
11151 $ ./true --version >&-
11152 ./true: write error: Bad file number
11153 $ ./true --version > /dev/full
11154 ./true: write error: No space left on device
11157 This version of @command{true} is implemented as a C program, and is thus
11158 more secure and faster than a shell script implementation, and may safely
11159 be used as a dummy shell for the purpose of disabling accounts.
11161 @node test invocation
11162 @section @command{test}: Check file types and compare values
11165 @cindex check file types
11166 @cindex compare values
11167 @cindex expression evaluation
11169 @command{test} returns a status of 0 (true) or 1 (false) depending on the
11170 evaluation of the conditional expression @var{expr}. Each part of the
11171 expression must be a separate argument.
11173 @command{test} has file status checks, string operators, and numeric
11174 comparison operators.
11176 @command{test} has an alternate form that uses opening and closing
11177 square brackets instead a leading @samp{test}. For example, instead
11178 of @samp{test -d /}, you can write @samp{[ -d / ]}. The square
11179 brackets must be separate arguments; for example, @samp{[-d /]} does
11180 not have the desired effect. Since @samp{test @var{expr}} and @samp{[
11181 @var{expr} ]} have the same meaning, only the former form is discussed
11187 test @var{expression}
11189 [ @var{expression} ]
11194 @mayConflictWithShellBuiltIn{test}
11196 If @var{expression} is omitted, @command{test} returns false.
11197 If @var{expression} is a single argument,
11198 @command{test} returns false if the argument is null and true otherwise. The argument
11199 can be any string, including strings like @samp{-d}, @samp{-1},
11200 @samp{--}, @samp{--help}, and @samp{--version} that most other
11201 programs would treat as options. To get help and version information,
11202 invoke the commands @samp{[ --help} and @samp{[ --version}, without
11203 the usual closing brackets. @xref{Common options}.
11205 @cindex exit status of @command{test}
11209 0 if the expression is true,
11210 1 if the expression is false,
11211 2 if an error occurred.
11215 * File type tests:: -[bcdfhLpSt]
11216 * Access permission tests:: -[gkruwxOG]
11217 * File characteristic tests:: -e -s -nt -ot -ef
11218 * String tests:: -z -n = !=
11219 * Numeric tests:: -eq -ne -lt -le -gt -ge
11220 * Connectives for test:: ! -a -o
11224 @node File type tests
11225 @subsection File type tests
11227 @cindex file type tests
11229 These options test for particular types of files. (Everything's a file,
11230 but not all files are the same!)
11234 @item -b @var{file}
11236 @cindex block special check
11237 True if @var{file} exists and is a block special device.
11239 @item -c @var{file}
11241 @cindex character special check
11242 True if @var{file} exists and is a character special device.
11244 @item -d @var{file}
11246 @cindex directory check
11247 True if @var{file} exists and is a directory.
11249 @item -f @var{file}
11251 @cindex regular file check
11252 True if @var{file} exists and is a regular file.
11254 @item -h @var{file}
11255 @itemx -L @var{file}
11258 @cindex symbolic link check
11259 True if @var{file} exists and is a symbolic link.
11260 Unlike all other file-related tests, this test does not dereference
11261 @var{file} if it is a symbolic link.
11263 @item -p @var{file}
11265 @cindex named pipe check
11266 True if @var{file} exists and is a named pipe.
11268 @item -S @var{file}
11270 @cindex socket check
11271 True if @var{file} exists and is a socket.
11275 @cindex terminal check
11276 True if @var{fd} is a file descriptor that is associated with a
11282 @node Access permission tests
11283 @subsection Access permission tests
11285 @cindex access permission tests
11286 @cindex permission tests
11288 These options test for particular access permissions.
11292 @item -g @var{file}
11294 @cindex set-group-ID check
11295 True if @var{file} exists and has its set-group-ID bit set.
11297 @item -k @var{file}
11299 @cindex sticky bit check
11300 True if @var{file} exists and has its @dfn{sticky} bit set.
11302 @item -r @var{file}
11304 @cindex readable file check
11305 True if @var{file} exists and read permission is granted.
11307 @item -u @var{file}
11309 @cindex set-user-ID check
11310 True if @var{file} exists and has its set-user-ID bit set.
11312 @item -w @var{file}
11314 @cindex writable file check
11315 True if @var{file} exists and write permission is granted.
11317 @item -x @var{file}
11319 @cindex executable file check
11320 True if @var{file} exists and execute permission is granted
11321 (or search permission, if it is a directory).
11323 @item -O @var{file}
11325 @cindex owned by effective user ID check
11326 True if @var{file} exists and is owned by the current effective user ID.
11328 @item -G @var{file}
11330 @cindex owned by effective group ID check
11331 True if @var{file} exists and is owned by the current effective group ID.
11335 @node File characteristic tests
11336 @subsection File characteristic tests
11338 @cindex file characteristic tests
11340 These options test other file characteristics.
11344 @item -e @var{file}
11346 @cindex existence-of-file check
11347 True if @var{file} exists.
11349 @item -s @var{file}
11351 @cindex nonempty file check
11352 True if @var{file} exists and has a size greater than zero.
11354 @item @var{file1} -nt @var{file2}
11356 @cindex newer-than file check
11357 True if @var{file1} is newer (according to modification date) than
11358 @var{file2}, or if @var{file1} exists and @var{file2} does not.
11360 @item @var{file1} -ot @var{file2}
11362 @cindex older-than file check
11363 True if @var{file1} is older (according to modification date) than
11364 @var{file2}, or if @var{file2} exists and @var{file1} does not.
11366 @item @var{file1} -ef @var{file2}
11368 @cindex same file check
11369 @cindex hard link check
11370 True if @var{file1} and @var{file2} have the same device and inode
11371 numbers, i.e., if they are hard links to each other.
11377 @subsection String tests
11379 @cindex string tests
11381 These options test string characteristics. You may need to quote
11382 @var{string} arguments for the shell. For example:
11388 The quotes here prevent the wrong arguments from being passed to
11389 @command{test} if @samp{$V} is empty or contains special characters.
11393 @item -z @var{string}
11395 @cindex zero-length string check
11396 True if the length of @var{string} is zero.
11398 @item -n @var{string}
11399 @itemx @var{string}
11401 @cindex nonzero-length string check
11402 True if the length of @var{string} is nonzero.
11404 @item @var{string1} = @var{string2}
11406 @cindex equal string check
11407 True if the strings are equal.
11409 @item @var{string1} != @var{string2}
11411 @cindex not-equal string check
11412 True if the strings are not equal.
11417 @node Numeric tests
11418 @subsection Numeric tests
11420 @cindex numeric tests
11421 @cindex arithmetic tests
11423 Numeric relational operators. The arguments must be entirely numeric
11424 (possibly negative), or the special expression @w{@code{-l @var{string}}},
11425 which evaluates to the length of @var{string}.
11429 @item @var{arg1} -eq @var{arg2}
11430 @itemx @var{arg1} -ne @var{arg2}
11431 @itemx @var{arg1} -lt @var{arg2}
11432 @itemx @var{arg1} -le @var{arg2}
11433 @itemx @var{arg1} -gt @var{arg2}
11434 @itemx @var{arg1} -ge @var{arg2}
11441 These arithmetic binary operators return true if @var{arg1} is equal,
11442 not-equal, less-than, less-than-or-equal, greater-than, or
11443 greater-than-or-equal than @var{arg2}, respectively.
11450 test -1 -gt -2 && echo yes
11452 test -l abc -gt 1 && echo yes
11455 @error{} test: integer expression expected before -eq
11459 @node Connectives for test
11460 @subsection Connectives for @command{test}
11462 @cindex logical connectives
11463 @cindex connectives, logical
11465 The usual logical connectives.
11471 True if @var{expr} is false.
11473 @item @var{expr1} -a @var{expr2}
11475 @cindex logical and operator
11476 @cindex and operator
11477 True if both @var{expr1} and @var{expr2} are true.
11479 @item @var{expr1} -o @var{expr2}
11481 @cindex logical or operator
11482 @cindex or operator
11483 True if either @var{expr1} or @var{expr2} is true.
11488 @node expr invocation
11489 @section @command{expr}: Evaluate expressions
11492 @cindex expression evaluation
11493 @cindex evaluation of expressions
11495 @command{expr} evaluates an expression and writes the result on standard
11496 output. Each token of the expression must be a separate argument.
11498 Operands are either integers or strings. Integers consist of one or
11499 more decimal digits, with an optional leading @samp{-}.
11500 @command{expr} converts
11501 anything appearing in an operand position to an integer or a string
11502 depending on the operation being applied to it.
11504 Strings are not quoted for @command{expr} itself, though you may need to
11505 quote them to protect characters with special meaning to the shell,
11506 e.g., spaces. However, regardless of whether it is quoted, a string
11507 operand should not be a parenthesis or any of @command{expr}'s
11508 operators like @code{+}, so you cannot safely pass an arbitrary string
11509 @code{$str} to expr merely by quoting it to the shell. One way to
11510 work around this is to use the @sc{gnu} extension @code{+},
11511 (e.g., @code{+ "$str" = foo}); a more portable way is to use
11512 @code{@w{" $str"}} and to adjust the rest of the expression to take
11513 the leading space into account (e.g., @code{@w{" $str" = " foo"}}).
11515 You should not pass a negative integer or a string with leading
11516 @samp{-} as @command{expr}'s first argument, as it might be
11517 misinterpreted as an option; this can be avoided by parenthesization.
11518 Also, portable scripts should not use a string operand that happens to
11519 take the form of an integer; this can be worked around by inserting
11520 leading spaces as mentioned above.
11522 @cindex parentheses for grouping
11523 Operators may be given as infix symbols or prefix keywords. Parentheses
11524 may be used for grouping in the usual manner. You must quote
11525 parentheses and many operators to avoid the shell evaluating them,
11528 When built with support for the GNU MP library, @command{expr} uses
11529 arbitrary-precision arithmetic; otherwise, it uses native arithmetic
11530 types and may fail due to arithmetic overflow.
11532 The only options are @option{--help} and @option{--version}. @xref{Common
11533 options}. Options must precede operands.
11535 @cindex exit status of @command{expr}
11539 0 if the expression is neither null nor 0,
11540 1 if the expression is null or 0,
11541 2 if the expression is invalid,
11542 3 if an internal error occurred (e.g., arithmetic overflow).
11546 * String expressions:: + : match substr index length
11547 * Numeric expressions:: + - * / %
11548 * Relations for expr:: | & < <= = == != >= >
11549 * Examples of expr:: Examples.
11553 @node String expressions
11554 @subsection String expressions
11556 @cindex string expressions
11557 @cindex expressions, string
11559 @command{expr} supports pattern matching and other string operators. These
11560 have higher precedence than both the numeric and relational operators (in
11561 the next sections).
11565 @item @var{string} : @var{regex}
11566 @cindex pattern matching
11567 @cindex regular expression matching
11568 @cindex matching patterns
11569 Perform pattern matching. The arguments are converted to strings and the
11570 second is considered to be a (basic, a la GNU @code{grep}) regular
11571 expression, with a @code{^} implicitly prepended. The first argument is
11572 then matched against this regular expression.
11574 If the match succeeds and @var{regex} uses @samp{\(} and @samp{\)}, the
11575 @code{:} expression returns the part of @var{string} that matched the
11576 subexpression; otherwise, it returns the number of characters matched.
11578 If the match fails, the @code{:} operator returns the null string if
11579 @samp{\(} and @samp{\)} are used in @var{regex}, otherwise 0.
11581 @kindex \( @r{regexp operator}
11582 Only the first @samp{\( @dots{} \)} pair is relevant to the return
11583 value; additional pairs are meaningful only for grouping the regular
11584 expression operators.
11586 @kindex \+ @r{regexp operator}
11587 @kindex \? @r{regexp operator}
11588 @kindex \| @r{regexp operator}
11589 In the regular expression, @code{\+}, @code{\?}, and @code{\|} are
11590 operators which respectively match one or more, zero or one, or separate
11591 alternatives. SunOS and other @command{expr}'s treat these as regular
11592 characters. (@acronym{POSIX} allows either behavior.)
11593 @xref{Top, , Regular Expression Library, regex, Regex}, for details of
11594 regular expression syntax. Some examples are in @ref{Examples of expr}.
11596 @item match @var{string} @var{regex}
11598 An alternative way to do pattern matching. This is the same as
11599 @w{@samp{@var{string} : @var{regex}}}.
11601 @item substr @var{string} @var{position} @var{length}
11603 Returns the substring of @var{string} beginning at @var{position}
11604 with length at most @var{length}. If either @var{position} or
11605 @var{length} is negative, zero, or non-numeric, returns the null string.
11607 @item index @var{string} @var{charset}
11609 Returns the first position in @var{string} where the first character in
11610 @var{charset} was found. If no character in @var{charset} is found in
11611 @var{string}, return 0.
11613 @item length @var{string}
11615 Returns the length of @var{string}.
11617 @item + @var{token}
11619 Interpret @var{token} as a string, even if it is a keyword like @var{match}
11620 or an operator like @code{/}.
11621 This makes it possible to test @code{expr length + "$x"} or
11622 @code{expr + "$x" : '.*/\(.\)'} and have it do the right thing even if
11623 the value of @var{$x} happens to be (for example) @code{/} or @code{index}.
11624 This operator is a @acronym{GNU} extension. Portable shell scripts should use
11625 @code{@w{" $token"} : @w{' \(.*\)'}} instead of @code{+ "$token"}.
11629 To make @command{expr} interpret keywords as strings, you must use the
11630 @code{quote} operator.
11633 @node Numeric expressions
11634 @subsection Numeric expressions
11636 @cindex numeric expressions
11637 @cindex expressions, numeric
11639 @command{expr} supports the usual numeric operators, in order of increasing
11640 precedence. These numeric operators have lower precedence than the
11641 string operators described in the previous section, and higher precedence
11642 than the connectives (next section).
11650 @cindex subtraction
11651 Addition and subtraction. Both arguments are converted to integers;
11652 an error occurs if this cannot be done.
11658 @cindex multiplication
11661 Multiplication, division, remainder. Both arguments are converted to
11662 integers; an error occurs if this cannot be done.
11667 @node Relations for expr
11668 @subsection Relations for @command{expr}
11670 @cindex connectives, logical
11671 @cindex logical connectives
11672 @cindex relations, numeric or string
11674 @command{expr} supports the usual logical connectives and relations. These
11675 have lower precedence than the string and numeric operators
11676 (previous sections). Here is the list, lowest-precedence operator first.
11682 @cindex logical or operator
11683 @cindex or operator
11684 Returns its first argument if that is neither null nor zero, otherwise
11685 its second argument if it is neither null nor zero, otherwise 0. It
11686 does not evaluate its second argument if its first argument is neither
11691 @cindex logical and operator
11692 @cindex and operator
11693 Return its first argument if neither argument is null or zero, otherwise
11694 0. It does not evaluate its second argument if its first argument is
11697 @item < <= = == != >= >
11704 @cindex comparison operators
11706 Compare the arguments and return 1 if the relation is true, 0 otherwise.
11707 @code{==} is a synonym for @code{=}. @command{expr} first tries to convert
11708 both arguments to integers and do a numeric comparison; if either
11709 conversion fails, it does a lexicographic comparison using the character
11710 collating sequence specified by the @env{LC_COLLATE} locale.
11715 @node Examples of expr
11716 @subsection Examples of using @command{expr}
11718 @cindex examples of @command{expr}
11719 Here are a few examples, including quoting for shell metacharacters.
11721 To add 1 to the shell variable @code{foo}, in Bourne-compatible shells:
11724 foo=`expr $foo + 1`
11727 To print the non-directory part of the file name stored in
11728 @code{$fname}, which need not contain a @code{/}:
11731 expr $fname : '.*/\(.*\)' '|' $fname
11734 An example showing that @code{\+} is an operator:
11742 expr abc : 'a\(.\)c'
11744 expr index abcdef cz
11747 @error{} expr: syntax error
11748 expr index + index a
11754 @chapter Redirection
11756 @cindex redirection
11757 @cindex commands for redirection
11759 Unix shells commonly provide several forms of @dfn{redirection}---ways
11760 to change the input source or output destination of a command. But one
11761 useful redirection is performed by a separate command, not by the shell;
11762 it's described here.
11765 * tee invocation:: Redirect output to multiple files or processes.
11769 @node tee invocation
11770 @section @command{tee}: Redirect output to multiple files or processes
11773 @cindex pipe fitting
11774 @cindex destinations, multiple output
11775 @cindex read from stdin and write to stdout and files
11777 The @command{tee} command copies standard input to standard output and also
11778 to any files given as arguments. This is useful when you want not only
11779 to send some data down a pipe, but also to save a copy. Synopsis:
11782 tee [@var{option}]@dots{} [@var{file}]@dots{}
11785 If a file being written to does not already exist, it is created. If a
11786 file being written to already exists, the data it previously contained
11787 is overwritten unless the @option{-a} option is used.
11789 A @var{file} of @samp{-} causes @command{tee} to send another copy of
11790 input to standard output, but this is typically not that useful as the
11791 copies are interleaved.
11793 The program accepts the following options. Also see @ref{Common options}.
11800 Append standard input to the given files rather than overwriting
11804 @itemx --ignore-interrupts
11806 @opindex --ignore-interrupts
11807 Ignore interrupt signals.
11811 The @command{tee} command is useful when you happen to be transferring a large
11812 amount of data and also want to summarize that data without reading
11813 it a second time. For example, when you are downloading a DVD image,
11814 you often want to verify its signature or checksum right away.
11815 The inefficient way to do it is simply:
11818 wget http://example.com/some.iso && sha1sum some.iso
11821 One problem with the above is that it makes you wait for the
11822 download to complete before starting the time-consuming SHA1 computation.
11823 Perhaps even more importantly, the above requires reading
11824 the DVD image a second time (the first was from the network).
11826 The efficient way to do it is to interleave the download
11827 and SHA1 computation. Then, you'll get the checksum for
11828 free, because the entire process parallelizes so well:
11831 # slightly contrived, to demonstrate process substitution
11832 wget -O - http://example.com/dvd.iso \
11833 | tee >(sha1sum > dvd.sha1) > dvd.iso
11836 That makes @command{tee} write not just to the expected output file,
11837 but also to a pipe running @command{sha1sum} and saving the final
11838 checksum in a file named @file{dvd.sha1}.
11840 Note, however, that this example relies on a feature of modern shells
11841 called @dfn{process substitution}
11842 (the @samp{>(command)} syntax, above;
11843 @xref{Process Substitution,,Process Substitution, bashref,
11844 The Bash Reference Manual}.),
11845 so it works with @command{zsh}, @command{bash}, and @command{ksh},
11846 but not with @command{/bin/sh}. So if you write code like this
11847 in a shell script, be sure to start the script with @samp{#!/bin/bash}.
11849 Since the above example writes to one file and one process,
11850 a more conventional and portable use of @command{tee} is even better:
11853 wget -O - http://example.com/dvd.iso \
11854 | tee dvd.iso | sha1sum > dvd.sha1
11857 You can extend this example to make @command{tee} write to two processes,
11858 computing MD5 and SHA1 checksums in parallel. In this case,
11859 process substitution is required:
11862 wget -O - http://example.com/dvd.iso \
11863 | tee >(sha1sum > dvd.sha1) \
11864 >(md5sum > dvd.md5) \
11868 This technique is also useful when you want to make a @emph{compressed}
11869 copy of the contents of a pipe.
11870 Consider a tool to graphically summarize disk usage data from @samp{du -ak}.
11871 For a large hierarchy, @samp{du -ak} can run for a long time,
11872 and can easily produce terabytes of data, so you won't want to
11873 rerun the command unnecessarily. Nor will you want to save
11874 the uncompressed output.
11876 Doing it the inefficient way, you can't even start the GUI
11877 until after you've compressed all of the @command{du} output:
11880 du -ak | gzip -9 > /tmp/du.gz
11881 gzip -d /tmp/du.gz | xdiskusage -a
11884 With @command{tee} and process substitution, you start the GUI
11885 right away and eliminate the decompression completely:
11888 du -ak | tee >(gzip -9 > /tmp/du.gz) | xdiskusage -a
11891 Finally, if you regularly create more than one type of
11892 compressed tarball at once, for example when @code{make dist} creates
11893 both @command{gzip}-compressed and @command{bzip2}-compressed tarballs,
11894 there may be a better way.
11895 Typical @command{automake}-generated @file{Makefile} rules create
11896 the two compressed tar archives with commands in sequence, like this
11897 (slightly simplified):
11900 tardir=your-pkg-M.N
11901 tar chof - "$tardir" | gzip -9 -c > your-pkg-M.N.tar.gz
11902 tar chof - "$tardir" | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11905 However, if the hierarchy you are archiving and compressing is larger
11906 than a couple megabytes, and especially if you are using a multi-processor
11907 system with plenty of memory, then you can do much better by reading the
11908 directory contents only once and running the compression programs in parallel:
11911 tardir=your-pkg-M.N
11912 tar chof - "$tardir" \
11913 | tee >(gzip -9 -c > your-pkg-M.N.tar.gz) \
11914 | bzip2 -9 -c > your-pkg-M.N.tar.bz2
11920 @node File name manipulation
11921 @chapter File name manipulation
11923 @cindex file name manipulation
11924 @cindex manipulation of file names
11925 @cindex commands for file name manipulation
11927 This section describes commands that manipulate file names.
11930 * basename invocation:: Strip directory and suffix from a file name.
11931 * dirname invocation:: Strip last file name component.
11932 * pathchk invocation:: Check file name validity and portability.
11933 * mktemp invocation:: Create temporary file or directory.
11937 @node basename invocation
11938 @section @command{basename}: Strip directory and suffix from a file name
11941 @cindex strip directory and suffix from file names
11942 @cindex directory, stripping from file names
11943 @cindex suffix, stripping from file names
11944 @cindex file names, stripping directory and suffix
11945 @cindex leading directory components, stripping
11947 @command{basename} removes any leading directory components from
11948 @var{name}. Synopsis:
11951 basename @var{name} [@var{suffix}]
11954 If @var{suffix} is specified and is identical to the end of @var{name},
11955 it is removed from @var{name} as well. Note that since trailing slashes
11956 are removed prior to suffix matching, @var{suffix} will do nothing if it
11957 contains slashes. @command{basename} prints the result on standard
11960 @c This test is used both here and in the section on dirname.
11961 @macro basenameAndDirname
11962 Together, @command{basename} and @command{dirname} are designed such
11963 that if @samp{ls "$name"} succeeds, then the command sequence @samp{cd
11964 "$(dirname "$name")"; ls "$(basename "$name")"} will, too. This works
11965 for everything except file names containing a trailing newline.
11967 @basenameAndDirname
11969 @acronym{POSIX} allows the implementation to define the results if
11970 @var{name} is empty or @samp{//}. In the former case, @acronym{GNU}
11971 @command{basename} returns the empty string. In the latter case, the
11972 result is @samp{//} on platforms where @var{//} is distinct from
11973 @var{/}, and @samp{/} on platforms where there is no difference.
11975 The only options are @option{--help} and @option{--version}. @xref{Common
11976 options}. Options must precede operands.
11984 basename /usr/bin/sort
11987 basename include/stdio.h .h
11991 @node dirname invocation
11992 @section @command{dirname}: Strip last file name component
11995 @cindex directory components, printing
11996 @cindex stripping non-directory suffix
11997 @cindex non-directory suffix, stripping
11999 @command{dirname} prints all but the final slash-delimited component of
12000 @var{name}. Slashes on either side of the final component are also
12001 removed. If the string contains no slash, @command{dirname} prints
12002 @samp{.} (meaning the current directory). Synopsis:
12008 @var{name} need not be a file name, but if it is, this operation
12009 effectively lists the directory that contains the final component,
12010 including the case when the final component is itself a directory.
12012 @basenameAndDirname
12014 @acronym{POSIX} allows the implementation to define the results if
12015 @var{name} is @samp{//}. With @acronym{GNU} @command{dirname}, the
12016 result is @samp{//} on platforms where @var{//} is distinct from
12017 @var{/}, and @samp{/} on platforms where there is no difference.
12019 The only options are @option{--help} and @option{--version}. @xref{Common
12027 # Output "/usr/bin".
12028 dirname /usr/bin/sort
12029 dirname /usr/bin//.//
12036 @node pathchk invocation
12037 @section @command{pathchk}: Check file name validity and portability
12040 @cindex file names, checking validity and portability
12041 @cindex valid file names, checking for
12042 @cindex portable file names, checking for
12044 @command{pathchk} checks validity and portability of file names. Synopsis:
12047 pathchk [@var{option}]@dots{} @var{name}@dots{}
12050 For each @var{name}, @command{pathchk} prints an error message if any of
12051 these conditions is true:
12055 One of the existing directories in @var{name} does not have search
12056 (execute) permission,
12058 The length of @var{name} is larger than the maximum supported by the
12061 The length of one component of @var{name} is longer than
12062 its file system's maximum.
12065 A nonexistent @var{name} is not an error, so long a file with that
12066 name could be created under the above conditions.
12068 The program accepts the following options. Also see @ref{Common options}.
12069 Options must precede operands.
12075 Instead of performing checks based on the underlying file system,
12076 print an error message if any of these conditions is true:
12080 A file name is empty.
12083 A file name contains a character outside the @acronym{POSIX} portable file
12084 name character set, namely, the ASCII letters and digits, @samp{.},
12085 @samp{_}, @samp{-}, and @samp{/}.
12088 The length of a file name or one of its components exceeds the
12089 @acronym{POSIX} minimum limits for portability.
12094 Print an error message if a file name is empty, or if it contains a component
12095 that begins with @samp{-}.
12097 @item --portability
12098 @opindex --portability
12099 Print an error message if a file name is not portable to all @acronym{POSIX}
12100 hosts. This option is equivalent to @samp{-p -P}.
12104 @cindex exit status of @command{pathchk}
12108 0 if all specified file names passed all checks,
12112 @node mktemp invocation
12113 @section @command{mktemp}: Create temporary file or directory
12116 @cindex file names, creating temporary
12117 @cindex directory, creating temporary
12118 @cindex temporary files and directories
12120 @command{mktemp} manages the creation of temporary files and
12121 directories. Synopsis:
12124 mktemp [@var{option}]@dots{} [@var{template}]
12127 Safely create a temporary file or directory based on @var{template},
12128 and print its name. If given, @var{template} must include at least
12129 three consecutive @samp{X}s in the last component. If omitted, the template
12130 @samp{tmp.XXXXXXXXXX} is used, and option @option{--tmpdir} is
12131 implied. The final run of @samp{X}s in the @var{template} will be replaced
12132 by alpha-numeric characters; thus, on a case-sensitive file system,
12133 and with a @var{template} including a run of @var{n} instances of @samp{X},
12134 there are @samp{62**@var{n}} potential file names.
12136 Older scripts used to create temporary files by simply joining the
12137 name of the program with the process id (@samp{$$}) as a suffix.
12138 However, that naming scheme is easily predictable, and suffers from a
12139 race condition where the attacker can create an appropriately named
12140 symbolic link, such that when the script then opens a handle to what
12141 it thought was an unused file, it is instead modifying an existing
12142 file. Using the same scheme to create a directory is slightly safer,
12143 since the @command{mkdir} will fail if the target already exists, but
12144 it is still inferior because it allows for denial of service attacks.
12145 Therefore, modern scripts should use the @command{mktemp} command to
12146 guarantee that the generated name will be unpredictable, and that
12147 knowledge of the temporary file name implies that the file was created
12148 by the current script and cannot be modified by other users.
12150 When creating a file, the resulting file has read and write
12151 permissions for the current user, but no permissions for the group or
12152 others; these permissions are reduced if the current umask is more
12155 Here are some examples (although note that if you repeat them, you
12156 will most likely get different file names):
12161 Create a temporary file in the current directory.
12168 Create a temporary file with a known suffix.
12170 $ mktemp --suffix=.txt file-XXXX
12172 $ mktemp file-XXXX-XXXX.txt
12177 Create a secure fifo relative to the user's choice of @env{TMPDIR},
12178 but falling back to the current directory rather than @file{/tmp}.
12179 Note that @command{mktemp} does not create fifos, but can create a
12180 secure directory in which the fifo can live. Exit the shell if the
12181 directory or fifo could not be created.
12183 $ dir=$(mktemp -p "$@{TMPDIR:-.@}" -d dir-XXXX) || exit 1
12185 $ mkfifo "$fifo" || @{ rmdir "$dir"; exit 1; @}
12189 Create and use a temporary file if possible, but ignore failure. The
12190 file will reside in the directory named by @env{TMPDIR}, if specified,
12191 or else in @file{/tmp}.
12193 $ file=$(mktemp -q) && @{
12194 > # Safe to use $file only within this block. Use quotes,
12195 > # since $TMPDIR, and thus $file, may contain whitespace.
12196 > echo ... > "$file"
12202 Act as a semi-random character generator (it is not fully random,
12203 since it is impacted by the contents of the current directory). To
12204 avoid security holes, do not use the resulting names to create a file.
12214 The program accepts the following options. Also see @ref{Common options}.
12221 @opindex --directory
12222 Create a directory rather than a file. The directory will have read,
12223 write, and search permissions for the current user, but no permissions
12224 for the group or others; these permissions are reduced if the current
12225 umask is more restrictive.
12231 Suppress diagnostics about failure to create a file or directory. The
12232 exit status will still reflect whether a file was created.
12238 Generate a temporary name that does not name an existing file, without
12239 changing the file system contents. Using the output of this command
12240 to create a new file is inherently unsafe, as there is a window of
12241 time between generating the name and using it where another process
12242 can create an object by the same name.
12245 @itemx --tmpdir[=@var{dir}]
12248 Treat @var{template} relative to the directory @var{dir}. If
12249 @var{dir} is not specified (only possible with the long option
12250 @option{--tmpdir}) or is the empty string, use the value of
12251 @env{TMPDIR} if available, otherwise use @samp{/tmp}. If this is
12252 specified, @var{template} must not be absolute. However,
12253 @var{template} can still contain slashes, although intermediate
12254 directories must already exist.
12256 @item --suffix=@var{suffix}
12258 Append @var{suffix} to the @var{template}. @var{suffix} must not
12259 contain slash. If @option{--suffix} is specified, @var{template} must
12260 end in @samp{X}; if it is not specified, then an appropriate
12261 @option{--suffix} is inferred by finding the last @samp{X} in
12262 @var{template}. This option exists for use with the default
12263 @var{template} and for the creation of a @var{suffix} that starts with
12268 Treat @var{template} as a single file relative to the value of
12269 @env{TMPDIR} if available, or to the directory specified by
12270 @option{-p}, otherwise to @samp{/tmp}. @var{template} must not
12271 contain slashes. This option is deprecated; the use of @option{-p}
12272 without @option{-t} offers better defaults (by favoring the command
12273 line over @env{TMPDIR}) and more flexibility (by allowing intermediate
12278 @cindex exit status of @command{mktemp}
12282 0 if the file was created,
12287 @node Working context
12288 @chapter Working context
12290 @cindex working context
12291 @cindex commands for printing the working context
12293 This section describes commands that display or alter the context in
12294 which you are working: the current directory, the terminal settings, and
12295 so forth. See also the user-related commands in the next section.
12298 * pwd invocation:: Print working directory.
12299 * stty invocation:: Print or change terminal characteristics.
12300 * printenv invocation:: Print environment variables.
12301 * tty invocation:: Print file name of terminal on standard input.
12305 @node pwd invocation
12306 @section @command{pwd}: Print working directory
12309 @cindex print name of current directory
12310 @cindex current working directory, printing
12311 @cindex working directory, printing
12314 @command{pwd} prints the name of the current directory. Synopsis:
12317 pwd [@var{option}]@dots{}
12320 The program accepts the following options. Also see @ref{Common options}.
12327 If the contents of the environment variable @env{PWD} provide an
12328 absolute name of the current directory with no @samp{.} or @samp{..}
12329 components, but possibly with symbolic links, then output those
12330 contents. Otherwise, fall back to default @option{-P} handling.
12335 @opindex --physical
12336 Print a fully resolved name for the current directory. That is, all
12337 components of the printed name will be actual directory names---none
12338 will be symbolic links.
12341 @cindex symbolic links and @command{pwd}
12342 If @option{-L} and @option{-P} are both given, the last one takes
12343 precedence. If neither option is given, then this implementation uses
12344 @option{-P} as the default unless the @env{POSIXLY_CORRECT}
12345 environment variable is set.
12347 @mayConflictWithShellBuiltIn{pwd}
12352 @node stty invocation
12353 @section @command{stty}: Print or change terminal characteristics
12356 @cindex change or print terminal settings
12357 @cindex terminal settings
12358 @cindex line settings of terminal
12360 @command{stty} prints or changes terminal characteristics, such as baud rate.
12364 stty [@var{option}] [@var{setting}]@dots{}
12365 stty [@var{option}]
12368 If given no line settings, @command{stty} prints the baud rate, line
12369 discipline number (on systems that support it), and line settings
12370 that have been changed from the values set by @samp{stty sane}.
12371 By default, mode reading and setting are performed on the tty line
12372 connected to standard input, although this can be modified by the
12373 @option{--file} option.
12375 @command{stty} accepts many non-option arguments that change aspects of
12376 the terminal line operation, as described below.
12378 The program accepts the following options. Also see @ref{Common options}.
12385 Print all current settings in human-readable form. This option may not
12386 be used in combination with any line settings.
12388 @item -F @var{device}
12389 @itemx --file=@var{device}
12392 Set the line opened by the file name specified in @var{device} instead of
12393 the tty line connected to standard input. This option is necessary
12394 because opening a @acronym{POSIX} tty requires use of the @code{O_NONDELAY} flag to
12395 prevent a @acronym{POSIX} tty from blocking until the carrier detect line is high if
12396 the @code{clocal} flag is not set. Hence, it is not always possible
12397 to allow the shell to open the device in the traditional manner.
12403 @cindex machine-readable @command{stty} output
12404 Print all current settings in a form that can be used as an argument to
12405 another @command{stty} command to restore the current settings. This option
12406 may not be used in combination with any line settings.
12410 Many settings can be turned off by preceding them with a @samp{-}.
12411 Such arguments are marked below with ``May be negated'' in their
12412 description. The descriptions themselves refer to the positive
12413 case, that is, when @emph{not} negated (unless stated otherwise,
12416 Some settings are not available on all @acronym{POSIX} systems, since they use
12417 extensions. Such arguments are marked below with ``Non-@acronym{POSIX}'' in their
12418 description. On non-@acronym{POSIX} systems, those or other settings also may not
12419 be available, but it's not feasible to document all the variations: just
12425 * Control:: Control settings
12426 * Input:: Input settings
12427 * Output:: Output settings
12428 * Local:: Local settings
12429 * Combination:: Combination settings
12430 * Characters:: Special characters
12431 * Special:: Special settings
12436 @subsection Control settings
12438 @cindex control settings
12444 @cindex two-way parity
12445 Generate parity bit in output and expect parity bit in input.
12451 @cindex even parity
12452 Set odd parity (even if negated). May be negated.
12459 @cindex character size
12460 @cindex eight-bit characters
12461 Set character size to 5, 6, 7, or 8 bits.
12466 Send a hangup signal when the last process closes the tty. May be
12472 Use two stop bits per character (one if negated). May be negated.
12476 Allow input to be received. May be negated.
12480 @cindex modem control
12481 Disable modem control signals. May be negated.
12485 @cindex hardware flow control
12486 @cindex flow control, hardware
12487 @cindex RTS/CTS flow control
12488 Enable RTS/CTS flow control. Non-@acronym{POSIX}. May be negated.
12493 @subsection Input settings
12495 @cindex input settings
12496 These settings control operations on data received from the terminal.
12501 @cindex breaks, ignoring
12502 Ignore break characters. May be negated.
12506 @cindex breaks, cause interrupts
12507 Make breaks cause an interrupt signal. May be negated.
12511 @cindex parity, ignoring
12512 Ignore characters with parity errors. May be negated.
12516 @cindex parity errors, marking
12517 Mark parity errors (with a 255-0-character sequence). May be negated.
12521 Enable input parity checking. May be negated.
12525 @cindex eight-bit input
12526 Clear high (8th) bit of input characters. May be negated.
12530 @cindex newline, translating to return
12531 Translate newline to carriage return. May be negated.
12535 @cindex return, ignoring
12536 Ignore carriage return. May be negated.
12540 @cindex return, translating to newline
12541 Translate carriage return to newline. May be negated.
12545 @cindex input encoding, UTF-8
12546 Assume input characters are UTF-8 encoded. May be negated.
12550 @kindex C-s/C-q flow control
12551 @cindex XON/XOFF flow control
12552 Enable XON/XOFF flow control (that is, @kbd{CTRL-S}/@kbd{CTRL-Q}). May
12559 @cindex software flow control
12560 @cindex flow control, software
12561 Enable sending of @code{stop} character when the system input buffer
12562 is almost full, and @code{start} character when it becomes almost
12563 empty again. May be negated.
12567 @cindex uppercase, translating to lowercase
12568 Translate uppercase characters to lowercase. Non-@acronym{POSIX}. May be
12569 negated. Note ilcuc is not implemented, as one would not be able to issue
12570 almost any (lowercase) Unix command, after invoking it.
12574 Allow any character to restart output (only the start character
12575 if negated). Non-@acronym{POSIX}. May be negated.
12579 @cindex beeping at input buffer full
12580 Enable beeping and not flushing input buffer if a character arrives
12581 when the input buffer is full. Non-@acronym{POSIX}. May be negated.
12586 @subsection Output settings
12588 @cindex output settings
12589 These settings control operations on data sent to the terminal.
12594 Postprocess output. May be negated.
12598 @cindex lowercase, translating to output
12599 Translate lowercase characters to uppercase. Non-@acronym{POSIX}. May be
12600 negated. (Note ouclc is not currently implemented.)
12604 @cindex return, translating to newline
12605 Translate carriage return to newline. Non-@acronym{POSIX}. May be negated.
12609 @cindex newline, translating to crlf
12610 Translate newline to carriage return-newline. Non-@acronym{POSIX}. May be
12615 Do not print carriage returns in the first column. Non-@acronym{POSIX}.
12620 Newline performs a carriage return. Non-@acronym{POSIX}. May be negated.
12624 @cindex pad instead of timing for delaying
12625 Use fill (padding) characters instead of timing for delays. Non-@acronym{POSIX}.
12630 @cindex pad character
12631 Use @acronym{ASCII} @sc{del} characters for fill instead of
12632 @acronym{ASCII} @sc{nul} characters. Non-@acronym{POSIX}.
12638 Newline delay style. Non-@acronym{POSIX}.
12645 Carriage return delay style. Non-@acronym{POSIX}.
12651 @opindex tab@var{n}
12652 Horizontal tab delay style. Non-@acronym{POSIX}.
12657 Backspace delay style. Non-@acronym{POSIX}.
12662 Vertical tab delay style. Non-@acronym{POSIX}.
12667 Form feed delay style. Non-@acronym{POSIX}.
12672 @subsection Local settings
12674 @cindex local settings
12679 Enable @code{interrupt}, @code{quit}, and @code{suspend} special
12680 characters. May be negated.
12684 Enable @code{erase}, @code{kill}, @code{werase}, and @code{rprnt}
12685 special characters. May be negated.
12689 Enable non-@acronym{POSIX} special characters. May be negated.
12693 Echo input characters. May be negated.
12699 Echo @code{erase} characters as backspace-space-backspace. May be
12704 @cindex newline echoing after @code{kill}
12705 Echo a newline after a @code{kill} character. May be negated.
12709 @cindex newline, echoing
12710 Echo newline even if not echoing other characters. May be negated.
12714 @cindex flushing, disabling
12715 Disable flushing after @code{interrupt} and @code{quit} special
12716 characters. May be negated.
12720 @cindex case translation
12721 Enable input and output of uppercase characters by preceding their
12722 lowercase equivalents with @samp{\}, when @code{icanon} is set.
12723 Non-@acronym{POSIX}. May be negated.
12727 @cindex background jobs, stopping at terminal write
12728 Stop background jobs that try to write to the terminal. Non-@acronym{POSIX}.
12735 Echo erased characters backward, between @samp{\} and @samp{/}.
12736 Non-@acronym{POSIX}. May be negated.
12742 @cindex control characters, using @samp{^@var{c}}
12743 @cindex hat notation for control characters
12744 Echo control characters in hat notation (@samp{^@var{c}}) instead
12745 of literally. Non-@acronym{POSIX}. May be negated.
12751 Echo the @code{kill} special character by erasing each character on
12752 the line as indicated by the @code{echoprt} and @code{echoe} settings,
12753 instead of by the @code{echoctl} and @code{echok} settings. Non-@acronym{POSIX}.
12759 @subsection Combination settings
12761 @cindex combination settings
12762 Combination settings:
12769 Same as @code{parenb -parodd cs7}. May be negated. If negated, same
12770 as @code{-parenb cs8}.
12774 Same as @code{parenb parodd cs7}. May be negated. If negated, same
12775 as @code{-parenb cs8}.
12779 Same as @code{-icrnl -onlcr}. May be negated. If negated, same as
12780 @code{icrnl -inlcr -igncr onlcr -ocrnl -onlret}.
12784 Reset the @code{erase} and @code{kill} special characters to their default
12791 @c This is too long to write inline.
12793 cread -ignbrk brkint -inlcr -igncr icrnl -ixoff
12794 -iuclc -ixany imaxbel opost -olcuc -ocrnl onlcr
12795 -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0
12796 ff0 isig icanon iexten echo echoe echok -echonl
12797 -noflsh -xcase -tostop -echoprt echoctl echoke
12801 and also sets all special characters to their default values.
12805 Same as @code{brkint ignpar istrip icrnl ixon opost isig icanon}, plus
12806 sets the @code{eof} and @code{eol} characters to their default values
12807 if they are the same as the @code{min} and @code{time} characters.
12808 May be negated. If negated, same as @code{raw}.
12815 -ignbrk -brkint -ignpar -parmrk -inpck -istrip
12816 -inlcr -igncr -icrnl -ixon -ixoff -iuclc -ixany
12817 -imaxbel -opost -isig -icanon -xcase min 1 time 0
12821 May be negated. If negated, same as @code{cooked}.
12825 Same as @option{-icanon}. May be negated. If negated, same as
12830 @cindex eight-bit characters
12831 Same as @code{-parenb -istrip cs8}. May be negated. If negated,
12832 same as @code{parenb istrip cs7}.
12836 Same as @option{-parenb -istrip -opost cs8}. May be negated.
12837 If negated, same as @code{parenb istrip opost cs7}.
12841 Same as @option{-ixany}. Non-@acronym{POSIX}. May be negated.
12845 Same as @code{tab0}. Non-@acronym{POSIX}. May be negated. If negated, same
12852 Same as @code{xcase iuclc olcuc}. Non-@acronym{POSIX}. May be negated.
12853 (Used for terminals with uppercase characters only.)
12857 Same as @code{echoe echoctl echoke}.
12861 Same as @code{echoe echoctl echoke -ixany intr ^C erase ^? kill C-u}.
12866 @subsection Special characters
12868 @cindex special characters
12869 @cindex characters, special
12871 The special characters' default values vary from system to system.
12872 They are set with the syntax @samp{name value}, where the names are
12873 listed below and the value can be given either literally, in hat
12874 notation (@samp{^@var{c}}), or as an integer which may start with
12875 @samp{0x} to indicate hexadecimal, @samp{0} to indicate octal, or
12876 any other digit to indicate decimal.
12878 @cindex disabling special characters
12879 @kindex u@r{, and disabling special characters}
12880 For GNU stty, giving a value of @code{^-} or @code{undef} disables that
12881 special character. (This is incompatible with Ultrix @command{stty},
12882 which uses a value of @samp{u} to disable a special character. GNU
12883 @command{stty} treats a value @samp{u} like any other, namely to set that
12884 special character to @key{U}.)
12890 Send an interrupt signal.
12894 Send a quit signal.
12898 Erase the last character typed.
12902 Erase the current line.
12906 Send an end of file (terminate the input).
12914 Alternate character to end the line. Non-@acronym{POSIX}.
12918 Switch to a different shell layer. Non-@acronym{POSIX}.
12922 Restart the output after stopping it.
12930 Send a terminal stop signal.
12934 Send a terminal stop signal after flushing the input. Non-@acronym{POSIX}.
12938 Redraw the current line. Non-@acronym{POSIX}.
12942 Erase the last word typed. Non-@acronym{POSIX}.
12946 Enter the next character typed literally, even if it is a special
12947 character. Non-@acronym{POSIX}.
12952 @subsection Special settings
12954 @cindex special settings
12959 Set the minimum number of characters that will satisfy a read until
12960 the time value has expired, when @option{-icanon} is set.
12964 Set the number of tenths of a second before reads time out if the minimum
12965 number of characters have not been read, when @option{-icanon} is set.
12967 @item ispeed @var{n}
12969 Set the input speed to @var{n}.
12971 @item ospeed @var{n}
12973 Set the output speed to @var{n}.
12977 Tell the tty kernel driver that the terminal has @var{n} rows. Non-@acronym{POSIX}.
12980 @itemx columns @var{n}
12983 Tell the kernel that the terminal has @var{n} columns. Non-@acronym{POSIX}.
12989 Print the number of rows and columns that the kernel thinks the
12990 terminal has. (Systems that don't support rows and columns in the kernel
12991 typically use the environment variables @env{LINES} and @env{COLUMNS}
12992 instead; however, GNU @command{stty} does not know anything about them.)
12993 Non-@acronym{POSIX}.
12997 Use line discipline @var{n}. Non-@acronym{POSIX}.
13001 Print the terminal speed.
13004 @cindex baud rate, setting
13005 Set the input and output speeds to @var{n}. @var{n} can be one of: 0
13006 50 75 110 134 134.5 150 200 300 600 1200 1800 2400 4800 9600 19200
13007 38400 @code{exta} @code{extb}. @code{exta} is the same as 19200;
13008 @code{extb} is the same as 38400. Many systems, including GNU/Linux,
13009 support higher speeds. The @command{stty} command includes support
13026 4000000 where the system supports these.
13027 0 hangs up the line if @option{-clocal} is set.
13031 @node printenv invocation
13032 @section @command{printenv}: Print all or some environment variables
13035 @cindex printing all or some environment variables
13036 @cindex environment variables, printing
13038 @command{printenv} prints environment variable values. Synopsis:
13041 printenv [@var{option}] [@var{variable}]@dots{}
13044 If no @var{variable}s are specified, @command{printenv} prints the value of
13045 every environment variable. Otherwise, it prints the value of each
13046 @var{variable} that is set, and nothing for those that are not set.
13048 The program accepts the following option. Also see @ref{Common options}.
13056 @cindex exit status of @command{printenv}
13060 0 if all variables specified were found
13061 1 if at least one specified variable was not found
13062 2 if a write error occurred
13066 @node tty invocation
13067 @section @command{tty}: Print file name of terminal on standard input
13070 @cindex print terminal file name
13071 @cindex terminal file name, printing
13073 @command{tty} prints the file name of the terminal connected to its standard
13074 input. It prints @samp{not a tty} if standard input is not a terminal.
13078 tty [@var{option}]@dots{}
13081 The program accepts the following option. Also see @ref{Common options}.
13091 Print nothing; only return an exit status.
13095 @cindex exit status of @command{tty}
13099 0 if standard input is a terminal
13100 1 if standard input is not a terminal
13101 2 if given incorrect arguments
13102 3 if a write error occurs
13106 @node User information
13107 @chapter User information
13109 @cindex user information, commands for
13110 @cindex commands for printing user information
13112 This section describes commands that print user-related information:
13113 logins, groups, and so forth.
13116 * id invocation:: Print user identity.
13117 * logname invocation:: Print current login name.
13118 * whoami invocation:: Print effective user ID.
13119 * groups invocation:: Print group names a user is in.
13120 * users invocation:: Print login names of users currently logged in.
13121 * who invocation:: Print who is currently logged in.
13125 @node id invocation
13126 @section @command{id}: Print user identity
13129 @cindex real user and group IDs, printing
13130 @cindex effective user and group IDs, printing
13131 @cindex printing real and effective user and group IDs
13133 @command{id} prints information about the given user, or the process
13134 running it if no user is specified. Synopsis:
13137 id [@var{option}]@dots{} [@var{username}]
13140 @vindex POSIXLY_CORRECT
13141 By default, it prints the real user ID, real group ID, effective user ID
13142 if different from the real user ID, effective group ID if different from
13143 the real group ID, and supplemental group IDs.
13144 In addition, if SELinux
13145 is enabled and the @env{POSIXLY_CORRECT} environment variable is not set,
13146 then print @samp{context=@var{c}}, where @var{c} is the security context.
13148 Each of these numeric values is preceded by an identifying string and
13149 followed by the corresponding user or group name in parentheses.
13151 The options cause @command{id} to print only part of the above information.
13152 Also see @ref{Common options}.
13159 Print only the group ID.
13165 Print only the group ID and the supplementary groups.
13171 Print the user or group name instead of the ID number. Requires
13172 @option{-u}, @option{-g}, or @option{-G}.
13178 Print the real, instead of effective, user or group ID. Requires
13179 @option{-u}, @option{-g}, or @option{-G}.
13185 Print only the user ID.
13192 @cindex security context
13193 Print only the security context of the current user.
13194 If SELinux is disabled then print a warning and
13195 set the exit status to 1.
13201 @macro primaryAndSupplementaryGroups{cmd,arg}
13202 Primary and supplementary groups for a process are normally inherited
13203 from its parent and are usually unchanged since login. This means
13204 that if you change the group database after logging in, @command{\cmd\}
13205 will not reflect your changes within your existing login session.
13206 Running @command{\cmd\} with a \arg\ causes the user and group
13207 database to be consulted afresh, and so will give a different result.
13209 @primaryAndSupplementaryGroups{id,user argument}
13211 @node logname invocation
13212 @section @command{logname}: Print current login name
13215 @cindex printing user's login name
13216 @cindex login name, printing
13217 @cindex user name, printing
13220 @command{logname} prints the calling user's name, as found in a
13221 system-maintained file (often @file{/var/run/utmp} or
13222 @file{/etc/utmp}), and exits with a status of 0. If there is no entry
13223 for the calling process, @command{logname} prints
13224 an error message and exits with a status of 1.
13226 The only options are @option{--help} and @option{--version}. @xref{Common
13232 @node whoami invocation
13233 @section @command{whoami}: Print effective user ID
13236 @cindex effective user ID, printing
13237 @cindex printing the effective user ID
13239 @command{whoami} prints the user name associated with the current
13240 effective user ID. It is equivalent to the command @samp{id -un}.
13242 The only options are @option{--help} and @option{--version}. @xref{Common
13248 @node groups invocation
13249 @section @command{groups}: Print group names a user is in
13252 @cindex printing groups a user is in
13253 @cindex supplementary groups, printing
13255 @command{groups} prints the names of the primary and any supplementary
13256 groups for each given @var{username}, or the current process if no names
13257 are given. If more than one name is given, the name of each user is
13259 the list of that user's groups and the user name is separated from the
13260 group list by a colon. Synopsis:
13263 groups [@var{username}]@dots{}
13266 The group lists are equivalent to the output of the command @samp{id -Gn}.
13268 @primaryAndSupplementaryGroups{groups,list of users}
13270 The only options are @option{--help} and @option{--version}. @xref{Common
13276 @node users invocation
13277 @section @command{users}: Print login names of users currently logged in
13280 @cindex printing current usernames
13281 @cindex usernames, printing current
13283 @cindex login sessions, printing users with
13284 @command{users} prints on a single line a blank-separated list of user
13285 names of users currently logged in to the current host. Each user name
13286 corresponds to a login session, so if a user has more than one login
13287 session, that user's name will appear the same number of times in the
13296 With no @var{file} argument, @command{users} extracts its information from
13297 a system-maintained file (often @file{/var/run/utmp} or
13298 @file{/etc/utmp}). If a file argument is given, @command{users} uses
13299 that file instead. A common choice is @file{/var/log/wtmp}.
13301 The only options are @option{--help} and @option{--version}. @xref{Common
13307 @node who invocation
13308 @section @command{who}: Print who is currently logged in
13311 @cindex printing current user information
13312 @cindex information, about current users
13314 @command{who} prints information about users who are currently logged on.
13318 @command{who} [@var{option}] [@var{file}] [am i]
13321 @cindex terminal lines, currently used
13323 @cindex remote hostname
13324 If given no non-option arguments, @command{who} prints the following
13325 information for each user currently logged on: login name, terminal
13326 line, login time, and remote hostname or X display.
13330 If given one non-option argument, @command{who} uses that instead of
13331 a default system-maintained file (often @file{/var/run/utmp} or
13332 @file{/etc/utmp}) as the name of the file containing the record of
13333 users logged on. @file{/var/log/wtmp} is commonly given as an argument
13334 to @command{who} to look at who has previously logged on.
13338 If given two non-option arguments, @command{who} prints only the entry
13339 for the user running it (determined from its standard input), preceded
13340 by the hostname. Traditionally, the two arguments given are @samp{am
13341 i}, as in @samp{who am i}.
13344 Time stamps are listed according to the time zone rules specified by
13345 the @env{TZ} environment variable, or by the system default rules if
13346 @env{TZ} is not set. @xref{TZ Variable,, Specifying the Time Zone
13347 with @env{TZ}, libc, The GNU C Library Reference Manual}.
13349 The program accepts the following options. Also see @ref{Common options}.
13357 Same as @samp{-b -d --login -p -r -t -T -u}.
13363 Print the date and time of last system boot.
13369 Print information corresponding to dead processes.
13375 Print a line of column headings.
13381 List only the entries that correspond to processes via which the
13382 system is waiting for a user to login. The user name is always @samp{LOGIN}.
13386 Attempt to canonicalize hostnames found in utmp through a DNS lookup. This
13387 is not the default because it can cause significant delays on systems with
13388 automatic dial-up internet access.
13392 Same as @samp{who am i}.
13398 List active processes spawned by init.
13404 Print only the login names and the number of users logged on.
13405 Overrides all other options.
13410 @opindex --runlevel
13411 Print the current (and maybe previous) run-level of the init process.
13415 Ignored; for compatibility with other versions of @command{who}.
13421 Print last system clock change.
13426 After the login time, print the number of hours and minutes that the
13427 user has been idle. @samp{.} means the user was active in the last minute.
13428 @samp{old} means the user has been idle for more than 24 hours.
13439 @opindex --writable
13440 @cindex message status
13441 @pindex write@r{, allowed}
13442 After each login name print a character indicating the user's message status:
13445 @samp{+} allowing @code{write} messages
13446 @samp{-} disallowing @code{write} messages
13447 @samp{?} cannot find terminal device
13455 @node System context
13456 @chapter System context
13458 @cindex system context
13459 @cindex context, system
13460 @cindex commands for system context
13462 This section describes commands that print or change system-wide
13466 * date invocation:: Print or set system date and time.
13467 * arch invocation:: Print machine hardware name.
13468 * nproc invocation:: Print the number of processors.
13469 * uname invocation:: Print system information.
13470 * hostname invocation:: Print or set system name.
13471 * hostid invocation:: Print numeric host identifier.
13472 * uptime invocation:: Print system uptime and load.
13475 @node date invocation
13476 @section @command{date}: Print or set system date and time
13479 @cindex time, printing or setting
13480 @cindex printing the current time
13485 date [@var{option}]@dots{} [+@var{format}]
13486 date [-u|--utc|--universal] @c this avoids a newline in the output
13487 [ MMDDhhmm[[CC]YY][.ss] ]
13491 Invoking @command{date} with no @var{format} argument is equivalent to invoking
13492 it with a default format that depends on the @env{LC_TIME} locale category.
13493 In the default C locale, this format is @samp{'+%a %b %e %H:%M:%S %Z %Y'},
13494 so the output looks like @samp{Thu Mar @ 3 13:47:51 PST 2005}.
13497 Normally, @command{date} uses the time zone rules indicated by the
13498 @env{TZ} environment variable, or the system default rules if @env{TZ}
13499 is not set. @xref{TZ Variable,, Specifying the Time Zone with
13500 @env{TZ}, libc, The GNU C Library Reference Manual}.
13502 @findex strftime @r{and @command{date}}
13503 @cindex time formats
13504 @cindex formatting times
13505 If given an argument that starts with a @samp{+}, @command{date} prints the
13506 current date and time (or the date and time specified by the
13507 @option{--date} option, see below) in the format defined by that argument,
13508 which is similar to that of the @code{strftime} function. Except for
13509 conversion specifiers, which start with @samp{%}, characters in the
13510 format string are printed unchanged. The conversion specifiers are
13516 * Time conversion specifiers:: %[HIklMNpPrRsSTXzZ]
13517 * Date conversion specifiers:: %[aAbBcCdDeFgGhjmuUVwWxyY]
13518 * Literal conversion specifiers:: %[%nt]
13519 * Padding and other flags:: Pad with zeros, spaces, etc.
13520 * Setting the time:: Changing the system clock.
13521 * Options for date:: Instead of the current time.
13523 * Date input formats:: Specifying date strings.
13525 * Examples of date:: Examples.
13528 @node Time conversion specifiers
13529 @subsection Time conversion specifiers
13531 @cindex time conversion specifiers
13532 @cindex conversion specifiers, time
13534 @command{date} conversion specifiers related to times.
13538 hour (@samp{00}@dots{}@samp{23})
13540 hour (@samp{01}@dots{}@samp{12})
13542 hour (@samp{ 0}@dots{}@samp{23}).
13543 This is a @acronym{GNU} extension.
13545 hour (@samp{ 1}@dots{}@samp{12}).
13546 This is a @acronym{GNU} extension.
13548 minute (@samp{00}@dots{}@samp{59})
13550 nanoseconds (@samp{000000000}@dots{}@samp{999999999}).
13551 This is a @acronym{GNU} extension.
13553 locale's equivalent of either @samp{AM} or @samp{PM};
13554 blank in many locales.
13555 Noon is treated as @samp{PM} and midnight as @samp{AM}.
13557 like @samp{%p}, except lower case.
13558 This is a @acronym{GNU} extension.
13560 locale's 12-hour clock time (e.g., @samp{11:11:04 PM})
13562 24-hour hour and minute. Same as @samp{%H:%M}.
13563 This is a @acronym{GNU} extension.
13565 @cindex epoch, seconds since
13566 @cindex seconds since the epoch
13567 @cindex beginning of time
13568 seconds since the epoch, i.e., since 1970-01-01 00:00:00 UTC.
13569 Leap seconds are not counted unless leap second support is available.
13570 @xref{%s-examples}, for examples.
13571 This is a @acronym{GNU} extension.
13573 second (@samp{00}@dots{}@samp{60}).
13574 This may be @samp{60} if leap seconds are supported.
13576 24-hour hour, minute, and second. Same as @samp{%H:%M:%S}.
13578 locale's time representation (e.g., @samp{23:13:48})
13580 @w{@acronym{RFC} 2822/@acronym{ISO} 8601} style numeric time zone
13581 (e.g., @samp{-0600} or @samp{+0530}), or nothing if no
13582 time zone is determinable. This value reflects the numeric time zone
13583 appropriate for the current time, using the time zone rules specified
13584 by the @env{TZ} environment variable.
13585 The time (and optionally, the time zone rules) can be overridden
13586 by the @option{--date} option.
13587 This is a @acronym{GNU} extension.
13589 @w{@acronym{RFC} 3339/@acronym{ISO} 8601} style numeric time zone with
13590 @samp{:} (e.g., @samp{-06:00} or @samp{+05:30}), or nothing if no time
13591 zone is determinable.
13592 This is a @acronym{GNU} extension.
13594 Numeric time zone to the nearest second with @samp{:} (e.g.,
13595 @samp{-06:00:00} or @samp{+05:30:00}), or nothing if no time zone is
13597 This is a @acronym{GNU} extension.
13599 Numeric time zone with @samp{:} using the minimum necessary precision
13600 (e.g., @samp{-06}, @samp{+05:30}, or @samp{-04:56:02}), or nothing if
13601 no time zone is determinable.
13602 This is a @acronym{GNU} extension.
13604 alphabetic time zone abbreviation (e.g., @samp{EDT}), or nothing if no
13605 time zone is determinable. See @samp{%z} for how it is determined.
13609 @node Date conversion specifiers
13610 @subsection Date conversion specifiers
13612 @cindex date conversion specifiers
13613 @cindex conversion specifiers, date
13615 @command{date} conversion specifiers related to dates.
13619 locale's abbreviated weekday name (e.g., @samp{Sun})
13621 locale's full weekday name, variable length (e.g., @samp{Sunday})
13623 locale's abbreviated month name (e.g., @samp{Jan})
13625 locale's full month name, variable length (e.g., @samp{January})
13627 locale's date and time (e.g., @samp{Thu Mar @ 3 23:05:25 2005})
13629 century. This is like @samp{%Y}, except the last two digits are omitted.
13630 For example, it is @samp{20} if @samp{%Y} is @samp{2000},
13631 and is @samp{-0} if @samp{%Y} is @samp{-001}.
13632 It is normally at least two characters, but it may be more.
13634 day of month (e.g., @samp{01})
13636 date; same as @samp{%m/%d/%y}
13638 day of month, space padded; same as @samp{%_d}
13640 full date in @acronym{ISO} 8601 format; same as @samp{%Y-%m-%d}.
13641 This is a good choice for a date format, as it is standard and
13642 is easy to sort in the usual case where years are in the range
13644 This is a @acronym{GNU} extension.
13646 year corresponding to the @acronym{ISO} week number, but without the century
13647 (range @samp{00} through @samp{99}). This has the same format and value
13648 as @samp{%y}, except that if the @acronym{ISO} week number (see
13650 to the previous or next year, that year is used instead.
13651 This is a @acronym{GNU} extension.
13653 year corresponding to the @acronym{ISO} week number. This has the
13654 same format and value as @samp{%Y}, except that if the @acronym{ISO}
13656 @samp{%V}) belongs to the previous or next year, that year is used
13658 It is normally useful only if @samp{%V} is also used;
13659 for example, the format @samp{%G-%m-%d} is probably a mistake,
13660 since it combines the ISO week number year with the conventional month and day.
13661 This is a @acronym{GNU} extension.
13665 day of year (@samp{001}@dots{}@samp{366})
13667 month (@samp{01}@dots{}@samp{12})
13669 day of week (@samp{1}@dots{}@samp{7}) with @samp{1} corresponding to Monday
13671 week number of year, with Sunday as the first day of the week
13672 (@samp{00}@dots{}@samp{53}).
13673 Days in a new year preceding the first Sunday are in week zero.
13675 @acronym{ISO} week number, that is, the
13676 week number of year, with Monday as the first day of the week
13677 (@samp{01}@dots{}@samp{53}).
13678 If the week containing January 1 has four or more days in
13679 the new year, then it is considered week 1; otherwise, it is week 53 of
13680 the previous year, and the next week is week 1. (See the @acronym{ISO} 8601
13683 day of week (@samp{0}@dots{}@samp{6}) with 0 corresponding to Sunday
13685 week number of year, with Monday as first day of week
13686 (@samp{00}@dots{}@samp{53}).
13687 Days in a new year preceding the first Monday are in week zero.
13689 locale's date representation (e.g., @samp{12/31/99})
13691 last two digits of year (@samp{00}@dots{}@samp{99})
13693 year. This is normally at least four characters, but it may be more.
13694 Year @samp{0000} precedes year @samp{0001}, and year @samp{-001}
13695 precedes year @samp{0000}.
13699 @node Literal conversion specifiers
13700 @subsection Literal conversion specifiers
13702 @cindex literal conversion specifiers
13703 @cindex conversion specifiers, literal
13705 @command{date} conversion specifiers that produce literal strings.
13717 @node Padding and other flags
13718 @subsection Padding and other flags
13720 @cindex numeric field padding
13721 @cindex padding of numeric fields
13722 @cindex fields, padding numeric
13724 Unless otherwise specified, @command{date} normally pads numeric fields
13725 with zeros, so that, for
13726 example, numeric months are always output as two digits.
13727 Seconds since the epoch are not padded, though,
13728 since there is no natural width for them.
13730 As a @acronym{GNU} extension, @command{date} recognizes any of the
13731 following optional flags after the @samp{%}:
13735 (hyphen) Do not pad the field; useful if the output is intended for
13738 (underscore) Pad with spaces; useful if you need a fixed
13739 number of characters in the output, but zeros are too distracting.
13741 (zero) Pad with zeros even if the conversion specifier
13742 would normally pad with spaces.
13744 Use upper case characters if possible.
13746 Use opposite case characters if possible.
13747 A field that is normally upper case becomes lower case, and vice versa.
13751 Here are some examples of padding:
13754 date +%d/%m -d "Feb 1"
13756 date +%-d/%-m -d "Feb 1"
13758 date +%_d/%_m -d "Feb 1"
13762 As a @acronym{GNU} extension, you can specify the field width
13763 (after any flag, if present) as a decimal number. If the natural size of the
13764 output of the field has less than the specified number of characters,
13765 the result is written right adjusted and padded to the given
13766 size. For example, @samp{%9B} prints the right adjusted month name in
13767 a field of width 9.
13769 An optional modifier can follow the optional flag and width
13770 specification. The modifiers are:
13774 Use the locale's alternate representation for date and time. This
13775 modifier applies to the @samp{%c}, @samp{%C}, @samp{%x}, @samp{%X},
13776 @samp{%y} and @samp{%Y} conversion specifiers. In a Japanese locale, for
13777 example, @samp{%Ex} might yield a date format based on the Japanese
13781 Use the locale's alternate numeric symbols for numbers. This modifier
13782 applies only to numeric conversion specifiers.
13785 If the format supports the modifier but no alternate representation
13786 is available, it is ignored.
13789 @node Setting the time
13790 @subsection Setting the time
13792 @cindex setting the time
13793 @cindex time setting
13794 @cindex appropriate privileges
13796 If given an argument that does not start with @samp{+}, @command{date} sets
13797 the system clock to the date and time specified by that argument (as
13798 described below). You must have appropriate privileges to set the
13799 system clock. The @option{--date} and @option{--set} options may not be
13800 used with such an argument. The @option{--universal} option may be used
13801 with such an argument to indicate that the specified date and time are
13802 relative to Coordinated Universal Time rather than to the local time
13805 The argument must consist entirely of digits, which have the following
13818 first two digits of year (optional)
13820 last two digits of year (optional)
13825 The @option{--set} option also sets the system clock; see the next section.
13828 @node Options for date
13829 @subsection Options for @command{date}
13831 @cindex @command{date} options
13832 @cindex options for @command{date}
13834 The program accepts the following options. Also see @ref{Common options}.
13838 @item -d @var{datestr}
13839 @itemx --date=@var{datestr}
13842 @cindex parsing date strings
13843 @cindex date strings, parsing
13844 @cindex arbitrary date strings, parsing
13847 @opindex next @var{day}
13848 @opindex last @var{day}
13849 Display the date and time specified in @var{datestr} instead of the
13850 current date and time. @var{datestr} can be in almost any common
13851 format. It can contain month names, time zones, @samp{am} and @samp{pm},
13852 @samp{yesterday}, etc. For example, @option{--date="2004-02-27
13853 14:19:13.489392193 +0530"} specifies the instant of time that is
13854 489,392,193 nanoseconds after February 27, 2004 at 2:19:13 PM in a
13855 time zone that is 5 hours and 30 minutes east of @acronym{UTC}.@*
13856 Note: input currently must be in locale independent format. E.g., the
13857 LC_TIME=C below is needed to print back the correct date in many locales:
13859 date -d "$(LC_TIME=C date)"
13861 @xref{Date input formats}.
13863 @item -f @var{datefile}
13864 @itemx --file=@var{datefile}
13867 Parse each line in @var{datefile} as with @option{-d} and display the
13868 resulting date and time. If @var{datefile} is @samp{-}, use standard
13869 input. This is useful when you have many dates to process, because the
13870 system overhead of starting up the @command{date} executable many times can
13873 @item -r @var{file}
13874 @itemx --reference=@var{file}
13876 @opindex --reference
13877 Display the date and time of the last modification of @var{file},
13878 instead of the current date and time.
13885 @opindex --rfc-2822
13886 Display the date and time using the format @samp{%a, %d %b %Y %H:%M:%S
13887 %z}, evaluated in the C locale so abbreviations are always in English.
13891 Fri, 09 Sep 2005 13:51:39 -0700
13894 This format conforms to
13895 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc2822.txt, Internet
13896 @acronym{RFCs} 2822} and
13897 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc822.txt, 822}, the
13898 current and previous standards for Internet email.
13900 @item --rfc-3339=@var{timespec}
13901 @opindex --rfc-3339=@var{timespec}
13902 Display the date using a format specified by
13903 @uref{ftp://ftp.rfc-editor.org/in-notes/rfc3339.txt, Internet
13904 @acronym{RFC} 3339}. This is a subset of the @acronym{ISO} 8601
13905 format, except that it also permits applications to use a space rather
13906 than a @samp{T} to separate dates from times. Unlike the other
13907 standard formats, @acronym{RFC} 3339 format is always suitable as
13908 input for the @option{--date} (@option{-d}) and @option{--file}
13909 (@option{-f}) options, regardless of the current locale.
13911 The argument @var{timespec} specifies how much of the time to include.
13912 It can be one of the following:
13916 Print just the full-date, e.g., @samp{2005-09-14}.
13917 This is equivalent to the format @samp{%Y-%m-%d}.
13920 Print the full-date and full-time separated by a space, e.g.,
13921 @samp{2005-09-14 00:56:06+05:30}. The output ends with a numeric
13922 time-offset; here the @samp{+05:30} means that local time is five
13923 hours and thirty minutes east of @acronym{UTC}. This is equivalent to
13924 the format @samp{%Y-%m-%d %H:%M:%S%:z}.
13927 Like @samp{seconds}, but also print nanoseconds, e.g.,
13928 @samp{2005-09-14 00:56:06.998458565+05:30}.
13929 This is equivalent to the format @samp{%Y-%m-%d %H:%M:%S.%N%:z}.
13933 @item -s @var{datestr}
13934 @itemx --set=@var{datestr}
13937 Set the date and time to @var{datestr}. See @option{-d} above.
13944 @opindex --universal
13945 @cindex Coordinated Universal Time
13947 @cindex Greenwich Mean Time
13950 Use Coordinated Universal Time (@acronym{UTC}) by operating as if the
13951 @env{TZ} environment variable were set to the string @samp{UTC0}.
13953 Universal Time is often called ``Greenwich Mean Time'' (@sc{gmt}) for
13954 historical reasons.
13958 @node Examples of date
13959 @subsection Examples of @command{date}
13961 @cindex examples of @command{date}
13963 Here are a few examples. Also see the documentation for the @option{-d}
13964 option in the previous section.
13969 To print the date of the day before yesterday:
13972 date --date='2 days ago'
13976 To print the date of the day three months and one day hence:
13979 date --date='3 months 1 day'
13983 To print the day of year of Christmas in the current year:
13986 date --date='25 Dec' +%j
13990 To print the current full month name and the day of the month:
13996 But this may not be what you want because for the first nine days of
13997 the month, the @samp{%d} expands to a zero-padded two-digit field,
13998 for example @samp{date -d 1may '+%B %d'} will print @samp{May 01}.
14001 To print a date without the leading zero for one-digit days
14002 of the month, you can use the (@acronym{GNU} extension)
14003 @samp{-} flag to suppress
14004 the padding altogether:
14007 date -d 1may '+%B %-d
14011 To print the current date and time in the format required by many
14012 non-@acronym{GNU} versions of @command{date} when setting the system clock:
14015 date +%m%d%H%M%Y.%S
14019 To set the system clock forward by two minutes:
14022 date --set='+2 minutes'
14026 To print the date in @acronym{RFC} 2822 format,
14027 use @samp{date --rfc-2822}. Here is some example output:
14030 Fri, 09 Sep 2005 13:51:39 -0700
14033 @anchor{%s-examples}
14035 To convert a date string to the number of seconds since the epoch
14036 (which is 1970-01-01 00:00:00 UTC), use the @option{--date} option with
14037 the @samp{%s} format. That can be useful in sorting and/or graphing
14038 and/or comparing data by date. The following command outputs the
14039 number of the seconds since the epoch for the time two minutes after the
14043 date --date='1970-01-01 00:02:00 +0000' +%s
14047 If you do not specify time zone information in the date string,
14048 @command{date} uses your computer's idea of the time zone when
14049 interpreting the string. For example, if your computer's time zone is
14050 that of Cambridge, Massachusetts, which was then 5 hours (i.e., 18,000
14051 seconds) behind UTC:
14054 # local time zone used
14055 date --date='1970-01-01 00:02:00' +%s
14060 If you're sorting or graphing dated data, your raw date values may be
14061 represented as seconds since the epoch. But few people can look at
14062 the date @samp{946684800} and casually note ``Oh, that's the first second
14063 of the year 2000 in Greenwich, England.''
14066 date --date='2000-01-01 UTC' +%s
14070 An alternative is to use the @option{--utc} (@option{-u}) option.
14071 Then you may omit @samp{UTC} from the date string. Although this
14072 produces the same result for @samp{%s} and many other format sequences,
14073 with a time zone offset different from zero, it would give a different
14074 result for zone-dependent formats like @samp{%z}.
14077 date -u --date=2000-01-01 +%s
14081 To convert such an unwieldy number of seconds back to
14082 a more readable form, use a command like this:
14085 # local time zone used
14086 date -d '1970-01-01 UTC 946684800 seconds' +"%Y-%m-%d %T %z"
14087 1999-12-31 19:00:00 -0500
14090 Or if you do not mind depending on the @samp{@@} feature present since
14091 coreutils 5.3.0, you could shorten this to:
14094 date -d @@946684800 +"%F %T %z"
14095 1999-12-31 19:00:00 -0500
14098 Often it is better to output UTC-relative date and time:
14101 date -u -d '1970-01-01 946684800 seconds' +"%Y-%m-%d %T %z"
14102 2000-01-01 00:00:00 +0000
14108 @node arch invocation
14109 @section @command{arch}: Print machine hardware name
14112 @cindex print machine hardware name
14113 @cindex system information, printing
14115 @command{arch} prints the machine hardware name,
14116 and is equivalent to @samp{uname -m}.
14120 arch [@var{option}]
14123 The program accepts the @ref{Common options} only.
14128 @node nproc invocation
14129 @section @command{nproc}: Print the number of available processors
14132 @cindex Print the number of processors
14133 @cindex system information, printing
14135 Print the number of processing units available to the current process,
14136 which may be less than the number of online processors.
14137 If this information is not accessible, then print the number of
14138 processors installed. If the @env{OMP_NUM_THREADS} environment variable is
14139 set, then it will determine the returned value. The result is guaranteed to be
14140 greater than zero. Synopsis:
14143 nproc [@var{option}]
14146 The program accepts the following options. Also see @ref{Common options}.
14152 Print the number of installed processors on the system, which may
14153 be greater than the number online or available to the current process.
14154 The @env{OMP_NUM_THREADS} environment variable is not honored in this case.
14156 @item --ignore=@var{number}
14158 If possible, exclude this @var{number} of processing units.
14165 @node uname invocation
14166 @section @command{uname}: Print system information
14169 @cindex print system information
14170 @cindex system information, printing
14172 @command{uname} prints information about the machine and operating system
14173 it is run on. If no options are given, @command{uname} acts as if the
14174 @option{-s} option were given. Synopsis:
14177 uname [@var{option}]@dots{}
14180 If multiple options or @option{-a} are given, the selected information is
14181 printed in this order:
14184 @var{kernel-name} @var{nodename} @var{kernel-release} @var{kernel-version}
14185 @var{machine} @var{processor} @var{hardware-platform} @var{operating-system}
14188 The information may contain internal spaces, so such output cannot be
14189 parsed reliably. In the following example, @var{release} is
14190 @samp{2.2.18ss.e820-bda652a #4 SMP Tue Jun 5 11:24:08 PDT 2001}:
14194 @result{} Linux dum 2.2.18 #4 SMP Tue Jun 5 11:24:08 PDT 2001 i686 unknown unknown GNU/Linux
14198 The program accepts the following options. Also see @ref{Common options}.
14206 Print all of the below information, except omit the processor type
14207 and the hardware platform name if they are unknown.
14210 @itemx --hardware-platform
14212 @opindex --hardware-platform
14213 @cindex implementation, hardware
14214 @cindex hardware platform
14215 @cindex platform, hardware
14216 Print the hardware platform name
14217 (sometimes called the hardware implementation).
14218 Print @samp{unknown} if the kernel does not make this information
14219 easily available, as is the case with Linux kernels.
14225 @cindex machine type
14226 @cindex hardware class
14227 @cindex hardware type
14228 Print the machine hardware name (sometimes called the hardware class
14234 @opindex --nodename
14237 @cindex network node name
14238 Print the network node hostname.
14243 @opindex --processor
14244 @cindex host processor type
14245 Print the processor type (sometimes called the instruction set
14246 architecture or ISA).
14247 Print @samp{unknown} if the kernel does not make this information
14248 easily available, as is the case with Linux kernels.
14251 @itemx --operating-system
14253 @opindex --operating-system
14254 @cindex operating system name
14255 Print the name of the operating system.
14258 @itemx --kernel-release
14260 @opindex --kernel-release
14261 @cindex kernel release
14262 @cindex release of kernel
14263 Print the kernel release.
14266 @itemx --kernel-name
14268 @opindex --kernel-name
14269 @cindex kernel name
14270 @cindex name of kernel
14271 Print the kernel name.
14272 @acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) calls this
14273 ``the implementation of the operating system'', because the
14274 @acronym{POSIX} specification itself has no notion of ``kernel''.
14275 The kernel name might be the same as the operating system name printed
14276 by the @option{-o} or @option{--operating-system} option, but it might
14277 differ. Some operating systems (e.g., FreeBSD, HP-UX) have the same
14278 name as their underlying kernels; others (e.g., GNU/Linux, Solaris)
14282 @itemx --kernel-version
14284 @opindex --kernel-version
14285 @cindex kernel version
14286 @cindex version of kernel
14287 Print the kernel version.
14294 @node hostname invocation
14295 @section @command{hostname}: Print or set system name
14298 @cindex setting the hostname
14299 @cindex printing the hostname
14300 @cindex system name, printing
14301 @cindex appropriate privileges
14303 With no arguments, @command{hostname} prints the name of the current host
14304 system. With one argument, it sets the current host name to the
14305 specified string. You must have appropriate privileges to set the host
14309 hostname [@var{name}]
14312 The only options are @option{--help} and @option{--version}. @xref{Common
14318 @node hostid invocation
14319 @section @command{hostid}: Print numeric host identifier
14322 @cindex printing the host identifier
14324 @command{hostid} prints the numeric identifier of the current host
14325 in hexadecimal. This command accepts no arguments.
14326 The only options are @option{--help} and @option{--version}.
14327 @xref{Common options}.
14329 For example, here's what it prints on one system I use:
14336 On that system, the 32-bit quantity happens to be closely
14337 related to the system's Internet address, but that isn't always
14342 @node uptime invocation
14343 @section @command{uptime}: Print system uptime and load
14346 @cindex printing the system uptime and load
14348 @command{uptime} prints the current time, the system's uptime, the
14349 number of logged-in users and the current load average.
14351 If an argument is specified, it is used as the file to be read
14352 to discover how many users are logged in. If no argument is
14353 specified, a system default is used (@command{uptime --help} indicates
14354 the default setting).
14356 The only options are @option{--help} and @option{--version}.
14357 @xref{Common options}.
14359 For example, here's what it prints right now on one system I use:
14363 14:07 up 3:35, 3 users, load average: 1.39, 1.15, 1.04
14366 The precise method of calculation of load average varies somewhat
14367 between systems. Some systems calculate it as the average number of
14368 runnable processes over the last 1, 5 and 15 minutes, but some systems
14369 also include processes in the uninterruptible sleep state (that is,
14370 those processes which are waiting for disk I/O). The Linux kernel
14371 includes uninterruptible processes.
14373 @node SELinux context
14374 @chapter SELinux context
14376 @cindex SELinux context
14377 @cindex SELinux, context
14378 @cindex commands for SELinux context
14380 This section describes commands for operations with SELinux
14384 * chcon invocation:: Change SELinux context of file
14385 * runcon invocation:: Run a command in specified SELinux context
14388 @node chcon invocation
14389 @section @command{chcon}: Change SELinux context of file
14392 @cindex changing security context
14393 @cindex change SELinux context
14395 @command{chcon} changes the SELinux security context of the selected files.
14399 chcon [@var{option}]@dots{} @var{context} @var{file}@dots{}
14400 chcon [@var{option}]@dots{} [-u @var{user}] [-r @var{role}] [-l @var{range}] [-t @var{type}] @var{file}@dots{}
14401 chcon [@var{option}]@dots{} --reference=@var{rfile} @var{file}@dots{}
14404 Change the SELinux security context of each @var{file} to @var{context}.
14405 With @option{--reference}, change the security context of each @var{file}
14406 to that of @var{rfile}.
14408 The program accepts the following options. Also see @ref{Common options}.
14413 @itemx --no-dereference
14415 @opindex --no-dereference
14416 @cindex no dereference
14417 Affect symbolic links instead of any referenced file.
14419 @item --reference=@var{rfile}
14420 @opindex --reference
14421 @cindex reference file
14422 Use @var{rfile}'s security context rather than specifying a @var{context} value.
14427 @opindex --recursive
14428 Operate on files and directories recursively.
14431 @xref{Traversing symlinks}.
14434 @xref{Traversing symlinks}.
14437 @xref{Traversing symlinks}.
14444 Output a diagnostic for every file processed.
14446 @item -u @var{user}
14447 @itemx --user=@var{user}
14450 Set user @var{user} in the target security context.
14452 @item -r @var{role}
14453 @itemx --role=@var{role}
14456 Set role @var{role} in the target security context.
14458 @item -t @var{type}
14459 @itemx --type=@var{type}
14462 Set type @var{type} in the target security context.
14464 @item -l @var{range}
14465 @itemx --range=@var{range}
14468 Set range @var{range} in the target security context.
14474 @node runcon invocation
14475 @section @command{runcon}: Run a command in specified SELinux context
14478 @cindex run with security context
14481 @command{runcon} runs file in specified SELinux security context.
14485 runcon @var{context} @var{command} [@var{args}]
14486 runcon [ -c ] [-u @var{user}] [-r @var{role}] [-t @var{type}] [-l @var{range}] @var{command} [@var{args}]
14489 Run @var{command} with completely-specified @var{context}, or with
14490 current or transitioned security context modified by one or more of @var{level},
14491 @var{role}, @var{type} and @var{user}.
14493 If none of @option{-c}, @option{-t}, @option{-u}, @option{-r}, or @option{-l}
14494 is specified, the first argument is used as the complete context.
14495 Any additional arguments after @var{command}
14496 are interpreted as arguments to the command.
14498 With neither @var{context} nor @var{command}, print the current security context.
14500 The program accepts the following options. Also see @ref{Common options}.
14508 Compute process transition context before modifying.
14510 @item -u @var{user}
14511 @itemx --user=@var{user}
14514 Set user @var{user} in the target security context.
14516 @item -r @var{role}
14517 @itemx --role=@var{role}
14520 Set role @var{role} in the target security context.
14522 @item -t @var{type}
14523 @itemx --type=@var{type}
14526 Set type @var{type} in the target security context.
14528 @item -l @var{range}
14529 @itemx --range=@var{range}
14532 Set range @var{range} in the target security context.
14536 @cindex exit status of @command{runcon}
14540 126 if @var{command} is found but cannot be invoked
14541 127 if @command{runcon} itself fails or if @var{command} cannot be found
14542 the exit status of @var{command} otherwise
14545 @node Modified command invocation
14546 @chapter Modified command invocation
14548 @cindex modified command invocation
14549 @cindex invocation of commands, modified
14550 @cindex commands for invoking other commands
14552 This section describes commands that run other commands in some context
14553 different than the current one: a modified environment, as a different
14557 * chroot invocation:: Modify the root directory.
14558 * env invocation:: Modify environment variables.
14559 * nice invocation:: Modify niceness.
14560 * nohup invocation:: Immunize to hangups.
14561 * stdbuf invocation:: Modify buffering of standard streams.
14562 * su invocation:: Modify user and group ID.
14563 * timeout invocation:: Run with time limit.
14567 @node chroot invocation
14568 @section @command{chroot}: Run a command with a different root directory
14571 @cindex running a program in a specified root directory
14572 @cindex root directory, running a program in a specified
14574 @command{chroot} runs a command with a specified root directory.
14575 On many systems, only the super-user can do this.@footnote{However,
14576 some systems (e.g., FreeBSD) can be configured to allow certain regular
14577 users to use the @code{chroot} system call, and hence to run this program.
14578 Also, on Cygwin, anyone can run the @command{chroot} command, because the
14579 underlying function is non-privileged due to lack of support in MS-Windows.}
14583 chroot @var{option} @var{newroot} [@var{command} [@var{args}]@dots{}]
14584 chroot @var{option}
14587 Ordinarily, file names are looked up starting at the root of the
14588 directory structure, i.e., @file{/}. @command{chroot} changes the root to
14589 the directory @var{newroot} (which must exist) and then runs
14590 @var{command} with optional @var{args}. If @var{command} is not
14591 specified, the default is the value of the @env{SHELL} environment
14592 variable or @command{/bin/sh} if not set, invoked with the @option{-i} option.
14593 @var{command} must not be a special built-in utility
14594 (@pxref{Special built-in utilities}).
14596 The program accepts the following options. Also see @ref{Common options}.
14597 Options must precede operands.
14601 @itemx --userspec=@var{user}[:@var{group}]
14602 @opindex --userspec
14603 By default, @var{command} is run with the same credentials
14604 as the invoking process.
14605 Use this option to run it as a different @var{user} and/or with a
14606 different primary @var{group}.
14608 @itemx --groups=@var{groups}
14610 Use this option to specify the supplementary @var{groups} to be
14611 used by the new process.
14612 The items in the list (names or numeric IDs) must be separated by commas.
14616 Here are a few tips to help avoid common problems in using chroot.
14617 To start with a simple example, make @var{command} refer to a statically
14618 linked binary. If you were to use a dynamically linked executable, then
14619 you'd have to arrange to have the shared libraries in the right place under
14620 your new root directory.
14622 For example, if you create a statically linked @command{ls} executable,
14623 and put it in @file{/tmp/empty}, you can run this command as root:
14626 $ chroot /tmp/empty /ls -Rl /
14629 Then you'll see output like this:
14634 -rwxr-xr-x 1 0 0 1041745 Aug 16 11:17 ls
14637 If you want to use a dynamically linked executable, say @command{bash},
14638 then first run @samp{ldd bash} to see what shared objects it needs.
14639 Then, in addition to copying the actual binary, also copy the listed
14640 files to the required positions under your intended new root directory.
14641 Finally, if the executable requires any other files (e.g., data, state,
14642 device files), copy them into place, too.
14644 @cindex exit status of @command{chroot}
14648 125 if @command{chroot} itself fails
14649 126 if @var{command} is found but cannot be invoked
14650 127 if @var{command} cannot be found
14651 the exit status of @var{command} otherwise
14655 @node env invocation
14656 @section @command{env}: Run a command in a modified environment
14659 @cindex environment, running a program in a modified
14660 @cindex modified environment, running a program in a
14661 @cindex running a program in a modified environment
14663 @command{env} runs a command with a modified environment. Synopses:
14666 env [@var{option}]@dots{} [@var{name}=@var{value}]@dots{} @c
14667 [@var{command} [@var{args}]@dots{}]
14671 Operands of the form @samp{@var{variable}=@var{value}} set
14672 the environment variable @var{variable} to value @var{value}.
14673 @var{value} may be empty (@samp{@var{variable}=}). Setting a variable
14674 to an empty value is different from unsetting it.
14675 These operands are evaluated left-to-right, so if two operands
14676 mention the same variable the earlier is ignored.
14678 Environment variable names can be empty, and can contain any
14679 characters other than @samp{=} and @acronym{ASCII} @sc{nul}.
14680 However, it is wise to limit yourself to names that
14681 consist solely of underscores, digits, and @acronym{ASCII} letters,
14682 and that begin with a non-digit, as applications like the shell do not
14683 work well with other names.
14686 The first operand that does not contain the character @samp{=}
14687 specifies the program to invoke; it is
14688 searched for according to the @env{PATH} environment variable. Any
14689 remaining arguments are passed as arguments to that program.
14690 The program should not be a special built-in utility
14691 (@pxref{Special built-in utilities}).
14693 Modifications to @env{PATH} take effect prior to searching for
14694 @var{command}. Use caution when reducing @env{PATH}; behavior is
14695 not portable when @env{PATH} is undefined or omits key directories
14696 such as @file{/bin}.
14698 In the rare case that a utility contains a @samp{=} in the name, the
14699 only way to disambiguate it from a variable assignment is to use an
14700 intermediate command for @var{command}, and pass the problematic
14701 program name via @var{args}. For example, if @file{./prog=} is an
14702 executable in the current @env{PATH}:
14705 env prog= true # runs 'true', with prog= in environment
14706 env ./prog= true # runs 'true', with ./prog= in environment
14707 env -- prog= true # runs 'true', with prog= in environment
14708 env sh -c '\prog= true' # runs 'prog=' with argument 'true'
14709 env sh -c 'exec "$@@"' sh prog= true # also runs 'prog='
14712 @cindex environment, printing
14714 If no command name is specified following the environment
14715 specifications, the resulting environment is printed. This is like
14716 specifying the @command{printenv} program.
14718 For some examples, suppose the environment passed to @command{env}
14719 contains @samp{LOGNAME=rms}, @samp{EDITOR=emacs}, and
14720 @samp{PATH=.:/gnubin:/hacks}:
14725 Output the current environment.
14727 $ env | LC_ALL=C sort
14730 PATH=.:/gnubin:/hacks
14734 Run @command{foo} with a reduced environment, preserving only the
14735 original @env{PATH} to avoid problems in locating @command{foo}.
14737 env - PATH="$PATH" foo
14741 Run @command{foo} with the environment containing @samp{LOGNAME=rms},
14742 @samp{EDITOR=emacs}, and @samp{PATH=.:/gnubin:/hacks}, and guarantees
14743 that @command{foo} was found in the file system rather than as a shell
14750 Run @command{nemacs} with the environment containing @samp{LOGNAME=foo},
14751 @samp{EDITOR=emacs}, @samp{PATH=.:/gnubin:/hacks}, and
14752 @samp{DISPLAY=gnu:0}.
14754 env DISPLAY=gnu:0 LOGNAME=foo nemacs
14758 Attempt to run the program @command{/energy/--} (as that is the only
14759 possible path search result); if the command exists, the environment
14760 will contain @samp{LOGNAME=rms} and @samp{PATH=/energy}, and the
14761 arguments will be @samp{e=mc2}, @samp{bar}, and @samp{baz}.
14763 env -u EDITOR PATH=/energy -- e=mc2 bar baz
14769 The program accepts the following options. Also see @ref{Common options}.
14770 Options must precede operands.
14776 @item -u @var{name}
14777 @itemx --unset=@var{name}
14780 Remove variable @var{name} from the environment, if it was in the
14785 @itemx --ignore-environment
14788 @opindex --ignore-environment
14789 Start with an empty environment, ignoring the inherited environment.
14793 @cindex exit status of @command{env}
14797 0 if no @var{command} is specified and the environment is output
14798 125 if @command{env} itself fails
14799 126 if @var{command} is found but cannot be invoked
14800 127 if @var{command} cannot be found
14801 the exit status of @var{command} otherwise
14805 @node nice invocation
14806 @section @command{nice}: Run a command with modified niceness
14810 @cindex scheduling, affecting
14811 @cindex appropriate privileges
14813 @command{nice} prints or modifies a process's @dfn{niceness},
14814 a parameter that affects whether the process is scheduled favorably.
14818 nice [@var{option}]@dots{} [@var{command} [@var{arg}]@dots{}]
14821 If no arguments are given, @command{nice} prints the current niceness.
14822 Otherwise, @command{nice} runs the given @var{command} with its
14823 niceness adjusted. By default, its niceness is incremented by 10.
14825 Niceness values range at least from @minus{}20 (process has high priority
14826 and gets more resources, thus slowing down other processes) through 19
14827 (process has lower priority and runs slowly itself, but has less impact
14828 on the speed of other running processes). Some systems
14829 may have a wider range of nicenesses; conversely, other systems may
14830 enforce more restrictive limits. An attempt to set the niceness
14831 outside the supported range is treated as an attempt to use the
14832 minimum or maximum supported value.
14834 A niceness should not be confused with a scheduling priority, which
14835 lets applications determine the order in which threads are scheduled
14836 to run. Unlike a priority, a niceness is merely advice to the
14837 scheduler, which the scheduler is free to ignore. Also, as a point of
14838 terminology, @acronym{POSIX} defines the behavior of @command{nice} in
14839 terms of a @dfn{nice value}, which is the nonnegative difference
14840 between a niceness and the minimum niceness. Though @command{nice}
14841 conforms to @acronym{POSIX}, its documentation and diagnostics use the
14842 term ``niceness'' for compatibility with historical practice.
14844 @var{command} must not be a special built-in utility (@pxref{Special
14845 built-in utilities}).
14847 @mayConflictWithShellBuiltIn{nice}
14849 The program accepts the following option. Also see @ref{Common options}.
14850 Options must precede operands.
14853 @item -n @var{adjustment}
14854 @itemx --adjustment=@var{adjustment}
14856 @opindex --adjustment
14857 Add @var{adjustment} instead of 10 to the command's niceness. If
14858 @var{adjustment} is negative and you lack appropriate privileges,
14859 @command{nice} issues a warning but otherwise acts as if you specified
14862 For compatibility @command{nice} also supports an obsolete
14863 option syntax @option{-@var{adjustment}}. New scripts should use
14864 @option{-n @var{adjustment}} instead.
14868 @cindex exit status of @command{nice}
14872 0 if no @var{command} is specified and the niceness is output
14873 125 if @command{nice} itself fails
14874 126 if @var{command} is found but cannot be invoked
14875 127 if @var{command} cannot be found
14876 the exit status of @var{command} otherwise
14879 It is sometimes useful to run a non-interactive program with reduced niceness.
14882 $ nice factor 4611686018427387903
14885 Since @command{nice} prints the current niceness,
14886 you can invoke it through itself to demonstrate how it works.
14888 The default behavior is to increase the niceness by @samp{10}:
14899 The @var{adjustment} is relative to the current niceness. In the
14900 next example, the first @command{nice} invocation runs the second one
14901 with niceness 10, and it in turn runs the final one with a niceness
14905 $ nice nice -n 3 nice
14909 Specifying a niceness larger than the supported range
14910 is the same as specifying the maximum supported value:
14913 $ nice -n 10000000000 nice
14917 Only a privileged user may run a process with lower niceness:
14921 nice: cannot set niceness: Permission denied
14923 $ sudo nice -n -1 nice
14928 @node nohup invocation
14929 @section @command{nohup}: Run a command immune to hangups
14932 @cindex hangups, immunity to
14933 @cindex immunity to hangups
14934 @cindex logging out and continuing to run
14937 @command{nohup} runs the given @var{command} with hangup signals ignored,
14938 so that the command can continue running in the background after you log
14942 nohup @var{command} [@var{arg}]@dots{}
14945 If standard input is a terminal, it is redirected from
14946 @file{/dev/null} so that terminal sessions do not mistakenly consider
14947 the terminal to be used by the command. This is a @acronym{GNU}
14948 extension; programs intended to be portable to non-@acronym{GNU} hosts
14949 should use @samp{nohup @var{command} [@var{arg}]@dots{} </dev/null}
14953 If standard output is a terminal, the command's standard output is appended
14954 to the file @file{nohup.out}; if that cannot be written to, it is appended
14955 to the file @file{$HOME/nohup.out}; and if that cannot be written to, the
14956 command is not run.
14957 Any @file{nohup.out} or @file{$HOME/nohup.out} file created by
14958 @command{nohup} is made readable and writable only to the user,
14959 regardless of the current umask settings.
14961 If standard error is a terminal, it is normally redirected to the same file
14962 descriptor as the (possibly-redirected) standard output.
14963 However, if standard output is closed, standard error terminal output
14964 is instead appended to the file @file{nohup.out} or
14965 @file{$HOME/nohup.out} as above.
14967 To capture the command's output to a file other than @file{nohup.out}
14968 you can redirect it. For example, to capture the output of
14972 nohup make > make.log
14975 @command{nohup} does not automatically put the command it runs in the
14976 background; you must do that explicitly, by ending the command line
14977 with an @samp{&}. Also, @command{nohup} does not alter the
14978 niceness of @var{command}; use @command{nice} for that,
14979 e.g., @samp{nohup nice @var{command}}.
14981 @var{command} must not be a special built-in utility (@pxref{Special
14982 built-in utilities}).
14984 The only options are @option{--help} and @option{--version}. @xref{Common
14985 options}. Options must precede operands.
14987 @cindex exit status of @command{nohup}
14991 125 if @command{nohup} itself fails, and @env{POSIXLY_CORRECT} is not set
14992 126 if @var{command} is found but cannot be invoked
14993 127 if @var{command} cannot be found
14994 the exit status of @var{command} otherwise
14997 If @env{POSIXLY_CORRECT} is set, internal failures give status 127
15001 @node stdbuf invocation
15002 @section @command{stdbuf}: Run a command with modified I/O stream buffering
15005 @cindex standard streams, buffering
15006 @cindex line buffered
15008 @command{stdbuf} allows one to modify the buffering operations of the
15009 three standard I/O streams associated with a program. Synopsis:
15012 stdbuf @var{option}@dots{} @var{command}
15015 Any additional @var{arg}s are passed as additional arguments to the
15018 The program accepts the following options. Also see @ref{Common options}.
15022 @item -i @var{mode}
15023 @itemx --input=@var{mode}
15026 Adjust the standard input stream buffering.
15028 @item -o @var{mode}
15029 @itemx --output=@var{mode}
15032 Adjust the standard output stream buffering.
15034 @item -e @var{mode}
15035 @itemx --error=@var{mode}
15038 Adjust the standard error stream buffering.
15042 The @var{mode} can be specified as follows:
15047 Set the stream to line buffered mode.
15048 In this mode data is coalesced until a newline is output or
15049 input is read from any stream attached to a terminal device.
15050 This option is invalid with standard input.
15053 Disable buffering of the selected stream.
15054 In this mode data is output immediately and only the
15055 amount of data requested is read from input.
15058 Specify the size of the buffer to use in fully buffered mode.
15059 @multiplierSuffixesNoBlocks{size}
15063 NOTE: If @var{command} adjusts the buffering of its standard streams
15064 (@command{tee} does for e.g.) then that will override corresponding settings
15065 changed by @command{stdbuf}. Also some filters (like @command{dd} and
15066 @command{cat} etc.) don't use streams for I/O, and are thus unaffected
15067 by @command{stdbuf} settings.
15069 @cindex exit status of @command{stdbuf}
15073 125 if @command{stdbuf} itself fails
15074 126 if @var{command} is found but cannot be invoked
15075 127 if @var{command} cannot be found
15076 the exit status of @var{command} otherwise
15080 @node su invocation
15081 @section @command{su}: Run a command with substitute user and group ID
15084 @cindex substitute user and group IDs
15085 @cindex user ID, switching
15086 @cindex super-user, becoming
15087 @cindex root, becoming
15089 @command{su} allows one user to temporarily become another user. It runs a
15090 command (often an interactive shell) with the real and effective user
15091 ID, group ID, and supplemental groups of a given @var{user}. Synopsis:
15094 su [@var{option}]@dots{} [@var{user} [@var{arg}]@dots{}]
15097 @cindex passwd entry, and @command{su} shell
15099 @flindex /etc/passwd
15100 If no @var{user} is given, the default is @code{root}, the super-user.
15101 The shell to use is taken from @var{user}'s @code{passwd} entry, or
15102 @file{/bin/sh} if none is specified there. If @var{user} has a
15103 password, @command{su} prompts for the password unless run by a user with
15104 effective user ID of zero (the super-user).
15110 @cindex login shell
15111 By default, @command{su} does not change the current directory.
15112 It sets the environment variables @env{HOME} and @env{SHELL}
15113 from the password entry for @var{user}, and if @var{user} is not
15114 the super-user, sets @env{USER} and @env{LOGNAME} to @var{user}.
15115 By default, the shell is not a login shell.
15117 Any additional @var{arg}s are passed as additional arguments to the
15120 @cindex @option{-su}
15121 GNU @command{su} does not treat @file{/bin/sh} or any other shells specially
15122 (e.g., by setting @code{argv[0]} to @option{-su}, passing @option{-c} only
15123 to certain shells, etc.).
15126 @command{su} can optionally be compiled to use @code{syslog} to report
15127 failed, and optionally successful, @command{su} attempts. (If the system
15128 supports @code{syslog}.) However, GNU @command{su} does not check if the
15129 user is a member of the @code{wheel} group; see below.
15131 The program accepts the following options. Also see @ref{Common options}.
15134 @item -c @var{command}
15135 @itemx --command=@var{command}
15138 Pass @var{command}, a single command line to run, to the shell with
15139 a @option{-c} option instead of starting an interactive shell.
15146 @cindex file name pattern expansion, disabled
15147 @cindex globbing, disabled
15148 Pass the @option{-f} option to the shell. This probably only makes sense
15149 if the shell run is @command{csh} or @command{tcsh}, for which the @option{-f}
15150 option prevents reading the startup file (@file{.cshrc}). With
15151 Bourne-like shells, the @option{-f} option disables file name pattern
15152 expansion (globbing), which is not likely to be useful.
15160 @c other variables already indexed above
15163 @cindex login shell, creating
15164 Make the shell a login shell. This means the following. Unset all
15165 environment variables except @env{TERM}, @env{HOME}, and @env{SHELL}
15166 (which are set as described above), and @env{USER} and @env{LOGNAME}
15167 (which are set, even for the super-user, as described above), and set
15168 @env{PATH} to a compiled-in default value. Change to @var{user}'s home
15169 directory. Prepend @samp{-} to the shell's name, intended to make it
15170 read its login startup file(s).
15174 @itemx --preserve-environment
15177 @opindex --preserve-environment
15178 @cindex environment, preserving
15179 @flindex /etc/shells
15180 @cindex restricted shell
15181 Do not change the environment variables @env{HOME}, @env{USER},
15182 @env{LOGNAME}, or @env{SHELL}. Run the shell given in the environment
15183 variable @env{SHELL} instead of the shell from @var{user}'s passwd
15184 entry, unless the user running @command{su} is not the super-user and
15185 @var{user}'s shell is restricted. A @dfn{restricted shell} is one that
15186 is not listed in the file @file{/etc/shells}, or in a compiled-in list
15187 if that file does not exist. Parts of what this option does can be
15188 overridden by @option{--login} and @option{--shell}.
15190 @item -s @var{shell}
15191 @itemx --shell=@var{shell}
15194 Run @var{shell} instead of the shell from @var{user}'s passwd entry,
15195 unless the user running @command{su} is not the super-user and @var{user}'s
15196 shell is restricted (see @option{-m} just above).
15200 @cindex exit status of @command{su}
15204 125 if @command{su} itself fails
15205 126 if subshell is found but cannot be invoked
15206 127 if subshell cannot be found
15207 the exit status of the subshell otherwise
15210 @cindex wheel group, not supported
15211 @cindex group wheel, not supported
15213 @subsection Why GNU @command{su} does not support the @samp{wheel} group
15215 (This section is by Richard Stallman.)
15219 Sometimes a few of the users try to hold total power over all the
15220 rest. For example, in 1984, a few users at the MIT AI lab decided to
15221 seize power by changing the operator password on the Twenex system and
15222 keeping it secret from everyone else. (I was able to thwart this coup
15223 and give power back to the users by patching the kernel, but I
15224 wouldn't know how to do that in Unix.)
15226 However, occasionally the rulers do tell someone. Under the usual
15227 @command{su} mechanism, once someone learns the root password who
15228 sympathizes with the ordinary users, he or she can tell the rest. The
15229 ``wheel group'' feature would make this impossible, and thus cement the
15230 power of the rulers.
15232 I'm on the side of the masses, not that of the rulers. If you are
15233 used to supporting the bosses and sysadmins in whatever they do, you
15234 might find this idea strange at first.
15237 @node timeout invocation
15238 @section @command{timeout}: Run a command with a time limit
15242 @cindex run commands with bounded time
15244 @command{timeout} runs the given @var{command} and kills it if it is
15245 still running after the specified time interval. Synopsis:
15248 timeout [@var{option}] @var{duration} @var{command} [@var{arg}]@dots{}
15251 @var{command} must not be a special built-in utility (@pxref{Special
15252 built-in utilities}).
15254 The program accepts the following options. Also see @ref{Common options}.
15255 Options must precede operands.
15258 @item -k @var{duration}
15259 @itemx --kill-after=@var{duration}
15261 @opindex --kill-after
15262 Ensure the monitored @var{command} is killed by also sending a @samp{KILL}
15263 signal, after the specified @var{duration}. Without this option, if the
15264 selected signal proves not to be fatal, @command{timeout} does not kill
15267 @item -s @var{signal}
15268 @itemx --signal=@var{signal}
15271 Send this @var{signal} to @var{command} on timeout, rather than the
15272 default @samp{TERM} signal. @var{signal} may be a name like @samp{HUP}
15273 or a number. Also see @xref{Signal specifications}.
15277 @var{duration} is an integer followed by an optional unit:
15279 @samp{s} for seconds (the default)
15280 @samp{m} for minutes
15284 A duration of 0 disables the associated timeout.
15286 @cindex exit status of @command{timeout}
15290 124 if @var{command} times out
15291 125 if @command{timeout} itself fails
15292 126 if @var{command} is found but cannot be invoked
15293 127 if @var{command} cannot be found
15294 the exit status of @var{command} otherwise
15298 @node Process control
15299 @chapter Process control
15301 @cindex processes, commands for controlling
15302 @cindex commands for controlling processes
15305 * kill invocation:: Sending a signal to processes.
15309 @node kill invocation
15310 @section @command{kill}: Send a signal to processes
15313 @cindex send a signal to processes
15315 The @command{kill} command sends a signal to processes, causing them
15316 to terminate or otherwise act upon receiving the signal in some way.
15317 Alternatively, it lists information about signals. Synopses:
15320 kill [-s @var{signal} | --signal @var{signal} | -@var{signal}] @var{pid}@dots{}
15321 kill [-l | --list | -t | --table] [@var{signal}]@dots{}
15324 @mayConflictWithShellBuiltIn{kill}
15326 The first form of the @command{kill} command sends a signal to all
15327 @var{pid} arguments. The default signal to send if none is specified
15328 is @samp{TERM}. The special signal number @samp{0} does not denote a
15329 valid signal, but can be used to test whether the @var{pid} arguments
15330 specify processes to which a signal could be sent.
15332 If @var{pid} is positive, the signal is sent to the process with the
15333 process ID @var{pid}. If @var{pid} is zero, the signal is sent to all
15334 processes in the process group of the current process. If @var{pid}
15335 is @minus{}1, the signal is sent to all processes for which the user has
15336 permission to send a signal. If @var{pid} is less than @minus{}1, the signal
15337 is sent to all processes in the process group that equals the absolute
15338 value of @var{pid}.
15340 If @var{pid} is not positive, a system-dependent set of system
15341 processes is excluded from the list of processes to which the signal
15344 If a negative @var{pid} argument is desired as the first one, it
15345 should be preceded by @option{--}. However, as a common extension to
15346 @acronym{POSIX}, @option{--} is not required with @samp{kill
15347 -@var{signal} -@var{pid}}. The following commands are equivalent:
15356 The first form of the @command{kill} command succeeds if every @var{pid}
15357 argument specifies at least one process that the signal was sent to.
15359 The second form of the @command{kill} command lists signal information.
15360 Either the @option{-l} or @option{--list} option, or the @option{-t}
15361 or @option{--table} option must be specified. Without any
15362 @var{signal} argument, all supported signals are listed. The output
15363 of @option{-l} or @option{--list} is a list of the signal names, one
15364 per line; if @var{signal} is already a name, the signal number is
15365 printed instead. The output of @option{-t} or @option{--table} is a
15366 table of signal numbers, names, and descriptions. This form of the
15367 @command{kill} command succeeds if all @var{signal} arguments are valid
15368 and if there is no output error.
15370 The @command{kill} command also supports the @option{--help} and
15371 @option{--version} options. @xref{Common options}.
15373 A @var{signal} may be a signal name like @samp{HUP}, or a signal
15374 number like @samp{1}, or an exit status of a process terminated by the
15375 signal. A signal name can be given in canonical form or prefixed by
15376 @samp{SIG}. The case of the letters is ignored, except for the
15377 @option{-@var{signal}} option which must use upper case to avoid
15378 ambiguity with lower case option letters. For a list of supported
15379 signal names and numbers see @xref{Signal specifications}.
15384 @cindex delaying commands
15385 @cindex commands for delaying
15387 @c Perhaps @command{wait} or other commands should be described here also?
15390 * sleep invocation:: Delay for a specified time.
15394 @node sleep invocation
15395 @section @command{sleep}: Delay for a specified time
15398 @cindex delay for a specified time
15400 @command{sleep} pauses for an amount of time specified by the sum of
15401 the values of the command line arguments.
15405 sleep @var{number}[smhd]@dots{}
15409 Each argument is a number followed by an optional unit; the default
15410 is seconds. The units are:
15423 Historical implementations of @command{sleep} have required that
15424 @var{number} be an integer, and only accepted a single argument
15425 without a suffix. However, GNU @command{sleep} accepts
15426 arbitrary floating point numbers (using a period before any fractional
15429 The only options are @option{--help} and @option{--version}. @xref{Common
15432 @c sleep is a shell built-in at least with Solaris 11's /bin/sh
15433 @mayConflictWithShellBuiltIn{sleep}
15438 @node Numeric operations
15439 @chapter Numeric operations
15441 @cindex numeric operations
15442 These programs do numerically-related operations.
15445 * factor invocation:: Show factors of numbers.
15446 * seq invocation:: Print sequences of numbers.
15450 @node factor invocation
15451 @section @command{factor}: Print prime factors
15454 @cindex prime factors
15456 @command{factor} prints prime factors. Synopses:
15459 factor [@var{number}]@dots{}
15460 factor @var{option}
15463 If no @var{number} is specified on the command line, @command{factor} reads
15464 numbers from standard input, delimited by newlines, tabs, or spaces.
15466 The @command{factor} command supports only a small number of options:
15470 Print a short help on standard output, then exit without further
15474 Print the program version on standard output, then exit without further
15478 Factoring the product of the eighth and ninth Mersenne primes
15479 takes about 30 milliseconds of CPU time on a 2.2 GHz Athlon.
15482 M8=`echo 2^31-1|bc` ; M9=`echo 2^61-1|bc`
15483 /usr/bin/time -f '%U' factor $(echo "$M8 * $M9" | bc)
15484 4951760154835678088235319297: 2147483647 2305843009213693951
15488 Similarly, factoring the eighth Fermat number @math{2^{256}+1} takes
15489 about 20 seconds on the same machine.
15491 Factoring large numbers is, in general, hard. The Pollard Rho
15492 algorithm used by @command{factor} is particularly effective for
15493 numbers with relatively small factors. If you wish to factor large
15494 numbers which do not have small factors (for example, numbers which
15495 are the product of two large primes), other methods are far better.
15497 If @command{factor} is built without using GNU MP, only
15498 single-precision arithmetic is available, and so large numbers
15499 (typically @math{2^{64}} and above) will not be supported. The single-precision
15500 code uses an algorithm which is designed for factoring smaller
15506 @node seq invocation
15507 @section @command{seq}: Print numeric sequences
15510 @cindex numeric sequences
15511 @cindex sequence of numbers
15513 @command{seq} prints a sequence of numbers to standard output. Synopses:
15516 seq [@var{option}]@dots{} @var{last}
15517 seq [@var{option}]@dots{} @var{first} @var{last}
15518 seq [@var{option}]@dots{} @var{first} @var{increment} @var{last}
15521 @command{seq} prints the numbers from @var{first} to @var{last} by
15522 @var{increment}. By default, each number is printed on a separate line.
15523 When @var{increment} is not specified, it defaults to @samp{1},
15524 even when @var{first} is larger than @var{last}.
15525 @var{first} also defaults to @samp{1}. So @code{seq 1} prints
15526 @samp{1}, but @code{seq 0} and @code{seq 10 5} produce no output.
15527 Floating-point numbers
15528 may be specified (using a period before any fractional digits).
15530 The program accepts the following options. Also see @ref{Common options}.
15531 Options must precede operands.
15534 @item -f @var{format}
15535 @itemx --format=@var{format}
15536 @opindex -f @var{format}
15537 @opindex --format=@var{format}
15538 @cindex formatting of numbers in @command{seq}
15539 Print all numbers using @var{format}.
15540 @var{format} must contain exactly one of the @samp{printf}-style
15541 floating point conversion specifications @samp{%a}, @samp{%e},
15542 @samp{%f}, @samp{%g}, @samp{%A}, @samp{%E}, @samp{%F}, @samp{%G}.
15543 The @samp{%} may be followed by zero or more flags taken from the set
15544 @samp{-+#0 '}, then an optional width containing one or more digits,
15545 then an optional precision consisting of a @samp{.} followed by zero
15546 or more digits. @var{format} may also contain any number of @samp{%%}
15547 conversion specifications. All conversion specifications have the
15548 same meaning as with @samp{printf}.
15550 The default format is derived from @var{first}, @var{step}, and
15551 @var{last}. If these all use a fixed point decimal representation,
15552 the default format is @samp{%.@var{p}f}, where @var{p} is the minimum
15553 precision that can represent the output numbers exactly. Otherwise,
15554 the default format is @samp{%g}.
15556 @item -s @var{string}
15557 @itemx --separator=@var{string}
15558 @cindex separator for numbers in @command{seq}
15559 Separate numbers with @var{string}; default is a newline.
15560 The output always terminates with a newline.
15563 @itemx --equal-width
15564 Print all numbers with the same width, by padding with leading zeros.
15565 @var{first}, @var{step}, and @var{last} should all use a fixed point
15566 decimal representation.
15567 (To have other kinds of padding, use @option{--format}).
15571 You can get finer-grained control over output with @option{-f}:
15574 $ seq -f '(%9.2E)' -9e5 1.1e6 1.3e6
15580 If you want hexadecimal integer output, you can use @command{printf}
15581 to perform the conversion:
15584 $ printf '%x\n' `seq 1048575 1024 1050623`
15590 For very long lists of numbers, use xargs to avoid
15591 system limitations on the length of an argument list:
15594 $ seq 1000000 | xargs printf '%x\n' | tail -n 3
15600 To generate octal output, use the printf @code{%o} format instead
15603 On most systems, seq can produce whole-number output for values up to
15604 at least @math{2^{53}}. Larger integers are approximated. The details
15605 differ depending on your floating-point implementation, but a common
15606 case is that @command{seq} works with integers through @math{2^{64}},
15607 and larger integers may not be numerically correct:
15610 $ seq 18446744073709551616 1 18446744073709551618
15611 18446744073709551616
15612 18446744073709551616
15613 18446744073709551618
15616 Be careful when using @command{seq} with outlandish values: otherwise
15617 you may see surprising results, as @command{seq} uses floating point
15618 internally. For example, on the x86 platform, where the internal
15619 representation uses a 64-bit fraction, the command:
15622 seq 1 0.0000000000000000001 1.0000000000000000009
15625 outputs 1.0000000000000000007 twice and skips 1.0000000000000000008.
15630 @node File permissions
15631 @chapter File permissions
15634 @include getdate.texi
15638 @node Opening the software toolbox
15639 @chapter Opening the Software Toolbox
15641 An earlier version of this chapter appeared in
15642 @uref{http://www.linuxjournal.com/article.php?sid=2762, the
15643 @cite{What's GNU?} column of @cite{Linux Journal}, 2 (June, 1994)}.
15644 It was written by Arnold Robbins.
15647 * Toolbox introduction:: Toolbox introduction
15648 * I/O redirection:: I/O redirection
15649 * The who command:: The @command{who} command
15650 * The cut command:: The @command{cut} command
15651 * The sort command:: The @command{sort} command
15652 * The uniq command:: The @command{uniq} command
15653 * Putting the tools together:: Putting the tools together
15657 @node Toolbox introduction
15658 @unnumberedsec Toolbox Introduction
15660 This month's column is only peripherally related to the GNU Project, in
15661 that it describes a number of the GNU tools on your GNU/Linux system and how they
15662 might be used. What it's really about is the ``Software Tools'' philosophy
15663 of program development and usage.
15665 The software tools philosophy was an important and integral concept
15666 in the initial design and development of Unix (of which Linux and GNU are
15667 essentially clones). Unfortunately, in the modern day press of
15668 Internetworking and flashy GUIs, it seems to have fallen by the
15669 wayside. This is a shame, since it provides a powerful mental model
15670 for solving many kinds of problems.
15672 Many people carry a Swiss Army knife around in their pants pockets (or
15673 purse). A Swiss Army knife is a handy tool to have: it has several knife
15674 blades, a screwdriver, tweezers, toothpick, nail file, corkscrew, and perhaps
15675 a number of other things on it. For the everyday, small miscellaneous jobs
15676 where you need a simple, general purpose tool, it's just the thing.
15678 On the other hand, an experienced carpenter doesn't build a house using
15679 a Swiss Army knife. Instead, he has a toolbox chock full of specialized
15680 tools---a saw, a hammer, a screwdriver, a plane, and so on. And he knows
15681 exactly when and where to use each tool; you won't catch him hammering nails
15682 with the handle of his screwdriver.
15684 The Unix developers at Bell Labs were all professional programmers and trained
15685 computer scientists. They had found that while a one-size-fits-all program
15686 might appeal to a user because there's only one program to use, in practice
15691 difficult to write,
15694 difficult to maintain and
15698 difficult to extend to meet new situations.
15701 Instead, they felt that programs should be specialized tools. In short, each
15702 program ``should do one thing well.'' No more and no less. Such programs are
15703 simpler to design, write, and get right---they only do one thing.
15705 Furthermore, they found that with the right machinery for hooking programs
15706 together, that the whole was greater than the sum of the parts. By combining
15707 several special purpose programs, you could accomplish a specific task
15708 that none of the programs was designed for, and accomplish it much more
15709 quickly and easily than if you had to write a special purpose program.
15710 We will see some (classic) examples of this further on in the column.
15711 (An important additional point was that, if necessary, take a detour
15712 and build any software tools you may need first, if you don't already
15713 have something appropriate in the toolbox.)
15715 @node I/O redirection
15716 @unnumberedsec I/O Redirection
15718 Hopefully, you are familiar with the basics of I/O redirection in the
15719 shell, in particular the concepts of ``standard input,'' ``standard output,''
15720 and ``standard error''. Briefly, ``standard input'' is a data source, where
15721 data comes from. A program should not need to either know or care if the
15722 data source is a disk file, a keyboard, a magnetic tape, or even a punched
15723 card reader. Similarly, ``standard output'' is a data sink, where data goes
15724 to. The program should neither know nor care where this might be.
15725 Programs that only read their standard input, do something to the data,
15726 and then send it on, are called @dfn{filters}, by analogy to filters in a
15729 With the Unix shell, it's very easy to set up data pipelines:
15732 program_to_create_data | filter1 | ... | filterN > final.pretty.data
15735 We start out by creating the raw data; each filter applies some successive
15736 transformation to the data, until by the time it comes out of the pipeline,
15737 it is in the desired form.
15739 This is fine and good for standard input and standard output. Where does the
15740 standard error come in to play? Well, think about @command{filter1} in
15741 the pipeline above. What happens if it encounters an error in the data it
15742 sees? If it writes an error message to standard output, it will just
15743 disappear down the pipeline into @command{filter2}'s input, and the
15744 user will probably never see it. So programs need a place where they can send
15745 error messages so that the user will notice them. This is standard error,
15746 and it is usually connected to your console or window, even if you have
15747 redirected standard output of your program away from your screen.
15749 For filter programs to work together, the format of the data has to be
15750 agreed upon. The most straightforward and easiest format to use is simply
15751 lines of text. Unix data files are generally just streams of bytes, with
15752 lines delimited by the @acronym{ASCII} @sc{lf} (Line Feed) character,
15753 conventionally called a ``newline'' in the Unix literature. (This is
15754 @code{'\n'} if you're a C programmer.) This is the format used by all
15755 the traditional filtering programs. (Many earlier operating systems
15756 had elaborate facilities and special purpose programs for managing
15757 binary data. Unix has always shied away from such things, under the
15758 philosophy that it's easiest to simply be able to view and edit your
15759 data with a text editor.)
15761 OK, enough introduction. Let's take a look at some of the tools, and then
15762 we'll see how to hook them together in interesting ways. In the following
15763 discussion, we will only present those command line options that interest
15764 us. As you should always do, double check your system documentation
15765 for the full story.
15767 @node The who command
15768 @unnumberedsec The @command{who} Command
15770 The first program is the @command{who} command. By itself, it generates a
15771 list of the users who are currently logged in. Although I'm writing
15772 this on a single-user system, we'll pretend that several people are
15777 @print{} arnold console Jan 22 19:57
15778 @print{} miriam ttyp0 Jan 23 14:19(:0.0)
15779 @print{} bill ttyp1 Jan 21 09:32(:0.0)
15780 @print{} arnold ttyp2 Jan 23 20:48(:0.0)
15783 Here, the @samp{$} is the usual shell prompt, at which I typed @samp{who}.
15784 There are three people logged in, and I am logged in twice. On traditional
15785 Unix systems, user names are never more than eight characters long. This
15786 little bit of trivia will be useful later. The output of @command{who} is nice,
15787 but the data is not all that exciting.
15789 @node The cut command
15790 @unnumberedsec The @command{cut} Command
15792 The next program we'll look at is the @command{cut} command. This program
15793 cuts out columns or fields of input data. For example, we can tell it
15794 to print just the login name and full name from the @file{/etc/passwd}
15795 file. The @file{/etc/passwd} file has seven fields, separated by
15799 arnold:xyzzy:2076:10:Arnold D. Robbins:/home/arnold:/bin/bash
15802 To get the first and fifth fields, we would use @command{cut} like this:
15805 $ cut -d: -f1,5 /etc/passwd
15806 @print{} root:Operator
15808 @print{} arnold:Arnold D. Robbins
15809 @print{} miriam:Miriam A. Robbins
15813 With the @option{-c} option, @command{cut} will cut out specific characters
15814 (i.e., columns) in the input lines. This is useful for input data
15815 that has fixed width fields, and does not have a field separator. For
15816 example, list the Monday dates for the current month:
15818 @c Is using cal ok? Looked at gcal, but I don't like it.
15829 @node The sort command
15830 @unnumberedsec The @command{sort} Command
15832 Next we'll look at the @command{sort} command. This is one of the most
15833 powerful commands on a Unix-style system; one that you will often find
15834 yourself using when setting up fancy data plumbing.
15837 command reads and sorts each file named on the command line. It then
15838 merges the sorted data and writes it to standard output. It will read
15839 standard input if no files are given on the command line (thus
15840 making it into a filter). The sort is based on the character collating
15841 sequence or based on user-supplied ordering criteria.
15844 @node The uniq command
15845 @unnumberedsec The @command{uniq} Command
15847 Finally (at least for now), we'll look at the @command{uniq} program. When
15848 sorting data, you will often end up with duplicate lines, lines that
15849 are identical. Usually, all you need is one instance of each line.
15850 This is where @command{uniq} comes in. The @command{uniq} program reads its
15851 standard input. It prints only one
15852 copy of each repeated line. It does have several options. Later on,
15853 we'll use the @option{-c} option, which prints each unique line, preceded
15854 by a count of the number of times that line occurred in the input.
15857 @node Putting the tools together
15858 @unnumberedsec Putting the Tools Together
15860 Now, let's suppose this is a large ISP server system with dozens of users
15861 logged in. The management wants the system administrator to write a program that will
15862 generate a sorted list of logged in users. Furthermore, even if a user
15863 is logged in multiple times, his or her name should only show up in the
15866 The administrator could sit down with the system documentation and write a C
15867 program that did this. It would take perhaps a couple of hundred lines
15868 of code and about two hours to write it, test it, and debug it.
15869 However, knowing the software toolbox, the administrator can instead start out
15870 by generating just a list of logged on users:
15880 Next, sort the list:
15883 $ who | cut -c1-8 | sort
15890 Finally, run the sorted list through @command{uniq}, to weed out duplicates:
15893 $ who | cut -c1-8 | sort | uniq
15899 The @command{sort} command actually has a @option{-u} option that does what
15900 @command{uniq} does. However, @command{uniq} has other uses for which one
15901 cannot substitute @samp{sort -u}.
15903 The administrator puts this pipeline into a shell script, and makes it available for
15904 all the users on the system (@samp{#} is the system administrator,
15905 or @code{root}, prompt):
15908 # cat > /usr/local/bin/listusers
15909 who | cut -c1-8 | sort | uniq
15911 # chmod +x /usr/local/bin/listusers
15914 There are four major points to note here. First, with just four
15915 programs, on one command line, the administrator was able to save about two
15916 hours worth of work. Furthermore, the shell pipeline is just about as
15917 efficient as the C program would be, and it is much more efficient in
15918 terms of programmer time. People time is much more expensive than
15919 computer time, and in our modern ``there's never enough time to do
15920 everything'' society, saving two hours of programmer time is no mean
15923 Second, it is also important to emphasize that with the
15924 @emph{combination} of the tools, it is possible to do a special
15925 purpose job never imagined by the authors of the individual programs.
15927 Third, it is also valuable to build up your pipeline in stages, as we did here.
15928 This allows you to view the data at each stage in the pipeline, which helps
15929 you acquire the confidence that you are indeed using these tools correctly.
15931 Finally, by bundling the pipeline in a shell script, other users can use
15932 your command, without having to remember the fancy plumbing you set up for
15933 them. In terms of how you run them, shell scripts and compiled programs are
15936 After the previous warm-up exercise, we'll look at two additional, more
15937 complicated pipelines. For them, we need to introduce two more tools.
15939 The first is the @command{tr} command, which stands for ``transliterate.''
15940 The @command{tr} command works on a character-by-character basis, changing
15941 characters. Normally it is used for things like mapping upper case to
15945 $ echo ThIs ExAmPlE HaS MIXED case! | tr '[:upper:]' '[:lower:]'
15946 @print{} this example has mixed case!
15949 There are several options of interest:
15953 work on the complement of the listed characters, i.e.,
15954 operations apply to characters not in the given set
15957 delete characters in the first set from the output
15960 squeeze repeated characters in the output into just one character.
15963 We will be using all three options in a moment.
15965 The other command we'll look at is @command{comm}. The @command{comm}
15966 command takes two sorted input files as input data, and prints out the
15967 files' lines in three columns. The output columns are the data lines
15968 unique to the first file, the data lines unique to the second file, and
15969 the data lines that are common to both. The @option{-1}, @option{-2}, and
15970 @option{-3} command line options @emph{omit} the respective columns. (This is
15971 non-intuitive and takes a little getting used to.) For example:
15993 The file name @file{-} tells @command{comm} to read standard input
15994 instead of a regular file.
15996 Now we're ready to build a fancy pipeline. The first application is a word
15997 frequency counter. This helps an author determine if he or she is over-using
16000 The first step is to change the case of all the letters in our input file
16001 to one case. ``The'' and ``the'' are the same word when doing counting.
16004 $ tr '[:upper:]' '[:lower:]' < whats.gnu | ...
16007 The next step is to get rid of punctuation. Quoted words and unquoted words
16008 should be treated identically; it's easiest to just get the punctuation out of
16012 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' | ...
16015 The second @command{tr} command operates on the complement of the listed
16016 characters, which are all the letters, the digits, the underscore, and
16017 the blank. The @samp{\n} represents the newline character; it has to
16018 be left alone. (The @acronym{ASCII} tab character should also be included for
16019 good measure in a production script.)
16021 At this point, we have data consisting of words separated by blank space.
16022 The words only contain alphanumeric characters (and the underscore). The
16023 next step is break the data apart so that we have one word per line. This
16024 makes the counting operation much easier, as we will see shortly.
16027 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16028 > tr -s ' ' '\n' | ...
16031 This command turns blanks into newlines. The @option{-s} option squeezes
16032 multiple newline characters in the output into just one. This helps us
16033 avoid blank lines. (The @samp{>} is the shell's ``secondary prompt.''
16034 This is what the shell prints when it notices you haven't finished
16035 typing in all of a command.)
16037 We now have data consisting of one word per line, no punctuation, all one
16038 case. We're ready to count each word:
16041 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16042 > tr -s ' ' '\n' | sort | uniq -c | ...
16045 At this point, the data might look something like this:
16058 The output is sorted by word, not by count! What we want is the most
16059 frequently used words first. Fortunately, this is easy to accomplish,
16060 with the help of two more @command{sort} options:
16064 do a numeric sort, not a textual one
16067 reverse the order of the sort
16070 The final pipeline looks like this:
16073 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16074 > tr -s ' ' '\n' | sort | uniq -c | sort -n -r
16083 Whew! That's a lot to digest. Yet, the same principles apply. With six
16084 commands, on two lines (really one long one split for convenience), we've
16085 created a program that does something interesting and useful, in much
16086 less time than we could have written a C program to do the same thing.
16088 A minor modification to the above pipeline can give us a simple spelling
16089 checker! To determine if you've spelled a word correctly, all you have to
16090 do is look it up in a dictionary. If it is not there, then chances are
16091 that your spelling is incorrect. So, we need a dictionary.
16092 The conventional location for a dictionary is @file{/usr/dict/words}.
16093 On my GNU/Linux system,@footnote{Redhat Linux 6.1, for the November 2000
16094 revision of this article.}
16095 this is a sorted, 45,402 word dictionary.
16097 Now, how to compare our file with the dictionary? As before, we generate
16098 a sorted list of words, one per line:
16101 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16102 > tr -s ' ' '\n' | sort -u | ...
16105 Now, all we need is a list of words that are @emph{not} in the
16106 dictionary. Here is where the @command{comm} command comes in.
16109 $ tr '[:upper:]' '[:lower:]' < whats.gnu | tr -cd '[:alnum:]_ \n' |
16110 > tr -s ' ' '\n' | sort -u |
16111 > comm -23 - /usr/dict/words
16114 The @option{-2} and @option{-3} options eliminate lines that are only in the
16115 dictionary (the second file), and lines that are in both files. Lines
16116 only in the first file (standard input, our stream of words), are
16117 words that are not in the dictionary. These are likely candidates for
16118 spelling errors. This pipeline was the first cut at a production
16119 spelling checker on Unix.
16121 There are some other tools that deserve brief mention.
16125 search files for text that matches a regular expression
16128 count lines, words, characters
16131 a T-fitting for data pipes, copies data to files and to standard output
16134 the stream editor, an advanced tool
16137 a data manipulation language, another advanced tool
16140 The software tools philosophy also espoused the following bit of
16141 advice: ``Let someone else do the hard part.'' This means, take
16142 something that gives you most of what you need, and then massage it the
16143 rest of the way until it's in the form that you want.
16149 Each program should do one thing well. No more, no less.
16152 Combining programs with appropriate plumbing leads to results where
16153 the whole is greater than the sum of the parts. It also leads to novel
16154 uses of programs that the authors might never have imagined.
16157 Programs should never print extraneous header or trailer data, since these
16158 could get sent on down a pipeline. (A point we didn't mention earlier.)
16161 Let someone else do the hard part.
16164 Know your toolbox! Use each program appropriately. If you don't have an
16165 appropriate tool, build one.
16168 As of this writing, all the programs we've discussed are available via
16169 anonymous @command{ftp} from: @*
16170 @uref{ftp://gnudist.gnu.org/textutils/textutils-1.22.tar.gz}. (There may
16171 be more recent versions available now.)
16173 None of what I have presented in this column is new. The Software Tools
16174 philosophy was first introduced in the book @cite{Software Tools}, by
16175 Brian Kernighan and P.J. Plauger (Addison-Wesley, ISBN 0-201-03669-X).
16176 This book showed how to write and use software tools. It was written in
16177 1976, using a preprocessor for FORTRAN named @command{ratfor} (RATional
16178 FORtran). At the time, C was not as ubiquitous as it is now; FORTRAN
16179 was. The last chapter presented a @command{ratfor} to FORTRAN
16180 processor, written in @command{ratfor}. @command{ratfor} looks an awful
16181 lot like C; if you know C, you won't have any problem following the
16184 In 1981, the book was updated and made available as @cite{Software Tools
16185 in Pascal} (Addison-Wesley, ISBN 0-201-10342-7). Both books are
16186 still in print and are well worth
16187 reading if you're a programmer. They certainly made a major change in
16188 how I view programming.
16190 The programs in both books are available from
16191 @uref{http://cm.bell-labs.com/who/bwk, Brian Kernighan's home page}.
16192 For a number of years, there was an active
16193 Software Tools Users Group, whose members had ported the original
16194 @command{ratfor} programs to essentially every computer system with a
16195 FORTRAN compiler. The popularity of the group waned in the middle 1980s
16196 as Unix began to spread beyond universities.
16198 With the current proliferation of GNU code and other clones of Unix programs,
16199 these programs now receive little attention; modern C versions are
16200 much more efficient and do more than these programs do. Nevertheless, as
16201 exposition of good programming style, and evangelism for a still-valuable
16202 philosophy, these books are unparalleled, and I recommend them highly.
16204 Acknowledgment: I would like to express my gratitude to Brian Kernighan
16205 of Bell Labs, the original Software Toolsmith, for reviewing this column.
16207 @node GNU Free Documentation License
16208 @appendix GNU Free Documentation License
16212 @node Concept index
16219 @c Local variables:
16220 @c texinfo-column-for-description: 32